Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 145

In the previous section, interworking among the legacy systems has been described. To support seamless mobile communications services to subscribers during the inter‐system movement, the 5G system also provides interworking capabilities to operators. However, the 5G system supports interworking with the LTE/EPS only. For interworking between the 5G system and the LTE/EPS, the 3GPP defines a new inter core networks logical interface called N26 between the Access and Management Function (AMF) in 5G core network and the MME in the LTE/EPC network. It may be noted that interworking between the LTE/EPS and the 5G system can also take place without the presence of the N26 interface. Further, depending on the availability of the N26 interface between the 5GC/AMF and LTE/EPS MME for interworking between them, a UE can operate in one of the following modes:

 Single Registration Mode, where the N26 logical interface is available between the 5GC/AMF and LTE/EPS MME.

 Dual Registration Mode, where the N26 logical interface is not available between the 5GC/AMF and LTE/EPS MME.

Interworking between the 5G and the LTE/EPS with or without the N26 logical interface shall be described later in Chapter 16.