Transcoding Question

[juan_cye_ccna]

Hi,

this is the scenario: two regions A and B, inside A  and B g711 is used, between A and B g729 is used. Transcoding resources  are local in A and B regions, if user B starts a call to user in A  region, what does region use transcoding resources?

I appreciate your comments.

[ronpatel]

Hi,

As you have said region configuration. I believe you have Cisco CUCM.

You do not need to have transcoder in this case , as Cisco Ip Phone can understand both G.711 and G.729 codecs.

You need tanscoder when you have end points which do not speek in same codecs.

Regards

Ronak Patel

[Chris Deren]

In addition, media resources are not invoked based on which region/DP they are using, but rather which MRG/MRGL they belong. Baiscaully device invoking transcoding needs to have access to the transcoder via its DP/MRG/MRGL configuration. But as stated not all devices required transcoding and most Cisco phones support most codecs and do native transcoding via onboard DSPs.

HTH,

Chris

[juan_cye_ccna]

Thanks Chris and Ronak,

this topic is confused, I have red some cisco documents but so far it´s not clear. Do you have any source doc where i can clear this topic?

I appreciate your help.

[Chris Deren]

If you can elaborate what you are confused on we can provide more explanation, meanwhile to get detailed information on how it works check out CUCM SRND:

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_implementation_design_guides_list.html

and System Guide:

http://www.cisco.com/en/US/products/sw/voicesw/ps556/prod_maintenance_guides_list.html

HTH,

Chris

[juan_cye_ccna]

Chris,

i have spent a lot of hours trying to solve issues with my customers, all of then related with transcoding. For instance, How can i identify what device utilizes transcoding resources if they are required when user in region A place a call to user in region B and they are separated by wan link? every region has it's own transconding resources, region A codec g711, region B codec g723. I hope that you can understand me.

[Chris Deren]

Most of the time you do not need any transcoders, you certainly do not need transcoders between Cisco phones as they can negotiate any codec supported by Cisco.  Some example of applications requiring transcoders are Contact Center systems, i.e. UCCX, IP-IVR, voicemail systems even though by default they do native software transcoding, you may need transcoders for SIP trunk connectivity, for example when carrier delivers calls as G711, but you need to send them to remote locations as G729, etc.  So, easy rule of thumb: no transcoders between phones are needed, transcoders for certain applications may be needed, so evaluate each application before deployment to understand its capabilities.

HTH,

Chris

[ronpatel]

Hi,

In very simple words...

If both end deivce do not support same codec, you need transcoders. Since IP phone supports same codec, you do not need transcoder.

Regards

Ronak Patel

[juan_cye_ccna]

Hi,

but again, if user in region A place a call to user in region B, what's device doing transcoding? gateway in region A(g711) or gateway in region  B (g723)? 

[Chris Deren]

Between phones the transcoding is native in the phones so, if user A at location A calls user B at location B and codec via region configuration is defined to be g729 between the locations and G711 within a location, phones will negotiate g729 without the need for external transcoder.

Now, lets say user at site A calls IP-IVR at site B, IP-IVR is installed with G711 codec.  When phone A connects to IP-IVR during the codec negotiation it will be deterimed that the 2 devices cannot have the same capabilities for this call and CUCM will attempt to invoke an external transcoder.  The transcoder is located based on call initiator's configuration, so CUCM will check phone A's Device Pool/MRGL configuration to find available transcoder resources in the MRGL--> MRG, if none is found and none are defined as default unassigned to any MRGs, the call will fail and caller will hear fast busy tone.

Transcoders are always hardware resources, so you need PVDM modules on voice gateways to provide it.

HTH, please rate all useful posts!

Chris

[juan_cye_ccna]

Chris, thanks for your help.

[Chris Deren]

I guess you are not completely satisfied with the answers hence the low rating. Is there something I missed?

Chris

[Tracy Larson]

was wondering the same thing, great answer. Ill bump it up.

[Aaron Harrison]

I'll second that... (+5)

[Chris Deren]

Thanks guys, looks like I just got killed with too many (undeserving)  good ratings :-)

Chris