PCRF for RADIUS based Broadband networks
PCRF (Policy & Charging Rules Function) is at the heart of any modern communications service provider’s core network and it controls the way services are delivered and charged for customers. The standard developed mainly for 3G and newer standards and requires a real-time DIAMETER based access network. But most CSPs worldwide today still have a RADIUS based network but would like to benefit from the use cases made possible by PCRF like fair-usage and tiered service plans. AdvOSS offers a complete PCRF solution for Radius based networks.
Overview
Business Case
Interface Points
Solution Options
Organizational Benefits


Policy based Service Control

The solution sits in the AAA path and uses several RADIUS based techniques to provide control of services such as bandwidth management, QoS management, service profile modification, subscriber redirection to web portals etc. The key techniques in this regard include:

  • RADIUS Access Accept with service profile attributes
  • RADIUS Change of Authorization (CoA)
  • RADIUS Disconnect Message
  • RADIUS Mid-session Re-Authorization either periodically or when allotted quota expires
  • RADIUS Interim Accounting updates

PCRF Solution Requirements for RADIUS based NAS clients

It may be difficult to provide all use cases enabled by a fully compliant Diameter based PCRF based network over Radius interface. This is because PCC compliant Policy Enforcement points (PCEF) as well as Application Functions (AF) send Diameter based events to PCRF to act upon them and apply policies if required. This may not be possible in RADIUS based Access network elements. However, several triggers can be sent to AdvOSS AAA from Application Servers via its exposed API. Furthermore, the use cases described above are in fact categories of many use cases that can be offered by CSPs and thus gain substantial advantages of Policy driven service control.

In order for the RADIUS based PCRF solution to work and realize major use cases, certain pre-requisites need to be met by RADIUS based NAS clients such as Policy Enforcement Points, Access Gateways and Servers. Either the NAS clients accept service policy based control parameters only on start of session, or they also support fine grained control in the middle of an ongoing session.

RADIUS provides the following mechanisms, some or all of which need to be supported by NAS clients for realization of policy driven service control and NAS clients must support one or more of these mechanisms.

RADIUS Access Accept Packet

An Access Accept packet, sent as a result of successful initial Authentication/Authorization may include subscriber profile information. The profile information may contain parameters in RADIUS attributes that define the subscriber service parameters for bandwidth, QoS and access control.

RADIUS Change of Authorization (CoA)

NAS client supports RADIUS Change Of Authorization (CoA) request that enables asynchronous sending of RADIUS based control commands from RADIUS server to NAS clients.

RADIUS Disconnect Message

If RADIUS Disconnect Message is also supported, it further improves control of service parameters for AAA under PCRF control, by terminating the session on different conditions and triggering events.

RADIUS Re-Authorization and Interim Accounting

NAS clients send mid-session AAA requests that may take one of the following forms:

  • Periodic Re-Authorization via RADIUS Access Request
  • Periodic Interim Accounting Packets with volume usage update during the session

If CoA is not supported by a RAIUS AAA client, many Policy use cases can still be realized through a combination of Access Accept and Disconnect Message, although CoA gives much advanced and fine grained control of policy based actions such as given below:

Policy based Actions enabled by CoA

AAA may take different actions under PCRF control using CoA commands, some of which include:

  • Dynamic Bandwidth control i.e. upgrade/downgrade
  • Redirection of subscriber traffic to captive or other types of web-portals for hot-lining, top-up, bill day alerts, bill shock prevention etc.
  • Dynamic QoS control e.g. reducing queuing delays in Access Service Gateways for a subscriber session by prioritizing the traffic; prioritizing delay sensitive traffic such as VOIP, video etc.

DPI based polices

DPI based enforcement points acting as NAS clients need to support one or more of the following features to realize Policy driven DPI use cases:

  • RADIUS attributes for DPI policy installation. These can be passed to DPI in one of the following ways:
    • Access Accept packets on initial Authentication/Authorization and mid-session Re-Authorization
    • CoA packets sent asynchronously from AAA to DPI during an ongoing subscriber data session
  • Native API exposed by DPI platform. This can be either SOAP/XML based, or other web-based standard API e.g. REST API. The DPI policy profiles can be installed using this API dynamically on the DPI platform. The trigger for a change in policy can be provided by arrival of AAA packets on start or mid of a subscriber sessions, or any other scheduled event in the system. Please note that AAA packets may or may not arrive from the DPI platform itself. AAA is fully capable of installing and updating policies in a DPI other than the NAS client that sent the AAA packet.
  • IF the DPI is able to send events about flow creation and termination etc. to its controlling policy server via a mechanism other than Diameter e.g. through AdvOSS exposed REST API or web-services API, then many of the advanced PCRF use cases could be realized in the RADIUS solution.