Alphabetic list of terms

Numeric

2DS

A variant of the standard G.703 framing required by most E1 DPNSS providers in the U.K. See also G.703.

2-wire continuity test

In a Signaling System 7 (SS7) network, a test in which a TAOS unit sends a 2010Hz tone (for a T1 line) or a 2000Hz tone (for an E1 line) and expects to receive a 1780Hz tone in order to verify that the physical link between the central office (CO) switch and the unit is available. The TAOS unit supports both incoming and outgoing 2-wire continuity checks for T1 and E1 lines. You can select the type of check to perform on a per-line basis. Both the native 2-wire continuity check (GR-246-CORE Section B.2) and 4-wire-to-2-wire emulation (GR-246-CORE Section B.3) are supported. Compare with 4-wire continuity test. See also 4-wire-to-2-wire continuity test, continuity test, SS7 network.

3DES-CBC

Triple data encryption standard-cypher block chaining. 3DES-CBC is a variant of DES-CBC. 3DES-CBC encrypts each block of data three times, using a different key each time. See also 40DES-CBC, DES-CBC.

3.1kHz audio-bearer service

A service that sends a data call over a voice trunk. Because echo cancellation corrupts data transmitted on voice trunks, each switch should turn off echo cancellation on the trunks handling 3.1kHz audio-bearer service. The 3.1kHz audio-bearer service is sometimes referred to as data over subscriber bearer service (DOSBS).

4-wire continuity test

In a Signaling System 7 (SS7) network, a test in which a TAOS unit verifies that the physical link between the central office (CO) switch and the unit is available. For a T1 line, the TAOS unit sends a 2010Hz tone and expects to receive a 2010Hz tone in return. For an E1 line, the TAOS unit sends a 2000Hz tone and expects to receive a 2000Hz tone in return.

The 4-wire continuity test requires one end of a line to place a channel into loopback state while the other end sends the tone. The check concludes successfully if the tone sent on the outgoing path is received on the return path within acceptable quality and timing limits. The 4-wire check procedure cannot detect potential inadvertent loops in the line path or in line facilities, and cannot be used when the other exchange is analog. For these reasons, the procedure known as a 2-wire continuity test is recommended by the International Telecommunications Union Telecommunication Standardization Sector (ITU-T).

Compare with 2-wire continuity test, 4-wire-to-2-wire continuity test. See also continuity test, SS7 network.

4-wire-to-2-wire continuity test

In a Signaling System 7 (SS7) network, a test in which a TAOS unit sends a 1780Hz tone and expects to receive a 2010Hz tone (for a T1 line) or a 2000Hz tone (for an E1 line) in order to verify that the physical link between the central office (CO) switch and the unit is available. Compare with 4-wire continuity test. See also 2-wire continuity test, continuity test, SS7 network.

7-bit mode

See ASCII mode.

8-bit binary mode

See binary mode.

10Base2

A 50-ohm coaxial RG-58u cable with a data rate of 10Mbps and a maximum length of 180 meters. 10Base2 does not include a built-in transceiver. It is also known as thin Ethernet or thinnet.

10Base5

A 50-ohm coaxial RG-6 cable with a data rate of 10Mbps and a maximum length of 500 meters. It is also known as thick Ethernet or thicknet.

10BaseT

The 802.3 IEEE standard for operating a 10Mbps Ethernet network with twisted-pair cabling and a wiring hub. 10BaseT is also known as UTP Ethernet and twisted-pair Ethernet. See also 10BaseT hub.

10BaseT hub

A hub providing a common termination point for hosts connected to 10BaseT wiring. See also 10BaseT.

40DES-CBC

40-bit data encryption standard-cypher block chaining. 40DES-CBC is the same algorithm as DES-CBC, but it uses a 40-bit key. See also 3DES-CBC, DES-CBC.

40-bit data encryption standard-cypher block chaining

See 40DES-CBC.

100BaseFX

A dual-fiber cable standard designed for 100Mbps Fiber Distributed Data Interface (FDDI). Compare with 100BaseT, 100BaseT4, 100BaseTX.

100BaseT

The 802.3 IEEE standard for operating a 100Mbps Ethernet network. 100BaseT differs from the 10BaseT standard by requiring higher-grade cable or more wiring pairs, with cable lengths that are only a tenth as long as 10BaseT cable lengths. Compare with 100BaseFX, 100BaseT4, 100BaseTX. See also 10BaseT.

100BaseT4

A 4-pair, category-3, half-duplex cable with a data rate of 33.3Mbps per pair, and a maximum length of 100 meters. Compare with 100BaseFX, 100BaseT, 100BaseTX.

100BaseTX

A 2-pair, category-5, half-duplex cable with a data rate of 33.3Mbps per pair, and a maximum length of 100 meters. The 100BaseTX standard was designed for 100Mbps Fiber Distributed Data Interface (FDDI) and Copper Distributed Data Interface (CDDI). Compare with 100BaseFX, 100BaseT, 100BaseT4. See also CDDI, FDDI.

802.2

An IEEE protocol specification for the media access control (MAC) header of an Internetwork Packet Exchange (IPX) frame in NetWare 3.12 or later. An 802.2 frame contains the Logical Link Control (LLC) protocol header in addition to the MAC header. Compare with 802.3, Ethernet II, SNAP. See also IPX frame, LLC protocol, MAC.

802.3

An IEEE protocol specification for the media access control (MAC) header of an Internetwork Packet Exchange (IPX) frame in NetWare 3.11 or earlier. An 802.3 frame does not contain the Logical Link Control (LLC) protocol header in addition to the MAC header. The 802.3 frame is also called Raw 802.3. Compare with 802.2, Ethernet II, SNAP. See also IPX frame, LLC protocol, MAC.

802.5

An IEEE protocol specification for the physical layer and media access control (MAC) sublayer of a token-ring topology. 802.5 implements token passing over shielded twisted pair (STP) cabling and offers data rates of 4 or 16Mbps. See also STP cable.

802.6

An IEEE media access control (MAC) standard used on local area networks (LANs). 802.6 is also known as the Distributed Queue Dual Bus (DQDB) protocol.

A

AAL

Asynchronous Transfer Mode (ATM) adaptation layer. The AAL is a protocol that translates higher-layer data from its native size and format to the size and format of an ATM cell, enabling engineers to adapt the ATM layer to particular services. The AAL consists of two sublayers: the convergence sublayer (CS) and the segmentation and reassembly (SAR) sublayer. See also ATM, ATM layer, convergence sublayer, SAR.

ABR

(1) Area border router. An ABR is an Open Shortest Path First (OSPF) router that belongs to both a regular area and the backbone area. See also area, backbone area, OSPF protocol.

(2) Available bit rate. ABR is an Asynchronous Transfer Mode (ATM) service class that handles bursty LAN traffic and data that is tolerant of delays and cell loss. ABR is a best-effort, managed service. Compare with CBR, UBR, VBR-nonreal time, VBR-real time. See also ATM.

absolute congestion

In a frame relay network, a congested condition that occurs when the queue length reaches the threshold of 64 buffers, and no room remains in the queue. When the average queue length (AQL) exceeds the threshold for absolute congestion, all incoming frames are discarded, and the forward explicit congestion notification (FECN) and backward explicit congestion notification (BECN) bits are set. Compare with mild congestion, severe congestion. See also BECN, congestion, FECN.

acceptance policy

A set of rules that determine the path and route information the TAOS unit accepts from a Border Gateway Protocol (BGP) peer for further processing. Compare with advertisement policy, injection policy. See also BGP, policy.

Accept Packet Pass-Through Call message

See ACCP message.

Accept Pass-Through Call message

See ACST message.

Access Accept packet

A packet sent by the RADIUS server to inform the TAOS unit that a client's request for access has been granted. See also RADIUS server.

Access Challenge packet

A request for the user to enter a password in a hand-held token card. The token-card server sends the Access Challenge packet through the RADIUS server and the TAOS unit to the user. See also RADIUS server, token card, token-card server.

access concentrator

A device that efficiently forwards data, handling incoming calls for a network point of presence (POP). In general, an access concentrator supports dial-in modem calls, ISDN connections, dedicated links, frame relay traffic, and multiprotocol routing. See also dedicated circuit, dial-in modem access, frame relay concentrator, ISDN, POP.

access link

See A-link.

Access Password Ack packet

A response from the RADIUS server, informing the TAOS unit that it has accepted a new password. See also RADIUS server.

Access Password Reject packet

A response from the RADIUS server, informing the TAOS unit that it has rejected a new password. See also RADIUS server.

Access Password Request packet

A password-change request that a TAOS unit sends to the RADIUS server. See also RADIUS server.

access rate

The data rate of the user access channel.

Access Reject packet

A packet the RADIUS server sends to inform the TAOS unit that it has not granted a client's request for access. The RADIUS server sends an Access Reject packet if the user enters an unknown username, fails to enter the correct password, or enters an expired password. See also RADIUS server.

Access Request packet

A packet that a TAOS unit sends to the RADIUS server on behalf of a client attempting to establish a connection. See also RADIUS server.

access router

A device that supports basic routing protocols and enables remote users to gain access to a corporate backbone network.

Access SS7 Gateway Control Protocol

See ASGCP.

access tandem switch

A tandem switch that provides equal-access connections for carriers by linking local end-office switches. An access tandem switch aggregates voice and data calls from several local switches, then connects to a tandem switch in another area's network to move calls from one region to another. Typically, the tandem switch receives toll traffic and uses its trunks to process and route the traffic to and from another service provider's end-office switch.

accounting

A way to log information in RADIUS about Start session, Stop session, and Failure-to-start session events. When a TAOS unit recognizes one of these events, it sends an accounting request to RADIUS. When the accounting server receives the request, it combines the information into a record and timestamps it. Each type of accounting record contains attributes associated with an event type, and can show the number of packets the TAOS unit transmitted and received, the protocol in use, the username and IP address of the client, and other session information. See also accounting server, Failure-to-start session, Start session, Stop session.

accounting checkpoint

A RADIUS feature that provides periodic session information to enable accurate session billing even if the RADIUS accounting server does not receive a Stop packet. Typically, when RADIUS accounting is enabled and a Point-to-Point Protocol (PPP) connection terminates, the TAOS unit sends a Stop packet to the RADIUS accounting server, which stores the packets for use in billing. If the checkpoint feature is also enabled and the RADIUS accounting server fails to receive a Stop packet for any reason, it can still close off the session billing on the basis of the last Checkpoint packet it received. See also accounting, Checkpoint packet, Checkpoint record.

Accounting Request packet

A request for accounting information. A TAOS unit sends an Accounting Request packet to the RADIUS accounting server. See also accounting server, RADIUS.

Accounting Response packet

A packet containing accounting information. A RADIUS accounting server sends an Accounting Response packet to the TAOS unit. See also accounting server, RADIUS.

accounting server

The RADIUS daemon with accounting enabled. See also accounting, RADIUS daemon.

ACCP message

Accept Packet Pass-Through Call message. A call-confirmation message sent by a TAOS unit to a Signaling System 7 (SS7) signaling gateway. An ACCP message verifies the call-setup information that the TAOS unit used for routing the call to its destination. Compare with RCCP message. See also signaling gateway, SS7.

ACD

Automatic call distributor. An ACD is a telephone service that handles incoming calls on the basis of the number called. Many companies offering sales and service support use ACD to validate callers, make outgoing responses or calls, forward calls to the correct party, enable callers to record messages, gather usage statistics, and balance the use of telephone lines.

ACE authentication

A form of token-card authentication in which RADIUS forwards a connection request to a Security Dynamics ACE/Server. The ACE/Server sends an Access Challenge packet back through the RADIUS server and the TAOS unit to the user dialing in. The user sees the challenge message, obtains the current token from his or her card, and enters the token.

The token travels back through the TAOS unit and the RADIUS server to the ACE/Server. The ACE/Server sends a response to the RADIUS server, specifying whether the user has entered the proper username and token. If the user enters an incorrect token, the ACE/Server returns another challenge, and the user can again attempt to enter the correct token. The server sends up to three challenges. After three incorrect tries, the TAOS unit terminates the call.

See also ACE token, authentication, RADIUS server, token, token card, token-card authentication, token-card server.

ACE token

A randomly generated access code that a user obtains from a SecurID token card. The code changes every 60 seconds. See also ACE authentication, token card.

ACF message

Admission Confirmation message. Upon successful call authentication, an H.323 registration, admission, and status (RAS) message sent by the MultiVoice® Access Manager (MVAM) device to a MultiVoice® gateway in response to an Admission Request (ARQ) message. An ACF message contains the network routing information that an ingress MultiVoice® gateway uses to connect the call. See also H.323, MultiVoice®, MVAM, RAS.

ACK

Acknowledgment. An ACK is a packet that the system uses to acknowledge a successful transmission. When a device receives a packet, it sends back either an ACK packet or a negative acknowledgment (NAK) packet to the sending device. If all the data arrived without corruption, the receiving device sends an ACK. If some of the data is missing or corrupted, the receiving device sends a NAK, which acts as a request that the sender retransmit the data.

Acknowledge Request Test Echo message

See ARTE message.

Acknowledge Send Tones message

See ASTN message.

acknowledgment

See ACK.

ACM

Address Complete message. An ACM is sent from a signaling gateway to the SS7 network to acknowledge that the gateway has received the information required to route the call. See also signaling gateway, SS7 network.

ACR

Allowed cell rate. In an Asynchronous Transfer Mode (ATM) configuration, an available bit rate (ABR) service value specifying the maximum rate (in cells per second) at which a device is allowed to send data. See also ABR, ATM.

ACR message

Release Channel Completed message. An IP Device Control (IPDC) protocol call-control message sent between the remote access server (RAS) and the signaling gateway, reporting that the call channel is closed. At a minimum, this message reports the disconnect-cause code that identifies how the call was terminated and the source port type, source module number, source line number, and source channel number assigned to that call. Compare with RCR message. See also IPDC, RAS, signaling gateway.

ACST message

Accept Pass-Through Call Setup message. An ACST message is a notification that the TAOS unit sends to the Softswitch to notify the device that two channels have been connected. Compare with RCST message. See also Softswitch.

active hub

A multiport device that amplifies local area network (LAN) transmission signals on a network, enabling them to be transmitted over a much greater distance than is possible with a passive hub. Compare with passive hub, smart hub. See also hub.

active open

A client-initiated operation that enables a device to establish a TCP link with a server at a fixed IP address.

A-D conversion

See analog-to-digital conversion.

add-on number

One or more numbers that a TAOS unit uses to build a multichannel MP, MP+, AIM, or BONDING call.

A multichannel call begins as a single-channel connection to one telephone number. The calling unit then requests additional numbers to connect additional channels, and stores the add-on numbers it receives from the answering unit. To add channels to the call, the calling unit integrates the add-on numbers with the telephone number it dialed initially. Typically, the numbers assigned to the channels share a group of leading digits. The add-on numbers are the rightmost digits identifying each telephone number, excluding the digit(s) that the telephone numbers have in common.

Address Complete message

See ACM.

address resolution

A method of mapping a logical address (such as an IP address) to a hardware address (such as a MAC address). See also ARP, hardware address, IP address, logical address, MAC address.

Address Resolution Protocol

See ARP.

ADI

Analog Devices, Inc. ADI is a company that provides the firmware version for the MultiDSP module See also MultiDSP.

adjacency

A relationship formed between neighboring Open Shortest Path First (OSPF) routers for the purpose of exchanging routing information. An OSPF router dynamically detects its neighboring routers by sending Hello packets to the multicast address AllSPFRouters. It then attempts to form adjacencies (Figure 1).

Figure 1. Adjacency between neighboring routers

Neighbors exchange databases and build a consistent, synchronized database between them. When an OSPF router detects a change on one of its interfaces, it modifies its link-state database and multicasts the change to its adjacent neighbor, which in turn propagates the change to its adjacent neighbor, until all routers within an area have synchronized link-state databases. This method of updating routing information results in quick convergence among routers.

See also area, convergence, link-state database, OSPF protocol, router.

admin cost

An Asynchronous Transfer Mode (ATM) routing metric that measures the administrative cost associated with the logical port. See also ATM, CDV, end-to-end delay, logical port.

administrative weight

In a Private Network-to-Network Interface (PNNI) configuration, a value used to specify preferential use of a link or node for a specific service category. Administrative weight is one of the elements of topology-state information exchanged among the nodes. Other such elements include a dynamic assessment of available bandwidth, assigned metrics, and other possible attribute values. All the elements affect how the most efficient link is chosen at a given time. See also PNNI protocol.

Admission Confirmation message

See ACF message.

Admission Reject message

See ARJ message.

Admission Request message

ARQ message.

ADSL

Asymmetric digital subscriber line. ADSL is a standard that enables devices attached to twisted-pair copper wiring to transmit data at rates from 1.5Mbps to 9Mbps downstream, and 16Kbps to 640Kbps upstream. ADSL devices can transmit data at distances of up to 18,000 feet. ADSL configurations can use more bandwidth in one direction than the other. Compare with HDSL, IDSL, RADSL, SDSL, SHDSL, VDSL. See also DSL.

ADSL transceiver unit

See ATU.

ADSL transceiver unit--central office

See ATU-C.

ADSL transceiver unit--remote

See ATU-R.

Advanced Mobile Phone Service

See AMPS.

advertisement policy

A set of rules that determines the path and route information the TAOS unit advertises to a Border Gateway Protocol (BGP) peer. Compare with acceptance policy, injection policy. See also BGP, policy.

AESA format

ATM end system address format. AESA format can be the format used for an ATM end-point address assigned to a TAOS unit's ATM interface. AESA addresses are required for IP over ATM.

An AESA address is a 20-byte, 40-digit hexadecimal number. The first 13 bytes are the address prefix, or network portion of the address. The last 7 bytes are the host portion of the address. Depending on the AESA format chosen, the content of each byte of the address varies, as shown in Figure 2. All of the supported AESA formats divide the address into the initial domain part (IDP) and the domain-specific part (DSP).

AESA addresses use one of the following formats:

Figure 2 shows how each format divides the 20-byte address into subfields. The shaded portion represents the address prefix, which is always the first 13 bytes.

Figure 2. Subfields in the AESA address formats

See also ATM, custom AESA format, DCC AESA format, E.164 AESA format, ICD AESA format.

AFI

Authority and format identifier. The AFI is part of the network-level address header of an Asynchronous Transfer Mode (ATM) cell. It is a subfield of the initial domain part (IDP) of an ATM end system address (AESA). The AFI identifies the type of AESA address in use: custom AESA, data country code (DCC) AESA, E.164 AESA, or international code designator (ICD) AESA. Compare with IDI. See also AESA format, ATM, custom AESA format, DCC AESA format, E.164 AESA format, ICD AESA format, IDP.

agent

A network device that provides Simple Network Management Protocol (SNMP) information to a manager application running on another computer. The agent and manager share a database of information, called the management information base (MIB). The manager polls the agent for information at regular intervals. When an unusual system event occurs, the agent can use a message called a traps-PDU to send unsolicited information to the manager. See also manager, MIB, SNMP, traps-PDU.

aggregation

The process of combining multiple prefixes from one or several routes so that a single prefix and route can be advertised. Route aggregation reduces the amount of information that a device running Border Gateway Protocol (BGP) must store and exchange with its BGP peers. See also BGP.

AH

Authentication Header. AH is an Internet Protocol Security (IPSec) protocol that uses a shared secret to run portions of a data packet through digest algorithms to create a digital fingerprint. The receiving system performs the same process and compares the fingerprints. Matching fingerprints verify that the packet was sent by the right source and was not altered in transit. AH works with the message-digest algorithm 5 (MD5), secure hash algorithm 1 (SHA1), message-digest algorithm 5--hash-based message authentication code (MD5-HMAC), and SHA1-HMAC authentication algorithms. Compare with ESP. See also IPSec protocol, MD5, MD5-HMAC, SHA1, SHA1-HMAC.

AIM

Ascend Inverse Multiplexing. AIM manages the connection of two remotely located inverse multiplexers. See also inverse multiplexer, inverse multiplexing.

AIM port

A port that supports Ascend Inverse Multiplexing (AIM) and BONDING (Bandwidth on Demand Interoperability Group) functionality. See also AIM, BONDING.

AIS

Alarm Indication signal. An AIS is an all-ones signal that a device sends when it detects an error condition or receives an error notification.

alarm

A signal that indicates that the system has detected a security violation or error. See also Blue Alarm signal, RAI signal, Red Alarm signal.

Alarm Indication signal

See AIS.

alarm relay

A mechanism whose contacts remain open on the back panel's terminal block during normal operation. If you enable them, the alarm relay contacts close during loss of power, hardware failure, or a system reset. You can also specify whether the contacts close when the bit error rate exceeds a certain value, or when all T1 PRI lines go out of service.

a-law

An International Telecommunication Union Telecommunication Standardization Sector (ITU-T) standard for sampling data by means of pulse code modulation (PCM). A-law is most commonly used outside of North America and Japan. Compare with mu-law. See also PCM.

A-link

Access link. In a Signaling System 7 (SS7) configuration, an A-link is a signaling link that does not carry any data traffic. See also SS7.

Allowed cell rate

See ACR.

Alternate mark inversion

See AMI.

alternate path

An Open Shortest Path First (OSPF) path on which the system reroutes a permanent virtual circuit (PVC) if a trunk fails.

ALTN message

Answer to LTN message. An ALTN message is sent by a TAOS unit to a Softswitch. It is a response to a Listen for Tones (LTN) message, and provides data about the status of the listening process, including information about whether the LTN request timed out and whether the maximum number of tones was received. See also LTN message, Softswitch.

ALU

Average line utilization. ALU is the average amount of bandwidth used on a line over a user-specified period of time. A TAOS unit uses ALU when determining whether to add or subtract bandwidth from a multichannel call. See also DBA protocol.

Always On/Dynamic ISDN

See AO/DI.

amber frame

A type of packet frame that enables you to identify packets passing through the frame relay network. The network forwards amber frames with the discard eligibility (DE) bit set, enabling the network to discard the packet if it passes through a congested node. Congested nodes that must discard packets use color designations to determine which frames to discard. Red frames are discarded first, followed by amber frames, and then green frames. Compare with green frame, red frame. See also congestion, DE, frame relay.

AMCP message

Accept Modify Packet Pass-Through Call message. On a MultiVoice® network, an AMCP message is sent by a TAOS unit to a Signaling System 7 (SS7) signaling gateway and specifies that the unit modifies one or more of the following values for a Voice over IP (VoIP) call:

Compare with RMCP message. See also MultiVoice®, SS7.

American National Standards Institute

See ANSI.

AMI

Alternate mark inversion. Used on T1 lines, AMI is a signaling method in which the 1 bits have alternating priority. See also T1 line.

AMPS

Advanced Mobile Phone Service. AMPS is a standard system for analog cellular telephone service. Introduced by American Telephone and Telegraph (AT&T) in 1983, AMPS is the most widely used cellular system in the United States. The service uses frequency ranges between 800MHz and 900MHz. Each provider can use half of the 824MHz to 849MHz range for receiving signals, and half the 869MHz to 894MHz range for transmission.

analog data

Data that can change continuously and have any value in a range. Examples of analog data are the time of day represented by clock hands and the temperature represented by a liquid thermometer. Compare with digital data. See also analog signal.

Analog Devices, Inc.

See ADI.

analog line

A line that transmits data by means of an analog signal. See also analog signal.

analog loopback

A test that checks whether the modem or data terminal equipment (DTE) is causing errors in data transmission. During an analog loopback, the system sends data between the local modem and the local DTE. Errors in transmission indicate a problem with the modem, DTE, or the interface between them. Compare with digital loopback. See also local loopback, loopback, remote loopback.

analog signal

A type of signal that encodes data transmitted over wire or through the air, commonly represented as an oscillating wave. An analog signal can transmit analog or digital data. It takes any value in a range, and changes smoothly between values. A radio station uses analog signals to send analog music data, while a modem uses analog signals to transmit digital data. Compare with digital signal. See also analog data.

analog-to-digital conversion

A process in which an analog signal is modified into a digital signal. Analog-to-digital conversion takes place, for example, when an analog modem call reaches a digital modem. Compare with digital-to-analog conversion. See also analog signal, digital modem, digital signal, modem.

ANI

Automatic number identification. ANI is a mechanism that informs the called party of the calling party's telephone number. See also caller identification, CLID.

ANM

Answer message. An ANM is sent between a signaling gateway and an SS7 network. For an incoming call, the signaling gateway sends an ANM to inform the SS7 network that the path is set up to divert the Internet call. For an outgoing call, the SS7 network send an ANM to the signaling gateway, indicating that the central office (CO) switch is ready to receive the call at the identified circuit. CO, signaling gateway, SS7 network.

Annex A

See frame relay Annex A.

Annex D

See frame relay Annex D.

ANSI

American National Standards Institute. ANSI creates standards for networking and communications. It is the U.S. representative to the International Organization for Standardization (ISO). See also ISO.

ANSI T1.617 Annex D

See frame relay Annex D.

Answer message

See ANM.

answer number

The telephone number used for routing incoming calls. See also call routing.

Answer to LTN message

See ALTN message.

AO/DI

Always On/Dynamic ISDN. AO/DI is a networking service that enables you to send and receive data through a dedicated X.25 connection over an ISDN D channel, ISDN B channel, or dedicated 56K line.

In a traditional ISDN environment, data moves across B channels, and signaling information moves across the D channel. Because signaling information uses a small percentage of available D-channel bandwidth, AO/DI was developed to maximize bandwidth usage while reducing the necessity that all data travel over the B channels.

A TAOS unit uses switched ISDN B channels only when required, on the basis of increased bandwidth use. Through its use of AO/DI, X.25, and Bandwidth Allocation Control Protocol (BACP), a TAOS unit avoids dial-up charges and the use of switched B channels whenever it sends or receives data over the X.25 connection. Among the functions that can use AO/DI are the following:

For TAOS units, AO/DI enables you to use X.25 bandwidth of up to 9600bps. If a data transfer requires more bandwidth, the TAOS unit adds dial-up B channels by means of BACP. See also BACP, B channel, D channel, X.25.

APP

Ascend Password Protocol. APP is a User Datagram Protocol (UDP) that enables a user to respond to password challenges received from an authentication server.

applet

A small software module that runs on a Java Virtual Machine (JVM) inside a Web browser. See also JVM.

Application layer

The highest layer of the OSI Reference Model. The Application layer provides applications with access to the network. File transfer, email, and network management software are examples of Application-layer programs. Protocols such as File Transfer Protocol (FTP), Rlogin, Simple Network Management Protocol (SNMP), and Telnet provide Application-layer services. See also FTP, OSI Reference Model, Rlogin, SNMP, Telnet.

APS

Automatic protection switching. On a Stinger® unit, a feature that provides line redundancy for a trunk aggregation module. With APS, a working channel has a dedicated standby channel. If the working channel fails, the standby channel is activated.See also Stinger®, trunk aggregation module.

APX 8000

A carrier-class remote access server (RAS), a unit that combines a fault-tolerant design with high port density.

AQL

Average queue length. AQL is a time-average algorithm that the frame relay switch executes each time it queues a frame for transmission. The AQL value is compared against a precalculated threshold. When the AQL is less than or equal to the threshold, maximum throughput and minimum delay occur. See also absolute congestion, congestion, congestion management, mild congestion, severe congestion.

ARCnet

Attached Resource Computer Network. ARCnet is a baseband network architecture with a transmission rate of up to 2.5Mbps. Because it is relatively inexpensive and easy to set up, ARCnet is typically used for smaller networks.

area

A portion of an Open Shortest Path First (OSPF) autonomous system. An area acts as its own network. All area-specific routing information stays within the area, all routers within an area have a synchronized link-state database, and each database within an area is unique. On a TAOS unit, an area number uses dotted decimal notation, but it is not an IP address. To tie the areas together, some routers belong to a backbone area and one other type of area. These routers are called area border routers (ABRs). In Figure 3, all of the routers are ABRs.

Figure 3. Dividing an autonomous system into areas

See also ABR, autonomous system, backbone area, link-state database, normal area, NSSA, OSPF protocol, router, stub area.

area border router

See ABR.

area ID

See area number.

area number

A portion of a Switched Multimegabit Data Service (SMDS) address, or a number denoting an Open Shortest Path First (OSPF) area. In an SMDS address, the area number can be four bytes long, and is sometimes referred to as an area ID. An OSPF area number is expressed in dotted decimal notation, but it is not an IP address. See also OSPF protocol, SMDS.

ARJ message

Admission Reject message. An H.323 registration, admission, and status (RAS) message sent by the MultiVoice® Access Manager (MVAM) device to a MultiVoice® gateway in response to an Admission Request (ARQ) message if the call was not authenticated. Compare with ACF message, ARQ message. See also H.323, MultiVoice®, MVAM, RAS.

ARP

Address Resolution Protocol. ARP is a protocol in the TCP/IP protocol suite. By mapping an IP address to a physical hardware address, ARP enables a unit to identify hosts on an Ethernet LAN. See also Ethernet, Proxy ARP, TCP/IP.

ARQ message

Admission Request message. An H.323 registration, admission, and status (RAS) message sent from a MultiVoice® gateway to a MultiVoice® Access Manager (MVAM) device, requesting authorization for a calling end point. When the multiple logical gateway feature is enabled on a MultiVoice® gateway, an incoming call request causes the gateway to send an ARQ message that includes:

Compare with ACF message, ARJ message. See also H.323, MultiVoice®, MVAM, RAS.

ARTE message

Acknowledge Request Test Echo message. An IP Device Control (IPDC) protocol heartbeat message sent by a signaling gateway in response to a Request Test Echo (RTE) message from a TAOS unit. See also IPDC, RTE message.

AS

See autonomous system.

ASBR

Autonomous system border router. An ASBR is an Open Shortest Path First (OSPF) router that handles communication between autonomous systems by using an Exterior Gateway Protocol (EGP), as shown in Figure 4.

Figure 4. Autonomous system border routers (ASBRs)

ASBRs perform calculations related to external routes. A TAOS unit imports external routes by means of Routing Information Protocol (RIP) when it establishes a WAN link with a caller that does not support OSPF, and the ASBR calculations are always performed.

Compare with ABR. See also autonomous system, EGP, external route, OSPF protocol.

Ascend Access Event Request packet

A packet containing either a notification that the TAOS unit has started up or a request for the RADIUS server to record the number of open sessions. See also RADIUS server.

Ascend Access Event Response packet

A response from the RADIUS server, either reporting that the TAOS unit has started up or specifying the number of open sessions and informing the TAOS unit that the server has received and recorded the unit's ID. See also RADIUS server.

Ascend Access New Pin packet

A response from the RADIUS server, informing the TAOS unit that it should request access again, but with the next personal identification number (PIN) in the sequence. See also RADIUS server.

Ascend Access Next Code packet

A response from the RADIUS server, informing the TAOS unit that it should request access again, but with the next password in the sequence. See also RADIUS server.

Ascend callback

A callback method in which a TAOS unit uses a username and password to detect callback during the authentication phase (after going off hook). The originating caller is charged for the initial call. Compare with CBCP callback, CLID callback, DNIS callback. See also callback.

Ascend Inverse Multiplexing

See AIM.

Ascend Password Expired packet

A response from RADIUS server to the TAOS unit, indicating that the password the user entered matches the one in the user profile, but has expired. (That is, the Access Request packet sent a valid but expired password.) See also RADIUS server.

Ascend Terminate Session packet

A response from the RADIUS server, informing the TAOS unit that it should terminate the session and display the message sent in the packet. See also RADIUS server.

Ascend Tunnel Management Protocol

See ATMP.

ASCII

American Standard Code for Information Interchange. ASCII is a character-encoding system used on local area networks (LANs). The 128 standard ASCII characters are composed of seven bits and have the values 0--127. The extended ASCII character set contains another 128 values.

ASCII mode

A Telnet mode for terminal-server users. In ASCII mode, bit 8 is set to 0 (zero). ASCII mode is also called standard 7-bit mode or network virtual terminal (NVT) ASCII. This mode is the default if no other mode is specified. Compare with binary mode, transparent mode. See also Telnet, Telnet mode.

ASCII text file

A file that contains only letters, numbers, and punctuation symbols. An ASCII text file cannot include hidden text-formatting codes. See also ASCII.

ASE

Autonomous system external. A TAOS unit uses the term ASE to denote external routes it imports into its Open Shortest Path First (OSPF) database. The TAOS unit redistributes these routes by means of OSPF ASE advertisements, and propagates its OSPF routes to remote WAN routers running Routing Information Protocol (RIP). See also external route, OSPF protocol, RIP, router.

ASE type 5

Autonomous system external type 5. ASE type 5 is an external route originated by an area border router (ABR) as a link state advertisement (LSA). An Open Shortest Path First (OSPF) normal area allows type 5 LSAs to be transmitted throughout it. A not-so-stubby area (NSSA) and a stub area do not receive or originate type 5 LSAs. However, for NSSAs, all routes imported to OSPF have the P-bit set (P stands for propagate). When the P-bit is enabled, ABRs translate type 7 LSAs to type 5 LSAs, which can then be transmitted to the backbone. These external routes are considered type 7 LSAs. Compare with ASE type 7. See also ABR, ASE, autonomous system, external route, LSA, normal area, NSSA, OSPF protocol, stub area.

ASE type 7

Autonomous system external type 7. ASE type 7 is a type of link state advertisement (LSA) defined for not-so-stubby areas (NSSAs) in Open Shortest Path First (OSPF) version 2. For NSSAs, all routes imported to OSPF have the P-bit set (P stands for propagate). When the P-bit is enabled, ABRs translate type 7 LSAs to type 5 LSAs, which can then be transmitted to the backbone. These external routes are considered type 7 LSAs. Compare with ASE type 5. See also ASE, autonomous system, LSA, NSSA, OSPF protocol, stub area.

ASGCP

Access SS7 Gateway Control Protocol. ASGCP enables you to integrate a TAOS unit into a Signaling System 7 (SS7) network. With an ASGCP-Q.931+ license, a TAOS unit can decrease congestion on the Public Switched Telephone Network (PSTN) caused by users connecting to the Internet. Compare with IPDC. See also PSTN, SS7, SS7 network.

ASN.1

Abstract Syntax Notation One. In the OSI Reference Model, ASN.1 is a notation for describing data structures on a network. It provides a consistent syntax when transferring data between different systems. See also OSI Reference Model.

AS path list

See autonomous system path list.

ASTN message

Acknowledge Send Tones message. A message sent by a TAOS unit to a Signaling System 7 (SS7) signaling gateway to confirm that the call-progress tones or voice announcements requested by a Send Tones (STN) message have been played. Compare with STN message. See also signaling gateway, SS7, VoIP.

asymmetric digital subscriber line

See ADSL.

asynchronous communications server

A LAN server that enables a network user to dial out of the network and into the Public Switched Telephone Network (PSTN), or to access dedicated lines for asynchronous communications. An asynchronous communications server is also called a dial-in/dial-out server or a modem server. See also asynchronous transmission.

asynchronous PPP

A mode for sending Point-to-Point Protocol (PPP) packets. In asynchronous mode, the characters that form the data packets are sent at irregular intervals, without a clocking signal. Figure 5 illustrates a single-channel asynchronous PPP call in which the calling device is a modem.

Figure 5. Asynchronous PPP connection

Asynchronous PPP is commonly used in lower-speed transmission and less-expensive transmission systems. See also asynchronous transmission, PPP.

Asynchronous Transfer Mode

See ATM.

Asynchronous Transfer Mode (ATM) adaptation layer

See AAL.

asynchronous transmission

A mode in which the sending and receiving serial hosts know where a character begins and ends because each byte is framed with additional bits, called a start bit and a stop bit. A start bit indicates the beginning of a new character. It is always 0 (zero). A stop bit marks the end of the character. It appears after the parity bit if parity bits are in use.

An asynchronous link uses the type of serial communication provided by a PC COM port. A dial-in modem or V.120 terminal adapter (TA) initiates an asynchronous host-to-network or host-to-host connection. The call can use Point-to-Point Protocol (PPP) encapsulation, V.120 encapsulation, or raw (unencapsulated) Transport Control Protocol (TCP).

A TAOS unit routes an asynchronous call to a digital modem as a voice call, and then to the terminal-server software. If the terminal server does not detect a PPP packet, it begins a login sequence. If the terminal server detects a PPP packet, it passes the call on to the router, where it is handled as a regular PPP connection. The caller never sees the terminal-server interface.

See also asynchronous PPP, digital modem, PPP, TCP, terminal server, V.120, V.120 TA.

async PPP

See asynchronous PPP.

AT command set

A set of standard instructions used to activate functions on a modem. Originally developed by Hayes Microcomputer Products, the AT command set is now used by almost all modem manufacturers. See also modem.

ATM

Asynchronous Transfer Mode. ATM is a packet-switched, broadband network architecture central to broadband ISDN (B-ISDN). It ensures reliable delivery of packets and provides very high bandwidth, enabling data, voice, and video transmissions to occupy the same line.

ATM is based on connections, not channels. The term asynchronous refers to the way in which ATM achieves its unchannelized bandwidth allocation. ATM sends data associated with a connection only when there is actual data to send. This functionality is in contrast to that found in channelized or time-division multiplexing (TDM) networks, in which a special bit pattern must be sent in every time slot representing a channel, even when the connection is idle.

In the past, companies built large voice, data, and television networks to accommodate each specific kind of data transmission. Duplication of effort and tremendous cost outlays resulted. Because many of these networks were built for peak load conditions, the average usage was typically very low, leading to excessive costs. Many organizations needed to find ways to use a single network infrastructure and assign bandwidth on an as-needed basis.

ATM lets both private corporations and public service providers build unchannelized networks to make more efficient use of the underlying bandwidth on the network. By offering scalable rates from 1.5Mbps to 155Mbps or higher, ATM services can make the WAN transparent for applications. And unlike frame relay or other data services, ATM can easily accommodate delay-sensitive traffic such as voice and video.

ATM uses very short, fixed-length packets called cells. The ATM cell is 53 bytes long, consisting of a 5-byte header containing an address, and a fixed 48-byte information field. To handle the various data types on a network, ATM supports five service classes: constant bit rate (CBR), variable bit rate (VBR)-real time, variable bit rate (VBR)-nonreal time, available bit rate (ABR), and unspecified bit rate (UBR).

ATM is also known as cell relay. See also ABR, ATM, B-ISDN, broadband, CBR, cell, packet-switched network, packet switching, UBR, VBR-nonreal time, VBR-real time.

ATM cell

A 53-byte, fixed-length Asynchronous Transfer Mode (ATM) data packet that contains the following fields:

See also ATM, CLP, GFC, HEC, payload, PT field, VCI, VPI.

ATM circuit

A point-to-point permanent virtual circuit (PVC) established on the TAOS unit in an Asynchronous Transfer Mode (ATM) configuration. An ATM circuit can make use of any two physical interfaces in the system.

ATM contract

See QoS contract.

ATM direct

A feature that enables a TAOS unit to concentrate incoming Point-to-Point Protocol (PPP) calls onto an Asynchronous Transfer Mode (ATM) interface. ATM-direct aggregates multiple PPP connections and forwards them as a combined data stream. An upstream device then examines the packets and routes them appropriately. In Figure 6, the TAOS unit forwards the data stream from two PPP dial-in hosts across the same ATM link.

Figure 6. ATM-direct concentrating PPP calls to an ATM interface

An ATM-direct connection is not a full-duplex tunnel between a PPP dial-in user and a remote device. Although the TAOS unit does not route the packets onto the ATM link, it must use the router to send packets received across ATM back to the appropriate PPP caller. For this reason, ATM-direct connections must enable IP routing.

See also ATM, IP routing, PPP.

ATM direct trunk

A logical-port configuration that enables you to make a direct trunk connection between two Asynchronous Transfer Mode (ATM) switches. See also ATM.

ATM end system address format

See AESA format.

ATM Flow-Control processor

An Asynchronous Transfer Mode (ATM) network-management system that uses binary, hop-by-hop, closed-loop flow-control algorithms that shift network congestion to the edge of the network. See also ATM.

ATM framer

A device that multiplexes Asynchronous Transfer Mode (ATM) cells into the SONET payload and extracts cells from the SONET payload for reassembly into packets. See also SONET.

ATM IISP-DCE

ATM Interim Interswitch Signaling Protocol for data circuit-terminating equipment. A logical-port configuration that enables you to connect two Asynchronous Transfer Modem (ATM) switches by means of IISP DCE ports. This service routes switched virtual circuits (SVCs) through a mixed-vendor switch network. Compare with ATM IISP-DTE. See also ATM, logical port, SVC.

ATM IISP-DTE

ATM Interim Interswitch Signaling Protocol for data terminal equipment. A logical-port configuration that enables you to connect two Asynchronous Transfer Mode (ATM) switches by means of IISP DTE ports. This service routes switched virtual circuits (SVCs) through a mixed-vendor switch network. Compare with ATM IISP-DCE. See also ATM, logical port, SVC.

ATM layer

The core layer of the Asynchronous Transfer Mode (ATM) standard. The ATM layer routes the cells across the network, performing both multiplexing and demultiplexing functions. See also AAL, ATM.

ATMP

Ascend Tunnel Management Protocol. ATMP provides a tunneling mechanism between two TAOS units across the Internet or a frame relay network. The protocol uses standard Generic Routing Encapsulation (GRE) protocol and is based on the User Datagram Protocol (UDP) and Internet Protocol (IP). ATMP provides a virtual private network (VPN) solution over the backbone resources of Internet service providers (ISPs) and carriers. Without ATMP, each mobile client and remote user has to dial directly into the network, resulting in long-distance charges. With ATMP, users can make a local call and have the transmission securely tunneled.

Figure 7 shows an ATMP tunnel between two TAOS units. A mobile client, such as a traveling salesperson, initiates the connection. The unit that authenticates the mobile client is the ATMP Foreign Agent. The unit that gains access to the home network is the ATMP Home Agent. The home network is the destination network for mobile clients. In Figure 7, the mobile client is a salesperson who logs in to an ISP (the Foreign Agent) to access her home network.

Figure 7. ATMP tunnel across the Internet

As described in RFC 1701, GRE hides packet contents and enables transmission of packets that the Internet would otherwise not accept. When you use ATMP with a TAOS unit, you can transmit either IP packets that use unregistered addresses or Internetwork Packet Exchange (IPX) packets from roaming clients. See also Foreign Agent, frame relay, GRE protocol, Home Agent, home network, IP, IPX protocol, ISP, mobile client, UDP, VPN.

ATM service class

A method of designating the type of Asynchronous Transfer Mode (ATM) service in use. ATM supports five service classes to handle the various data types on a network. Each service class ensures optimal network usage and guaranteed end-to-end delivery. The five ATM service classes are constant bit rate (CBR), variable bit rate (VBR)-real time, variable bit rate (VBR)-nonreal time, available bit rate (ABR), and unspecified bit rate (UBR). See also ABR, ATM, CBR, UBR, VBR-nonreal time, VBR-real time.

ATM service interworking feeder

A feature that enables the system to feed frame relay network traffic into an Asynchronous Transfer Mode (ATM) network so that a frame relay end user can communicate with an ATM end user. See also ATM, frame relay network.

ATM Setup message

An Asynchronous Transfer Mode (ATM) signaling message that enables a device to select the desired bandwidth and quality of service (QoS) levels when establishing a connection. The Setup message is sent by the calling user to the network and by the network to the called user. Key information elements of the Setup message include the following:

See also ATM, called-party number, CLID, QoS.

ATM SVC

ATM switched virtual circuit. An ATM SVC is a point-to-point switched connection between Asynchronous Transfer Mode (ATM) interfaces. An ATM SVC provides a lower-cost, usage-based alternative to an ATM permanent virtual circuit (PVC). Like other types of switched connections, SVCs can be initiated by a dial-in or a dial-out call.

A dial-in ATM SVC terminates locally. The TAOS unit receives the call on an ATM interface. An example of a terminating SVC is shown in Figure 8.

Figure 8. Terminating SVC on an ATM interface

A dial-out ATM SVC is initiated as an outgoing call on an ATM interface. Dial-out can be initiated explicitly, or it can take place on the basis of IP routing. Figure 9 shows a Pipeline® unit using Point-to-Point Protocol (PPP) to dial in to a MAX TNT® unit. The MAX TNT® unit establishes the incoming call and then dials out on an ATM interface on the basis of IP routing, just as it would for another type of switched dial-out call.

Figure 9. Dial-out SVC on an ATM interface

Unlike PVCs, which require dedicated connections, SVCs are on-demand connections and must use ATM end-point addresses to identify the interface and route to it. See also ATM, PPP, PVC, SVC.

ATM switched virtual circuit

See ATM SVC.

ATM UNI-DCE interface

ATM User-to-Network Interface for data circuit-terminating equipment. On an ATM UNI-DCE interface, the TAOS unit acts as the network side communicating with the user side (UNI-DTE) of an Asynchronous Transfer Mode (ATM) device. The logical port communicates with ATM customer premises equipment (CPE) over permanent virtual circuits (PVCs) and switched virtual circuits (SVCs). Compare with ATM UNI-DTE interface. See also ATM, CPE, PVC, SVC.

ATM UNI-DTE interface

ATM User-to-Network Interface for data terminal equipment. On an ATM UNI-DTE interface, the TAOS unit acts as the user side communicating with the network-side DCE switch. The logical port communicates with an Asynchronous Transfer Mode (ATM) switch over permanent virtual circuits (PVCs) and switched virtual circuits (SVCs). Compare with ATM UNI-DCE interface. See also ATM, CPE, PVC, SVC.

AT switch

See access tandem switch.

Attached Resource Computer Network

See ARCnet.

attenuation

The reduction in the strength of a signal over distance, expressed in decibels per kilometer (dB/km) or per 100 feet. Factors affecting attenuation are the frequency range of the signal, wire shielding, and cable type. Unshielded twisted pair (UTP) cable suffers from the most attenuation, while fiberoptic cable has very little attenuation. See also attenuator, UTP cable.

attenuator

A device that reduces the amplitude of a signal. See also attenuation.

attribute

A characteristic, similar to a parameter, in a RADIUS user profile or pseudo-user profile. RADIUS attributes can be assigned values to specify usernames and passwords and to configure routing, call management, and usage restrictions. See also pseudo-user profile, RADIUS, RADIUS server, user profile.

attribute set

In a transparent tunneling configuration, a set of RADIUS attributes that share the same tag number. A user's profile includes a primary attribute set, which specifies all of the values required to set up the tunnel, and additional attribute sets that can be used to establish a tunnel if the primary server is unavailable. See also tag.

attribute-value pair

See AVP.

ATU

ADSL transceiver unit. An ATU is a hardware device used with ADSL service. It connects to an Ethernet interface on one end and a telephone jack on the other. See also ADSL, ATU-C, ATU-R.

ATU-C

ADSL transceiver unit--central office. An ATU device for the central office (CO) side. Compare with ATU-R. See also ADSL, ATU, CO.

ATU-R

ADSL transceiver unit--remote. An ATU customer premises equipment (CPE) device. Compare with ATU-C. See also ADSL, ATU, CPE.

audio codec

Audio coder-decoder. A device that encodes analog voice data into a digital signal for transmission over a digital medium. See also codec, G.711 audio codec, G.728 codec, RT-24 codec.

audio coder-decoder

See audio codec.

AUI

Auxiliary unit interface. An AUI is a 15-pin D-type connector for Ethernet connections. It typically links a cable to a network interface card (NIC). An AUI is also known as a Digital, Intel, Xerox (DIX) connector. See also Ethernet, NIC.

authentication

A method of identifying the users permitted to gain access to network resources. Authentication is the first line of defense against unauthorized access to your network. Each TAOS unit supports a variety of authentication methods. You can use

When a TAOS unit is shipped from the factory, it is set to not require any authentication.

See also cache-token authentication, called-number authentication, CHAP, CLID authentication, expect-send script, PAP, PAP-Token authentication, PAP-Token-CHAP authentication, token card, token-card authentication, token-card server.

Authentication Header

See AH.

authentication key

A shared secret passed between a TAOS unit and an authentication server. An authentication key can be one of the following types:

See also authentication server, OSPF protocol, RADIUS, TACACS protocol, TACACS+ protocol.

authentication request

A request that a TAOS unit sends to an authentication server on behalf of a client requesting access. See also authentication response, authentication server.

authentication response

A response from an authentication server, notifying the TAOS unit that a user's request for access has been either granted or denied. See also authentication request, authentication server.

authentication server

An external server, such as a RADIUS, TACACS, TACACS+, or token-card server, that verifies whether a user requesting access to the network has permission to use network resources. See also RADIUS, RADIUS server, TACACS protocol, TACACS+ protocol, token-card server.

authentication timeout

The number of seconds between retries to an authentication server. If the TAOS unit is acting as a RADIUS, TACACS, or TACACS+ client, the unit waits the specified number of seconds for a response to an authentication request. If it does not receive a response within that time, it times out and sends the authentication request to the next authentication server. If the TAOS unit is acting as a Defender or SecurID client (both of which support only one server address), it waits the specified number of seconds before assuming that the server is unavailable. See also authentication server, RADIUS, RADIUS server, TACACS protocol, TACACS+ protocol.

authenticator field

In a RADIUS packet, a field that enables the system to authenticate transmissions between the TAOS unit and the authentication server. See also authentication, authentication server, CHAP, DES, encryption, RADIUS, RC4.

authority and format identifier

See AFI.

authority zone

A portion of the domain-name hierarchy associated with a name server.

authorization

Permission for a user to carry out tasks after he or she has access to the LAN. Authorization occurs after authentication is complete. See also authentication.

autobaud

A method of training up to a set modem data rate. If a DSL remote transceiver unit cannot train to this data rate, it will connect at the closest rate to which it can train (the modem's ceiling rate). See also modem rate control.

auto-BERT

Automatic bit-error-rate test. During an auto-BERT, a TAOS unit monitors the entire data stream between coder-decoders (codecs). At the end of the time period, if any channels have failed, the TAOS unit clears them, redials, and repeats the test. The maximum number of errors that can accumulate per channel is 65,000. The TAOS unit reports the total number of errors for each channel during the current call, but not the error rate. The unit resets the error display for the current call to 0 (zero) when the call disconnects.

automatic-at-startup rate adaptation

A type of rate adaptation that specifies that the customer premises equipment (CPE) initializes at a minimum specified bit rate and target noise margin. If the CPE fails to achieve the minimum bit rate in either direction, it cannot initialize, and it sends a message that the requested bit rate was too high. If the CPE can support a higher bit rate than the specified minimum, it can train up to a higher rate within the acceptable noise margin. Each direction can have a different minimum and maximum bit rate for the fast or interleaved asymmetric digital subscriber line (ADSL) channel. Compare with operator-controlled rate adaptation. See also ADSL, CPE.

automatic bit-error-rate test

See auto-BERT.

automatic call distributor

See ACD.

automatic LIM port redundancy

Automatic line interface module port redundancy. A feature that enables a Stinger® unit to detect a line interface module (LIM) port failure and automatically transfer the port connection to the same port on the spare LIM. When automatic LIM port redundancy is activated, the primary LIM port is monitored. If modem errors exceed the specified thresholds, the port connection to the primary LIM is transferred to the spare (secondary) LIM. Monitoring continues on the secondary LIM port. If modem errors again exceed thresholds, the connection is transferred back to the primary LIM port and the automatic redundancy process stops. See also LIM, LIM port redundancy.

automatic LIM redundancy

Automatic line interface module redundancy. A feature that enables a Stinger® unit to detect a line interface module (LIM) failure and automatically set up all the virtual channels of that LIM on the spare. When automatic LIM redundancy is activated, the primary LIM is monitored. If modem errors exceed the specified thresholds, all connections to the pri