Codec Used By IP Phone in CUCM

[tkavithas87]

WHen IP phones are registerd in cucm,regions define the maximum codec.But when there is a call between two ip phones (registerd in a cucm)   which codec they use?Is there a way to difine which codec they should use ?

[Ayodeji Okanlawon]

The codec they use depends on the region matrix between them.

E.g Phone A=RegA

Phone b=RegB

RegA----RegB=G729 (region a and b are configured to use g729)

Then in this scenario the phones will use G729.

If the regions are configured to use G711, then the phones will use G711.

The region is set at the device pool level.

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[tkavithas87]

The Region defines the maximum  codec rate .It doesnt decide which codec the phone should be used.But there should be a default codec or there should be a way to define which codec it should  use .

[Chris Deren]

there is in version 9.0, you can set those up via codec preference configuration:

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/rel_notes/9_0_1/delta/CUCM_BK_N38FD301_00_new-and-changed-information_chapter_01.html#CUCM_RF_C0735CE6_00

HTH,

Chris

[Jaime Valencia]

You're correct, it really only gives you the illusion that you choose which codec you use. As Chris mentioned, you only get real control on 9.X

Before that, there is a hard-coded list of the codecs and the order on which they will be chosen given X amount of BW.

HTH

java

if this helps, please rate

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[Ayodeji Okanlawon · Accepted solution]

You are right and I have used that illustration to help clarify the codec selection. Accodring to SRND

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/cac.html#wp1127327

Locations and Regions Settings

Locations work in conjunction with regions to define the characteristics of a network link. Regions define the type of compression or bit rate (8 kbps or G.729, 64 kbps or G.722/G.711, and so forth) that is used on the link, and locations define the amount of available bandwidth for the link. You assign each device in the system to both a region (by means of a device pool) and a location (by means of a device pool or by direct configuration on the device itself).

You can configure regions in Unified CM to define:

•The Max Audio Bit Rate used for intraregion calls

•The Max Audio Bit Rate used for interregion calls

•The Max Video Call Bit Rate (Includes Audio) used for intraregion calls and interregion calls

•The link loss type for interregion calls (Possible link loss types are Low Loss and Lossy.)

Unified CM Support for Locations and Regions

Cisco Unified Communications Manager supports 2000 locations and 2000 regions with Cisco MCS-7845 servers. To deploy up to 2000 locations and regions, you must configure the following service parameters in the Clusterwide Parameters > (System - Location and Region) and Clusterwide Parameters > (System - RSVP) configuration menus:

•Default Intraregion Max Audio Bit Rate

•Default Interregion Max Audio Bit Rate

•Default Intraregion Max Video Call Bit Rate (Includes Audio)

•Default Interregion Max Video Call Bit Rate (Includes Audio)

•Default Intraregion and Interregion Link Loss Type

When adding regions, you should then select Use System Default for the Max Audio Bit Rate and Max Video Call Bit Rate values

In summary when you set your max audio bit rate to use 8kbps, the codec will be g729. When you set it to 64kps, it will either be g722 or g711. If in your cluster you disable the use of G722 codec then you will oly have g711.

As far as I am aware, there is no where you speficy a codec. This is what te old CUCM version (prior to 8.X ) i think used to have.

What you can do is if you want to use g711 then you need to disable G722. With G729 its easier because when you specify max audio bit rate of 8kpbs, G729 will be used.

Hope it helps

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[tkavithas87]

Thanks All for helpful guides