SIP 重定向

SIP Redirect

The SIP Redirect feature allows the IMG to respond to the 3xx class of SIP messages returned from a redirect server. The 3xx responses provide information about a user's 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 the call.  The redirect server may reply to the 2020 IMG with a 300 response which has a list of contacts to try to connect with. The 2020 IMG will try each one of those contacts one at a time, until the call is completed, to a maximum of 10 attempts. The 2020 IMG only accepts a redirect to another endpoint in the SIP network and the SIP endpoint does not have to be one of the configured as an external gateway within WebUI.

The SIP Redirect feature is enabled by default but can be disabled through the 3XX Redirect Support field in the SIP Profile WebUI Page.

 

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 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 2020 IMG 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