Enterasys ANG-3000 Guide de l'utilisateur télécharger pdf (Page 160)

126 XSR User’s Guide

Controlling Congestion in Frame Relay Networks Chapter 7

Configuring Frame Relay

XSR(config-if<S1/0>)#no shutdown

XSR(config-if<S1/0>)#media-type V35

XSR(config-if<S1/0>)#encapsulation frame-relay

XSR(config-if<S1/0>)#frame-relay lmi-type ansi

XSR(config-if<S1/0>)#frame-relay traffic-shaping

XSR(config)#interface serial 1/0.1 multi-point

XSR(config-subif<S1/0.1>)#frame-relay interface-dlci 16

XSR(config-fr-dlci<S1/0.1-16>)#class STG

XSR(config-fr-dlci<S1/0.1-16>)#no shutdown

XSR(config-fr-dlci<S1/0.1-16>#ip address 210.16.0.1 255.255.0.0

Under normal circumstances, a DLCI is authorized to transmit a number of

bits per an interval of time. The number of bits is composed of adding Bc and

Be values (8000, 8000 = 16000 bits). The interval allowed to transmit this

quantity of bits is based on the formula: Bc/CIR (8000/64000 = 125

milliseconds). So under normal non-congested conditions, this DLCI should

transmit up to 16000 bits every 125 milliseconds.

NOTE

When adaptive shaping is enabled and BECNs are received, the XSR

becomes congested and lowers the output rate on the DLCI. Other DLCIs’

throughput is not affected.

Upon receiving the first BECN, the Be amount is removed from the equation.

Now the DLCI can transmit 8000 bits every 125 milliseconds. If no more

BECNs are received within 3 seconds, 1/2 of the Be amount is added back

each 3-second interval until the Be is fully restored.

Upon receiving additional BECNs within three seconds, the CIR is reduced

by 7/8ths of the current CIR. Every three seconds that BECNs are received,

the CIR will be reduced by an additional 7/8ths of the new CIR value, until

the new CIR value is 1/2 of the original CIR value. One-half of the original

CIR is called the minimum CIR, a non-configurable parameter.

Once BECNs stop being received, the current CIR begins to recover the

original CIR at a rate of 1/16th of the original CIR every 3 seconds: 1/16th

facilitates a graceful, slower recovery in the hope of preventing network

thrashing when all devices start recovering from congestion. After CIR is

fully recovered, Be is reintroduced at a rate of 1/2 of Be every 3 seconds.

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