The Sy interface - between PCRF and OCS

Now I have more work to do then I had and it's all focused on GGSN node part and additional equipment not covered by 3GPP specs.Few months ago, in comments some of you asked me to look deeper into the Sy interface. Have to admit that hadn't have much time lately and.. let's be honest, some kind of a mood to research, put together and publish new articles.

Back to the point where we should start.
     

The Sy interface overview

The Sy reference point is defined between the PCRF and the OCS. Big picture of the relationships between functional entities are shown in Fig 1. below.

Fig. 1. Sy overview

As you may (even should) notice on Fig 1. above are simoultaneously SPR and UDR. Those entities work separetly, that means if there is SPR with Sp interface, there is no UDR with Ud interface in the network. Those were put one one figure to save space. Cojunction or means there is the one OR the other. When UDC architecture is used, the SPR with Sp interface, whenever mentioned in this document, is replaced by UDR and Ud.

Gx interface - sitting between PCRF and PCEF

After you are familiar with OFCS (Offline Charging System) and OCS (Online Charging System) time has come to be more up to date with interfaces that are being used to exchange signaling data. At first I will talk about Gx interface which is responsible for Offline Charging, but not only.

The Gx reference point is located between the Policy Control and Charging Rules Function (PCRF) and the Policy and Charging Enforcement Function (PCEF). The Gx reference point is used for provisioning and removal of Policy and Charging Control (PCC) rules from the PCRF to the PCEF and the transmission of traffic plane events from the PCEF to the PCRF. The Gx reference point can be used for charging control, policy control or both by applying AVPs relevant to the application.

As you probably know, it's always good to start from big picture. Here we go.

Fig. 1. Gx reference point at the Policy and Charging Control (PCC) architecture

So at first, few information about..