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Dialogic® 1000 and 2000 Media Gateways (DMG series)

On Answer mode returns call connection result too quickly

Problem Description:
Even though the Dialogic DMG1000 Media Gateway is configured for a connection mode of ‘On Answer’ the connection message sent to respond to a call request is sent back to the application before the call destination has answered.

Solution Summary:
Check the configuration of your gateway to make sure that the Outbound Call Connection Timeout value is not set too low.

Technical Discussion
The DMG1000 Media Gateway is configurable in two different connection modes. The first is ‘On Answer’ and the second is ‘Immediate’

The ‘On Answer’ mode allows the gateway to perform call progress analysis on all outbound calls to intelligently report the connection state of a call. The ‘Immediate’ mode provides no call progress reporting at all and will report connection immediately after it is completed dialing an outbound call.

The Outbound Call Connection Timeout value is designed to act as a sentinel value with regards to call progress detection on any outbound calls and thus has an impact on how quickly the connection response gets sent back to the application in response to a call request.

When the gateway is configured for a connection mode of ‘On Answer’ and an outbound call request is made the firmware listens for call progress tones to know the state of the outbound call. Typically the connection response to sent back to the application if either a break in ringback is heard or if voice detection is activated by the destination party answering the call. It is at this point when the connection response is sent back to the application to alert of the connected state of the call.

The Outbound Call Connection Timeout value ensures that, should a call be answered before ringback is heard to begin and / or voice detection is not triggered, the call will still be transitioned into a connected state once this timer expires. This makes sure that the call will not stay in a pending connection state for too long of a period of time after the call has been made. This feature was implemented to account for cases where calls are placed to automated systems that may answer quickly before ringback is presented, and may not offer any type of outbound audio prompt once the call is answered.

The current versions of DMG1000 Media Gateway software (Version 4.0, Service Update 5) allow the Outbound Call Connection Timeout value to be configured for a value as low as 0 milliseconds.

Using a value this low causes the gateway to act as though it is configured for a connection mode of ‘Immediate’. This is because the call progress timer expires before any tones become available once a call has been dialed.

The text shown below is a segment of a gateway trace showing the call activity of an outbound call request (IP to Circuit). The gateway has been configured with a connection mode of ‘On Answer’ and an Outbound Call Connection Timeout value of 0 milliseconds.

Notes:

• Only the technically relevant portions of the trace shave been outlined here. Parts of the trace that have had data removed for brevity are marked with the text ‘<snip>’
• Follow the comments in the trace for an explanation of the call flow.
• The destination number in the trace has been altered.
• The trace shows a gateway configured to use SIP as a VoIP protocol.

The trace commands used to gather this data were:

trace default
trace time on

It is recommended by Dialogic Customer Support that, when using the gateway configured for the ‘On Answer’ connection mode, that the Outbound Call Connection Timeout value be left at its default setting of 10000 milliseconds.

The value configured for the Outbound Call Connection Timeout value can be viewed in two ways.

• Via the web interface by navigating to the ‘Gateway’ page and scrolling down till you find the ‘Telephony’ section of the page.
• Via the exported config.ini file by navigating to the import/export page and clicking the ‘export’ button, then opening the exported file in a text editor (ie: Microsoft Windows Notepad) and searching for the variable named ‘telConnectToutMs’. If you save the config.ini file to disk you can alter the value and then import the file back again to change the setting.

Glossary of Acronyms / Terms

PBX	Private Branch Exchange
SIP	Session Initiation protocol

Related Documentation:
PBX IP-Media Gateway Users Guide

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