I'm a newby setting up the system. Configured 2 Grandstream GPX-2000 phones. They registered and I was able to place calls from each to the other. Problem is that they appear to go to sleep after 3 - 5 minutes and I have to reboot the phones to get them to work again. This is consistent. Also, when this happens there is no indication on the phones' displays that there is anything amiss. I would appreciate any advice.