SIP Header Fields
Following the start line (or the status line of a response) are various headers providing
additional details regarding the request or the response. These headers, then, contain
parameters providing the details. This section provides an overview of all of the headers
defined (and known at the time of this publication) for use within the IMS. They
can be found in RFC 3261, published by the IETF, as well as various specifications
published by the 3GPP.
Accept When an endpoint subscribes to event notification, it uses the ACCEPT header
to identify what the endpoint can support. For example, if the endpoint is a server
building a URI list for a subscriber, then it will send the SUBSCRIBE method containing
one or more ACCEPT headers. Each of the headers will define the format that the
server is able to support for the URI list.
The ACCEPT header can also be sent within a response to identify media types and
format types that are supported by the endpoint. For example, if an INVITE is sent
with an SDP calling for video in a specific format, but the endpoint does not support
video in that format, it can return a response with the ACCEPT header identifying the
formats supported. The response could be 415 Unsupported Media Type.
The ACCEPT header can also be accompanied by the ACCEPT-ENCODING header,
which identifies the supported encoding for the content.
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