Network testing software recommendations

We are a small company struggling to make the installations of Asterisk based systems work. We continually have issues with call quality, dropping, lights not coming on and such. The company we get our systems from always point to the network. In one situation we installed new wiring, switches and still had problems. Can anyone here suggest 1. easy to use and interpret 2. Inexpensive or even free testing software to check or pre-qualify networks we either setup or are required to install into?

Thanks

wireshark