Allied Telesis Rapier Switch - Manual

Copyright © 2003 Allied Telesyn International, Corp.
While every effort has been made to ensure that the information contained within this applicaton note is
accurate, Allied Telesyn International can not accept any liability for errors in, or omissions arising from the use
of this information.
Allied Telesyn Ingress Rate Limiting on
Rapier-i Switches
Introduction
This application note describes the Ingress Rate Limiting feature on the Allied
Telesyn Rapier-i series switches, and explains the effect that configuring
Ingress Rate Limiting on a switch port can have on a TCP session flowing
through that port.
You can find further information about this topic in the Documentation Set for
your Allied Telesyn device, from
www.alliedtelesyn.co.nz/documentation/
documentation.html , and from the References section at the end of this
document.
Ingress rate limiting is set with the INGRESSLIMIT parameter of the SET
SWITCH PORT command. It allows you to specify the maximum bandwidth
for traffic ingressing specified ports.
How ingress rate limiting works on the Rapier-i
Ingress Rate Limiting on the Rapier - i series switches uses what is known as a
‘token bucket’ model, where an arriving packet gains ingress to the port by
removing ‘admission tokens’ from a bucket. The larger the packet, the more
tokens it needs. Tokens are added to the bucket at a rate that is set by the
configured Ingress Rate Limit. Once the bucket is full, no further tokens can be
stockpiled. A packet arriving at the port will be accepted only if the bucket
contains sufficient tokens. A burst of traffic will cause the rapid depletion of
the tokens in the bucket and, once the bucket is empty, packets will be
dropped. On the Rapier-i series switches, there is no facility for queueing
incoming packets. Until the bucket is replenished, the packets are dropped. See
Figure 1 on page 2.
A guide to Ingress Rate
Limiting on Rapier-i
Switches.