12.2.1.2 Processing the Responses
The UAC will receive responses to the request from the transaction
layer. If the client transaction returns a timeout, this is treated
as a 408 (Request Timeout) response.
The behavior of a UAC that receives a 3xx response for a request sent
within a dialog is the same as if the request had been sent outside a
dialog. This behavior is described in Section 8.1.3.4.
Note, however, that when the UAC tries alternative locations, it
still uses the route set for the dialog to build the Route header
of the request.
When a UAC receives a 2xx response to a target refresh request, it
MUST replace the dialog's remote target URI with the URI from the
Contact header field in that response, if present.
20.10 Contact
A Contact header field value provides a URI whose meaning depends on
the type of request or response it is in.
A Contact header field value can contain a display name, a URI with
URI parameters, and header parameters.
This document defines the Contact parameters "q" and "expires".
These parameters are only used when the Contact is present in a
REGISTER request or response, or in a 3xx response. Additional
parameters may be defined in other specifications.
When the header field value contains a display name, the URI
including all URI parameters is enclosed in "<" and ">". If no "<"
and ">" are present, all parameters after the URI are header
parameters, not URI parameters.