Glossary - Network

A B C D E F G H I J K L M N O P Q R S T U V W X-Y-Z Numeric 10BASE2 Ethernet running on thin coax network cable at 10 Mbps. 10BASE5 Ethernet running on thick wire network cable at 10 Mbps. 10BASE-T Ethernet running on unshielded twisted pair (UTP) cable at 10 Mbps. Point-to-point network media, with one end of cable typically going to repeater/hub and other to network device. 100BASE-TX Ethernet running on unshielded twisted pair (UTP) cable at 100 Mbps. Point-to-point network media, with one end of cable typically going to repeater/hub and other to network device. Back to Top A AAL (ATM Adaptation Layer) A collection of standard Asynchronous Transfer Mode (ATM) protocols that adapt user traffic to the cell format. AAL is subdivided into the convergence sub-layer (CS), and the Segmentation And Reassembly (SAR) sub-layer. There are several types of AALs -- AAL0, AAL1, AAL2, AAL3/4 and AAL5 -- to support the various AAL service classes. AAL0 (AAL Type 0) Null protocol. No cell adaptation occurs. AAL1 (AAL Type 1) Used for transporting time-dependent Constant Bit Rate (CBR) traffic, such as audio and video, and emulating Time Division Multiplexer (TDM)-based circuits, such as digital signal level 1 (DS1) and E1. Timing information must be exchanged between the source and the destination. AAL1 supports QoS Class A (defined under QoS in this glossary). AAL2 (AAL Type 2) Used for supporting time-dependent slow or Variable Bit Rate Real Time (VBR-RT) connection-oriented traffic (e.g., packetized and compressed audio and video). Timing information must be exchanged between the source and the destination. AAL2 supports QoS Class B (defined under QoS in this glossary). AAL 3/4 (AAL Type 3 and 4) Used for supporting both connectionless and connection-oriented Variable Bit Rate Non-Real Time (VBR-NRT) traffic. AAL3 supports quality of service (QoS) class C while AAL4 supports QoS class D. AAL3 and AAL4 are combined into one type. AAL3/4 also performs re-sequencing and cell identification operations. AAL3/4 services are suitable for supporting interworking with frame relay, SMDS and X.25. AAL5 (AAL Type 5) Used for supporting connection-oriented variable bit rate VBR-NRT data traffic and signaling messages. AAL5 supports quality of service (QoS) Class X. AAL5 services are suitable for supporting interworking with most data networking protocols, such as frame relay, SMDS, Ethernet and Internet Protocol (IP). AAL5 is more popular and easier to implement than AAL3/4. ABR (Available Bit Rate) One of five Asynchronous Transfer Mode (ATM) service categories. In this service type, the network attempts to pass the maximum number of cells but does not guarantee cell delivery. ABR supports Variable Bit Rate (VBR) data traffic with flow control, a minimum guaranteed data transmission rate, and specified performance parameters. In exchange for regulating user traffic flow, the network offers minimal cell loss of accepted traffic. Traffic parameters are Peak Cell Rate (PCR) and Maximum Cell Rate (MCR). Quality of Service (QoS) parameters are Cell Loss Ratio (CLR) and Cell Error Rate (CER). Access Network Portion of public switched network that connects access nodes to individual subscribers. Predominantly passive twisted pair copper wiring. Access Nodes Points on edge of the Access Network that concentrate individual access lines into smaller number of feeder lines. May also perform various forms of protocol conversion. Examples are Digital Loop Carrier systems concentrating individual voice lines to T1 lines, cellular antenna sites, PBXs, and Optical Network Units (ONUs). ACK Acknowledgement. Address Prefix String of 0 or more bits up to maximum of 152 bits that is lead portion of one or more ATM addresses. Address Resolution Procedure by which client associates LAN destination with ATM address of another client or the BUS. Administrative Domain Collection of managed entities grouped for administrative reasons. ADPCM (Adaptive Differential Pulse Code Modulation) (1) Reduced bit rate variant of PCM audio encoding. (See also PCM.) This algorithm encodes difference between actual audio sample amplitude and predicted amplitude and adapts resolution based on recent differential values. (2) Coding scheme standardized by CCITT (See CCITT) that allows analog voice to be carried on 32 kbps digital channel instead of standard 64 kbps PCM channel. ADSI (Analog Display Services Interface) Protocol that simplifies use of advanced features by displaying text messages, generated by a remote computer or central office switch, on a user's telephone display or television set. ADSL (Asymmetric Digital Subscriber Line) Modems attached to twisted pair copper wiring that transmit from 1.5 to 9 Mbps downstream (to subscriber) and from 16 to 800 kbps upstream, depending on line distance. AIN (Advanced Intelligent Network) Bellcore's switching concept that centralizes significant amount of intelligence rather than constantly placing more information in central office switch. AMI (Alternate Mark Inversion) Line coding format used on T1 facilities that transmits ones by alternate positive and negative pulses. AMPS Advanced Mobile Phone Service (US), the name applied to the original analog cellular system. Still the predominant cellular transmission scheme. ANSI (American National Standards Institute) U.S. body and standards-setting organization, not arm of the government. Accredits various other standards setting committees. API (Application Programming Interface) A set of calling conventions that define how a service is invoked through a software package. AppleTalk Communications protocol developed by Apple Computer to allow networking between Macintoshes. All Macintosh computers have LocalTalk port, running AppleTalk over 230K bps serial line. Also runs over Ethernet (EtherTalk) and Token Ring (TokenTalk) network media. Application Layer The top layer of the network protocol stack. The application layer is concerned with the semantics of work, such as formatting electronic mail messages. (The lower layers of the network address how to represent that data and how to reach the foreign node.) Application-Level Firewall Firewall system providing service by processes that maintain complete TCP connection state and sequencing. Often re-addresses traffic so outgoing traffic appears to have originated from firewall, rather than internal host. APPN (Advanced Peer to Peer Network) IBM network architecture for building dynamic routing across arbitrary network topologies. Intended as an eventual replacement for SNA, IBM's static routed, hierarchical network architecture. ARP (Address Resolution Protocol) Used to dynamically discover the low-level physical network hardware address that corresponds to the high-level Internet Protocol (IP) address for a given host. ARP is limited to physical network systems that support broadcast packets that can be heard by all hosts on the network. ARP is defined in Request for Comments (RFC) 826. ASCII (American Standard Code for Information Interchange) A seven-level code (128 possible characters) used for data transfer. ASP (Abstract Service Primitive) Implementation-independent description of interaction between service-user and service-provider at particular service boundary, as defined by Open Systems Interconnection (OSI). Asynchronous Time Division Multiplexing Multiplexing technique in which transmission capability is organized in unassigned time slots that are assined to cells upon request of each application's instantaneous real need. Asynchronous Transmission A transmission method that sends units of data one character at a time. Characters are preceded by start bits and followed by stop bits, which provide synchronization at the receive terminal. ATM (Asynchronous Transfer Mode) A standard implementation of cell relay, a packet switching technique using packets of a fixed length, called cells. It is asynchronous because the recurrence of cells containing information from an individual user is not periodic. ATM Address Defined in UNI Specification as 3 formats, each having 20 bytes in length, including country, area and end-system identifiers. ATM-ARP (ATM Address Resolution Protocol) An address resolution protocol for mapping Asynchronous Transfer Mode (ATM) and Internet Protocol (IP) addresses. (Each host is assigned a unique IP address.) ATM-ARP can be used for discovering local area network (LAN) hosts attached to an ATM network or in classical IP over ATM. ATM Layer Link Section of an ATM Layer connection between two adjacent active ATM Layer entities (ATM-entities). ATM Link Virtual path link (VPL) or virtual channel link (VCL). ATM Peer-to-Peer Connection Virtual channel connection (VCC) or virtual path connection (VPC). ATM Traffic Descriptor Generic list of traffic parameters that can be used to capture the intrinsic traffic characteristics of requested ATM connection. ATM User-User Connection Association established by ATM Layer to support communication between two or more ATM service users (i.e., between two or more next higher entities or between two or more ATM-entities). Communications over an ATM Layer connection may be either bidirectional or unidirectional. Same Virtual Channel Identifier (VCI) issued for both directions of connection at interface. ATM25 ATM Forum-defined 25.6Mbit/s cell-based user interface based on IBM token ring network. ATU-C and ATU-R (ADSL Transmission Unit, Central or Remote) Device at end of ADSL line that stands between line and first item of equipment in subscriber premises or telephone switch. May be integrated within access node. AUI (Attachment Unit Interface) 15-pin shielded, twisted pair Ethernet cable used (optionally) to connect between network devices and MAU. Authentication Process of determining identity of user attempting to access system. Authentication token Portable device used for authenticating user. Operates by challenge/response, time-based code sequences or other techniques. May include paper-based lists of one-time passwords. Authorization Process of determining what types of activities are permitted. Usually, authorization in context of authentication. Autobaud Automatic determination and matching of transmission speed. Auto-Negotiate Clause 28 of the IEEE 802.3u standard specifies MAC sublayer for identification of speed and duplex mode of connection being supported by device. Support optional for individual vendors. Auto-sense Auto-Negotiation in Clause 28 of IEEE 802.3u standard. Ability of 10/100 Ethernet device to interpret speed or duplex mode of attached device and adjust to that rate. AWG (American Wire Gauge) System that specifies wire size. Gauge varies inversely with wire diameter size. Back to Top B Backbone Main cable in network. Bandwidth on Demand Feature that allows remote access device to initiate second connection to particular site. Used to increase amount of data transferred to that site to increase desired threshold. Network manager configuring remote access server will specify number of bits or percentage of connection bandwidth threshold to trigger the secondary connection. Multilink PPP is emerging standard to allow this feature to be interoperable. Currently, the only way to ensure correct operation is to use devices on both end from same vendor. Baseband LAN Local Area Network that uses single carrier frequency over single channel. Ethernet, Token Ring and Arcnet LANs use baseband transmission. Bastion host System hardened to resist attack. Installed on network to potentially come under attack. Often component of firewalls or may be outside Web server or public access system. Generally runs some form of general purpose operating system (e.g., UNIX, VMS, WNT, etc.) rather than ROM-based or firmware operating system. Baud Unit of signal frequency in signals per second. Not synonymous with bits per second as signals can represent more than one bit. Baud equals bits per second only when signal represents single bit. BBC (Broadband Bearer Capability) Bearer class field that is part of initial address message. BCD (Binary Coded Decimal) Form of coding of each octet within cell, where each bit has one of two allowable states, 1 or 0. BECN (Backward Explicit Congestion Notification) An indicator bit in the frame relay header to notify the source of traffic that the virtual circuit is passing through a congested switch. It is set on any traffic flowing from the destination back to the source that passes through the congested switch. BER (Bit Error Rate) (1) Measure of transmission quality generally shown as negative exponent, (e.g., 10-7 or 1 in 107 bits in error or 1 in 10,000,000 bits in error). (2) Measure of transmission accuracy as ratio of bits received in error to bits sent (e.g., 10-9 or 1 error in 1,000,000,000 bits) is common in voice and data transmission systems. Best Effort A Quality of Service (QoS) class in which no specific traffic parameters and no absolute guarantees are provided. Best effort includes Undefined Bit Rate (UBR) and Available Bit Rate (ABR). BETRS (Basic Exchange Telecommunications Radio Service) Simplest form is "fixed cellular." Form of wireless local exchange service where handoff is not required. BGP (Border Gateway Protocol) An exterior gateway protocol defined in Request for Comments (RFC) 1267 and 1268. Big-Endian A format for storage or transmission of binary data in which the most significant bit (or byte) comes first. Binaries Binary, machine-readable forms of programs that are compiled or assembled, as opposed to source language forms of programs. Binary Characteristic of having only two states, such as current on and current off. Binary number system uses only ones and zeros. BIP (Bit Interleaved Parity) Method used at PHY layer to monitor error performance of link. Check bit or word is sent in link overhead covering previous block or frame. Bit errors in payload will be detected and may be reported as maintenance information. B-ISDN (Broadband Integrated Digital Network) Digital network with ATM switching operating at data rates in excess of 1.5 Mbps. ATM enables transport and switching of voice, data, image, and video over same infrastructure. BISUP (Broadband ISDN User's Part) SS7 protocol that defines signaling messages to control connections and services. Bit (binary digit) Smallest unit of data processing information. Assumes value of 1 or 0. BNC Standardized connector used with Thinnet and coaxial cable. BOC (Bell Operating Company) Any of 22 regulated telephone companies organized into seven Regional Bell holding companies. See RBOC and RHC. BOOTP (Bootstrap Protocol) Used for booting diskless nodes. Described in Request for Comments (RFC) 951 and 1084. Border Node Logical node in a specified peer group, with at least one link that crosses peer group boundary. Bps (bits per second) Units of transmission speed. BRI (Basic Rate Interface) ISDN scheme identified as 2B1D that permits two “bearer?channels, each operating at 64 kbps, and one “data? channel, operating at 16 kbps, to be carried over single twisted pair. Bridge A device interconnecting Local Area Networks (LANs) at the Open Systems Interconnection (OSI) data link layer, and filtering and forwarding frames according to Media Access Control (MAC) addresses. Broadband Wide-band technology capable of supporting voice, video and data, possibly using multiple channels. Broadband Access Access capable of supporting one or more broadband services. Broadband Network Network that uses multiple carrier frequencies to transmit multiplexed signals on single cable. Several networks may coexist on single cable without interfering with one another. Broadcast Data transmission to all addresses or functions. Brouter Device that routes specific protocols, such as TCP/IP and IPX, and bridges other protocols, thereby combining functions of both routers and bridges. Bus LAN topology in which all nodes are connected to single cable, considered equal, and receive all transmissions on the medium. BUS (Broadcast and Unknown Server) Server that handles data sent by LE Client to broadcast MAC address (FFFFFFFFFFFF), all multicast traffic, and initial unicast frames sent by LAN Emulation Client. BW (bandwidth) Numerical measurement of throughput of system or network. Byte Data unit of eight bits. Back to Top C CAC (Carrier Access Code) Five to seven-digit number that identifies which interexchange carrier call uses. Subscribers dial these digits with each long distance call or pre-subscribe to particular carrier and let digital switch software add CAC. CAC (Connection Admission Control) Set of actions taken by network during call setup phase (or during call re-negotiation) to determine whether connection request should be accepted or rejected (or whether request for re-allocation can be accommodated). Call Association between two or more users or between user and network entity that is established by use of network capabilities. Association may have zero or more connections. CAT-5 (Category 5 UTP) Unshielded twisted pair (UTP) standard cabling, commonly used with fast Ethernet and asynchronous transfer mode (ATM) interfaces for higher-speed cell transmission (more than 50 Mbps). CBR (Constant Bit Rate) One of the five Asynchronous Transfer Mode (ATM) classes of service. CBR supports the transmission of a continuous bit-stream of information, such as voice and video traffic, which require a constant amount of bandwidth allocated to a connection during the transmission. CC (Continuity Cell) A cell used periodically to check whether a connection is idle or has failed. Continuity checking is one of the Operation Administration And Maintenance (OAM) function types for fault management. CCITT (Comit?Consultatif Internationale de Telegraphique et Telephonique) International group operating under auspices of International Telecommunications Union (ITU) and charged with establishing telecommunications standards. Name recently changed to ITU-TSS (International Telecommunications Union-Telecommunications Standards Sector). CCR (Current Cell Rate) The currently acceptable transmission rate for an end-system as defined by RM cells within Available Bit Rate (ABR). The field in the RM cell indicates the current complying cell rate (i.e., ACR) a user can transmit over a Virtual Channel (VC) connection. CDMA (Code Division Multiple Access) Digital transmission scheme claimed to be more efficient than other systems and to offer up to 20 times more call handling capacity than analog cellular systems. CDPD Cellular Digital Packet Data CD-ROM (Compact Disk-Read Only Memory) Used by computer to store large amounts of data. CDV (Cell Delay Variation) A Quality of Service (QoS) parameter that measures the difference between the transfer delay of a single cell transfer delay and the expected transfer delay. This parameter is important for time-sensitive virtual circuits such as Constant Bit Rate (CBR) and Variable Bit Rate Real Time (VBR-RT). CDVT (Cell Delay Variation Tolerance) Used in Constant Bit Rate (CBR) traffic, it specifies the acceptable tolerance of the CDV (jitter). Cell The 53-byte basic information unit within an Asynchronous Transfer Mode (ATM) network. The user traffic is segmented into cells at the source and reassembled at the destination. An ATM cell consists of a 5-byte ATM header and a 48-byte ATM payload, which contains the user data. CER (Cell Error Rate) A Quality of Service (QoS) parameter that measures the number of transmitted cells that are erroneous over a specific period of time (i.e., those that contain errors when they arrive at the destination). CES (Circuit Emulation Service) An Asynchronous Transfer Mode (ATM) service in which Constant Bit Rate (CBR) virtual circuits use AAL1 to emulate an end-to-end physical circuit by providing a time division multiplexer (TDM)-like virtual circuit between local access circuits. Challenge/response Authentication technique where server sends unpredictable challenge to user, who computes response using some form of authentication token. Channel Data path between two nodes. Channelized T1/E1 T1 or E1 service that is divided into individual 64 Kbps channels, as opposed to unchannelized service, which uses the entire bandwidth of the T1 (1.544 Mbps) or E1 (2.048 Mbps). Channelized T1 or E1 lines can consist of switched lines with either in-band signaling or leased lines. CHAP (Challenge Handshake Authentication Protocol) Authentication scheme for PPP where password is required to begin connection and during the connection. Failure to provide correct password during login or challenge mode results in disconnect. Checksum A computed value which is dependent upon the contents of a packet. This value is sent along with the packet when it is transmitted. The receiving system computes a new checksum based upon the received data and compares this value to the value sent with the packet. If the two values are the same, the receiver has a high degree of confidence that the data was received correctly. CIR (Committed Information Rate) A term used in frame relay that defines the information rate the network is committed to providing the user. CLEC Competitive LEC CLID (Caller ID) Service that permits subscribers to see telephone number and/or name of calling party. Frequently, “call blocking?is offered, allowing calling parties to block display of their telephone numbers. CLP (Cell Loss Priority) A 1-bit field in the Asynchronous Transfer Mode (ATM) cell header specifying whether a cell is more or less likely to be discarded by an ATM network experiencing congestion. CLR (Cell Loss Ratio) A Quality of Service (QoS) parameter that gives the ratio of the lost cells to the total number of transmitted cells. CMIP (Common Management Interface Protocol) ITU-TSS standard for message formats and procedures used to exchange management information to operate, administer, maintain, and provision a network. CO (Central Office) A telephone company office that connects to all local loops in a given area and where circuit switching of customer lines occurs. Coaxial Cable Electrical cable with solid wire conductor at its center, surrounded by insulating materials and an outer metal screen conductor with an axis of curvature coinciding with inner conductor. Examples are standard Ethernet cable and Thinwire Ethernet cable. COD (Connection Oriented Data) Data requiring sequential delivery of its component PDUs to assure correct functioning of its supported application (e.g., voice or video). CODEC (Coder/Decoder) Electronic circuit converts analog voice signals into digital signals for transmission and switching, and digital signal to analog voice signals so they can be used by telephone. Collision Result of two network nodes transmitting on same channel at same time. Transmitted data is not usable. Collision Detect Signal indicating one or more stations are contending with local station's transmission. Signal is sent by the Physical layer to the Data Link layer on Ethernet/IEEE 802.3 node. Communication Server Dedicated, standalone system that manages communications activities for other computers. Concentrator A wiring hub in a star-topology network. Sometimes refers to a device containing multiple modules of network equipment. Configuration Phase in which LE Client discovers LE Service. Connection (1) ATM connection consists of concatenation of ATM Layer links to provide end-to-end information transfer capability to access points. (2) In switched virtual connection environments, LAN Emulation Management entities set up connections between each other using UNI signaling. Connection-Oriented The data communication method in which communication proceeds through three well-defined phases: connection establishment, data transfer, and connection release. Transmission Control Protocol (TCP) is a connection-oriented protocol. Connectionless The data communication method in which communication occurs between hosts with no previous setup. Packets between two hosts may take different routes, as each is independent of the other. User Datagram Protocol (UDP) is a connectionless protocol. Console Terminal used to configure network devices at boot (start-up) time. Core Network Combination of switching offices and transmission plant connecting switching offices together. Linked by several competing Interexchange networks in U.S. local exchange. Now extends to national boundaries in rest of world. CPE (Customer Premise Equipment) Telecommunications equipment provided for and/or installed by a service provider at a home or enterprise. CRC (Cyclic Redundancy Check) A data transmission error-detection scheme. A polynomial algorithm is performed on the data, and the resultant checksum is appended at the end of the frame. The receiving equipment performs a similar algorithm. Crosstalk Noise passed between communications cables or device elements. CRS (Cell Relay Service) A bearer service offered by an asynchronous transfer mode (ATM) network to the end users delivers Asynchronous Transfer Mode (ATM) cells directly over the network. Cryptographic Checksum One-way function applied to file to produce unique “fingerprint?of file for later reference. Primary means of detecting file system tampering on UNIX. CS (Convergence Sublayer) (1) General procedures and functions that convert between ATM and non-ATM formats, describing functions of upper half of AAL layer. (2) Used to describe conversion functions between non-ATM protocols, such as frame relay or SMDS and ATM protocols above AAL layer. CSA (Canadian Standards Association) One of several bodies that develops telecommunications standards. CSMA/CD (Carrier Sense Multiple Access with Collision Detection) A protocol in which stations listen to the bus and only transmit when the bus is free. If a collision occurs, the packet is retransmitted after a random time-out. Ethernet uses CSMA/CD. CSPDN Circuit Switched Public Data Network CSTA Computer Supported Telephony Application (ECMA) CSU (Channel Service Unit) Equipment installed on customer premises to terminate a DDS or T1 circuit. CSUs provide network protection and diagnostic capabilities. CTD (Cell Transfer Delay) A quality of service (QoS) parameter that measures the average time for a cell to be transferred from its source to its destination over a virtual channel (VC) connection. CTD is the sum of any coding, decoding, segmentation, reassembly, propagation, processing, and queuing delays. CTI Computer Telephony Integration CTIA Cellular Telecommunications Industry Association Cut-through Technique for examining incoming packets where Ethernet switch looks only at first few bytes of packet before forwarding or filtering it. Faster than looking at whole packet but allows some bad packets to be forwarded. Back to Top D DA (Destination Address) Information sent in forward direction indicating address of called station or customer. DA (Destination MAC Address) Six-octet value that uniquely identifies endpoint sent in IEEE LAN frame headers to indicate frame destination. DACS (Digital Access and Cross Connect System) A time-slot switch that allows T1 or E1 lines to be remapped electronically at the DS-0 (64 Kbps) level. Also called DCS or DXS. Data Connections Data VCCs connect LECs to each other and to Broadcast and Unknown Server. Carry Ethernet/IEEE 802.3 or IEEE 802.5 data frames as well as flush messages. Data-driven attack Attack is encoded in innocuous-seeming data that is executed by user or other software to implement attack. Concern it may get through firewall in data form and launch attack against system behind firewall. AKA denial of service attack. Data Encryption Transformation of data into unreadable, meaningless data through a cryptographic transformation using key. Decryption turns unintelligible data into meaningful data using a key. Datagram A packet or string of bytes carrying and routing data and sufficient information from source to destination. Data Link Layer Layer 2 of the Open System Interconnection (OSI) model. Layer 2 is concerned with transmitting units of information or frames, and associated error-checking. It establishes, maintains, and releases data-link connections between elements in a network. dB (Decibel) Logarithmic unit describing ratio of two powers. dBm (Decibel Referenced to a Milliwatt) Ratio of two power levels, in which the second is one milliwatt. DCC (Data Country Code) Specifies country in which address is registered. Codes are given in ISO 3166. Field length is two octets. Digits are encoded in Binary Coded Decimal (BCD) syntax. Codes left justified and padded on right with hexadecimal value "F" to fill two octets. DCE (Data Communication Equipment) Generic definition of computing equipment that attaches to network via DTE. DDS (Digital Data Service) 56 or 64 kbps digital private line channel. DECnetTM Digital Equipment Corporation (DEC) proprietary network architecture running on point-to-point, X.25 and Ethernet networks. DEK (Data Encryption Key) Used for encrypting message text and computing message integrity checks (signatures). DES (Data Encryption Standard) A popular, standard encryption scheme. Dial on Demand Automatic detection, based on network manager’s pre-defined parameters, of need to initiate dial-up connection to a remote network. Dialback Security feature that ensures people do not log into modems to which they should not have access. When connection is requested, system checks user name for validity, then “dials back?number associated with that user name. Digital Certificate Package of information, digitally signed by trusted authority (usually referred to as a CA or Notary), that binds a public key to owner. Usually consists of identifier field, public key field, serial number (of certificate), activation and expiration date, and signature field. X.509 defines a standard format. Dijkstra's Algorithm Algorithm sometimes used to calculate routes given link and nodal state topology database. Distributed Processing System in which each computer or node in network performs its own processing and manages some of its data while network facilitates communications between nodes. DLC (Digital Loop Carrier) Digital transmission system designed for subscriber loop plant. Multiplexes many circuits onto very few wires or onto single fiber pair. DLCI (Data Link Connection Identifier) A unique number assigned to a Permanent Virtual Connection (PVC) endpoint in a Frame Relay network. DLPI (Data Link Provider Interface) UNIX International Specification, Revision 2.0.0, OSI Work Group, August 1991. DMS (Digital Multiplex Systems) (1) System that combines number of digital circuits. (2) Prefix for Northern Telecom family of digital central office switches (DMS-10, DMS-100/200, DMS-250, DMS-300, and DMS-500.) DNS spoofing Assuming DNS name of another system by corrupting name service cache of victim system or compromising domain name server for valid domain. Domain See Administrative Domain. Domain Name Text name appended to host name to form unique host name across Internets. Download Transfer of a file or information from one network node to another. Generally refers to transferring a file from big node, such as server, to a small node, such as terminal or printer. DPN (Data Packet Network) (1) Network in which “bundles?of information are transmitted, one after another. Differs from circuit network, in which entire circuit is dedicated to particular user. (2) Prefix for Northern Telecom’s DPN data networking switches. DS0 (Digital Subscriber Level Zero) A 64 Kbps unit of transmission bandwidth. A worldwide standard speed for digitizing one voice conversation, and more recently, for data transmission. Twenty-four DS0s (24x64 Kbps) equal one Digital Signal Level 1 (DS1). DS1 (Digital Signal Level 1) Framing specification used in transmitting digital signals at 1.544 Mbps on a T1 facility or 2.048 Mbps on an E1 facility. DS2 Channel For a T1 line, a 6.312 Mbps channel that consists of four Digital Signal Level 1 (DS1) channels. For an E1 line, an 8.45 Mbps channel that consists of four DS1 channels. DS3 Channel A 44.736 Mbps line consisting of seven DS2 channels. Also called a T3 line. DS3 PLCP (Physical Layer Convergence Protocol) Alternate method used by older T carrier equipment to locate ATM cell boundaries. Recently been moved to informative appendix of the ATM DS3 specification and replaced by HEC method. DSL (Digital Subscriber Line) A modem technology for transmitting information at high speeds on existing copper telephone lines to homes and businesses. DSL requires runs of usually less than 20,000 feet to a central telephone office. Types of DSL include Asymmetric DSL (ADSL), Symmetric DSL (SDSL), and High Bit Rate DSL (HDSL). DSLAM (Digital Subscriber Line Access Multiplexer) Device that takes number of ADSL subscriber lines and concentrates these to single ATM line. DSS1 (Digital Subscriber Signaling System #1) N-ISDN UNI Signaling. DSS2 (Digital Subscriber Signaling System #2) B-ISDN UNI Signaling. DSU (Data Service Unit) (1) Equipment used to attach users' computing equipment to a public network. (2) Device located on the customer’s premises that converts a digital data signal to a digital transmission signal. DSU (Digital Service Unit) A user device interfacing to a digital circuit, such as DDS or T1 when com-bined with a Channel Service Unit (CSU). The DSU converts the user’s data stream to bipolar format for transmission. DTE (Data Terminal Equipment) (1) Generic definition of external networking interface equipment, such as modem. (2) Name applied to a piece of terminal equipment. Dual homed gateway System with two or more network interfaces, each of which is connected to different networks. With firewall, acts to block or filter some or all traffic trying to pass between networks. DWS (Dialable Wideband Service) Alternative name for Multirate ISDN, providing dialed data connectivity at desired bandwidth on per call basis (from 128 kbps through 1.536 Mbps in 64 kbps increments). Back to Top E E.164 Public network addressing standard with maximum of 15 digits. ATM uses E.164 addressing for public network addressing. E1 The 2.048 Mbps digital carrier system common in Europe. E3 The European standard for high-speed digital transmission operating at 34 Mbps. ECMA Previously European Computer Manufacturers Association ECSA (Exchange Carrier Standard Association) Standards body sponsored by exchange carriers and accredited by American National Standards Institute (ANSI). Recently changed to Alliance for Telecommunications Industry Solutions (ATIS). ECTF Enterprise Computer Telephony Forum EGP (Exterior Gateway Protocol) A protocol that distributes routing information to the routers connecting autonomous systems. Today, the term “router?is commonly used in place of the term “gateway.? There is also a routing protocol called EGP, defined in STD 18, Request for Comments (RFC) 904. EIA Electronics Industry Association ELA (Emulated LAN) The Asynchronous Transfer Mode (ATM) segment of a virtual local area network (VLAN) based on the ATM forum Local Area Network Emulation (LANE) standard. A VLAN consists of an ELAN segment and traditional LAN segment. EMI (Electromagnetic Interference) Electromagnetic waves emitted by some electrical devices that distort or overwhelm other communications signals. Encapsulation Encapsulating data is a technique used by layered protocols in which a low level protocol accepts a message from a higher-level protocol, then places it in the data portion of the lower-level frame. The logistics of encapsulation require that packets traveling over a physical network contain a sequence of headers. Encrypting router See tunneling router and virtual private network. Enterprise Network An information infrastructure that often combines private and public facilities to cover all of the locations operated by a single company or corporate enterprise with a single communications fabric. ESF (Extended Superframe Format) A T1 framing format that uses the framing bit to provide mainte-nance and diagnostic functions. Ethernet Most popular LAN technology in use today, with configuration rules defined by IEEE standard 802.3. 10 Mbps, CSMA/CD baseband network that runs over thin coax, thick coax, twisted pair or fiber optic cable. EtherTalk Apple Computer's protocol for Ethernet transmissions. ETSI (European Telecommunications Standards Institute) Primary telecommunications standards organization. Back to Top F FCC Federal Communications Commission FCS (Frame Check Sequence) Any mathematical formula that derives numeric value based on bit pattern of transmitted block of information and uses that value at receiving end to determine existence of any transmission errors. FDDI (Fiber Distributed Data Interface) An American National Standards Institute (ANSI) standard for fiber-optic links with data rates up to 100 Mbps. FEC (Forward Error Correction) Technique for detection and correction of errors in digital data stream. Frequently used in data transmission systems. Redundant bits are transmitted along with payload. Location and value of these bits in message allows receiving station to detect and correct errors. FECN (Forward Explicit Congestion Notification) A bit set by a frame relay network to notify an interface (DTE) that congestion avoidance procedures should be initiated by the receiving device. Fiber Optics A transmission medium consisting of thin glass filaments. Light beams travel through the fiber-optic line, carrying large amounts of data over long distances. File Server Computer that stores data for network users and provides network access to that data. Filtering Process where an Ethernet switch or bridge reads contents of packet, finds that packet does not need to be forwarded, and drops it. Filtering rate is rate at which device can receive packets and drop them without any loss of incoming packets or delay in processing. Firewall System or combination of systems that enforces boundary between two or more networks, controlling access from one to the other. Firmware Alterable programs in semipermanent storage, such as some type of read-only or flash reprogrammable memory. Flash ROM See ROM. Flow Control A congestion control mechanism in which an Asynchronous Transfer Mode (ATM) system implements flow control. FOTS (Fiber Optic Transmission System) Generic term applied to any fiber optic transmission system. Fractional T1 A service provided by carriers in which a full T1 link is leased to the customer, but the service charge is calculated based only on the number of timeslots used. FRAD (Frame Relay Access Device) A device responsible for framing data with header and trailer infor-mation (control information) before presenting the frame to the frame relay switch. Fragment A piece of a packet. When a router is forwarding an Internet Protocol (IP) packet to a network that has a maximum packet size smaller than the forwarded packet size, it is forced to break up that packet into multiple fragments. These fragments will be reassembled by the IP layer at the destination host. Frame A data link layer “packet?that contains the header and trailer information required by the physical medium. Network layer packets are encapsulated to become frames. The terms packet, datagram, segment, and message are also used to describe logical information groupings. Frame Relay A network interface providing high-speed frame or packet transmission with minimum delay and an efficient use of bandwidth. Frame Relay Frame A variable-length unit of data in frame relay format that is transmitted as pure data through a frame relay network. Framing At the physical and data link layers of the Open System Interconnection (OSI) model, bits are fit into units called frames. Frames contain source and destination information, flags to designate the start and end of the frame, plus information about the integrity of the frame. All other information, such as network protocols and the actual payload of data, is encapsulated in a packet, which is encapsulated in the frame. FRS (Frame-Relay Service) Connection oriented service capable of carrying up to 4096 bytes per frame. FTP (File Transfer Protocol) A protocol that allows a user on one host to access and transfer files to and from another host over a network. FTP is usually the name of the program the user invokes to execute the protocol. The Internet Protocol (IP) version is defined in STD 9, Request for Comments (RFC) 959. FTTC (Fiber to the Curb) Fiber placed in long distance network, feeder plant, and distribution plant. Fiber then proceeds to curb, with copper going from curb to home. FTTH (Fibre to the Home) Network where optical fibre runs from telephone switch to subscriber's location or home. FTTK (Fiber to the Kerb) See Fiber to the Curb. Full Duplex A circuit or device permitting transmission in two directions at the same time. FUNI (Frame User Network Interface) A frame-based interface which supports signaling and Quality of Service (QoS) to an Asynchronous Transfer Mode (ATM). To inter-operate with a frame relay end system, the ATM switch should support FRF.8, which is the frame relay/ATM service Internetworking specification. Back to Top G G.703 ITU-T Recommendation, “Physical/Electrical Characteristics of Hierarchical Digital Interfaces.?/font> G.704 ITU-T Recommendation, “Synchronous Frame Structures Used at Primary and Secondary Hierarchy Levels.?/font>