VOIP (Skype, Lync) 'stutters' with my ISP. How can I prove it?

Question

When I am on VOIP calls (Skype or Lync) most of the time the calls suffer quality issues where the person on the other end cuts out. 4 perfect seconds, then 1 to 1/2 a second of what the other person is saying gets cut out, 4 perfect seconds... repeat.

When I use the quality monitoring tool in Skype, it shows < .03% of the packets are dropping. Other than that, it looks fine. I have tried a different pc, and even tried bypassing my router and connecting directly to the DSL modem. This ISP is the only choice I have in my area (AT&T DSL) and I work from home so I need a solid connection. Bandwidth seems solid: http://www.speedtest.net/result/2422840929.png:

but I don't know how to isolate exactly what the issue is.

1. What kind of information do I need/tools can I use to collect data to show my ISP that they are the issue?
2. Is there anything possible they can do about this?

Answer 1

I see you use some kind of DSL, probably ADSL.

How long are the periods of outage in your VoIP usage, when the voice disappears?

If they are very brief (under a second), then you might want to determine whether interleaving is used on your line, and what is the number of milliseconds of data that gets interleaved (you can often have an idea regarding this by running traceroute and looking at the first hop after your modem). Interleaving may only be enabled by an ISP, and it delays your packets by a specified number of milliseconds, but such delay makes your transmissions be immune to a lot of interference issues that may otherwise cause the packets to not be transmitted correctly and in full.

If the delays are longer than a second and are very infrequent (e.g. minutes, hours or days apart), then there may be other problems with your DSL line — perhaps your modem thinks that it can get a higher throughput by re-establishing the connection, in which case you might be able to change its settings to not do such silly things.

You might solve this problem by either increasing latency (ask your ISP for higher interleaving that will increase your ping reliability at the price of ping time), or by decreasing your bandwidth (either through the settings in the modem, or [with the nowadays uber-controlling ISPs, more likely] by downgrading the plan you subscribe to).

In any case, to show your ISP that there is an issue, you can use the tool named mtr.