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Chapter 1 Overview of the Cisco IP Phone Models 7905G and 7912G
SIP Overview
1-10
Cisco IP Phone Models 7905G and 7912G Administrator Guide (SIP)
OL-4277-01
SIP Servers
SIP servers include the following:
• Proxy servers—Receive SIP requests from a client and forward them to the
next SIP server in the network. Proxy servers can provide functions such as
authentication, authorization, network access control, routing, reliable
request retransmission, and security.
• Redirect servers—Receive SIP requests, strip out the address in the request,
check its address tables for any other addresses that may be mapped to the one
in the request, and return the results of the address mapping to the client.
Basically, redirect servers provide the client with information about the next
one or more hops that a message should take and then the client contacts the
next hop server or UAS directly.
• Registrar servers—Process requests from UACs for registration of their
current location. Registrar servers are often colocated with redirect or proxy
servers.