CM7.1.5 SIP Trunk issue

[chuankokping]

Hi,

I am having a CM7.1.5 which use to build a SIP-trunk connection with an Alcatel Omni PCX Enterprise release9.0. The SIP-trunk is already up.

Problem is, i have no problem calling to other party thru the SIP trunk with codec G711. but once i changed the codec to G729 for both CM and Alcatel side, the conversation is 1 way (which is opposite party can hear what i am talking but i cannot hear what they are talking). During the conversation, i check on the call statistic on my Cisco IP phone, it show both receive and send are in G729, but there is no packet receive from opposite side but i am keep sending packet to opposite side.

I have sniffed the phone traffic, i found a weird situation,

1. when using codec G711, the RTP traffic is actually from Cisco IP phone to the Cisco CM. 

2. When using codec G729, the RTP traffic is actually from Cisco IP phone to the Alcatel SIP card.

But the only thing that i change is only the region (codec) attached to the device pool

anyone face the issue before?

please advise.

Thanks

[htluo]

I guess you have the "require MTP" option checked on the SIP trunk, so CUCM was acting like a MTP.  CUCM was software MTP which can handle G.711 but not G.729.

Try uncheck the "require MTP" option on the SIP trunk and reset.  See if it makes any difference?

Or you may use hardware-based MTP such as a IOS router.

Michael

[chuankokping]

i have tried to uncheck the MTP, but it still the same. is there any other option other than change my sip trunk connection by using IOS router?

[htluo]

Did you reset the SIP trunk(from CUCM)?  Could you do another packet capture to see if the packets still going to CUCM?

With "Require MTP" unchecked, packets SHOULD NOT go to CUCM anymore.

By the way, if you decided to use IOS MTP, you don't have to connect the SIP trunk there.  You just need to configure MTP DSP resource from the router and get it registered to CUCM.

Michael

[chuankokping]

i will tried it again see whether it works.

BTW, if let's say i would try the IOS MTP, the opposite party (Alcatel Omni PCX) still have to point to the IOS router rather than poiting to my CM, right?

[htluo · Accepted solution]

No connection change is required.  Alcatel still points to CUCM.

The IOS router can be anywhere that has TCP/IP connection to the CUCM.  The IOS router doesn't need any connection to Alcatel.

You need to configure DSP farm on the router and get it registered to CUCM.  Then you put that resource in the MRG (Media Resource Group) and MRGL (Media Resource Group List).  Then assign the MRGL to the SIP trunk.

Whenever MTP is required for the SIP trunk, CUCM will look up the MRGL to find the MTP resource.  You may reference CUCM documentation for more details.

Hope this helps.

Michael

[chuankokping]

Thanks Michael

It works perfectly.

[chuankokping]

i will tested it out.

thanks for your advise.