SIP INFO Method - DTMF

The IMG 2020 supports the SIP INFO Method. The SIP INFO Method is designed to transmit application level control information such as DTMF tones along the SIP signaling path. Transport of DTMF signaling is of great importance since there is a large existing base of DTMF applications. The transmitting of tones is achieved during a call and is independent of the RTP or Media Stream. The mid-session signaling information is transported over the signaling path. This method allows information such as DTMF digits to be transported in a reliable way. Consider a phone banking application for example. After a user is asked by an IVR to enter an amount to be transferred the user then enters the digits consecutively. If the IVR does not receive one of the DTMF digits or the digit order changes due to out-of-order delivery, the transaction may result in an unpredictable money transfer. Thus, a reliable transport channel is desired. The SIP INFO method uses the underlying SIP reliability and in-order delivery of information makes DTMF signaling resilient to unreliable packet delivery even under bursty loss.

The SIP INFO method is not used to change the state of a SIP call. The signaling  path is the path taken by SIP RE-INVITE's, BYE's and other SIP requests that are tied to an individual session. The SIP INFO Method will allow SIP proxy servers to receive and potentially act on mid-session signaling information.

The SIP INFO Method - DTMF feature allows the use of the SIP INFO method to send a DTMF digit to another gateway. The voice stream is established after a successful SIP 200 OK-ACK message sequence.

 This feature is enabled using the SIP DTMF Support pane. There are two ways of using the INFO Method for DTMF:

• INFO Using Pattern

• INFO DTMF Digit Relay

Both will be described below.

INFO Using Pattern

After voice has been connected, hit the # or * in a set pattern until the configured pattern is matched. After a match, the IMG 2020 will send a character in the SIP INFO message to the endpoint that the original 200 OK ACK came from. In the call flow below, it is sent to the Application Server. The SIP INFO Method message will contain a SIP header of Signal (showing the character) and the duration header (Displaying the duration in milliseconds to play the character signal).

Call Flow - # character in SIP INFO

The following shows a SIP INFO header with the changes:

INFO sip:8570@150.129.39.105:5060 SIP/2.0
Via: SIP/2.0/UDP 150.129.38.217:5060; rport;branch=z9hG4bK-1170-1145483948-19998-190
Call-ID: 1c5-403-3192006215856-MFG_5-0@10.129.38.217 CSeq: 2 INFO
Max-Forwards: 70
To: <sip:8570@150.129.39.105>;tag=75001a07
From: <sip:3280@150.129.38.217>;tag=95ffcd055e0f78f7d5d397020e89288de8b1
User-Agent: Dialogic-Open-SIP/10.3.1.56 MFG_5 0
Timestamp: 04192006215908
Accept: application/ sdp
Content-Length: 26
Content-Type: application/ dtmf-relay
Signal = #
Duration = 120

SIP INFO Header Information

The existing header of the SIP INFO method will be modified to carry the digit.

• Signal parameter - used to carry the # or * character in the SDP.  

• Duration parameter - used in the SDP to store the length of time in milliseconds to play the digit.

• Content-Type header - will be changed to dtmf-relay when this feature is invoked.   

INFO using DTMF Digit Relay

Using the INFO DTMF Digit Relay method, the IMG 2020 supports out-of-band tone passage of a single DTMF digit (0- 9, *, #, a, b, c, d) using the SIP INFO method. On the TDM side, the IMG 2020 will send out a single DTMF digit in the INFO if it receives a digit from a TDM Channel (no pattern match required).

Call Flow - Digit Relay

Example Call Trace of INFO Message: TDM-to-SIP

INFO sip:10.129.39.95:5060 SIP/2.0
Via: SIP/2.0/UDP 10.129.39.49:5060;rport;branch=z9hG4bK-
16cf-1182872402-19997-319
Call-ID: 5331-400-5262007153956-YUE_NODE-0@10.129.39.49
CSeq: 2 INFO
Max-Forwards: 70
To: <sip:22233333@10.129.39.95:5060>;tag=1
From: <sip:123@10.129.39.49>;tag=95ffcd055e0f78f7d5d397020e89288dc959
User-Agent: Dialogic-SIP/10.3.3.172 YUE_NODE 0
Accept: application/sdp
Content-Type: application/dtmf-relay
Content-Length: 26
Signal= 6
Duration= 100

Digits Received from IP Side

The IMG 2020 will send out a single DTMF digit in the INFO message if it receives a SIP INFO request that has the Content-Type set to application\dtmf-relay. When the Content-Type header of incoming INFO request has value application/dtmf-relay, the IMG 2020 will look for a DTMF digit in the Signal= line and the digit interval in the Duration= line. If there is more than one digit in the Signal= line from incoming INFO, the IMG 2020 will only accept first digit. If the Duration= line is not present, the interval will be set to 100.

Initial Configuration

The procedure below explains how to configure SIP INFO Method - DTMF on the IMG 2020. Before configuring, the IMG 2020 must have an initial configuration created on it. Follow the Basic Configurations procedure before proceeding. 

Create SIP Signaling Gateway Profile (SGP)

Create a SIP Profile and SIP DTMF support objects.

• Right click on the Dialogic object and select New Profiles. The Profiles object is a parent or container object and no configuration is needed here. Refer to the Profiles topic for more information on this topic.

• Right click on the Profiles object and select New SIP Profiles. The SIP Profiles object is a parent or container object also and no configuration is required here. Refer to the SIP Profiles topic for more information on this object.

• Right click on the SIP Profiles object and select New SIP Profile. The first profile that gets created is a Default SIP Profile and cannot be modified. Disregard this profile.

• Right click on the SIP Profiles object and select New SIP Profile again. Either enter a Name into the name field that identifies this profile or accept the default entry. In this procedure, the SIP Profile was labeled SIP_INFO_Method_DTMF_Profile. Refer to the SIP Profile - SGP topic for more information on configuring the remaining fields in this object.

• Right click on the SIP Profile object just created and select SIP DTMF Support. The Method field in the SIP DTMF Support object is by default set to Disable. Select either INFO with Pattern, Subscribe, or Info DTMF digit relay from drop down menu. Refer to the SIP Profile - DTMF Support topic for more information on configuring the remaining fields.

Configure External SIP Remote Gateway

The  SIP External Remote Gateway object links the IMG 2020 to the SIP Gateway within the SIP network. The SIP Profile with the SIP INFO Method configured on it is linked to the Gateway through this object. Follow the procedure below to configure the External Gateway object.

• Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a container object and no configuration is needed in this object. Refer to External Network Elements for more information.

• Right click on External Network Elements object and select New External Gateways. The External Gateways object is also a container object. Under the External Gateways object, multiple individual gateways can be created. Refer to External Gateways topic for more information.

• Right click on External Gateways and select New External Gateway. In the name field either enter a name that identifies the gateway being configured or accept the default name. In this example, the name given was SIP_INFO_DTMF_GW Refer to the screen capture and table below.

Refer to the topic for more information on configuring the External Gateway object.

Configure SIP Signaling

The configuration above displays how to configure the SIP Profile and External SIP Gateway so that the SIP INFO Method - DTMF functionality is configured. The next step is to configure the SIP signaling stack and SIP Channel Groups. Refer to the Configure SIP (Single SIP IP) topic for a procedure on how to configure the SIP functionality.

Configure TDM side

Refer to Configure SS7 for information on configuring the SS7/TDM side including stacks and channel groups. 

Additional Information

The IMG 2020 will return a 488 if an INFO message with the Content-Type set to application/dtmf-relay is received and:

• the IMG 2020 configuration is not set to INFO DTMF relay.

• the IMG 2020 configuration is set to INFO DTMF relay, but the Signal= line contains unrecognizable character.