When I was in call my extension was unreachable

Hi,

My Organization is using Asterisk 1.2.7.1 with approximately 60 extensions. The problem is one of my extension is configured in my house with IP Phone using internet connection. When i call any number from that extension, that particular extension goes UNREACHABLE at that time only. After i hangup that phone it shows REACHABLE. So, If anybody calls me when i was in call, I couldn’t recive the second call.

Please help me sort out this problem.

Thankyou

Regards,
Krishna Kumar