LLQ+CBWFQ to prioritize VoIP on Customer router connected to Service provider router

[helenio]

Hello,

  have to configure LLQ+CBWFQ to prioritize VoIP traffic and Guarantee BW to Signalling traffic and Best effort for all other traffic.

I have a CISCO 2901 ver 15.1.4 and the output interface is a subinterface of the GigabitEthernet0/1 interface (GigabitEthernet0/1.3113) due to fact that Service provider interface need a tagged VLAN 3113 for input traffic.

Service provider router limit the input traffic to 10Mbps on is Ethernet 100Mbps interface therefore as input traffic reach the 10Mbps the traffic is dropped or shaped (I don’t know).

First as from my understanding I have to configure shape in the output subinterface:

http://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/10104-qos-subint.html#applyingaservicepolicy

and then apply a service policy child to the parent policy map.

Therefore:

!

class-map match-all VOICE

match ip dscp ef ! IP Phones mark Voice to EF

!

class-map match-any CALL-SIGNALING

match ip dscp cs3 ! Future Call-Signaling marking

match ip dscp af31 ! Current Call-Signaling marking

!

policy-map SES-policy

 class VOICE

  priority 2000 !Max BW 2Mbps 

 class CALL-SIGNALING

  bandwith 1000

  ! Garated BW 1Mbps

 class class-default

  fair-queue ! All other data gets fair-queuing

!

policy-map WAN-shape-policy-out

 class class-default

  shape average 10m

  service-policy SES-policy

!

GigabitEthernet0/1.3113

service-policy WAN-shape-policy-out

Please may you help me to understand if the way it work is like this:

In front of my 2901 router there is a provider router that allow only 10Mbps (even if the interface is a 1000Mbps/full duplex) therefore if from my LAN there is a internet traffic that need more than 10Mbps the "shape average 10m command" on parent policy start to drop packet this will drive to congestion that call the child policy where VOICE traffic goes on LLQ and signalling on CBWFQ and all other traffic to fair-queue mechanism.

Is that correct ? My doubt is that provider limit traffic to 10Mbps even if the provider interface is 100Mbps therefore I have to start to do QoS already at 10Mbs, is that correct ?

[Joseph W. Doherty]

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Posting

Yes, you understand correctly.

However, I believe on many Cisco devices, the shaper doesn't count L2 overhead but providers often police CIR as a L2 values.  So, what you may need to do is shape about 10 to 20% slower then the CIR rate to allow for L2 overhead.

Also with your policy, I would suggest your class-default also use the bandwidth statement.

Optionally, you might also use FQ in your CALL-SIGNALING or you might eliminate this as a class as FQ in class-default may be "good enough".