| 1000Base-CX | A two-wire STP implementation of Gigabit Ethernet.
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| 1000Base-LX | A two-wire fiber implementation of Gigabit Ethernet using long-wave laser.
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| 1000Base-SX | A two-wire fiber implementation of Gigabit Ethernet using short-wave laser signals.
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| 1000Base-T | A four-wire UTP implementation of Gigabit Ethernet.
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| 100Base-FX | A two-wire fiber implementation of Fast Ethernet.
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| 100Base-T4 | A four-wire UTP implementation of Fast Ethernet.
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| 100Base-TX | A two-wire UTP implementation of Fast Ethernet.
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| 10Base2 | The thin coaxial cable implementation of Standard Ethernet.
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| 10Base5 | The thick coaxial cable implementation of Standard Ethernet.
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| 10Base-F | The fiber implementation of Standard Ethernet.
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| 10Base-T | The twisted-pair implementation of Standard Ethernet.
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| 10Base-E | The extended implementation of Ten-Gigabit Ethernet.
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| 10Base-L | A fiber implementation of Ten-Gigabit Ethernet using long-wave laser.
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| 10Base-S | A fiber implementation of Ten-Gigabit Ethernet using short-wave laser.
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| 1-persistent strategy | A CSMA persistence strategy in which a station sends a frame immediately if the line is idle.
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| 2B1Q encoding | A line encoding technique in which each pulse represents 2 bits.
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| 4B/5B encoding | A block coding technique in which 4 bits are encoded into a 5-bit code.
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| 4-dimensional, 5-level pulse amplitude modulation (4D-PAM5) | An encoding scheme used by 1000Base-T.
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| 56K modem | A modem technology using two different data rates: one for uploading and one for downloading from the Internet.
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| 800 service | A telephone service free to the caller.
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| 8B/10B encoding | A block coding technique in which 8 bits are encoded into a 10-bit code.
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| 8B/6T encoding | A block coding technique in which 8 bits are encoded into a 6-bit code.
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| 900 service | A telephone service paid by the caller.
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| Abstract Syntax Notation 1 (ASN.1) | A standard for representing simple and structured data.
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| access control | The determination of link control through a data link protocol.
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| access rate | In Frame Relay, the data rate that can never be exceeded.
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| access point | A central base station in a BSS.
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| acknowledgment (ACK) | A response sent by the receiver to indicate the successful receipt and acceptance of data.
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| active close | In the client-server model, the closing of a communication by the client.
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| active document | In the World Wide Web, a document executed at the local site using Java.
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| active open | In the client-server model, the opening of a communication by the client.
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| adaptive delta modulation | A delta modulation technique in which the value of delta changes according to the amplitude of the analog signal.
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| add/drop multiplexer | A SONET device that multiplexes signals from different sources or demultiplexes a signal to multiple destinations.
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| additive increase | With slow start, a congestion avoidance strategy in which the window size is increased by just one segment instead of exponentially.
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| Address Resolution Protocol (ARP) | In TCP/IP, a protocol for obtaining the physical address of a node when the Internet address is known.
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| ADSL Lite | A splitterless ADSL. This technology allows an ASDL Lite modem to be plugged directly into a telephone jack and connected to the computer. The splitting is done at the telephone company.
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| Advanced Encryption Standard (AES) | A secret-key cryptosystem adapted by NIST to replace DES.
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| address aggregation | A mechanism in which the blocks of addresses for several organizations are aggregated into one larger block.
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| address space | The total number of addresses used by a protocol.
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| address-mask request and reply ICMP | Messages that find the network mask.
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| Advanced Mobile Phone System (AMPS) | A North American analog cellular phone system using FDMA.
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| Advanced Research Projects Agency (ARPA) | The government agency that funded ARPANET.
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| Advanced Research Projects Agency Network (ARPANET) | The packet-switching network that was funded by ARPA.
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| ALOHA | The original random multiple access method in which a station can send a frame any time it has one to send.
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| alternate mark inversion (AMI) | A digital-to-digital bipolar encoding method in which the amplitude representing 1 alternates between positive and negative voltages.
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| American National Standards Institute (ANSI) | A national standards organization that defines standards in the United States.
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| American Standard Code for Information Interchange (ASCII) | A character code developed by ANSI and used extensively for data communication.
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| amplitude | The strength of a signal, usually measured in volts, amperes, or watts.
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| amplitude modulation (AM) | An analog-to-analog conversion method in which the carrier signal's amplitude varies with the amplitude of the modulating signal.
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| amplitude shift keying (ASK) | A modulation method in which the amplitude of the carrier signal is varied to represent binary 0 or 1.
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| analog | A continuously varying entity.
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| analog data | Data that are continuous and smooth and not limited to a specific number of values.
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| analog hierarchy | A telephone company system in which multiplexed signals are combined into successively larger groups for more efficient transmission.
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| analog leased service | A service featuring a dedicated line between two users.
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| analog signal | A continuous waveform that changes smoothly over time.
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| analog switched service | A temporary analog connection between two users.
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| analog-to-analog modulation | The representation of analog information by an analog signal.
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| analog-to-digital conversion | The representation of analog information by a digital signal.
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| angle of incidence | In optics, the angle formed by a light ray approaching the interface between two media and the line perpendicular to the interface.
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| anonymous FTP | A protocol in which a remote user can access another machine without an account or password.
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| anycast address | An address that defines a group of computers with addresses that have the same beginning.
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| aperiodic signal | A signal that does not exhibit a pattern or repeating cycle.
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| applet | A computer program for creating an active Web document. It is usually written in Java.
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| application adaptation layer (AAL) | A layer in ATM protocol that breaks user data into 48-byte payloads.
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| application layer | The fifth layer in the Internet model; provides access to network resources.
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| application programming interface (API) | A set of declarations, definitions, and procedures followed by programmers to write client-server programs.
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| area | A collection of networks, hosts, and routers all contained within an autonomous system.
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| area border router | A router inside an area that summarizes the information about the area and sends it to other areas.
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| area identification | A 32-bit field that defines the area within which the routing takes place.
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| association | A connection in SCTP
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| asymmetric digital subscriber line (ADSL) | A communication technology in which the downstream data rate is higher than the upstream rate.
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| asynchronous balanced mode (ABM) | In HDLC, a communication mode in which all stations are equal.
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| asynchronous connectionless link (ACL) | A link between a Bluetooth master and slave in which a corrupted payload is retransmitted.
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| Asynchronous Transfer Mode (ATM) | A wide area protocol featuring high data rates and equal-sized packets (cells); ATM is suitable for transferring text, audio, and video data.
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| asynchronous transmission | Transfer of data with start and stop bit(s) and a variable time interval between data units.
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| ATM LAN | A LAN using ATM technology.
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| ATM layer | A layer in ATM that provides routing, traffic management, switching, and multiplexing services.
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| ATM switch | An ATM device providing both switching and multiplexing functions.
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| attachment unit interface (AUI) | A 10Base5 cable that performs the physical interface functions between the station and the transceiver.
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| attenuation | The loss of a signal's energy due to the resistance of the medium.
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| audio | Recording or transmitting of sound or music.
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| authenticating state | In PPP, an optional state that verifies the identity of the receiver.
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| Authentication Header (AH) Protocol | A protocol defined by IPSec at the network layer that provides integrity to a message through the creation of a digital signature by a hashing function.
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| authentication server (AS) | The KDC in the Kerberos protocol.
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| authentication | Verification of the sender of a message.
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| automatic repeat request (ARQ) | An error-control method in which correction is made by retransmission of data.
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| automatic tunneling | Tunneling in which the receiving host has an IPv6 compatible address; no reconfiguration is necessary.
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| autonegotiation | A Fast Ethernet feature that allows two devices to negotiate the mode or data rate.
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| autonomous system (AS) | A group of networks and routers under the authority of a single administration.
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| autonomous system boundary router | Routers responsible for dissipating information about other autonomous systems into the current system.
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| available bit rate (ABR) | The minimum data rate in ATM at which cells can be delivered.
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| back off | In multiple access, waiting before re-sending after a collision.
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| backbone router | A router inside the backbone.
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| backbone | A network that connects smaller networks in an organization.
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| backward explicit congestion notification (BECN) | A bit in the Frame Relay packet that notifies the sender of congestion.
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| bandwidth on demand | A digital service that allows subscribers higher speeds through the use of multiple lines.
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| bandwidth | The difference between the highest and the lowest frequencies of a composite signal. It also measures the information-carrying capacity of a line or a network.
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| bandwidth-delay product | A measure of the number of bits that can be sent while waiting for news from the receiver.
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| banyan switch | A multistage switch with microswitches at each stage that route the packets based on the output port represented as a binary string.
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| Barker sequence | A sequence of 11 bits used for spreading.
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| baseband transmission | Transmission of digital or analog signal without modulation using a low-pass channel.
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| band-pass channel | A channel that can pass a range of frequencies.
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| base header | In IPv6, the main header of the datagram.
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| baseline wandering | In decoding a digital signal, the receiver calculates a running average of the received signal power. This average is called the baseline. A long string of 0s and 1s can cause a drift in the baseline (baseline wandering) and make it difficult for the receiver to decode correctly.
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| Basic Encoding Rule (BER) | A standard that encodes data to be transferred through a network.
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| Basic Latin | ASCII character set.
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| basic service set (BSS) | The building block of a wireless LAN as defined by the IEEE 802.11 standard.
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| baud rate | The number of signal elements transmitted per second. A signal element consists of one or more bits.
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| Bayone-Neill-Concelman (BNC) connector | A common coacxial cable connector.
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| best-effort delivery | The unreliable transmission mechanism by IP that does not guarantee message delivery.
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| bidirectional authentication | An authentication method involving a challenge and a response from sender to receiver and vice versa.
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| bidirectional frame (B-frame) | An MPEG frame that is related to the preceding and following I-frame or P-frame.
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| binary exponential backup | In contention access methods, a retransmission delay strategy used by a system to delay access.
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| binary notation | Representation of IP addresses in binary.
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| biphase | A type of polar encoding where the signal changes at the middle of the bit interval. Manchester and differential Manchester are examples of biphase encoding.
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| bipolar encoding | A digital-to-digital encoding method in which 0 amplitude represents binary 0 and positive and negative amplitudes represent alternate 1s.
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| bipolar with 8-zero substitution (B8ZS) | A scrambling technique in which a stream of 8 zeros are replaced by a predefined pattern to improve bit synchronization.
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| bipolar n-zero substitution (BnZS) | An encoding method to provide synchronization for long strings of 0s.
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| bit | binary digit; the smallest unit of data(0 or 1)
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| bit interval | The time required to send one bit.
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| bit padding | In TDM, the addition of extra bits to a device's source stream to force speed relationships.
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| bit rate | The number of bits transmitted per second.
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| bit stuffing | In a bit-oriented protocol, the process of adding an extra bit in the data section of a frame to prevent a sequence of bits from looking like a flag.
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| bit-oriented protocol | A protocol in which the data frame is interpreted as a sequence of bits.
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| bits per second (bps) | A measurement of data speed; bits transmitted per second.
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| block cipher | An encryption/decryption algorithm that has a block of bits as its basic unit.
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| block code | An error detection/correction code in which data are divided into units called datawords. Redundant bits are added to each dataword to create a codeword.
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| block coding | A coding method to ensure synchronization and detection of errors.
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| blocking | An event that occurs when a switching network is working at its full capacity and cannot accept more input.
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| blocking port | A port on a bridge that does not forward a frame.
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| Bluetooth | A wireless LAN technology designed to connect devices of different functions such as telephones and notebooks in a small area such as a room.
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| BNC connector | A common coaxial cable connector.
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| Bootstrap Protocol (BOOTP) | The protocol that provides configuration information from a table (file).
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| Border Gateway Protocol (BGP) | An interautonomous system routing protocol based on path vector routing.
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| bridge | A network device operating at the first two layers of the Internet model with filtering and forwarding capabilities.
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| broadband transmission | Transmission of signals using modulation of a higher frequency signal. The term implies a wide-bandwidth data combined from different sources.
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| broadcast address | An address that allows transmission of a message to all nodes of a network.
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| broadcast/unknown server (BUS) | A server connected to an ATM switch that can multicast and broadcast frames.
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| broadcasting | Transmission of a message to all nodes in a network.
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| browser | An application program that displays a WWW document. A browser usually uses other Internet services to access the document.
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| BSS-transition mobility | In a wireless LAN, a station that can move from one BSS to another but is confined inside one ESS.
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| bucket brigade attack | See man-in-the middle attack
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| burst error | Error in a data unit in which two or more bits have been altered.
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| bursty data | Data with varying instantaneous transmission rates.
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| bus topology | A network topology in which all computers are attached to a shared medium.
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| byte | A group of eight bits.
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| byte stuffing | In a byte-oriented protocol, the process of adding an extra byte in the data section of a frame to prevent a byte from looking like a flag.
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| byte-oriented protocol | A protocol in which the data section of the frame is interpreted as a sequence of bytes (characters).
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| cable modem | A technology in which the TV cable provides Internet access.
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| cable modem transmission system (CMTS) | A device installed inside the distribution hub that receives data from the Internet and passes them to the combiner.
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| cable TV network | A system using coaxial or fiber optic cable that brings multiple channels of video programs into homes.
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| caching | The storing of information in a small, fast memory.
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| Caesar cipher | A shift cipher used by Julius Caesar with the key value of 3.
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| carrier extension | A technique in Gigabit Ethernet that increases the minimum length of the frame to achieve a higher maximum cable length.
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| carrier sense multiple access (CSMA) | A contention access method in which each station listens to the line before transmitting data.
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| carrier sense multiple access with collision avoidance (CSMA/CA) | An access method in which collision is avoided.
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| carrier sense multiple access with collision detection (CSMA/CD) | An access method in which stations transmit whenever the transmission medium is available and retransmit when collision occurs.
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| carrier signal | A high frequency signal used for digital-to-analog or analog-to-analog modulation. One of the characteristics of the carrier signal (amplitude, frequency, or phase) is changed according to the modulating data.
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| cell | A small, fixed-size data unit; also, in cellular telephony, a geographical area served by a cell office.
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| cell network | A network using the cell as its basic data unit.
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| cellular telephony | A wireless communication technique in which an area is divided into cells. A cell is served by a transmitter.
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| Certification Authority (CA) | An agency such as a federal or state organization that binds a public key to an entity and issues a certificate.
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| Challenge Handshake Authentication Protocol (CHAP) | In PPP, a three-way handshaking protocol used for authentication.
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| channel | A communications pathway.
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| channelization | A multiple access method in which the available bandwidth of a link is shared in time.
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| character-oriented protocol | See byte-oriented protocol
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| checksum | A field used for error detection. It is formed by adding bit streams using one's complement arithmetic and then complementing the result.
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| chip | In CDMA, a number in a code that is assigned to a station.
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| choke point | A packet sent by a router to the source to inform it of congestion.
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| chunk | A unit of transmission in SCTP.
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| cipher | An encryption/decryption algorithm.
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| cipher block chaining (CBC) mode | A DES and triple DES operation mode in which the encryption (or decryption) of a block depends on all previous blocks.
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| cipher feedback mode (CFM) | A DES and triple DES operation mode in which data is sent and received 1 bit at a time, with each bit independent of the previous bits.
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| cipher stream mode (CSM) | A DES and triple DES operation mode in which data is sent and received 1 byte at a time.
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| cipher suite | AA list of possible ciphers.
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| ciphertext | The encrypted data.
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| circuit switching | A switching technology that establishes an electrical connection between stations using a dedicated path.
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| cladding | Glass or plastic surrounding the core of an optical fiber; the optical density of the cladding must be less than that of the core.
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| class A address | An IPv4 address with the first octet between 0 and 127.
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| class B address | An IPv4 address with the first octet between 128 and 191.
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| class C address | An IPv4 address with the first octet between 192 and 223.
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| class D address | An IPv4 multicast address.
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| class E address | An IPv4 address reserved for special purposes.
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| classful addressing | An IPv4 addressing mechanism in which the IP address space is divided into 5 classes: A, B, C, D, and E. Each class occupies some part of the whole address space.
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| classless addressing | An addressing mechanism in which the IP address space is not divided into classes.
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| Classless InterDomain Routing (CIDR) | A technique to reduce the number of routing table entries when supernetting is used.
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| client process | A running application program on a local site that requests service from a running application program on a remote site.
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| client-server model | The model of interaction between two application programs in which a program at one end (client) requests a service from a program at the other end (server).
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| closed-loop congestion control | A method to alleviate congestion after it happens.
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| coaxial cable | A transmission medium consisting of a conducting core, insulating material, and a second conducting sheath.
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| code division multiple access (CDMA) | A multiple access method in which one channel carries all transmissions simultaneously.
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| codeword | The encoded dataword.
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| ColdFusion | A dynamic web technology that allows the fusion of data items coming from a conventional database.
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| collision | The event that occurs when two transmitters send at the same time on a channel designed for only one transmission at a time; data will be destroyed.
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| collision domain | The length of the medium subject to collision.
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| committed burst size | The maximum number of bits in a specific time period that a Frame Relay network must transfer without discarding any frames.
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| committed information rate (CIR) | The committed burst size divided by time.
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| common carrier | A transmission facility available to the public and subject to public utility regulation.
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| Common Gateway Interface (CGI) | A standard for communication between HTTP servers and executable programs. CGI is used in creating dynamic documents.
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| community antenna TV (CATV) | A cable network service that broadcasts video signals to locations with poor or no reception.
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| compatible address | An IPv6 address consisting of 96 bits of zero followed by 32 bits of IPv4.
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| competitive local exchange carrier (CLEC) | A telephone company that cannot provide main telephone services; instead, other services such as mobile telephone service and toll calls inside a LATA are provided.
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| complementary code keying (CCK) | An HR-DSSS encoding method that encodes four or eight bits into one symbol.
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| composite signal | A signal composed of more than one sine wave.
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| concurrent client | A client running the same time as another client of the same process.
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| concurrent server | A server that can process many requests at the same time and share its time between many requests.
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| congestion avoidance | In Frame Relay, a method using two bits that explicitly notify the source and destination of congestion.
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| congestion control | A method to manage network and internetwork traffic to improve throughput.
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| congestion | Excessive network or internetwork traffic causing a general degradation of service.
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| connecting device | A tool that connects computers or networks.
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| connection control | The technique used by the transport layer to deliver segments.
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| connection establishment | The preliminary setup necessary for a logical connection prior to actual data transfer.
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| connection termination | A message sent to end a connection.
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| connectionless iterative server | A connectionless server that processes one request at a time.
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| connectionless service | A service for data transfer without connection establishment or termination.
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| connection-oriented concurrent server | A connection-oriented server that can serve many clients at the same time.
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| connection-oriented service | A service for data transfer involving establishment and termination of a connection.
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| constant bit rate (CBR) | The data rate of an ATM service class that is designed for customers requiring real-time audio or video services.
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| constellation diagram | A graphical representation of the phase and amplitude of different bit combinations in digital-to-analog modulation.
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| Consultative Committee for International Telegraphy and Telephony (CCITT) | An international standards group now known as the ITU-T.
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| contention | An access method in which two or more devices try to transmit at the same time on the same channel.
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| control connection | The FTP connection used for control information (commands and responses).
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| controlled access | A multiple access method in which the stations consult one another to determine who has the right to send.
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| convergence sublayer (CS) | In ATM protocol, the upper AAL sublayer that adds a header or a trailer to the user data.
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| cookie | A string of characters that holds some information about the client and must be returned to the server untouched.
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| core | The glass or plastic center of an optical fiber.
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| Core-Based Tree (CBT) | In multicasting, a group-shared protocol that uses a center router as the root of the tree.
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| country domain | A subdomain in the Domain Name System that uses two characters as the last suffix.
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| CRC checker | The process that validates the CRC remainder.
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| CRC generator | The process that creates the CRC remainder.
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| critical angle | In refraction, the value of the angle of incidence that produces a 90-degree angle of refraction.
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| crossbar switch | A switch consisting of a lattice of horizontal and vertical paths. At the intersection of each horizontal and vertical path, there is a crosspoint that can connect the input to the output.
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| crosspoint | The junction of an input and an output on a crossbar switch.
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| crosstalk | The noise on a line caused by signals traveling along another line.
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| cryptography | The science and art of transforming messages to make them secure and immune to attacks.
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| cyclic code | A linear cod in which the cyclic shifting (rotation) of each codeword creates another code word.
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| CSNET | A network sponsored by the National Science Foundation originally intended for universities.
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| cycle | The repetitive unit of a periodic signal.
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| cyclic redundancy check (CRC) | A highly accurate error-detection method based on interpreting a pattern of bits as a polynomial.
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| data element | The smallest entity that can represent a piece of information. A bit.
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| data connection | The FTP connection used for data transfer.
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| data encryption standard (DES) | The U.S. government standard encryption method for nonmilitary and nonclassified use.
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| data exchange protocol | A protocol that uses the secret key to encrypt the data for secrecy and to encrypt the message digest for integrity.
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| data level | The number of different symbols used to represent a digital signal.
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| data link connection identifier (DLCI) | A number that identifies the virtual circuit in Frame Relay.
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| data link control | The responsibilities of the data link layer: flow control and error control.
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| data link layer | The second layer in the Internet model. It is responsible for node-to-node delivery.
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| Data Over Cable System Interface Specifications (DOCSIS) | A standard for data transmission over an HFC network.
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| data rate | The number of data elements sent in one second.
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| data transfer phase | The intermediate phase in circuit-switched or virtual-circuit network in which data transfer takes place.
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| data transparency | See transparency.
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| datagram approach (to packet switching) | A data transmission method in which each data unit is independent of others.
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| datagram | In packet switching, an independent data unit.
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| datagram network | A packet-switched network in which packets are independent from each other.
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| dataword | The smallest block of data in block coding.
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| datagram socket | A structure designed to be used with a connectionless protocol such as UDP.
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| DC component | See direct current.
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| de facto standard | A protocol that has not been approved by an organized body but adopted as a standard through widespread use.
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| de jure standard | A protocol that has been legislated by an officially recognized body.
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| deadlock | A situation in which a task cannot proceed because it is waiting for an even that will never occur.
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| decibel (dB) | A measure of the relative strength of two signal points.
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| decryption | Recovery of the original message from the encrypted data.
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| default mask | The mask for a network that is not subnetted.
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| default routing | A routing method in which a router is assigned to receive all packets with no match in the routing table.
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| Defense Advanced Research Projects Agency (DARPA) | A government organization, which, under the name of ARPA funded ARPANET and the Internet.
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| delta modulation | An analog-to-digital conversion technique in which the value of the digital signal is based on the difference between the current and the previous sample values.
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| delayed response strategy | A technique used by IGMP to prevent unnecessary traffic on a LAN.
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| demodulation | The process of separating the carrier signal from the information-bearing signal.
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| demodulator | A device that performs demodulation.
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| demultiplexer (DEMUX) | A device that separates a multiplexed signal into its original components.
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| denial of service attack | A form of attack in which the site is flooded with so many phony requests that is eventually forced to deny service.
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| dense wave-division multiplexing (DWDM) | A WDM method that can multiplex a very large number of channels by spacing channels closer together.
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| destination-unreachable message | An ICMP error-reporting message sent to a source when a router cannot route a datagram or a host cannot deliver a datagram.
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| dibit | A unit of data consisting of two bits.
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| differential Manchester encoding | A digital-to-digital polar encoding method that features a transition at the middle of the bit interval as well as an inversion at the beginning of each 1 bit.
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| Differentiated Services (DS or Diffserv) | A class-based QoS model designed for IP.
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| Diffie-Hellman protocol | A key management protocol that provides a one-time session key for 2 parties.
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| digest | A condensed version of a document.
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| digital AMPS (D-AMPS) | A second-generation cellular phone system that is a digital version of AMPS.
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| digital data | Data represented by discrete values or conditions.
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| digital data service (DDS) | A digital version of an analog leased line with a rate of 64 Kbps.
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| digital service unit (DSU) | A device that allows the connection of a user's device to a digital line.
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| digital signal (DS) service | A telephone company service featuring a hierarchy of digital signals.
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| digital signal | A discrete signal with a limited number of values.
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| digital signature | A method to authenticate the sender of a message.
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| digital subscriber line (DSL) | A technology using existing telecommunication networks to accomplish high-speed delivery of data, voice, video, and multimedia.
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| digital subscriber line access multiplexer (DSLAM) | A telephone company site device that functions like an ADSL modem.
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| digital-to-analog conversion | The representation of digital information by an analog signal.
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| digital-to-digital conversion | The representation of digital information by a digital signal.
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| digitization | Conversion of analog information to digital information.
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| digital-to-analog modulation | The representation of digital information by an analog signal.
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| digital-to-digital encoding | The representation of digital information by a digital signal.
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| Dijkstra's algorithm | In link state routing, an algorithm that finds the shortest path to other routers.
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| direct current (DC) | A zero-frequency signal with a constant amplitude.
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| direct delivery | A delivery in which the final destination of the packet is a host connected to the same physical network as the sender.
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| direct sequence spread spectrum (DSSS) | A wireless transmission method in which each bit to be sent by the sender is replaced by a sequence of bits called a chip code.
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| discard eligibility (DE) | A bit that defines that a packet can be discarded if there is congestion in the network.
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| discrete cosine transform (DCT) | A JPEG phase in which a transformation changes the 64 values so that the relative relationships between pixels are kept but the redundancies are revealed.
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| discrete multitone technique (DMT) | A modulation method combining elements of QAM and FDM.
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| Distance Vector Multicast Routing Protocol (DVMRP) | A protocol based on distance vector routing that handles multicast routing in conjunction with IGMP.
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| distance vector routing | A routing method in which each router sends its neighbors a list of networks it can reach and the distance to that network.
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| distortion | Any change in a signal due to noise, attenuation, or other influences.
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| distributed coordination fucntion (DCF) | The basic access method in wireless LANs; stations contend with each other to get access to the channel.
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| distributed database | Information stored in many locations.
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| distributed interframe space (DIFS) | In wireless LANs, a period of time that a station waits before sending a control frame.
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| distributed processing | A strategy in which services provided for the network reside at multiple sites.
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| distribution hub | In an HFC network, a site that modulates and distributes signals.
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| DNS server | A computer that holds information about the name space.
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| domain | A subtree of the domain name space.
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| domain name | In the DNS, a sequence of labels separated by dots.
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| domain name space | A structure for organizing the name space in which the names are defined in an inverted-tree structure with the root at the top.
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| Domain Name System (DNS) | A TCP/IP application service that converts user-friendly names to IP addresses.
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| dotted-decimal notation | A notation devised to make the IP address easier to read; each byte is converted to its decimal equivalent and then set off from its neighbor by a decimal.
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| downlink | Transmission from a satellite to an earth station.
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| downloading | Retrieving a file or data from a remote site.
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| downstream data band | In an HFC network, the 550 to 750 MHz band for data from the Internet to the subscriber premises.
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| dual stack | Two protocols (IPv4 and IPv6) on a station.
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| duplex mode | See full-duplex mode.
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| dynamic document | A Web document created by running a CGI program at the server site.
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| Dynamic Domain Name System (DDNS) | A method to update the DNS master file dynamically.
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| Dynamic Host Configuration Protocol (DHCP) | An extension to BOOTP that dynamically assigns configuration information.
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| dynamic mapping | A technique in which a protocol is used for address resolution.
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| dynamic routing | Routing in which the routing table entries are updated automatically by the routing protocol.
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| E lines | The European equivalent of T lines.
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| echo-request and reply message | An ICMP query message that determines whether two systems (hosts or routers) can communicate with each other.
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| effective bandwidth | The bandwidth that the network needs to allocate for the flow of traffic; a function of three values: average data rate, peak data rate, and maximum burst size.
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| electromagnetic spectrum | The frequency range occupied by electromagnetic energy.
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| electronic code block (ECB) mode | A DES and triple DES operation method in which a long message is divided into 64-bit blocks before being encrypted separately.
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| electronic mail (email) | A method of sending messages electronically based on mailbox addresses rather than a direct host-to-host exchange.
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| Electronics Industries Association (EIA) | An organization that promotes electronics manufacturing concerns. It has developed interface standards such as EIA-232, EIA-449, and EIA-530.
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| email | See electronic mail.
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| Encapsulating Security Payload (ESP) | A protocol defined by IPSec that provides privacy as well as a combination of integrity and message authentication.
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| encapsulation | The technique in which a data unit from one protocol is placed within the data field portion of the data unit of another protocol.
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| encryption | Converting a message into an unintelligible form that is unreadable unless decrypted.
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| end office | A switching office that is the terminus for the local loops.
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| end system | A sender or receiver of data.
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| ephemeral port number | A port number used by the client.
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| error control | The detection and handling of errors in data transmission.
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| error correction by retransmission | The process of correcting bits by resending the data.
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| error-reporting message | An ICMP message sent to the source to report an error.
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| ESS-transition mobility | A station in a wireless LAN that can move from one ESS to another.
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| establishing state | In PPP, a state in which communication begins and options are negotiated.
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| Ethernet | A local area network using CSMA/CD access method. See IEEE Project 802.3.
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| even parity | An error-detection method in which an extra bit is added to the data unit so that the total number of 1s becomes even.
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| excess burst size | In Frame Relay, the maximum number of bits in excess of Bc that the user can send during a predefined period of time.
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| Extended Service Set (ESS) | A wireless LAN service composed of two or more BSSs with APs as defined by the IEEE 802.11 standard.
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| extension header | Extra headers in the IPv6 datagram that provide additional functionality.
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| exterior routing | Routing between autonomous systems.
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| external link LSA | A message that announces all the networks outside the AS.
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| extranet | A private network that uses the TCP/IP protocol suite that allows authorized access from outside users.
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| Fast Ethernet | Ethernet with a data rate of 100 Mbps.
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| fast retransmission | Retransmission of a segment in TCP protocol when three acknowledgements have been received that imply the loss or corruption of that segment.
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| Fast Ethernet | See 100Base-T.
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| Federal Communications Commission (FCC) | A government agency that regulates radio, television, and telecommunications.
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|
| fiber distributed data interface (FDDI) | A high-speed (100-Mbps) LAN, defined by ANSI, using fiber optics, dual ring topology, and the token-passing access method. Today an FDDI network is also used as a MAN.
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| fiber link Ethernet | Ethernet using fiber optic media.
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| fiber node | In an HFC network, the location of the optical fiber and coaxial fiber juncture.
|
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|
| fiber-optic cable | A high-bandwidth transmission medium that carries data signals in the form of pulses of light. It consists of a thin cylinder of glass or plastic, called the core, surrounded by a concentric layer of glass or plastic called the cladding.
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| File Transfer Protocol (FTP) | In TCP/IP, an application layer protocol that transfers files between two sites.
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| filtering | A process in which a bridge makes forwarding decisions.
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| finite state machine | A machine that goes through a limited number of states.
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|
| firewall | A device (usually a router) installed between the internal network of an organization and the rest of the Internet to provide security.
|
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|
|
| first-in, first-out (FIFO) queue | A queue in which the first item in is the first item out.
|
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|
| flag | A bit pattern or a character added to the beginning and the end of a fame to separate the frames.
|
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|
|
| flag field | In an HDLC frame, an 8-bit synchronization sequence that identifies the beginning or end of a frame.
|
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|
| flat name space | A method to map a name to an address in which there is no hierarchical structure.
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|
| flooding | Saturation of a network with a message.
|
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|
| flow control | A technique to control the rate of flow of frames (packets or messages).
|
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|
| flow label | An IPv6 mechanism to enable the source to request special handling of a packet.
|
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|
| footprint | An area on Earth that is covered by a satellite at a specific time.
|
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|
| forward error correction | Correction of errors at the receiver.
|
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|
|
| forward explicit congestion notification (FECN) | A bit in the Frame Relay packet that notifies the destination of congestion.
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| forwarding | Placing the packet in its route to its destination.
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| forwarding port | A port on a bridge that forwards a received frame.
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|
| Fourier analysis | The mathematical technique used to obtain the frequency spectrum of an aperiodic signal if the time-domain representation is given.
|
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|
|
| fragmentation offset | A field in the IP header used in fragmentation to show the relative position of the fragment with respect to the whole datagram.
|
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|
|
| fragmentation | The division of a packet into smaller units to accommodate a protocol's MTU.
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|
| frame | A group of bits representing a block of data.
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|
|
| frame bursting | A technique in CSMA/CD Gigabit Ethernet in which multiple frames are logically connected to each other to resemble a longer frame.
|
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|
|
| frame check sequence (FCS) | The HDLC error-detection field containing either a 2- or 4-byte CRC.
|
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|
|
| Frame Relay | A packet-switching specification defined for the first two layers of the Internet model. There is no network layer. Error checking is done on end-to-end basis instead of on each link.
|
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|
|
| Frame Relay assembler/disassembler (FRAD) | A device used in Frame Relay to handle frames coming from other protocols.
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|
| frequency | The number of cycles per second of a periodic signal.
|
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|
| framing bit | A bit used for synchronization purposes in TDM.
|
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|
|
| frequency division multiple access (FDMA) | A multiple access method in which the bandwidth is divided into channels.
|
|
|
|
| frequency hopping spread spectrum (FHSS) | A wireless transmission method in which the sender transmits at one carrier frequency for a short period of time, then hops to another carrier frequency for the same amount of time, hops again for the same amount of time, and so on. After N hops, the cycle is repeated.
|
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|
|
| frequency modulation (FM) | An analog-to-analog modulation method in which the carrier signal's frequency varies with the amplitude of the modulating signal.
|
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|
|
| frequency shift keying (FSK) | A digital-to-analog encoding method in which the frequency of the carrier signal is varied to represent binary 0 or 1.
|
|
|
|
| frequency-division multiple access (FDMA) | An access method technique in which multiple sources use assigned bandwidth in a data communication band.
|
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|
| frequency | The number of cycles per second of a periodic signal.
|
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|
|
| frequency-division multiplexing (FDM) | The combining of analog signals into a single signal.
|
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|
| frequency-domain plot | A graphical representation of a signal's frequency components.
|
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|
|
| full-duplex mode | A transmission mode in which communication can be two way simultaneously.
|
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|
| full-duplex switched Ethernet | Ethernet in which each station, in its own separate collision domain, can both send and receive.
|
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|
|
| fully qualified domain name (FQDN) | A domain name consisting of labels beginning with the host and going back through each level to the root node.
|
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|
| fundamental frequency | The frequency of the dominant sine wave of a composite signal.
|
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|
| gatekeeper | In the H.323 standard, a server on the LAN that plays the role of the registrar server.
|
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|
|
| gateway | A device used to connect two separate networks that use different communication protocols.
|
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|
| general header | A part of an HTTP request or response message that gives general information about the message.
|
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|
| generic domain | A subdomain in the domain name system that uses generic suffixes.
|
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|
| geographical routing | A routing technique in which the entire address space is divided into blocks based on physical landmasses.
|
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|
| geosynchronous Earth orbit | An orbit that allows a satellite to remain fixed above a certain spot on earth.
|
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|
|
| Gigabit Ethernet | Ethernet with a 1000 Mbps data rate.
|
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|
|
| gigabit medium independent interface (GMII) | In Gigabit Ethernet, a specification that defines how the reconciliation sublayer is to be connected to the transceiver.
|
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|
| global Internet | The Internet.
|
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|
|
| Global Positioning System (GPS) | An MEO public satellite system consisting of 24 satellites and used for land and sea navigation. GPS is not used for communications.
|
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|
| Global System for Mobile Communication (GSM) | A second-generation cellular phone system used in Europe.
|
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|
| Globalstar | An LEO satellite system with 48 satellites in six polar orbits with each orbit hosting eight satellites.
|
|
|
|
| Go-Back-N ARQ | An error-control method in which the frame in error and all following frames must be retransmitted.
|
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|
|
| grafting | Resumption of multicast messages.
|
|
|
|
| ground propagation | Propagation of radio waves through the lowest portion of the atmosphere (hugging the earth).
|
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|
|
| group | An analog signal created by 12 voice channels multiplexed together.
|
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|
|
| group membership | Belonging to a group.
|
|
|
|
| group-shared tree | A multicast routing feature in which each group in the system shares the same tree.
|
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|
|
| guard band | A bandwidth separating two signals.
|
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|
|
| guided media | Transmission media with a physical boundary.
|
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|
|
| H.323 | A standard designed by ITU to allow telephones on the public telephone network to talk to computers (called terminals in H.323) connected to the Internet.
|
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|
|
| half-duplex mode | A transmission mode in which communication can be two-way but not at the same time.
|
|
|
|
| Hamming code | A method that adds redundant bits to a data unit to detect and correct bit errors.
|
|
|
|
| Hamming distance | The number of differences between the corresponding bits in two datawords.
|
|
|
|
| handoff | Changing to a new channel as a mobile device moves from one cell to another.
|
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|
|
| handshake protocol | A protocol to establish or terminate a connection.
|
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|
|
| harmonics | Components of a digital signal, each having a different amplitude, frequency, and phase.
|
|
|
|
| hash function | An algorithm that creates a fixed-size digest from a variable-length message.
|
|
|
|
| hashed-message authentication code (HMAC) | A MAC based on a keyless hash function such as SHA-1.
|
|
|
|
| head end | A cable TV office.
|
|
|
|
| header | Control information added to the beginning of a data packet. Also, in an email, the part of the message that defines the sender, the receiver, the subject of the message, and other information.
|
|
|
|
| header translation | Conversion of the IPv6 header to IPv4.
|
|
|
|
| hertz (Hz) | Unit of measurement for frequency.
|
|
|
|
| hexadecimal colon notation | In IPv6, an address notation consisting of 32 hexadecimal digits, with every four digits separated by a colon.
|
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|
|
| hierarchical name space | A name space made of several parts, with each succeeding part becoming more and more specific.
|
|
|
|
| hierarchical routing | A routing technique in which the entire address space is divided into levels based on specific criteria.
|
|
|
|
| high bit rate digital subscriber line (HDSL) | A service similar to the T1-line that can operate at lengths up to 3.6 km.
|
|
|
|
| High Rate Direct Sequence Spread Spectrum (HR-DSSS) | A signal generation method similar to DSSS except for the encoding method (CCK).
|
|
|
|
| High-level Data Link Control (HDLC) | A bit-oriented data link protocol defined by the ISO. It is used in X.25 protocol. A subset, called link access procedure (LAP), is used in other protocols. It is also a base for many data link protocols used in LANs.
|
|
|
|
| homepage | A unit of hypertext or hypermedia available on the Web that is the main page for an organization or an individual.
|
|
|
|
| hop count | The number of nodes along a route. It is a measurement of distance in routing algorithms.
|
|
|
|
| hop limit | An IPv6 field that limits the number of routers that a packet can visit.
|
|
|
|
| hop-to-hop delivery | Transmission of frames from one node to the next.
|
|
|
|
| horn antenna | A scoop-shaped antenna used in terrestrial microwave communication.
|
|
|
|
| host | A station or node on a network.
|
|
|
|
| host file | A file, used when the Internet was small, that mapped host names to host addresses.
|
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|
|
| hostid | The part of an IP address that identifies a host.
|
|
|
|
| host-specific routing | A routing method in which the full IP address of a host is given in the routing table.
|
|
|
|
| hub | A central device in a star topology that provides a common connection among the nodes.
|
|
|
|
| Huffman encoding | A statistical compression method using variable-length codes to encode a set of symbols.
|
|
|
|
| hybrid network | A network with a private internet and access to the global Internet.
|
|
|
|
| hybrid-fiber-coaxial (HFC) network | The second generation of cable networks; uses fiber optic and coaxial cable.
|
|
|
|
| hypermedia | Information containing text, pictures, graphics, and sound that are linked to other documents through pointers.
|
|
|
|
| hypertext | Information containing text that is linked to other documents through pointers.
|
|
|
|
| HyperText Markup Language (HTML) | The computer language for specifying the contents and format of a web document. It allows additional text to include codes that define fonts, layouts, embedded graphics, and hypertext links.
|
|
|
|
| HyperText Transfer Protocol (HTTP) | An application service for retrieving a web document.
|
|
|
|
| idle state | In PPP, a state in which the link is inactive.
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|
|
| image file | In FTP, the default format for transferring binary files. The file is sent as continuous streams of bits without any interpretation or encoding.
|
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|
|
| incumbent local exchange carrier (ILEC) | A telephone company that provided services before 1996 and is the owner of the cabling system.
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|
| indirect delivery | A delivery in which the source and destination of a packet are in different networks.
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|
| infrared wave | A wave with a frequency between 300 GHz and 400 THz; usually used for short-range communications.
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|
| inner product | A number produced by multiplying two sequences, element by element, and summing the products.
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|
| Institute of Electrical and Electronics Engineers (IEEE) | A group consisting of professional engineers which has specialized societies whose committees prepare standards in members' areas of specialty.
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| Integrated Services (IntServ) | A flow-based QoS model designed for IP.
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| integrity | A data quality of being noncorrupted.
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|
| interactive audio/video | Real-time communication with sound and images.
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|
| interautonomous system routing protocol | A protocol to handle transmissions between autonomous systems.
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|
| interdomain routing | Routing among autonomous systems.
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|
| interexchange carrier (IXC) | A long-distance company that, prior to the Act of 1996, provided communication services between two customers in different LATAs.
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|
| interface | The boundary between two pieces of equipment. It also refers to mechanical, electrical, and functional characteristics of the connection.
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|
| interference | Any undesired energy that interferes with the desired signals.
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|
| interframe space (IFS) | In wireless LANs, a time interval between two frames to control access to the channel.
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|
| Interim Standard 95 (IS-95) | One of the dominant second-generation cellular telephony standards in North America.
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|
| interior routing | Routing inside an autonomous system.
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|
| interleaving | Taking a specific amount of data from each device in a regular order.
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|
|
| International Organization of Standardization (ISO) | A worldwide organization that defines and develops standards on a variety of topics.
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|
| International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) | A standards organization formerly known as the CCITT.
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| internet | A collection of networks connected by internetworking devices such as routers or gateways.
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| Internet | A global internet that uses the TCP/IP protocol suite.
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| Internet address | A 32-bit or 128-bit network-layer address used to uniquely define a host on an internet using the TCP/IP protocol.
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| Internet Architecture Board (IAB) | The technical adviser to the ISOC; oversees the continuing development of the TCP/IP protocol suite.
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|
| Internet Assigned Numbers Authority (IANA) | A group supported by the U.S. government that was responsible for the management of Internet domain names and addresses until October 1998.
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|
| Internet Control Message Protocol (ICMP) | A protocol in the TCP/IP protocol suite that handles error and control messages.
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|
| Internet Control Message Protocol, version 6 (ICMPv6) | A protocol in IPv6 that handles error and control messages.
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|
| Internet Corporation for Assigned Names and Numbers (ICANN) | A private, nonprofit corporation managed by an international board that assumed IANA operations.
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|
| Internet draft | A working Internet document (a work in progress) with no official status and a six-month lifetime.
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| Internet Engineering Steering Group (IESG) | An organization that oversees the activity of IETF.
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|
| Internet Engineering Task Force (IETF) | A group working on the design and development of the TCP/IP protocol suite and the Internet.
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| Internet Group Management Protocol (IGMP) | A protocol in the TCP/IP protocol suite that handles multicasting.
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| Internet Key Exchange (IKE) | A protocol designed to create security associations in SADBs.
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|
| Internet Mail Access Protocol, version 4 (IMAP4) | A complex and powerful protocol to handle the transmission of electronic mail.
|
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|
|
| Internet Mobile Communication for year 2000 (ITM-2000) | An ITU issued blueprint that defines criteria for third generation cellular telephony.
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| Internet model | A 5-layer protocol stack that dominates data communications and networking today.
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| Internet Network Information Center (INTERNIC) | An agency responsible for collecting and distributing information about TCP/IP protocols.
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| Internet Protocol (IP) | The network-layer protocol in the TCP/IP protocol suite governing connectionless transmission across packet switching networks.
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| Internet Protocol next generation (IPng) | See Internet Protocol version 6 (IPv6).
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|
| Internet Protocol version 4 (IPv4) | The current version of Internet Protocol.
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|
| Internet Protocol, version 6 (IPv6) | The sixth version of the Internetworking Protocol; it features major IP addressing changes.
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|
| Internet Research Task Force (IRTF) | A forum of working groups focusing on long-term research topics related to the Internet.
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|
| Internet Security Association and Key Management Protocol (ISAKMP) | A protocol designed by the national Security Agency (NSA) that actually implements the exchanges defined in IKE.
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| Internet service provider (ISP) | Usually, a company that provides Internet services.
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|
| Internet Society (ISOC) | The nonprofit organization established to publicize the Internet.
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|
| Internet standard | A thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is a formalized regulation that must be followed.
|
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| Internetwork Protocol Control Protocol (IPCP) | In PPP, the set of protocols that establish and terminate a network layer connection for IP packets.
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| internetwork (internet) | A network of networks.
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| internetworking | Connecting several networks together using internetworking devices such as routers and gateways.
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|
| intracoded frame (I-frame) | An independent frame that is not related to any other frame and appearing at regular intervals.
|
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|
| intranet | A private network that uses the TCP/IP protocol suite.
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|
| inverse domain | A subdomain in the DNS that finds the domain name given the IP address.
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|
| inverse multiplexing | Taking data from one source and breaking it into portions that can be sent across lower-speed lines.
|
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|
| IP datagram | The Internetworking Protocol data unit.
|
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|
|
| IP Security (IPSec) | A collection of protocols designed by the IETF (Internet Engineering Task Force) to provide security for a packet carried on the Internet.
|
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|
| IrDA port | A port that allows a wireless keyboard to communicate with a PC.
|
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|
|
| Iridium | A 66-satellite network that provides communication from any Earth site to another.
|
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|
|
| ISDN user port (ISUP) | A protocol at the upper layer of SS7 that provides services similar to those of an ISDN network.
|
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|
|
| isochronous transmission | A type of transmission in which the entire stream of bits is synchronized under the control of a common clock.
|
|
|
|
| iterative resolution | Resolution of the IP address in which the client may send its request to multiple servers before getting an answer.
|
|
|
|
| iterative server | In the client-server model, a server that can serve only one client at a time.
|
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|
|
| jamming signal | In CSMA/CD, a signal sent by the first station that detects collision to alert every other station of the situation.
|
|
|
|
| Java | A programming language used to create active Web documents.
|
|
|
|
| jitter | A phenomenon in real-time traffic caused by gaps between consecutive packets at the receiver.
|
|
|
|
| Joint Photographic Experts Group (JPEG) | A standard for compressing continuous-tone picture.
|
|
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|
| jumbo group | An analog signal created by six multiplexed master groups.
|
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|
| Karn's Algorithm | An algorithm that does not include the retransmitted segments in calculation of round-trip time.
|
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|
|
| keepalive message | A message that establishes a relationship between the two routers.
|
|
|
|
| keepalive timer | A timer that prevents a long idle connection between two TCPs.
|
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|
| Kerberos | An authentication protocol used by Windows 2000.
|
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|
| key | A number that a cipher operates on.
|
|
|
|
| key distribution center (KDC) | In secret key encryption, a trusted third party that shares a key with each user.
|
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|
| LAN emulation (LANE) | Local area network emulation using ATM switches.
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|
| LAN emulation client (LEC) | In ATM LANs, client software that receives services from a LES.
|
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|
| LAN emulation server (LES) | In ATM LANs, server software that creates a virtual circuit between the source and destination.
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|
|
| layered architecture | A model based on ordered tiers.
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|
| leaky bucket algorithm | An algorithm to shape bursty traffic.
|
|
|
|
| least-cost tree | An MOSPF feature in which the tree is based on a chosen metric instead of shortest path.
|
|
|
|
| leave report | An IGMP message sent by a host when no process is interested in a specific group.
|
|
|
|
| legacy ATM LAN | LAN in which ATM technology is used as a backbone to connect traditional LANs.
|
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|
|
| line coding | Converting binary data into signals.
|
|
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|
| linear block code | A block code in which adding two codewords creates another codeword.
|
|
|
|
| line-of-sight propagation | The transmission of very high frequency signals in straight lines directly from antenna to antenna.
|
|
|
|
| Link Control Protocol (LCP) | A PPP protocol responsible for establishing, maintaining, configuring, and terminating links.
|
|
|
|
| link local address | An OPv6 address used by a private LAN.
|
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|
|
| link state advertisement (LSA) | In OSPF, a method that disperses information.
|
|
|
|
| link state database | In link state routing, a database common to all routers and made from LSP information.
|
|
|
|
| link state packet (LSP) | In link state routing, a small packet containing routing information sent by a router to all other routers.
|
|
|
|
| link state routing | A routing method in which each router shares its knowledge of changes in its neighborhood with all other routers.
|
|
|
|
| link state update packet | A packet that provides information about a specific route or routes.
|
|
|
|
| link | The physical communication pathway that transfers data from one device to another.
|
|
|
|
| load | The number of packets sent to a network.
|
|
|
|
| local access and transport area (LATA) | An area covered by one or more telephone companies.
|
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|
|
| local access | Using a terminal directly connected to the computer.
|
|
|
|
| local address | The part of an email address that defines the name of a special file, called the user mailbox, where all of the mail received for a user is stored for retrieval by the user agent.
|
|
|
|
| local area network (LAN) | A network connecting devices inside a single building or inside buildings close to each other.
|
|
|
|
| local area network emulation (LANE) | Software that enables an ATM switch to behave like a LAN switch.
|
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|
|
| local call service | A telephone service handling local calls, usually charging a flat monthly fee.
|
|
|
|
| local exchange carrier (LEC) | A telephone company that handles services inside a LATA.
|
|
|
|
| local Internet service provider | The same as an Internet service provider.
|
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|
|
| local ISP | The same as an Internet service provider.
|
|
|
|
| local loop | The link that connects a subscriber to the telephone central office.
|
|
|
|
| local management information (LMI) | A protocol used in Frame Relay to provide. management features.
|
|
|
|
| logical address | An address defined in the network layer.
|
|
|
|
| logical link control (LLC) | The upper sublayer of the data link layer as defined by IEEE Project 802.2.
|
|
|
|
| Logical Link Control and Adaptation Protocol (L2CAP) | A Bluetooth layer used for data exchange on an ACL link.
|
|
|
|
| logical tunnel | The encapsulation of a multicast packet inside a unicast packet to enable multicast routing by non-multicast routers.
|
|
|
|
| longest mask matching | The technique in CIDR in which the longest prefix is handled first when searching a routing table.
|
|
|
|
| low Earth orbit (LEO) | A polar satellite orbit with an altitude between 500 and 2000 km. A satellite with this orbit has a rotation period of 90 to 120 minutes.
|
|
|
|
| low-pass channel | A channel that passes frequencies between 0 and f.
|
|
|
|
| mail transfer agent (MTA) | An SMTP component that transfers the mail across the Internet.
|
|
|
|
| management Information Base (MIB) | The database used by SNMP that holds the information necessary for management of a network.
|
|
|
|
| Manchester encoding | A digital-to-digital polar encoding method in which a transition occurs at the middle of each bit interval for the purpose of synchronization.
|
|
|
|
| man-in-the-middle attack | A key management problem in which an intruder intercepts and sends messages between the intended sender and receiver.
|
|
|
|
| mapped address | An IPv6 address used when a computer that has migrated to Ipv6 wants to send a packet to a computer still using IPv4.
|
|
|
|
| mask | For IPv4, a 32-bit binary number that gives the first address in the block (the network address) when ANDed with an address in the block.
|
|
|
|
| master | The one Bluetooth station in a piconet that controls all the others.
|
|
|
|
| master group | An analog signal created by 10 multiplexed supergroups.
|
|
|
|
| maximum burst size | The maximum length of time traffic is generated at the peak rate.
|
|
|
|
| maximum transfer unit (MTU) | The largest size data unit a specific network can handle.
|
|
|
|
| media player | A help application that plays an audio/video file; used by a browser.
|
|
|
|
| media server | A server accessed by a media player to download an audio/video file.
|
|
|
|
| medium access control (MAC) sublayer | The lower sublayer in the data link layer defined by the IEEE 802 project. It defines the access method and access control in different local area network protocols.
|
|
|
|
| medium attachment unit (MAU) | See transceiver.
|
|
|
|
| medium bandwidth | The difference between the highest and lowest frequencies a medium can support.
|
|
|
|
| medium dependent interface (MDI) | In Fast Ethernet, implementation-specific hardware that connects the transceiver to the medium.
|
|
|
|
| medium Earth orbit (MEO) | A satellite orbit positioned between the two Van Allen belts. A satellite at this orbit takes six hours to circle the earth.
|
|
|
|
| medium independent interface (MII) | In Fast Ethernet hardware that connects an external transceiver to the reconciliation layer.
|
|
|
|
| membership report | An IGMP message sent by a host or router interested in joining a specific group.
|
|
|
|
| mesh topology | A network configuration in which each device has a dedicated point-to-point link to every other device.
|
|
|
|
| message access agent (MAA) | A client-server program that pulls the stored email messages.
|
|
|
|
| message authentication | A security measure in which the sender of the message is verified for every message sent.
|
|
|
|
| message authentication code | A keyed hash function.
|
|
|
|
| message transfer agent (MTA) | An SMTP component that transfers the message across the Internet.
|
|
|
|
| metric | A cost assigned for passing through a network.
|
|
|
|
| metropolitan area network (MAN) | A network that can span a geographical area the size of a city.
|
|
|
|
| minimum Hamming distance | In a set of words, the smallest Hamming distance between all possible pairs.
|
|
|
|
| microwave | Electromagnetic waves ranging from 2 GHz to 40 GHz.
|
|
|
|
| minislot | In an HFC network, a time slot for timesharing of the upstream channels.
|
|
|
|
| mixer | A device that combines real-time signals from different sources into one signal.
|
|
|
|
| mobile host | A host that can move from one network to another.
|
|
|
|
| mobile switching center (MSC) | In cellular telephony, a switching office that coordinates communication between all base stations and the telephone central office.
|
|
|
|
| mobile telephone switching office (MTSO) | An office that controls and coordinates communication between all of the cell offices and the telephone control office.
|
|
|
|
| modem | A device consisting of a modulator and a demodulator. It converts a digital signal into an analog signal (modulation) and vice versa (demodulation).
|
|
|
|
| modification detection code (MDC) | The digest created by a hash function.
|
|
|
|
| modular arithmetic | Arithmetic that uses a limited range of integers (O to n-1).
|
|
|
|
| modulation | Modification of one or more characteristics of a carrier wave by an information-bearing signal.
|
|
|
|
| modulus | The upper limit in modular arithmetic (n).
|
|
|
|
| modulator | A device that converts a digital signal to an analog signal suitable for transmission across a telephone line.
|
|
|
|
| monoalphabetic substitution | An encryption method in which each occurrence of a character is replaced by another character in the set.
|
|
|
|
| motion picture experts group (MPEG) | A method to compress videos.
|
|
|
|
| MT-RJ | A fiber-optic cable connector.
|
|
|
|
| multicast address | An address used for multicasting.
|
|
|
|
| multicast backbone (MBONE) | A set of internet routers supporting multicasting through the use of tunneling.
|
|
|
|
| Multicast Open Shortest Path First (MOSPF) | A multicast protocol that uses multicast link state routing to create a source-based least cost tree.
|
|
|
|
| multicast router | A router with a list of loyal members related to each router interface that distributes the multicast packets.
|
|
|
|
| multicasting | A transmission method that allows copies of a single packet to be sent to a selected group of receivers.
|
|
|
|
| multihoming service | A service provided by SCTP that allows a computer to be connected to different networks.
|
|
|
|
| multiline transmission, 3-level (MLT-3) encoding | A line coding scheme featuring 3 levels of signals and transitions at the beginning of the 1 bit.
|
|
|
|
| multimode graded-index fiber | An optical fiber with a core having a graded index of refraction.
|
|
|
|
| multimode step-index fiber | An optical fiber with a core having a uniform index of refraction. The index of refraction changes suddenly at the core/cladding boundary.
|
|
|
|
| multiple access (MA) | A line access method in which every station can access the line freely.
|
|
|
|
| multiple unicasting | Sending multiple copies of a message, each with a different unicast address.
|
|
|
|
| multiplexer (MUX) | A device used for multiplexing.
|
|
|
|
| multiplexing | The process of combining signals from multiple sources for transmission across a single data link.
|
|
|
|
| multiplicative decrease | A congestion avoidance technique in which the threshold is set to half of the last congestion window size, and the congestion window size starts from one again.
|
|
|
|
| Multipurpose Internet Mail Extension (MIME) | A supplement to SMTP that allows non-ASCII data to be sent through SMTP.
|
|
|
|
| multistage switch | An array of switches designed to reduce the number of crosspoints.
|
|
|
|
| multistream service | A service provided by SCTP that allows data transfer to be carried using different streams.
|
|
|
|
| n2 problem | A problem due to the large number of keys needed in symmetric key distribution.
|
|
|
|
| Nagle's algorithm | An algorithm that attempts to prevent silly window syndrome at the sender's site; both the rate of data production and the network speed are taken into account.
|
|
|
|
| name space | All the names assigned to machines on an internet.
|
|
|
|
| name-address resolution | Mapping a name to an address or an address to a name.
|
|
|
|
| national service provider (NSP) | A backbone network created and maintained by a specialized company.
|
|
|
|
| Needham-Schroeder protocol | A key management protocol using multiple challenge-response interactions between 2 entities.
|
|
|
|
| negative acknowledgment (NAK) | A message sent to indicate the rejection of received data.
|
|
|
|
| netid | The part of an IP address that identifies the network.
|
|
|
|
| network | A system consisting of connected nodes made to share data, hardware, and software.
|
|
|
|
| network access point (NAP) | A complex switching station that connects backbone networks.
|
|
|
|
| network address | An address that identifies a network to the rest of the Internet; it is the first address in a block.
|
|
|
|
| network address translation (NAT) | A technology that allows a private network to use a set of private addresses for internal communication and a set of global Internet addresses for external communication.
|
|
|
|
| network allocation vector (NAV) | In CSMA/CA, the amount of time that must pass before a station can check the line for idleness.
|
|
|
|
| Network Control Protocol (NCP) | In PPP, a set of control protocols that allows the encapsulation of data coming from network layer protocols.
|
|
|
|
| network interface card (NIC) | An electronic device, internal or external to a station, that contains circuitry to enable the station to be connected to the network.
|
|
|
|
| network layer | The third layer in the Internet model, responsible for the delivery of a packet to the final destination.
|
|
|
|
| network link LSA | An LSA packet that announces the existence of all of the routers connected to the network.
|
|
|
|
| Network Virtual Terminal (NVT) | A TCP/IP application protocol that allows remote login.
|
|
|
|
| networking state | A PPP state in which packets of user data and packets for control are transmitted.
|
|
|
|
| network-specific routing | Routing in which all hosts on a network share one entry in the routing table.
|
|
|
|
| network-to-network interface (NNI) | In ATM, the interface between two networks.
|
|
|
|
| next header | In IPv6, an 8-bit field defining the header that follows the base header in the datagram.
|
|
|
|
| next-hop routing | A routing method in which only the address of the next hop is listed in the routing table instead of a complete list of the stops the packet must make.
|
|
|
|
| node | An addressable communication device (e.g., a computer or router) on a network.
|
|
|
|
| node-to-node delivery | Transfer of a data unit from one node to the next.
|
|
|
|
| noise | Random electrical signals that can be picked by the transmission medium and result in degradation or distortion of the data.
|
|
|
|
| noiseless channel | An error-free channel.
|
|
|
|
| noisy channel | A channel that can produce error in data transmission.
|
|
|
|
| nonce | A large random number that is used once to distinguish a fresh authentication request from a used one.
|
|
|
|
| nonpersistent connection | A connection in which one TCP connection is made for each request/response.
|
|
|
|
| nonpersistent strategy | A random multiple access method in which a station waits a random period of time after a collision is sensed.
|
|
|
|
| nonrepudiation | A security aspect in which a receiver must be able to prove that a received message came from a specific sender.
|
|
|
|
| nonreturn to zero (NRZ) | A digital-to-digital polar encoding method in which the signal level is always either positive or negative.
|
|
|
|
| nonreturn to zero, invert (NRZ-I) | An NRZ encoding method in which the signal level is inverted each time a 1 is encountered.
|
|
|
|
| nonreturn to zero, level (NRZ-L) | An NRZ encoding method in which the signal level is directly related to the bit value.
|
|
|
|
| normal response mode (NRM) | In HDLC, a communication mode in which the secondary station must have permission from the primary station before transmission can proceed.
|
|
|
|
| Nyquist bit rate | The data rate based on the Nyquist theorem.
|
|
|
|
| notification message | A BGP message sent by a router whenever an error condition is detected or a router wants to close the connection.
|
|
|
|
| no-transition mobility | In wireless LANs, mobility confined inside a BSS or non-mobility.
|
|
|
|
| Nyquist theorem | A theorem that states that the number of samples needed to adequately represent an analog signal is equal to twice the highest frequency of the original signal.
|
|
|
|
| Oakley | A key creating protocol, developed by Hilarie Orman, which is one of the three components of IKE protocol.
|
|
|
|
| odd parity | An error-detection method in which an extra bit is added to the data unit such that the sum of all 1-bits becomes odd.
|
|
|
|
| omnidirectional antenna | An antenna that sends out or receives signals in all directions.
|
|
|
|
| on-demand audio/video | Another name for streaming stored audio/video.
|
|
|
|
| one's complement | A representation of binary numbers in which the complement of a number is found by complementing all bits.
|
|
|
|
| open message | A BGP message sent by a router to create a neighborhood relationship.
|
|
|
|
| open shortest path first (OSPF) | An interior routing protocol based on link state routing.
|
|
|
|
| open system | A model that allows two different systems to communicate regardless of their underlying architecture.
|
|
|
|
| Open Systems Interconnection (OSI) model | A seven-layer model for data communication defined by ISO.
|
|
|
|
| open-loop congestion control | Policies applied to prevent congestion.
|
|
|
|
| optical carrier (OC) | The hierarchy of fiber-optic carriers defined in SONET. The hierarchy defines up to 10 different carriers (OC-1, OC-3, OC-12, . . . , OC-192), each with a different data rate.
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| optical fiber | A thin thread of glass or other transparent material to carry light beams.
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| optional attribute | A BGP path attribute that need not be recognized by every router.
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| orbit | The path a satellite travels around the earth.
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| Orthogonal Frequency Division Multiplexing (OFDM) | A multiplexing method similar to FDM, with all the subbands used by one source at a given time.
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| orthogonal sequence | A sequence with special properties between elements.
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| Otway-Rees protocol | A key management protocol with less steps than the Needham-Schroeder method.
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| out-of-band signaling | Using two separate channels for data and control.
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| output feedback (OFB) mode | A mode similar to the CFB mode with one difference. Each bit in the ciphertext s independent of the previous bit or bits.
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| overhead | Extra bits added to the data unit for control purposes.
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| packet switching | Data transmission using a packet-switched network.
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| packet | Synonym for data unit, mostly used in the network layer.
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| packet-filter firewall | A firewall that forwards or blocks packets based on the information in the network-layer and transport-layer headers.
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| packet-switched network | A network in which data are transmitted in independent units called packets.
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| page | A unit of hypertext or hypermedia available on the Web.
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| parabolic dish antenna | An antenna shaped like a parabola used for terrestrial microwave communication.
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| parallel transmission | Transmission in which bits in a group are sent simultaneously, each using a separate link.
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| parameter-problem message | An ICMP message that notifies a host that there is an ambiguous or missing value in any field of the datagram.
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| parity bit | A redundant bit added to a data unit (usually a character) for error checking.
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| parity check | An error-detection method using a parity bit.
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| partially qualified domain name (PQDN) | A domain name that does not include all the levels between the host and the root node.
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| passive open | The state of a server as it waits for incoming requests from a client.
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| Password Authentication Protocol (PAP) | A simple two-step authentication protocol used in PPP.
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| path layer | A SONET layer responsible for the movement of a signal from its optical source to its optical destination.
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| path overhead | Control information used by the SONET path layer.
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| path | The channel through which a signal travels.
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| path vector routing | A routing method on which BGP is based; in this method, the ASs through which a packet must pass are explicitly listed.
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| P-box | A hardware circuit used in encryption that connects input to output.
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| peak amplitude | The maximum signal value of a sine wave.
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| peak data rate | The maximum data rate of the traffic.
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| peer-to-peer process | A process on a sending and a receiving machine that communicate at a given layer.
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| per hop behavior (PHB) | In the Diffserv model, a 6-bit field that defines the packet-handling mechanism for the packet.
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| period | The amount of time required to complete one full cycle.
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| periodic signal | A signal that exhibits a repeating pattern.
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| permanent virtual circuit (PVC) | A virtual circuit transmission method in which the same virtual circuit is used between source and destination on a continual basis.
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| persistence timer | A technique to handle the zero window-size advertisement.
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| persistent connection | A connection in which the server leaves the connection open for more requests after sending a response.
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| persistent strategy | In CSMA, a strategy in which the station sends a frame after sensing the line.
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| Personal Communication System (PCS) | A generic term for a commercial cellular system that offers several kinds of communication services.
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| phase modulation (PM) | An analog-to-analog modulation method in which the carrier signal's phase varies with the amplitude of the modulating signal.
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| phase shift keying (PSK) | A digital-to-analog modulation method in which the phase of the carrier signal is varied to represent a specific bit pattern.
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| phase | The relative position of a signal in time.
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| PHY sublayer | The transceiver in Fast Ethernet.
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| physical address | The address of a device used at the data link layer (MAC address).
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| physical layer signaling (PLS) sublayer | An Ethernet sublayer that encodes and decodes data.
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| physical layer | The first layer of the Internet model, responsible for the mechanical and electrical specifications of the medium.
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| physical topology | The manner in which devices are connected in a network.
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| piconet | A Bluetooth network.
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| piggybacking | The inclusion of acknowledgment on a data frame.
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| pipelining | In Go-Back-n ARQ, sending several frames before news is received concerning previous frames.
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| pixel | A picture element of an image.
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| plain old telephone system (POTS) | The conventional telephone network used for voice communication.
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| plaintext | In encryption/decryption, the original message.
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| playback buffer | A buffer that stores the data until they are ready to be played.
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| point coordination function (PCF) | In wireless LANs, an optional and complex access method implemented in an infrastructure network.
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| point of presence (POP) | A switching office where carriers can interact with each other.
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| point-to-point access | See point-to-point connection.
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| point-to-point connection | A dedicated transmission link between two devices.
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| point-to-point link | A dedicated transmission link between two devices.
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| Point-to-Point Protocol (PPP) | A protocol for data transfer across a serial line.
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| poison reverse | A feature added to split horizon in which a table entry that has come through on interface is set to infinity in the update packet.
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| polar encoding | A digital-to-analog encoding method that uses two levels (positive and negative) of amplitude.
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| policy routing | A path vector routing feature in which the routing tables are based on rules set by the network administrator rather than a metric.
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| poll | In the primary/secondary access method, a procedure in which the primary station asks a secondary station if it has any data to transmit.
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| poll/final (P/F) bit | A bit in the control field of HDLC; if the primary is sending, it can be a poll bit; if the secondary is sending, it can be a final bit.
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| poll/select | An access method protocol using poll and select procedures. See poll. See select.
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| polling | An access method in which one device is designated as a primary station and the others as the secondary stations. The access is controlled by the primary station.
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| polyalphabetic substitution | An encryption method in which each occurrence of a character can have a different substitute.
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| polynomial | An algebraic term that can represent a CRC divisor.
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| port | In a URL, the port number of the server.
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| port address | In TCP/IP protocol an integer identifying a process.
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| port number | An integer that defines a process running on a host.
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| Post Office Protocol, version 3 (POP3) | A popular but simple SMTP mail access protocol.
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| p-persistent | A CSMA persistence strategy in which a station sends with probablity p if it finds the line idle.
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| p-persistent strategy | A CSMA persistence strategy in which a station sends with probability p if it finds the line idle.
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| preamble | The 7-byte field of an IEEE 802.3 frame consisting of alternating 1s and 0s that alert and synchronize the receiver.
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| predicted frame (P-frame) | An MPEG frame which contains only the changes from the preceding frame.
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| prefix | The common part of an address range.
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| predictive encoding | In audio compression, encoding only the differences between the samples.
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| presentation layer | The sixth layer of the OSI model responsible for translation, encryption, authentication, and data compression.
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| Pretty Good Privacy (PGP) | A protocol that provides all four aspects of security in the sending of email.
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| primary server | A server that stores a file about the zone for which it is an authority.
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| primary station | In primary/secondary access method, a station that issues commands to the secondary stations.
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| priority queueing | A queuing technique in which packets are assigned to a priority class, each with its own queue.
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| privacy | A security aspect in which the message makes sense only to the intended receiver.
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| private key | In conventional encryption, a key shared by only one pair of devices, a sender and a receiver. In public-key encryption, the private key is known only to the receiver.
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| private network | A network that is isolated from the Internet.
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| process | A running application program.
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| process-to-process delivery | Delivery of a packet from the sending process to the destination process.
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| product block | A combination of P-boxes and S-boxes to get a more complex cipher block.
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| Project 802 | The project undertaken by the IEEE in an attempt to solve LAN incompatibility. See also IEEE Project 802.
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| propagation speed | The rate at which a signal or bit travels; measured by distance/second.
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| propagation time | The time required for a signal to travel from one point to another.
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| Protocol Independent Multicast (PIM) | A multicasting protocol family with two members, PIM-DM and PIM-SM; both protocols are unicast-protocol dependent.
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| Protocol Independent Multicast, Dense Mode (PIM-DM) | A source-based routing protocol that uses RPF and pruning/grafting strategies to handle multicasting.
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| Protocol Independent Multicast, Sparse Mode (PIM-SM) | A group-shared routing protocol that is similar to CBT and uses a rendezvous point as the source of the tree.
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| protocol | Rules for communication.
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| protocol suite | A stack or family of protocols defined for a complex communication system.
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| proxy ARP | A technique that creates a subnetting effect; on server answers ARP requests for multiple hosts.
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| proxy firewall | A firewall that filters a message based on the information available in the message itself (at the application layer).
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| proxy server | A computer that keeps copies of responses to recent requests.
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| pruning | Stopping the sending of multicast messages from an interface.
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| pseudoheader | Information from the IP header used only for checksum calculation in UDP and TCP packet.
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| pseudorandom noise (PN) | A pseudorandom code generator used in FHSS.
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| public key | In public-key encryption, a key known to everyone.
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| public key infrastructure (PKI) | A hierarchical structure of CA servers.
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| public-key cryptography | A method of encryption based on a nonreversible encryption algorithm. The method uses two types of keys: The public key is known to the public; the private key (secret key) is known only to the receiver.
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| pulse amplitude modulation (PAM) | A technique in which an analog signal is sampled; the result is a series of pulses based on the sampled data.
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| pulse code modulation (PCM) | A technique that modifies PAM pulses to create a digital signal.
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| pulse stuffing | In TDM, a technique that adds dummy bits to the input lines with lower rates.
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| pure ALOHA | The original ALOHA.
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| pulse rate | The number of symbols per second.
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| quadbit | A unit of data consisting of four bits.
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| quadrature amplitude modulation (QAM) | A digital-to-analog modulation method in which the phase and amplitude of the carrier signal vary with the modulating signal.
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| quality of service (QoS) | A set of attributes related to the performance of the connection.
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| quantization | The assignment of a specific range of values to signal amplitudes.
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| query message | An ICMP message that helps a host or a network manager get specific information from a router or another host. Or, an IGMP message that requests group information from a router or a host. Or, a DNS message that requests information.
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| queue | A waiting list.
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| radio wave | Electromagnetic energy in the 3-KHz to 300-GHz range.
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| random access | A medium access category in which each station can access the medium without being controlled by any other station.
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| ranging | In an HFC network, a process that determines the distance between the CM and the CMTS.
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| rate adaptive asymmetrical digital subscriber line (RADSL) | A DSL-based technology that features different data rates depending on the type of communication.
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| raw socket | A structure designed for protocols that directly use the services of IP and use neither stream sockets nor datagram sockets.
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| read-only memory (ROM) | Permanent memory with contents that cannot be changed.
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| Real-Time Streaming Protocol (RTSP) | An out-of-band control protocol designed to add more functionality to the streaming audio/video process.
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| Real-time Transport Control Protocol (RTCP) | A companion protocol to RTP with messages that control the flow and quality of data and allow the recipient to send feedback to the source or sources.
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| Real-time Transport Protocol (RTP) | A protocol for real-time traffic; used in conjunction with UDP.
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| receiver window | In the TCP sliding window protocol, the window at the receiver site.
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| reconciliation sublayer | A Fast Ethernet sublayer which passes data in 4-bit format to the MII.
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| recursive resolution | Resolution of the IP address in which the client sends its request to a server that eventually returns a response.
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| redirection | An ICMP message type that informs the sender of a preferred route.
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| redundancy | The addition of bits to a message for error control.
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| Reed-Solomon | A complex, but efficient, cyclic code.
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| reflection | The phenomenon related to the bouncing back of light at the boundary of two media.
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| refraction | The phenomenon related to the bending of light when it passes from one medium to another.
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| regenerator | A device that regenerates the original signal from a corrupted signal. See also repeater.
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| regional cable head (RCH) | In an HFC network, the main distribution site.
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| regional ISP | A small ISP that is connected to one or more NSPs.
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| registrar | An authority to register new domain names.
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| registrar server | In SIP, a server that knows the IP address of the callee.
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| reliability | A QoS flow characteristic; dependability of the transmission.
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| remote access | Using a terminal that is not directly connected to a computer.
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| remote bridge | A device that connects LANs and point-to-point networks; often used in a backbone network.
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| remote host | The computer that a user wishes to access while seated physically at another computer.
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| remote server | A program run at a site physically removed from the user.
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| rendezvous router | A router that is the core or center for each multicast group; it becomes the root of the tree.
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| rendezvous-point tree | A group-shared tree method in which there is one tree for each group.
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| repeater | A device that extends the distance a signal can travel by regenerating the signal.
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| replay attack | The resending of a message that has been intercepted by an intruder.
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| Request for Comment (RFC) | A formal Internet document concerning an Internet issue.
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| request header | A part of the HTTP request message that specifies the client's configuration and the client's preferred document format.
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| resolver | The DNS client that is used by a host that needs to map an address to a name or a name to an address.
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| Resource Reservation Protocol (RSVP) | A signaling protocol to help IP create a flow and make a resource reservation to improve QoS.
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| retransmission time-out | The expiration of a timer that controls the retransmission of packets.
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| response header | A part of the HTTP response message that specifies the server's configuration and special information about the request.
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| response message | A DNS message type that returns information.
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| retransmission timer | A timer that controls the waiting time for an acknowledgment of a segment.
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| return to zero (RZ) | A digital-to-digital encoding technique in which the voltage of the signal is zero for the second half of the bit interval.
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| reuse factor | In cellular telephony, the number of cells with a different set of frequencies.
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| Reverse Address Resolution Protocol (RARP) | A TCP/IP protocol that allows a host to find its Internet address given its physical address.
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| reverse path broadcasting (RPB) | A technique in which the router forwards only the packets that have traveled the shortest path from the source to the router.
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| reverse path forwarding (RPF) | A technique in which the router forwards only the packets that have traveled the shortest path from the source to the router.
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| reverse path multicasting (RPM) | A technique that adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes.
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| Rijndael algorithm | An algorithm named after its two Belgian inventors, Vincent Rijmen and Joan Daemen that is the basis of AES.
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| ring topology | A topology in which the devices are connected in a ring. Each device on the ring receives the data unit from the previous device, regenerates it, and forwards it to the next device.
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| Rivest, Shamir, Adleman (RSA) encryption | See RSA encryption.
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| RJ45 | A coaxial cable connector.
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| roaming | In cellular telephony, the ability of a user to communicate outside of his own service provider's area.
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| root server | In DNS, a server whose zone consists of the whole tree. A root server usually does not store any information about domains but delegates its authority to other servers, keeping references to those servers.
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| rotary dialing | Accessing the switching station through a phone that sends a digital signal to the end office.
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| rotation cipher | A keyed or keyless cipher in which the input bits are rotated to the left or right to create output bits.
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| round-trip time (RTT) | The time required for a datagram to go from a source to a destination and then back again.
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| route | A path traveled by a packet.
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| router | An internetworking device operating at the first three OSI layers. A router is attached to two or more networks and forwards packets from one network to another.
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| router link LSA | An LSA packet that advertises all of the links of a router.
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| router-solicitation and advertisement message | An ICMP message sent to obtain and disperse router information.
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| Routing Information Protocol (RIP) | A routing protocol based on the distance vector routing algorithm.
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| routing table | A table containing information a router needs to route packets. The information may include the network address, the cost, the address of the next hop, and so on.
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| routing | The process performed by a router; finding the next hop for a datagram.
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| RSA encryption | A popular public-key encryption method developed by Rivest, Shamir, and Adleman.
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| sampling rate | The number of samples obtained per second in the sampling process.
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| sampling | The process of obtaining amplitudes of a signal at regular intervals.
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| satellite network | A combination of nodes that provides communication form one point on the earth to another.
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| S-box | An encryption device made of decoders, P-boxes, and encoders.
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| scatternet | A combination of piconets.
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| scrambling | In digital-to-digital conversion, modifying part of the rules in line coding scheme to create bit synchronization.
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| search algorithm | A rule for finding the next hop.
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| secondary server | In DNS, a server that transfers the complete information about a zone from another server (primary or secondary) and stores the file on its local disk.
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| secondary station | In poll/select access method, a station that sends a response in answer to a command from a primary station.
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| secret-key encryption | A security method in which the key for encryption is the same as the key for decryption; both sender and receiver have the same key.
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|
| Secure Hash Algorithm 1 (SHA-1) | A hash algorithm designed by the National Institute of Standards and Technology (NIST). It was published as a Federal Information Processing Standard (FIPS).
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| Secure Socket Layer (SSL) | A protocol designed to provide security and compression services to data generated from the application layer.
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| Security Association (SA) | An IPSec signaling protocol that creates a logical connection between 2 hosts.
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| Security association database (SADB) | A database defining a set of single security associations.
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| security parameter index (SPI) | A parameter that uniquely distinguish on security association from the others.
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| security | The protection of a network from unauthorized access, viruses, and catastrophe.
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| segment | The packet at the TCP layer. Also, the length of transmission medium shared by devices.
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| segmentation and reassembly (SAR) | The lower AAL sublayer in the ATM protocol in which a header and/or trailer may be added to produce a 48-byte element.
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| segmentation | The splitting of a message into multiple packets; usually performed at the transport layer.
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| select | In poll/select access method, a procedure in which the primary station asks a secondary station if it is ready to receive data.
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| selective-repeat ARQ | An error-control method in which only the frame in error is resent.
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| self-synchronization | Synchronization of long strings of 1s or 0s through the coding method.
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| semantics | The meaning of each section of bits.
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| sender window | In the TCP sliding window protocol, the window at the sender site.
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|
| sequence number | The number that denotes the location of a frame or packet in a message.
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| serial transmission | Transmission of data one bit at a time using only one single link.
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| server | A program that can provide services to other programs, called clients.
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| server control point (SCP) | In SS7 terminology, the node that controls the whole operation of the network.
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| service-point address | See port address.
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| Session Initiation Protocol (SIP) | In voice over IP, an application protocol that establishes, manages, and terminates a multimedia session.
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| session layer | The fifth layer of the OSI model, responsible for the establishment, management, and termination of logical connections between two end users.
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| setup phase | In virtual circuit switching, a phase in which the source and destination use their global addresses to help switches make table entries for the connection.
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| S-frame | An HDLC frame used for supervisory functions such as acknowledgment, flow control, and error control; it contains no user data.
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| Shannon capacity | The theoretical highest data rate for a channel.
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| shielded twisted-pair (STP) | Twisted-pair cable enclosed in a foil or mesh shield that protects against electromagnetic interference.
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|
| shift cipher | The simplest monoalphabetic cipher in which the plaintext and ciphertext consist of letters. In the encryption algorithm, the characters are shifted down the character list; in the decryption algorithm, the characters are shifted up the character list.
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|
| shift register | A register in which each memory location, at a time click, accepts the bit at its input port, stores the new bit, and displays it on the output port.
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|
| short interframe space (SIFS) | In CSMA/CA, a period of time that the destination waits after receiving the RTS.
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| shortest path tree | A routing table formed by using the Dijkstra algorithm.
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| signal | Electromagnetic waves propagated along a transmission medium.
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| signaling connection control point (SCCP) | In SS7, the control points used for special services such as 800 calls.
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|
| signal element | The shortest section of a signal (time-wise) that represents a data element.
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| signal point (SP) | In SS7 terminology, the user telephone or computer is connected to the signal points.
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| signal rate | The number of signal elements sent in one second.
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| Signal transport port (STP) | In SS7 terminology, the node used by the signaling network.
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| Signaling System Seven (SS7) | The protocol that is used in the signaling network.
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| signal level | The number of values allowed in a particular signal.
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| signal-to-noise ratio (SNR) | The signal strength divided by the noise, both in decibels.
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| silly window syndrome | A situation in which a small window size is advertised by the receiver and a small segment sent by the sender.
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| simple and efficient adaptation layer (SEAL) | An AAL layer designed for the Internet (AAL5).
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| simple bridge | A networking device that links two segments; requires manual maintenance and updating.
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| Simple Mail Transfer Protocol (SMTP) | The TCP/IP protocol defining electronic mail service on the Internet.
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| Simple Network Management Protocol (SNMP) | The TCP/IP protocol that specifies the process of management in the Internet.
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| Simple Protocol | The simple protocol we used to show an access method without flow and error control.
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| simplex mode | A transmission mode in which communication is one way.
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| sine wave | An amplitude-versus-time representation of a rotating vector.
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| single-bit error | Error in a data unit in which only one single bit has been altered.
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| single-mode fiber | An optical fiber with an extremely small diameter that limits beams to a few angles, resulting in an almost horizontal beam.
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| site local address | An IPv6 address for a site having several networks, but not connected to the Internet.
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| SKEME | A protocol for key exchange designed by Hugo Krawcyzk. It is one of the three protocols that form the basis of IKE.
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| sky propagation | Propagation of radio waves into the ionosphere and then back to earth.
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| slash notation | A shorthand method to indicate the number of 1s in the mask.
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| slave | In a piconet, a station under control of a master.
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| sliding window | A protocol that allows several data units to be in transition before receiving an acknowledgment.
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| sliding window ARQ | An error-control protocol using sliding window concept.
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| slotted ALOHA | The modified ALOHA access method in which time is divided into slots and each station is forced to start sending data only at the beginning of the slot.
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| slow convergence | A RIP shortcoming apparent when a change somewhere in the internet propagates very slowly through the rest of the internet.
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| slow start | A congestion-control method in which the congestion window size increases exponentially at first.
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| socket address | A structure holding an IP address and a port number.
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| socket | An end point for a process; two sockets are needed for communication.
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| socket interface | An API based on UNIX that defines a set of system calls (procedures) that are an extension of system calls used in UNIX to access files.
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| solicited response | A RIP response sent only in answer to a request.
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| source address (SA) | The address of the sender of the message.
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| source quench | A method, used in ICMP for flow control, in which the source is advised to slow down or stop the sending of datagrams because of congestion.
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| source routing bridge | A source or destination station that performs some of the duties of a transparent bridge as a method to prevent loops.
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| source routing | Explicitly defining the route of a packet by the sender of the packet.
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| source-based tree | A tree used for multicasting by multicasting protocols in which a single tree is made for each combination of source and group.
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| source quench message | An ICMP message sent to slow down or stop the sending of datagrams.
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| source-to-destination delivery | The transmission of a message from the original sender to the intended recipient.
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| space propagation | A type of propagation that can penetrate the ionosphere.
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| space-division switching | Switching in which the paths are separated from each other spatially.
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| spanning tree | A tree with the source as the root and group members as leaves; a tree that connects all of the nodes.
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| spanning tree algorithm | An algorithm that prevents looping when two LANs are connected by more than one bridge.
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| spatial compression | Compressing an image by removing redundancies.
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| special-query message | An IGMP query message sent by a router to ensure that no host or router is interested in continuing membership in a group.
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| specific host on this network | A special address in which the netid is all 0s and the hostid is explicit.
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| spectrum | The range of frequencies of a signal.
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| split horizon | A method to improve RIP stability in which the router selectively chooses the interface from which updating information is sent.
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| spread spectrum | A wireless transmission technique that requires a bandwidth several times the original bandwidth.
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| Standard Ethernet | The conventional Ethernet operating at 10 mbps.
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| star backbone | A backbone in which the logical topology is a star.
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| star topology | A topology in which all stations are attached to a central device (hub).
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| start bit | In asynchronous transmission, a bit to indicate the beginning of transmission.
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| start frame delimiter (SFD) | A 1-byte field in the IEEE 802.3 frame that signals the beginning of the readable (nonpreamble) bit stream.
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| state transition diagram | A diagram to illustrate the states of a finite state machine.
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| static document | On the World Wide Web, a fixed-content document that is created and stored in a server.
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| static mapping | A technique in which a list of logical and physical address correspondences is used for address resolution.
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| static routing | A type of routing in which the routing table remains unchanged.
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| stationary host | A host that remains attached to one network.
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| statistical TDM | A TDM technique in which slots are dynamically allocated to improve efficiency.
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| status line | In the HTTP response message a line that consists of the HTTP version, a space, a status code, a space, a status phrase.
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| stop bit | In asynchronous transmission, one or more bits to indicate the end of transmission.
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| stop-and-wait ARQ | An error-control protocol using stop-and-wait flow control.
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| Stop-and-Wait Protocol | A protocol in which the sender sends on frame, stops until it receives confirmation from the receiver, and then sends the next frame.
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| store-and-forward switch | A switch that stores the frame in an input buffer until the whole packet has arrived.
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| straight tip connector | A type of fiber-optic cable connector using a bayonet locking system.
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| Stream Control Transmission Protocol (SCTP) | The transport layer protocol designed for Internet telephony and related applications.
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| stream socket | A structure designed to be used with a connection-oriented protocol such as TCP.
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| streaming live audio/video | Broadcast data from the Internet that a user can listen to or watch.
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| streaming stored audio/video | Data downloaded as files from the Internet that a user can listen to or watch.
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| strong collision | Creating two message with the same digest.
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| Structure of Management Information (SMI) | In SNMP, a component used in network management.
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| STS multiplexer/demultiplexer | A SONET device that multiplexes and demultiplexes signals.
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| stub link | A network that is connected to only one router.
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| subnet | subnetwork.
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| subnet address | The network address of a subnet.
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| subnet mask | The mask for a subnet.
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| subnetwork | A part of a network.
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| subscriber channel connector | A fiber-optic cable connector using a push/pull locking mechanism.
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| substitution cipher | A bit-level encryption method in which n bits substitute for another n bits as defined by P-boxes, encoders, and decoders.
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| suffix | For a network, the varying part (similar to the hostid) of the address. In DNS, a string used by an organization to define its host or resources.
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| summary link to AS boundary router LSA | An LSA packet that lets a router inside an area know the route to an autonomous boundary router.
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| summary link to network LSA | An LSA packet that finds the cost of reaching networks outside of the area.
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| supergroup | A signal composed of five multiplexed groups.
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| supernet | A network formed from two or more smaller networks.
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| supernet mask | The mask for a supernet.
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| supervisory frame | See S-frame.
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| switch | A device connecting multiple communication lines together.
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| switched Ethernet | An Ethernet in which a switch, replacing the hub, can direct a transmission to its destination.
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| switched virtual circuit (SVC) | A virtual circuit transmission method in which a virtual circuit is created and in existence only for the duration of the exchange.
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| switched/56 | A temporary 56-Kbps digital connection between two users.
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| switching office | The place where telephone switches are located.
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| symmetric digital subscriber line (SDSL) | A DSL-based technology similar to HDSL, but using only one single twisted-pair cable.
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| symmetric key | The key used for both encryption and decryption.
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| symmetric-key cryptography | A cipher in which the same key is used for encryption and decryption.
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| synchronization points | Reference points introduced into the data by the session layer for the purpose of flow and error control.
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| synchronous connection oriented (SCO) link | In a Bluetooth network, a physical link created between a master and a slave that reserves specific slots at regular intervals.
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| Synchronous Digital Hierarchy (SDH) | The ITU-T equivalent of SONET.
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| Synchronous Optical Network (SONET) | A standard developed by ANSI for fiber optic technology that can transmit high-speed data. It can be used to deliver text, audio, and video.
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| synchronous payload envelope (SPE) | The part of the SONET frame containing user data and transmission overhead.
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| synchronous TDM | A TDM technique in which each input has an allotment in the output even when it is not sending data.
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| synchronous transmission | A transmission method that requires a constant timing relationship between the sender and the receiver.
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| synchronous transport module (STM) | A signal in the SDH hierarchy.
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| synchronous transport signal (STS) | A signal in the SONET hierarchy.
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| syndrome | A sequence of bit generated by applying the error checking function to a codeword.
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| syntax | The structure or format of data, meaning the order in which they are presented.
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| T lines | A hierarchy of digital lines designed to carry speech and other signals in digital forms. The hierarchy defined T-1, T-2, T-3, and T-4 lines.
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| tandem office | The toll office in a telephone network.
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| tag | A formatting instruction embedded in an HTML document.
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| TCP timer | The timers used by TCP to handle retransmission, zero window-size advertisements, long idle connections, and connection termination.
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| TCP/IP protocol suite | A group of hierarchical protocols used in an internet.
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| TDM bus | A time-division switch in which the input and output lines are connected to a high-speed bus through microswitches.
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| teardown phase | In virtual circuit switching, the phase in which the source and destination inform the switch to erase their entry.
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| telecommunications | Exchange of information over distance using electronic equipment.
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| teleconferencing | Audio and visual communication between remote users.
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| Teledesic | A system of satellites that provides fiber-optic communication (broadband channels, low error rate, and low delay)
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| telephone user port (UTP) | A protocol at the upper layer of SS7 that is responsible for setting up voice calls.
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| TELNET | See Terminal Network.
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| temporal compression | An MPEG compression method in which redundant frames are removed.
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| Ten-Gigabit Ethernet | The new implementation of Ethernet operating at 10 Gbps.
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| Terminal Network (TELNET) | A general purpose client-server program that allows remote login.
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| three-way handshaking | A sequence of events for connection establishment or termination consisting of the request, then the acknowledgment of the request, and then confirmation of the acknowledgment.
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| terminating state | A PPP state in which several packets are exchanged between the two ends for house cleaning and closing the link.
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| terminator | An electronic device that prevents signal reflections at the end of a cable.
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| thick Ethernet | See 10Base5.
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| thin Ethernet | See 10Base2.
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| three-layer switch | A switch at the network layer; a router.
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| three-way handshake | A sequence of events for connection establishment or termination consisting of the request, then the acknowledgment of the request, and then confirmation of the acknowledgment.
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| throughput | The number of bits that can pass through a point in one second.
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| ticket | An encrypted message containing a session key.
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| ticket-granting server (TGS) | A Kerberos server that issues tickets.
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| time division duplexing TDMA (TDD-TDMA) | In a Bluetooth network, a kind of half-duplex communication in which the slave and receiver send and receive data, but not at the same time (half-duplex).
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| time division multiple access (TDMA) | A multiple access method in which the bandwidth is just one time-shared channel.
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| time to live (TTL) | The lifetime of a packet.
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| time-division multiplexing (TDM) | The technique of combining signals coming from low-speed channels to share time on a high-speed path.
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| time-division switching | A circuit-switching technique in which time-division multiplexing is used to achieve switching.
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| time-domain plot | A graphical representation of a signal's amplitude versus time.
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| time-exceeded message | An ICMP message sent to inform a source that (1) its datagram has a time-to-live value of zero, or (2) the fragments of a message have not been received within a set time limit.
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| time-slot interchange (TSI) | A time-division switch consisting of RAM and a control unit.
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| timestamp | An IP header option used to record the time of datagram processing by a router. Also, a method to handle jitter in interactive real-time audio/video.
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| timestamp-request and reply message | An ICMP message sent to determine the round-trip time or to synchronize clocks.
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| time-waited timer | A TCP timer used in connection termination that allows late segments to arrive.
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| T-lines | A hierarchy of digital lines designed to carry speech and other signals in digital forms. The hierarchy defines T-1, T-2, T-3, and T-4 lines.
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| token | A small packet used in token-passing access method.
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| token bucket | An algorithm that allows idle hosts to accumulate credit for the future in the form of tokens.
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| token passing | An access method in which a token is circulated in the network. The station that captures the token can send data.
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| Token Ring | A LAN using a ring topology and token-passing access method.
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| toll call service | An inter-LATA or intra-LATA telephone service charged to the caller.
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| topology | The structure of a network including physical arrangement of devices.
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| touch-tone dialing | A telephone dialing method in which each key is represented by two small bursts of analog signals.
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| traffic | Messages on a network.
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| traffic control | A method for shaping and controlling traffic in a wide area network.
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| traffic shaping | A mechanism to control the amount and the rate of the traffic sent to the network to improve QoS.
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| trailer | Control information appended to a data unit.
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| transaction capablities application port (TCAP) | A protocol at the upper layer of SS7 that provides remote procedure calls that let an application program on a computer invoke a procedure on another computer.
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| transceiver | A device that both transmits and receives.
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| transceiver cable | In Ethernet, the cable that connects the station to the transceiver. Also called the attachment unit interface.
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| transient link | A network with several routers attached to it.
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| transition state | The different phases through which a PPP connection goes.
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| translation | Changing from one code or protocol to another.
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| Transmission Control Protocol (TCP) | A transport protocol in the TCP/IP protocol suite.
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| Transmission Control Protocol/Internetworking Protocol (TCP/IP) | A five-layer protocol suite that defines the exchange of transmissions across the Internet.
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| transmission medium | The physical path linking two communication devices.
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| transmission path (TP) | In ATM, the physical connection between two switches.
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| transmission rate | The number of bits sent per second.
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| transparency | The ability to send any bit pattern as data without it being mistaken for control bits.
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| transparent bridge | Another name for a learning bridge.
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| transparent data | Data that can contain control bit patterns without being interpreted as control.
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| Transport Layer Security (TLS) | A security protocol at the transport level designed to provide security on the WWW.
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| transport layer | The fourth layer in the Internet and OSI model; responsible for reliable end-to-end delivery and error recovery.
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| transpositional cipher | A character-level encryption method in which the position of the character changes.
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| trellis-coded modulation | A modulation technique that includes error correction.
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| trilateration | A two-dimensional method of finding a location given the distances from 3 different points.
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| triangulation | A two-dimensional method of finding a location given the distances from 3 different points.
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| tribit | A unit of data consisting of three bits.
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| triple DES | An algorithm compatible with DES that uses three DES blocks and two 56-bit keys.
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| Trivial File Transfer Protocol (TFTP) | An unreliable TCP/IP protocol for file transfer that does not require complex interaction between client and server.
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| trunk | Transmission media that handle communications between offices.
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| tunneling | In multicasting, a process in which the multicast packet is encapsulated in a unicast packet and then sent through the network. In VPN, the encapsulation of an encrypted IP datagram in a second outer datagram. For IPv6, a strategy used when two computers using IPv6 want to communicate with each other when the packet must pass through a region that uses IPv4.
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| twisted-pair cable | A transmission medium consisting of two insulated conductors in a twisted configuration.
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| twisted-pair Ethernet | An Ethernet using twisted-pair cable; 10Base-T.
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| two-dimensional parity check | An error detection method in two dimensions.
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| two-layer switch | A bridge with many ports and a design that allows better (faster) performance.
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| type of service (TOS) | A criteria or value that specifies the handling of the datagram.
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| U-frame | An HDLC unnumbered frame carrying link management information.
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| unbalanced configuration | An HDLC configuration in which one device is primary and the others secondary.
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| unguided medium | A transmission medium with no physical boundaries.
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| unicast address | An address belonging to one destination.
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| unicast message | A message sent to just one destination.
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| unicast routing | The sending |