Busy Signals

Phthano

Is it possible to receive a busy signal from a telephone if you are calling someone as they call you? That is, caused by you each dialing the call at the same time, not because all available circuits on the network are busy.

GnomeTank

I believe, so yes. This happens every once and a while when my wife and I "cross call" each other. It's random, because sometimes I'll just hit her voice mail, but other times I'll get the busy signal.

Bionic Monkey

Phthano wrote: »

Is it possible to receive a busy signal from a telephone if you are calling someone as they call you? That is, caused by you each dialing the call at the same time, not because all available circuits on the network are busy.

Yes. I've actually had it happen to me once as a kid. Assuming the system hasn't changed that much in 20 years, I see no reason it wouldn't still be possible.

Phthano

This sort of thing is very difficult to look up, so an expert in the area is needed. I would have thought that if no actual connection is made the line would be considered open and it would just pickup on the end you are receiving a dialtone.

Donkey Kong

If the connections "cross" (that is, both are told the other line is open because negotiation is taking place at the same time) both parties get a busy signal. Negotiation happens in the pause between finishing dialing the number and ringing starting (but not for the entire pause, other things happen there too, especially when calling across networks or calling cell phones).

It's hard to re-create this situation to prove it happens because negotiation usually lasts only a fraction of a second unless the phone system hiccups. That's why it's so rare to get a busy signal rather than interruption by call waiting or forwarding to voicemail.