4.4.1 Gateway Control Session Establishment

29.2133GPPPolicy and charging control signalling flows and Quality of Service (QoS) parameter mappingRelease 17TS

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

Figure 4.4.1.1 Gateway Control Session Establishment.

1. The BBERF receives a message or indication that it needs to establish a Gateway Control session.
For case 2a, as defined in clause 4.0, the BBERF detects that a UE has been assigned a Local IP address that the UE may use as a Care-of Address in MIP registrations (see 3GPP TS 23.402 [21], clause 6.3).
For case 2b, as defined in clause 4.0, the BBERF detects that the UE requests an IP-CAN session to be established (see 3GPP TS 23.402 [21], clauses 4.5.2 and 5.6.1) or, at BBERF relocation, to be resumed with a certain APN (see 3GPP TS 23.402 [21], clauses 5.7.1 and 5.7.2) or the UE requests a pre-registration with this BBERF (see 3GPP TS 23.402 [21], clause 9.3.1).

2. For the non-roaming case, the BBERF initiates a Gateway Control session with the H-PCRF by sending a CCR to the H-PCRF with the CC-Request-Type AVP set to the value INITIAL_REQUEST. The BBERF provides UE identity information and the IP-CAN type, User Location Information, User CSG Information (if received from the access network) and the indication of the BBERF support for the extended TFT filters.
For case 2a, as defined in clause 4.0, the BBERF provides the CoA assigned to the UE.
For case 2b, as defined in clause 4.0,the BBERF provides the PDN identifier and PDN connection identifier, if multiple PDN connections for the same APN are supported and, if applicable, a Session-Linking-Indicator to indicate if the session linking has to be deferred. The BBERF provides, when available, the APN-AMBR and Default-EPS-Bearer-QoS.

NOTE: The BBERF support is a prerequisite for the PCRF enabling the possibility for usage of the extended TFT filter in the IP-CAN session(s).

If applicable for the IP-CAN type, the BBERF additionally provides Network-Request-Support AVP to indicate whether NW-initiated procedures are supported.

When the UE is roaming, the steps 2a-2c are executed instead of step 2:

2a. The BBERF initiates a Gateway Control session with the V-PCRF by sending a CCR to the V-PCRF with the CC-Request-Type AVP set to the value INITIAL_REQUEST. The BBERF provides UE identity information and the IP-CAN type, User Location Information and User CSG Information (if received from the access network).
For case 2a, as defined in clause 4.0, the BBERF provides the CoA assigned to the UE.
For case 2b, as defined in clause 4.0, the BBERF provides the PDN identifier and, if applicable, a Session-Linking-Indicator AVP to indicate if the session linking has to be deferred. The BBERF provides, when available, the APN-AMBR and Default-EPS-Bearer-QoS.

If applicable for the IP-CAN type, the BBERF additionally provides Network-Request-Support AVP to indicate whether NW-initiated procedures are supported.

2b. The V-PCRF determines based on the UE identity information that the request is for a roaming user. The V-PCRF checks whether the V-PCRF needs to send the CCR to the H-PCRF based on the roaming agreements. For the Visited Access case, the V-PCRF does not send the CCR to the H-PCRF if the Session-Linking-Indicator AVP was received indicating that the session linking has to be deferred.

NOTE: If the V-PCRF does not send the CCR to the H-PCRF, the PCRF may generate QoS rules based on VPLMN roaming agreements.

2c. For case 2a:

– If there is an already established S9 session for this roaming user, the V-PCRF sends a CCR to the H-PCRF with the CC-Request-Type AVP set to the value UPDATE_REQUEST. The V-PCRF includes in the CCR the information received in step 2a.

For case 2b and for the visited case or for the home routed case and if the Session-Linking-Indicator AVP is not received or it indicates SESSION_LINKING_IMMEDIATE, the following procedures apply:

– If there is not an already established S9 session for this roaming user, the V-PCRF sends a CCR to the H-PCRF with the CC-Request-Type AVP set to the value INITIAL_REQUEST. The V-PCRF includes the Subsession-Enforcement-Info AVP within the CCR with a new S9 subsession identifier assigned by the V-PCRF to this Gateway Control Session within the Subsession-Id AVP, and the Subsession-Operation AVP set to the value ESTABLISHMENT.

– If there is an already established S9 session for this roaming user and not an already established S9 subsession for the PDN connection corresponding to the Gateway Control Session, the V-PCRF sends a CCR to the H-PCRF with the CC-Request-Type AVP set to the value UPDATE_REQUEST. The V-PCRF includes the Subsession-Enforcement-Info AVP within the CCR with a new S9 subsession identifier assigned by the V-PCRF to this Gateway Control Session within the Subsession-Id AVP, and the Subsession-Operation AVP set to the value ESTABLISHMENT.

– If there is an already established S9 session for this roaming user and an already established S9 subsession for the PDN connection corresponding to the Gateway Control Session, the V-PCRF sends a CCR to the H-PCRF with the CC-Request-Type AVP set to the value UPDATE_REQUEST. The V-PCRF includes the Subsession-Enforcement-Info AVP within the CCR command with the S9 subsession identifier assigned by the V-PCRF for this Gateway Control Session within the Subsession-Id AVP, the Subsession-Operation AVP set to the value MODIFICATION, and the BBERF identity within AN-GW-Address AVP.

For case 2b and for the home routed case and if the Session-Linking-Indicator AVP was received indicating that the session linking has to be deferred, following procedure applies:

– The V-PCRF sends a CCR to the H-PCRF with the CC-Request-Type AVP set to the value UPDATE_REQUEST. The V-PCRF includes the Subsession-Enforcement-Info AVP within the CCR with a new S9 subsession identifier assigned by the V-PCRF to this Gateway Control Session within the Subsession-Id AVP, the Subsession-Operation AVP set to the value ESTABLISHMENT and the Session-Linking-Indicator AVP set to the value “SESSION_LINKING_DEFERRED”.

3. The H-PCRF stores the information received in the CCR. The H-PCRF determines the network scenario that applies (case 2a or 2b) as described in clause 4.0.

For case 2a, the H-PCRF may correlate the UE identity information with already established Gx sessions for the same UE.
For case 2b, for non roaming case, the H-PCRF links the Gateway Control session with the already established Gx Session and acts as follows:

– if the Session-Linking-Indicator was received indicating that the session linking has to be deferred, defers the session linking till the associated IP-CAN session establishment or modification is received.

– if the Session-Linking-Indicator was not received or indicates that the session linking has to be performed immediately, links the Gateway Control session with the already established Gx Session.

4. If the H-PCRF requires subscription-related information and does not have it, the H-PCRF sends a request to the SPR in order to receive the information.

5. The SPR replies with the subscription related information containing the information about the allowed service(s), QoS information, PCC Rules information and may include MPS EPS Priority, MPS Priority Level and IMS Signalling Priority of establishment a PS session with priority.

NOTE: For steps 4 and 5: The details associated with the Sp reference point are not specified in this Release. The SPR’s relation to existing subscriber databases is not specified in this Release.

6. For case 2a, the H-PCRF may prepare for the installation of QoS rules if available;

For case 2b, the H-PCRF may

– At IP-CAN session establishment, if the session linking was not deferred, select or generate and store PCC Rule(s) in preparation for the anticipated Gx session and derive the QoS rules from them. If MPS EPS Priority, MPS Priority Level, and IMS Signalling Priority are present for the user, the PCRF takes the information into account. If the session linking was deferred, the PCC rules are not generated;

– At BBERF relocation and at pre-registration, if the Session-Linking-Indicator was not received or indicates that the session linking has to be performed immediately, prepare for the installation of QoS rules, derived from the active PCC rules, at the target BBERF;

7. The H-PCRF stores the selected QoS Rules and PCC Rules. If applicable the H-PCRF selects the Bearer Control Mode that will apply during the Gateway Control session.

8. For the non-roaming case, the H-PCRF acknowledges the Gateway Control Session by sending a CCA to the BBERF. The H-PCRF includes:

– The selected BCM, if applicable for the IP-CAN type

– If NW-initiated procedures are available, the available QoS rules

– If BCM is UE-only, the QoS rules that correspond to the request from the BBERF

– Default-EPS-Bearer-QoS and APN-AMBR when applicable

– The event triggers

When the UE is roaming, the steps 8a-8e are executed instead of step 8:

8a. The H-PCRF acknowledges the Gateway Control Session by sending a CCA to the V-PCRF. The H-PCRF includes

– The selected BCM, if applicable for the IP-CAN type

– If NW-initiated procedures are available, the available QoS rules for the home routed case or the available PCC rules for the visited access case

– If BCM is UE-only, the QoS rules that correspond to the request from the V-PCRF for the home routed case or the PCC rules that correspond to the request from the V-PCRF for the visited access case

– For the case 2a, the QoS rules when the available QoS rules are not related to any IP-CAN session

– Default-EPS-Bearer-QoS and APN-AMBR when applicable

– Event triggers

8b. The V-PCRF enforces visited operator policies regarding QoS authorization requested by the H-PCRF as indicated by the roaming agreements.

8c. If the V-PCRF denies an authorization, it informs the H-PCRF and may provide the acceptable QoS Information for the service.

8d. The H-PCRF may provide new or modified QoS rules to the V-PCRF

8e. If V-PCRF receives the PCC rules from the H-PCRF, the V-PCRF extracts the QoS rules from the PCC rules. The V-PCRF acknowledges the Gateway Control Session establishment by sending a CCA to the BBERF. The V-PCRF includes the selected BCM if applicable for the IP-CAN type, any applicable QoS rules and event triggers.

9. The BBERF installs and enforces the received QoS Rules.

10. The BBERF sends an Establish Gateway Session Control Response to ack the Gateway Control Session Request.