Ryan Courtnage wrote:
Hello all,
Everyone has probably experienced this at some point in the past:
You pick up your analog phone. Rather than hearing dialtone, you are connected with someone who has just called you. Neither you nor them heard a ring.
Maybe it's just me, but it seems these "freak incidents" would occur more frequently years ago, than now.
I've now experienced this a couple of times with an * system (TDM400p - quad FXO):
A SIP exten dials digits which are answered by a Zap trunk. As soon as Zap answers, the SIP extension is connected with an inbound (PSTN) caller (who was expecting to hear an IVR).
My questions are: Who's to blame (telco, tdm card, * config, gremlins)? Is this avoidable?
Thanks Ryan
Really no one is to "blame"
This is known as Glare, or a head on ( collision )
Take a basic Telephony course before attempting to become a telecom engineer.
Back in the "good old days" a PBX would have analog trunks that were ground start, and tip was open when idle. The PBX would have an interface that knew this, and if it found ground on the tip would move to the next outgoing trunk. Ground was applied to the trunk by the CO BEFORE it was rung. The ring signal would then start whatever sequence in the PBX was necessary to answer the call.
I gather that the FXO card doesn't support a ground start trunk at all, being nothing more than a modem given a new lease on life.
Something other than a X100 or TDM400 is needed, and analog Ground start trunks from the Telco are called for for proper two way operation.
GS trunks are certainly still available in the US and probably elsewhere.
If you need enough trunks, perhaps a PRI instead?
John Novack
_______________________________________________ Asterisk-Users mailing list [email protected] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
