5.7 Handover and Tracking area Update Procedures for PMIP-based S5/S8 Interface

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

5.7.0 Intra-LTE TAU and Inter-eNodeB Handover without Serving GW Relocation

This clause contains the procedure steps that vary between the GTP and PMIP variant of S5 and S8 for the TAU with MME without Serving GW change procedure defined in TS 23.401 [4], clause 5.3.3.2 as well as Inter-eNodeB Handover without Servig GW change procedures as described in TS 23.401 [4], clauses 5.5.1.1.2 and 5.5.1.2.2.

The procedure is shown in Figure 5.7.2-1. The parameters to be provided to the PGW, as described in TS 23.401 [4], are sent by the Serving GW via the PCRF to the PGW.

5.7.1 Intra-LTE TAU and Inter-eNodeB Handover with Serving GW Relocation

This clause contains the procedure steps that vary between the GTP and PMIP variant of S5 and S8 for the TAU with MME and Serving GW change procedure defined in TS 23.401 [4], clause 5.3.3.1 as well as Inter-eNodeB Handover with CN Node Relocation described in TS 23.401 [4], clause 5.5.1.2.

In case of a Serving GW relocation, the target Serving GW must establish a Gateway Control Session with the PCRF to perform policy controlled functions such as Bearer-Binding. The source Serving GW relinquishes its Gateway Control Session with the PCRF in step B.

Figure 5.7.1-1: Intra-LTE and Inter-eNodeB Handover with Serving GW Relocation

This procedure concerns both the non-roaming (S5) as in Figure 4.2.1-1 and roaming case (S8) as in Figure 4.2.1-2. In the roaming case, the vPCRF in the VPLMN forwards messages between the Serving GW and the hPCRF in the HPLMN. In the case of Local Breakout as in Figure 4.2.3-4, the vPCRF also forwards messages sent between the PDN GW and the hPCRF. In the non-roaming case, the vPCRF is not involved at all.

The optional interaction steps between the gateways and the PCRF in the procedures in Figure 5.7.1-1 only occur if dynamic policy provisioning is deployed. Otherwise policy may be statically configured with the gateway.

A.1) The Target Serving GW initiates the Gateway Control Session Establishment Procedure with the PCRF as specified in TS 23.203 [19]. As part of the procedure the Serving GW informs the PCRF of the RAT type, UE Location Information IE and the user CSG information, if available. The PCRF sends information to the Serving GW enabling bearer binding and other behaviour. The Target Serving GW checks whether the QoS rules provided by the PCRF aligns with the TFT and Bearer Level QoS of the EPS bearer contexts. If there is a mismatch, the Target Serving GW initiates appropriate EPS bearer procedures.

NOTE 1: The Target Serving GW preserves the Bearer Binding that have already been established by the Source Serving GW. To enable this the EPS Bearer ID, TFT is transferred before Step A as follows: across S10 in Forward Relocation Request and across S11 in Create Session Request. The Event Triggers indicate to the Serving GW under what conditions to report events to the PCRF.

NOTE 2: The PCRF provides to the Target Serving GW the QoS rules which were active at the Source Serving GW before the handover. Any change of the QoS rules is performed via an additional QoS Rule Provision Procedure after the handover.

A.2) The PCRF may update the PCC rules at the PDN GW by initiating the PCC Rules Provision Procedure as specified in TS 23.203 [19]. The PCRF also notifies the PDN GW of the UE Location Information IE and user CSG information (if this has been received from the Serving GW preceding step A.1).

A.3) The new Serving GW performs a PMIPv6 Proxy Binding Update (MN NAI, Lifetime, Access Technology Type option, APN, GRE key for downlink traffic, Additional Parameters) message in order to re-establish the user plane as a result of the Serving GW relocation. The MN NAI identifies the UE for whom the message is being sent. Within Access Technology Type option an indication for RAT (E-UTRAN) type is set; an indication for handover between MAGs for the same interface is also set. If multiple PDN connections for the given APN are supported by the Serving GW then the APN and the EPS bearer identity of the default bearer disambiguates which PDN connection this message refers to, otherwise the APN itself identifies the PDN connection of the UE. The additional parameters may include protocol configuration options and other information.

A.4) The PDN GW acknowledges the Binding Update by sending a Proxy Binding Ack (MN NAI, Lifetime, UE Address Info, GRE key for uplink traffic, Charging ID, Additional Parameters) message to the Serving GW. If the EPS bearer identity is included in the Proxy Binding Update, the PDN GW shall acknowledge if multiple PDN connections to the given APN are supported. A PMIP tunnel is established at this point between the PDN GW and the Serving GW. The UE Address Info includes one or more IP addresses. The Additional Parameters may contain protocol configuration options and other information. The Charging Id provided is the Charging Id previously assigned to the PDN connection.

A.5) If the Serving GW is relocated, the PDN GW shall send End Marker Indication message to the source SGW immediately after switching the path. If the source Serving GW has downlink user plane established, the source Serving GW shall send one or more "end marker" packets to the source eNodeB immediately after receiving this indication in order to assist the reordering function in the target eNodeB. Otherwise the souce Serving GW shall ignore the message and shall not send Downlink Data Notification.

Editor’s note: The protocol detail of "End Marker Indication" is FFS and is to be studied in CT WG4.

NOTE 3: The Serving GW learns from the PBA whether the PDN GW supports multiple PDN connections to the same APN or not.

Steps between A.4 and B.1 are described in TS 23.401 [4], clauses 5.3.3.1 and 5.5.1.

B.1) The old Serving GW initiates the Gateway Control Session Termination Procedure with the PCRF as specified in TS 23.203 [19]. The Serving GW ceases to perform Bearer Binding and associated policy controlled functions.

Procedures on the MME for X2 and S1 handover are described in clause 5.5 of TS 23.401 [4]. If the MME receives a rejection to an S1 interface procedure (e.g. EPS bearer(s) request) from the eNodeB with an indication that an X2/S1 handover is in progress and if during the handover procedure the MME detects that the Serving GW or/and the MME needs be relocated, the MME rejects any EPS bearer(s) request received since handover procedure started and includes an indication that the request has been temporarily rejected due to handover procedure in progress.

For PMIP based S5/S8, if dynamic PCC is deployed and with Serving GW relocation, when the Source Serving GW receives an indication from the MME that the PCRF initiated dedicated bearer procedure was temporarily rejected due to handover, the Source Serving GW starts a locally configured guard timer. The Source Serving GW shall re-attempt, up to a pre-configured number of times, at expiry of the guard timer or abort the procedure if it determines that Serving GW is relocated based on receiving the Delete Session request message from the MME.

5.7.2 TAU/RAU or Handover between GERAN A/Gb Mode or UTRAN Iu Mode and E-UTRAN

In case of inter-RAT TAU/RAU or handovers, the Serving GW may or may not be relocated. The PMIP based S5/S8 variants procedure steps for inter-RAT TAU/RAU or handover without Serving GW relocation are shown in Figure 5.7.2-1 and those corresponding to a change of Serving GW are shown in Figure 5.7.2-2.

The procedures in this clause correspond to the following Figures in TS 23.401 [4]:

– Figure 5.3.3.2-1 [UTRAN Iu mode to E-UTRAN] Tracking Area Update.

– Figure 5.3.3.3-1E-UTRAN to UTRAN/GERAN RA Update.

– Figure 5.3.3.6-1 E-UTRAN to GERAN A/Gb mode Routeing Area Update.

– Figure 5.5.2.1.3-1: E-UTRAN to UTRAN Iu mode Inter RAT HO, execution phase.

– Figure 5.5.2.2.3-1: UTRAN Iu mode to E-UTRAN Inter RAT HO, execution phase.

– Figure 5.5.2.3.3-1: E-UTRAN to GERAN A/Gb mode Inter RAT HO, execution phase.

– Figure 5.5.2.4.3-1: GERAN A/Gb mode to E-UTRAN Inter RAT HO, execution phase.

In TS 23.401 [4], the clauses corresponding to Figure 5.7.2-1 and Figure 5.7.2-2 cover both the case of Serving GW relocation and no Serving GW relocation. In case of no Serving GW relocation, Steps (A) in the above figures are between the un-changed Serving GW and the PCRF and the Steps (B) in those figures do not apply, as shown in Figure 5.7.2-1. In case of Serving GW relocation, Steps (A) in the above figure are between the target Serving GW and the PCRF and the Steps (B) is between the source Serving GW and the PCRF, as shown in Figure 5.7.2-2.

In case of no Serving GW relocation, the S‑GW signals the change of RAT to the PCRF. In addition, if the Serving GW has received the User Location Information IE or the user CSG information from the MME, this information is also sent to the PCRF. If PCC rules provided to the PDN-GW have changed, the PCRF updates these rules at the PDN-GW. The PCRF sends the RAT Type change or User Location Information and user CSG information, if received from the Serving- GW, to the PDN GW.

The user plane already exists between the Serving GW and the PDN GW and remains unchanged. In case of RAU or handover to 2G/3G, user plane routing is assumed to proceed over the S4 interface towards the S2/S3 SGSN. When an inter-RAT TAU occurs, the enhanced packet core may signal this event to the PDN GW, for example to inform the PDN GW of a RAT type change. In the case of a PMIP-based S5 and S8, a Modify Bearer Request is not sent from the Serving GW to the PDN GW. Instead, the PCRF in the HPLMN reports the change of event. The PCRF signals any change in the policy resulting from the event to the PDN GW, provisioning updated policy and charging rules.

In case dynamic PCC is not deployed, a change of RAT type will not be signalled to the PDN GW using PMIP based S5/S8 interfaces, if no change of Serving GW has occurred.

Figure 5.7.2-1: Inter-RAT TAU/RAU or Handover without Serving GW relocation

This procedure applies to the Non-Roaming (Figure 4.2.1-1), Roaming (Figure 4.2.1-2) and Local Breakout (Figure 4.2.3-4) cases. For the Roaming and Local Breakout cases, the vPCRF forwards messages between the Serving GW and the hPCRF. In the Local Breakout case, the vPCRF forwards messages between the PDN GW and the hPCRF.

The optional interaction steps between the gateways and the PCRF in the procedures in Figure 5.7.2-1 only occur if dynamic policy provisioning is deployed. Otherwise policy may be statically configured with the gateway.

A.1) The Serving GW informs the PCRF about the change of RAT type and UE Location Information IE and user CSG information (if this has been received from the MME preceding step A) by initiating the Gateway Control and QoS Policy Rules Request Procedure as specified in TS 23.203 [19].

A.2) The PCRF updates the PCC rules at the PDN GW by initiating the PCC Rules Provision Procedure as specified in TS 23.203 [19] if the PCC rules have changed based on the RAT type reported by the Serving GW in step A.1. Further, the hPCRF notifies the PDN GW of the change in RAT and the UE Location Information IE and user CSG information (if this has been received from the Serving GW preceding step A.1).

Step A.2 may be initiated before A.1 completes.

If dynamic PCC is deployed and during the handover with MME relocation without serving GW relocation, when the Serving GW receives an indication from the MME that the PCRF initiated dedicated bearer procedure was temporarily rejected due to handover, the Serving GW starts a locally configured guard timer. The Serving GW shall re-attempt, up to a pre-configured number of times, when it either detects that the handover is completed or failed using message reception or at expiry of the guard timer.

The following procedure describes inter-RAT TAU/RAU or Handover in the case of Serving Gateway relocation for PMIP-based S5/S8.

Figure 5.7.2-2: Inter-RAT TAU/RAU or Handover with Serving GW Relocation

This procedure concerns both the non-roaming (S5) as in Figure 4.2.1-1 and roaming case (S8) as in Figure 4.2.1-2. In the roaming case, the vPCRF in the VPLMN forwards messages between the Serving GW and the hPCRF in the HPLMN. In the case of Local Breakout as in Figure 4.2.3-4, the vPCRF forwards messages sent between the PDN GW and the hPCRF as well. In the non-roaming case, the vPCRF is not involved at all.

If dynamic policy provisioning is not deployed, the optional steps in the procedure are not applied.

A.1) The Target Serving Gateway initiates a Gateway Control Session Establishment Procedure with the PCRF, as specified in TS 23.203 [19] and informs the PCRF of the new RAT type, UE Location Information IE and user CSG information (if this has been received from the MME preceding step A). The Target Serving GW checks whether the QoS rules provided by the PCRF aligns with the TFT and Bearer Level QoS of the EPS bearer contexts. If there is a mismatch, the Target Serving GW initiates appropriate EPS bearer procedures.

NOTE 1: The PCRF provides to the Target Serving GW the QoS rules which were active at the Source Serving GW before the handover. Any change of the QoS rules is performed via an additional QoS Rule Provision Procedure after the handover.

A.2) The PCRF sends an updated policy to the PDN GW by initiating the Policy and Charging Rules Provision Procedure as specified in TS 23.203 [19]. This contains any effected PCC rules and Event Triggers resulting from the preceding step that may require enforcement or event reporting to be performed by the PDN GW. The UE Location Information IE and user CSG information are also sent to the PDN GW from the PCRF (if this has been received from the Serving GW preceding step A.1).

A.3) The Target Serving GW sends a Proxy Binding Update (MN NAI, Lifetime, Access Technology Type, APN, GRE key for downlink traffic, Additional Parameters) message in order to re-establish the user plane as a result of the Serving GW relocation. The MN NAI identifies the UE for whom the message is being sent. Access Technology Type is set to indicate 3GPP access to EPS; an indication for handover between MAGs for the same interface is also set. If multiple PDN connections for the given APN are supported by the Serving GW then the APN and the EPS bearer identity of the default bearer disambiguates which PDN connection this message refers to, otherwise the APN itself identifies the PDN connection of the UE. The additional parameters may include protocol configuration options and other information.

A.4) The PDN GW acknowledges the Binding Update by sending a Proxy Binding Ack (MN NAI, Lifetime, UE Address Info, GRE key for uplink traffic, Charging ID, Additional Parameters) message to the Target Serving GW. If the EPS bearer identity is included in the Proxy Binding Update the PDN GW shall acknowledge if multiple PDN connections to the given APN are supported. A PMIP tunnel is established at this point between the PDN GW and the Target Serving GW. The UE Address Info includes one or more IP addresses. The Additional Parameters may contain protocol configuration options and other information. The Charging Id provided is the Charging Id previously assigned to the PDN connection.

NOTE 2: The Serving GW learns from the PBA whether the PDN GW supports multiple PDN connections to the same APN or not.

A.5) If the Serving GW is relocated, the PDN GW shall send End Marker Indication message to the source SGW immediately after switching the path. If the source Serving GW has downlink user plane established, the source Serving GW shall send one or more "end marker" packets to the source eNodeB or source S4 SGSN immediately after receiving this indication. Otherwise, the source Serving GW shall ignore the message and shall not send Downlink Data Notification.

Editor’s note: The protocol detail of "End Marker Indication" is FFS and is to be studied in CT WG4.

Steps between A.4 and B.1 are described in the clauses of TS 23.401 [4], containing the figures referenced in Figure 5.7.2-1 above.

B.1) The old Serving GW initiates the Gateway Control Session Termination Procedure with the PCRF, as specified in TS 23.203 [19]. The S‑GW provides information to enable the PCRF to uniquely identify the IP‑CAN session. This results in the removal of the Gateway Control session in S‑GW.