8.18 GA-PSR Specific Signalling Procedures

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

8.18.1 Packet Paging for GPRS Data Service

The Core Network sends a PS page for a mobile station that is currently GPRS attached via the GAN.

Figure 35: Packet Paging for GPRS

1. The Core Network sends a PAGING PS for a mobile station that is currently GPRS attached via the GAN. This message contains always IMSI and it may also contain P-TMSI.

2. GANC identifies the MS registration context using the IMSI provided by the CN and pages the MS using the GA-PSR PS PAGE message on the existing TCP signalling connection. The GA-PSR PS PAGE message on the Up interface includes the P-TMSI, if received in the PAGING PS message from the CN, else it includes the MS IMSI.

3. The mobile station sends any LLC-PDU to respond to the page, activating GA-PSR TC, if needed. The uplink LLC-PDU is forwarded to the GANC using the GPRS data or signalling transfer mechanism as described in clause 8.17.2.3.

4. The GANC forwards the LLC-PDU to the Core Network via the standard Gb interface procedures.

8.18.2 Packet Paging for CS Domain Service

The Core Network may send a CS page for a mobile station that is currently GPRS attached via the GAN.

Figure 36: Packet Paging for CS Service

1. The Core Network sends a PAGING CS for a GAN registered mobile station via the Gb interface. The mobile station is currently GPRS attached via the GAN. The PAGING CS message always contains IMSI as Mobile Identity and it may also contain TMSI.

2. GANC identifies the MS registration context using the IMSI provided by the CN and pages the MS using the GA-CSR PAGING REQUEST message on the existing TCP signalling connection. The GA-CSR PAGING REQUEST message on the Up interface includes the TMSI, if received in the PAGING CS message from the CN, else it includes the MS IMSI.

3-4. The mobile station initiates the standard CS page response procedure via the GAN as described in clause 8.11.

8.18.3 GPRS Suspend Procedure

The GPRS Suspend procedure is invoked if a mobile station is unable to support simultaneous voice and data services and is transitioning to dedicated mode.

Figure 37: GPRS Suspend

1. While transitioning to dedicated mode and if unable to support simultaneous voice and data services, the mobile station sends a GA-CSR GPRS SUSPENSION REQUEST message to the GANC to suspend downlink GPRS traffic. The request is transferred via the existing TCP signalling connection and includes TLLI and Suspension Cause parameters as per standard GPRS.

2. The GANC initiates and completes the standard GPRS Suspend procedure as defined for Gb interface.

8.18.4 GPRS Resume Procedure

If the GPRS service has been suspended while the mobile station entered the dedicated mode, it needs to be resumed when the mobile station leaves the dedicated mode.

Figure 38: GPRS Resume

Initially, the MS is in the dedicated mode and the GPRS service is suspended.

1. The Core Network sends a Clear Command message to release the resources associated with the dedicated mode procedure.

2. The GANC responds with a Clear Complete message.

3. Optionally, the GANC may initiate the standard BSSGP GPRS resume procedure.

4. The GANC sends a GA-CSR RELEASE message to instruct the MS to release the GA-CSR Connection. The message includes GPRS resumption indication as per standard GSM/GPRS to indicate whether or not the network successfully resumed GPRS service.

5. The MS replies with a GA-CSR RELEASE COMPLETE message and resumes GPRS service internally.

6. Optionally, if the Core Network indicated unsuccessful resumption, the MS initiates GPRS service resumption as per standard GPRS.

8.18.5 MS Initiated Downlink Flow Control

The principle of the MS Initiated Downlink Flow Control is that the MS sends to the GANC flow control parameters, which allow the GANC to perform standard Gb interface procedures towards CN for downlink Flow Control either on MS or PFC level.

The following figure illustrates the message flow involved in the normal case when the MS sends a GAN flow control request to the GANC as an indication that the MS is not able to handle current data rate. The GANC will utilize the standard MS based Gb interface flow control mechanism to adjust the data rate.

Figure 39: Downlink Flow Control

1. The MS detects a flow control condition related to the downlink data traffic.

2. The MS constructs a flow control request message (GA-PSR FC REQ) that is sent to the GANC via the GA-PSR TC and starts a GA-PSR downlink flow control timer to continue monitoring the flow control condition. The message includes the flow control adjustment IE to specify the required data rate correction.

3. Upon receiving the indication, the GANC calculates adjusted flow control parameters for the MS and sends the corresponding request to the Core Network to reduce the downlink data rate for the MS. The Core Network adjusts the downlink data rate for the MS as per request.

4. Upon the expiry of the GA-PSR downlink flow control timer, the MS evaluates the flow control condition and if it has not been resolved, calculates the adjustment again and forwards another request to the GANC.

5. The GANC processes the request and sends another request to the Core Network to adjust the downlink data rate for the MS.

6. The GA-PSR downlink flow control timer expires again.

7. Steps 4 to 6 are repeated until the flow control condition is resolved.

8.18.6 Uplink Flow Control

The principle of the Uplink Flow Control is that the GANC sends to the MS flow control parameters, which guide the MS on sending of GPRS data towards the GANC.

The following figure illustrates the message flow involved in the normal case when the GANC initiates GAN flow control procedure when it is not able to handle current uplink data rate.

Figure 40: Uplink Flow Control

1. The GANC detects a flow control condition related to the uplink data traffic associated with a specific MS.

2. The GANC constructs a flow control request message (GA-PSR-FC-REQ) that is sent to the MS via the GA‑PSR TC and starts a timer to continue monitoring the flow control condition. The message includes the flow control adjustment IE to specify the required data rate correction. Upon receiving the message, the MS adjusts the uplink data rate accordingly.

3. After the timer expires, the GANC evaluates the flow control condition and if it has not been resolved, calculates the adjustment again and forwards another request to the MS.

4. The GANC timer expires again. The GANC evaluates the flow control condition and determines that the condition has been resolved. Based on the GANC algorithm that is implemented, it may gradually increase the uplink data rate using the same GA-PSR-FC-REQ message.

5. The flow control condition does not exist any more and the procedure is complete.