9.10 Mobile Originated CS Call

3GPP43.318Generic Access Network (GAN)Release 16Stage 2TS

The description of the procedure in this sub-clause assumes the MS is in GAN Iu mode; i.e., it has successfully registered with the GANC and GA-RRC is the serving RR entity for CS services in the MS. It also assumes that no GA-RRC signalling connection for the CS domain exists between the MS and GANC; i.e., the CS domain GA-RRC sublayer entity in the MS is in the GA-RRC-IDLE state. If the CS domain GA-RRC sublayer entity in the MS is already in the GA-RRC-CONNECTED state, step 1 is skipped.

Figure 50: Mobile Originated CS Call

1. The CS GA-RRC Connection Establishment procedure is performed as described in clause 9.7.1.

2. The MS sends the CM Service Request message to the GANC within the GA-RRC INITIAL DIRECT TRANSFER message. The message includes the CN Domain identity (CS).

3. The GANC establishes an SCCP connection to the MSC and forwards the NAS PDU (i.e., the CM Service Request message) to the MSC using the RANAP Initial UE Message. The message includes the Domain Indicator set to value ‘CS domain’. Subsequent NAS messages between the MS and MSC will be sent between GANC and MSC using the RANAP Direct Transfer message.

4. The MSC may optionally authenticate the MS using standard UTRAN authentication procedures.

5. The MSC normally initiates the Security Mode Control procedure described in clause 9.8.

6. The MS sends the Setup message providing details on the call to the MSC and its bearer capability and supported codecs. This message is contained within the GA-RRC UL DIRECT TRANSFER between the MS and the GANC. The GANC forwards the Setup message to the MSC.

7. The MSC indicates it has received the call setup and it will accept no additional call-establishment information using the Call Proceeding message to the GANC. The GANC forwards this message to the MS in the GA-RRC DL DIRECT TRANSFER message.

8. The MSC requests the GANC to assign call resources using the RANAP RAB Assignment Request message. The MSC includes the RAB ID, the CN Transport Layer Address and the CN Iu Transport Association for user data.

9. The Iu bearer is established per standard Iu procedures. In the case of the ATM-based Iu-cs interface, this may include the exchange of ALCAP signalling between the GANC and the MSC to setup the ATM virtual circuit. For both ATM and IP-based Iu-cs interface types, Iu bearer establishment may also include the Iu UP initialization exchange, if Iu UP support mode is required as indicated by the MSC in the RANAP RAB Assignment Request message.

10. The GANC sends the GA-RRC ACTIVATE CHANNEL message to the MS including bearer path setup information such as:

– CN Domain ID (i.e., indicating CS domain).

– RAB ID (provided by the MSC in step 8).

– RAB Configuration (based on RAB parameters provided by the MSC in step 8).

– Multi-rate codec configuration.

– UDP port & the IP address for the uplink RTP stream.

– Voice sample size.

11. The MS sends the GA-RRC ACTIVATE CHANNEL ACK to the GANC indicating that the MS has successfully established a CS bearer channel for the call and including the UDP port for the downlink RTP stream.

12. The GANC signals the completion of the RAB establishment to the MS with the GA-RRC ACTIVATE CHANNEL COMPLETE message.

13. The GANC signals to the MSC that the RAB has been established by sending a RANAP RAB Assignment Response message.

14. The MSC signals to the MS, with the Alerting message, that the B-Party is ringing. The message is transferred to the GANC and GANC forwards the message to the MS in the GA-RRC DL DIRECT TRANSFER. If the MS has not connected the audio path to the user, it shall generate ring back to the calling party. Otherwise, the network-generated ring back will be returned to the calling party.

15. The MSC signals that the called party has answered, via the Connect message. The message is transferred to the GANC and GANC forwards the message to the MS in the GA-RRC DL DIRECT TRANSFER. The MS connects the user to the audio path. If the MS is generating ring back, it stops and connects the user to the audio path.

16. The MS sends the Connect Ack message in response, and the two parties are connected for the voice call. This message is contained within the GA-RRC UL DIRECT TRANSFER between the MS and the GANC. The GANC forwards the Connect Ack message to the MSC.

17. Bi-directional voice traffic flows between the MS and MSC through the GANC.