思科网络词典—A
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2008-2-1 12:16:18
Procedure used in T1 transmission facilities in which each of the 24 T1 subchannels devotes 1 bit of every sixth frame to the carrying of supervisory signaling information.Also called 24th channel signaling.
AAA
authentication, authorization, and accounting. Pronounced “triple a."
AAL
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: CS and SAR. AALs differ on the basis of the source-destination timing used, whether they use CBR or 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. See also AAL1, AAL2, AAL3/4, AAL5, ATM, ATM layer, CS, and SAR.
AAL1
ATM adaptation layer. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic. See also AAL.
AAL2
ATMadaptation 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. See also AAL.
AAL3/4
ATM adaptation layer 3/4. One of four AALs (merged from two initially distinct adaptation layers) recommended by the ITU-T. AAL3/4 supports both connectionless and connection-oriented links, but is primarily used for the transmission of SMDS packets over ATM networks. See also AAL.
AAL5
ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler
processing requirements in exchange for reduced bandwidth capacity and
error-recovery capability. See also AAL and SEAL.
AARP
AppleTalk Address Resolution Protocol. Protocol in the AppleTalk protocol stack that maps a data-link address to a network address.
AARP probe packets Packets transmitted by AARP that determine if a randomly selected node ID is being used by another node in a nonextended AppleTalk network. If the node ID is not being
used, the sending node uses that node ID. If the node ID is being used, the sending node chooses a different ID and sends more AARP probe packets. See also AARP.
ABCD signaling
4-bit telephony line signaling coding in which each letter represents 1 of the 4 bits. This is often associated with CAS or robbed-bit signaling on a T1 or E1 telephony trunk.
ABM
Asynchronous Balanced Mode. HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to-point communications between two stations, where either station can initiate transmission.
ABR
1. available bit rate. QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response toinformation they receive describing the status of the network and its capability to successfully deliver data. Compare with CBR, UBR, and VBR.
2. area border router. Router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas.
Abstract Syntax Notation One
See ASN.1.
access device
Hardware component used in your signaling controller system: access server or mux.
access list
List kept by routers to control access to or from the router for a number of services (for example, to prevent packets with a certain IP address from leaving a particular interface on the router).
access method
1. Generally, the way in which network devices access the network medium.
2. Software within an SNA processor that controls the flow of information through a network.
access server
Communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. Performs both synchronous and asynchronous routing of supported protocols. Sometimes called a network access server. See also communication server.
access unit
See AU.
accounting management
One of five categories of network management defined by ISO for management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage. See also configuration management, fault management, performance management, and security management.
ACD
automatic call distribution. Device or service that automatically reroutes calls to customers in geographically distributed locations served by the same CO. See also CO.
ACELP
algebraic code excited linear prediction.
ACF
Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing. See also ACF/NCP.
ACF/NCP
Advanced Communications Function/Network Control Program. The primary SNA NCP. ACF/NCP resides in the communications controller and interfaces with the SNA access method in the host processor to control network communications. See also ACF and NCP.
ACK
See acknowledgment.
acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) occurred. Sometimes abbreviated ACK. Compare to NAK.
ACOM
Term used in G.165, “General Characteristics of International Telephone Connections and International Telephone Circuits: Echo Cancellers.” ACOM is the combined loss achieved by the echo canceller, which is the sum of the echo return loss, echo return loss
enhancement, and nonlinear processing loss for the call.
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AAA
authentication, authorization, and accounting. Pronounced “triple a."
AAL
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: CS and SAR. AALs differ on the basis of the source-destination timing used, whether they use CBR or 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. See also AAL1, AAL2, AAL3/4, AAL5, ATM, ATM layer, CS, and SAR.
AAL1
ATM adaptation layer. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic. See also AAL.
AAL2
ATMadaptation 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. See also AAL.
AAL3/4
ATM adaptation layer 3/4. One of four AALs (merged from two initially distinct adaptation layers) recommended by the ITU-T. AAL3/4 supports both connectionless and connection-oriented links, but is primarily used for the transmission of SMDS packets over ATM networks. See also AAL.
AAL5
ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler
processing requirements in exchange for reduced bandwidth capacity and
error-recovery capability. See also AAL and SEAL.
AARP
AppleTalk Address Resolution Protocol. Protocol in the AppleTalk protocol stack that maps a data-link address to a network address.
AARP probe packets Packets transmitted by AARP that determine if a randomly selected node ID is being used by another node in a nonextended AppleTalk network. If the node ID is not being
used, the sending node uses that node ID. If the node ID is being used, the sending node chooses a different ID and sends more AARP probe packets. See also AARP.
ABCD signaling
4-bit telephony line signaling coding in which each letter represents 1 of the 4 bits. This is often associated with CAS or robbed-bit signaling on a T1 or E1 telephony trunk.
ABM
Asynchronous Balanced Mode. HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to-point communications between two stations, where either station can initiate transmission.
ABR
1. available bit rate. QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response toinformation they receive describing the status of the network and its capability to successfully deliver data. Compare with CBR, UBR, and VBR.
2. area border router. Router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas.
Abstract Syntax Notation One
See ASN.1.
access device
Hardware component used in your signaling controller system: access server or mux.
access list
List kept by routers to control access to or from the router for a number of services (for example, to prevent packets with a certain IP address from leaving a particular interface on the router).
access method
1. Generally, the way in which network devices access the network medium.
2. Software within an SNA processor that controls the flow of information through a network.
access server
Communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. Performs both synchronous and asynchronous routing of supported protocols. Sometimes called a network access server. See also communication server.
access unit
See AU.
accounting management
One of five categories of network management defined by ISO for management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage. See also configuration management, fault management, performance management, and security management.
ACD
automatic call distribution. Device or service that automatically reroutes calls to customers in geographically distributed locations served by the same CO. See also CO.
ACELP
algebraic code excited linear prediction.
ACF
Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing. See also ACF/NCP.
ACF/NCP
Advanced Communications Function/Network Control Program. The primary SNA NCP. ACF/NCP resides in the communications controller and interfaces with the SNA access method in the host processor to control network communications. See also ACF and NCP.
ACK
See acknowledgment.
acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) occurred. Sometimes abbreviated ACK. Compare to NAK.
ACOM
Term used in G.165, “General Characteristics of International Telephone Connections and International Telephone Circuits: Echo Cancellers.” ACOM is the combined loss achieved by the echo canceller, which is the sum of the echo return loss, echo return loss
enhancement, and nonlinear processing loss for the call.
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