Region Configuration in CUCM

[techToddler]

Hello Friends,

Appreciate your help on this forum. I am here again with another scenario to get hep with.

I have a phone configured to go out to PSTN. When I dial out it looks good. And the gateway see the call fine with G711ulaw.

But I tried changing the codec to G729 in the incoming dial-peer in the gateway and checked. Gateway sees the call as G729 which is again fine.

So What I did is, created two regions. General and Gateway. In General I applied like below,

From General to Default - 8 Kbps

From General to General - 64 kbps

From General to Gateway - 64 Kbps

And the same way on Gateway Region as well. 

From Gateway to Default - 8 Kbps

From Gateway to General - 64 kbps

From Gateway to Gateway - 64 Kbps

Again created two Device pool and assigned each region to them. 

DP going to the phone has General and DP going to trunk has gateway. 

I haven't created a MRGL nor it is assigned to anything as of now. 

So how is this working...My Understanding is like below, correct me if I am wrong,

Phone -----(G711)--- CUCM----(G711)---Trunk-----(G711)----Gateway.

My question is, what is the default region doing? will that take any impact if yes where?

Suppose If I set the Phone and CUCM settings to have G729 and the gateway to have G711 - how is this conversion happens? Really need to understand this part.  

Please help....

Sanjay

[Vivek Batra]

Hi Sanjay,

Thumb rule is when call is made between two devices, inter-region relationship determines which codec to be used. You didn't define which protocol you're using between CM and gateway but I assume it would be eitehr SIP or H.323 since you've referred dial-peer being used.

So, following settings come into picture to determine codec to be used;

1. Phone region. Let say it's region_phones

2. Trunk/gateway region in CM. Let say it's region_gw

3. Codecs configured under inbound dial-peer in gateway.

Now if inter-region bandwidth in CM between region_phones and region_gw is configured as 64 Kbps, any codec equal to or less than G711 can be used viz G711 or G729 or iLbc etc. Actual codec will depend on dial-peer configuration in gateway. If only G711 is configured in gateway, that codec will be used. If more than one codec is configured in gateway, codec used will depend on the priority configured under regions.

If inter-region bandwidth in CM is configured as 8 Kbps, G729 will be used as long as dial-peer configuration has G729 enabled.

So how is this working...My Understanding is like below, correct me if I am wrong,

Phone -----(G711)--- CUCM----(G711)---Trunk-----(G711)----Gateway.

My question is, what is the default region doing? will that take any impact if yes where?

Since you've defined G711 between general (phone) and gateway region, respective codec will be used. Default region won't come into picutre in this case because none of the entity involved in this call is using default region.

Just to clarify, media will not pass through CUCM. It will be directly between phone and gateway.

Suppose If I set the Phone and CUCM settings to have G729 and the gateway to have G711 - how is this conversion happens? Really need to understand this part.  

This depends on region configuration. If inter-region between phone and trunk only allows 8 Kbps bandwidth, call will certainly fail as gateway is not ready to encode RTP in G729. Practically you would not configure in that way but just to understand, you can use transcoder.

You need to put transcoder in a region so that between phones and transcoders region, 8 kbps bandwidth is allowed and between transcoders and trunks region, 64 kbps bandwidth is allowed. Assign this transcoder under MRG/MRGL to trunk/gateway. Doing so, call flow will be as follows;

Phone -> G729 -> Transcoder -> G711 -> Gateway

Let us know if you've more questions on the subject.

- Vivek

[techToddler]

Hello Vivek,

Sorry about the delayed response. 

Okay, we use SIP Protocol.

My understanding on Region got cleared somehow with your explanation, thanks for that but I too have few questions....

1. Suppose I have a SCCP Phone that is registered to CUCM and the CUCM communicates to the Gateway with SIP. In this scenario, how is the region used. I mean we put up a region in DP and thats what the phone gonna use. But how about the CUCM and Gateway leg. I assume the DP in the trunk or the codec used in Dial-peer will be used,. Which one?

2. Do you know a debug that I can use to see if a Transcoder is used on a call like this?

Regards

Sanjay. 

[Vivek Batra · Accepted solution]

1. Irrespective of device type being involved in a call, there is no interaction with how region and codec selection is applied. When SCCP (or any device) makes call through gateway, inter-region relationship between phone and gateway will be used. This is from CUCM perspective. But as you might be aware that codec selection is two way process. What codecs CUCM can use will be defined by CUCM. Same is applicable for gateway, what codecs gateway can use will be defined under dial-peer. Now during call setup between gateway and CUCM, one of the codec will be used based on SDP offer/answer.

2. In gateway, you can simply use show sccp connection to see which all dsp resources used by gateway in runtime.

- Vivek

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[techToddler]

Thank You Vivek.

Regards

Sanjay