header
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... the URI is found in the Route header). The procedures defined here
in no way affect this URI (i.e., the URI ...
... source IP address where the request came
from, using the port contained in the Via header. For reliable
transport protocols, the response is sent over the connection ...
... transport protocols, to the source
address of the request, and the port in the Via header field. The
procedures here are invoked when a server attempts to send to that
location and that response fails (the specific conditions are
...
...
In these cases, the server examines the value of the sent-by
construction in the topmost Via header. If it contains a numeric IP
address, the server attempts to send the response to that address,
...
... address,
using the transport protocol from the Via header, and the port from
sent-by, if present, else the default for that transport protocol ...
... transport protocol.
The transport protocol in the Via header can indicate "TLS", which
refers to TLS ...
... TLS", "_sip"
otherwise, and the transport from the topmost Via header ("TLS"
implies that the transport protocol ...
... element needs to construct a SIP URI for inclusion
in a Contact header in a REGISTER, or in a Record-Route ...