Avaya Configuring ATM Services Manual de usuario descargar pdf (Pagina 65)

Understanding ATM, MPOA, and ATM Router Redundancy Concepts

117374-B Rev. 00

1-39

Multi-Protocol Over ATM Concepts

As defined by the ATM Forum, Multi-Protocol Over ATM (MPOA) maps routed

and bridged traffic flows to ATM SVCs, thus mitigating the performance

limitations imposed by hop-by-hop routing of individual packets. This technique

of mapping identifiable traffic flows to virtual channels creates network

“shortcuts” between source and destination, and is generally referred to as

cut-through or zero-hop routing.

Cut-through routing is based on the fact that, in most cases, data transfer occurs at

a steady rate of flow. For example, data or file transfer from one legacy Ethernet

LAN to a remote counterpart usually involves multiple frames. A file transfer of

approximately 45 KB requires about 30 Ethernet frames, all addressed to the same

destination.

In an MPOA environment it is possible to identify the recipient from addressing

data contained within the first frame and establish an SVC to the recipient. Then

all 30 or so frames can be broken down into about 900 ATM cells and transmitted

to the recipient via the virtual channel provided by the SVC.

Network performance improves as the cells follow a predetermined direct path, in

contrast to the hop-by-hop routing of the Ethernet frames. Network performance

is improves markedly in the case of steady-stream deterministic data flows, such

as video.

MPOA Logical Components

MPOA operations are based on logical components, which can be implemented in

various configurations of hardware and software. MPOA logical components

relevant to NHRP include the following.

•MPOA client

The MPOA client (MPC) resides in an ATM edge device adjacent to the Bay

router. BayRS does not provide MPC functionality. MPC’s primary function is

to act, in ATM terminology, as an ingress or egress point for traffic using

network cut-throughs.

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Avaya Configuring ATM Services Manual de usuario Pagina 65