8 GA-PSR elementary procedures

3GPP44.318Generic Access Network (GAN)Mobile GAN interface layer 3 specificationRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.1 GA-PSR Transport Channel (GA-PSR TC) Overview

The GA-PSR Transport Channel is defined as a UDP based point to point GA-PSR connection between the MS and the GANC utilized for GPRS user data transfer. The life-time of the GA-PSR TC is controlled by the TU4001 timer. The duration of the TU4001 timer is provided to the MS as one of the GAN system parameters in the GA-RC REGISTER ACCEPT message. In the same way as other GAN system parameters, the GANC can update the TU4001 timer using the standard mechanism for GAN system parameters update. The MS shall store the TU4001 timer for future use and updates the value when requested.

8.2 MS Initiated GA-PSR Transport Channel (GA-PSR TC) Activation

The MS initiated GA-PSR TC activation is triggered by the uplink GPRS user data request when the GA-PSR is in the GA-PSR-STANDBY state. The following message flow depicts the messages and timers involved in this procedure:

Figure 8.2.1: MS initiated GA-PSR TC Activation

8.2.1 Initiation of the GA-PSR TC Activation by the MS

Upon receiving the uplink user data transfer request from the LLC for LLC SAPI 3, 5, 9 or 11 and while the MS GA-PSR is in the GA-PSR-STANDBY state, the MS shall,

– send a GA-PSR-ACTIVATE-UTC-REQ message,

– start timer TU4002,

– set the uplink packet sequence number to 0,

– set the expected downlink packet sequence number to 0 and

8.2.2 Processing of the GA-PSR TC Activation Request by the GANC

Upon receiving the GA-PSR-ACTIVATE-UTC-REQ message from the MS, if the GANC accepts this request, it:

– allocates the IP address and the UDP port number to be used by the MS for GPRS user data transport,

– sends the GA-PSR-ACTIVATE-UTC-ACK message to the MS with the cause indicating successful activation,

– sets downlink packet sequence number to 0 and

– sets the expected uplink packet sequence number to 0.

8.2.3 Processing of the GA-PSR TC Activation Acknowledgment by the MS

Upon receiving the GA-PSR-ACTIVATE-UTC-ACK message while the MS initiated GA-PSR TC activation is in progress, the MS shall stop timer TU4002, create and store the corresponding GA-PSR TC information and the MS GA-PSR shall transition into GA-PSR-ACTIVE state. The MS GA-PSR shall start TU4001 timer and forward any outstanding uplink user data packets. The TU4001 timer is restarted whenever any user data packet is sent to or received from the GANC.

8.2.4 Abnormal Cases

8.2.4.1 GA-PSR TC Activation Collision

If the GANC receives a GA-PSR-ACTIVATE-UTC-REQ message from the MS while the network initiated GA-PSR TC activation procedure is in progress, the GANC aborts the network initiated activation procedure and responds to the MS with the GA-PSR-ACTIVATE-UTC-ACK message including the cause indicating successful activation. The message includes GANC IP address and GANC UDP port to be used for the uplink GPRS user data transport.

If the MS receives a GA-PSR-ACTIVATE-UTC-REQ message from the GANC while the MS initiated GA-PSR TC activation procedure is in progress, the MS shall silently discard the request and wait for the acknowledgment related to the MS initiated activation already in progress.

8.2.4.2 Timer TU4002 Expires during GA-PSR TC Activation

If timer TU4002 expires in the MS, the MS shall remain in GA-PSR-STANDBY state and declare the procedure as failed to the upper layers.

8.2.4.3 GANC Receives Duplicate GA-PSR TC Activation Request

If the GANC receives a GA-PSR TC activation message from the MS with an active GA-PSR TC, it responds with the GA-PSR-ACTIVATE-UTC-ACK message to the MS and the cause indicates successful activation. The message includes GANC IP address and GANC UDP port allocated to the existing GA-PSR TC. In parallel, if the MS provided new UDP port number, the GANC updates the GA-PSR TC attributes accordingly.

After sending the GA-PSR-ACTIVATE-UTC-ACK message, the GANC

– sets the downlink packet sequence number to 0 and

– sets the expected uplink packet sequence number to 0

8.2.4.4 GANC Rejects GA-PSR TC Activation

If the GANC decides to reject GA-PSR TC activation, it shall send a GA-PSR-ACTIVATE-UTC-ACK message to the MS with the failure cause code and shall not include GANC IP address and UDP port number. The following rejection cause values are supported:

– "No available resources" indicates that the GANC failed to allocate required resources.

– "GANC failure" indicates internal GANC failure.

– "Not authorized for data service" indicates that the MS is not authorized to use data services via GAN.

Upon receiving the GA-PSR-ACTIVATE-UTC-ACK message indicating failure, the MS shall declare the procedure as failed to the upper layers.

8.2.4.5 MS Aborts GA-PSR TC Activation due to Lower Layer Failure

If a lower layer failure is detected while waiting for GA-PSR-ACTIVATE-UTC-ACK message, the MS shall declare the procedure as failed and send the corresponding indication to upper layers. Further, the MS shall act according to sub-clause 9.5.

8.3 Network Initiated GA-PSR Transport Channel (GA-PSR TC) Activation

The GANC initiated GA-PSR TC activation is triggered by the downlink GPRS user data request when the corresponding GA-PSR TC does not exist or as a result of PS handover from a GERAN/UTRAN cell to a GAN cell if PS handover is supported by the GANC. The following message flow depicts the messages and timers associated with this procedure:

Figure 8.3.1: Network initiated GA-PSR TC Activation

8.3.1 Initiation of the GA-PSR TC Activation by the GANC

Upon receiving the downlink user data transfer request associated with LLC SAPI 3, 5, 9 or 11 and if there is no GA-PSR TC associated with the specific MS or upon receiving a PS Handover Request message from the SGSN and if PS handover is supported, the GANC allocates the IP address and the UDP port number to be used by the MS for GPRS user data transport and sends a GA-PSR-ACTIVATE-UTC-REQ message to the MS. The GANC also:

– sets the downlink packet sequence number to 0 and

– sets the expected uplink packet sequence number to 0

8.3.2 Processing of the GA-PSR TC Activation Request by the MS

Upon receiving the GA-PSR-ACTIVATE-UTC-REQ message from the GANC, the MS shall verify the following:

– the GA-PSR is in GA-PSR-STANDBY state

– the GA-PSR TC does not exist

– the GPRS service is not suspended

Assuming successful verification, the MS shall allocate UDP port number for the MS GPRS user data transport and store the associated information. In parallel, the MS GA-PSR shall transition to GA-PSR-ACTIVE state and start TU4001 timer. Subsequently, the MS shall send the GA-PSR-ACTIVATE-UTC-ACK message to the GANC with the cause indicating successful activation. The message includes the MS UDP port to be used for the downlink GPRS user data transport.

After the MS has sent the GA-PSR-ACTIVATE-UTC-ACK message, it shall:

– set the uplink packet sequence number to 0 and

– set the expected downlink packet sequence number to 0

8.3.3 Processing of the GA-PSR TC Activation Acknowledgment by the GANC

Upon receiving the GA-PSR-ACTIVATE-UTC-ACK message while the GANC initiated GA-PSR TC activation is in progress as a result of a downlink user data transfer request, the GANC forwards any outstanding downlink user data packets.

Upon receiving the GA-PSR-ACTIVATE-UTC-ACK message while the GANC initiated GA-PSR TC activation is in progress as a result of receiving a PS Handover Request message from the SGSN, the GANC sends a PS Handover Request Ack message to the SGSN and may start blind transmission of downlink user data.

Both uplink and downlink packet sequence number for user data are set to 0 after successful GA-PSR TC activation.

8.3.4 Abnormal Cases

8.3.4.1 GA-PSR TC Activation Collision

8.3.4.2 MS Rejects GA-PSR TC Activation when the GPRS Service is suspended

If the MS determines that the GPRS service is suspended when the GA-PSR-ACTIVATE-UTC-REQ is received, it shall send a GA-PSR-ACTIVATE-UTC-ACK message to the GANC with the failure cause code set to "GPRS Suspended".

Upon receiving the GA-PSR-ACTIVATE-UTC-ACK message indicating that the GPRS service is suspended, the GANC aborts the activation procedure.

8.3.4.3 MS Receives GA-PSR TC Activation Request while GA-PSR TC active

If the MS receives a GA-PSR TC activation message from the GANC while the GA-PSR TC is active, it shall send the GA-PSR-ACTIVATE-UTC-ACK message to the GANC. The message shall include MS UDP port allocated to the existing GA-PSR TC. In parallel, if the GANC provided new IP Address and UDP port number, the MS shall update the GA-PSR TC attributes accordingly.

After sending the GA-PSR-ACTIVATE-UTC-ACK message, the MS shall:

– set uplink packet sequence number to 0 and

– set the expected downlink packet sequence number to 0

8.4 MS Initiated Deactivation of GA-PSR Transport Channel

When the TU4001expires, the MS GA-PSR initiates deactivation of the GA-PSR TC by sending the request to the GANC as per following message flow:

Figure 8.4.1: MS initiated GA-PSR TC Deactivation

8.4.1 GA-PSR TC Deactivation Initiation by the MS

When the TU4001 timer expires and if there are no outstanding uplink GPRS user data messages to be transferred, the MS GA-PSR shall send the GA-PSR-DEACTIVATE-UTC-REQ message to the GANC to request the deactivation of the transport channel. In parallel, the MS shall start TU4002 timer to wait for the confirmation.

8.4.2 Processing of GA-PSR TC Deactivation Request by the GANC

Upon receipt of a GA-PSR-DEACTIVATE-UTC-REQ message from the MS, the GANC releases the GA-PSR TC and sends the GA-PSR-DEACTIVATE-UTC-ACK message to the MS indicating successful deactivation; i.e. the cause IE is set to "success".

8.4.3 Processing of GA-PSR TC Deactivation Acknowledgment by the MS

Upon receipt of a GA-PSR-DEACTIVATE-UTC-ACK message from the GANC, the MS GA-PSR shall stop TU4002 timer, and release the GA-PSR TC. In parallel, the MS GA-PSR shall transition to GA-PSR-STANDBY state.

8.4.4 Abnormal Cases

8.4.4.1 Timer TU4002 Expires during GA-PSR TC Deactivation

If timer TU4002 expires in the MS, the MS shall transit to GA-PSR-STANDBY state and declare the procedure as failed to the upper layers.

8.4.4.2 GANC Rejects GA-PSR TC Deactivation

The following scenarios cover the cases when the GANC rejects GA-PSR TC Deactivation:

– If the corresponding GA-PSR TC does not exist on the network side, the GANC responds with a GA-PSR-DEACTIVATE-UTC-ACK message indicating successful deactivation.

– If there is outstanding downlink GPRS user data for the specified MS, the GANC forwards the data packets instead and ignores the deactivation request.

8.4.4.3 Uplink User Data Transfer is initiated while GA-PSR TC Deactivation is in Progress

If the MS LLC initiates the uplink user data transfer after the MS GA-PSR has sent the deactivation request to the GANC, the MS GA-PSR shall complete the deactivation procedure first and than initiate a new GA-PSR TC activation procedure to enable data transfer.

8.4.4.4 Downlink User Data Transfer is received while the GA-PSR TC Deactivation is in Progress

If the MS receives any downlink user data packets while waiting for the GA-PSR-DEACTIVATE-UTC-ACK message response, it shall abort the deactivation procedure (i.e. stop timer TU4002) and restart TU4001 timer.

8.4.4.5 Unexpected GA-PSR-DEACTIVATE-UTC-ACK response

If the MS receives an unexpected GA-PSR-DEACTIVATE-UTC-ACK message response while the GA-PSR is in GA-PSR-ACTIVE state, the MS GA-PSR shall stop TU4001 timer, and release the GA-PSR TC. In parallel, the MS GA-PSR shall transition to GA-PSR-STANDBY state.

If the MS receives an unexpected GA-PSR-DEACTIVATE-UTC-ACK message response while the GA-PSR is in GA-PSR-STANDBY state, the message is silently discarded.

8.4.4.6 Unexpected GA-PSR-ACTIVATE-UTC-REQ

If the MS receives an unexpected GA-PSR-ACTIVATE-UTC-REQ message while waiting for GA-PSR-DEACTIVATE-UTC-ACK message response, the MS ignores the request and continues waiting for deactivation response.

8.4.4.7 MS Aborts GA-PSR TC Deactivation due to Lower Layer Failure

If a lower layer failure is detected while waiting for GA-PSR-DEACTIVATE-UTC-ACK message, the MS shall declare the procedure as failed and send the corresponding indication to upper layers. Further, the MS shall act according to sub-clause 9.5.

8.5 GANC Initiated Deactivation of GA-PSR Transport Channel

The GANC may initiate the deactivation of the GA-PSR TC by sending the request to the MS as per following message flow:

Figure 8.5.1: Network initiated GA-PSR TC Deactivation

8.5.1 GA-PSR TC Deactivation Initiation by the GANC

When the GANC decides to deactivate GA-PSR TC channel, it shall send GA-PSR-DEACTIVATE-UTC-REQ message to the MS to request the deactivation.

8.5.2 Processing of GA-PSR TC Deactivation Request by the MS

Upon receipt of a GA-PSR-DEACTIVATE-UTC-REQ message from the GANC, the MS shall release the GA-PSR TC and send the GA-PSR-DEACTIVATE-UTC-ACK message to the GANC indicating successful deactivation; i.e. the cause IE is set to "success". In parallel, the MS GA-PSR shall transition to GA-PSR-STANDBY state.

8.5.3 Processing of GA-PSR TC Deactivation Acknowledgment by the GANC

Upon receipt of a GA-PSR-DEACTIVATE-UTC-ACK message from the MS, the GANC shall release the GA-PSR TC.

8.5.4 Abnormal Cases

8.5.4.1 MS Rejects GA-PSR TC Deactivation

The following scenarios cover the cases when the MS rejects GA-PSR TC Deactivation:

– If the corresponding GA-PSR TC does not exist on the MS side, the MS shall respond with a GA-PSR-DEACTIVATE-UTC-ACK message indicating successful deactivation.

– If there is outstanding uplink GPRS user data, the MS forwards the data packets instead and ignores the deactivation request.

8.5.4.2 Uplink User Data Transfer is received while GA-PSR TC Deactivation is in Progress

If the MS LLC initiates the uplink user data transfer after the MS has received a deactivation request from the GANC, the MS shall complete the deactivation procedure first and than initiate a new GA-PSR TC activation procedure to enable data transfer.

If the MS LLC initiates the uplink user data transfer before the MS has received a deactivation request from the GANC, the MS shall treat that as normal uplink user data transfer as defined in sub-clause 8.7.1.

8.5.4.3 Downlink User Data Transfer is initiated while the GA-PSR TC Deactivation is in Progress

If the GANC receives any downlink user data packets while waiting for the GA-PSR-DEACTIVATE-UTC-ACK response, it shall complete the deactivation procedure first and than initiate a new GA-PSR TC activation procedure to enable data transfer.

8.6 Implicit Deactivation of GA-PSR Transport Channel

If the GAN deregistration is performed for a mobile station with an active GA-PSR TC, the GANC automatically releases the associated GA-PSR TC. The MS shall release the GA-PSR TC upon GAN deregistration.

This includes the scenarios where an implicit GAN deregistration is performed by either the MS or GANC due to lower layer failures.

8.7 GA-PSR GPRS User Data Transport

While the corresponding GA-PSR TC is available, both mobile station and GANC can initiate GPRS user data transfer automatically using GA-PSR UNITDATA service as illustrated in the following figure:

Figure 8.7.1: GA-PSR GPRS User Data transport

The GPRS user data packets are tunnelled using UDP transport as specified for GA-PSR Transport Channel. Each packet is assigned a sequence number in the range of 0 to 65535 sequentially. The sequence number is set to 0 after reaching the maximum – 65535.

8.7.1 MS Initiates Uplink GPRS User Data Transfer

Assuming that the GA-PSR TC has been already activated as specified in sub-clauses 8.2 or 8.3, the MS GA-PSR is able to immediately forward any uplink GPRS user data packets to the GANC. Upon the request from the LLC to transfer an uplink LLC PDU with GPRS user data identified with LLC SAPI 3, 5, 9 or 11, the MS GA-PSR shall restart TU4001 timer and encapsulate the complete LLC PDU within a GA-PSR UNITDATA message.

Subsequently, the MS shall send the GA-PSR UNITDATA message to the GANC using the existing GA-PSR TC; i.e. using the corresponding GANC IP address and UDP port number.

The MS shall increment the uplink packet sequence number for each GA-PSR-UNITDATA message sent to the GANC.

8.7.2 Processing of the Uplink GPRS User Data Message by the GANC

Upon receiving the uplink user data message from the MS, the GANC extracts the received LLC PDU and available message parameters, relays the PDU to the SGSN via the Gb interface using the BSSGP uplink unitdata procedure as per standard GPRS.

The GANC increments the expected uplink packet sequence number for each GA-PSR-UNITDATA message received from the MS.

8.7.3 GANC Initiates Downlink GPRS User Data Transfer

Assuming that the GA-PSR TC has been already activated as specified in sub-clause 8.2 or 8.3, the GANC is able to immediately forward any downlink GPRS user data packets to the MS. Upon receiving a downlink packet for the MS, the GANC sends the GA-PSR UNITDATA message to the MS using the existing GA-PSR TC; i.e. using the corresponding MS IP address and UDP port number.

The GANC increments the downlink packet sequence number for each GA-PSR-UNITDATA message sent to the MS.

8.7.4 Processing of the Downlink GPRS User Data Message by the MS

Upon receiving the downlink user data message from the GANC, the MS GA-PSR shall restart TU4001 timer, extract the received LLC PDU and TLLI and forward the PDU to the LLC layer via the GRR SAP as per standard GPRS.

The MS shall increment the expected downlink packet sequence number for each GA-PSR-UNITDATA message received from the GANC.

8.7.5 Abnormal Cases

8.7.5.1 GANC Receives an Uplink User Data Message while the GA-PSR TC Activation Procedure is in progress

Upon receiving an uplink message while the GA-PSR TC activation procedure is in progress (TU4002 timer is still running), the GANC will process the request as if the GA-PSR TC was active.

8.7.5.2 GANC Receives an Uplink User Data Message and the GA-PSR TC is not active

Upon receiving an uplink message that is associated with a GA-PSR TC that does not exist, the GANC will process the message as defined in sub-clause 8.7.2. The GANC may disregard the uplink packet sequence number in this case. Further, the GANC initiates GA-PSR TC activation procedure as defined in sub-clause 8.3.

8.7.5.3 Handling of out-of-sequence packets

Packets received out-of-sequence should be dropped.

8.7.5.4 MS Receives a Downlink User Data Message while the GA-PSR TC Activation Procedure is in progress

Upon receiving a downlink message while the GA-PSR TC activation procedure is in progress (TU4002 timer is still running), the MS GA-PSR shall process the request as if the transport channel was active. The MS shall not initiate uplink GPRS user data transfer until the GA-PSR TC activation procedure is successfully completed (as specified in the subclause 8.2). The MS shall use the IP address and UDP port number received in the GA-PSR ACTIVATE UTC ACK message for sending uplink GPRS user data packets to the GANC on that transport channel.

8.7.5.5 Uplink User Data Transfer Failed due to Lower Layer Failure

If a lower layer failure is detected while attempting to send an uplink user data packet, the MS shall declare the procedure as failed and send the corresponding indication to upper layers.

8.8 GA-PSR GPRS Signalling and SMS Messages Transport

While the MS is registered for GAN services, the corresponding TCP session for signalling transport is always available and, assuming that the MS GA-CSR and GA-PSR are attached to GSM/GPRS SAPs, both mobile station and GANC can initiate GPRS signalling message transfer using GA-PSR DATA service as illustrated in the following figure. The GA-PSR-DATA transport mechanism is utilized for all GPRS GMM/SM signalling and SMS messages.

Figure 8.8.1: GA-PSR GPRS Signalling and SMS Messages transport

8.8.1 MS Initiates Uplink GPRS Signalling/SMS Message Transfer

Upon the request form the LLC to transfer an uplink LLC PDU carrying GPRS signalling message (identified with LLC SAPI 1) or GPRS SMS message (LLC SAPI 7), the MS GA-PSR shall encapsulate the complete LLC PDU within a GA-PSR DATA message and send the message to the GANC using the existing signalling TCP session.

8.8.2 Processing of the Uplink GA-PSR DATA Message by the GANC

Upon receiving the uplink GA-PSR DATA message from the MS, the GANC extracts the received LLC PDU and available message parameters and, relays the PDU to the SGSN via the Gb interface using the BSSGP uplink unitdata procedure as per standard GPRS.

8.8.3 GANC Initiates Downlink GA-PSR DATA Transfer

Upon receiving a downlink LLC PDU with GPRS signalling (identified with LLC SAPI 1) or SMS message (LLC SAPI 7), the GANC encapsulates the complete LLC PDU within a GA-PSR DATA message and sends the message to the MS using the existing signalling TCP session.

8.8.4 Processing of the Downlink GA-PSR DATA Message by the MS

Upon receiving the GA-PSR-DATA message that includes the downlink GPRS signalling or SMS LLC PDU from the GANC, the MS shall extract the received LLC PDU and TLLI and forward the PDU to the LLC layer via the GRR SAP as per standard GPRS.

8.8.5 Abnormal Cases

8.8.5.1 Downlink or Uplink User Data Transfer Failed due to Lower Layer Failure

If a lower layer failure is detected while attempting to send an uplink GPRS signalling or SMS message, the MS GA-PSR shall act according to sub-clause 9.5.

8.9 Packet paging for packet service

The following figure depicts interactions involved in the packet paging procedure via GAN.

Figure 8.9.1: Packet Paging

8.9.1 PS Paging Request Processing by the GANC

Upon receiving a Paging PS request from the SGSN for GAN registered MS, the GANC sends the GA-PSR-PS-PAGE message to the MS via the signalling TCP session.

8.9.2 PS Paging Request Processed by the MS

Upon receiving a GA-PSR-PS-PAGE message from the GANC, the MS GA-PSR shall forward the indication to the GMM layer using the GMMRR SAP as per standard GPRS. Subsequently, the MS shall send an uplink LLC PDU as a page response per standard GPRS. The MS may either send GA-PSR-DATA or GA-PSR-UNITDATA message as described in sub-clauses 8.7 and 8.8.

8.9.3 Processing of the PS Paging Response by the GANC

Since the MS responds to a PS Paging with any LLC PDU encapsulated within the standard GA-PSR-DATA or GA-PSR-UNITDATA message, the GANC will process the message as any other GPRS signalling/SMS or user data message. The processing of uplink GPRS data messages is described in sub-clause 8.7 and for the uplink GPRS signalling messages in sub-clause 8.8.

8.10 GPRS Suspend Procedure

The following figure depicts interaction involved in the GPRS Suspend procedure.

Figure 8.10.1 GPRS Suspend

8.10.1 GPRS Suspension Initiation by the MS

While transitioning to dedicated mode and if unable to support simultaneous CS and PS services, the MS shall request the suspension of the downlink GPRS data transfer by sending a GA- CSR GPRS SUSPENSION REQUEST message to the GANC

8.10.2 GPRS Suspend Request Processing by the GANC

Upon receiving a GA- CSR GPRS SUSPENSION REQUEST message from the MS, the GANC completes the GPRS suspend procedure via the Gb interface as defined in [19].

8.11 MS Initiated Downlink Flow Control

The MS initiated downlink flow control procedure is based on standard GPRS downlink flow control mechanism enhanced for GAN service. The MS implements the flow control algorithm to monitor and calculate the data rate that could be supported based on the current conditions. When the flow control condition is detected (e.g. the utilization of the buffers reaches a high watermark level), the MS re-calculates the estimated data rate that could be supported and sends the flow control request to the GANC to adjust the data rate accordingly. The following message flow depicts the messages and timers associated with this procedure:

Figure 8.11.1: MS initiated Downlink Flow Control

Initially, before detecting a flow control condition, the flow control condition does not exist in the MS. In this state, the MS GA-PSR monitors the average downlink data rate and the utilization of resources (e.g. downlink buffers), and when utilization exceeds a certain threshold, a downlink flow control condition is detected.

When the downlink flow control condition is detected, the MS sends the GA-PSR-DFC-REQ message to the GANC and starts the TU4003 timer. Whenever the timer expires, the MS checks the downlink flow control condition, and if it continues to exist, the MS restarts the timer, and sends another GA-PSR-DFC-REQ message to the GANC. The MS remains in this state while the flow control condition persists. As soon as the flow control condition is resolved, the MS deactivates the TU4003 timer and transitions to the default state in which no downlink flow control condition exists.

In case TU4003 is running and the CS traffic channel is activated or released or in case of GA-CSR state transition, MS may request the GANC flow control parameters to adjust existing flow control by sending GA-PSR-DFC-REQ message to the GANC and if so it shall restart the timer TU4003.

8.11.1 Initiation of the Downlink Flow Control by the MS

Upon detecting the downlink flow control condition, the MS shall initiate a downlink flow control procedure by sending a GA-PSR-DFC-REQ message to the GANC via the existing GA-PSR TC. The message includes new estimated data rate that can be supported. At the same time the MS shall start timer TU4003 to continue monitoring the flow control condition. The timer TU4003 is specified in sub-clause 12.

8.11.2 Processing of the Downlink Flow Control Request by the GANC

Upon receiving the GA-PSR-DFC-REQ message from the MS, the GANC initiates downlink flow control procedure over the Gb interface as per standard GPRS.

8.11.3 Processing of the TU4003 Timer Expiry by the MS

When the TU4003 timer expires, the MS shall re-evaluate the flow control condition and perform the following based on the outcome of the evaluation:

– If the flow control condition still exists (e.g. downlink buffer utilization is still above the low watermark level), the MS shall calculate a new data rate that can be supported and forward the corresponding GA-PSR-DFC-REQ message to the GANC via the existing GA-PSR TC. Simultaneously, the MS shall start timer TU4003 to continue monitoring the downlink data transfer.

– If the flow condition has been resolved (e.g. buffer utilization is below the low mark level), the MS shall not restart the TU4003 timer and shall stop sending flow control requests to the GANC.

8.12 Uplink Flow Control

The uplink flow control procedure is used to dynamically manage sharing of the available Gb interface bandwidth. The following message flow depicts the messages and timers associated with this procedure:

Figure 8.12.1: Uplink Flow Control

Upon receiving the request, the MS GA-PSR adjusts the uplink data rate as per request.

8.12.1 Initiation of the Uplink Flow Control by the GANC

Upon detecting the uplink flow control condition, the GANC initiates an uplink flow control procedure by sending a GA-PSR-UFC-REQ message to the MS via the existing GA-PSR TC. The request is PFC based if the packet flow management procedures are supported.

The GANC shall never request the uplink data rate that is lower than the guaranteed uplink bit rate specified for that PFC. The guaranteed bit rate can be ignored by the GANC if the Traffic Class is Interactive class or Background class.

8.12.2 Processing of the Uplink Flow Control Request by the MS

Upon receiving the GA-PSR-UFC-REQUEST message from the GANC, the MS adjusts the uplink data rate accordingly.

8.12.3 Resetting of the Uplink Flow Control Condition by the GANC

After the uplink flow control condition is resolved and the current conditions allow the uplink data rate to be reset to normal level, the GANC initiates an uplink flow control condition reset by sending a GA-PSR-UFC-REQUEST message to the MS via the existing GA-PSR TC. This message includes the reset indicator.

8.12.4 Abnormal Cases

8.12.4.1 GA-PSR TC Deactivation is in Progress

If the MS receives a GA-PSR-UFC-REQUEST message while the GA-PSR TC deactivation is in progress, the MS shall ignore the flow control request.

8.13 PS handover to GAN A/Gb mode

8.13.1 Initiation

If PS handover to GAN A/Gb mode is supported by both the MS and the source BSS/RNC it may be used to prevent an MS from performing an autonomous rove-in to GAN A/Gb mode in favour of using PS handover to perform a cell change. PS handover from a GERAN cell to a GAN A/Gb mode cell may be triggered as described in 3GPP TS 44.060 [45]. PS handover from a UTRAN cell to a GAN A/Gb mode cell may be triggered as described in 3GPP TS 25.331 [40].

The procedure for PS handover to a GAN A/Gb mode cell results in the target GANC allocating the MS a GA-PSR Transport Channel in response to receiving a PS Handover Request message from the SGSN (see sub-clause 8.3 and 3GPP TS 43.129 [49]). When the source BSS/RNC is informed about the successful allocation of the GA-PSR Transport Channel it responds by sending the MS a PS Handover Command message (source BSS) or a Handover from UTRAN Command message (source RNC).

If the target GANC supports blind transmission it may begin transmitting downlink data on the allocated GA-PSR Transport Channel prior to determining that PS handover to the GAN A/Gb mode cell has been successfully completed. Otherwise, it may discard downlink data that becomes available prior to detecting the successful completion of the PS handover to the GAN A/Gb mode cell. An MS that supports blind transmission enables the reception of downlink data upon being allocated a GA-PSR Transport Channel (i.e. prior to switching to GAN A/Gb mode).

8.13.2 Successful completion of the PS handover to GAN A/Gb mode

From the MS perspective the procedure for PS handover to a GAN A/Gb mode cell is started upon reception of the PS Handover Command message or the Handover from UTRAN Command message and completed upon sending a GA-PSR HANDOVER COMPLETE message to the GANC.

From the source BSS/RNC perspective the procedure for PS handover to a GAN A/Gb mode cell is started upon deciding to perform PS handover of an MS to a GAN A/Gb mode cell and completed upon being told by the SGSN to release all ongoing radio resources.

From the target GANC perspective the procedure for PS handover to a GAN A/Gb mode cell is started upon receiving a PS Handover Request message and completed upon receiving a GA-PSR HANDOVER COMPLETE message from the MS. Upon receiving this message the GANC shall indicate PS handover completion to the SGSN.

8.13.3 Abnormal Cases

Upon receiving a PS Handover Command message or a Handover from UTRAN Command message in the source cell the MS may experience the following abnormal conditions:

– If connectivity has been lost on the GA-PSR Transport Channel before the MS has transmitted a GA-PSR HANDOVER COMPLETE message it shall abort the PS handover to GAN A/Gb mode. The MS shall remain in the source cell and provide a failure notification as described in 3GPP TS 44.060 [45] for a GERAN cell or in 3GPP TS 25.331 [40] for a UTRAN cell.

8.14 PS handover from GAN A/Gb mode

8.14.1 Initiation

If PS handover from GAN A/Gb mode is supported by both the MS and the GANC it may be used to prevent an MS from performing an autonomous rove-out from GAN A/Gb mode in favour of using PS handover to perform a cell change.

Figure 8.14.1: PS handover from GAN A/Gb mode, successful case

Figure 8.14.2: PS handover from GAN A/Gb mode, failure case

The MS and the GANC inform each other of whether or not they support PS handover during GAN registration. If supported, PS handover may be triggered by the MS based on:

– local measurements of GAN coverage signal quality;

– user initiated change of operational mode to GERAN/UTRAN preferred or GERAN/UTRAN only;

– reception of a GA-PSR UPLINK QUALITY INDICATION message from the GANC indicating one of the following in the UL Quality Indication IE:

– Radio problem (unacceptable uplink performance).

– Network problem.

– Unknown problem.

Upon experiencing any of these trigger conditions an MS may at any point trigger the PS handover procedure in the source GANC by sending a GA-PSR HANDOVER INFORMATION message.

A GA-PSR HANDOVER INFORMATION message sent by an MS shall include a list of candidate GERAN/UTRAN cells ranked in order of preference based on the most recent lists available from the candidate radio access technologies and including the received signal strength for each identified GERAN or UTRAN cell. The list of candidate cells may include only GERAN cells, only UTRAN cells or both, as permitted by the Handover Reporting Control IE (see sub-clause 11.2.113). If no Handover Reporting Control IE was included in the most recently received GA-RC REGISTER ACCEPT message, there is no restriction on the cells that may be listed. Upon sending this message the MS shall start timer TU4004.

8.14.2 Reception of GA-PSR HANDOVER INFORMATION by the GANC

Upon reception of a GA-PSR HANDOVER INFORMATION message the source GANC triggers PS handover to a GERAN/UTRAN target cell by sending a PS Handover Required message to the SGSN. This results in the allocation of radio resources/RABs in the target cell (see 3GPP TS 43.129 [49]). When the source GANC is informed by the SGSN about the successful allocation of radio resources/RABs in the target cell it responds by sending the MS a GA-PSR HANDOVER COMMAND message. While the PS handover procedure is ongoing but prior to sending the MS a GA-PSR HANDOVER COMMAND message, the GANC may send the MS one or more instances of the GA-PSR HANDOVER CONTINUE message to prevent timer TU4004 from expiring in the MS.

8.14.3 Reception of GA-PSR HANDOVER CONTINUE by the MS

Upon reception of a GA-PSR HANDOVER CONTINUE message from the GANC the MS shall proceed as follows:

– If timer TU4004 is running it shall be restarted.

– If timer TU4004 is not running the MS shall discard the GA-PSR HANDOVER CONTINUE message.

8.14.4 Reception of GA-PSR HANDOVER COMMAND by the MS

The GA-PSR HANDOVER COMMAND message should only indicate a target cell which was reported by the MS in the GA-PSR HANDOVER INFORMATION message.

– For the case of PS handover to a GERAN cell, the GA-PSR Handover Command message shall include the set of PSI or SI messages required for mobile station to operate in the new cell within the PS Handover to GERAN PSI IE or PS Handover to GERAN SI IE (see A/Gb mode to A/Gb mode PS handover described in 3GPP TS 44.060 [45]).

– For the case of PS handover to a GERAN cell the MS shall ignore the value of the Page Mode, Global TFI and Container ID information elements included in the PS HANDOVER COMMAND message carried within the GA-PSR Handover Command message.

– For the case of PS Handover to a GERAN cell, the PS Handover Command message created by the target BSS shall always indicate the PS Handover type as being non-synchronized (see 3GPP TS 44.060 [45]).

Upon reception of a GA-PSR HANDOVER COMMAND message from the GANC the MS shall:

– stop timer TU4004.

– suspend all NAS layer signalling transmissions;

– start the connection establishment to the target BSS/RNC by using the contents of the PS Handover to GERAN Command IE or PS Handover to UTRAN Command IE (included in the GA-PSR HANDOVER COMMAND message) which contains either a PS Handover Command message (see 3GPP TS 44.060 [45]) created by the target BSS (for PS handover to a GERAN cell) or a Handover to UTRAN Command message (see 3GPP TS 25.331 [40]) created by the target RNC (for PS handover to a UTRAN cell). These encapsulated messages carry information about the target cell identifier and radio parameters relevant for the target radio access technology.

8.14.5 Successful completion of the PS Handover from GAN A/Gb mode

From the MS perspective the procedure for PS handover from a GAN A/Gb mode cell is started upon reception of the GA-PSR HANDOVER COMMAND message from the GANC and completed using procedures applicable to the target radio access technology (see Note 1). Upon successfully completing the PS handover from a GAN A/Gb mode cell the MS shall:

– switch to GERAN/UTRAN mode (i.e. switch the serving RR to GSM RR or UTRAN RRC).

– enter GA-RC-REGISTERED state.

– either deregister from GAN A/Gb mode as defined in sub-clause 6.4 or remain in the GA-RC-REGISTERED state but consider the GA-PSR Transport Channel previously used in the GAN A/Gb mode cell as implicitly released.

From the source GANC perspective the procedure for PS handover from a GAN A/Gb mode cell is started upon receiving a GA-PSR HANDOVER INFORMATION message from the MS and deciding to perform PS handover to a GERAN/UTRAN cell. It is completed upon being told by the SGSN to delete the packet flow contexts corresponding to that MS (see Note 2).

From the target BSS/RNC perspective the procedure for PS handover from a GAN A/Gb mode cell is started upon receiving a PS Handover Request message (target BSS) or a Relocation Request message (target RNC) from the SGSN and completed upon receiving confirmation from the MS that it has arrived in the target cell (see Note 1).

NOTE 1: The requirements concerning the establishment of the radio connection towards the target radio access technology and the corresponding signalling procedures are outside of the scope of this specification.

NOTE 2: The target RAT informs the source RAT (e.g. by sending a Forward Relocation Complete message) that PS handover was successful so that the local release of the GA-PSR Transport Channel can be triggered.

8.14.6 Abnormal Cases

If timer TU4004 expires the MS shall either rove-out to GERAN/UTRAN mode or remain in GANA/Gb mode if the conditions that caused the MS to initiate PS handover have been resolved. In the latter case, the MS may subsequently re-initiate PS handover based on the triggering events described in clause 8.14.1.

If the MS is unable to act on the GA-PSR HANDOVER COMMAND message it shall discard it, send the source GANC a GA-PSR HANDOVER FAILURE message and resume normal operation as if the GA-PSR HANDOVER COMMAND message had not been received. The GA-PSR cause value in the GA-PSR HANDOVER FAILURE message shall be set to "PS handover failure – incorrect handover command".

If the MS is able to act on the GA-PSR HANDOVER COMMAND message but is unable to establish the radio connection towards the target radio access technology it shall return to the old cell, send the source GANC a GA-PSR HANDOVER FAILURE message and resume normal operation as if the GA-PSR HANDOVER COMMAND message had not been received. The GA-PSR cause value in the GA-PSR HANDOVER FAILURE message shall be set to "PS handover failure – target RAT access failure".

For the case of PS handover to a GERAN cell, if the GA-PSR Handover Command message does not contain the minimum set of PSI or SI messages required for mobile station to operate in the new cell (see A/Gb mode to A/Gb mode PS handover described in 3GPP TS 44.060 [45]), the MS shall send the source GANC a GA-PSR HANDOVER FAILURE message and resume normal operation as if the GA-PSR HANDOVER COMMAND message had not been received. The GA-PSR cause value in the GA-PSR HANDOVER FAILURE message shall be set to "PS handover failure – missing SI/PSI information".

For the case of PS handover to a GERAN cell, if the PS HANDOVER COMMAND message carried within the GA-PSR Handover Command message does not provide resources for at least one uplink TBF in the new cell, the MS shall send the source GANC a GA-PSR HANDOVER FAILURE message and resume normal operation as if the GA-PSR HANDOVER COMMAND message had not been received. The GA-PSR cause value in the GA-PSR HANDOVER FAILURE message shall be set to "PS handover failure – no uplink TBF allocation".

8.14.7 Reception of GA-PSR HANDOVER FAILURE by the GANC

Upon reception of a GA-PSR HANDOVER FAILURE message from an MS the GANC shall initiate the release of resources in the target radio access technology.