how can i troubleshoot voip call.
i have a voip phone adaptor and using it with public ip and at remote site my friend have a same voip phone adaptor with public ip configure but when i call him from my phone i get error tone and call is not routed.

second problem is that in same senario somtime my friend get ringing and i get ring back tone but my friend pickup the phone no speech is between us.

sometime i gets one way speech beteen us.

please how to troubleshoot such type of call problem in voip.
please suggest any software so i can analysis the packet coming and going out of my network and also some tools so that i can find actual cause of call routing problem.