Research Of Multimedia Services Based On IP Network And Implementation Of Session Timer Mechanism

Mobile communication is evolving from 2G into 3G, wireless system uses advanced CDMA technology, meantime on core network, it's also changing from circuit switch to packet switch. Utilizing of 2.5G mobile communication system, brings people much more fresh mobile date services. While the characteristic of high bandwidth of 3G mobile communication is likely to put date services even further progress.IP multimedia subsystem is the subsystem of IP multimedia services, which 3GPP brings forward in release 5 standard version. It marshals the most advanced conception and technology in mobile operation field, and provides a uniform system construction and basic establishment for IP multimedia services.The design ideal of IMS is to provide services of IMS through any IP network while regardless of exact access ways. Construct design of IMS is under the ideal of separate signaling control and media bearer, take layered design method. By doing so, transmission and bear service will be separated from the signaling control system of IMS, while services in higher layer can be run above IMS signaling net.IMS is based on SIP system, while SIP is a signaling control protocol of text under client/server working ways, and refers to the standard and protocol of internet, thus it has characteristic of concise, open, extendable and repeated use. IMS employ the call control mechanism of SIP to establish, manage or terminate all kinds of media services, including Internet multimedia conferences, Internet call, far-distance education and far-distance medical, etc. Each kind of user equipment can establish end to end IP communication trough IMS, and reserves needed service quality.In IMS network, negotiation of media is processed through SDP, defining in RFC 2327, and it's a protocol of application layer which is based on text for describing session in multimedia. Description of SDP can be bore and controlled by many kinds of transmission protocols, such as SIP, HTTP, etc. Integration of SDP&SIP is the most typical in IMS, SIP protocol is used for call control, while message body is load of SDP discription. SDP can be extended to support the negotiation of QoS, in order to provide multimedia session in IMS, which is guaranteed by QoS.SIP and SDP are two important composing modules of IMS, they've been through many crucial extensions, so as to perfect its application. This dissertation is focused on studying one kind of extension for SIP-Session Timer, combining the study for construction of application server, and put the characteristics of Session Timer into reality in application server.SIP(RFC3261) doesn't define a mechanism to enable proxy server or application serve to survey whether session is still under active status, and in some situations (for example UA sends a BYE request to terminate a session,but fails to be carried to server due to network problems) there're possibilities for proxies to be timed out. While in telecom field, any time-out example will lead to paralysis for the whole system, which may cause inestimable results to the operator. Therefore, it's very important for SIP server to establish heartbeat mechanism for a session.Session timer is an extension with an eye to solve this problem. Simply speaking, it's UA sends out session refresh request periodically using re-invite or update message so as to keep the session active. The interval of period is required from negotiation between UAC and UAS. If there's no refresh request in a negotiation period, then UAC or UAS will send bye release resource to the other end. CSCF network element, as proxy server, can delete related resource; application server of B2BUA as UAC or UAS, also carries its point to release resource.Viewing that application servers mainly provide many kinds of increment services for consumers, implement of session timer have to take into consideration for the effects which session timer deals with services in server.The Session Timer mechanism is defined in RFC4028. There are no clear restrictions for some exceptional situations, so we must think over how to design the implementation in order to make the server robuster, stronger, and more reliable.The paper include below issues:1. The author research the main services in the Application Server in the IMS,a important point is about early media ring, call hold, and call retrieve services.2. Researches comprehensively on session timer mechanism, mainly including the detailed analysis on the UAC rules and on the UAS rules which defined in RFC4028.3. Studys the construction of application server, and emphasizes analyzing the effects in every situation of operation of application server, caused by carrying out SESSION TIMER, including the basic call scene, multimedia conference scene, a third party control scene, re-negotiation scene.4. Proposes the project of implementing session timer in application server, and lists details, and mainly describes general design and detail design.5. Proves the implement is feasible and correct through examples of system test, exemplification and analysis on them.Based on study for IMS system and the session timer mechanism defined in RFC 4028, this paper investigates the implement project to proceed this mechanism in application server, and list out exact implement. And the implement of session timer mechanism provides powerful support for the reliability design of SIP server in IMS network.Currently, IMS is becoming an irreversible trend of telecom industry. For operators, one of the advantages of IMS is that using its open structure, they can provide users with integrated, diversified services. The implementation of session timer mechanism in this paper provides an important guarantee of the reliability for the main force business -- application server. The Session Timer mechanism will be a basic demand of reliability for SIP server in IMS business network, so the implementation of Session Timer has very important significance for improving the competitiveness of the SIP server on the market.