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QoS for voice on 828 devices

One of my customers is connected to my backbone by use of two 828 devices having a line of 1 Mbps in between. My backbone is running Mpls and I am trying to apply QoS for voice on these 828's. I tried priority queueing. Though the configuration looks working, whenever the traffic exceeds 700 - 800 kbps, the quality of voice degrades seriously.

My config is like: (similar on both sides)

class-map match-any voice_priority

match access-group 110



policy-map voice

class voice_priority

priority 256

class class-default




interface ATM0.1 point-to-point

bandwidth 1024

ip address

no snmp trap link-status

pvc 0/35

cbr 1024

encapsulation aal5snap

service-policy output voice



access-list 110 permit ip any host 89.*.*.200

access-list 110 permit ip any host 89.*.*.202

Can you advice any other solution? Could rsvp be used?

I appreciate any help.




Re: QoS for voice on 828 devices


are you sure the ACL does describe the voice traffic?

Seems a little strange that anything leaving your site towards 89.0.6.X is voice. I would assume you better use voip source IP to destination IPs in the ACL. An even better approach would be to use NBAR through

class-map match-all voice_priority

match protocol rtp audio

To check your policy use "show policy-map inetrface" and look out for matches in the voice class. Also check for drops, as also too much voip traffic could cause issues.

At last: a simple approach would be to use "auto aos voip".

The suggested adjustments depend on feature availability in your IOS. An upgrade might be required.

Hope this helps!

Regards, Martin

Community Member

Re: QoS for voice on 828 devices

Dear Martin;

Thanks for your reply.

The customer has their voice boxes at these ip's. So all the traffic flowing through these ip's contain voice packets.

I am now trying to mark the "dcsp ef" bit at the entrance (ethernet) and then after catching them at the ATM interface, allocate a certain bandwidth for this.

Since the device is 828, I don't think that NBAR would be supported, though I have the latest IOS image installed.

Thanks so much for your answer.



Re: QoS for voice on 828 devices


marking for sure is a good approach to solve the issue. What I also meant: is the ACL really capturing ALL voip traffic? No other IPs can be the destination? Voip f.e. is routed directly between voip phones.

So an ACL specifying all source IPs would probably be more effective.

In case you mark and match on the markings: make sure to set all Catalyst LAN ports voip traffic is crossing to trusted. Otherwise the first switch will remark to 0 and it wont work as expected.

Regards, Martin

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