8.11 Mobile Terminated Call Flow

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

Figure 23: Mobile Terminated Call

The description of the procedure in this clause assumes the MS is in GAN A/Gb mode i.e. it has successfully registered with the GANC and GA-CSR is the serving RR entity in the MS.

1. A mobile-terminated call arrives at the CN. The CN sends a Paging message to the GANC identified through the last Location Update received by it and includes the TMSI if available. The IMSI of the mobile being paged is always included in the request.

2. GANC identifies the MS registration context using the IMSI provided by the CN. It then pages the MS using the GA-CSR PAGING REQUEST message. The message includes the TMSI, if available in the request from the CN, else it includes only the IMSI of the mobile.

3. The MS responds with a GA-CSR PAGING RESPONSE including the MS Classmark and ciphering key sequence number. The MS enters dedicated mode and the GA-CSR state changes to GA-CSR-DEDICATED.

4. The GANC establishes an SCCP connection to the CN. The GANC then forwards the paging response to the CN using the Complete Layer 3 Information message.

5. The CN may optionally authenticate the MS using standard GERAN authentication procedures.

6. The CN may optionally update the ciphering configuration in the MS, via the GANC, as described in clause 8.8.

7. The CN initiates call setup using the Setup message sent to the MS via GANC. GANC forwards this message to the MS in the GA-CSR DL DIRECT TRANSFER message.

8. The MS responds with Call Confirmed using the GA-CSR UL DIRECT TRANSFER after checking it’s compatibility with the bearer service requested in the Setup and modifying the bearer service as needed. If the Setup included the signal information element, the MS alerts the user using the indicated signal, else the MS alerts the user after the successful configuration of the user plane. The GANC forwards the Call Confirmed message to the CN.

9. The CN initiates the assignment procedure with the GANC, which triggers the setup of the GA-CSR traffic channel, the same as steps 8-13 in the MO call scenario (see sub-clause 8.10).

10. The MS signals that it is alerting the user, via the Alerting message contained in the GA-CSR UL DIRECT TRANSFER. The GANC forwards the Alerting message to the CN. The CN sends a corresponding alerting message to the calling party.

11. The MS signals that the called party has answered, via the Connect message contained in the GA-CSR UL DIRECT TRANSFER. The GANC forwards the Connect message to the CN. The CN sends a corresponding Connect message to the calling party and through connects the audio. The MS connects the user to the audio path.

12. The CN acknowledges via the Connect Ack message to the GANC. GANC forwards this message to the MS in the GA-CSR DL DIRECT TRANSFER. The two parties on the call are connected on the audio path.

13. Bi-directional voice traffic flows between the MS and CN through the GANC.