Session Initiation Protocol

Session Initiation Protocol (SIP) is a new and emerging protocol that is used to establish and release the connection between two end systems. It is used in preference to the older H323 protocol. Both protocols provide a similar set of services but SIP is much simpler because it has less logical components. This paper describes the implementation of a VoIP application using SIP as the handshaking protocol. The implementation of the SIP is performed with the aid of Libsip++ library from Columbia University. The audio signal is transmitted via the Microsoft´s Windows API. The VoIP system was created using Delphi 5.0. As the Lipsip++ was created using Microsoft´s C++ 6.0, some incompatibility problem arises. There will be a section discussing these problems and it´s solution. The VoIP system consists of a SIP server and two user agent. The SIP server is linked to a HTTP server to facilitate the update of user configuration via Internet. This paper will also introduce a new function called chatboard that will facilitate users with speech handicap.