tained in the Contact header just received. ACK sip:Bob@131.160.1.112 SIP/2.0 Via: SIP/2.0/UDP workstation1000.university.com:5060 From: Laura Brown <sip:Laura.Brown@university.com> To: Bob Johnson <sip:Bob.Johnson@company.com>;tag=314159 SIP: Protocol Operation Call-ID: 12345678@workstation1000.university.com CSeq: 1 ACK Contact: Laura Brown <sip:Laura@workstation1000.university.com> BYE from Laura to Bob Now Laura is ready to finish the call SO her UA sends a BYE request. This BYE request is also sent directly to Bob's UA using the Contact header previously received. Note that the Cseq has been increased. This BYE request belongs to a new transaction. BYE ip:Bob@131.160.1.112 SIP/2.0 Via: SIP/2.0/UDP vorkstation1000.university.com:5060 From: Laura Brown ksip:Laura.Brown@university.com> To: Bob Johnson <sip:Bob.Johnson@company.com>;tag=314159 Call-ID: 12345678@workstation1000.university.com CSeq: 2 BYE Contact: Laura Brown <sip:Laura@workstation1000.university.com> Final Response from Bob to Laura Bob's UA receives the BYE request, terminates the audio session, and returns a 200 OK response for the BYE. SIP/2.0 200 OK Via: SIP/2.0/UDP workstation1000.university.com:5060 From: Laura Brown <sip:Laura.Brown@university.com> To: Bob Johnson <sip:Bob.Johnson@company.com>;tag=314159 Call-ID: 2345678@workstation1000.university.com CSeq: 2 BYE Contact: Bob Johnson <sip:Bob@131.160.1.112> The example above shows how all the headers that were explained previously in this chapter work together to establish a voice session. We can already see that SIP protocol opertion is pretty simple and easy to understand. CHAPTER Extending SIP: . The SIP Toolkit Chapter 6 Session Initiation Protocol (SIP) is designed SO that its core functionality is present in every implementation. This provides interoperability on a global scale. Every SIP implementation can capitalize on the fact that any other SIP implementation will be able to understand all of the mechanisms described in the SIP Request for Comments (RFC) [RFC 2543]. However, some 