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VoIP over ADSL and QOS issues

Excuse my ignorance on the subject, but we have recently implemented a complete Cisco IP telephony solution, using Call Manager across dozens of sites. At our smaller offices, with maybe a 5-10 people, we have installed VoIP phones, connected via Cisco 877 router, and then over a 2MB ADSL Private Access Broadband service. Data is also going over these lines, and the calls are breaking up. QOS isn't possible over ADSL - but can the router be configured to implement some kind of QOS? Would anyone ever recommend attempting to do this? We feel our supplier has led us up a path to a solution that will never work.


Re: VoIP over ADSL and QOS issues


I have to agree unless the ADSL provder would guarantee you a level of QoS, unlikely, then this should never go over ADSL.

I dont know what your set up is but you could look at GRE tunnels to impliment some form of QoS

or if you can get it you could look at a V3PN connection.

But yes due to the nature of ADSL and the internet latency this should not have been promoted as a solution for an effective voice network. Even if you do add qos to the router then this will not be carried over by the ISP and will in effect be dropped, so the next step would be to look at the GRE tunnel but again this can be affected by the internet latency, though better than nothing. Suggest you speak to your supplier and let me know there solution does not work so how do they propose to sort it

You can get DSL that will have QoS that would help but from what your are saying this is not in your case. Check with whoever is providing your DSL and find out what QoS if any they can provide

Hope this helps


Re: VoIP over ADSL and QOS issues

Hi Alan,

Generally the small cable modem /DSL providers do not guarantee any type of QoS, but you can optimize it on your 877.

What you do is shape your traffic to their recommended level, and then do QoS within that.

For brevity, let's say you've already defined your voice traffic and voice signaling in class maps. Your DSL we'll say is 750 kb/sec upload.

policy-map shaper

class class-default

shape average 750000

service-policy shaper-child

policy-map shaper-child

class voice-traffic

priority percent 50

set dscp ef

class voice-signaling

bandwidth 50

set dscp cs3

interface WAN 0/0

service-policy out shaper



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