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New Member

QOS help for voice traffic


our customer has 2 sites , HQ site and a branch site which are connected together via frame relay connection . In HQ site there are Nortel IP phones for all the users and it is working fine.

The customer needed to add some IP phones (Nortel) in the branch site.After adding some IP phones , the users in the branch site can call any user in HQ site but sometime there is a delay.

i need your help about the QOS configuration needed on all switches and routers of our customer to overcome that delay . the network is small and very simple.

please find the attached file for the topology and the configuration.

waiting your replies.



New Member

Re: QOS help for voice traffic

While not an expert on QoS here is my advice.

Setup your Nortel phones to mark voice traffic with some type of CoS markings.... 5 would probably be the most commonly used one for VoIP.

Set your switchports that connect to the IP Phones to trust these markings.

Then create some class-maps on your routers to match your voice traffic based on what you have classified them as (cos 5)

Then crate some policy-maps and use LLQ to give your voice class-map priority over anything else being sent over the WAN.

So it could look something like this;

On your access layer switch ports that connect to your IP Phones configure them to trust to cos from the IP Phones

(config-if)#mls qos trust cos

Then on your routers

class-map VOIP

match cos 5

policy-map critical

class VOIP

priority 2000

SO here we matched traffic with a cos vale of 5 (voip traffic in this case) then created a policy map to use LLQ for voip traffic with a strict bandwidth priority reservation of 2000Kb.

Then apply that to your WAN interface

(config-if)#service-policy output critical

So that pretty much guarantees your VoIP traffic 2000Kb of bandwidth no matter what else is happening on the WAN.

Now obviously you need to tailor this to suit your needs, and you would also need to create other class-maps for your other network traffic and probably implement some type of queuing for your non voip traffic (CBWFQ would do)