[c-nsp] QoS DSL/L2TP PP Subscribers

[James Bensley]

Hi All,

I have access to some Cisco 7206VXRs with NPE-G1s running image
c7200-adventerprisek9-mz.122-33.SRE9.bin. These are LNSs for an ISP
terminating DSL connections as PPP sessions over an L2TP tunnel.

I would like to deploy QoS on this LNS towards the subscribers as the
ISP is providing VoIP services, so I'd like to prioritise traffic from
the ISP VoIP subnet towards the subscribers.

I have read the following pages;
http://www.cisco.com/en/US/docs/ios/12_2sb/feature/guide/sbsbpssq.html
http://www.gossamer-threads.com/lists/cisco/bba/116104
http://doccieshavespecialpowers.wordpress.com/2009/10/14/virtual-access-service-policy/

It looks very simple, thus I assume I have miss-understood something :)

I create a simple policy on the LNS as follows;

!
class-map match-all CM-VOIP-INFRA
 match access-group 100
!
policy-map PM-Shape-DSL
 class class-default
 ! Shape an ADSL1 connection to 800Kbps
 shape average 800000
 service-policy PM-Prio-VOIP
!
policy-map PM-Prio-VOIP
 class CM-VOIP-Traffic
 ! Guarantee 200Kbps for voice
 bandwidth 200
!
access-list 100 remark ACL-VOIP-INFRA
access-list 100 permit ip 10.0.0.0 0.0.0.255 any

Then I simply apply it with an AV pair on the user's RADIUS account, as follows;

 cisco-avpair = "sub-qos-policy-out=PM-Shape-DSL"

Is it really that basic?


In the example above I have shaped the connection to 800k. In real
life though all the DSL circuits are sync'ing at different rates of
course, which the LNS knows about (I guess the RADIUS server passes
this back to the LNS, or does it come straight from the LAC of the
wholesale DSL provider?);

Picking a random DSL PPP session on the LNS:

LNS#show int virtual-access 11 | i BW
  MTU 1500 bytes, BW 7616 Kbit/sec, DLY 100000 usec,

Checking from that CPE:
CPE#show dsl int atm0/0/0 | i Speed
Speed (kbps):           7616               0           960               0

So, how can I (can it be done at all?) set the shape average bandwidth
in the LNS parent policy to be the circuit speed provided to the LNS,
because that will always be varying?

Many thanks for your time and help.

Kind regards,
James.