ATM Subsystem Traffic Management

High-speed ATM networks support a variety of applications with different traffic and quality of service (QOS) requirements. For example, multimedia and time critical data applications require guaranteed levels of delay and throughput, while other applications can tolerate variations in delay and throughput (LAN traffic). This diversity requires different congestion management methods.

The 3Com ONcore ATM subsystem supports the ATM Reserved Bandwidth (RB) service type of traffic.

In theReserved Bandwidth (RB) service, an application needs to establish a traffic contract with the network before transmitting data. The traffic contract consists of a

specified QOS class and a set

of traffic descriptors. Through resource allocation, the

network

either

provides

the

desired

QOS

for

the

ATM connection

or

refuses

the call.

 

For this method,

the

source

must

be

accurately

modelled

and

able

to

precisely

descri

its traffic pattern. The allocated bandwidth

is usually less than the

peak

rate

in

ord

benefit from statistical multiplexing gains which may cause

congestion. A

source

 

 

policing scheme ensures that the

source

conforms

itself

to

the contract by

means

of

a

"leaky

bucket"

rate

control.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The use of selective and global

backpressure

for traffic

management in

the

ATM

 

 

subsystem gives the 3Com ONcore

ATM network an

addedSelective value.

 

 

 

 

 

 

 

backpressure

temporarily

stops

one

virtual

Globalconnectionbackpressure.

 

 

 

 

 

 

 

 

temporarily stops

an

ATM

link.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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3Com 6416SW manual ATM Subsystem Traffic Management, Atm