Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 73

The NAS contains all the mobility, connection, and SM‐related signaling protocols and procedures that terminate at the CN end. Using NAS signaling protocols, a UMTS UE or LTE or 5G UE communicates with the UMTS or LTE or 5G CN. Note that NAS uses the services of the AS protocols. In this case, the UMTS UTRAN or the LTE E‐UTRAN or 5G NG‐RAN simply forwards those transparent NAS‐related signaling messages to their respective CN.

Figure 3.10 in the previous section shows the protocols that are grouped into AS and NAS types in the case of the LTE system only where the NAS layer terminates at the LTE/EPC MME.

NAS signaling protocols are typically used for the following services:

 CS CN procedures, such as MM and connection management (CM).

 GPRS PS core network procedures, such as mobility, SM bearer management, and security management.

 LTE/EPS core network procedures, such as the mobility, connection, and SM, bearer management, security management, EPS ciphering, and integrity protection function.

 5G core network procedures, such as the mobility, connection, and PDU SM, security management, ciphering, and integrity protection function.

Table 3.7 shows the various NAS protocol messages exchanged between MS/UE and its concerned core network in GSM/GPRS/UMTS and LTE/EPS networks.

Example 3.8 below illustrates the typical messages flows associated with a MM layer (NAS) ATTACH procedure in the case of the LTE/EPS network.

Table 3.7 NAS protocol messages from GSM to LTE system.

System	Type of Call	CM Message	SM Message	MM Message
GSM/ UMTS	CS	Call Estb., Call Setup	–	Location Area Update
GPRS/ UMTS	PS	Call Establishments, Call Setup	Primary and Secondary PDP Context Managements	Routing Area Update, Network Attach, Detach
LTE/EPS	PS	[Fall‐back] Call Establishments, Call Setup	Default and Dedicated Bearer Managements	Tracking Area Update, Network Attach, Detach