5.2.2202 Accepted

The 202 Accepted response [3] indicates that the UAS has received and understood the request, but that the request may not have been authorized or processed by the server. It is commonly used in responses to SUBSCRIBE (see Section 4.1.7), REFER (see Section 4.1.10), and sometimes MESSAGE (see Section 4.1.11) methods.

5.2.3204 No Notification

The 204 No Notification response [4] is used in response to a SUBSCRIBE request that was successful but no notification associated with the request will be sent. This conditional notification can be suppressed using the

header field.

5.3 Redirection

Redirection class responses are generally sent by a SIP server acting as a redirect server in response to an INVITE, as described in Section 3.5.2. A UAS, however, can also send a redirection class response to implement certain types of call forwarding features. There is no requirement that a UAC receiving a redirection response must retry the request to the specified address. The UAC can be configured to automatically generate a new INVITE upon receipt of a redirection class response without requiring user intervention. In addition, proxies may also automatically send an ACK to a redirect and proxy the INVITE to the new location provided in the Contact URI of the redirection. To prevent looping, the server must not return any addresses contained in the request Via header field, and the client must check the address returned in the Contact header field against all other addresses tried in an earlier call attempt. Note that this type of transaction looping is different from request looping.

5.3.1300 Multiple Choices

This redirection response contains multiple Contact header fields, which indicate that the location service has returned multiple possible locations for the sip or sips URI in the Request-URI. The order of the Contact header fields is assumed to be significant. That is, they should be tried in the order in which they were listed in the response.