In the SS7 domain,
this parameter is set to identify any transit networks that were used to carry the
call to its destination. It may or may not be populated.
User Service Information User Service Information is mapped into the Session Description
Protocol (SDP) found in the message body of the SIP message. Likewise, the media, bandwidth,
and access lines are mapped from the SIP SDP into the USI parameter in the SS7
message. Tables 5.7 and 5.8 provide mapping between the two protocols.
There are a number of different responses that can be sent on either the SS7 or the
SIP sides of the network.
Interworking with VoIP
When interfacing with another SIP-based network, the network access is the same as
to the PSTN. In other words, access to the IMS network is granted through the MGCF
and BGCF functions.
There is no interworking between protocols. The IMS entities should support simple
SIP (based on RFC 3261), so interworking with other SIP entities is not an issue. When
sending SIP messaging with IMS-specific extensions into the VoIP network, the VoIP
entities respond according to the procedures outlined in RFC 3261.
The S-CSCF is capable of supporting simple SIP as well and is therefore able to process
these messages when received from a VoIP network. When forwarding messages
to a VoIP network outside of the IMS domain, SIP procedures are used.
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