9.16 GA-RRC Packet Transport Channel Management Procedures

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

The GA-RRC Packet Transport Channel (GA-RRC PTC) provides the association between the MS and the network for the transport of PS domain user data over the Up interface in GAN Iu mode.

The endpoint addresses of the PTC are identified by the IP addresses and UDP ports assigned to the PTC in the MS and GANC during the PTC activation procedure. The GA-RRC PTC is strictly limited to operating over the Up interface and as such all downlink GA-RRC messages sent by the GANC shall terminate at the MS and all uplink GA-RRC messages sent by the MS shall terminate at the GANC.

Multiple PTC instances between a MS and the GANC may be activated at the same time, using the same endpoint addresses. Each PTC instance is assigned unique GA-RRC Tunnel Endpoint IDs (one on the MS and one on the GANC) during the activation procedure.

The MS and GANC manage the activation and deactivation of the PTC instances based on the requests for RAB assignment from the SGSN and the configurable PTC Timer.

9.16.1 States of the GA-RRC Packet Transport Channel

The PS domain GA-RRC sublayer entity in the MS when in the GA-RRC-CONNECTED state can be in one of two PTC substates for each PTC: PTC-INACTIVE or PTC-ACTIVE.

– PTC-INACTIVE: This is the initial/default PTC substate of the PS domain GA-RRC sublayer entity in the MS when in the GA-RRC-CONNECTED state in GAN Iu mode. The MS is not able to send or receive PS domain user data to or from the network using the PTC. The PTC must be activated before domain user data can be transferred via the PTC. When the PTC has been successfully activated between the MS and the GANC, the PS domain GA-RRC sublayer entity in the MS transitions to the PTC-ACTIVE substate for this PTC.

– PTC-ACTIVE: The PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state for this PTC and the PTC is active between the MS and the GANC and the MS is able to send and receive PS domain user data to and from the GANC.

The following are the possible triggers for GA-RRC PTC activation:

– The GANC initiates PTC activation when the GANC receives the RAB Assignment message from the SGSN; i.e., the MS receives a GA-RRC ACTIVATE CHANNEL message from the GANC;

– The GANC initiates PTC activation when the GANC receives the Relocation Request message from the SGSN; i.e., the MS receives a GA-RRC RELOCATION REQUEST message from the GANC including PTC information.

On successful PTC activation and in parallel with transition to the PTC-ACTIVE substate, the MS starts the PTC Timer for this PTC. When the PTC Timer expires, the MS sends a message to the GANC to initiate PTC deactivation, as defined in clause 9.16.4. On successful PTC deactivation, the MS transitions to the PTC-INACTIVE substate for this PTC.

At any time while the PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-ACTIVE substate, the MS may receive the GA-RRC DEACTIVATE CHANNEL message for this PTC. The MS de-activates the PTC and transitions to the PTC-INACTIVE substate.

At any time while the PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-ACTIVE substate, the MS may receive the GA-RRC RELEASE message indicating the PS domain. In addition to requesting release of the PS GA-RRC connection, this is interpreted by the MS as an implicit PTC de-activation command; i.e. all active PTCs are deactivated.

At any time while in GAN Iu mode, if the serving RR entity is switched to GSM-RR, UTRAN RRC or E-UTRAN RRC, the PS domain GA-RRC sublayer entity in the MS is disconnected from the GPRS SAPs and the MS enters GERAN/UTRAN/E-UTRAN mode. Simultaneously, the MS shall de-activate the associated PTC(s) regardless of the PTC Timer status for these PTC(s).

The PS domain GA-RRC sublayer entity in the MS maintains one PTC for each active PDP context. The PTC Timer is restarted whenever any uplink user data packet is sent or downlink user data packet is received related to the PDP context.

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

9.16.2 PTC Activation

9.16.2.1 PTC Activation when GANC receives RAB Assignment Request

The following figure depicts the Packet Transport Channel activation procedure when the GANC receives the RAB Assignment Request message from the SGSN, assuming the PS domain GA-RRC sublayer entity in MS is in the GA-RRC-IDLE state. If the PS domain GA-RRC sublayer entity in MS is already in the GA-RRC-CONNECTED state, step 1 is skipped.

Figure 59: PTC activation based on RAB Assignment Request

1. The GA-RRC Connection Establishment procedure is performed as described in clause 9.7. The PS domain GA-RRC sublayer entity in the MS transitions to the GA-RRC-CONNECTED state and the PTC-INACTIVE substate.

2. Additional PS signalling procedures are performed; e.g., to initiate PDP context activation.

3. The SGSN initiates the RAB Assignment procedure and includes the RAB ID, the CN Transport Layer Address (IP address) and the CN Iu Transport Association (GTP-U Tunnel Endpoint Identifier, TEID) for user data. Note that the SGSN may initiate the activation of multiple RABs via a single RAB Assignment Request message; in this case, the SGSN sends the above parameters for each RAB to the GANC.

4. The GANC sends the GA-RRC ACTIVATE CHANNEL message to the MS to request activation of the Packet Transport Channel(s). The message includes the CN Domain ID, RAB ID, a TEID that the GANC assigns to the MS for downlink data transfer, the GANC PTC IP Address (i.e., the destination address for PTC GA-RRC PDU messages from the MS) and the GANC TEID assigned by the GANC for uplink data transfer, for each of the RABs.

5. The MS acknowledges the activation of the PTC(s).

6. The GANC signals the completion of the RAB establishment to the MS with the GA-RRC ACTIVATE CHANNEL COMPLETE message. On receipt of the message, the PS domain GA-RRC sublayer entity in the MS transitions to the PTC-ACTIVE substate for each PTC and starts the PTC Timer for each PTC.

7. The GANC sends the RAB Assignment Response message to the SGSN to complete the RAB Assignment procedure. The GANC includes the RAB ID, the RAN Transport Layer Address (i.e., the GANC’s Iu-PS IP address) and the RAN Iu Transport Association (i.e., the TEID that the GANC assigned to the MS).

8. Additional PS signalling procedures are performed; e.g., to complete the PDP context activation.

9. The MS transfers uplink user data by sending a GA-RRC PDU message to the GANC PTC IP address received in step 4. The message includes the GANC TEID received in step 4, which allows the GANC to relay the GA-RRC PDU message payload using the correct GTP-U tunnel on the Iu-PS interface. The GANC relays the message payload to the SGSN in the Iu-PS G-PDU message.

10. The SGSN transfers downlink user data by sending a Iu-PS G-PDU message to the GANC Iu-PS IP address received in step 7. The message includes the MS TEID received in step 7, which allows the GANC to relay the Iu-PS G-PDU message payload using the correct PTC on the Up interface. The GANC relays the message payload to the MS in the GA-RRC PDU message.

9.16.2.2 PTC Activation when GANC receives Relocation Request

The following figure depicts the Packet Transport Channel activation procedure when the GANC receives the Relocation Request message from the SGSN.

Figure 59a: PTC activation based on Relocation Request

1. The MS has successfully registered with the GANC. The MS, GANC and SGSN perform signalling procedures related to PS handover, as described in sub-clause 9.23.

2. The SGSN sends the Relocation Request message to the GANC and includes the RAB ID, the CN Transport Layer Address (IP address) and the CN Iu Transport Association (GTP-U Tunnel Endpoint Identifier, TEID) for user data. Note that the SGSN may request the relocation of multiple RABs via a single Relocation Request message; in this case, the SGSN sends the above parameters for each RAB to the GANC.

3. The GANC sends the GA-RRC RELOCATION REQUEST message to the MS to request activation of the Packet Transport Channel(s) for PS handover purposes. The message includes the RAB ID, a TEID that the GANC assigns to the MS for downlink data transfer, the GANC PTC IP Address (i.e., the destination address for PTC GA-RRC PDU messages from the MS) and the GANC TEID assigned by the GANC for uplink data transfer, for each of the RABs.

4. The MS acknowledges the activation of the PTC(s) in the GA-RRC RELOCATION REQUEST ACK message. The PS domain GA-RRC sublayer entity in the MS transitions to the GA-RRC-CONNECTED state and the PTC-ACTIVE substate for each PTC and starts the PTC Timer for each PTC.

5. The GANC sends the Relocation Request Ack message to the SGSN to complete the handover preparation procedure. The GANC includes the RAB ID, the RAN Transport Layer Address (i.e., the GANC’s Iu-PS IP address) and the RAN Iu Transport Association (i.e., the TEID that the GANC assigned to the MS) for each RAB.

6. PS handover is performed, as described in sub-clause 9.23.

7. The MS transfers uplink user data by sending a GA-RRC PDU message to the GANC PTC IP address received in step 3. The message includes the GANC TEID received in step 3, which allows the GANC to relay the GA-RRC PDU message payload using the correct GTP-U tunnel on the Iu-PS interface. The GANC relays the message payload to the SGSN in the Iu-PS G-PDU message.

8. The SGSN transfers downlink user data by sending a Iu-PS G-PDU message to the GANC Iu-PS IP address received in step 5. The message includes the MS TEID received in step 5, which allows the GANC to relay the Iu-PS G-PDU message payload using the correct PTC on the Up interface. The GANC relays the message payload to the MS in the GA-RRC PDU message.

9.16.3 PTC Data transfer

The following figure illustrates the transfer of GPRS user data packets via the GAN Packet Transport Channel.

Figure 60: PTC Data Transfer

1. If required, the GA-RRC PTC is activated as specified in clause 9.16.2. Upon the GA-RRC PTC activation, the PS domain GA-RRC sublayer entity in the MS enters the PTC-ACTIVE substate and starts the PTC Timer.

2. The MS transfers uplink user data by sending a GA-RRC PDU message to the GANC and restarts the PTC Timer. The GANC relays the message payload to the SGSN in the Iu-PS G-PDU message.

3. The SGSN transfers downlink user data by sending a Iu-PS G-PDU message to the GANC. The GANC relays the message payload to the MS in the GA-RRC PDU message. On receipt of the message, the PS domain GA-RRC sublayer entity in the MS restarts the PTC Timer.

9.16.4 MS initiated PTC De-activation

The following figure depicts the scenario when the MS initiates the de-activation of a Packet Transport Channel after the PTC Timer for that PTC expires.

Figure 61: MS initiated PTC de-activation

The PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-ACTIVE substate.

1. The PTC Timer associated with one of the active PTCs expires.

2. The MS sends the GA-RRC DEACTIVATE CHANNEL REQUEST message to the GANC, including the CN Domain ID, the RAB ID to identify the PTC and indicating the normal release as a cause for deactivation.

3. The GANC sends a RAB Release Request message to the SGSN to request the release of the associated RAB. Note that the GANC may also initiate Iu Release in this case, based on local policy settings.

4. The SGSN responds with the RAB Assignment Request indicating release.

5. The GANC sends the GA-RRC DEACTIVATE CHANNEL message to the MS, including the CN Domain ID and the RAB ID.

6. The MS de-activates the PTC, sends the GA-RRC DEACTIVATE CHANNEL COMPLETE message to the GANC and the PS domain GA-RRC sublayer entity in the MS transitions to the PTC-INACTIVE substate for this PTC.

7. The GANC sends the RAB Assignment Response message to notify the SGSN that the RAB Release procedure is complete.

9.16.5 MS initiated PTC Re-activation

The following figure depicts the scenario when the MS initiates re-activation of the Packet Transport Channel while the PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED and the MS is in the PMM-CONNECTED state; e.g., a PS signalling connection and active PDP context exists between the MS and CN but the PTC was previously de-activated by the MS due to PTC Timer expiry.

Figure 62: MS initiated PTC re-activation

The PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-INACTIVE substate. The MS is in the PMM-CONNECTED state (i.e., a PS signalling connection and an active PDP context exists).

1. The MS has a PDU to send. The MS sends the Service Request message (with Service type value "Data") to the GANC in the GA-RRC UL DIRECT TRANSFER message.

2. The GANC forwards the Service Request over the existing signalling connection to the SGSN using the RANAP Direct Transfer message.

3. The SGSN normally initiates the Security Mode Control procedure described in clause 9.8.

4. The SGSN responds with a Service Accept message.

5. The GANC forwards the message to the MS.

6. The MS, GANC and SGSN perform the RAB assignment and the PTC activation as described in steps 3-7 in clause 9.16.2.1.

7. The MS transfers the uplink user data by sending a GA-RRC PDU message to the GANC and starts the PTC Timer. The GANC relays the message to the SGSN in the Iu-PS G-PDU message. Additional data transfer may take place.

9.16.6 Network initiated PTC De-activation

The following figure depicts the scenario when the network initiates de-activation of one or more Packet Transport Channel(s).

Figure 63: Network initiated PTC de-activation

The PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-ACTIVE substate for one or more PTCs.

1. Optionally, the GANC may initiate the PTC de-activation procedure; e.g., as a result of an error handling procedure. If so, the GANC sends the RAB Release Request message to the SGSN.

2. The SGSN sends a RAB Assignment Request to request the release of the associated RAB(s). The release request may include one or more RABs.

3. The GANC requests deactivation of the associated GA-RRC PTC(s) by sending the GA-RRC DEACTIVATE CHANNEL message to the MS, including the CN Domain ID and RAB ID(s).

4. The MS de-activates the PTC(s), sends the GA-RRC DEACTIVATE CHANNEL COMPLETE message to the GANC and transitions to the PTC-INACTIVE substate for the PTC(s).

5. The GANC sends the RAB Assignment Response message to notify the SGSN that the RAB Release procedure is complete.

9.16.7 Network initiated PTC Re-activation

9.16.7.1 Active PDP Context, PS Signalling Connection Exists

The following figure depicts the scenario when the network initiates re-activation of the GA-RRC PTC while the PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED and the MS is in the PMM-CONNECTED state; e.g., a PS signalling connection and active PDP context exists between the MS and CN but the associated PTC was previously de-activated.

Figure 64: Network initiated PTC re-activation, scenario 1

The PS domain GA-RRC sublayer entity in the MS is in the GA-RRC-CONNECTED state and the PTC-INACTIVE substate. The MS is in the PMM-CONNECTED state (i.e., a PS signalling connection and an active PDP context exists).

1. The SGSN has a PDU to send to the MS. The SGSN may optionally initiate the Security Mode Control procedure described in clause 9.8.

2. The MS, GANC and SGSN perform the RAB assignment and PTC activation as described in steps 3-7 in clause 9.16.2.1.

3. The SGSN sends the downlink PDU. Additional data transfer may take place.

9.16.7.2 Active PDP Context, No PS Signalling Connection

The following figure depicts the scenario when the network initiates re-activation of the Packet Transport Channel while the MS is in the PMM-CONNECTED state; e.g., no PS signalling connection exists but an active PDP context exists between the MS and CN.

Figure 65: Network initiated PTC re-activation, scenario 2

Initially, the SGSN receives downlink user data to transfer to the MS and the Iu connection is not established. The MS is in the PMM-CONNECTED state.

1. The SGSN sends the RANAP Paging message to the MS via the GANC to locate the user. The paging request indicates paging for PS Domain signalling.

2. The GANC forwards the paging information to the MS in the GA-RRC PAGING REQUEST message.

3. The MS responds with a GA-RRC INITIAL DIRECT TRANSFER message. The PS domain GA-RRC sublayer entity in the MS transitions to the GA-RRC-CONNECTED state.

4. The GANC establishes an SCCP connection to the SGSN and forwards the Service Request message (with Service type value "Paging response") to the SGSN using the RANAP Initial UE Message. Subsequent NAS messages between the MS and core network will be sent between GANC and SGSN using the RANAP Direct Transfer message.

5. The SGSN may optionally authenticate the MS using standard UTRAN authentication procedures.

6. The SGSN normally initiates the Security Mode Control procedure described in clause 9.8.

7. The MS, GANC and SGSN perform the RAB assignment and the GA-RRC PTC activation as described in steps 3-7 in clause 9.16.2.1.

8. The MS and SGSN exchange user data transfer via the established PTC as defined in clause 9.16.3.

9.16.8 Implicit PTC De-activation due to MS De-registration

As part of the GAN de-registration procedure, the GANC needs to release all resources allocated to the MS. GAN de-registration may be initiated either explicitly by the MS or implicitly by the GANC if the loss of the signalling connection is detected (as described in clause 9.4.2).

Figure 66: Implicit PTC deactivation

Initially, the PS domain GA-RRC sublayer entity in the MS is in the PTC-ACTIVE substate for one or more GA-RRC PTCs associated with the MS.

1. The GAN de-registration procedure is initiated for the MS either by the MS or GANC.

2. Optionally, any outstanding resources associated with the CS Domain are released.

3. Optionally, if there are any outstanding resources associated with the PS Domain, the GANC initiates the Iu release procedure to the SGSN to release the corresponding RABs.

4. The SGSN reponds with Iu Release Command.

5. Upon receiving the Iu Release Command, the GANC implicitly de-activates (i.e., locally) all associated PTCs and…

6. …responds to the SGSN with an Iu Release Complete message.

9.16.9 PTC Modification

The GANC may initiate the packet transport channel (PTC) modification procedure when it determines that one or more active PTCs require modification; e.g., based on information received from the SGSN in the RAB Assignment Request message or based on local GANC logic. For example, the GANC may initiate this procedure if it detects "packet loss" and handover to GERAN/UTRAN is not possible or desired. CS channel modification and PTC modification use the same messages and the same basic message flows, but differ in the content of the messages.

The GANC may modify the following PTC parameters:

– RAB Configuration

– GANC TEID

– MS TEID

– GANC UDP Port

– GANC IP Address

Figure 66a: PTC Modification

1. One or more PTC(s) are activated as described in sub-clause 9.16.2.

2. The GANC sends the GA-RRC MODIFY CHANNEL message to the MS to modify parameters for one or more
of the activated PTCs.

3. The MS responds with the GA-RRC MODIFY CHANNEL ACKNOWLEDGE message to the GANC.