[cisco-voip] Strange behaviour of CME

[Nick Matthews]

It's part of the negotiation that happens with SCCP.  The phone advertises
every codec it is capable of, the gateway passes that information on, and
once the call is ready to complete, each device chooses which of the
available codecs they are going to use.  If one device advertises a list of
codecs that doesn't match the other side, the call will not complete.  It
would complete if there was a transcoder.

-nick

On Wed, Jan 26, 2011 at 1:20 AM, Cisco Voip <cisco_newbie at yahoo.com> wrote:

> Ok i get my confusion.
>
> The codec between R1 and R2 was g729, while the default codec between R1
> and IPC-1 is g711. How did IPC knew that it has to use g729 instead of g711
> ?
>
> Please clarify this
>
> ------------------------------
> *From:* Nick Matthews <matthnick at gmail.com>
> *To:* Cisco Voip <cisco_newbie at yahoo.com>
> *Cc:* ccieid1ot <ccieid1ot at gmail.com>; cisco-voip at puck.nether.net
> *Sent:* Wed, January 26, 2011 10:32:29 AM
>
> *Subject:* Re: [cisco-voip] Strange behaviour of CME
>
> The phone supports multiple codecs.  They simply have different
> priorities.  The reason you always see g711 instead of g729 is because g711
> has a higher priority.  The modern phones (7942/7962 and above) support
> something like 7+ codecs.
>
> -nick
>
> On Tue, Jan 25, 2011 at 11:37 PM, Cisco Voip <cisco_newbie at yahoo.com>wrote:
>
>> Dear Sir,
>>
>> As a followup, by default SCCP phones use codec g711. So did you mean that
>> phones automatically switched to g729 ? i totally believe your point but for
>> my further studies can you also refer me any cisco config guide to
>> strengthen my concept
>>
>> Pls verify my above point
>>
>> ------------------------------
>> *From:* Nick Matthews <matthnick at gmail.com>
>> *To:* ccieid1ot <ccieid1ot at gmail.com>
>> *Cc:* Cisco Voip <cisco_newbie at yahoo.com>; cisco-voip at puck.nether.net
>> *Sent:* Wed, January 26, 2011 5:10:12 AM
>> *Subject:* Re: [cisco-voip] Strange behaviour of CME
>>
>> Transcoding is only required when there is a codec mismatch.  In this case
>> it's something like:
>>
>> Phone 1:
>> g711ulaw
>> g711alaw
>> g729r8
>> g729br8
>> g722
>> ...
>> etc
>>
>> GW1 to GW2:
>> g729r8
>>
>> Phone 2:
>> same as above phone 1
>>
>>
>> Since g729r8 is available by all, there is no need for transcoding.
>>
>> -nick
>>
>> On Tue, Jan 25, 2011 at 2:47 PM, ccieid1ot <ccieid1ot at gmail.com> wrote:
>>
>>> The phones has built in dsp to do the transcoding.
>>>
>>> duy
>>> ccie #27737 voice
>>>
>>> tmobile g2
>>> On Jan 25, 2011 10:03 AM, "Cisco Voip" <cisco_newbie at yahoo.com> wrote:
>>> > Hi all.
>>> >
>>> > I have setup the current setup in my lab
>>> >
>>> > IPcommunicator-1
>>> >
>>> ------------------R1-GW-------------------R2-GW-------------IPcommunicator-2
>>> >
>>> > SCCP (g711) default (g729)
>>> >
>>> > On R1 i simply created a dial-peer voice 2141 voip, and defined the
>>> session
>>> > target and destination pattern, and also codec to be g729r8. Now when i
>>> call
>>> > from IPc-1 to IPc-2, the call is successful !!
>>> >
>>> > I have set this up in dynamips and 2 IPcs are infact vmware machines.
>>> What i
>>> > dont understand is, why there was no need for transcoding ? the default
>>> codec
>>> > between R1-GW and IPc-1 is g711, while between R1-GW and R2-GW, i set
>>> it to
>>> > g729, so isnt transcoding needed here ?
>>> >
>>> >
>>> >
>>> >
>>>
>>> _______________________________________________
>>> cisco-voip mailing list
>>> cisco-voip at puck.nether.net
>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>
>>>
>>
>>
>
>
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