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PCF is a policy control function that enables various service providers to control and manage the network. Policies are basically the protocols that are required to manage the network. Controlling and management of 5G network occurs by adding complex policies decision which is based on the network subscriber and all the subscriber information which are stored. PCF has various flexible policy designs and these designs can help telecom operators to generate and test various other policies as well. PCF interworks with e.g BSF (Binding Support Function) for storing all the subscriber session binding information and this information can be accessed by the PCF. The PCF can also access UDR (Unified Data Repository) for storing and accessing subscriber information. It supports voice over 5G (Vo5G) and various OTT (Over the top) use cases. It has the support for Vo5G (Voice over 5G) and also can support handovers from 4G to 5G subscriber sessions and it can also change QoS (Quality of service) on the different 5G sessions.  It will be able to support multiple deployment options from PLMN (Public land mobile network) level and slice specific parameters. 

Policy Control Function separates the processing and state corresponding to the logical grouping of various components. A Policy function is composed of all the necessary microservices to provide all the necessary information. The integration of PCF with a variety of common services. This integration of the services is required for the data collection, data analysis, various visualization services, etc. 

Policy Control Services supported by PCF:

  • Session management policy control service: It covers the enforcement control of all the policy-related decisions which are further related to the quality of service, charging, etc. It also covers service flow detection, packet routing, traffic forwarding, and traffic usage reporting. Various policy decisions can be distributed among various functions such as UPF (User Plane Function), RAN (Radio Access Network), and the UE (User equipment) depending on the policy types and the Network slice selection function.
  • Access and Mobility policy control service: It has the Enforcement control of the different decisions of policies related to the Radio Access technologies and the frequency selection priorities defined. It covers all the Service Area Restrictions that are executed in the UE and also enables location tracking for a UE to get all the periodic updates on the subscriber’s current location. 
  • Policy Authorization (PA): It could be able to support  APP session establishments, termination, and the notification to terminate the features. It will be able to support various PCC (Policy and Charging Control) rule authorization and Authentication for the application flow information. It provides good gating control. 

Policy control requirements:

  • Gating control requirements: The gating control should be applied by the UPF (User Plane Function) on a basis of service data flow. In order to enable the PCF gating control decisions, the AF (Application function) shall report various session events like session termination, session modification, and session releases to the PCF. 
  • QoS Control requirements: It shall be possible to apply QoS control on the basis of service data flow. 
  • QoS control at QoS Flow level: It shall be possible for the PCC framework to support control of various QoS reservation procedures. 
  • QoS control at PDU session: It shall be possible for the Policy control function so that it can provide the authorized session-AMBR (Aggregate Maximum Bit-rate) values, the default values of 5QI (5G Quality Indicator), and ARP (Address Resolution Protocol) values. 
  • Subscriber spending limit requirements: It is possible to enforce various policies which are based on the subscriber spending limits. The CHF (Charging Function) shall maintain various policy controllers so that they can track spendings for the subscriptions. 
  • Usage monitoring control requirements: The various requirements to monitor parameters of both the volume and the time usage. It is possible to apply usage monitoring for the accumulated usage of various network resources on the basis of sessions and the users. 

The PCF uses usage monitoring so that it can make various policy decisions shall be set and it can send the application thresholds to the SMF (Session Management Function) for all the monitoring. In this, the Session Management Function shall notify the PCF when a threshold is reached and after that, it can report the accumulated usage for the usage monitoring. When both the time and the usage monitoring are provided to the SMF, the accumulated usage shall be reported when the thresholds are reached properly. PDU session-level usage monitoring is not dependent on the access which is used to carry an SDU (Service Data Unit). 

PCF interacts with:

  • Interactions between PCF and AF
  • Interactions between PCF and SMF
  • Interactions between PCF and AMF
  • Interactions between V-PCF and H-PCF
  • Interactions between PCF and UDR
  • Interactions between SMF and CHF 
  • Interactions between PCF and CHF
  • Interactions between SMF and NEF 
  • Interactions between PCF and NEF 
  • Interactions between NWDAF and PCF 

PCF Functionality:

  • Policy and charging control for a service data flows
  • PDU session related policy control
  • PDU session event reporting to the AF (Application Function). 

Input for PCC decisions:

  • SUPI (5G Subscription Permanent Identifier)
  • PEI (Permanent Equipment Identifier)
  • Location of the subscriber
  • Service area restrictions
  • RAT (Radio access technology) type
  • Access type
  • Serving PLMN identifier
  • Time zone
  • Allowed NSSAI (Network Slice Selection Identity management) 
  • IPv4 and IPv6 addresses, etc. 

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