[c-nsp] Egress QoS on FE links with less than 100Mbps speeds

[Lobo]

We're doing some Catalyst testing to roll out QoS on our Ethernet 
network and have come up against a hurdle.  On most of our backbone 
links in a MAN, the actual bandwidth between one C/O to another C/O is 
not always 100Mbps.  There are times when the link is only capable of 
hitting say 80Mbps (we're a wireless isp) or less.

Since we have to use a FE port for this type of connection, do the 
switches believe that they have 100Mbps of bandwidth to play with when 
putting packets into the appropriate queues?

I'm a bit confused as to how the switches work in this fashion.  If I 
were using CAT5 cables or fiber this would be simple to understand as 
the bandwidth would be fixed.  :)

This is an example of a configuration on a 3550-24 that I'm using:


interface FastEthernet0/x
mls qos trust dscp
wrr-queue bandwidth 40 35 25 1
wrr-queue cos-map 1 0 1
wrr-queue cos-map 2 2
wrr-queue cos-map 3 3 4 6 7
wrr-queue cos-map 4 5
priority-queue out
!

The switches that we use are 2950, 3550, 3750 and 6524s.

With MQC and "layer 3" QoS, I would know how to fix this by simply using 
the "bandwidth" command on the physical interface and basing my output 
policy-map to use "bandwidth percent" for each class.  Layer 2 QoS 
doesn't seem to work this way though.

Any help would be appreciated.

Thanks.

Jose