Yealink W52P in Ring Group

[sbaig04@yahoo.com]

I have a base station and four W52P wireless phones. In my Server I have created a Ring Group and put the extensions for these four phones. When I dial to this Ring Group then all four phones don't ring at the same time. Sometime only three phones ring and one of the four phones doesn't ring. Some other times all four phones ring and after couple of rings two phones drop. I tried to figure out the cause for the past two days but remained unsuccessful. Do you think it is a network problem or these wireless phones are not designed to work in a ring group? Please help.