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

[Oliver Boehmer (oboehmer)]

> 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