General Definitions Figure 1/X.353 shows the composition of systems in the Public Maritime Mobile Satellite Service. For definition of the various elements see Recommendation X.350. The mobile satellite data switching exchange (MSDSE) is defined in ??.7 of Recommendation X.350. Role of the MSDSE A MSDSE will at the same time act as an international gateway and as an interface to the mobile earth stations. Within an ocean area a public maritime mobile earth station may set up or receive data calls from any MSDSE in that region. Each ocean area may contain a number of MSDSEs. One MSDSE may have access to more than one satellite@ and thus may serve more than one ocean area. One MSDSE may serve one or more public maritime mobile systems. The MSDSE may be connected to more than one international data switching exchange (IDSE) in a PDN. The MSDSE may also be connected to IDSEs in different PDNs. This Recommendation assumes that a PDN does not connect to more than one MSDSE serving the same ocean area and Public Maritime Mobile Satellite System (such as INMARSAT Standard A@ B and C).