Telecom network have seen major changes in recent past. Legacy telecom networks worked on Time Division Multiplexing (TDM) technology where the network consists of TDM switches connected to each other in various topologies and phones are connected to these switches through dedicated channels. Signaling is used for call establishment and media channels are used for actually carrying the voice.

There has been lot of development in last decade for packetizing voice and transporting it through IP network called Voice over IP (VoIP). Session Initiation Protocol (SIP) is a signaling protocol which is used for establishing multimedia sessions on the IP networks. This paper gives basics of SIP and how it can be used for implementing advanced applications.