SIP (Session Initiation Protocol) is a signaling protocol used to create, manage and terminate sessions in an IP based network. A session could be a simple two-way telephone call or it could be a collaborative multi-media conference session. This makes possible to implement services like voice-enriched e-commerce, web page click-to-dial or Instant Messaging with buddy lists in an IP based environment. Don’t worry if you don’t know about these services. You don’t need to know them before you learn about SIP.