SIP Overview

1. An application layer control protocol (works with both IPv4 and IPv6), that can
   
   
   1. establish modify and terminate multimedia sessions (conferences), such as IP telephony calls
      
   2. invite participants to existing sessions (like multicast conferences)
      
   3. existing sessions can be modified by adding/removing media from an existing session
      
   4. transparently supports name mapping and redirection services (support to personal mobility)
      
   5. a single externally visible ID can be maintained regardless of the network location (SIP URI)
      
2. creation and management of session between internet endpoints, some of the things involves in doing so are
   
   
   1. discovering one another (using proxy servers)
      
   2. registering on the network (to be visible to others)
      
   3. agreeing on parameters of the session
      
3. SIP supports five facets of establishing and terminating multimedia communications
   
   
   1. location of user (end system to be used for communication)
      
   2. availability of user (willingness of the called party, to engage in communication)
      
   3. capabilities of user (media and media parameters)
      
   4. session setup (ringing, establishment of session parameters)
      
   5. session management (transfer/termination of sessions, modifying session parameters, and invoking services)
      
   
   
4. needs other protocols to provide the service providing a complete multimedia architecture, some of them are
   
   
   1. SDP (Session Description Protocol)
      
   2. RTP (Real-time Transport Protocol), RTCP (Real-time Transport Control Protocol), RTSP (Real Time Streaming Protocol)
      
   3. MEGACO (Media Gateway Control Protocol)
      
5. security services provided by SIP
   
   
   1. denial-of-service prevention
      
   2. authentication
      
   3. integrity protection
      
   4. encryption and privacy services
      
6. What SIP does not offer
   
   
   1. No services, but primitives to be used and implement different services
      
   2. No conference control services (like floor control and voting)
      
   3. No Network Resource Reservation (as SIP messages and sessions can pass through entirely different networks)