SIP And DTMF

SIP WG

48th IETF

July 31-August 4, 2000

Bert Culpepper, Skip Cave

48th IETF SIP WG 2

DTMF Related Proposals

• The SIP INFO Method– draft-ietf-sip-info-method-04.txt

– Draft describes the use of the SIP INFO Method for mid-call signaling along the SIP signaling path. DTMF is one data type described.

• Sample Uses of SIP INFO with Varying Reliability Needs– draft-kuthan-sip-infopayload-00.txt (expired)

– Draft describes mid-session signaling and reliable in-order delivery using the SIP INFO method. Describes DTMF digit strings in INFO message bodies. Suggests MGCP/Megaco MIME content support in Gateway Controllers.

48th IETF SIP WG 3

DTMF Transmission Techniques

• Contained in Media (RTP Stream)– Doesn’t work with compressed media.

– Requires “ports” in service platforms.

• Special Encoding in RTP (RFC 2833)– Can be sent separate from other media (Supports 3pcc).

– Requires RFC 2833 encoder/decoder.

• RFC 2833 Encoded Data Using INFO Method– Can be sent along the call signaling path (Supports 3pcc).

– Requires RFC 2833 encoder/decoder.

• DTMF Using INFO Method (draft-choudhuri-sip-info-digit-00.txt)– Can be sent along the call signaling path (Supports 3pcc).

– Text-based encoding of DTMF.

– No “out-of-order” issues.

– Draft goes beyond DTMF transmission by describing collection attributes to be used by a client.

48th IETF SIP WG 4

DTMF Transmission Techniques (cont.)

• MGCP/Megaco-Based Event Detection and Reporting Using INFO Method (draft-culpepper-sip-info-event-00.txt)

– Can be sent along the call signaling path (Supports 3pcc).

– MGCP/Megaco text-based encoding of DTMF.

– No “out-of-order” issues.

– Specific to networks containing MGCP/Megaco-based Media Gateways and Media Gateway Controllers.

– Goes beyond DTMF transmission by describing MGC enabled event detection and reporting at the MG. Leverages MGCP/Megaco compliant DTMF collection and reporting capabilities.

G ateway G ateway

M G C M G C

A pplicatio n/M edia S erver

S IP -T

M G C P /M egaco

S IP -T

R T P R T P

R T P

M G C P /M egaco

P S T N P S T N

48th IETF SIP WG 5

Preferred Support Mechanism in SIP

• Recent discussions on the SIP list indicate preferred method for DTMF transmission is RFC 2833 encoded packets transported via RTP.

• However, it’s still not a “closed” issue.

Issues to Consider

• DTMF in a packet network is application control.

• Session-related Services Platforms require user interaction independent of the primary media. (When voice recognition is not employed by the service.)

• SIP is the IETF protocol currently carrying telephony signaling around a packet network (there is MGCP/Megaco at the edges). And in this role, mid-call signaling in SIP can support carrying today's PSTN enhanced services. However, other protocols exist for control and event reporting capabilities.