8.16 GA-PSR Transport Channel Management Procedures

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

The GA-PSR Transport Channel (GA-PSR TC) management procedures are the basic GA-PSR procedures specified to facilitate the control of the GA-PSR connection for the user data transfer. A UDP based GA-PSR connection between the MS and the GANC for GPRS data transfer is referred to as the GA-PSR Transport Channel.

The GA-PSR Transport Channel consists of the following:

– The IP address and destination UDP port number to be used for GPRS data transfer at both the GANC and MS.

– The GA-PSR Channel Timer.

The MS or GANC will activate a GA-PSR Transport Channel only when needed; i.e. when the GPRS user data transfer is initiated.

The GA-PSR can be in two different states, GA-PSR-STANDBY or GA-PSR-ACTIVE state. The state of the GA-PSR and the corresponding transport channel are always synchronized.

– In GA-PSR-STANDBY state:

– The MS is not able to send or receive GPRS data to and from the GANC. The GANC or the MS needs to activate the GA-PSR Transport Channel before sending any GPRS data.

– A corresponding GA-PSR Transport Channel does not exist. When the GA-PSR Transport Channel is activated, the MS enters the GA-PSR-ACTIVE state.

– In GA-PSR-ACTIVE state:

– The MS is able to send and receive GPRS data to and from the GANC. Furthermore there exists a corresponding GA-PSR Transport Channel for this MS.

A GA-PSR Channel Timer is also defined to control the transition from GA-PSR-ACTIVE to GA-PSR-STANDBY state as follows:

– The MS GA-PSR layer implements a timer that is started when the MS enters GA-PSR-ACTIVE state and restarted each time a LLC-PDU is transmitted to or received from the network. When the timer expires, the MS deactivates the GA-PSR Transport Channel and the MS GA-PSR enters GA-PSR-STANDBY state.

The GA-PSR Channel Timer value is returned to the MS as part of the GAN Registration procedure (i.e. in GA-RC REGISTER ACCEPT message).

8.16.1 MS initiated Activation of GA-PSR Transport Channel

Figure 29 depicts the MS initiated GA-PSR Transport Channel activation procedure. The basic idea is that the GANC and MS can dynamically negotiate the IP address and UDP port numbers for data transfer. This procedure can facilitate the GANC load balancing; moreover, it allows the GANC to optimize the processing and maintain the context for active users only.

Figure 29: Activation of GA-PSR Transport Channel

Initially, the MS GA-PSR is in the GA-PSR-STANDBY state as the LLC layer requests the transfer of one or more uplink LLC-PDUs. As the MS GA-PSR is in GA-PSR-STANDBY state, the corresponding GA-PSR Transport Channel does not exist. This is a trigger for the MS to activate the GA-PSR Transport Channel (TC).

1. The GA-PSR-layer sends a GA-PSR ACTIVATE UTC REQ message to the GANC to request the activation of the GA-PSR Transport Channel. This message contains MS UDP port number that the GANC can use for the downlink transfer.

2. The GANC replies with a GA-PSR ACTIVATE UTC ACK message that contains the IP-address and the UDP port number to be used for the uplink user data transfer. Upon receiving the acknowledgment, the MS GA-PSR transitions to GA-PSR-ACTIVE state.

3. After successful GA-PSR TC activation, the MS forwards the LLC-PDU to the GANC IP-address and UDP-port received in the acknowledgment message using GA-PSR UNITDATA message. The GANC forwards the LLC‑PDU and other parameters to the core network as per procedure described in clause 8.17.2.3 (not shown in the sequence). The MS restarts the GA-PSR Channel Timer.

4. The GANC receives a downlink user data message for the MS as per procedure described in clause 8.17.2.2 (not shown in the sequence) while the GA-PSR TC is still active. The LLC-PDU and the required parameters are sent to the MS encapsulated in a GA-PSR UNITDATA message using the associated GA-PSR Transport Channel information (MS IP-address and UDP-port received in step 1).

8.16.2 MS initiated Deactivation of the GA-PSR Transport Channel

The following message sequence depicts the scenario when the MS deactivates the GA-PSR Transport Channel after the GA-PSR Channel Timer expires. In addition, when a PS handover from GAN A/Gb mode to GERAN/UTRAN mode is successfully completed both the GANC and the MS shall consider the GA-PSR Transport Channel as implicitly deactivated and the MS shall stop the GA-PSR Channel Timer.

Figure 30: Deactivation of GA-PSR Transport Channel

1. GA-PSR-layer in the MS sends the GA-PSR DEACTIVATE UTC REQ message to the GANC to request the deactivation of the GA-PSR Transport Channel. The message includes cause parameter to indicate "normal deactivation".

2. The GANC deletes the related MS information associated with the GA-PSR Transport Channel and replies to the MS with a GA-PSR DEACTIVATE UTC ACK message. Upon receiving the acknowledgment message, the MS enters GA-PSR-STANDBY state.

8.16.3 Implicit Deactivation of the GA-PSR Transport Channel due to MS Deregistration

When a GA-RC DEREGISTER message is received by the GANC or if the MS is implicitly deregistered, the GA-PSR Transport Channel associated with the MS, if any, is automatically released by the GANC.

8.16.4 Network initiated GA-PSR Transport Channel Activation

Figure 31 depicts a scenario when the GANC activates a GA-PSR Transport Channel for a GAN registered MS. This scenario covers the following cases:

– The GANC receives a downlink user data packet (LLC PDU) from the core network and the specified MS does not have an active GA-PSR Transport Channel.

– PS Handover to GAN A/Gb mode is initiated in support of one or more PS domain services.

Figure 31: Network initiated GA-PSR Transport Channel Activation

1. The GANC sends a GA-PSR ACTIVATE UTC REQ message to the MS to request the activation of the corresponding GA-PSR TC. The message contains the GANC IP address and UDP port number assigned to the GA-PSR TC and the MS GA-PSR transitions to GA-PSR-ACTIVE state.

2. The MS replies with a GA-PSR ACTIVATE UTC ACK message that contains the selected UDP-port number. Subsequently, the MS enters GA-PSR-ACTIVE state and starts the GA-PSR Channel Timer.

3. The GANC forwards the previously received downlink LLC-PDU to the MS using GA-PSR UNITDATA message as per procedure described in clause 8.17.1. For the case of PS handover to a GAN cell the reception of downlink LLC PDUs is enabled in the MS upon allocation of the GA-PSR Transport Channel in step 1.

4. The GA-PSR Transport Channel is active and the MS can send the uplink data using GA-PSR UNITDATA procedure described in clause 8.17.1. For the case of PS handover to a GAN cell the MS enables the transmission of uplink LLC PDUs on the allocated GA-PSR Transport Channel upon successful completion of the PS handover procedure.