[SIPForum-discussion] enforcing a variable policy on codec choice

[Andrew Yu]

Hi Bill,

As spoken, this feature has to be support by the ip phone. Personally, i 
don't "hear" much difference between g729 & g711, I would usually set my 
ip phone codec to the following order:

   1. 711a
   2. 711u
   3. G729

As you can see my codec preference is 711. Unless you can ask your 
provider to allow only 729 on their network, you will end up terminating 
with 711. My provider only allow 729 on their network, so my ip phone 
will have 729 over on their network. Alternatively, simply configure 729 
for both LAN & WAN.

Andrew

William Flanagan wrote:
> Thanks, Andrew, helps a lot.
>
> Perhaps you (or anybody) has an insight into how the IP phone knows 
> that a particular number is on the other end of a low-bandwidth link 
> (and thus should be contacted using compression, VAD, etc.).  In using 
> some VoIP services, I've been able to configure the codec on the phone 
> (changed from compressed to G.711, for example), but it's been one 
> choice for all calls. 
>
> It's not reasonable to ask the person placing the call to reconfigure 
> the phone (or even to know that such an action should be taken).  Any 
> ideas on how to enforce a policy that varies the codec?
>
> Thanks,
> Bill
>
> Andrew Yu wrote:
>> Hi William,
>>
>> Codec selection depends on the endpoint where it is internally 
>> configured with its codec priority, if you require the endpoint to 
>> select 711 internally but 729 over the WAN, this is a feature that 
>> the endpoint will have to support. SIP & SDP RFCs does not enforce 
>> any policy on the choice of media codec. I hope this helps. Thanks.
>>
>> Andrew
>>
>> William Flanagan wrote:
>>> Hi,
>>>
>>> In reading the SIP and SDP RFCs, I see no obvious mechanism to 
>>> enforce a policy on the choice of voice codec (for compression ratio 
>>> or bandwidth usage) that would vary by called party.  For example, 
>>> one might prefer G.711 locally, but require G.729 over the WAN.  
>>> Does any one know of such a deployment?
>>>
>>> Thanks,
>>> Bill
>>>
>>> -- 
>>> Flanagan Consulting     
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>>
>>
>
> -- 
> Flanagan Consulting 	 In Converged Networking
>  We Have the Experience
>
> ------------------------------------------------------------------------
> 45472 Holiday Dr. #3, Sterling, VA 20166 USA
> Ph:  +1.703.242.8381    Fx:  +1.703.242.8391
> www.flanagan-consulting.com
>
> Flanagan Consulting is a Service Mark of W. A. Flanagan, Inc.
>  
>
> "Beware of false knowledge; it is more dangerous than ignorance."
>                                        --George Bernard Shaw
> ------------------------------------------------------------------------
>
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