Outgoing call picks up incoming call

I recently installed an Asterisk system at my company, and it has worked great. We are having one issue, however. We have 6 analog lines that the system uses. On occasion, someone will pick up their phone (Polycom IP501), get a dial tone, and dial the external number they want. They don’t hear ringing, and find out that they have answered an incoming call.

It sounds to me like they are dialing the number, and then asterisk picks up one of the analog lines to place the call at the same time that an incoming call is coming on that line. It hasn’t answered the call yet (usually 1 or 2 rings), so it doesn’t know that the line is busy.

Is there anyway to remedy this situation? I can try to provide a better explanation if I’m not clear. Thanks!

This will happen when using Analog lines. It is called glare. To help prevent it, for outbound calls use zap/G1 so it starts at the highest channel and works down as inbound calls come in on the first channel and work up. This of course assumes the telco doesn’t send calls randomly to the lines.