9.9 NAS Signalling Procedures

3GPP43.318Generic Access Network (GAN)Release 17Stage 2TS

After GA-RRC connection establishment, NAS PDUs may be transferred from CN-to-MS and from MS-to-CN.

The initial NAS PDU from the MS to a core network domain is transferred in the GA-RRC INITIAL DIRECT TRANSFER message as illustrated in the following figure. This scenario assumes that a GA-RRC connection already exists between the MS and GANC; if not, the procedure described in clause 9.7.1 is performed before step 1.

Figure 47: Initial MS-to-CN NAS signalling

1. The MS receives a request from the NAS layer to establish a signalling connection to a core network domain. The request also includes a request to transfer an uplink NAS PDU. The MS encapsulates the NAS PDU within a GA-RRC INITIAL DIRECT TRANSFER message and sends the message to the GANC. The message includes the CN Domain identity (CS or PS). It also includes the Intra Domain NAS Node Selector (IDNNS) to be used by the GANC to route the establishment of a signalling connection to a CN node within the indicated CN domain (i.e., using IuFlex).

2. The GANC establishes a signalling connection to the indicated core network domain entity and relays the received NAS-PDU to the CN via the RANAP Initial UE Message message.

Subsequent NAS PDUs from the MS to the core network domain entity are transferred in the GA-RRC UPLINK DIRECT TRANSFER message as illustrated in the following figure.

Figure 48: MS-to-CN NAS signalling

1. The MS receives a request from the NAS layer to transfer an uplink NAS PDU. Assuming the required signalling connection already exists, the MS encapsulates the NAS PDU within a GA-RRC UL DIRECT TRANSFER message and sends the message to the GANC. The message includes the CN Domain identity (CS or PS).

2. The GANC relays the received NAS-PDU to the CN via the RANAP Direct Transfer message.

NAS PDUs from the core network to the MS are transferred in the GA-RRC DOWNLINK DIRECT TRANSFER message as illustrated in the following figure.

Figure 49: CN-to-MS NAS signalling

1. For CN-to-MS NAS signalling, the CN sends a NAS PDU to the GANC via the RANAP Direct Transfer message.

2. The GANC encapsulates the NAS PDU within a GA-RRC DL DIRECT TRANSFER message and forwards the message to the MS via the existing TCP connection. The message includes the CN Domain identity (CS or PS).