Avaya a500 Guia Do Utilizador

Glossary

Gl-2

Cajun A500 ATM Switch User Guide

ATM Adaptation Layer 

(AAL) continued

AAL 5 accommodates bursty LAN data traffic with less overhead than        

AAL 3/4. Also known as the Simple And Efficient Adaptation Layer 

(SEAL), AAL 5 uses a conventional five-byte header. It does not 

support cell multiplexing.

ATM Address

Consists of 20 bytes. Addressing is hierarchical, as in a phone network, 

using prefixes similar to area codes and exchanges. ATM switches 

share address information with attached endstations and maintain 

endstation addresses in routing tables.

ATM Address Resolution 

Protocol (ATMARP)

Maps IP addresses to ATM hardware addresses. The process works in 

much the same way as conventional ARP works when mapping 

network-layer addresses to addresses at the MAC (Media Access 

Control) layer.

ATM Forum

Organization that develops and defines ATM standards. Principal 

members participate in committees and vote on specifications.

ATM Forum LAN 

Emulation

Provides connectivity between LAN-attached endstations and devices, 

and ATM-attached endstations and devices.

Authenticator

The end of the link requiring the authentication. The authenticator 

specifies the authentication protocol to be used in the 

Configure-Request during Link Establishment phase.

Available Bit Rate (ABR)

A class of service in which the ATM network makes a “best effort” to 

meet the traffic’s bit-rate requirements. ABR requires the transmitting 

endstation to assume responsibility for data that cannot get through, 

and does not guarantee delivery.

Bandwidth

The difference in Hertz (Hz) between the highest and lowest 

frequencies of a transmission channel. Usually identifies the amount 

of data that can be sent through a given circuit.

Best Effort

A Quality of Service (QoS) class in which no traffic parameters are 

specified and no guarantee is given that traffic will be delivered. ATM’s 

Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) are both 

“best effort” services.

BOOTP

The IETF’s boot protocol that lets an IP endstation acquire its IP 

address and boot file from a server. Defined by RFC 951.

BOOTP Relay Agent

A software entity within each device that captures BOOTP requests 

and responses, and forwards them appropriately. Defined by RFC 

1532.

Broadcast Frame

An Ethernet frame transmitted with a broadcast destination address; it 

is intended to be received by all endstations. In this documentation, a 

broadcast frame is considered a multicast frame.

Broadcast and Unknown 

Server (BUS)

Handles data sent by a LAN Emulation Client (LEC) to the broadcast 

MAC address. This includes all multicast traffic, and initial unicast 

frames that are sent by a LAN emulation client before the data direct 

target ATM address is resolved (before a data direct VCC is 

established).

Cell

An ATM cell consists of 53 bytes or “octets.” Of these, five constitute 

the header; the remaining 48 carry the data payload.