The IMG supports SIP-T for interworking between SIP and SS7 ISUP for call setup, call tear down, and conversion of message formats for SIP Bridging, that is, a call that originates in the PSTN, goes into a SIP network, and terminates in the PSTN again.

SIP-T provides ISUP transparency between the PSTN switches handling the call by encapsulating the incoming ISUP messages in the body of the SIP message. The ingress IMG places the incoming ISUP messages in the SIP body and the ISUP messages generated by the egress IMG are the ones present in the SIP body. For mid-call messaging, The INFO message is used to transport mid-call signaling messages that do not have a one-to-one mapping to SS7 ISUP messages like INR and INF.


Why Enable SIP-T ?:

You should implement SIP-T (SIP for Telephones) when a call is passing from the PSTN, through a SIP network, and back to the PSTN, so that no SS7 information is lost.


SIP Bridging: