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CUCM - Nortel SIP Trunk + Codec Transrating


Hi all,

we configured the SIP trunk between CUCM 7.1.5 & Nortel CS 1000 M 7.5.

We are facing the problem in Incoming calls.

CUCM Configuration:

G.729 Payload : 30 ms

MTP required : Yes ( Using IOS Software MTP)

Whenever Nortel Sends the SIP invite (Early Offer) "ptime"  value 20 ms. When the Cisco Endpoint answers the call , it failed with Cause code 47 since Software MTP not capable of doing the transrating.

Is any other way we achieve the codec transrating from 20 to 30 ms  without the transcoding resource with help of invloving CUBE ?

Thanks in Advance

5 Replies 5

You need to configure IOS hardware MTP for transrating. IOS software cant do transrating. This is because beacuse re-packetization requires DSP resources

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Hi ,

IOS Hardware Mtp only support G711 codec. When you configure the hardware mtp with codec g729

we will get the maximum session value 0 only.

dspfarm profile 1 mtp

codec g711u

maximum session hardware <1-96>

dspfarm profile 2 mtp

codec g729r8

maximum session hardware <0-0>



You are correct....According to the SRND. It looks like you cant do G729 on hardware IOS MTP.

Why dont you want to use G711 MTP?

The link below and excerpts from SRND

Hardware MTP (Cisco NM-HDV2, NM-HD-1V/2V/2VE, 2800 and 3800 Series Routers)

This hardware uses the PVDM-2 modules for providing DSPs.

Each DSP can provide 16 G.711 mu-law or a-law MTP sessions or six G.729 or G.729b MTP sessions.

Hardware MTP (Cisco 2900 and 3900 Series Routers with PVDM3)

These routers use the PVDM3 DSPs natively on the motherboards or PVDM2 with an adaptor on the motherboard or on service modules.

The capacity of each DSP type varies from 16 G.711 a-law or mu-law sessions for the PVDM3-16 to 256 G.711 sessions for the PVDM3-256.

Hardware MTP (Cisco WS-SVC-CMM-ACT)

This module has four DSPs that may be configured individually.

Each DSP can support 128 G.711 mu-law or a-law MTP sessions.

Hardware MTP (Catalyst WS-X6608-T1 and WS-X6608-E1)

Codec support is G.711 mu-law or a-law, G.729 or G.729b.

Configuration is done at the port level. Eight ports are available per module.

Each port configured as an MTP resources provides 24 sessions.

Note You cannot configure G.729 or G.729b codecs when configuring hardware MTP resources in Cisco IOS. However, Unified CM can use hardware transcoding resources as MTPs if all other MTP resources are exhausted or otherwise unavailable

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How are you getting on with this?

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May be you should stablish a packetization time for all the network and directly avoid the problem. All systems to 20 or 30.


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