Introduction It is necessary to specify the interworking of Signalling System No. 5 and the signalling system used in the INMARSAT Standard A system. This is because: a) it may be desirable that a Maritime Satellite Switching Centre (MSSC)1) be connected to an international switching centre (ISC) by employing System No. 5 on circuits between the MSSC and the ISC; b) the signalling systems used in the Maritime Mobile-Satellite Service will be different from System No. 5. Therefore it would be necessary to establish rules by which signalling events in one system may be related to corresponding events in the other system. It is desirable that the interworking be such that the full capability of both System No. 5 and the maritime satellite signalling system can be utilized. This Recommendation considers only automatic interworking between the MSSC and an ISC utilizing System No. 5. For description of the INMARSAT Standard A signalling system@ see Annex A to Recommendation Q.1101. 1) For definition@ see Recommendation Q.1101.