The following are "generalizations" about VoIP network quality needs. Without specifics, it's impossible to comment with a whole lot of authority, but here are some things to think about.

The most important thing for VoIP is to have solid latency with no packet loss.

"Solid latency" means a latency that doesn't change a whole bunch. Even a high latency can support a VoIP connection if it's consistent. The higher the latency, the more "lag" between the time you talk and the time the other side hears you, but this is only noticeable at the point where you stop talking and you expect them to answer back - a big "silence" there might indicate high latency (kind of like talking from the US to Australia via a satellite link - the latency on a standard phone line via satellite gives noticable lag).

Packet loss is a real killer for VoIP - each lost packet needs to either be retransmitted, or it will mean a small portion of the voice is lost. Either of these can cause delays and garbled voice.

Getting a lot of variance in latency is similar to packet loss, but instead of packets not arriving at all, packets might arrive out of order. At some point, the voice service will start to drop late-arriving packets because they arrive too late and are no longer relevant to the voice that is currently being played. A combination of early and late packets is a challenge. This is often called "jitter".

Now, high latency is something that should be minimized, but in the absense of packet loss and "jitter", the sound quality of the call will still be high, just slightly dealyed. Once you start to add jitter or packet loss, latency can make the call quality worse, however.

The ideal situation is to have a solid black line in the time graph of PingPlotter, similar to the image below. This would result in a relatively good voice connection. If you start to see significantly more spikes and more red, the connection quality will degrade.

You're *shooting* for packet loss < 2% (2% can still cause problems, but usually not), and latency variations of no more than about 50-100ms. An occasional variation bigger than this isn't an issue, but constant large variations will cause problems.