Implementation of the FOKUS PoCCA

The PoCCA prototype @ FOKUS was validated within the Open IMS Playground, allowing policy enforcement on access networks from IMS signaling.

The FOKUS PoCCA consists of the following components:

P-CSCF

The P-CSCF is part of the Open IMS Core project development tree. Besides all the functionalities that the PCSCF brings as part of the IMS session control layer it also implements a Diameter interface to the policy architecture.

The implementation is based on the CDiameterPeer stack from FOKUS and aligns with the specification from 3GPP up to Release7 (interfaces Gq and Rx). It allows the exchange of the information needed to perform policy and charging control on the multimedia sessions being established. The messages exchanged include the parameters offered by the clients in the SDP description of the sessions. Support for ETSI TISPAN's RACS interoperability (interface Gq') is under development and will be added soon.

PCRF

The FOKUS PCRF implementation performs access, resource and policy control on the sessions being established in the IMS network. It supports the 3GPP Rel. 7 Rx and Gx interfaces (again based on the CDiameterPeer).

The main information units used in the PCRF are the policy rules. With their help, policies that e.g. monitor the assignment of bandwidth are executed. They allow performing admission control, resource control and QoS enforcement. The FOKUS PCRF lets you define policies for the behavior of the events happening in the Gx interface, which is also a Diameter interface in which the necessary information for the bearer level detection of IP flows is exchanged.

The main goal of the initial version of the PCRF has been the compliance with the specification and the robustness and performance of the implementation.

PCEF

The PCEF is an element that is placed in the access network gateway. For the GPRS/UMTS access it is collocated in the GGSN. To test the validity of the FOKUS PoCCA a simple PCEF has been developed to be implemented in a Packet Data Network Gateway for WLAN or WiMAX access networks. It performs access control and reactive QoS control based on IP flow monitoring. It is able to detect events and to report them back to the PCRF, which then performs new decisions to be enforced in the PCEF node.