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Troubleshooting Gateway Alarm - Gateway Status: Reachable but UnAvailable

Symptom:
 
The Dialogic® Integrated Media Gateway may display a major alarm: "Gateway Alarm, Gateway Status: Reachable but UnAvailable" in the Dialogic® Gate Control Element Management System (GCEMS) EventView (IMG 1004 or IMG 1010) or the EventView tab in the WebUI (IMG 2020).

{All screenshots in this article were taken using ClientView and an IMG 1010, but apply equally to the IMG 2020 when viewing the corresponding panes in the WebUI.}

GCEMS alarm log (IMG 1004 or IMG 1010) or Event Log (IMG 2020) :

 Mar 29 2011 09:14:11     **Major: Node 0: Gateway Alarm, Gateway Status: Reachable but UnAvailable, Gateway Id: 1026, Gateway IP Address: 10.129.51.5:5060, Retry After: 5 Seconds
 Mar 29 2011 09:14:13       Major: Cleared: Node 0: Gateway Alarm, Gateway Status: Reachable and Available, Gateway Id: 1026, Gateway IP Address: 10.129.51.5:5060

While the alarm is on and being cleared, IMG will temporarily stop sending calls to that gateway for the time specified in the Retry-After header field which was received in one of the above responses, once the timer expires, calls should resume.

Reason for the issue:

IMG 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 

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.
 

Solution:

This feature is configured in the SIP SGP Profile pane: this feature is 'enabled' by default but can be disabled.

Product List:

Dialogic® IMG 1004 Integrated Media Gateway
Dialogic® IMG 1010 Integrated Media Gateway
Dialogic® IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic® BorderNet™ 2020 Session Border Controller

Related Documentation:

IMG 1004 / IMG 1010: SIP Retry-After Header - Receive
IMG 2020: SIP Retry-After Header - Receive