01-18-2012 03:53 AM - edited 03-16-2019 09:04 AM
One of our customers wants us to implement QoS for VoIP on their WAN link.
The customer end of it seems to be easy to set up (Cisco 881), but I have no idea how I should do this on our 6500 that is responsible for terminating customer WAN Links on layer 3 (using subinterfaces).
It seems like the 6500 doesn't support the policy-map command "priority" on subinterfaces.
See the attached drawing for topology, equipment and config details.
Does anyone have any suggestions to how I should implement QoS for VoIP on customer WAN links with the equipment I have today?
01-18-2012 05:06 AM
You would have to place the policy-map on the physical interface, not the sub-interface. You can match against an extended ACL for the priority classes. This would allow you to only admit the appropriate client traffic into that class.
As a side note: Layer two WAN designs, such as the one you've shown above, have a critical flaw with QoS. The provider edge switch (and all the equipment within the carrier's cloud) is not running QoS. This leaves open the possibility that oversubscription/delay/jitter/loss may occur FROM the provider TO your customer edge equipment. All you can control is egress control FROM you TO the provider. Two easy examples:
Layer three WAN designs, typically MPLS these days, is more conducive to QoS.
01-18-2012 07:00 AM
Thanks for enlightening me on this issue.
Do you have any suggestions on what the config would look like on the 6500?
Also, how much bandwidth should I reserve for Voice-Data and Voice-Control?
01-18-2012 01:50 PM
The bandwidth reservation amounts are a design decision. You need to understand how many calls are involved; the Cisco UC SRND has a section on Bandwidth Provisioning that can help you understand how much to assign. There is also a Voice Codec Bandwidth Calculator available.
As for sample configurations: the QoS SRND has a section on the 6500 which includes sample configurations. While that section is intended for the access-layer it will show you the MQC configuration and ways the supervisor/ASICs function. The WAN Aggregator section more directly maps to your use case.
PS- Yes, I know it's a lot of documentation. QoS - particularly at the head-end - is requires a lot of thought.
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