# SIP overview

The Session Initiation Protocol (SIP) is an internet protocol that enables two or more users to establish a communication path and exchange data. This exchange of data is called a session. The data can be audio, video, or text. SIP enables users to identify each other, establish a connection, agree on a data format, exchange information, and end the communication.

## Protocol layers

SIP is a layered protocol as defined in RFC 3261. Each layer provides a processing stage with defined functionality. The following table describes these layers:

Layer | Description
Application layer | Provides an interface to an application that enables the application to communicate with other applications.
Transport layer | Splits data into packets for transmission and reassembles them when the packets are received. Hides the details of transport from the upper layers.
Network layer | Packages the data with the correct address information.
Datalink layer and physical layer | The datalink layer creates an error free transmission channel. The physical layer moves the actual data from one point to another.

The following illustration shows the SIP layers:

The functionality of each layer includes the services and functions of all of the layers below it.