Table Of Contents


Authentication, authorization, and accounting. Pronounced "triple a."
ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers: the convergence sublayer (CS) and the segmentation and reassembly sublayer (SAR). AALs differ on the basis of the source-destination timing used, whether they use constant bit rate (CBR) or variable bit rate (VBR), and whether they are used for connection-oriented or connectionless mode data transfer. At present, the four types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5.
ATM adaptation layer 2. One of four AALs recommended by the ITU-T. AAL2 is used for connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic.
ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 is used for connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic.
Advanced Integration Module. Hardware with components that provide specialized processing.
Alarm-indication signal. In a T1 transmission, an all-ones signal transmitted in lieu of the normal signal to maintain transmission continuity and to indicate to the receiving terminal that a transmission fault is located either at or upstream from the transmitting terminal.
Automatic number identification (calling party number).
Application programming interface.
Application server. A logical entity serving a specific application instance. An example of an application server is an MGC handling the Q.931 and call processing for D channels terminated by the signaling gateways.
Application server process. A process instance of an application server. Examples of application server processes are primary or backup MGC instances.
Asynchronous Transfer Mode. International standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as E3, SONET, and T3.

Process in which telephony signaling is passed from a gateway to a separate control for processing. With such a scheme, the gateway does not need to interpret the signaling information.
Physical connection between an interface processor or card and the data buses and the power distribution buses inside a chassis.
Bit error rate. Ratio of received bits that contain errors.
Basic Rate Interface. ISDN interface composed of two B channels and one D channel for circuit-switched communication of voice, video, and data.

Channel-associated signaling. The transmission of signaling information within the voice channel. CAS signaling often is referred to as robbed-bit signaling because user bandwidth is being robbed by the network for other purposes.
Command-line interface. An interface that allows the user to interact with the operating system by entering commands and optional arguments. The UNIX operating system and DOS provide CLIs.
Central office.
Cyclic redundancy check. Error-checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and compares the calculated remainder to a value stored in the frame by the sending node.
Channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to together with DSU as CSU/DSU.

Dialed-number identification service. Same as called party number.
Digital signal level 0. Single time slot on a DS1 (also known as T1) digital interface; that is, a 64-kbps, synchronous, full-duplex data channel, typically used for a single voice connection on a PBX. Alternatively, framing specification used in transmitting digital signals over a single channel at 64-kbps on a T1 facility.
Digital signal level 3. Framing specification used for sending digital signals at 44.736 Mbps on a T3 facility.
Digital signal processor. A DSP segments the voice signal into frames and stores them in voice packets.
DSP resource pool
A collection of DSP resources available to a network module or VWIC on the router. These resources are found on another network module or on an AIM.
Data service unit. Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility, such as T1 or E1. The DSU also is responsible for such functions as signal timing. Often referred to together with CSU as CSU/DSU.
Dual-tone multifrequency.

recEive and transMit (or ear and mouth). A signaling technique for two-wire and four-wire telephone and trunk interfaces. One of four common forms of CAS signaling; the others are loopstart, groundstart, and EANA.
Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 34.368 Mbps. E3 lines can be leased for private use from common carriers.
Equal Access North American. One of four common forms of CAS signaling; the others are loopstart, groundstart, and E&M.

Capability to re-route signaling traffic as required between related ASPs in the event of failure or if the currently used ASP is unavailable (from primary MGC to backup MGC, for example). Failover also applies to the return to service of a previously unavailable process.
Frame check sequence.
Far-end alarm code.
Field-programmable gate array. A programmable memory device.
Frame Relay
Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it generally is considered a replacement.
Foreign Exchange subscriber (as in FXS-loop-start and FXS-ground-start). FXS loop and ground start protocols are a type of signaling used to indicate the beginning of a call. The FXS interface is used on the line-side access to CO (for example, communication between CO and key system).

One of four common forms of CAS signaling; the others are loopstart, EANA, and E&M.
Generic transparency descriptor.

high-level data-ink control. Bit-oriented synchronous data-link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data-encapsulation method on synchronous serial links using frame characters and checksums.
High-Speed Serial Interface. Network standard for high-speed (up to 52 Mbps) serial connections over WAN links.
High-performance voice compression modules.

Information element.
Institute of Electrical and Electronics Engineers. IEEE is a professional organization whose activities include the development of communications and network standards. IEEE LAN standards are the predominant LAN standards today.
Internet Engineering Task Force. Task force consisting of over 80 working groups responsible for developing Internet standards. The IETF operates under the auspices of ISOC.
Inverse multiplexing over ATM, a standard defined by the ATM Forum. IMA provides economical, high-bandwidth ATM WAN access by enabling multiple T1 or E1 ATM links to be combined and to appear as one physical link to higher layers.
Integrated Services Digital Network. Communication protocol offered by telephone companies that permits telephone networks to carry data, voice, and other source traffic.
International Telecommunication Union.
International Telecommunication Union Telecommunication Standardization Sector. International body that develops worldwide standards for telecommunications technologies. The ITU-T carries out the functions of the former CCITT.
ISDN Q.921 User Adaptation Layer. Provides for the transport of signaling protocol between a SG and MGC including transporting Q.921/Q.931 boundary primitives, communication between layer management modules, and management of active associations.
Interactive voice response. Term used to describe systems that provide information in the form of recorded messages over telephone lines in response to user input in the form of spoken words or, more commonly, DTMF signaling. Examples include banks that allow you to check your balance from any telephone and automated stock quote systems.

Layer 1
Physical layer of the OSI reference model defined in ITU X.200. It is responsible for the electric signal being sent and received. This can be viewed as a bit stream coming in, and going out, of the system. Scope must be considered when using this term. For example, Layer 1 on a T1 is 1.544 Mbps but Layer 1 on a DS-0 timeslot in the T1 is 64 kbps.
Layer 2
Data link layer of the OSI reference model defined in ITU X.200. It is responsible for point-to-point delivery of a PDU. Layer 2 protocols have two basic classes: reliable (meaning delivery is guaranteed or an error is reported) and unreliable (meaning delivery might not occur with no indication to the upper layers).
Layer 3
Network layer of the OSI reference model defined in ITU X.200. It is responsible for the network routing and delivery of messages. Examples of Layer 3 protocols include the X.25 packet level protocol and the Internet Protocol. Q.931 is not considered a Layer 3 protocol because it does not route or deliver messages.
LAN Extender (interface).
One of four common forms of CAS signaling; the others are groundstart, EANA, and E&M.

Maintenance Data Link (MDL) message defined in the ANSI T1.107a-1990 specification. Also, the Cisco Message Definition Language—a high-level language used to specify protocols and protocol conversion operations on the VSC.
multifrequency or multiple frequency. Interoffice address signaling method in which 10 decimal digits and five auxiliary signals are each represented by a pair of the following frequencies: 700, 900, 1100, 1300, 1500 and 1700 Hz.
Media gateway. A media gateway terminates PSTN facilities (trunks), packetizes the PCM stream into IP/ATM and/or forwards packets into the IP/ATM network. Optionally, media gateways can provide signaling backhaul.
Media gateway controller. Provides call control capability to handle signaling traffic from a variety of sources. It also manages connections and resources of its media gateways. Can also be called a call agent.
Media Gateway Control Protocol.
Multiservice interchange. Feature that allows TDM connections between MIX-enabled ports.

Non-Facility Associated Signaling. An ISDN service that allows a single D channel to control multiple PRI interfaces. Use of a single D channel to control multiple PRI interfaces can free one B channel on each interface to carry other traffic.
Networking Products Marketplace.
NFAS group
A PRI channel group (the group of interfaces) under control of a single D channel. The channel group can include all the ISDN channels on multiple T1 controllers. Cisco IOS supports ten PRI interfaces in an NFAS group with a primary D channel and a backup D channel. Five NFAS groups are supported in a single chassis.
NFAS member
A PRI interface in an NFAS group. For example, an NFAS group might include serial interfaces 1/0:23, 1/1:23, and 2/0:23 if T1 controllers 1/0, 1/1, and 2/0 are configured for NFAS.

Online insertion and removal. Feature that permits the addition, the replacement, or the removal of cards without interrupting the system power, entering console commands, or causing other software or interfaces to shut down.

Private branch exchange. Privately owned central switching office.
Protocol data unit. Another name for packet.
Private integrated services network exchange. A PBX or key system which, in a BRI voice application, uses QSIG signaling.
Private Integrated Services Network. An ISDN providing services to a specific set of users (contrary to public ISDN which provides services to the general public).
Phase-locked loop. An electronic circuit that synchronizes itself to an external reference signal. It locks itself onto the phase or onto the average frequency of the incoming signal, dynamically tracks it, and outputs a related but more useful version. Among the typical applications of a PLL in digital circuits are synchronizing a system to a single clock source and jitter filtering (removing phase noise).
Plain old telephone service.
Point-to-Point Protocol. Successor to SLIP that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. Whereas SLIP was designed to work with IP, PPP was designed to work with several network layer protocols, such as IP, IPX, and ARA. PPP also has built-in security mechanisms, such as CHAP and PAP. PPP relies on two protocols: LCP and NCP.
Primary Rate Interface. ISDN interface to primary rate access. Primary rate access consists of a single 64-kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data.
Public switched telephone network. General term referring to the variety of telephone networks and services in place worldwide. Sometimes called plain old telephone service (POTS).
Permanent virtual circuit. A PVC is a virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and teardown in situations where certain virtual circuits must exist all the time. In ATM terminology, a PVC is called a permanent virtual connection.

Q.921, Q.931
ITU-T specifications for the ISDN UNI data link layer. Q.931 deals with signaling to establish, maintain, and clear ISDN network connections.
Q (point of the ISDN model) Signaling. Signaling standard. Common-channel signaling protocol based on ISDN Q.931 standards and used by many digital PBXs.

Remote Authentication Dial-In User Service. Database for authenticating modem and ISDN connections and for tracking connection time.
Redundant Link Manager.

Service access point.
Segmentation and reassembly. In ATM, the processes of dividing PDUs into 48-byte pieces of payload data at the source for transport, and then reassembling them into a stream at the destination.
Special Exchange Subscriber (as in SAS loop-start and ground-start). Identical to FXS loop and ground start in functionality, but use of the A and B bits are different. (SAS transmitted B Bits are complementary to FXS transmitted B bits. SAS received A bits are complementary to FXS received A bits).
Switched circuit network. A network that carries traffic within channelized bearers of predefined sizes.
Stream Control Transmission Protocol. General IP transport protocol defined by the SIGTRAN working group of the IETF.
Signaling gateway. Transmits PSTN signaling at the edge of an IP/ATM network. It backhauls the signaling to a media gateway controller.
Simple Gateway Control Protocol.
signaling gateway
Gateway that supports only signaling traffic (no bearer traffic.) For example, a gateway that terminates SS7 A-links is a signaling gateway.
One of the working groups of the IETF.
Session manager.
A structure in raw message that contains all decoded supplementary service information.
Less than the standard rate of transmission, which is defined at the voice-grade rate of 64 kbps.

T1 channel-associated signaling.
Digital WAN carrier facility. T3 sends DS3-formatted data at 44.736 Mbps through the telephone switching network.
Toolkit Command Language. A scripting language used for gateway products both internally and externally to Cisco IOS software code.
Transmission Control Protocol.
Time-division multiplexing. Technique in which information from multiple channels can be allocated bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to each channel regardless of whether the station has data to send.
Terminal endpoint identifier.

User Adaptation Layer.
Upper Layer Protocol. The logical higher-layer application which uses the services of SCTP.

Voice feature card. Voice-processing card that resides in one of the slots in the Cisco AS5800 platform. Up to five DSP modules (DSPM) can be installed onto the VFC to perform voice processing for up to 30 B channels and potentially 60 B channels. The VFC is a multi-DSP coprocessing card and software package that adds VoIP capabilities to the Cisco AS5800.
Voice interface card. Provides voice-specific ports, including foreign exchange station (FXS), foreign exchange office (FXO), ear and mouth (E&M), and basic rate interchange (BRI).
Voice over IP. VoIP has the capability of carrying normal telephony-style voice over an IP-based Internet with circuit-based telephone-like functionality, reliability, and voice quality. In VoIP, the digital signal processor (DSP) segments the voice signal into frames, which then are coupled in groups of two and stored in voice packets. These voice packets are transported using IP in compliance with International Telecommunication Union Telecommunication Standardization Sector (ITU-T) specification H.323. VoIP is a blanket term that generally refers to the Cisco standards-based (H.323, and so forth) approach to IP voice traffic.
Card that can operate as a VIC or as a WIC, providing physical connection to WAN or voice networks.

Wide-area network interface card.

Refer to the Internetworking Terms and Acronyms for terms not included in this glossary.