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The “3GPP Trust Domain” in Figure 5.2-1 captures the Functional entities that shall be part of the 3GPP Domain (the Network). Although the Figure 5.2-1 shows that the IN-CSE and IN-AE are outside of the 3GPP Domain, the IN-CSE may be part of the Operator domain (Fig. 4.2-1b).
The 3GPP Trust Domain provides three (3) Interfaces to SCS/CSE (Service Capability Server/Common Service Entity) for MTC:
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The Service Capability Server (SCS) is a 3GPP term that refers to an entity which connects to the 3GPP Trust Domain to communicate with UEs used for Machine Type Communication (MTC).
