×

Warning message

  • Cisco Support Forums is in Read Only mode while the site is being migrated.
  • Cisco Support Forums is in Read Only mode while the site is being migrated.

Codec Selection - G711 instead of G729

Unanswered Question
Oct 13th, 2006
User Badges:

I just brought up a site that should use only G729 between other sites and internally. Reviewing CDR data I see a occasional call using G711. Most of these calls go to Unity but I can see no reason why this would be. There are also calls to Unity that use the correct G729 codec. I have verified that the regions are all set up correctly and that all of these phones are in the correct Device Pool that contains the G729 Region. I see no errors indicating a lack of transcoder resources. Any advice on how troubleshoot would be appreciated.


Thanks!

Steve

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4 (1 ratings)
Loading.
thisisshanky Fri, 10/13/2006 - 09:42
User Badges:
  • Purple, 4500 points or more

Steve,


For the calls that use g729, do you see a particular range of extensions, or a single extension from which the call originate, or is it purely random phones each time.

s.casper_2 Fri, 10/13/2006 - 15:41
User Badges:

There are only 8 phones at the site and I see most of them. I set up a test phone at my site and used the remote device pool. I placed some test calls and checked the codec each time at the phone - it indicated g729 for RX and TX. CDR indicated as combination of g711 and g729. I woder if this is normal. One call leg would use G729 the other say to Unity would use g711.

s.casper_2 Fri, 10/13/2006 - 16:50
User Badges:

Ok now I am really confused!


I place a inbound PSTN DID call to a gateway which routes my call to an IP phone in my g729 region. At the gateway the DSP indicates the codec as g729br8. Is the DSP in this gateway(2811 with PVDM2-48)acting as a transcoder?


I thought a transcoding resource would be needed to bridge the PSTN g711 call to the termination at an IP phone in a g729 region.


Thanks!

Steve

Aaron Harrison Sat, 10/14/2006 - 02:23
User Badges:
  • Super Bronze, 10000 points or more
  • Community Spotlight Award,

    Member's Choice, May 2015

Hi


Basically when a call comes in from the PSTN the gateway can use G711 (which would consume 1 dsp resource) or G729 (which would consume 2)... so if your regions setup specifies g729 the gateway will convert the call from PSTN to IP using g729 provided it has the DSP capacity.


You would only need another device to transcode if one of the endpoints is unable to support the specified codec (i.e. G729 - for example contact centre or Voicemail applications may be installed to support only G711 and would therefore require a transcoder). In this case the endpoint that doesn't support g729 would encode to g711, and then the third-party device in the conversation would trancode from g711 to g729.


Regards


Aaron


Please rate helpful posts...

s.casper_2 Sat, 10/14/2006 - 05:17
User Badges:

Thank you for the clarification. Couple of more questions:


1. Is a transcoder required when the inbound call forwards to Unity?


2. I assume then that the gateway takes care os the g729 to g711 conversion on an outbound call. How about an IP phone to IP phone connection?


3. When conferencing does the conference DSP also convert g711 and g729 streams?


Thanks!

Steve

Aaron Harrison Sat, 10/14/2006 - 10:02
User Badges:
  • Super Bronze, 10000 points or more
  • Community Spotlight Award,

    Member's Choice, May 2015

Hi


1. By default, Unity supports g711 only... but you can enable g729. If you have not enabled g729, a transcoder is needed... if you have enabled it it isn't required (http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_troubleshooting_guide_chapter09186a0080153e41.html#1083387).


2. All cisco phones support g729 and g711 amongst other codecs. The media goes directly between the two phones, and since both ends support all codecs no transcoder is needed - the phones have the necessary processing power.


3. It depends - if you use the software conference bridge on the CM server, it only supports g711. In this case you would require a transcoder to be available for any parties using g729. Hardware conference bridges (i.e. routers armed with appropriately configured DSPs) can accept either codec.


Regards


Aaron


Please take the time to rate helpful posts...

Actions

This Discussion