SIP - Headers
A header is a component of a SIP message that conveys information about the message. It is structured as a sequence of header fields.
SIP header fields in most cases follow the same rules as HTTP header fields. Header fields are defined as Header: field, where Header is used to represent the header field name, and field is the set of tokens that contains the information. Each field consists of a fieldname followed by a colon (":") and the field-value (i.e., field-name: field-value).
SIP Headers - Compact Form
Many common SIP header fields have a compact form where the header field name is denoted by a single lower case character. Some examples are given below −
SIP Header Format
The following image shows the structure of a typical SIP header.
Headers are categorized as follows depending on their usage in SIP −