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.

Gy interface - sitting between OCS and PCEF

Last time I tried to cover Gx interface topic, with many details such as Diameter based PCC rules flow, short description on PCEF and PCRF functions, and Policy Charging and Control (PCC) itself. Every thing what I just mentioned you can find here. Almost whole article is based on information mentioned earlier. I will put links to every section if needed.

Gy is between Online Charging System (OCS) and PCEF. In most cases PCEF is based inside PDN GW (Packed Data Network Gateway) or just short PGW.

Gy interface allows online credit control for service data flow based charging. 

As always, today is also good way to start with a quite high level abstract figure. So.. please enjoy.

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

The basic structure follows a mechanism where the online client (in OCS represented by CTF) requests resource allocation and reports credit control information to the Online Charging System (OCS). As described earlier charging could be based on different Charging Scenarios.

Online Charging System (OCS) - introduction to Gy interface

Previously I wrote about network elements and interfaces between them, now it's time to write about most important thing in a mobile network, from operator's side.
How to charge customers for the fact they are using mobiles to many activities, including web surfing. Today I'm going to present some informations about Online Charging System (OCS), how does it work, its call flow basics scenarios, and last but not least basic principles.

As always is good to know about what we will be talking about, so please have a look at high level architecture concept of online charging.
Ro is reference point from the Charging Trigger Function (CTF) to the Charging Data Function (CDF) and the Online Charging Function (OCF) respectively, and are intended for the transport of charging events. Ro reference point is equivalent to Gy interface.

Fig. 1. Online charging high level architecture

Where:
CTF: Charging Trigger Function
CDF: Charging Data Function
CGF: Charging Gateway Function
BD: Billing Domain. This may also be a billing mediation device / post-processing system.