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FXO Disconnect Problem

Viewing 9 posts - 1 through 9 (of 9 total)
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  • #28133

    Hi all,
    I am having a problem wil Cisco FXO cards in a 2600 not disconnecting an incomming call…

    Note that this is connected to the UK phone system.

    I am aware that answer supervision is the key here and I have polarity reversal set.

    If an incomming call hangs up, then the IP phone continues to ring.

    Equally if an incomming call is cleared down at the IP phone first, then the line still shows as busy.

    Really, I am looking for the definitive answer for the required config for the BT phone system.

    The cards I have are VIC-2FXO (not -M or -EU.

    teodor georgiev

    are you sure that the PSTN switch sends a polarity reversal down the line on answer/disconnect ?


    Basically, I am not 100% sure! I believe that the UK system uses this method from what I have read.

    Its my first look at VoIP connecting to the PSTN.

    Teodor Georgiev

    I doubt. Ask the local phone company engineers if they provide polarity reversal on your line.


    You could test it yourself with a cheap volt-ohm-meter.

    It must be a old instrument, with a needle instead of a digital readout.
    You may get one on hardware stores and electronic shops.
    Use the DC scale, and put the voltimeter across the two phone wires in paralell when there is a call in progress.
    The reading should be around 15 to 30 volts, dc. When the remote PSTN person hangs up the line, the needle should peg all the way on the other direction for about a second or two, before returning to a normal voltage of 48 or 60 volts, depending on the equipment used on the central office .

    If you do not see that, you will need to enable tones supervision, trying to get the disconnect by making the Quintum “listen in ” into the conversation and disconecting the line by listening for the interrrup tone that happens a the end of the call.

    Best luck!!!
    Post back your findings!!

    PS At least on the old Tenor, you could not have tones supervision on anything but “loop start”

    If you have reverse battery or polarity reversal “on”, the tone supervision will not work.

    You could select them, but they will not operate.

    Teodor Georgiev

    Noname, give Marco a break in Quintum troubleshooting guide. He is actually asking about Cisco 2600 ;)))

    Noname to Teodor

    Darn!!!!! Twice in a week!!!

    Must be the early stages of old age!!!.

    My only hope is that someone else did learn from the post.

    Anyway, the way to test for battery reversal applies to any gateway .

    I found by accident another way to test the battery reversal on phone lines.

    I have a very cheap two lines phone on my desk.

    The LED that indicates wich line is busy works with power from the phone line.

    For that reason, if you make a call on the line and wait for the remote person to hang up, you see the flickering of the LED when the centrall office sends the battery reversal.

    That will be the ticket: Get a cheap phone with a iluminated dial pad or one LED.

    Compatible with Quintum, Cisco, an any other gateways.


    Thanks for the replies…

    I can put a ‘scope on the phone line and capture the waveform if it comes to that. I was hoping someone might just know the answer!

    Cisco tell me that the VIC-2FXO-M2 card is the way to go… this is an enhanced version of the -EU card.

    I have ordered a spare card and will retest with this combination.

    Thanks again for the replies.


    what is polarity reversal?

Viewing 9 posts - 1 through 9 (of 9 total)
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