How to make sure only a specific codec gets used?

Matthew Martin · ‎07-01-2015

Hello All,

I am trying to figure out how I can make sure our Faxing router (*Cisco 2821) uses ONLY a g711 codec when calls are made to this device?

Our system does support G.711, I know this because we are using g711ulaw for other areas of the phone system. But for some reason calls/faxes going to voice-port(s) on the 2821 are "eventually" negotiating to g729r8.

What I did to try and get this working was I created 1 new Device Pool (*called "FAX-DP") and 1 new Region (*called "FAX-RGN"). I set the device (*i.e. the voice voice-ports of the 2821 Gateway) on the Callmanager for the directory number that goes to the 2821, to this new Device Pool I created --> "FAX-DP". And in the new Device Pool's config I set the Region to the new region I just created called "FAX-RGN". Inside the Region configuration I set ALL relationships to every other Region to --> "64 kbps (G.722, G.711)".

So I attempted a few test faxes and phone calls to the DN configured to those voice-port(s) (*ports 2/0/3 and 2/0/4) and the "show voice call summ" command shows the following sequence below for the same call.
The sequence that happens when I call the number jumps from one codec to the next (*see below for the actual command output):
g729r8 --> g711ulaw --> t38 --> cisco --> g729r8

	Rtr-2821# show voice call summ
	PORT           CODEC     VAD VTSP STATE            VPM STATE
	============== ========= === ==================== ======================
	2/0/2         -          -  -                     FXSLS_ONHOOK             
	2/0/3         g729r8     n  S_CONNECT             FXSLS_CONNECT            
	2/0/4         -          -  -                     FXSLS_ONHOOK             



	Rtr-2821# show voice call summ
	PORT           CODEC     VAD VTSP STATE            VPM STATE
	============== ========= === ==================== ======================
	2/0/2         -          -  -                     FXSLS_ONHOOK             
	2/0/3         g711ulaw   n  S_CONNECT             FXSLS_CONNECT            
	2/0/4         -          -  -                     FXSLS_ONHOOK             



	Rtr-2821# show voice call summ
	PORT           CODEC     VAD VTSP STATE            VPM STATE
	============== ========= === ==================== ======================
	2/0/2         -          -  -                     FXSLS_ONHOOK             
	2/0/3         t38        n  S_CONNECT             FXSLS_CONNECT            
	2/0/4         -          -  -                     FXSLS_ONHOOK             



	Rtr-2821# show voice call summ
	PORT           CODEC     VAD VTSP STATE            VPM STATE
	============== ========= === ==================== ======================
	2/0/2         -          -  -                     FXSLS_ONHOOK             
	2/0/3         cisco      n  S_CONNECT             FXSLS_CONNECT            
	2/0/4         -          -  -                     FXSLS_ONHOOK             



	Rtr-2821# show voice call summ
	PORT           CODEC     VAD VTSP STATE            VPM STATE
	============== ========= === ==================== ======================
	2/0/2         -          -  -                     FXSLS_ONHOOK             
	2/0/3         g729r8     n  S_CONNECT             FXSLS_CONNECT            
	2/0/4         -          -  -                     FXSLS_ONHOOK

And I also collected the CallManager traces and found the call in there, and it's showing the Region to be the OLD region that the voice-port(s) used to be set to...
Not sure why it's not showing as the new device pool. If I go to that new Device Pool I created I see that the 2821 is the only associated device.

Any thoughts or suggestions would be greatly appreciated!

Thanks in Advance,
Matt

Marcelo Morais · ‎07-01-2015

Hi Matt,
first of all, when you configured your region in CUCM to '64 kbps (G.722, G.711)', in fact you are configuring this region to use up to 64 kbps, in other words, it could use for example: G.729.

It's important, when you configured your Gateway, to configure the 'codec preference' ... if you didn't do anything, then the Gateway uses the default (G.729r8), check the following configuration:

voice class codec 1
 codec preference 1 g711ulaw
 codec preference 2 g711alaw
 codec preference 3 g729r8

dial-peer voice 1 voip
 voice-class codec 1
 ....

Please, check your Gateway configuration and your 'codec preference'.

Hope this helps.

Matthew Martin · ‎07-02-2015

Hey Marcelo, thanks for the reply!

Yes, that's correct but I read that given the MAX bit rate setting in the region, it should try to use the codec that gives highest audio quality, right? So if g711ulaw is available, then it should use that over g729r8..? As far as I know...

The way this line is configured in CallManager is that the "Device" for the Directory Number was set to: "AALN/S2/SU/4@Rtr-2821" -AND- "AALN/S2/SU/3@Rtr-2821"
So the calls got sent directly to ports 2/0/3 and 2/0/4 and didn't need a dial-peer. I was trying to do a dial-peer yesterday, but wasn't sure if "pots" or "voip" was supposed to be used. What I thought I had read made it seem like the "dial-peer voice *** voip" was for outbound calling only, but I guess that is not correct?

Thanks Again for the reply!

Thanks,
Matt

will.alvord · ‎07-02-2015

Looks like you're using mgcp. In that case you can ignore the dial peers and other ios configs. What version of communications manager are you using? In later versions you're able to preference your codecs beyond just setting max bw.

Matthew Martin · ‎07-06-2015

Hey Will, thanks for the reply!

I believe I got it working... When I went back to the NEW Device Pool I created (*"FAX-DP") to double check my settings, it still had the OLD region that it was set to prior to me creating a new "FAX-RGN" Region.

So I changed the Region setting in the Device Pool's config to the new/correct region and made a few test calls, and the calls seemed to end with using g711ulaw. Then I sent a test fax and it actually went through this time.

But, to answer your question:
CallManager: 8.6.2.24901-1

I am curious to see what the other Codec settings are that you mentioned.

Thanks Again,
Matt

will.alvord · ‎07-06-2015

Audio codec preference list. They're referenced from regions. Pretty sure this feature was introduced in 9.

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/9_1_1/ccmcfg/CUCM_BK_A34970C5_00_admin-guide-91/CUCM_BK_A34970C5_00_admin-guide-91_chapter_0111.html#CUCM_RF_A43E787B_00