7.2 IP‑CAN Session Establishment

23.2033GPPPolicy and charging control architectureRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

This clause describes the signalling flow for IP‑CAN Session establishment as well as network prefix and/or IP address assignment to the UE. The AF is not involved.

Figure 7.2-1: IP‑CAN Session Establishment

This procedure concerns both roaming and non-roaming scenarios. In the roaming case when a Gateway Control Session is used, the V-PCRF should proxy the Gateway Control Session Establishment information between the BBERF in the VPLMN and the H-PCRF over S9 based on PDN-Id and roaming agreements.

For the Local Breakout scenario (Figure 5.1-4) the V-PCRF shall proxy the Indication and Acknowledge of IP‑CAN Session Establishment over S9 between the PCEF in the VPLMN and the H-PCRF. For TDF and solicited application reporting, the V-PCRF shall generate ADC rules from PCC Rules containing application detection and control information as instructed by the H-PCRF over S9. Then, the V-PCRF shall install PCC Rules to the PCEF and ADC Rules to the TDF, if applicable.

In the non-roaming case (Figure 5.1-1) the V-PCRF is not involved.

1. The BBERF initiates a Gateway Control Session Establishment procedure as defined in clause 7.7.1 (applicable to case 2a during initial attach and case 2b, as defined in clause 7.1).

2. The GW (PCEF) receives a request for IP‑CAN Bearer establishment. A PDN Connection Identifier may be included in the request. The GW (PCEF) accepts the request and assigns an IP address and (if requested) network prefix for the user.

3. The PCEF determines that the PCC authorization is required, requests the authorization of allowed service(s) and PCC Rules information. The PCEF includes the following information: UE Identity (e.g. MN NAI), a PDN identifier (e.g. APN), the IP‑CAN type and the IPv4 address and IPv6 network prefix, if available, the PDN Connection Identifier received for IP‑CAN Bearer establishment if multiple PDN connections to the same APN are supported and, if available, the default charging method and the IP‑CAN bearer establishment modes supported and information on whether PCEF is enhanced with ADC. It may also include the TDF IP address, in case of solicited application reporting, if applicable. If the UE has declared support for the extended TFT filter format and the PCEF does not prevent the use thereof, then the PCEF shall indicate that support to the PCRF. The PDN identifier, IP address(es) and UE identity enables identification of the IP‑CAN session. The IP‑CAN Type identifies the type of access from which the IP‑CAN session is established. If the service data flow is tunnelled at the BBERF, the PCEF shall provide information about the mobility protocol tunnelling encapsulation header. The PCEF may also include the Default Bearer QoS and APN-AMBR (applicable to case 1 and case 2a, as defined in clause 7.1). In case 2a the PCEF may also include charging ID information. If the GW/PCEF allocates a shorter IPv6 prefix for use with IPv6 Prefix Delegation, the GW/PCEF provides this shorter prefix as the IPv6 network prefix. If Charging Characteristics were received by GW/PCEF according to TS 23.401 [17] and TS 23.402 [18], the GW/PCEF also forwards Charging Characteristics to the PCRF. Based on local configuration the GW/PCEF may also include the following information: its control plane IPv4 and/or IPv6 address(es), an indication on how the APN was selected, indications on whether IP address(es) where statically or dynamically allocated, and the charging identifier of the default bearer to identify different records belonging to the same PDN connection, indication on whether the charging identifier is the only one for the IP‑CAN session. When the PCEF has received the IMEI(SV) in the request for IP‑CAN Bearer establishment received at step 2, the PCEF shall transfer this information to the PCRF.

NOTE 1: In case of TDF and solicited application reporting, either PCEF informs PCRF with TDF IP address, or PCRF has it preconfigured per each one of PCEFs.

4. If the PCRF does not have the subscriber’s subscription related information, it sends a request to the SPR in order to receive the information related to the IP‑CAN session. The PCRF provides the subscriber ID and, if applicable, the PDN identifier to the SPR. The PCRF may request notifications from the SPR on changes in the subscription information.

5. The PCRF stores the subscription related information containing the information about the allowed service(s) and PCC Rules information, and may include MPS EPS Priority, MPS Priority Level and IMS Signalling Priority for establishing a PS session with priority and may also include user profile configuration indicating whether application detection and control should be enabled for the IP-CAN session.

6. If the PCRF determines that the policy decision depends on the status of the policy counters available at the OCS and such reporting is not established for the subscriber, the PCRF sends an Initial Spending Limit Report Request as defined in clause 7.9.1. If policy counter status reporting is already established for the subscriber, and the PCRF determines that the status of additional policy counters are required, the PCRF sends an Intermediate Spending Limit Report Request as defined in clause 7.9.2.

7. The PCRF makes the authorization and policy decision. If MPS EPS Priority, MPS Priority Level, and IMS Signalling Priority are present for the user, the PCRF takes the information into account.

8. For the solicited application reporting, the PCRF requests the TDF to establish the relevant session towards PCRF and provides ADC Rules to the TDF, as per user profile configuration, if traffic steering control over Sd applies, ADC Rules may contain traffic steering control information. The PCRF shall include the following information: a PDN identifier (e.g. APN), the IPv4 address and/or IPv6 network prefix, if available, and may also include the UE Identity Information and the location/access network information, if available. If Charging Characteristics were received by the PCRF according to step 3 and charging is applicable for the TDF, the PCRF shall also forward received Charging Characteristics to the TDF. Additionally, if received from the PCEF and if charging is applicable for the TDF, the PCRF shall also forward the following parameters to the TDF: the GW/PCEF control plane IPv4 and/or IPv6 address (es), an indication on how the APN was selected, indications on whether IP address (es) where statically or dynamically allocated, and the PDN charging identifier of the default bearer. The PCRF may also subscribe to the Event Triggers applicable for the TDF, according to table 6.2.

NOTE 2: If Charging Characteristics are received by the PCRF from the PCEF, PCRF may take them into account when providing Charging information and Default charging method to the TDF.

9. If online charging is applicable for the TDF, and at least one ADC rule with charging parameters was activated, the TDF activates the online charging session, and provides relevant input information for the OCS decision. Depending on operator configuration, the TDF may request credit from the OCS for each charging key of the activated ADC rules.

10. If online charging is applicable for the TDF, the OCS provides the possible credit information to the TDF and may provide re-authorisation triggers for each of the credits.

11. The TDF sends an Ack (accept or reject of the ADC rule operation(s)) to inform the PCRF about the outcome of the actions related to the decision(s) received in step 8. The Ack also includes the list of Event Triggers to report, including the case when the OCS provides any credit re-authorisation trigger, e.g. PLMN change, Location change (serving CN node), which cannot be monitored at the TDF. The Event Triggers indicate to the PCRF what events to be forwarded from the PCRF to the TDF, once PCRF gets the corresponding Event Report from the PCEF/BBERF.

12. If traffic steering control over St applies, the PCRF determines the traffic steering control information needed for the IP-CAN session; the PCRF provides the UE IPv4 address and/or UE IPv6 prefix and one or more sets of traffic steering control information to the TSSF. The TSSF identifier is pre-configured on the PCRF per e.g. PCEF.

13. The TSSF sends an acknowledgement to the PCRF to inform the PCRF about the outcome of the actions related to the traffic steering control information received in step 12.

14. The PCRF sends the decision(s) including the chosen IP‑CAN bearer establishment mode and indicates whether the use of the extended TFT filter format is allowed in the IP-CAN session, to the PCEF. The GW (PCEF) enforces the decision. The PCRF may provide the default charging method and may include the following information: the PCC Rules to activate and the Event Triggers to report. If PCEF is enhanced with ADC, the applicable PCC rules are provided, according to the user profile configuration, if traffic steering control over Gx applies, PCC Rules may contain traffic steering control information. The Policy and Charging Rules allow the enforcement of policy associated with the IP‑CAN session. The Event Triggers indicate to the PCEF what events must be reported to the PCRF. If the TDF provided a list of Event Triggers to the PCRF in the previous step, the PCRF shall also provide those Event Triggers to the PCEF.

15. If online charging is applicable, and at least one PCC rule with charging parameters was activated, the PCEF activates the online charging session, and provides relevant input information for the OCS decision. Depending on operator configuration, the PCEF may request credit from the OCS for each charging key of the activated PCC rules.

16. If online charging is applicable, the OCS provides the possible credit information to the PCEF and may provide re-authorisation triggers for each of the credits.

In cases 2a and 2b, if the OCS provides any re-authorisation trigger, which cannot be monitored at the PCEF, the PCEF shall request PCRF to arrange those to be reported by the BBERF via the PCRF.

17. If at least one PCC rule was successfully activated and if online charging is applicable, and credit was not denied by the OCS, the GW (PCEF) acknowledges the IP‑CAN Bearer Establishment Request.

18. If network control applies the GW may initiate the establishment of additional IP-‑CAN bearers. See Annex A and Annex D for details.

19. If the PCRF in step 12 has requested an acknowledgement based on PCC rule operations, the GW (PCEF) sends the IP‑CAN Session Establishment Acknowledgement to the PCRF in order to inform the PCRF of the activated PCC rules result.