Head Technical and Business Development
at Nicheken Technologies Private Limited
Table of Contents
A important component in LTE network is the policy and charging control (PCC) function that brings together and enhances capabilities from earlier 3GPP releases to deliver dynamic control of policy and charging on a per subscriber and per IP flow basis.
The Policy Control and Charging Rules Function is responsible for policy control decision-making, as well as for controlling the flow-based charging functionalities in the Policy Control Enforcement Function (PCEF), which resides in the P-GW. The PCRF provides the QoS authorization (QoS class identifier [QCI] and bit rates) that decides how a certain data flow will be treated in the PCEF and ensures that this is in accordance with the user’s subscription profile.
PCRF provides service management and control of the 4G service. It dynamically manages and controls data sessions, enables new business models. Apart from this, PCRF LTE also has the functionality to make it easy for other devices out of the 3GPP network- like WiFi or fixed broadband devices- to access the 4G LTE network.
In other words, PCRF LTE is the policy manager of the new 4G LTE technology. All the quality of service (QoS) rules and regulations are distributed to the packet data network gateway by the PCRF LTE, making it a very valuable aspect of any organization’s policy and security management system.
The policy server or PCRF is a key component in the NDN. It provides the critical link between the service and transport layers and is the central decision point – the brain – of LTE networks. The PCRF provides the granular control of service quality, which is critical for managing resources, enabling seamless roaming, establishing new business models, and monetizing services.
A fundamental LTE concept is the ability to recognize and differentiate traffic flows. The degree and granularity with which that flow can be dynamically influenced largely determines the extent to which an operator can shape bandwidth, implement QoS, manage resource allocation, and create new applications. That’s where policy comes into play. The PCRF is the key network element that enables that fine-grained control, which is essential to successfully managing and monetizing LTE networks. As such, it is a strategic component and consideration in LTE network design.
The diagram shown below represents the PCRF reference architecture in LTE/IMS network
Figure 1: LTE PCRF reference network architecture
PCRF solution shall provide the following key capabilities as listed below:
PCRF will send the PCC rules based on subscriber profile and plan. There are two types of services.
The purpose of the PCC rule is to:
There are two different ways of applying/implementing PCC rules:
A PCC rule consists of:
The rule name shall be used to reference a PCC rule in the communication between the PCEF and the PCRF.
The service identifier shall be used to identify the service or the service component the service data flow relates to.
The service flow filter(s) shall be used to select the traffic for which the rule applies.
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 3GPP standards provide mechanisms to drop or downgrade lower-priority bearers in situations where the network become congested. Each bearer has an associated allocation and retention priority (ARP). The network looks at the ARP when determining if new dedicated bearers can be established through the radio base station.
The QCI specifies the treatment of IP packets received on a specific bearer.
QCI values impact several node-specific parameters, such as link layer configuration, scheduling weights, and queue management.
The 3GPP has defined a series of standardized QCI types, which are summarized in the below Table
Based on QCI values different services can be treated differently. Like some services will require a dedicated bearers while some may work via a non-dedicated bearers. Also the priority to these services has been defined.
Table 1: Quality of Class Indicator
The charging parameters define whether online and offline charging interfaces are used, what is to be metered in online/offline charging, at 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. 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.
For LTE HSI service, any one of the PCC rule (Dynamic or Predefined) will be installed according to the requirement.
PCRF uses the subscriber profile in the SPR and install the rule based on subscriber profile.
Input for policy decision:
The following important parameters will be considered by PCRF. There may be other parameters in the SPR which will be used by PCRF. But these parameters will be decided based on use case.
Table 2: SPR Parameters
Output given by PCRF:
Any one of the PCC rule (Dynamic or Predefined) will be installed according to the customer requirement.
Table 3: PCC Rule Name
The below call flow explains about interaction of PCRF with SAE-GW using dynamic PCC rule in LTE.
Figure 2: LTE Call Flow – Dynamic Rule
The below call flow explains about interaction of PCRF with SAE-GW using predefined PCC rule in LTE.
Figure 3: LTE Call Flow – Predefined Rule
For VoLTE service, Dynamic rule will be installed based on any one of the following.
Table 4: PCC Rule for VoLTE
PCRF will install the rule without any charging details for the IMS call to the SAE-GW. IMS node will interact with charging server for the IMS call. SAE-GW will use the default configuration regarding IMS call for charging server interaction.The below call flow explains about interaction of PCRF, SAE-GW and OCS based on dynamic rule sent by PCRF in CCA message for the IMS call.
Figure 4: VoLTE Call Flow
The following call model needs to be considered in calculating the TPS in each interface. This is Standard Call Model.
Call Model 1: UE Attach
Please find the below call flow for UE attach using SAE-GW and corresponding TPS calculation.
Figure 5: UE attach
Call Model 2: UE Detach
Please find the below call flow for UE detach using SAE-GW and corresponding TPS calculation.
Figure 6: UE detach
Call Model 3: Internet Access using DPI in the network
Please find the below call flow for UE accessing the internet and DPI in the network and corresponding TPS calculation. Assume, UE is already attached in the network.
Figure 7a: UE accessing internet and DPI
Figure 7b: UE accessing internet and DPI
Call Model 4: Internet Access using L4L7 Optimizer in the network
Please find the below call flow for UE accessing the internet and L4L7 Optimizer in the network. Assume, UE is already attached in the network.
Figure 8: UE accessing internet and L4L7 Optimizer
Call Model 5: Bandwidth Boost
Please find the below call flow for Bandwidth boost and corresponding TPS calculation. Assume, UE is already attached in the network.
Figure 9: Bandwidth Boost
Call Model 6: VoLTE – Outgoing Call
Please find the below call flow for VoLTE (Outgoing Call) and corresponding TPS calculation. Assume UE is already attached in the network.
Figure 10: VoLTE – Outgoing Call
Call Model 7: VoLTE – Incoming Call
Please find the below call flow for VoLTE (Incoming Call) and corresponding TPS calculation. Assume UE is already attached in the network.
Figure 11: VoLTE – Incoming Call