6.3.1 Updates to procedures specified in TS 23.401 [2]

23.2143GPPArchitecture enhancements for control and user plane separation of EPC nodesRelease 17TS

6.3.1.1 Procedures with PDN connection establishment

This clause defines interactions between the CP and UP function during the following procedures:

– E-UTRAN initial attach (clause 5.3.2.1 of TS 23.401 [2])

– UE requested PDN connectivity (clause 5.10.2 of TS 23.401 [2])

During the above procedures following is the nature of interactions between the CP and UP function:

– The new SGW-C selects a new SGW-U and creates an Sx session.

– The new PGW-C selects a new PGW-U and creates an Sx session.

– The old SGW-C releases the existing Sx session from the old SGW-U.

– The old PGW-C releases the existing Sx session from the old PGW-U.

– The SGW-C modifies the SGW-U to update with the F-TEIDu of the eNodeB and the PGW-U.

Figure 6.3.1.1-1: Interaction between CP and UP function during PDN connection establishment

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

For all the steps below upon receiving a Sx Session Termination Request, the SGW-U or PGW-U releseases all associated resources including the F-TEIDu allocated for the Sx session.

2a. The SGW-C may send an Sx Session Termination Request to the SGW-U to release the Sx session.

2b. The SGW-U sends an Sx Session Termination Response to the SGW-C confirming the release of the Sx session.

3a. The PGW-C may send an Sx Session Termination Request to the PGW-U to release the Sx session.

3b. The PGW-U sends an Sx Session Termination Response to the PGW-C confirming the release of the Sx session.

4. The relevant steps of the procedure as specified in the figure above are executed.

5a. The SGW-C may send an Sx Session Termination Request to the SGW-U to release the Sx session.

5b. The SGW-U sends an Sx Session Termination Response to the SGW-C confirming the release of the Sx session.

6a. The PGW-C may send an Sx Session Termination Request to the PGW-U to release the Sx session.

6b. The PGW-U sends an Sx Session Termination Response to the PGW-C confirming the release of the Sx session.

7. The relevant steps of the procedure as specified in the figure above are executed.

8a. The SGW-C shall select new SGW-U as specified in clause 5.12. The SGW-C sends an Sx Session Establishment Request to the selected SGW-U for creating an Sx session for the UE.

8b. The SGW-U allocates F-TEIDu for the default bearer. The SGW-U sends an Sx Session Establishment Response to the SGW-C confirming the successful creation of the Sx session. It includes the F-TEIDu it has allocated.

9. The relevant steps of the procedure as specified in the figure above are executed.

10a. The PGW-C shall select new PGW-U as specified in clause 5.12. The PGW-C sends an Sx Session Establishment Request to the selected PGW-U for creating an Sx session for the UE.

10b. The PGW-U allocates F-TEIDu for the bearer. The PGW-U sends an Sx Session Establishment Response to the PGW-C confirming the successful creation of the Sx session. It includes the F-TEIDu it has allocated.

11. The relevant steps of the procedure as specified in the figure above are executed.

12a. The SGW-C sends Session Modification Request to the SGW-U. The SGW-C shall include the F-TEIDu of the default bearer received from the PGW.

12b. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the success of the Sx session modification.

13. The relevant steps of the procedure as specified in the figure above are executed.

14a. The SGW-C sends an Sx Session Modification Request to the SGW-U. The SGW-C shall include the F-TEIDu of the default bearer received from the eNodeB.

14b. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the success of the Sx session modification.

15. The relevant steps of the procedure as specified in the figure above are executed.

16a. If the Handover Indication is included in step 15, the PGW-C updates the old PGW-U session corresponding to the non-3GPP access by sending "Sx session modification request" message to the PGW-U (session ID) and instructs the PGW-U to start routing the downlink packets to the SGW/SGW-U.

16b. The PGW-U sends "Sx session modification response" message to the PGW-C.

17. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.2 Procedures with SGW change

6.3.1.2.1 General

This clause covers the following two types of procedures involving SGW change:

– Type 1: Procedures in which only Create Session Request message is sent from MME/SGSN to SGW-C during SGW change.

– Type 2: Procedures in which Create Session Request message followed by Modify Bearer Request message are sent from MME/SGSN to SGW-C during SGW change.

6.3.1.2.2 Type 1

This clause defines interactions between the CP and UP function during the following procedures:

– Tracking Area Update procedure with Serving GW change (clause 5.3.3.1 of TS 23.401 [2]).

– Routing Area Update with MME interaction and with SGW change (clause 5.3.3.6 of TS 23.401 [2]).

– X2-based handover with Serving GW relocation (clause 5.5.1.1.3 of TS 23.401 [2]).

– MME triggered Serving GW relocation (clause 5.10.4 of TS 23.401 [2]).

Editor’s Note: "Tracking Area Update procedure with Serving GW change and data forwarding" (clause 5.3.3.1A of TS 23.401 [2]) is FFS.

During the above procedures following is the nature of interactions between the CP and UP function:

– The new SGW-C selects a new SGW-U and creates an Sx session.

– The PGW-C modifies the PGW-U to update with the F-TEIDu(s) of the new SGW-U.

– The old SGW-C releases the existing Sx session from the old SGW-U.

Figure 6.3.1.2.2-1: Interaction between CP and UP function during procedures with SGW change (Type 1)

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The new SGW-C shall select new SGW-U as specified in clause 5.12. The new SGW-C sends Sx Session Establishment Request to the selected SGW-U for creating an Sx session for the UE.

3. The SGW-U allocates an F-TEIDu for each and every bearer received in the Sx Session Establishment Request. The new SGW-U sends Sx Session Establishment Response to the new SGW-C confirming the successful creation of the Sx session. It includes the F-TEIDu it has allocated for each and every bearer.

4. The relevant steps of the procedure as specified in the figure above are executed.

5. The PGW-C sends an Sx Session Modification Request to the PGW-U. The PGW-C shall include the F-TEIDu(s) of the new SGW-U. Additionally, based on the interaction with the PCRF, the PGW-C may also update other Sx parameters for the PDN connection.

6. The PGW-U sends Sx Session Modification Response to the PGW-C confirming the success of the Sx session modification.

7. The relevant steps of the procedure as specified in the figure above are executed.

8. The old SGW-C sends Sx Session Termination Request to the old SGW-U to release the Sx session.

9. The old SGW-U sends Sx Session Termination Response to the old SGW-C confirming the release of the Sx session.

10. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.2.3 Type 2

This clause defines interactions between the CP and UP function during the following procedures:

– S1-based handover, normal (clause 5.5.1.2.2 of TS 23.401 [2]).

– E-UTRAN to UTRAN Iu mode Inter RAT handover (clause 5.5.2.1 of TS 23.401 [2]).

– UTRAN Iu mode to E-UTRAN Inter RAT handover (clause 5.5.2.2 of TS 23.401 [2]).

– E-UTRAN to GERAN A/Gb mode Inter RAT handover (clause 5.5.2.3 of TS 23.401 [2]).

– GERAN A/Gb mode to E-UTRAN Inter RAT handover (clause 5.5.2.4 of TS 23.401 [2]).

Editor’s Note: Most of the above procedures involve establishment and release of indirect data forwarding tunnel at the source and the target SGW. It is FFS if this needs to be supported in the CP and UP split architecture.

During the above procedures following is the nature of interactions between the CP and UP function:

– The new SGW-C selects a new SGW-U and creates an Sx session.

– The SGW-C modifies the Sx session at SGW-U to update the F-TEIDu(s) of the eNB.

– The PGW-C modifies the PGW-U to update with the F-TEIDu(s) of the new SGW-U.

– The old SGW-C releases the existing Sx session from the old SGW-U.

Figure 6.3.1.2.3-1: Interaction between CP and UP function during procedures with SGW change (Type 2)

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The new SGW-C shall select new SGW-U as specified in clause 5.12. The new SGW-C sends an Sx Session Establishment Request to the selected SGW-U for creating an Sx session for the UE. Usage Monitoring Rules may also be included in case of home-routed roaming scenario and if the inter-operator charging is required.

3. The SGW-U allocates F-TEIDu for each and every bearer received. The new SGW-U sends an Sx Session Establishment Response to the new SGW-C confirming the successful creation of the Sx session. It includes the F-TEIDu it has allocated for each and every bearer.

4. The relevant steps of the procedure as specified in the figure above are executed.

5. The SGW-C sends an Sx Session Modification Request to the SGW-U. It shall include the F-TEIDu of the eNB.

6. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the successful modification of the Sx session.

7. The relevant steps of the procedure as specified in the figure above are executed.

8. The PGW-C sends an Sx Session Modification Request to the PGW-U. The PGW-C shall include the F-TEIDu of the new SGW-U. Additionally, based on the interaction with the PCRF, the PGW-C may also update other Sx parameters for the PDN connection.

9. The PGW-U sends an Sx Session Modification Response to the PGW-C confirming the success of the Sx session modification.

10. The relevant steps of the procedure as specified in the figure above are executed.

11. The old SGW-C sends an Sx Session Termination Request to the old SGW-U to release the Sx session.

12. The old SGW-U sends an Sx Session Termination Response to the old SGW-C confirming the release of the Sx session.

13. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.3 Procedures with eNB F-TEIDu update

In this clause, interactions between the CP and UP function during the following procedures are considered:

– UE triggered Service Request (clause 5.3.4.1 of TS 23.401 [2]).

– Connection Resume procedure (clause 5.3.5A of TS 23.401 [2]).

– E-UTRAN initiated E-RAB modification procedure (clause 5.4.7 of TS 23.401 [2]).

– X2-based handover without Serving GW relocation (clause 5.5.1.1.2 of TS 23.401 [2]).

– S1-based handover without Serving GW change (clause 5.5.1.2.2 of TS 23.401 [2]).

During the above procedures following is the nature of interactions between the CP and UP function:

– The SGW-C modifies the Sx session at SGW-U to update the F-TEIDu(s) of the eNB.

– Based on the interaction with the PCRF, the PGW-C may modify the PGW-U to update other Sx parameters.

Figure 6.3.1.3-1: Interaction between CP and UP function during procedures with eNB F-TEIDu update

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The SGW-C sends an Sx Session Modification Request to the SGW-U. It shall include the new F-TEIDu of the eNB. Additionally, for the following procedures extra steps may apply:

– UE triggered Service Request: If the buffering of the data packets in the idle mode is performed in the SGW-C and if those buffered packets are still valid (e.g. data packets for which the buffering duration hasn’t expired yet), then SGW-C shall also provide those data packets to the SGW-U (as specified in clause 5.12) so that it can be sent to the eNB.

3. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the successful modification of the Sx session.

4. The relevant steps of the procedure as specified in the figure above are executed.

5. Based on the interaction with the PCRF, the PGW-C may update other Sx parameters for the PDN connection. Correspondingly, the PGW-C sends an Sx Session Modification Request to the PGW-U.

6. The PGW-U sends an Sx Session Modification Response to the PGW-C confirming the success of the Sx session modification.

7. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.4 Procedures with release of eNB F-TEIDu

This clause defines interactions between the CP and UP function during the following procedures:

– Connection Suspend procedure (clause 5.3.4A of TS 23.401 [2]).

– S1 release procedure (clause 5.3.5 of TS 23.401 [2]).

During the above procedures following is the nature of interactions between the CP and UP function:

– The SGW-C modifies the SGW-U to release the eNB F-TEIDu. Additionally, the SGW-C configures the SGW-U so that the downlink data packets can be buffered either in the SGW-C or in the SGW-U.

Figure 6.3.1.4-1: Interaction between CP and UP function during procedures with release of eNB F-TEIDu

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The SGW-C sends an Sx Session Modification Request to the SGW-U. It shall indicate the SGW-U to release the eNB F-TEIDu. Additionally, the SGW-C decides if the buffering of the downlink data packets shall be done in CP or the UP function, as specified in clause 5.9) and correspondingly informs the SGW-U for as follows:

– If the downlink data packets are to be buffered in the SGW-C, the SGW-C shall configure the SGW-U to forward the downlink data packets for all the bearers of the UE to the SGW-C, as specified in clause 5.6.

– If the downlink data packets are to be buffered in the SGW-U, the SGW-C shall indicate the same to SGW-U. Additionally, the following applies:

– if the Paging Policy Differentiation feature (as specified in clause 4.9 of TS 23.401 [2]) is supported by the SGW-C and SGW-U and based on operator’s policy if it is required to be activated for this UE, the SGW-C shall include an indication to provide the DSCP in TOS (IPv4) / TC (IPv6) value from the IP header of the first downlink data packet of each bearer.

– if the PDN GW Pause Charging procedure (as specified in clause 5.3.6A of TS 23.401 [2]) is supported by the SGW-C and SGW-U and based on operator’s policy if it is required to be activated for this UE, the SGW-C may provide the number/fraction of packets/bytes drop threshold value. When this threshold is reached, the SGW-U is required to provide an indication to the SGW-C.

3. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the successful modification of the Sx session.

4. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.5 Procedures when downlink data is buffered in the UP function

This clause defines interactions between the CP and UP function when then UE is in idle mode and buffering of the downlink data is performed in the UP function, during the following procedures:

– Network Triggered Service Request (clause 5.3.4.3 of TS 23.401 [2]).

– PDN GW Pause of Charging procedure (clause 5.3.6A of TS 23.401 [2]).

During the above procedures following is the nature of interactions between the CP and UP function:

– The SGW-U notifies the SGW-C that the first downlink data packet was received for a bearer.

NOTE: A bearer is identified in the SGW-U as a combination of PDR(s) and FAR(s).

– The SGW-U notifies the SGW-C that the drop threshold was reached.

Figure 6.3.1.5-1: Interaction between CP and UP when downlink data is buffered in the UP function

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. When the downlink data is received, the SGW-U starts buffering it.

On arrival of the first downlink data packet for a bearer, the SGW-U shall send an Sx report message (first packet indication) to the SGW-C. If the Paging Policy Differentiation feature (as specified in clause 4.9 of TS 23.401 [2]) is supported by the SGW-U and if it is activated by the SGW-C for this Sx session, the SGW-U shall also include the DSCP in TOS (IPv4) / TC (IPv6) value from the IP header of the downlink data packet.

If the SGW-C has provided the number/fraction of packets/bytes drop threshold value during the procedure with release of eNB F-TEIDu (clause 6.3.1.4), the SGW-U shall monitor that threshold. Once the threshold is reached the SGW-U shall send an Sx report message (drop threshold reached) to the SGW-C.

3. The relevant steps of the procedure as specified in the figure above are executed.

4. The SGW-C sends an Sx report Ack message to the SGW-U. Additionally, for the following procedures the following applies:

– Network Triggered Service Request: If DL Buffering Duration time and DL Buffering Suggested Packet Counts were received from the MME/SGSN (refer to clause 5.3.4.3, step  2 of TS 23.401 [2]) by the SGW-C then SGW-C shall include the same in the Sx report Ack message.

5. The relevant steps of the procedure as specified in the figure above are executed.

6.3.1.6 Procedures with release of PDN connection

This clause defines interactions between the CP and UP function during the following procedures:

– UE-initiated Detach procedure for E-UTRAN (clause 5.3.8.2.1 of TS 23.401 [2]).

– UE-initiated Detach procedure for GERAN/UTRAN with ISR activated (clause 5.3.8.2.2 of TS 23.401 [2]).

– MME-initiated Detach procedure (clause 5.3.8.3 of TS 23.401 [2]).

– SGSN-initiated Detach procedure with ISR activated (clause 5.3.8.3A of TS 23.401 [2]).

– HSS-initiated Detach procedure (clause 5.3.8.4 of TS 23.401 [2]).

– UE or MME requested PDN disconnection (clause 5.10.3 of TS 23.401 [2]).

During the above procedures following is the nature of interactions between the CP and UP function:

– The SGW-C terminates the Sx session at the SGW-U.

– The PGW-C terminates the Sx session at the PGW-U.

Figure 6.3.1.6-1: Interaction between CP and UP function during release of PDN connection

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The SGW-C sends an Sx Session Modification Request to the SGW-U. SGW-C shall indicate SGW-U to stop counting uplink packets for the affected bearers. SGW-C shall also indicate the SGW-U to discard uplink packets received from eNodeB for the affected bearers.

3. The SGW-U sends an Sx Session Modification Response to the SGW-C.

4. The relevant steps of the procedure as specified in the figure above are executed.

5. The PGW-C sends an Sx Session Termination Request to the PGW-U.

6. The PGW-U sends an Sx Session Termination Response to the PGW-C confirming the successful termination of the Sx session. Additionally, if the usage reporting is configured by the PGW-C (as specified in clause 5.3.2) the PGW-U shall provide the usage report(s) for the PDN connection (as specified in clause 5.3.3) to the PGW-C.

7. The relevant steps of the procedure as specified in the figure above are executed.

8. The SGW-C sends an Sx Session Termination Request to the SGW-U.

9. The SGW-U sends an Sx Session Termination Response to the SGW-C confirming the successful termination of the Sx session. Additionally, if the usage reporting is configured by the SGW-C (as specified in clause 5.3.2) the SGW-U shall provide the usage report(s) for the PDN connection (as specified in clause 5.3.3) to the SGW-C.

6.3.1.7 Procedures with modification of bearer

This clause defines interactions between the CP and UP function during the following procedures:

– Dedicated bearer activation (clause 5.4.1 of TS 23.401 [2]).

– PDN GW initiated bearer modification with bearer QoS update (clause 5.4.2.1 of TS 23.401 [2]).

– PDN GW initiated bearer modification without bearer QoS update (clause 5.4.3 of TS 23.401 [2]).

– PDN GW initiated bearer deactivation (clause 5.4.4.1 of TS 23.401 [2]).

– HSS Initiated Subscribed QoS Modification (clause 5.4.2.2 of TS 23.401 [2]).

– MME Initiated Dedicated Bearer Deactivation (clause 5.4.4.2 of TS 23.401 [2]).

During the above procedures following is the nature of interactions between the CP and UP function:

– The PGW-C modifies the Sx session at the PGW-U.

– The SGW-C modifies the Sx session at the SGW-U.

Figure 6.3.1.7-1: Interaction between CP and UP function during modification of bearer

1. Procedure as listed in this step is initiated as specified in the relevant clauses of this specification. The relevant steps of the procedure as specified in the figure above are executed.

2. The PGW-C sends an Sx Session Modification Request to the PGW-U. For "Dedicated bearer activation", PGW-C indicates PGW-U to allocate F-TEID for the new dedicated bearer. For "PGW/MME initiated bearer deactivation procedure", PGW-C shall indicate PGW-U to stop counting and stop forwarding downlink packets for the affected bearer(s).

3. The PGW-U sends an Sx Session Modification Response to the PGW-C confirming the successful modification of the Sx session.

4. The relevant steps of the procedure as specified in the figure above are executed.

5. The SGW-C may send an Sx Session Modification Request to the SGW-U. For "Dedicated bearer activation", SGW-C indicates SGW-U to allocate F-TEID for the new dedicated bearer.

6. The SGW-U sends an Sx Session Modification Response to the SGW-C confirming the successful modification of the Sx session.

7. The relevant steps of the procedure as specified in the figure above are executed.

8. The SGW-C sends an Sx Session Modification Request to the SGW-U. For dedicated bearer activation procedure, the SGW-C shall include the F-TEIDu of the activated bearer received from the eNodeB. For PDN GW/HSS initiated bearer modification with bearer QoS update procedure, SGW-C provides updated QoS parameters to SGW-U. For PDN GW/MME initiated bearer deactivation procedure, SGW-C shall indicate SGW-U to remove the PDR(s) for the affected bearer(s).

If the default bearer belonging to a PDN connection is deactivated, the SGW-C sends an Sx Session Termination Request to the SGW-U.

9. The SGW-U sends an Sx Session Modification Response or an Sx Session Termination Response to the SGW-C confirming the successful modification or termination of the Sx session.

10. The relevant steps of the procedure as specified in the figure above are executed.

11. The PGW-C sends an Sx Session Modification Request to the PGW-U. For dedicated bearer activation procedure, the PGW-C shall include the F-TEIDu of the activated bearer received from the SGW. For PDN GW/HSS initiated bearer modification with bearer QoS update procedure, PGW-C provides updates according to the changed QoS parameters and TFT (if applicable) to PGW-U. For "PDN GW initiated bearer modification without bearer QoS update" procedure, PGW-C provides updates according to the changed APN-AMBR and/or TFT to PGW-U. For PDN GW/MME initiated bearer deactivation procedure, PGW-C shall indicate PGW-U to remove the PDR(s) for the affected bearer(s).

If the default bearer belonging to a PDN connection is deactivated, the PGW-C sends an Sx Session Termination Request to the PGW-U.

12. The PGW-U sends an Sx Session Modification Response or an Sx Session Termination Response to the PGW-C confirming the successful modification or termination of the Sx session.

13. The relevant steps of the procedure as specified in the figure above are executed.