Design And Implmentation Of A Presence Server Based On Simple Specifications

The concept of Instant Communication comes from Internet and it is composed of two basic and as well typical applications, Instant Messaging (IM) and Presence. Presence application is responsible for delivering status information concerning user's willingness and ability to communicate in the network. As Next Generation Network (NGN) evolves to a new stage and the convergence of applications both in Internet and telecom network turns into a certain trend, the concept of Presence service has been introduced to the telecom network and thus has become a basis of constructing other multimedia value-added services.The feature of Presence is carried out by Presence Server, which is a typical service enabler in the telecom network. Generally, Presence Server collects, stores and distributes presence information. There are many kinds of solutions to implement a Presence Server, utilizing different protocols, standards or specifications. One of those mature specifications is SIMPLE. SIMPLE standardizes SIP extensions for IM and Presence. As SIP is made the main protocol in the NGN core network, SIMPLE becomes a popular subject in the research and developing area of IM and Presence. This paper focuses on the solution to design and implementation of a Presence Server which follows SIMPLE specifications.This paper is based on an actual project of developing a SIMPLE Presence Server. In the first part, Presence service related definitions are introduces in brief. Then key issues in SIMPLE Presence framework are discussed in detail, such as protocol extensions, data representations and service flows, etc. And next, this paper analyses the role of Presence Server in the network environment, checks the demands of terminal devices and network servers, and then generalizes functional requirements of Presence Server.After thorough research and analysis of requirements and constraints about SIMPLE Presence Server, in the second part, this paper presents a layered architecture and discusses key design issues for each layer. Special attention is paid on such detail designs as service logic processing, SIP message processing, subscription state machine and service data model, etc.Finally, the procedure for implementation and test of Presence Server is described. The result proves that the solution to design and implementation of SIMPLE Presence Server fulfils the demands of devices and servers in the network. And the prototype of Presence Server provides a reference for industry product.