Policy and Charging Control - LTE / HSPA / EPC ‘knowledge nuggets’


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Policy and Charging Control - LTE / HSPA / EPC ‘knowledge nuggets’

  1. 1. info@red-banana.org www.red-banana.org 1
  2. 2. info@red-banana.org www.red-banana.org The basic architecture for the LTE system including the EPC is shown in the diagram, with each of the network elements and key interface functions described in subsequent slides. The combination of logical functions performed by both the Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW) provide an access Gateway (a-GW) to support PS services between LTE-UEs and external packet-data networks, however the P-GW and S-GW functions can exist in the same physical network element 2
  3. 3. info@red-banana.org www.red-banana.org Policy and Charging Control functionality encompasses two main functions: - Flow Based Charging, including charging control and online credit control; - Policy control (e.g. gating control, QoS control, QoS signalling, etc.). 3
  4. 4. info@red-banana.org www.red-banana.org The diagram above shows the general architecture for Policy and Charging Control, with the main decisions being made at the Policy and Charging Rules Function (PCRF) The key policy control functions are: - Binding: generation of an association between an SDF and the IP-CAN bearer transporting that SDF - Gating control: blocking or allowing of packets belonging to an SDF to pass through to the desired endpoint - Event reporting: notification of and reaction to application events to trigger new behaviour in the user plane and reporting of events related to the resources in the GW(PCEF) - QoS control: authorisation and enforcement of the maximum QoS that is authorised for an SDF or an IP-CAN bearer - IP-CAN bearer establishment: for IP-CANs that support network initiated procedures for IP-CAN bearer establishment. The Gz reference point is functionally equivalent to Ga for Legacy PS domain and to Ga or Rf for Evolved PS domain, and hence is replaced by Ga or Rf within the common charging architecture. 4
  5. 5. info@red-banana.org www.red-banana.org The purpose of the PCC rule is to: - Detect a packet belonging to a service data flow. - The service data flow filters within the PCC rule are used for the selection of downlink IP CAN bearers. - The service data flow filters within the PCC rule are used for the enforcement that uplink IP flows are transported in the correct IP CAN bearer. - Identify the service the service data flow contributes to. - Provide applicable charging parameters for a service data flow. - Provide policy control for a service data flow. The PCEF shall select a PCC rule for each received packet by evaluating received packets against service data flow filters of PCC rules in the order of the precedence of the PCC rules. When a packet matches a service data flow filter, the packet matching process for that packet is completed, and the PCC rule for that filter shall be applied. There are two different types of PCC rules as defined in 3GPP TS 23.203: - Dynamic PCC rules. Dynamically provisioned by the PCRF to the PCEF via the Gx interface. These PCC rules may be either predefined or dynamically generated in the PCRF. Dynamic PCC rules can be installed, modified and removed at any time. - Predefined PCC rules. Preconfigured in the PCEF. Predefined PCC rules can be activated or deactivated by the PCRF at any time. Predefined PCC rules within the PCEF may be grouped allowing the PCRF to dynamically activate a set of PCC rules over the Gx reference point.
  6. 6. info@red-banana.org www.red-banana.org The rule name is used to reference a PCC rule in the communication between the PCEF and the PCRF. The service identifier is used to identify the service or the service component the service data flow relates to. The service flow filter(s) is used to select the traffic for which the rule applies. Wildcarded service data flow filter(s), for dynamic and predefined PCC rules can be defined. The gate status indicates whether the service data flow, detected by the service data flow filter(s), may pass (gate is open) or shall be discarded (gate is closed) in uplink and/or in downlink direction. The QoS information includes the QoS class identifier (authorized QoS class for the service data flow), the Allocation and Retention Priority (ARP) and authorized bitrates for uplink and downlink. The charging parameters define whether online and offline charging interfaces are used, what is to be metered in offline charging, on what level the PCEF shall report the usage related to the rule, etc. For different PCC rules with overlapping service data flow filter, the precedence of the rule determines which of these rules is applicable. When a dynamic PCC rule and a predefined PCC rule have the same precedence, the dynamic PCC rule takes precedence. PCC rule also includes Application Function record information for enabling charging correlation between the application and bearer layer if the AF has provided this information via the Rx interface. For IMS this includes the IMS Charging Identifier (ICID) and flow identifiers.
  7. 7. info@red-banana.org www.red-banana.org The PCRF shall indicate, via the Gx reference point, PCC rules to be applied at the PCEF. This may be using one of the following procedures: - PULL procedure (Provisioning solicited by the PCEF): In response to a request for PCC rules being made by the PCEF, as described in the preceding section, the PCRF shall provision PCC rules in the CC- Answer; or - PUSH procedure (Unsolicited provisioning): The PCRF may decide to provision PCC rules without obtaining a request from the PCEF, e.g. in response to information provided to the PCRF via the Rx reference point, or in response to an internal trigger within the PCRF. To provision PCC rules without a request from the PCEF, the PCRF shall include these PCC rules in an RA-Request message. No CCR/CCA messages are triggered by this RA-Request. For each request from the PCEF or upon the unsolicited provision the PCRF shall provision zero or more PCC rules. The PCRF may perform an operation on a single PCC rule by one of the following means: - To activate or deactivate a PCC rule that is predefined at the PCEF, the PCRF shall provision a reference to this PCC rule within a Charging-Rule-Name AVP and indicate the required action by choosing either the Charging-Rule-Install AVP or the Charging-Rule-Remove AVP. - To install or modify a PCRF-provisioned PCC rule, the PCRF shall provision a corresponding Charging- Rule-Definition AVP within a Charging-Rule-Install AVP. - To remove a PCC rule which has previously been provisioned by the PCRF, the PCRF shall provision the name of this PCC rule as value of a Charging-Rule-Name AVP within a Charging-Rule-Remove AVP. - If, for certain accesses, the PCRF performs the bearer binding, the PCRF may move previously installed or activated PCC rules from one IP CAN bearer to another IP CAN bearer. As an alternative to providing a single PCC rule, the PCRF may provide a Charging-Rule-Base-Name AVP within a Charging-Rule-Install AVP or the Charging-Rule-Remove AVP as a reference to a group of PCC rules predefined at the PCEF. With a Charging-Rule-Install AVP, a predefined group of PCC rules is activated. With a Charging-Rule-Remove AVP, a predefined group of PCC rules is deactivated.
  8. 8. info@red-banana.org www.red-banana.org The PCRF accepts input for PCC decision-making from the PCEF, the BBERF if present, the SPR and if the Application Function (AF) is involved, from the AF, as well as the PCRF may use its own pre-defined information. These different nodes should provide as much information as possible to the PCRF. Depending on the particular scenario all the information may not be available or is already provided to the PCRF. An example of an Application Function is the IMS Proxy Call Session Control Function (P-CSCF) 8
  9. 9. info@red-banana.org www.red-banana.org 1. The AF provides service information to the PCRF at a set-up of a new AF session or at a modification of an existing AF session. 2. The GW receives a request for bearer establishment or modification. 3. The GW determines that the PCC interaction is required and sends the Policy and Charging Rules request to the PCRF. The PCRF correlates the application and bearer sessions with the binding information (e.g. user's IP address) and, if available, the PCRF also retrieves the saved application service information in order to make the authorization and policy decision. 4. The PCRF may fetch the subscription related information from the SPR, if the PCRF does not have it and the SPR replies with the subscription related information, and the PCRF stores this. 5. The PCRF makes the authorization and policy decision and sends the decision(s) to the GW. 6. In this scenario, the PCEF interacts with the Online Charging System to receive request the service to be authorised (based SDF credit). 7. The GW can now enforce the decision and acknowledge the Bearer Establishment/Modification request. 9
  10. 10. info@red-banana.org www.red-banana.org 1.BBERF initiates Gateway Control Session Establishment procedure if involved 2.GW(PCEF) receives request for IP-CAN Bearer establishment and assigns IP address for UE 3.PCEF determines that the PCC authorization is required, requests the authorization of allowed service(s) and PCC Rules information. The PCEF may also include charging ID information. 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. 5.PCRF stores the subscription related information containing the information about the allowed service(s) and PCC Rules information. 6. PCRF makes the authorization and policy decision. 7. PCRF sends the decision(s) , including the chosen IP-CAN bearer establishment mode, to the PCEF which enforces the decision. 8. If online charging is applicable, and at least one PCC rule was activated, the PCEF activates the online charging session, providing relevant input information for the OCS decision. 9.The OCS provides the possible credit information to the PCEF and may provide re-authorisation triggers for each of the credits. 10.If at least one PCC rule was successfully activated and and credit was not denied by the OCS, the GW(PCEF) acknowledges the IP-CAN Bearer Establishment Request. 11.The GW may initiate the establishment of additional IP-CAN bearers.. 12. If the PCRF in step 7 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.
  11. 11. info@red-banana.org www.red-banana.org In the roaming case, when the users connectivity is via the home network, connectivity via the S9 interface allows transactions between PCRFs between the home and visited networks. This allows PCC rules to be modified locally in the visited network if required and also prevents the PCRF of the home network directly controlling the GW in the visited network
  12. 12. info@red-banana.org www.red-banana.org In the roaming case where the users connectivity breaks out to the external PDN via the visited network, QoS is controlled at both the SGW and PGW by the PCRF in the visited network. Once again however, the V-PCRF will interact with the H-PCRF to obtain PCC Rules etc.