SIP Event Notification Mechanism And Its Applications In SIP Conference State Notification Service

Now, software and hardware of IP conference base on H.323 protocols, H.323 Protocolsare videoconference criterions for LAN designed by ITU-T. They have been supported by alot of corporation, but they follow on the traditional telephone signal modules and changetranslation mode from circuit switch to packet switch. The complexity of H.323 results indifferent comprehension in different corporations so that these productions communicate isvery difficult. In addition, H.323' devices is difficult for expansibility therefore all systemsneed to be refresh for adding new services.SIP (Session Initiation Protocol) is introduced by IETF, it is an application-layer control(signaling) protocol for creating, modifying, and terminating sessions with one or moreparticipants. These sessions include Internet telephone calls, multimedia distribution, andmultimedia conferences. SIP' destination offers signaling for IP multimedia sessions, but itonly is used to communication peer to peer. So, it can't offer conference service. Research andimplement of SIP-based conference is difficult and complex. At present, a framework forconference with the SIP is only an internet-draft not a RFC document so that IETF is studyingand instituting it. Thus, research and implement of SIP-based conference framework hastheoretical and actual meaning.The Thesis firstly analyses IETF RFC3265 comment. RFC3265 extents signaling andheader fields according to RFC3261 and introduces a event notification mechanism. Throughsignaling of Subscribe/Notify and header fields of Event, Allow-Events, Subscription-State,Subscriber can subscribes event package what it wants. When subscribed events change,notifier transceives this event package to subscriber by Notify signaling. Event notificationmechanism primarily is used to Presence services , but it also can be used to the SIPconference system and implements conference state notification services by extentingsignaling, herder fields, message body of RFC3265.Through analysis and summarization of SIP-based tightly-coupled conferenceframework and compare of H.323 and SIP conference framework, this paper divides anddefines all the conference components. In SIP conference framework, the signaling protocol isSIP and we use RTP/RTCP to transmit media dataflows. The conference server is divided intothree functional entities, such as Focus, Mixer, Notification Service. Focus keeps the signalingconnection with the conference participants, Mixer treats the media dataflows andNotification Service maintains the conference states and will notify the subscriber when thestates change. So this conference architecture has a good interface to be managed andcontrolled. It also divides the module from treating signal dialogs and treating mediadataflows, so it has better scalability.The thesis also introduces the design scheme of conference status notification service.First of all, it put forwards design goal and requirement. It also defines framework ofnotification subsystem and its entity. Subsequently, it analyses and defines conference stateevent package. Event package is defined by XML-schema that includes namespaces, elements,sub-elements and attributes. Conference-info is top level elements. It shows thisXML-schema is defination of conference state and it has four sub-elements: user, sidebar,conf-ids, policy-uris. User element also has two sub-elements: user status and media stream.All elements have their attributes. Utimately, logical design is emphasesly explained thatincludes six modules: initialization, add user, sidebar notify, policy notify, user leave andrefresh status.At last, the thesis explains the process conference state notification services, it includesfour modules: Firstly, it implements the Subscribe/Notify signal and header fields to fit forrequirement of SIP conference protocol stack. Second, it finishes the communication of eventnotification by using Subscribe/Notify signal. Thirdly, it can utilizes XML parser to parseXML event package to Buffer, so it adds Buffer to Notify as package body and transceivesit .Focus and UA parse message body to produce DOM tree. This is because DOM tree islayered modes just like the SIP conference state instructure. Lastly, thread picks up nodes ofDOM tree and display them in the window by Gtk ctree programming. The thread can refreshctree window realtimely.