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  • 1.  Outgoing Trunk to Outgoing Trunk Transfer NO DISCONNECT SUPERVISION

    Posted 04-15-2021 05:42 AM
    Hi,

    CM 7.1
    G450 Gateway
    MM710
    ISDN E1 Trunk.

    From Avaya 9608 H.323 phone, We are trying to call an external mobile number and once it answers, we press Transfer key on IP phone and call another mobile number and then press Complete, but call transfer failed. List trace shows  "denial event 1740: No Disconnect Supervision"

    When I turn on Disconnect Supervision on Trunk group, call transfer is successful.
    " Disconnect Supervision - In? y Out? y "

    But when I enable Disconnect Supervision, I get following " WARNING: Setting this field to "y" may result in trunk lock-ups"
    Please suggest me how to fix this problem without breaking the existing trunk services.


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    Arslan Ali
    UC Consultant
    Vodafone
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  • 2.  RE: Outgoing Trunk to Outgoing Trunk Transfer NO DISCONNECT SUPERVISION

    Posted 04-16-2021 06:41 AM
    Is your trunk an E1 or a true ISDN-PRI?   If it's an ISDN-PRI it's extremely likely that you already have disconnect supervision enabled on the phone company side.  Since ISDN uses a separate D channel for signaling, disconnect supervision is a think.
    That warning is mostly for analog or DS0 connections without a D channel.  The way that you signal to the CO that you want to disconnect on those circuits is to wink (flip the polarity a few times) or ground out the channel for a half second.  The issue with those methods is that there is a chance that the CO sees it wrong and places the call on hold or grabs the second line -- causing the first line to lock up if the other side never hangs up.

    ------------------------------
    Nick Kwiatkowski
    Director of Design and Engineering
    Michigan State University
    East Lansing MI
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    Original Message


  • 3.  RE: Outgoing Trunk to Outgoing Trunk Transfer NO DISCONNECT SUPERVISION

    Posted 04-16-2021 09:10 AM
    Thanks for the information.
    Yes, We have E1 trunk with separate D channel.



    Original Message


  • 4.  RE: Outgoing Trunk to Outgoing Trunk Transfer NO DISCONNECT SUPERVISION

    Posted 04-16-2021 09:20 AM
    The disconnect supervision allows the system to know when either side has hung up so it's required for trunk-to-trunk transfers.  Enabling the option in the trunk group means you're telling the system that you believe the trunk supports this feature. Whether it does or not can be determined either by asking your trunk provider or through testing (make sure you try multiple calls, alternating who hangs up first and use status trunk to confirm the channels drop). 

    If your current trunk (I'm assuming it's a PRI) doesn't support it, consider implementing SIP trunks as they definitely do support disconnect supervision. 



    Original Message