Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 153

This chapter presented the seamless mobile communications services provided by operators to their subscribers through the interworking and interoperations of mobile communications networks operated by them. Interoperations among the networks are important to offer communication services to roaming users. Interworking and interoperations between two network elements or different networks are established by introducing new logical interfaces that connect enhanced or upgraded network elements. Core network elements, e.g. MSC, SGSN, and MME, are upgraded to support additional interworking functions in an LTE/EPS network.

This chapter also presented the UE mode of operations that enables a user to make a voice call over a legacy as well as an LTE/EPS network. UE mode of operations is important to achieve the interworking of mobile communications networks. The interworking features, i.e. CSFB and SRVCC, may be deployed as the separately licensed feature on top of an existing network. We then presented the routing methods, either through the home network or visited network, available to route the roaming user data to an external packet network. We closed this chapter with the functions that are required to be performed from the E‐UTRAN point of view to support VoLTE calls over IMS.