Summary

This annex describes the interworking between ISUP (ISDN User Parts of Signalling System No. 7) and H.225.0 Multimedia Call Control protocol. It specifies the necessary mapping an interworking function would utilize to achieve connectivity and functionality between an H.323 network and an ISDN User Part network.

This annex describes an interworking function when it is in a H.323 to PSTN gateway. The interworking function could reside in other elements of a H.323 network; this is for further study. The mapping described in this annex relates to a H.323 call to Circuit Switched Network Phone.

This annex does NOT attempt to define functionality in ISUP or Q.931 networks but seeks to show how the ISUP services and functions would interwork with ITU-T Rec. H.225.0. H.225.0 messages contain Q.931 information elements and as such parts of this annex have been derived from ITU‑T Rec. Q.699. This annex does NOT show the mapping between H.320 and H.323.

This revision of Annex C incorporates changes identified by the H.323 Implementors' Guide as well as further enhancing the number of features that can be interworked between ISUP and H.323. Of particular note is the inclusion of text to support interworking of the International Emergency Preference Scheme (IEPS).