This Recommendation describes Gateways which provide protocol interworking between H-Series multimedia terminals and other H-Series multimedia terminals, voice/voiceband terminals on GSTN, ISDN or PLMN, V.70 terminals on the GSTN, and multi-call applications on the GSTN. H.246 Gateways provide the required translation of control and media streams to allow interworking between terminals running different protocols. Annex A specifies H.323-H.320 interworking. Annex C specifies the interworking between ISUP (ISDN User Parts of Signalling System No. 7) and H.225.0. Annex E1 specifies the interworking between 2nd Generation Public Land Mobile Networks (PLMN) and H.323. Annex E2 specifies the interworking between 2nd Generation ANSI-41 PLMNs and H.323. Annex F specifies H.323-H.324 interworking. Amendment 1 amends Annex C (ISDN User Part function - H.225.0 interworking) in support of mapping user priority level and country/international network of call origination between H.225 and ISUP. Note that Annex B and Annex D do not exist, they were planned, but were never approved.