ion by sending a CLEND_CONF message to the MSIP server. This message contains only two fields; VER, and type, which in this case, is C_END_CONF. The MSIP server C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Conference ID 1 Byte 1 Byte 2 Bytes FIGURE 13.14 The SEND_CONF message format. MSIP Server 1 MSIP Client 1 MSIP Client 2 MSIP Client 3 C_END_CONF S_END_CONF S_END_CONF Session ended FIGURE 13.15 Message flow for session termination. first confirms that the message is received from the session chairman by check- ing the sender ID and comparing it with the chairman ID in the session table. If so, it will inform all the MSIP clients that are involved in the session about the session termination by sending an SEND_CONF message to all of them. The SEND_CONF contains three fields; VER, type, and conference ID. The conference ID is used by the MSIP server to identify which session is termi- nated. The SEND_CONF message format is as shown in Figure 13.14. After that, the server disconnects all clients from the session and then frees the session resources within the server. Figure 13.15 shows the messages flow for terminating a session. The session chairman is the only one allowed to terminate the session. If the MSIP server detects a network disconnection with the chairman, it will terminate the session automatically. C 2009 by Taylor & Francis Group, LLC Narrowcasting in SIP: Articulated Privacy Control Sabbir Alam, Michael Cohen, and Julián Villegas University of Aizu Ashir Ahmed Kyushu University CONTENTS 14.1 Introduction 14.2 Conferencing 14.3 Media Privacy: Narrowcasting Concept 14.4 System Design and Implementation 14.5 Conclusion and Future Research Acknowledgements References 14.1 Introduction In multimedia conferencing, media streams are exchanged between partici- pants upon session establishment by setting up communication channels within a group. By default, each participant receives a combined stream obtained by mixing other participants' media. Situations arise 