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The DTMF-relay of the Cisco CallManager SIP trunk fails to work with the SIP VoIP Telco because the terminating side does not receive the DTMF digits

Core Issue

In a call-processing environment that uses Session Initiation Protocol (SIP), use SIP trunks in order to configure a signaling interface with Cisco CallManager for SIP calls. SIP trunks, or signaling interfaces, connect Cisco CallManager clusters with a SIP proxy server. A SIP signaling interface uses port-based routing, and Cisco CallManager accepts calls from any gateway as long as the SIP messages arrive on the port that is configured as a SIP signaling interface. The SIP signaling interface uses requests and responses in order to establish, maintain, and terminate calls between two or more endpoints.

In order to choose this method, go to Device > Trunk and choose SIP Trunk in the Cisco CallManager Administration.

Also, configure route groups and route patterns that use the SIP trunks to route the SIP calls.

Refer to Understanding Session Initiation Protocol (SIP) for more information about SIP and how to configure SIP trunks.


Telco only supports G711U In-band Voice DTMF, and the Cisco CallManager SIP trunk only supports RFC 2833 RTP-NTE DTMF.

Use the Cisco Multiservice IP-to-IP Gateway (IPIPGW) and transcoder to transcode the RFC2833 RTP-NTE digits into In-band Voice G711U DTMF digits:

  1. Upgrade to Cisco IOS® 12.4(6)XE in order to enable the DTMF transcoding feature.

  2. Configure the dial-peer for Cisco CallManager in this way:

    dial-peer voice voip
    preference 1
    destination-pattern [1-8]T
    session protocol sipv2
    session target ipv4:x.x.x.x
    dtmf-relay rtp-nte
    codec g711ulaw
    no vad

  3. Configure the dial-peer for the SIP VoIP provider in this way:

    dial-peer voice voip
    description Outbound dial-peer
    translation-profile outgoing strip9
    destination-pattern 9T
    session protocol sipv2
    session target ipv4:y.y.y.y.
    codec g711ulaw
    no vad

  4. Configure the transcoder to register to the IPIPGW as:

    sccp local GigabitEthernet0/0
    sccp ccm identifier 1 version
    sccp ccm group 1
    associate ccm 1 priority 1
    associate profile 1 register MTP001795e45a80
    dspfarm profile 1 transcode
    codec g711ulaw
    codec g711alaw

    codec g729ar8
    codec g729abr8
    codec gsmfr
    maximum sessions 20
    associate application SCCP

Once these steps are complete, the IPIPGW transcoder starts to transcode the DTMF digits.

Refer to Understanding Session Initiation Protocol (SIP) and Understanding Cisco CallManager Trunk Types for more information on this.