RFC 3261
RFC 3261 SIP: Session Initiation Protocol June 2002
the set of proxies that need to be visited along the way
(present in the Route header field). A proxy compliant to
these mechanisms is also known as a loose router.
Message: Data sent between SIP elements as part of the protocol.
SIP messages are either requests or responses.
Method: The method is the primary function that a request is meant
to invoke on a server. The method is carried in the request
message itself. Example methods are INVITE and BYE.
Outbound Proxy: A proxy that receives requests from a client, even
though it may not be the server resolved by the Request-URI.
Typically, a UA is manually configured with an outbound proxy,
or can learn about one through auto-configuration protocols.
Parallel Search: In a parallel search, a proxy issues several
requests to possible user locations upon receiving an incoming
request. Rather than issuing one request and then waiting for
the final response before issuing the next request as in a
sequential search, a parallel search issues requests without
waiting for the result of previous requests.
Provisional Response: A response used by the server to indicate
progress, but that does not terminate a SIP transaction. 1xx
responses are provisional, other responses are considered
final.
Proxy, Proxy Server: An intermediary entity that acts as both a
server and a client for the purpose of making requests on
behalf of other clients. A proxy server primarily plays the
role of routing, which means its job is to ensure that a
request is sent to another entity "closer" to the targeted
user. Proxies are also useful for enforcing policy (for
example, making sure a user is allowed to make a call). A
proxy interprets, and, if necessary, rewrites specific parts of
a request message before forwarding it.
Recursion: A client recurses on a 3xx response when it generates a
new request to one or more of the URIs in the Contact header
field in the response.
Redirect Server: A redirect server is a user agent server that
generates 3xx responses to requests it receives, directing the
client to contact an alternate set of URIs.
Rosenberg, et. al. Standards Track [Page 23]