| Abstract
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The REGISTER function is used in a Session Initiation Protocol (SIP)
system primarily to associate a temporary contact address with an
address-of-record. This contact is generally in the form of a
Uniform Resource Identifier (URI), such as Contact:
and is generally dynamic and associated
with the IP address or hostname of the SIP User Agent (UA). The
problem is that network topology may have one or more SIP proxies
between the UA and the registrar, such that any request traveling
from the user's home network to the registered UA must traverse these
proxies. The REGISTER method does not give us a mechanism to
discover and record this sequence of proxies in the registrar for
future use. This document defines an extension header field, "Path"
which provides such a mechanism.
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