Pathping should show you at which Layer 3 hop the loss first appears. That should help you isolate the issue, which is a big step forward. However, it won't tell you what type of problem you have.
There are very few tools that will do that job. appareNet by jaalaM Technologies, is designed specifically for that. The challenge is getting resolution on the behavior - how precisely can you define the type of loss, how it varies with different kinds of traffic, and what other behaviors accompany the loss? In some senses, it is like imaging - to resolve the "shape" of the problem, you need a precise instrument and the capability of pattern recognition.
Pathping and other generally available tools are too crude to provide the necessary detailed information. And of course they don't have an expert system attached. Consequently it is left to the engineer to build up a mental picture and make educated guesses until the problem is resolved.
The two options open to you are:
i) Collect together as many of the available tools as you can lay hands on (like pathping, traceroute, iPerf, pchar), develop some familiarity and a regular practice with each one, and then apply them as problem arise to best effect.
ii) Get a more sophisticated network imaging system like appareNet that is automated and does on-the-fly diagnosis.
There isn't much in between that I am aware of.
If ii) isn't an option for you and i) isn't terribly inviting, contact me through SearchNetworking and we'll arrange to do a remote evaluation of the problem for you.
This was first published in May 2003