[Asterisk-Users] Freak incidents, who's to blame?

[Eric Wieling aka ManxPower]

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?

It's called "glare".

http://home.intekom.com/scotland/cookbook/146.htm
http://www.authorizedcom.com/lines_trunks.asp
http://www.beagle-ears.com/lars/engineer/telecom/bizphone.htm
http://www.zvon.org/tmRFC/RFC3064/Output/chapter4.html