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Part I: Fundamentals > SIP Overview - Pg. 43

CHAPTER SIP Overview 4 In this chapter, we will introduce SIP. First of all, we will define some key concepts in the SIP framework, such as sessions and addressing. Then the main functions of the protocol will be presented. After that, we will describe the different SIP enti- ties in the SIP architecture. We will also show a first example of how the SIP enti- ties are involved in a basic SIP call. 4.1 What is SIP? The Session Initiation Protocol is an application-level signaling protocol defined by the IETF in [RFC 3261] for the creation and management of sessions over an IP network. The term "session" refers to the media plane aspect of the communica- tion--that is, to the exchange of media (e.g., voice, video, and so on) among an association of participants. Sessions can be described using the Session Description Protocol (SDP) defined in [RFC 4566]. In order to create sessions, SIP messages carry SDP session descriptions that allow participants to agree on a set of parameters needed for the multimedia communication, such as transport addresses or media types. A key aspect here is that SIP, the signaling protocol, is independent of the session being established and of the mechanism used to describe it. SIP pro- vides the way to distribute this information between potential participants in the session. The Session Description Protocol defines a language to characterize the mul- timedia session. Some key pieces of information have to be present on a session description: 1. The types of media in the session 2. The available for each of the media types 3. The address (IP and port) where media packets should be sent . In Chapter 9, we will dive in detail into the Session Description Protocol. 43