5.1 Update PDP context/Bearer at P-CSCF failure
23.3803GPPIMS Restoration ProceduresRelease 17TS
These flows show the procedures performed by the network at P-CSCF failure after user initiated registration..
5.1.1 General requirements
The following points are considered as requirements for the purpose of these procedures.
1. P-CSCF discovery is performed by requesting and provisioning P-CSCF address(es) within Protocol Configuration Options (PCO), as specified in 3GPP TS 29.061 [9], clause 13a.2.1
2. The UE supports PCO IE, as specified in 3GPP TS 24.008 [4], clause 10.5.6.3.
3. For the GTP based S5 interface, GTPv1, as specified in 3GPP TS 29.060 [8] or GTPv2, as specified in 3GPP TS 29.274 [10] are supported by the GGSN/PDN-GW.
4. For the PMIP based S5 interface, PMIPv6, as specified in 3GPP TS 29.275 [15] is supported by the PDN-GW.
5.1.2 Network recovery information flow – Update PDP context / Bearer
Figure 5.1.2a: P-CSCF failure (new list of P-CSCFs in PCO)
1. The UE initiates an IP-CAN session.
2. P-CSCF discovery is performed. A list of P-CSCF addresses is received in CreatePDPContextResponse / CreateBearerResponse within the PCO IE.
3. The GGSN/PDN-GW sends CCR to request for PCC rules, as specified in 3GPP TS 29.212 [6].
4. The PCRF provides PCC rules to be applied in CCA.
5. The UE performs an initial registration towards a P-CSCF from the received list.
6. The P-CSCF sends Rx Push (see 3GPP TS 29.214 [7]) to provide the PCRF with the P-CSCF selected by the UE.
7. The PCRF sends Rx Push reponse.
8. The PCRF uses a Gx push procedure to provide the GGSN/PDN-GW with the P-CSCF address.
9. The GGSN/PDN-GW stores this address for the UE and sends Gx Push Rsp. Also, the GGSN/PDN-GW starts monitoring the health of the P-CSCF if not already done.
10. The P-CSCF sends 200 OK to the UE.
11. A failure in P-CSCF is detected via Gi/sGi by the GGSN/PDN-GW. The GGSN/PDN-GW sends a new PCO IE with a new list of P-CSCF addresses (which does not include the failed P-CSCF) to all UEs associated to the failed P-CSCF address.
12. The UEs acknowledge the request.
13. Upon receiving the new list of P-CSCFs, if the P-CSCF in use is missing, each UE performs an initial registration towards a new P-CSCF.
5.1.3 Network recovery information flow with S5 PMIP
Figure 5.1.3: P-CSCF failure with S5 PMIP
1 ~ 10. The IMS session is setup as described in clause 5.1.2 except S5 PMIP procedure is used between SGW and PGW.
11. Once a P-CSCF failure is detected via Gi/sGi by the PDN-GW, the PDN-GW shall send a PMIP UPN message (MN ID, APN, PDN connection ID, PCO, and Additional parameters) as specified in 3GPP TS 29.275 [15] and IETF draft-ietf-netext-update-notifications-12 [16]. The PCO contains a new list of P-CSCF address. The Notification reason shall indicate that update Bearer Context at P-CSCF failure is needed.
12. If the SGW supports the PMIP Update Notification message, it shall send Update Bearer Request message with the new list of P-CSCF address in the PCO to the MME/SGSN as part of the PGW initiated bearer modification without QoS update procedure as specified in 3GPP TS 23.401[17].
Once the Update Bearer Response message is received, the SGW shall response with a PMIP UPA message (MN ID, APN, PDN connection ID, PCO, and Additional parameters) as specified in 3GPP TS 29.275 [15] and IETF RFC 7077 [16].
13. If the PGW knows the SGW does not support the PMIP Update Notification procedure, the PGW shall skip step 11 and release the PMIP binding with cause code "Reactivation Requested".
14. Upon receiving the new list of P-CSCFs, the UE may perform an initial registration towards a new P-CSCF.