3GPP43.318Generic Access Network (GAN)Release 16Stage 2TS
Figure 22: Mobile Originated Call
The description of the procedure in this sub-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. The GA-CSR Connection Establishment procedure is performed as described in clause 8.7.1.
2. Upon request from the upper layers, the MS sends the CM Service Request to the GANC in the GA-CSR UL DIRECT TRANSFER.
3. The GANC establishes an SCCP connection to the CN and forwards the CM Service Request to the CN using the Complete Layer 3 Information. Subsequent layer-3 messages between mobile station and core network will be sent between GANC and CN via DTAP.
4. The CN may optionally authenticate the MS using standard GERAN authentication procedures.
5. The CN may optionally initiate the Ciphering Configuration procedure described in clause 8.8.
6. The MS sends the Setup message providing details on the call to the CN and its bearer capability and supported codecs. This message is contained within the GA-CSR UL DIRECT TRANSFER between the MS and the GANC. The GANC forwards the Setup message to the CN.
7. The CN indicates it has received the call setup and it will accept no additional call-establishment information using the Call Proceeding message to the GANC. GANC forwards this message to the MS in the GA-CSR DL DIRECT TRANSFER.
8. The CN requests the GANC to assign call resources using Assignment Request.
9. The GANC sends the GA-CSR ACTIVATE CHANNEL to the MS including bearer path setup information such as:
– Channel mode.
– Multi-rate codec configuration.
– UDP port & the IP address for the uplink RTP stream.
– Voice sample size.
– An indication of whether RFC 4867  octet-aligned mode (i.e., the default for GAN A/Gb mode) or bandwidth-efficient mode shall be used for the GA-CSR traffic channel. If an IP-based A-interface where bandwidth-efficient mode is used and the MS supports RFC 4867 bandwidth-efficient mode (see sub-clause 22.214.171.124), the GANC can enable "AoIP payload optimization" (i.e., avoiding the need for the GANC to do transcoding or conversion between RFC 4867 payload modes) by indicating that RFC 4867 bandwidth-efficient mode be used for the GA-CSR traffic channel.
10. The MS establishes the RTP path to the GANC. MS optionally sends idle RTP/UDP packets to the GANC but has not connected the user to the audio path.
11. The MS sends the GA-CSR ACTIVATE CHANNEL ACK to the GANC indicating the UDP port for the downlink RTP stream.
12. If a TDM-based A-interface channel is used for the call, the GANC establishes the downlink RTP path between itself and the MS. The GANC may start sending idle RTP/UDP packets to the MS.
13. The GANC signals to the CN that the call resources have been allocated by sending an Assignment Complete message.
14. The GANC signals the completion of the bearer path to the MS with the GA-CSR ACTIVATE CHANNEL COMPLETE message. An end-to-end audio path now exists between the MS and the CN. The MS can now connect the user to the audio path.
15. The CN 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-CSR 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.
16. The CN 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-CSR DL DIRECT TRANSFER. It connects the user to the audio path. If the mobile station is generating ring back, it stops and connects the user to the audio path.
17. The MS sends the Connect Ack in response, and the two parties are connected for the voice call. This message is contained within the GA-CSR UL DIRECT TRANSFER between the MS and the GANC. The GANC forwards the Connect Ack message to the CN.
18. Bi-directional voice traffic flows between the MS and CN through the GANC.