Glossary (See related pages) 1000Base-CX   A two-wire STP implementation of Gigabit Ethernet. 1000Base-LX   A two-wire fiber implementation of Gigabit Ethernet using long-wave laser. 1000Base-SX   A two-wire fiber implementation of Gigabit Ethernet using short-wave laser signals. 1000Base-T   A four-wire UTP implementation of Gigabit Ethernet. 100Base-FX   A two-wire fiber implementation of Fast Ethernet. 100Base-T4   A four-wire UTP implementation of Fast Ethernet. 100Base-TX   A two-wire UTP implementation of Fast Ethernet. 10Base2   The thin coaxial cable implementation of Standard Ethernet. 10Base5   The thick coaxial cable implementation of Standard Ethernet. 10Base-F   The fiber implementation of Standard Ethernet. 10Base-T   The twisted-pair implementation of Standard Ethernet. 10Base-E   The extended implementation of Ten-Gigabit Ethernet. 10Base-L   A fiber implementation of Ten-Gigabit Ethernet using long-wave laser. 10Base-S   A fiber implementation of Ten-Gigabit Ethernet using short-wave laser. 1-persistent strategy   A CSMA persistence strategy in which a station sends a frame immediately if the line is idle. 2B1Q encoding   A line encoding technique in which each pulse represents 2 bits. 4B/5B encoding   A block coding technique in which 4 bits are encoded into a 5-bit code. 4-dimensional, 5-level pulse amplitude modulation (4D-PAM5)   An encoding scheme used by 1000Base-T. 56K modem   A modem technology using two different data rates: one for uploading and one for downloading from the Internet. 800 service   A telephone service free to the caller. 8B/10B encoding   A block coding technique in which 8 bits are encoded into a 10-bit code. 8B/6T encoding   A block coding technique in which 8 bits are encoded into a 6-bit code. 900 service   A telephone service paid by the caller. Abstract Syntax Notation 1 (ASN.1)   A standard for representing simple and structured data. access control   The determination of link control through a data link protocol. access rate   In Frame Relay, the data rate that can never be exceeded. access point   A central base station in a BSS. acknowledgment (ACK)   A response sent by the receiver to indicate the successful receipt and acceptance of data. active close   In the client-server model, the closing of a communication by the client. active document   In the World Wide Web, a document executed at the local site using Java. active open   In the client-server model, the opening of a communication by the client. adaptive delta modulation   A delta modulation technique in which the value of delta changes according to the amplitude of the analog signal. add/drop multiplexer   A SONET device that multiplexes signals from different sources or demultiplexes a signal to multiple destinations. additive increase   With slow start, a congestion avoidance strategy in which the window size is increased by just one segment instead of exponentially. Address Resolution Protocol (ARP)   In TCP/IP, a protocol for obtaining the physical address of a node when the Internet address is known. 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. Advanced Encryption Standard (AES)   A secret-key cryptosystem adapted by NIST to replace DES. address aggregation   A mechanism in which the blocks of addresses for several organizations are aggregated into one larger block. address space   The total number of addresses used by a protocol. address-mask request and reply ICMP   Messages that find the network mask. Advanced Mobile Phone System (AMPS)   A North American analog cellular phone system using FDMA. Advanced Research Projects Agency (ARPA)   The government agency that funded ARPANET. Advanced Research Projects Agency Network (ARPANET)   The packet-switching network that was funded by ARPA. ALOHA   The original random multiple access method in which a station can send a frame any time it has one to send. alternate mark inversion (AMI)   A digital-to-digital bipolar encoding method in which the amplitude representing 1 alternates between positive and negative voltages. American National Standards Institute (ANSI)   A national standards organization that defines standards in the United States. American Standard Code for Information Interchange (ASCII)   A character code developed by ANSI and used extensively for data communication. amplitude   The strength of a signal, usually measured in volts, amperes, or watts. amplitude modulation (AM)   An analog-to-analog conversion method in which the carrier signal's amplitude varies with the amplitude of the modulating signal. amplitude shift keying (ASK)   A modulation method in which the amplitude of the carrier signal is varied to represent binary 0 or 1. analog   A continuously varying entity. analog data   Data that are continuous and smooth and not limited to a specific number of values. analog hierarchy   A telephone company system in which multiplexed signals are combined into successively larger groups for more efficient transmission. analog leased service   A service featuring a dedicated line between two users. analog signal   A continuous waveform that changes smoothly over time. analog switched service   A temporary analog connection between two users. analog-to-analog modulation   The representation of analog information by an analog signal. analog-to-digital conversion   The representation of analog information by a digital signal. 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. anonymous FTP   A protocol in which a remote user can access another machine without an account or password. anycast address   An address that defines a group of computers with addresses that have the same beginning. aperiodic signal   A signal that does not exhibit a pattern or repeating cycle. applet   A computer program for creating an active Web document. It is usually written in Java. application adaptation layer (AAL)   A layer in ATM protocol that breaks user data into 48-byte payloads. application layer   The fifth layer in the Internet model; provides access to network resources. application programming interface (API)   A set of declarations, definitions, and procedures followed by programmers to write client-server programs. area   A collection of networks, hosts, and routers all contained within an autonomous system. area border router   A router inside an area that summarizes the information about the area and sends it to other areas. area identification   A 32-bit field that defines the area within which the routing takes place. association   A connection in SCTP asymmetric digital subscriber line (ADSL)   A communication technology in which the downstream data rate is higher than the upstream rate. asynchronous balanced mode (ABM)   In HDLC, a communication mode in which all stations are equal. asynchronous connectionless link (ACL)   A link between a Bluetooth master and slave in which a corrupted payload is retransmitted. 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. asynchronous transmission   Transfer of data with start and stop bit(s) and a variable time interval between data units. ATM LAN   A LAN using ATM technology. ATM layer   A layer in ATM that provides routing, traffic management, switching, and multiplexing services. ATM switch   An ATM device providing both switching and multiplexing functions. attachment unit interface (AUI)   A 10Base5 cable that performs the physical interface functions between the station and the transceiver. attenuation   The loss of a signal's energy due to the resistance of the medium. audio   Recording or transmitting of sound or music. authenticating state   In PPP, an optional state that verifies the identity of the receiver. 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. authentication server (AS)   The KDC in the Kerberos protocol. authentication   Verification of the sender of a message. automatic repeat request (ARQ)   An error-control method in which correction is made by retransmission of data. automatic tunneling   Tunneling in which the receiving host has an IPv6 compatible address; no reconfiguration is necessary. autonegotiation   A Fast Ethernet feature that allows two devices to negotiate the mode or data rate. autonomous system (AS)   A group of networks and routers under the authority of a single administration. autonomous system boundary router   Routers responsible for dissipating information about other autonomous systems into the current system. available bit rate (ABR)   The minimum data rate in ATM at which cells can be delivered. back off   In multiple access, waiting before re-sending after a collision. backbone router   A router inside the backbone. backbone   A network that connects smaller networks in an organization. backward explicit congestion notification (BECN)   A bit in the Frame Relay packet that notifies the sender of congestion. bandwidth on demand   A digital service that allows subscribers higher speeds through the use of multiple lines. 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. bandwidth-delay product   A measure of the number of bits that can be sent while waiting for news from the receiver. banyan switch   A multistage switch with microswitches at each stage that route the packets based on the output port represented as a binary string. Barker sequence   A sequence of 11 bits used for spreading. baseband transmission   Transmission of digital or analog signal without modulation using a low-pass channel. band-pass channel   A channel that can pass a range of frequencies. base header   In IPv6, the main header of the datagram. 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. Basic Encoding Rule (BER)   A standard that encodes data to be transferred through a network. Basic Latin   ASCII character set. basic service set (BSS)   The building block of a wireless LAN as defined by the IEEE 802.11 standard. baud rate   The number of signal elements transmitted per second. A signal element consists of one or more bits. Bayone-Neill-Concelman (BNC) connector   A common coacxial cable connector. best-effort delivery   The unreliable transmission mechanism by IP that does not guarantee message delivery. bidirectional authentication   An authentication method involving a challenge and a response from sender to receiver and vice versa. bidirectional frame (B-frame)   An MPEG frame that is related to the preceding and following I-frame or P-frame. binary exponential backup   In contention access methods, a retransmission delay strategy used by a system to delay access. binary notation   Representation of IP addresses in binary. 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. bipolar encoding   A digital-to-digital encoding method in which 0 amplitude represents binary 0 and positive and negative amplitudes represent alternate 1s. 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. bipolar n-zero substitution (BnZS)   An encoding method to provide synchronization for long strings of 0s. bit   binary digit; the smallest unit of data(0 or 1) bit interval   The time required to send one bit. bit padding   In TDM, the addition of extra bits to a device's source stream to force speed relationships. bit rate   The number of bits transmitted per second. 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. bit-oriented protocol   A protocol in which the data frame is interpreted as a sequence of bits. bits per second (bps)   A measurement of data speed; bits transmitted per second. block cipher   An encryption/decryption algorithm that has a block of bits as its basic unit. 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. block coding   A coding method to ensure synchronization and detection of errors. blocking   An event that occurs when a switching network is working at its full capacity and cannot accept more input. blocking port   A port on a bridge that does not forward a frame. 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. BNC connector   A common coaxial cable connector. Bootstrap Protocol (BOOTP)   The protocol that provides configuration information from a table (file). Border Gateway Protocol (BGP)   An interautonomous system routing protocol based on path vector routing. bridge   A network device operating at the first two layers of the Internet model with filtering and forwarding capabilities. broadband transmission   Transmission of signals using modulation of a higher frequency signal. The term implies a wide-bandwidth data combined from different sources. broadcast address   An address that allows transmission of a message to all nodes of a network. broadcast/unknown server (BUS)   A server connected to an ATM switch that can multicast and broadcast frames. broadcasting   Transmission of a message to all nodes in a network. browser   An application program that displays a WWW document. A browser usually uses other Internet services to access the document. BSS-transition mobility   In a wireless LAN, a station that can move from one BSS to another but is confined inside one ESS. bucket brigade attack   See man-in-the middle attack burst error   Error in a data unit in which two or more bits have been altered. bursty data   Data with varying instantaneous transmission rates. bus topology   A network topology in which all computers are attached to a shared medium. byte   A group of eight bits. 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. byte-oriented protocol   A protocol in which the data section of the frame is interpreted as a sequence of bytes (characters). cable modem   A technology in which the TV cable provides Internet access. cable modem transmission system (CMTS)   A device installed inside the distribution hub that receives data from the Internet and passes them to the combiner. cable TV network   A system using coaxial or fiber optic cable that brings multiple channels of video programs into homes. caching   The storing of information in a small, fast memory. Caesar cipher   A shift cipher used by Julius Caesar with the key value of 3. carrier extension   A technique in Gigabit Ethernet that increases the minimum length of the frame to achieve a higher maximum cable length. carrier sense multiple access (CSMA)   A contention access method in which each station listens to the line before transmitting data. carrier sense multiple access with collision avoidance (CSMA/CA)   An access method in which collision is avoided. 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. 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. cell   A small, fixed-size data unit; also, in cellular telephony, a geographical area served by a cell office. cell network   A network using the cell as its basic data unit. cellular telephony   A wireless communication technique in which an area is divided into cells. A cell is served by a transmitter. Certification Authority (CA)   An agency such as a federal or state organization that binds a public key to an entity and issues a certificate. Challenge Handshake Authentication Protocol (CHAP)   In PPP, a three-way handshaking protocol used for authentication. channel   A communications pathway. channelization   A multiple access method in which the available bandwidth of a link is shared in time. character-oriented protocol   See byte-oriented protocol checksum   A field used for error detection. It is formed by adding bit streams using one's complement arithmetic and then complementing the result. chip   In CDMA, a number in a code that is assigned to a station. choke point   A packet sent by a router to the source to inform it of congestion. chunk   A unit of transmission in SCTP. cipher   An encryption/decryption algorithm. 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. 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. cipher stream mode (CSM)   A DES and triple DES operation mode in which data is sent and received 1 byte at a time. cipher suite   AA list of possible ciphers. ciphertext   The encrypted data. circuit switching   A switching technology that establishes an electrical connection between stations using a dedicated path. 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. class A address   An IPv4 address with the first octet between 0 and 127. class B address   An IPv4 address with the first octet between 128 and 191. class C address   An IPv4 address with the first octet between 192 and 223. class D address   An IPv4 multicast address. class E address   An IPv4 address reserved for special purposes. 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. classless addressing   An addressing mechanism in which the IP address space is not divided into classes. Classless InterDomain Routing (CIDR)   A technique to reduce the number of routing table entries when supernetting is used. client process   A running application program on a local site that requests service from a running application program on a remote site. 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). closed-loop congestion control   A method to alleviate congestion after it happens. coaxial cable   A transmission medium consisting of a conducting core, insulating material, and a second conducting sheath. code division multiple access (CDMA)   A multiple access method in which one channel carries all transmissions simultaneously. codeword   The encoded dataword. ColdFusion   A dynamic web technology that allows the fusion of data items coming from a conventional database. 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. collision domain   The length of the medium subject to collision. committed burst size   The maximum number of bits in a specific time period that a Frame Relay network must transfer without discarding any frames. committed information rate (CIR)   The committed burst size divided by time. common carrier   A transmission facility available to the public and subject to public utility regulation. Common Gateway Interface (CGI)   A standard for communication between HTTP servers and executable programs. CGI is used in creating dynamic documents. community antenna TV (CATV)   A cable network service that broadcasts video signals to locations with poor or no reception. compatible address   An IPv6 address consisting of 96 bits of zero followed by 32 bits of IPv4. 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. complementary code keying (CCK)   An HR-DSSS encoding method that encodes four or eight bits into one symbol. composite signal   A signal composed of more than one sine wave. concurrent client   A client running the same time as another client of the same process. concurrent server   A server that can process many requests at the same time and share its time between many requests. congestion avoidance   In Frame Relay, a method using two bits that explicitly notify the source and destination of congestion. congestion control   A method to manage network and internetwork traffic to improve throughput. congestion   Excessive network or internetwork traffic causing a general degradation of service. connecting device   A tool that connects computers or networks. connection control   The technique used by the transport layer to deliver segments. connection establishment   The preliminary setup necessary for a logical connection prior to actual data transfer. connection termination   A message sent to end a connection. connectionless iterative server   A connectionless server that processes one request at a time. connectionless service   A service for data transfer without connection establishment or termination. connection-oriented concurrent server   A connection-oriented server that can serve many clients at the same time. connection-oriented service   A service for data transfer involving establishment and termination of a connection. constant bit rate (CBR)   The data rate of an ATM service class that is designed for customers requiring real-time audio or video services. constellation diagram   A graphical representation of the phase and amplitude of different bit combinations in digital-to-analog modulation. Consultative Committee for International Telegraphy and Telephony (CCITT)   An international standards group now known as the ITU-T. contention   An access method in which two or more devices try to transmit at the same time on the same channel. control connection   The FTP connection used for control information (commands and responses). controlled access   A multiple access method in which the stations consult one another to determine who has the right to send. convergence sublayer (CS)   In ATM protocol, the upper AAL sublayer that adds a header or a trailer to the user data. cookie   A string of characters that holds some information about the client and must be returned to the server untouched. core   The glass or plastic center of an optical fiber. Core-Based Tree (CBT)   In multicasting, a group-shared protocol that uses a center router as the root of the tree. country domain   A subdomain in the Domain Name System that uses two characters as the last suffix. CRC checker   The process that validates the CRC remainder. CRC generator   The process that creates the CRC remainder. critical angle   In refraction, the value of the angle of incidence that produces a 90-degree angle of refraction. 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. crosspoint   The junction of an input and an output on a crossbar switch. crosstalk   The noise on a line caused by signals traveling along another line. cryptography   The science and art of transforming messages to make them secure and immune to attacks. cyclic code   A linear cod in which the cyclic shifting (rotation) of each codeword creates another code word. CSNET   A network sponsored by the National Science Foundation originally intended for universities. cycle   The repetitive unit of a periodic signal. cyclic redundancy check (CRC)   A highly accurate error-detection method based on interpreting a pattern of bits as a polynomial. data element   The smallest entity that can represent a piece of information. A bit. data connection   The FTP connection used for data transfer. data encryption standard (DES)   The U.S. government standard encryption method for nonmilitary and nonclassified use. data exchange protocol   A protocol that uses the secret key to encrypt the data for secrecy and to encrypt the message digest for integrity. data level   The number of different symbols used to represent a digital signal. data link connection identifier (DLCI)   A number that identifies the virtual circuit in Frame Relay. data link control   The responsibilities of the data link layer: flow control and error control. data link layer   The second layer in the Internet model. It is responsible for node-to-node delivery. Data Over Cable System Interface Specifications (DOCSIS)   A standard for data transmission over an HFC network. data rate   The number of data elements sent in one second. data transfer phase   The intermediate phase in circuit-switched or virtual-circuit network in which data transfer takes place. data transparency   See transparency. datagram approach (to packet switching)   A data transmission method in which each data unit is independent of others. datagram   In packet switching, an independent data unit. datagram network   A packet-switched network in which packets are independent from each other. dataword   The smallest block of data in block coding. datagram socket   A structure designed to be used with a connectionless protocol such as UDP. DC component   See direct current. de facto standard   A protocol that has not been approved by an organized body but adopted as a standard through widespread use. de jure standard   A protocol that has been legislated by an officially recognized body. deadlock   A situation in which a task cannot proceed because it is waiting for an even that will never occur. decibel (dB)   A measure of the relative strength of two signal points. decryption   Recovery of the original message from the encrypted data.