# SIP message formats

SIP is a text-based protocol. It uses SIP messages to send requests from a client to a server or to send responses from the server to the client. These messages use the following format:

Two methods are available to create the message body:

Method | Description
SIP IEs | Uses pre-defined SIP IEs to add session description protocol (SDP) information to the message. Refer to SIP information element values for a list of pre-defined values.
Transparent IEs | Formats the entire message body as a data array and includes that array as the SIP_IE_BODY element. For SDP information, this array is a string. The application must also supply the content-type header as a SIP IE so that the correct information appears in the SIP message. Refer to SIP information elements for a list. To add SIP_IE_BODY elements, use the NCC_SIP_INFO_ADD_DATA macro.