IMG 1010 - SIP INFO Method - Overview
- Kelli Higdon
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Overview:
The IMG 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 accomplished 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 types 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.
SIP INFO Method Uses:
The following are a few of the potential uses of the INFO message:
Carrying mid-call PSTN signaling messages between PSTN gateways.
Carrying DTMF digits generated during a SIP session.
Carrying wireless signal strength information in support of wireless mobility applications.
Carrying account balance information.
Carrying images or other non streaming information between the participants of a session.
Related Topics:
RFC 2976 - The SIP INFO Method
IMG 1010 - SIP INFO Method - DTMF
IMG 1010 - SIP INFO Method - SUBSCRIBE-NOTIFY
IMG 1010 - Pass through ‘+’ sign in the user part of URI
IMG 1010 - SIP INFO Method - Long Call Duration Auditing
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