Section 2 A Terms Flashcards
A&B bit signaling
Procedure used in T1 transmission facilities in which each of the 24 T1 subchannels devotes one bit of every sixth frame to the carrying of supervisory signaling information. Also called 24th channel signaling.
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 DBR 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.
AAL1
ATM adaptation layer 1. 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.
AAL2
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.
AAL3/4
ATM adaptation layer 3/4. One of four AALs (merger from two initially distinct adaptation layers) recommended by the ITU-T. AAL 3/4 supports both connectionless and connection oriented links, but is primarily used for the transmission of SMDS packets over ATM networks.
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 classic IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth over head and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.
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 whether 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.
ABM
Asynchronous Balanced Mode. An HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to- point communications between two stations, where either station can initiate transmission.
ABR
- 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 delays, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the statue 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.
AC
Alternating Current. An electrical power transmission system in which the direction of current flow alternates on a periodic basis.
Accelerator
A hardware addition to an existing computing device that increases the computer’s processing speed and capabilities.
Access
Referring to the ability of a computing device to use data or resources beyond its native capabilities.
Access List
List kept by routers to control access to or from the router for a number of services. For example, the list can prevent packets with a certain IP address from leaving a particular interface on the router.
Access Method
The type of Media Access Control method that a node uses to gain control of a network.
Accounting
One of five categories of network management defined by ISO for
Management
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.
Accuracy
Referring to how closely a test instrument’s measurements compare to a standard value, usually expressed as a percentage of the value measured.
ACF
Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing.
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.
Acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) has occurred. Sometimes abbreviated ACK.
ACR
Allows cell rate. Parameter defined by the ATM Forum for ATM traffic management. ACR varies between the MCR and the PCR, and is dynamically controlled using congestion control mechanisms.
ACSE
Association control service element. An OSI convention used to establish, maintain or terminate a connection between two applications.
Active Hub
Multiported device that amplifies LAN transmission signals.
Active Monitor
Device responsible for managing a Token Ring. A network node is selected to be the active monitor if it has the highest MAC address on the ring. The active monitor is responsible for management tasks such as ensuring that tokens are not lost or that frames do not circulate indefinitely.
Adapter
Hardware that allows a computing device physical access to a network.
Adaptive Routing
See dynamic routing.
ADCCP
Advanced Data Communications Control Protocol.
Address
A numerical designation that uniquely refers to a specific communication entity.
Addressed Call
Mode that permits control signals and commands to Mode
Addressed Call Mode
Mode that permits control signals and commands to
ACM to establish and terminate calls in V.25bis.
Address Mapping
Technique that allows different protocols to interoperate by translating addresses from one format to another. For example, when routing IP over X.25, the IP addresses must be mapped to the X.25 addresses so that the IP packets can be transmitted by the X.25 network. See also address resolution.
Address Mask
Bit combination used to describe which portion of anaddress refers to the network or subnet and which partrefers to the host. Sometimes referred to simply as mask.also subnet mask.
Address Resolution
When two addressing systems refer to the same entity, the process of translating or expressing the address of an entity on one system to the equivalent address of the same entity in the second system. For instance, translating an IP address to its given DNS name.
Address Space
The range of possible unique addresses allowed by an addressing scheme.
Adjacency
Relationship formed between selected neighboring routers and end nodes for the propose of exchanging routing information. Adjacency is based upon the use of a common media segment.
Adjacent Nodes
- In SNA, nodes that are connected to a given node with no intervening nodes. 2. In DECnet and OSI, nodes that share a common network segment (in Ethernet, FDDI, or Token Ring networks).
Administrative Distance
A rate of the trustworthiness of a routing information source. The higher the value, the lower the trustworthiness rating.
ADPCM
Adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals.
ADSU
ATM DSU. Terminal adapter used to access an ATM network via an HSSI-compatible device. See also DSU.
Advertising
Router process in which routing or service updates are sent at specified intervals so that other routers on the network can maintain lists of usable routes.
AEP
AppleTalk Echo Protocol. Used to test connectivity between two AppleTalk nodes. One node sends a packet to another node and receives a duplicate, or echo, of that packet.
AFP
AppleTalk Filing Protocol. The Apple proprietary specification for a network file system.
Agent
- An active process in a computer that is responsible for a certain type of activity when demanded by an outside entity. 2. In SNMP, the active process in a computing device that is responsible for determining the parameters defined in the MIB (Management Information Base) and reporting them on demand to a Console.
AIS
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 there is a transmission fault that is located either at, or upstream from, the transmitting terminal.