IMG 1010 - SIP Retry-After Header - Receive

Overview:

Feature 1523 adds to the IMG the ability to react when receiving the Retry-After Header in any one of the following responses after an INVITE message has been sent.

Response Value	Failure
404	Not Found (User not found)
413	Request Entity Too Large
480	Temporarily Unavailable
486	Busy Here
500	Server Internal Error
503	Service Unavailable
600	Busy Everywhere
603	Decline

When routed to a single gateway, the IMG will not resend an invite message back to this particular gateway for the time specified in the Retry-After header field which was received in one of the above responses. The maximum amount of time the IMG will wait after receiving the Retry-After Header will be 65535 seconds. This feature is configured in the SIP SGP Profile pane. See below for more information.

If a route list is configured on the IMG, the call will be rerouted to the next entry in the Route List. The IMG will not route subsequent calls to this initial gateway until the timer value indicated in the Retry-After header has elapsed. After timer has elapsed, the gateway will be available again and calls can be routed to it.

SIP Retry-After Header Diagram --> (Receive Retry-After)

Call Flow Diagram:

Procedure:

The IMG sends an invite message to a remote gateway.
The remote gateway cannot process the INVITE and sends a 4xx, 5xx, or 6xx response value as shown in Call Flow above. Within the response message is a SIP Retry-After Header with a wait time. See message below
- Retry-After: 17
When the retry header is validated the call is either rerouted or released depending on the configuration. Any subsequent calls will not be routed to this gateway until after the Timer expires. At that time normal routing and call setup will resume (This example would be 17 seconds).

Additional Information:

This feature is 'enabled' by default but can be disabled through SIP SGP profile.
If there is no retry-after header in the response to the initial INVITE, the port will return to its idle state.
If the Retry-Value is set to 0 seconds, the retry-after header will be ignored and the port will return to idle state.
If the Retry-Header Value is greater than 65535 seconds the value will be set to 65535 seconds.
The Retry-After header is NOT supported if the value is a date. See Below
- Retry-After: Mon, 2 Mar 2008 13:30:00 GMT
The Retry-After header is NOT supported if the value includes a duration. See Below
- Retry-After: 5; duration=3600

Configuration of SIP Retry-After feature: (Receive)

From the Dialogic IMG EMS object, right click and select New Profiles. A Profiles object will get created.
From the Profiles Object just created, right click and select New SIP SGP. This will create a SIP Profile Pane.
Within the SIP SGP pane click on the Retry-After Support field. From here the Retry After Support can be enabled or disabled. See Screen capture below