oftware that runs on end users' devices and is used by users to start a new session, to join a session, or to participate in a session. User: is a person who is registered to a MSIP server. He may or may not be taking part in a session run by the MSIP server. Chairman: is a user who starts a new session and invites other users to join the session. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Participant: is a user in a session who can actively participate or con- tribute to the session. Observer: is a user in a session who is allowed to only view and listen to the session but is not allowed to take active part in it. Based on the above, the chairman, participants, and observers are all users who are participating in a session via MSIP client entities with the session being managed by the MSIP server entity. Multipoint Session Initiation Protocol (MSIP) Entities The general network architecture contains MSIP server, MSIP client, and MSIP reflector. The architecture SHOULD contain at least one MSIP server and at least two MSIP clients. The MSIP reflector is optional. Figure 13.1 below shows the general architecture of MSIP entities. MSIP Client MSIP Client MSIP Client MSIP Client MSIP Server MSIP Server MSIP Client MSIP Client MSIP Reflector MSIP Client MSIP Client MSIP Server MSIP Server MSIP Client MSIP Client MSIP Client MSIP Client FIGURE 13.1 The general architecture of MSIP. C 2009 by Taylor & Francis Group, LLC Multipoint Extensions for SIP 13.2.1 MSIP Reflector Behavior The MSIP reflector is in charge of reflecting all session control messages to all MSIP servers involved in the session. Once it is started, it waits for connections from MSIP servers. The MSIP reflector must only accept connections from MSIP servers. The MSIP reflector holds information on MISP servers as well as information on sessions handled by MSIP servers. The information is stored in two different tables. The tables are: Session data list Remote MSIP servers list 13.2.2 MSIP Server Behavior T