[cisco-bba] Support for "percent" directive in per-session QoS

[Robert Blayzor]

David Freedman wrote:
> I believe this is possible reading the documentation at
> http://www.cisco.com/en/US/products/ps6566/products_feature_guide09186a0080610dad.html
> 
> there is mention of it, but the question I want to ask is :
> 
> how does it know what the available bandwidth is such to be able to
> calculate the percentage?
> 
> I mean, with a standard CBWFQ attached to an interface, it derrives this
> from the interface bandwidth, but for vaccess QoS we are required to
> nest the CBWFQ under a shaper, so does the percentage directive
> use the shape average rate of this shaper?
> 
> Does anybody use this directive (interested for those whom use it for a
> priority queue) and does it work?


I've been down this road before quite a few times.  The fact is, in 
order for you to be able to use percentages, it has to know how much 
bandwidth is available, period.

Depending on the interface, that differs, ie: ATM vs Ethernet.


ie: For an ATM T1 you may have something like the following sent back 
via RADIUS:

cisco-avpair     atm:peak-cell-rate=1536
cisco-avpair     atm:sustainable-cell-rate=1536
cisco-avpair     atm:vc-qos-policy-out=max-voice


and a policy as such in the router:

policy-map max-voice
   class voip-rtp
     priority percent 70
   class voip-sig
     bandwidth percent 5
   class class-default
     fair-queue


AFAIK, strict priority queues don't work on virtual interfaces. (at 
least not the last time I tried)


On Ethernet you'd have something slightly different:

cisco-avpair      sub-qos-policy-out=voip-vlan-3m

policy-map max-voice
   class voip-rtp
     priority percent 70
   class voip-sig
     bandwidth percent 3
   class class-default
     fair-queue
policy-map voip-vlan-3m
   class class-default
     shape average 3000000 30000
    service-policy max-voice



So you'll have to do "nested" QoS policies.  Shape/police first, then queue.

At least this worked for me, YMMV.


-- 
Robert Blayzor
INOC
rblayzor at inoc.net
http://www.inoc.net/~rblayzor/

Profanity is the one language all programmers know best.


-- 
Robert Blayzor
INOC
rblayzor at inoc.net
http://www.inoc.net/~rblayzor/

My Other machine is your Linux Box