he MSIP server is the heart of the session. It controls all the entities involved in the session. The MSIP server holds information on the users and sessions handled by the MSIP server. It also holds information on the MSIP reflector that can be used. The information is stored in three different tables. The tables are: Session data list MSIP reflectors list Users info list The MSIP server takes full control of all entities involved. The input and output transmissions from the MSIP server consist of control communications (TCP/IP). Once started, the MSIP server searches for the MSIP reflector (if available) and opens a connection to it. The main MSIP Server is the MSIP server that the chairman (the user who starts the session) is logged into. This is the MSIP server that will manage the entire session. 13.2.3 MSIP Client Behavior The main functions of the MSIP client entity are as the control and session monitor, which does all the coordination and synchronization for the MSIP client entity. It provides controls for the following: Login/logout Create session and join session Switch status (available, busy, or away) The MSIP client provides a communication interface with the MSIP server. It also provides a users list and servers list. Finally, it provides feedback of MSIP client and MSIP server messages to users. The local MSIP clients are the client entities connected to the local MSIP server's local-area network (LAN), while the client entities from different LANs are known as remote MSIP clients. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security 13.3 Control Messages Since MSIP is an application layer signaling protocol, it uses the data field in TCP/IP to send its own messages. The first field of the message is the MSIP header (version). A header is used to avoid possible conflict with other applications using the same communication port. The second message field contains the message type. Figure 13.2 shows the general format of MSIP messages. There are essentially six pha