7.3 DRA Procedures

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

7.3.1 General

A DRA implemented as a Diameter Redirect Agent or a Diameter Proxy Agent shall be compliant to IETF RFC 6733 [61], except when noted otherwise in this document.

7.3.2 DRA Information Storage

The DRA shall maintain PCRF routing information per IP-CAN session or per UE-NAI, depending on the operator’s configuration.

The DRA shall select the same PCRF for all the Diameter sessions established for the same UE in case 2a.

As there’s only one S9 session per UE, the V-DRA/H-DRA shall select the same V-PCRF/H-PCRF respectively for the same UE in the roaming case.

The DRA has information about the user identity (UE NAI), the UE Ipv4 address and/or Ipv6 prefix, the APN (if available), the PCEF identity (if available) and the selected PCRF identity for a certain IP-CAN Session.

NOTE 1: The DRA derives the PCEF identity from the Origin-Host AVP of the CCR command received from the PCEF.

The DRA finds the correct PCRF by matching the user identity (if available), IPv4 address or IPv6 address/prefix (if available) and APN (if available) received in the message from the BBERF/PCEF/AF/TDF/ RCAF/V-PCRF with the corresponding information stored the DRA.

NOTE 2: If the DRA does not use the IP address to find the PCRF and the user identity in the IP‑CAN and the application level identity for the user are of different kinds (e.g. user identity is the IP-CAN is IMSI and application level identity for the user is SIPURI), the DRA needs to maintain, or have access to, the mapping between the identities. Such mapping is not subject to specification within this TS.

NOTE 3: An IPv6 address provided over Rx matches an IPv6 prefix stored in the DRA binding if the IPv6 address belongs to the IPv6 (sub-)network prefix.

When matching the APNs to each other, the DRA shall apply the procedures in Annex I.

For the PCRF selection over the Rx reference point, the DRA may additionally match the IP domain Id received in the message from the AF with the PCEF identity stored in the DRA to find the correct PCRF.

NOTE 4: In order to correlate the PCEF Identity and the domain identity, the DRA uses configured mapping between those identities.

For the PCRF selection over the Rx reference point, when the APN related to the IP-CAN session is dedicated for the purpose of offering services to remote UEs via a ProSe UE-to-network relay UE, the DRA shall use the UE IPv6 prefix alone to find the correct PCRF.

The PCRF routing information stored for an IP-CAN session in the DRA shall be removed after the IP-CAN session is terminated. In case of DRA change (e.g. inter-operator handover), the information about the IP-CAN session stored in the old DRA shall be removed.

The PCRF routing information stored per UE in the DRA may be removed when no more IP-CAN and gateway control sessions are active for the UE.

7.3.3 Capabilities Exchange

In addition to the capabilities exchange procedures defined in IETF RFC 6733 [61], the Redirect DRA and Proxy DRA shall advertise the specific applications it supports (e.g., Gx, Gxx, Rx, Np,S9 and for unsolicited application reporting, Sd) by including the value of the application identifier in the Auth-Application-Id AVP and the value of the 3GPP (10415) in the Vendor-Id AVP of the Vendor-Specific-Application-Id AVP contained in the Capabilities‑Exchange-Request and Capabilities-Exchange-Answer commands.

7.3.4 Redirect DRA

7.3.4.1 Redirecting Diameter Requests

A DRA implemented as a Diameter redirect agent shall redirect the received Diameter request message by carrying out the procedures defined in clause 6.1.7 of IETF RFC 6733 [61]. The Client shall use the value within the Redirect-Host AVP of the redirect response in order to obtain the PCRF identity. The DRA may provide the Redirect-Host-Usage AVP in the redirect response to provide a hint to the Client about how the cached route table entry created from the Redirect-Host AVP is to be used as described in clause 6.13 of IETF RFC 6733 [61].

The two most revelant redirect host usage scenarios for PCC from IETF RFC 6733 [61]are:

– If the PCRF routing information is per UE-NAI, the DRA shall set the Redirect-Host-Usage AVP to ALL_USER. The DRA client may contact the DRA on IP-CAN session termination.

– If the PCRF routing information is per IP-CAN session, the DRA shall set the Redirect-Host-Usage AVP to ALL_SESSION. The DRA client shall contact the DRA on IP-CAN session termination.

The DRA may also provide the Redirect-Max-Cache-Time AVP in the redirect response to indicate to the Client the lifetime of the cached route table entry created from the Redirect-Host and Redirect-Host-Usage AVP values as described in clause 6.14 of IETF RFC 6733 [61].

If the DRA is maintaining PCRF routing information per IP-CAN session, the DRA shall be aware of Gx and Gxx Diameter termination requests as defined in 3GPP TS 29.212 [9] in order to detect whether release of DRA bindings is required. Otherwise the DRA clients shall use cached route table entry created from the Redirect-Host, Redirect-Host-Usage and Redirect-Max-Cache-Time AVPs to determine whether DRA interaction is required.

The DRA shall be aware of IP-CAN Session modification requests over Gx which is to update the Ipv4 address of the UE by the PCEF.

If the client is the AF, the DRA (redirect) does not need to maintain Diameter sessions and Diameter Base redirect procedures are applicable. Therefore, an AF should not send an AF session termination request to the DRA.

7.3.4.2 DRA binding removal

If the DRA binding is per IP-CAN session and the IP-CAN session is terminated or if the DRA binding is per UE and the last IP-CAN session is terminated (eg. From an indication by the BBERF/PCEF) the Redirect DRA shall remove the associated DRA binding information and responds with a Diameter redirect answer message.

7.3.5 Proxy DRA

The DRA shall support the functionality of a Diameter proxy agent as defined in IETF RFC 6733 [61].

When the DRA receives a request from a client, it shall check whether it already has selected a PCRF for the UE or the UE’s IP-CAN session; if it does have a PCRF already selected for that UE or UE’s IP-CAN session, it shall proxy the request to the corresponding PCRF. If the request is an IP-CAN session termination or gateway control session termination, the DRA shall check whether PCRF routing information shall be removed as specified in clause 7.3.3. If the DRA does not have a PCRF already selected, it shall follow one of the procedures below:

– If the request is an IP-CAN session establishment or gateway control session establishment, it shall select a PCRF to handle all sessions for that UE or UE’s IP-CAN session. It shall then proxy the request to the selected PCRF.

– Otherwise, if the request is not an IP-CAN session establishment or gateway control session establishment, it shall reject the request by returning a DIAMETER_UNABLE_TO_COMPLY error code.

If a DRA is deployed in a PCRF’s realm, clients of the DRA shall send the first request of a session to the DRA handling the PCRF’s realm. Clients of the DRA shall as well send IP-CAN session termination and gateway control termination requests to the DRA. A client of the DRA shall be capable of sending every message of a session to the DRA. A client of the DRA may be configured to bypass the DRA on session modification messages and AF session termination messages by sending these types of messages directly to the PCRF.

7.3.6 PCRF selection by BBERF/PCEF (non-roaming case)

The PCEF (e.g. P-GW) or BBERF (e.g. Non-3GPP Access, S-GW) shall provide the DRA of the PCRF realm with identity parameters upon the first interaction between the access entity and the PCRF realm.

If the redirect agent is used for DRA, the DRA shall use the redirecting requests procedure as specified in IETF RFC 6733 [61], and include the PCRF identity in the Redirect-Host AVP in the Diameter reply sent to the PCEF or the BBERF.

If proxy agent is used for DRA, the DRA should use the proxy procedure as specified in IETF RFC 6733 [61]. For PA2 solution (described in clause 7.1), only session establishment, session modification with the UE’s Ipv4 address updated and session termination messages shall be sent through the DRA.

The identity parameters from the PCEF or BBERF may comprise the UE’s Ipv4 address in the Framed-IP-Address AVP and/or the UE’s Ipv6 prefix in the Framed-Ipv6-Prefix AVP, PDN information in the Called-Station-Id AVP and user identity in the Subscription-Id AVP.

7.3.7 PCRF selection by AF

If the AF has the realm identification (i.e. FQDN from a UE NAI) and is located in the HPLMN, the AF sends the user identity in the Subscription-Id AVP and PDN information (i.e. APN) if available in the Called-Station-Id AVP in a Diameter request to the DRA which acts as a Diameter agent.

For an AF serving mission critical communication services (e.g. MCPTT), the AF shall derive the realm of the PCRF based on the IP address and, based on the PLMN ID, construct the Diameter destination realm and use that destination realm in the initial request to address the DRA.

NOTE 1: An AF serving mission critical communication services as defined in 3GPP TS 23.280 [64] can be independent from a PLMN and is not guaranteed to have any realm identification.

If the AF does not have proper knowledge about the user identity and the AF is located in the HPLMN, the AF may use pre-configured information to find the DRA.

NOTE 1A: How the AF which is a third party or non-IMS application server finds the DRA if it does not have the proper knowledge about the user identity is out of scope of this specification.

The AF shall provide the DRA of the PCRF realm with identity parameters upon the first interaction between the AF and the PCRF realm.

If redirect agent is used for DRA, the DRA shall use the redirecting requests procedure as specified in IETF RFC 6733 [61], and include the PCRF identity in the Redirect-Host AVP in the Diameter reply sent to the AF.

If proxy agent is used for DRA, the DRA should use the proxy procedure as specified in IETF RFC 6733 [61]. For PA2 solution (described in clause 7.1), only AF session establishment messages shall be sent through the DRA.

The parameters from the AF may comprise the UE IP address in either the Framed-IP-Address AVP or the Framed-Ipv6-Prefix AVP, PDN information in the Called-Station-Id AVP, user identity in the Subscription-Id AVP and domain Identity in the IP-Domain-Id AVP (3GPP TS 23.203 [2]).

NOTE 2: In case the user identity in the IP‑CAN and the application level identity for the user are of different kinds (e.g. user identity is the IP-CAN is IMSI and application level identity for the user is SIPURI), the DRA needs to maintain, or have access to, the mapping between the identities. Such mapping is not subject to specification within this TS.

7.3.8 PCRF selection in a roaming scenario

In the roaming case, a V-DRA is needed in the visited PLMN when there are more than one PCRFs per realm. The V-DRA will ensure that all the related Diameter sessions for a UE are handled by the same V-PCRF.

The BBERF in the visited access and home routed cases, the PCEF in the case of visited access and the AF when located in the visited PLMN may use pre-configured information (e.g. based on PDN) to find the V-DRA, and then find theV-PCRF. Other possible options are Dynamic peer discovery, or DNS-based.

The V-PCRF can find the H-DRA based on the UE NAI, and then find the H-PCRF by the H-DRA.

The V-PCRF shall provide the H-DRA of the H-PCRF realm with identity parameters upon the first interaction between the V-PCRF and the H-PCRF realm.

If redirect agent is used for H-DRA, the H-DRA shall use the redirecting requests procedure as specified in IETF RFC 6733 [61], and include the H-PCRF identity in the Redirect-Host AVP in the Diameter reply sent to the V-PCRF.

If proxy agent is used for H-DRA, the H-DRA should use the proxy procedure as specified in IETF RFC 6733 [61]. For PA2 solution (described in clause 7.1), only session establishment, session modification with the UE’s Ipv4 address updated and, only for the Gx, Gxx and S9 interfaces, termination messages shall be sent through the H-DRA.

The identity parameters from the V-PCRF may comprise the same parameters sent by the PCEF or the BBERF to the V-PCRF, i.e. the user identity (UE NAI), APN, the UE’s Ipv4 address and/or Ipv6 prefix (3GPP TS 23.203 [2]).

If redirect agent or PA2 is used for H-DRA, and the V-PCRF receives establishment message from the AF in the VPLMN, the V-PCRF may send the message to the H-PCRF directly (e.g. based on the stored information provided by H-DRA during the IP-CAN session establishment).

7.3.9 PCRF selection by TDF for unsolicited application reporting

The TDF uses pre-configured information to find the DRA.

The TDF shall provide the DRA of the PCRF realm with identity parameters upon the first interaction between the TDF and the PCRF realm.

If redirect agent is used for DRA, the DRA shall use the redirecting requests procedure as specified in IETF RFC 6733 [61], and include the PCRF identity in the Redirect-Host AVP in the Diameter reply sent to the TDF.

If proxy agent is used for DRA, the DRA should use the proxy procedure as specified in IETF RFC 6733 [61]. For PA2 solution (described in subclause 7.1), only TDF session establishment messages shall be sent through the DRA.

The parameters from the TDF may comprise the UE IP address in either the Framed-IP-Address AVP or the Framed-Ipv6-Prefix AVP and PDN information in the Called-Station-ID AVP.

NOTE: The TDF located in the HPLMN finds the H-PCRF for the roaming UE with home routed access case. The TDF located in the VPLMN finds the V-PCRF for the roaming UE with visited access case.

7.3.10 PCRF selection by RCAF

For initial Non-Aggregated RUCI reporting, the RCAF shall provide the identity parameters to the DRA of the PCRF realm.

The identity parameters from the RCAF may comprise PDN information in the Called-Station-Id AVP and user identity in the Subscription-Id AVP.

In the roaming with home-routed access case, the RCAF can find the H-DRA based on the IMSI, and then find the H-PCRF by the H-DRA.The RCAF shall provide the H-DRA of the H-PCRF realm with identity parameters upon the first interaction between the RCAF and the H-PCRF realm.

In the roaming with visited case, the RCAF shall provide the V-DRA of the V-PCRF realm with identity parameters upon the first interaction between the RCAF and the V-PCRF realm.

If the redirect agent is used for DRA, the DRA shall use the redirecting requests procedure as specified in IETF RFC 6733 [61], and include the PCRF identity in the Redirect-Host AVP in the Diameter reply sent to the RCAF.

If proxy agent is used for DRA, the DRA should use the proxy procedure as specified in IETF RFC 6733 [61].

For subsequent non-aggregated or aggregated RUCI reporting, the RCAF shall include the PCRF identity within the Destination-Host AVP for direct PCRF selection. The PCRF identity shall be responded by the PCRF within the PCRF-Address AVP in the initial non-aggregated RUCI reporting, for identifying the same destination PCRF in the subsequent non-aggregated or aggregated RUCI reporting.