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WAN QOS for Avaya VoIP

I have DSL/ATM link between my primary site and remote location. Speeds at the remote site are upstream is 128k to 384k and the downstream 384k-1.5mbps. I have Cisco 827 at the remote site and Cisco 2600 at the main site. Connected Avaya VoIP phones at the remote site that hook into my Difinity voice switch at the main site. Phones work fine when I don't use any data apps on the PCs. Conversations get jittery when I start running data apps. Sounds like I need QOS between the routers. Has someone done this with Avaya before?


Re: WAN QOS for Avaya VoIP


with a 128 kbps link one problem will be jitter caused by large data packets. To transport 1500 byte you need about 90 ms. A voip packet has to wait for that time to be serviced in case data transmission just started or voip doesn´t have to wait when no data is present. As a result you will have jitter up to 90 ms with a 128 kbps uplink.

The best solution for this problem in your case is a second PVC for voice traffic.

You should check with your DSL provider whether this can be arranged.

Second you need to make sure that voip gets enough bandwidth. In order to achieve this you need to describe voip traffic to the router in a class-map. In your case source and destination IP might be sufficient. And then configure LLQ for the voip class in both directions.

Hope this helps


Community Member

Re: WAN QOS for Avaya VoIP


Thanks for the response. I am thinking about upping this links speed to more than 386k. I will speak with my ISP about second Pvc. Can this be done over the same pair coming from CO? I would like to ask you more about QOS. Can you give an idea of what the policy would look like? I understand that it would be applied to Ethernet0 on at the remote location (Cisco827) and should it also be applied to ATM interface (Cisco 2600) at the main site?

Re: WAN QOS for Avaya VoIP


I have seen one provider in Germany offering it, no knowledge about the rest of the world. So technically it can be done (DSL with two ATM PVC over the same copper wire pair), but then there is the difference between technology and SP products.

So the QoS policy would depend on the possibilities you have. There is probably not too much sense in writing precise policies for all possible cases first. Anyhow, autoqos could give you a hint about what a policy should look like.

To give you an impression:

class-map match-all VoIP

match protocol rtp audio

class-map match-all VoIPsignal

match ip address 100

class-map match-all Business

match protocol citrix

policy-map OUT

class VoIP

priority percent 30

set ip dscp ef

class VoIPsignal

bandwidth remaining percent 5

set ip dscp cs3

class Business

bandwidth remaining percent 20

set ip dscp af11

class class-default



interface ethernet0

service-policy output out

This is just an example and by no means ment to e used in your network.

Did it help? Then please rate it.


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