| A & B bit signaling | Used in T1 transmission facilities and sometimes called "24th channel signaling". Each of the 24 T1 channels in this procedure uses one bit of every sixth frame to send supervisory signaling information. |
| AAL | ATM Adaptation Layer: A service-dependant sublayer of the
Data Link layer,which accepts data from other applications and brings it
to the ATM layer in 48-byte ATM payload segments. CS and SAR are the two
sublayers that form AALs. Currently, the four types of AAL recommended by
the ITU-T are AAL1,AAL2,AAL3/4, and AAL5. AALs are differentiated by the
source-destination timing they use, whether they are CBR or VBR, and whether
they are used for connection-orientated or connectionless mode data transmission. See also: AAL1,AAL2,AAL3/4,AAL5,ATM, and ATM layer. |
| AAL1 | ATM Adaptation Layer 1: One of the four AALs recommended by
the ITU-T, it is used for connection-oriented, time-sensitive services that
need constant bit rates, such as isochronous traffic and uncompressed video. See also: AAL |
| AAL2 |
ATM Adaptation Layer 2: One of the four AALs recommended by the ITU-T,
it is used for connection-oriented services that support a variable bit
rate, such as voice traffic. |
| AAL3/4 | ATM Adaptation Layer 3/4: One of the four AALs (a product
of two initially distinct layers)recommended by the ITU-T, supporting both
connectionless and connection-oriented links. Its primary use is in sending
SMDS packets over ATM networks. See also: AAL |
| AAL5 |
ATM Adaptation Layer 5: One of the four AALs recommended by the ITU-T,
it is used to support connection-oriented VBR services primarily to transfer
classical IP over ATM and LANE traffic. This least complex of the AAL
recommendations uses SEAL, offering lower bandwidth costs and simpler
processing requirements but also providing reduced bandwidth and error-recovery
capacities. |
| AARP | AppleTalk Address Resolution Protocol: The protocol in an AppleTalk stack that maps data-link addresses to network addresses. |
| AARP probe packets | Packets sent by the AARP to determine whether a given node
ID is being used by another node in a nonextended AppleTalk network. If
the node ID is not in use,the sending node appropriates that node's ID.
If the node ID is in use, the sending node will select a different ID and
then send out more AARP probe packets. See also: AARP |
| ABM | Asynchronous Balanced Mode: When two stations can initiate a transmission, ABM is an HDLC (or one of its derived protocols) communication technology that supports peer-oriented, point-to-point communications between both stations |
| ABR | Area Border Router: An OSPF router that is located on the border of one or more OSPF areas. ABRs are used to connect OSPF areas to the OSPF backbone area. |
| access layer | One of the layers in Cisco's three-layer hierarchical model. The access layer provides users with access to the internetwork |
| access link | Is a link used with switches and is only part of one Virtual LAN (VLAN). Trunk lines carry information from multiple VLANs. |
| access list | A set of test conditions kept by routers that determines "interesting traffic"to and from the router for various services on the network. |
| access method | The manner in which network devices approach gaining access to the network itself. |
| access server | Also know as "network access server," it is a communications process connecting asynchronous devices to a LAN or WAN through network and terminal emulation software, providing synchronous or asynchronous routing of supporting protocols. |
| acknowledgment | Verification sent from one network device to another signifying
that an event has occurred. May be abbreviated as ACK. Contrast with: NAK. |
| ACR | allowed cell rate: A designation defined by the ATM Forum
for managing ATM traffic. Dynamically controlled using congestion control
measures, the ACR varies between the minimum cell rate (MCR)and the peak
cell rate (PCR). See also: MCR and PCR |
| active monitor | The mechanism used to manage a Token Ring. The network node with the highest MAC address on the ring becomes the active monitor and is responsible for management tasks such as preventing loops and ensuring tokens are not lost. |
| address learning | Used with transparent bridges to learn the hardware addresses of all devices on an internetwork. The switch then filters the network with the known hardware(MAC) addresses. |
| address mapping | By translating network addresses from one format to another, this methodology permits different protocols to operate interchangeably. |
| address mask | A bit combination descriptor identifying which portion of
an address refers to the network or subnet and which part refers to the
host. Sometimes simply called the mask. See also: subnet mask |
| address resolution | The process used for resolving differences between
computer addressing schemes. Address resolution typically defines a method
for tracing Network layer (Layer 3) addresses to Data-Link layer (Layer
2) addresses. See also: address mapping |
| adjacency | The relationship made between defined neighboring routers and end nodes, using a commom media segment, to exchange routing information. |
| administrative distance | A number between 0 and 225 that expresses the value of trustworthiness of a routing information source. The lower the number, the higher the integrity rating. |
| administrative weight | A value designated by a network administrator to rate the preference given to a network link. It is one of four link metrics exchanged by PTSPs to test ATM network resouce availability. |
| ADSU | ATM Data Service Unit: The terminal adapter used to connect
to an ATM network through an HSSI-compatible mechanism. See also: DSU |
| advertising | The process whereby routing or service updates are transmitted at given intervals, allowing other routers on the network to maintain a record of viable routes. |
| AEP | AppleTalk Echo Protocol: A test for connectivity between two AppleTalk nodes where one node sends a packet to another and receives an echo, or copy, in response. |
| AFI | Authority and Format Identifier: The part of an NSAP ATM address that delineates the type and format of an IDI section of an ATM address. |
| AFP | AppleTalk Filing Protocol: A Presentation-layer protocol, supporting AppleShare and Mac OS File Sharing, that permits users to share files and applications on a server. |
| AIP | ATM Interface Processor: Supporting AAL3/4 and AAL5, this
interface for Cisco 7000 series routers minimizes performance bottlenecks
at the UNI. See also: AAL3/4 and AAL5 |
| algorithim | A set of rules or process used to solve a problem. In networking, algorithms are typically used for finding the best route for traffic from a source to its destination. |
| alignment error | An error occuring in Ethernet networks, in whicha received frame has extra bits; that is, a number not divisible by eight. Alignment errors are generally the result of frame damage caused by collisions. |
| all-routes explorer packet | An explorer packet that can move across an entire SRB network,
tracing all possible paths to a given destination. Also known as an all-ring
explorer packet. See also: explorer packet, local explorer packet, and spanning explorer packet. |
| AM |
Amplitude Modulation: A modulation method that represents information by varying the amplitude of the carrier signal. See also: modulation |
| AMI |
Alternate Mark Inversion: A line-code type on T1 and E1 circuits that
shows zeros as "01" during each bit cell, and ones "11"
or "00," alternately, during each bit cell. The sending device
must maintain ones density in AMI but not independantly of data stream.
Also known as binary-coded, alternate mark inversion. |
| amplitude | An analog or digital waveform's highest value. |
| analog transmission | Signal messaging whereby information is represented by various combinations of signal amplitude, frequency, and phase. |
| ANSI | American National Standards Institute: The organization of corporate, government, and other volunteer members that cooridnate standards-related activities, approves U.S. national standards, and developes U.S. positions in international standards organizations. ANSI assists in the creation of international and U.S. standards in disciplines such as communications, networkinf, and a variety of technical fields. It publishes over 13,000 standards, for engineered products and technologies ranging from screw threads to networking protocols. ANSI is a member of the IEC and ISO. |
| anycast | An ATM address that can be shared by more than one end system, allowing requests to be routed to a node that provides a particular service. |
| AppleTalk | Currently in two versions, the group of communication protocols
designed by Apple Computer for use in Macintosh environments. The earlier
Phase 1 protocol supports one physical network with only one network number
and resides in one zone. The later Phase 2 protocol support more than one
logical network on a single physical network, allowing networks to exist
in more than one zone. See also: zone |
| Application layer | Layer 7 if the OSI reference network model, supplying services to application procedures (such as electronic mail or file transfer) that are outside the OSI model. This layer chooses and determines the availability of communicating partners along withthe resources necessary to make connection, coordinates partnering applications, and forms a consensus on procedures for controlling data integrity and error recovery. |
| ARA | AppleTalk Remote Access: A protocol for Macintosh users establishing their access to resources and data from a remote AppleTalk location. |
| area | A logical, rather than physical, set of segments (based on
either CLNS, DECnet, or OSPF) along with their attached devices. Areas are
commonly connected to others using routers to create a single autonomous
system. See also: autonomous system |
| ARM | Asynchronous Response Mode: An HDLC communication mode using primary station and at least one additional station, in which transmission can be initiated from either the primary or one of the sacondary units. |
| ARP | Address Resolution Protocol: Defined in RFC 826, the protocol
that traces IP addresses to MAC addresses. See also: RARP |
| ASBR | Autonous System Boundary Router: An area border router place
between an OSPF autonomous system and a non-OSPF network that operates both
OSPF and an additional routing protocol, such as RIP. ASBRs must be located
in a non-stub OSPF area. See also: ABR, non-stub area, and OSPF |
| ASCII | Ammerican Standard Code for Information Interchange: An 8-bit code for representing characters, consisting of seven data bits plus one parity bit. |
| ASICs | Application-Specific Intgrated Circuits: Used in layer-2 switches to make filtering decisions. The ASIC looks in the filter table of MAC addresses and detirmines which port the destination hardware address of a recieved hardware address is destined for. The frame will be allowed to traverse only that one segment. If the hardware address is unknown, the frame is forwarded out all ports. |
| ASN.1 | Abstact Syntax Notation One: An OSI language used to describe types of data that is dependent of computer structures and depicting methods. Described by the ISO International Standard 8824. |
| AppleTalk Session Protocol: A protocol employing ATP to establish, maintain,
and tear down sessions, as well as sequence requests. See also: ATP | |
| AST | Automatic Spanning Tree: A function that supplies one path
for spanning explorer frames traveling from one node in the network to another,
supporting the automatic resolution of spanning trees inSRB networks. AST
is based on IEEE 802.1 standard. See also: IEEE 802.1 and SRB |
| asynchronous transmission | Digital signals sent withoue percise timing, usually with different frequencies
and phase relationships. Asynchronous transmission generally enclose individule
characters in control bits (called start and stop bits) that show the beginning
and end character. Contrast with: isochronous transmission and synchronous transmission. |
| ATCP | AppleTalk Control Program: The protocol for establishing and configuring
AppleTalk over PPP, defined in RFC 1378. See also: PPP |
| ATDM | Asynchronous Time-Division Multiplexing: A technique for sending information,
it differs from normal TDM in that the time slots are assigned when necessary
rather than preassigned to certain transmitters. Contrast with: FDM, statistical multiplexing, and TDM |
| ATG | Address Translation Gateway: The mechanism wihtin Cisco DECnet routing software that enables routers to route multiple, independent DECnet networks and to establish user-designated address translation for chosen nodes between networks. |
| ATM | Asynchronous Transfer Mode: The international standard, indentified by fixed-length 53-byte cells, for transmitting cells in multiple service systems, such as voice, video, or data. Transit delays are reduced because the fixed-length cells permit processing to occur in hardware. ATM is designed to maximize the benefits of high-speed transmission media, such as SONET,E3, and T3. |
| ATM ARP server | A device that supplies logical subnets running classical IP over ATM with address-resolution services. |
| ATM endpoint | The initiating or terminating connection in an ATMnetwork. ATM endpoints include servers, workstations, ATM-to-LAN switches, and ATM routers. |
| ATM Forum | The international organization founded jointly by Northern Telecom, Sprint,, Cisco Systems, and NET/ADAPTIVE in 1991 to develop and promote standards-based implementation agreements for ATM technology. The ATM FOrum broadens offical standards developed by ANSI and ITU-T and createsa implementation agreements before offical standards are published. |
| ATM layer | A sublayer of the Data Link layer in an ATM network that is service independent.
To create standard 53-byte ATM cells, the ATM layer recieves 48-byte segments
from AAL and attaches 5-byte header to each. These cells are then sent to
the Physical layer for transmission across the physical medium. See also: AAL |
| ATMM | ATM Management: A procedure that runs on ATM switches, managing rate enforcement
and VCI translation. See also: ATM |
| ATM user-user connection | A connection made by the ATM layer to supply communication between at
least two ATM service users, such as ATMM processes. These communications
can be uni- or bidirectional, using one or two VCCs, respectively. See also: ATM layer and ATMM |
| ATP | AppleTalk Transaction Protocol: A transport-level protocol that enables reliable transactions between two sockets, where one requests the other to perform a given task and to report the results. ATP fastens the request and response together, assuring a loss-free exchange of request-response pairs. |
| attenuation | In communication, weakening or loss of signal energy, typically caused by distance. |
| AURP | AppleYalk Update-based Routing Protocol: A technique for encapsulating
AppleTalk traffic in the header of a foriegn protocol that allows the connection
of at least two noncontiguous AppleTalk internetworks through a foreign
network ( such as TCP/IP ) to create an AppleTalk WAN. The connection made
is called an AURP tunnel. By exchanging routing information between exterior
routers, the AURP maintains routing tables for the complete AppleTalk WAN. See also: AURP tunnel. |
| AURP tunnel | A connection made in an AURP WAN that acts as a single, virtual link between
AppleTalk internetworks seperated physically by a foreign network such as
TCP/IP network. See also: AURP |
| authority zone | A portion of the domain-name tree associated with DNS for which one name
server is the authority. See also: DNS |
| auto duplex | A setting on layer-1 or layer-2 devices that sets the duplex of a switch or hub port automatically. |
| automatic call reconnect | A function that enables automatic call rerouting away from a failed trunk line. |
| autonomous confederation | A collection of self-governed systems that depend more on thier own network accessibility and routing information than on information recieved from other systems or groups. |
| autonomous switching | The ability of Cisco routers to process packets more quickly by using the ciscoBus to switch packets independently of the system processor. |
| autonomous system (AS) | A group of networks under mutual administration that share the same routing methodology. Autonomous systems are subdivided by areas and must be assigned an individual 16-bit number by the IANA. |
| autoreconfiguration | A procedure executed by nodes within the failure domain of a Token Ring, wherein nodes automatically perform diagnostics, trying to reconfigure the network around failed areas. |
| auxiliary port | The console port on the back of Cisco routers that allows you to dial the router and make console configuration settings. |
| B8ZS | Binary 8-Zero Substitution: A line-code type, interpreted at the remote end of the connection, that uses special code substitution whenever eight consecutive zeros are transmitted over the link on T1 and E1 circuits. This technique assures ones density independent of the data stream. Also known as bipolar 8-zero substitution. |
| backbone | The basic portion of the network that provides the primary path for traffic sent to and initiated from other networks. |
| back end | A node or software program supplying services to a front end. |
| bandwidth | The gap between the highest and lowest frequencies employed by network signals. More commonly, it refers to the rated throughput capacity of a network protocol or medium. |
| baseband | A feature of a network technology that uses only one carrier frequency, for example Ethernet. Also named narrowband. |
| Basic Management Setup | Used with Cisco routers when in setup mode. Only provides enough management and configuration to get the router working so someone can telnet into the router and configure it. |
| baud | Synonymous with bits per seconds(bps), if each signal element represents one bit. It is a unit of signaling speed equivilant to the number of seperate signal elements transmitted per second. |
| B channel | Bearer Channel: A full-duplex, 64Kbps channel in ISDN that transmits user data. |
| beacon | An FDDI device or Token Ring frame that points to a serious problem with the ring, such as a broken cable. The beacon frame carries the address of the station thought to be down. |
| BECN | Backward Explicit Congestion Notification: BECN is the bit set by a Frame Relay network in frames moving away from frames headed into a congested path. A DTE that recieves frames with the BECN may ask higher-level protocols to take necessary flow control measures. |
| BGP4 | BGP Version 4: Version 4 of the interdomain routing protocol most commonly used on the Internet. BGP4 supports CIDR and uses route-counting mechanisms to decrease the size of routing tables. |
| binary | A two-character numbering method that uses ones and zeros. The binary numbering system underlies all digital representation of information. |
| BIP | Bit Interleaved Parity: A method used in ATM to monitor errors on a link, sending a check bit or word in the link overhead for the previous block or frame. This allows bit errors in transmission to be found and delivered as maintenance information. |
| BISDN | |
| bit-oriented protocol | |
| Boot ROM | |
| border gateway | |
| BPDU | |
| BRI | |
| bridge | |
| broadband | |
| broadcast | |
| broadcast domain | |
| broadcast storm | |
| buffer | |
| bus topology | |
| bus | |
| BUS | |
| BX.25 | |
| bypass mode | |
| bypass relay | |
| byte-oriented protocol |