This is the first
66 Chapter 3
part of the handshake required to establish a dialog. The following responses are
defined:
?– 200 OK This is sent to indicate that the receiver has accepted the request and
the session can begin (once the ACK is sent by the requestor).
?– 202 Accepted This is sent to indicate the request has been accepted but more
processing is required prior to completing the request.
The ACCEPTED response is sent to notify the requestor that the request has been
received but more processing is required prior to a dialog being established. The dialog
is not established until the ACK method is sent by the requestor. This requires the 200
OK responses. The 202 ACCEPTED responses are typically used with instant messaging,
for example.
3xx Redirect Responses In SIP networks, a session can be redirected to another location.
For example, if a request is sent to a cell phone that has been made unavailable,
the profile for the user may dictate that calls be sent to another device, located elsewhere
in the network. The redirect responses are then used to notify the requestor
that the request is being redirected to another address. Here are the redirect responses
currently defined:
?– 300 Multiple Choices This is sent to the client to provide additional addresses
for a subscriber as alternate destinations.
?– 301 Moved Permanently The CONTACT header provides a new address for the
subscriber, which is then used by the receiving device??™s software to update address
books, etc.
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