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.<br>
<br>-nick<br><br><div class="gmail_quote">On Wed, Jan 26, 2011 at 1:20 AM, Cisco Voip <span dir="ltr"><<a href="mailto:cisco_newbie@yahoo.com">cisco_newbie@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div>Ok i get my confusion.<br><br>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 ?<br>
<br>Please clarify this<br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><div class="im">
<hr size="1"><b><span style="font-weight: bold;">From:</span></b> Nick Matthews <<a href="mailto:matthnick@gmail.com" target="_blank">matthnick@gmail.com</a>><br></div><b><span style="font-weight: bold;">To:</span></b> Cisco Voip <<a href="mailto:cisco_newbie@yahoo.com" target="_blank">cisco_newbie@yahoo.com</a>><br>
<b><span style="font-weight: bold;">Cc:</span></b> ccieid1ot <<a href="mailto:ccieid1ot@gmail.com" target="_blank">ccieid1ot@gmail.com</a>>; <a href="mailto:cisco-voip@puck.nether.net" target="_blank">cisco-voip@puck.nether.net</a><br>
<b><span style="font-weight: bold;">Sent:</span></b> Wed, January
26, 2011 10:32:29 AM<div><div></div><div class="h5"><br><b><span style="font-weight: bold;">Subject:</span></b> Re: [cisco-voip] Strange behaviour of CME<br></div></div></font><div><div></div><div class="h5"><br>
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.<br>
<br>-nick<br><br><div class="gmail_quote">On Tue, Jan 25, 2011 at 11:37 PM, Cisco Voip <span dir="ltr"><<a rel="nofollow" href="mailto:cisco_newbie@yahoo.com" target="_blank">cisco_newbie@yahoo.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div>Dear Sir, <br><br>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 <br>
<br>Pls verify my above point<br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><div>
<font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Nick Matthews <<a rel="nofollow" href="mailto:matthnick@gmail.com" target="_blank">matthnick@gmail.com</a>><br><b><span style="font-weight: bold;">To:</span></b> ccieid1ot <<a rel="nofollow" href="mailto:ccieid1ot@gmail.com" target="_blank">ccieid1ot@gmail.com</a>><br>
<b><span style="font-weight: bold;">Cc:</span></b> Cisco Voip <<a rel="nofollow" href="mailto:cisco_newbie@yahoo.com" target="_blank">cisco_newbie@yahoo.com</a>>;
<a rel="nofollow" href="mailto:cisco-voip@puck.nether.net" target="_blank">cisco-voip@puck.nether.net</a><br><b><span style="font-weight: bold;">Sent:</span></b> Wed, January 26, 2011 5:10:12 AM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [cisco-voip] Strange behaviour of CME<br>
</font><br>
</div><div><div></div><div>Transcoding is only required when there is a codec mismatch. In this case it's something like:<br><br>Phone 1:<br>g711ulaw<br>g711alaw<br>g729r8<br>g729br8<br>g722<br>...<br>etc<br>
<br>GW1 to GW2:<br>g729r8<br><br>Phone 2:<br>
same as above phone 1<br><br><br>Since g729r8 is available by all, there is no need for transcoding.<br><br>-nick<br><br><div class="gmail_quote">On Tue, Jan 25, 2011 at 2:47 PM, ccieid1ot <span dir="ltr"><<a rel="nofollow" href="mailto:ccieid1ot@gmail.com" target="_blank">ccieid1ot@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><p>The phones has built in dsp to do the transcoding.</p>
<p>duy<br>
ccie #27737 voice</p>
<p>tmobile g2</p><div><div></div><div>
<div class="gmail_quote">On Jan 25, 2011 10:03 AM, "Cisco Voip" <<a rel="nofollow" href="mailto:cisco_newbie@yahoo.com" target="_blank">cisco_newbie@yahoo.com</a>> wrote:<br>> Hi all. <br>> <br>
> I have setup the current setup in my lab<br>
> <br>> IPcommunicator-1 <br>> ------------------R1-GW-------------------R2-GW-------------IPcommunicator-2<br>> <br>> SCCP (g711) default (g729)<br>> <br>
> On R1 i simply created a dial-peer voice 2141 voip, and defined the session <br>> target and destination pattern, and also codec to be g729r8. Now when i call <br>> from IPc-1 to IPc-2, the call is successful !!<br>
> <br>> I have set this up in dynamips and 2 IPcs are infact vmware machines. What i <br>> dont understand is, why there was no need for transcoding ? the default codec <br>> between R1-GW and IPc-1 is g711, while between R1-GW and R2-GW, i set it to <br>
> g729, so isnt transcoding needed here ?<br>> <br>> <br>> <br>> <br></div>
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