fair-que command for cisco serial interface

happy420golucky

So yeah, I was troubleshooting and ISDN problem at work the other day, and noticed the people before me configured a fast serial interface with the "fair-que" command. Does anybody have a quick link or can give a rough explaination what this command does. Thanks in advance!

PCHoldmann

Quick explanation: The fair-queue command enables a feature called Weighted Fair Queue (WFQ), and is enabled by default on E1 (2.048Mbps) and slower interfaces. On faster interfaces, the interface uses FIFO (First In First Out) queuing, where the fist packet received is sent out before other packets, based on the start of the packet. This could be a problem in instances like when you have a large packet (i.e. FTP) that is received before a smaller (i.e. Telnet) packet. The Telnet packet could be entirely received before the FTP packet, and be waiting behind the larger packet. With fair-queuing (the predecessor of WFQ), the smaller packet could be sent out before the larger packet. WFQ adds weighting based on flows, and is what is actually enabled by the fair-queue command. Basically, WFQ uses bandwidth on and interface more efficiently, and should probably not be disabled (using the no fair-queue command) unless you have a good reason.

Peter