The IMG 2020 has the ability to react when receiving the Retry-After Header in any one of the following responses after an INVITE message has been sent. Refer to SIP Retry-After Header - Transmit for information on the transmit side.
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 2020 will not re-send an INVITE message back to this particular gateway for the time specified in the Retry-After header field received in one of the above responses. The maximum amount of time after receiving the Retry-After Header IMG 2020 will wait is 65535 seconds. This feature is configured in the SIP SGP Profile pane. See below for more information.
(When Route List is Configured): If a route list is configured, the call will be rerouted to the next gateway entry in the Route List. The IMG 2020 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
The IMG 2020 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).
Configuration of SIP Retry-After feature: (Receive)
Initial Configuration
The procedure below explains how to configure the IMG 2020 to respond to a received SIP Retry-After Header from a remote gateway if SIP congestion is determined. Before configuring the outbound SIP Retry-After feature, the IMG 2020 must have an initial configuration created on it. Follow the Basic Configurations procedure before proceeding.
Create SIP Profile (SGP)
Right click on the Profiles object and select New SIP Profiles. The SIP Profiles object is a parent or container object. No configuration is needed here. Refer to the SIP Profiles topic for more information on this object.
Right click on the SIP Profiles object and select New SIP Profile. The first profile that gets created is a Default SIP Profile and cannot be modified. Disregard this profile.
Right click on the SIP Profiles object and select New SIP Profile again. In the SIP Profile object that appears, either enter a name that identifies this SIP Profile or accept the default name already entered. In this example the SIP Profile was labeled Retry_After_Profile.
Right click on the SIP Profile object just created and select New SIP Advanced Settings. Verify the Retry-After Support field is defaulted to Enabled.
Create SIP Signaling
The Retry-After functionality is configured in the SIP Signaling object as described below. When creating the SIP signaling object,
Right click on the IMG 2020 physical node and select New Signaling. The Signaling object is a parent or container object and no configuration is needed here. Refer to the Signaling topic for more information on this object.
Right click on the Signaling object created and select New SIP. In the IP Operation Mode field, select whether the SIP stack will be configured for Single IP or Multiple IP Mode.
In the Retry-After field, enter the number of seconds (Range = 1 to 65535 seconds). This value will be transmitted back to the remote inbound gateway via the Retry-After header that is part of the 503 Service Unavailable response. Below in the Additional Information section there are two examples of how the Retry-After headers are formatted.
Retry-After Alarm Info |
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Refer to topic for more information.
Right click on the SIP Signaling object and select New SIP IP Address. Refer to the SIP Signaling - IP Address topic for more information on configuring the fields in this object.
Configure SIP Signaling (Cont)
The configuration above displays how to configure the SIP Profile and SIP Signaling stack so the SIP Retry-After Header feature is configured. The next step is to configure the SIP Channel Group, SIP remote gateway, and any other remaining SIP objects not displayed in the configuration above. Refer to the Configure SIP (Single SIP IP) topic for a procedure that describes how to configure the remaining SIP functionality. This procedure can be used to finish the SIP configuration for this feature.
Additional Information
This feature is enabled by default but can be disabled through SIP Profile object.
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
The Retry-After header is NOT supported if the value includes a duration. See Below