[c-nsp] How to QoS Voice on a Cisco LNS (How to attachaservice-policy to a Virtual-Interface?)

[Kinczli Zoltán]

Oliver,

  Isn't class-based shaping available on v-access interfaces?
(config either via v-template OR aaa cloning)

 So, a child policy (pq-cbwfq, aka llq) inside class-based shaping
would do the trick Alexander wants. Just like Cameron suggested.
And just like it works on GRE tunnels. Nor GRE tunnels, neither
v-access interfaces have pkysical interface stuctures associoated
to them, so they do not 'inherently' support queueing, which is pretty
well understood here. But the class-based shaping buils a queue,
and the child policy can act on that queue. Of course, this 'works'
(guaranties QoS) only if the physical interface itself is not congested...
But that's a different question.

 The cited document http://www.cisco.com/warp/public/105/pppoe_qos_dsl.html
mentiones restrictions for PPPoE client/server side, but the LNS is nor
PPPoE client, nor PPPoE server.

 12.3(8)T introduced Classification, Policing and Marking on LAC
(PPPoE server) http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123t/123t_8/gtqoslac.htm
So, it's not only marking.

regards,
 -zoltan



-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
Sent: Wednesday, February 16, 2005 4:28 PM
To: Alexander Lucke; cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] How to QoS Voice on a Cisco LNS (How to
attachaservice-policy to a Virtual-Interface?)



> I have a problem with QoS and hope that someone else already solved
> such a problem and can help me here. 
> 
> What I need to do is prioritizing Voice traffic on SDSL lines.
> 
> For the upstream part, this is no problem as the CPE (a small cisco
> router) can do QoS on the ethernet interface. My problem is the
> downstream part. My LNS (Cisco 7206VXR/300) gets the PPPoE-DSL
> sessions via L2TP over a FastEthernet interface. I configured some
> vpdn-groups and some virtual-templates and everything works fine with
> normal data traffic.     
> 
> My problem is that - when reading some documentation (e.g.
> http://www.cisco.com/warp/public/105/pppoe_qos_dsl.html) - it seems
> impossible to do a "session based queueing/shaping/whatever". It
> seems only to support marking.   

correct.
 
> Did anybody solve this issue? How is it possible to let an LNS
> prioritize Voice traffic in the downstream direction? 
> 
> And No, we do not have access to the DSLAMs or the DSL aggregation
> network but let's assume that we don't have congestion (no
> overbooking ;-) here.  

If you only want to offer preferred treatment for voice packets between
LNS and LAC, you could use L2TP tos-reflect (i.e. copy the TOS into the
L2TP IP header) and do LLQ on the egress interface towards the LAC and
on the path between LNS and LAC. This obviously does not allow for
per-user voice policing, but it avoids dropping voice packets in case
there is congestion between LNS and LAC..

	oli

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