Research And Implementation Of The Go Interface Of IMS PDF Network Element

This paper describes the analysis, design & development details for the IMS PDF (Policy Decision Function) Go interface, and summarizes my ideas, conclusion & innovation on protocol, implementation & software development methodology during my development work.PDF is the key network element for QoS control in IMS. PDF connects the AF (by Gq interface) at application layer and GGSN (by Go interface) at transport layer, and works as the bridge of two layers.PDF's major functionality is to achieve the service-based QoS control. PDF is a new network element defined in 3GPP R5．Due to related to the QoS, charging topics which are greatly concerned by operator, both standardization organization and operator attach importance to PDF. With the background of isolated application layer and transport layer network architecture, PDF is becoming more and more important due to its position in network and its continuously added new functionalities.This paper pays a lot of pagers on Go protocol stack details. Go protocol stack can be divided into four layers: COPS, COPS-PR, PIB and RFC3520 for AT encoding/decoding, and it is payload bearer relationship between layers. Go protocol stack is complex and difficult to understand. So this paper has a lot pages on the details analysis and summary of Go protocol stack.I'm fortunate to join the PDF project and designed and implemented the first commercial Go interface in the industry as a key developer. During my development work, besides the software design, coding and testing, I have also some ides on reusable analysis for isolated application layer and transport layer network architecture, COPS protocol extension method. By the way, I also have some deep understanding on a software development methodology, Continuous Integration.Some important mechanisms, such as AT and Binding mechanism and end-to-end QoS mapping mechanism, are also investigated. The paper also describes the basic message flow of PDF and one PDF's highlight function-Prevent-Misuse. This paper simply describes the basic concept of QoS and the IMS architecture.Due to the PDF evolution step is fast, the paper give a simple description at the end of the documentation.