5.2 Inform UE about 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..

5.2.1 General requirements

The following points are considered as requirements for the purpose of these procedures.

1. P-CSCF discovery is performed by requesting P-CSCF address(es) via DHCP method, 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 PMIPv6 based S5 interface, PMIPv6, as specified in 3GPP TS 29.275 [15] is supported by the PDN-GW.

5.2.2 Network recovery information flow – Inform UE at P-CSCF failure

Figure 5.2.2a: P-CSCF failure for DHCP based scenarios

1-2. The UE initiates an IP-CAN session.

3. P-CSCF discovery is performed using DHCP based method. The GGSN/PDN-GW relays/send the list of P-CSCF addresses in DHCP response.

NOTE: The DHCP response can include either a list of P-CSCF IPv4/IPv6 addresses or a list of FQDNs (see IETF RFC 3361 [11] and IETF RFC 3319 [13]). If P-CSCF FQDNs were provided, the UE uses DNS SIP server resolution mechanism (see IETF RFC 3263 [12])

4. The GGSN/PDN-GW sends CCR to request for PCC rules, as specified in 3GPP TS 29.212 [6].

5. The PCRF provides PCC rules to be applied in CCA.

6. The UE performs an initial registration towards the P-CSCF received.

7. The P-CSCF sends Rx Push (see 3GPP TS 29.214 [7]) to provide the PCRF with the P-CSCF selected by the UE,

8. The PCRF sends Rx Push reponse.

9. The PCRF uses a Gx push procedure to provide the GGSN/PDN-GW with the P-CSCF address.

10. 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.

11. The P-CSCF sends 200 OK to the UE.

12. A failure in P-CSCF is detected via Gi/sGi by the GGSN/PDN-GW. The GGSN/PDN-GW informs to all UEs associated to the failed P-CSCF address that the P-CSCF is not available.

13. The UEs acknowledge the request.

14. The UE requests P-CSCF addresses (if needed) via new DHCP request.

15. The UE selects a new P-CSCF and initiates an initial IMS registration.

5.2.3 Network recovery information flow – Inform UE at P-CSCF failure with S5 PMIP

Figure 5.2.3-1: P-CSCF failure for DHCP based scenarios with S5 PMIP

1 ~ 11. Same as figure 5.2.2a step 1 ~ 11

12. A failure in P-CSCF is detected via Gi/sGi by the GGSN/PDN-GW. The GGSN/PDN-GW informs to all UEs associated to the failed P-CSCF address that the P-CSCF is not available.

– 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 RFC 7077 [16]. The PCO contains a P-CSCF failure Indicator. The Notification reason shall indicate that there is a P-CSCF failure.

– If the SGW supports the PMIP Update Notification message, it shall send Update Bearer Request message with the P-CSCF failure Indicator in the PCO to the MME 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].

– If the PGW knows the SGW does not support the PMIP Update Notification procedure, the PGW may release the PMIP binding with cause code "Reactivation Requested".

13 ~ 15. Same as figure 5.2.2a step 13 ~15.

5.3 Network recovery information flow – UE uses keep alive mechanism

Figure 5.3a: P-CSCF failure detected by UE

1. After establishment of an IP-CAN session and acquiring P-CSCF addresses, the UE performs initial registration towards a P-CSCF.

2. If registration is successful, the UE monitors the P-CSCF health according to IETF RFC 6223 [14]

3. When a failure is detected, the UE acquires new P-CSCF addresses (if needed) and performs an initial registration.