[cisco-voip] Strange behaviour of CME

[Nick Matthews]

Yes, the CME (R1 or R2) tells the endpoint (CIPC) what codec to use.

-nick

On Wed, Jan 26, 2011 at 11:35 PM, Cisco Voip <cisco_newbie at yahoo.com> wrote:

> Dear Sir,
>
> I dont have words to express my gratitude. Thanks alot
>
> Just one thing, pls spare some time to help me clarify. When phone boots
> up, it will tell all the codec using capabilities exchange process. In my
> case R1 already knew what IPC-1 is capable of. Same goes to R2 and IPC-2. So
> when IPC-1 makes a call to IPC-2 (or vice versa), its upto R1 and R2 to
> negotiate which codec phones will use ? or will phones negotiate end to end
> which codecs they will use ?
>
> ------------------------------
> *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 7:49:11 PM
>
> *Subject:* Re: [cisco-voip] Strange behaviour of CME
>
> 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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