Fair-queueing on an ATM interface

[ten]

Hello,

We are using a 7513 router that is running 12.2 IOS.

When I tried to configure fair-queueing on a DS3 ATM interface the command was unsupported.

I can configure fair-queueing on serial interfaces on the same router.

Any ideas why it would not be avaiable on an ATM interface?

[smif101]

Weighted fair queueing was designed for low speed serial circuits, not high speed interfaces. If you want to provide queueing on the is interface you will need to implement CBWFQ. For example:

Router(config)#class-map class-ip

Router(config-cmap)#match protocol ip

Router(config)#class-map class-ipx

Router(config-cmap)#match protocol ipx

Router(config)#policy-map policy-cbwfq

Router(config-pmap)#class class-ip

Router(config-pmap-c)#bandwidth percent 40

Router(config-pmap)#class class-ipx

Router(config-pmap-c)#bandwidth 20

Router(config)#interface atm 0

Router(config-if)#service-policy output policy-cbwfq

Jason Smith

www.smif101.com

[scottmac]

ATM as a technology is already "fair."

By using fixed-sized small packets (cells), each stream is segmented and sent independently. the fixed-size, small cells provide (more) predictable throughput and latency.

At the receiving end, most ATM systems use / can use a "per VC queueing:" each stream gets it's own queue ... when the frame is done being reassembled, it's sent on ... smaller frames get built and sent before big frames.

Fair queueing was designed to allow smaller frames (like telnet, 3270, etc) to get out of the system in a timely fashion .... even if the rest of the traffic is large / huge database frames.

The combination of efficient switching and per-VC queuing keep thing "fair" over ATM. If you wish to impose some "unfairness," you can apply a QOS contract to assign stream/VC priorities.

FWIW

Scott