The SIP Redirect feature allows the IMG 2020 to respond to the 3xx class of SIP messages returned from a redirect server. The 3xx responses provide information about a users new location, or alternative services that may be able to satisfy the call. This feature is based on RFC 3261 section 8.1.3.4 and RFC 2543.
In a SIP network it is very common to have a re-direct server which determines where to route a call. The redirect server may reply to the IMG 2020 with a 3xx response which has a list of contacts to try to connect with. The IMG 2020 will try each one of those contacts one at a time, until the call is completed, to a maximum of 10 attempts. The IMG 2020 only accepts a redirect to another endpoint in the SIP network and the SIP endpoint does not have to be one of the configured external gateways within the Web GUI.
The SIP Redirect feature is enabled by default but can be disabled through the 3xx Redirect Support field in the SIP Profile - SGP Web GUI Page.
The IMG 2020 can also act as the Redirect Server. Refer to the topic for information on this
Call Flow
Supported 3xx Redirect Responses
3xx responses give information about the user's new location or alternative services that might be able to satisfy the call.
300 Multiple Choices - The address in the request resolved to several choices, each with its own specific location, and the user (or UA) can select a preferred communication end point and redirect its request to that location.
301 Moved Permanently - The user can no longer be found at the address in the Request-URI, and the requesting client SHOULD retry at the new address given by the Contact header field (Section 20.10). The requester SHOULD update any local directories, address books, and user location caches with this new value and redirect future requests to the address(es) listed.
302 Moved Temporarily - The requesting client SHOULD retry the request at the new address(es), given by the Contact header field (Section 20.10. The Request-URI of the new request uses the value of the Contact header field in the response.
305 Use Proxy - 305 provides information for next hop to reach the proxy server. The requested resource MUST be accessed through the proxy given by the Contact field. The Contact field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 (Use Proxy) responses MUST only be generated by UASs.
3xx Response Mapping
If the SIP Redirect Feature has been disabled, the IMG 2020 will map the 3xx responses to 4xx responses as shown below:
Redirection (3xx) Response | Maps to 4xx (client error) response |
300 Multiple choices | 410 Gone |
301 Moved Permanently | 410 Gone |
302 Moved Temporarily | 480 Temporarily Unavailable |
305 Use Proxy | 410 Gone |
380 Alternative Service | 410 Gone |
any other 3xx response | 410 Gone |
Additional Information
The maximum number of redirects supported is ten.
The same IP Profile is used for all attempts.
Once a contact has responded with a 180 Ringing or 183, the IMG 2020 will not make any more redirect attempts.
Simultaneous redirects are not supported.
Redirection to another Channel Group is not supported accept if using IMG 1010 - SIP Redirect IMG Initiated 302.
3xx Responses for Registration Requests is not supported.
380 Responses will be mapped to 410 Gone error code and released.
305 Response will be mapped to 410 Gone error code and released.
Location changes are not saved internally.
The IMG 2020 cannot be redirected back to the PSTN