Content for TS 23.380 Word version: 19.0.0

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8.1 General 8.2 PCRF/PCF bypass procedures 8.2.1 General Requirement 8.2.2 Establishment of EPS bearer/QoS flow used for IMS signalling with PCRF/PCF bypassing 8.2.3 IMS MO procedure of PCRF/PCF bypass 8.2.4 IMS MT procedure of PCRF/PCF bypass 8.2.5 Dedicated IMS bearer termination procedure of PCRF/PCF bypass

8 Recovery after PCRF/PCF failure |R19| p. 59

8.1 General p. 59

The following clauses show the requirements and information flows of IMS Restoration Procedures for the PCRF/PCF service interruption in each of the scenarios where they apply.

8.2 PCRF/PCF bypass procedures p. 59

These flows show the procedures performed by the network at PCRF/PCF failure where the QoS procedure can continue without interacting with the PCRF/PCF.

8.2.1 General Requirement p. 59

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

The P-CSCF supports detection of all PCRF/PCF instances failure. Upon detection of such failure, the P-CSCF initiates the PCRF/PCF bypass procedure by transmitting an enhanced H.248 MOD request to the IMS-AGW.
IMS-AGW supports the transmission of RTCP Receiver Report (RR) packets via the EPS bearer/QoS flow for IMS signalling to UE when receiving an enhanced H.248 MOD request from P-CSCF.
PGW-C/SMF supports to establish the EPS bearer/QoS flow for IMS signalling bearer for IMS signalling using locally provisioned PCC policy when detecting that all the PCF/PCRF instances fail.
PGW-C/SMF supports to provision a PDR (containing an application Id to detect RTCP RR packets) and associate it with a URR to request the PGW-U/UPF to report upon detecting the RTCP RR packets, after detecting that all the PCF/PCRF instances fail.
PGW-C/SMF supports to establish the dedicated IMS bearer for IMS media using locally provisioned PCC policy when PGW-U/UPF reports detecting the RTCP/RR packets.
PGW-C/SMF supports to request PGW-U/UPF to report when there is no traffic running on the dedicated bearer for longer than the idle time and initiate bearer termination procedure for the dedicated IMS bearer.

8.2.2 Establishment of EPS bearer/QoS flow used for IMS signalling with PCRF/PCF bypassing p. 60

Before an IMS subscriber initiates an IMS registration procedure on an IMS network, an EPS bearer/QoS flow used for IMS signalling must be established. Figure 8.2.2-1 below illustrates the establishment procedure of EPS bearer/QoS flow for the IMS signalling in the case of all the PCRF/PCF instances failure.

Copy of original 3GPP image for 3GPP TS 23.380, Fig. 8.2.2-1: EPS bearer/QoS flow establishment procedure for IMS signalling of PCRF/PCF bypass

Figure 8.2.2-1: EPS bearer/QoS flow establishment procedure for IMS signalling of PCRF/PCF bypass
(⇒ copy of original 3GPP image)

Step 1-2.

UE A sends a PDN Connectivity Request message or PDU Session Establishment Request to the MME/AMF to request a PDN connection. The MME/AMF allocates a bearer ID and sends a Create Session Request message to the PGW-C/SMF or invokes the Nsmf_PDUSession_CreateSMContext Request to SMF.

Step 3.

The PGW-U/SMF shall provision a PDR containing an application ID to match RTCP RR Packets and associate it with a URR to request the UPF to report upon detecting those packets. If the PGW-C/SMF detects that all the PCRF/PCF instances in the network fail, then it uses local PCC policy to establish an EPS bearer/QoS flow for IMS signalling (QCI/5QI=5) for IMS signalling.

Step 4.

The subsequent procedure of the EPS bearer/QoS flow establishment proceeds.

Step 5.

After the EPS bearer/QoS flow for IMS signalling is established, UE A initiates the initial registration procedure which specified in TS 23.228.

8.2.3 IMS MO procedure of PCRF/PCF bypass p. 60

Figure 8.2.3-1 below illustrates the IMS MO procedure in the case of all the PCRF/PCF instances failure.

Copy of original 3GPP image for 3GPP TS 23.380, Fig. 8.2.3-1: IMS MO procedure of PCRF/PCF bypass

Figure 8.2.3-1: IMS MO procedure of PCRF/PCF bypass
(⇒ copy of original 3GPP image)

Step 1-3.

UE A initiates an initial INVITE request to the P-CSCF to establish an IMS session. The P-CSCF routes the INVITE request to the I-/S-CSCF. Then the I-/S-CSCF returns a 183 response to the P-CSCF.

Step 4-7.

The P-CSCF detects that all the PCRF/PCF instances fail, and starts the PCRF/PCF bypass procedure by sending an enhanced H.248 MOD request to the IMS-AGW. After receiving the enhanced H.248 MOD request, the IMS-AGW sends RTCP RR packets to distinguish with the normal SIP messages to UE A in the EPS bearer/QoS flow for the IMS signalling, and returns an H.248 MOD response to the P-CSCF.

Step 8-9.

The PGW-U/UPF detects the RTCP RR packets and send a PFCP Session Report Request message to the PGW-C/SMF to report the receiving of RTCP RR packets as specified in step 3-5 in clause 8.2.2.

Step 10-12.

The PGW-C/SMF returns a PFCP Session Report Response to the PGW-U/UPF and uses local PCC policy to establish the dedicated IMS bearer for IMS media by sending a PFCP Session Modification request message to provide the relevant PDR and QER corresponding to the dedicated IMS bearer to the PGW-U/UPF. The subsequent procedure of the dedicated IMS bearer establishment proceeds.

Step 13-14.

The P-CSCF sends a183 response to UE A and the subsequent procedure of IMS originating session proceeds.

8.2.4 IMS MT procedure of PCRF/PCF bypass p. 61

Figure 8.2.4-1 below illustrates the IMS terminating session procedure in the case of all the PCRF/PCF instances failure.

Copy of original 3GPP image for 3GPP TS 23.380, Fig. 8.2.4-1: IMS MT procedure of PCRF/PCF bypass

Figure 8.2.4-1: IMS MT procedure of PCRF/PCF bypass
(⇒ copy of original 3GPP image)

Step 1-4.

The I-/S-CSCF in the terminating network receives an incoming INVITE request and routes it to UE B through the P-CSCF. UE B sends a 183 response to the P-CSCF.

Step 5-8.

The P-CSCF detects that all the PCRF/PCF instances fail, and starts the PCRF/PCF bypass procedure by sending an enhanced H.248 MOD request to the IMS-AGW. After receiving the enhanced H.248 MOD request, the IMS-AGW sends RTCP RR packets to distinguish with the normal SIP messages to UE B in the EPS bearer/QoS flow for IMS signalling and returns an H.248 MOD response to the P-CSCF.

Step 9-10.

The PGW-U/UPF detects the RTCP RR packets and sends a PFCP Session Report Request message to the PGW-C/SMF to report the receiving of RTCP RR packets as specified in step 3-5 in clause 8.2.2.

Step 11-12.

The PGW-C/SMF uses local PCC policy to establish the dedicated IMS bearer for IMS media and returns a PFCP Session Report Response to the PGW-U/UPF. The subsequent procedure of the dedicated IMS bearer establishment proceeds.

Step 13-15.

The P-CSCF sends a 183 response to the originating network through the I-/S-CSCF and the subsequent procedure of IMS terminating session proceeds.

8.2.5 Dedicated IMS bearer termination procedure of PCRF/PCF bypass p. 62

When releasing the established IMS session, the normal dedicated IMS bearer termination procedure cannot be performed in the case of all PCRF/PCF instances failure. The SMF/PGW-C needs to request the UPF/PGW-U to report there is no traffic running on the dedicated bearer by provisioning an idle time which is configured by the operator, then the PGW-U/UPF report there is no traffic over the dedicated IMS bearer for longer than the idle time, the PGW-C/SMF initiate bearer termination procedure for the dedicated IMS bearer.