Tuesday, August 17, 2010

Teachable moment

In all of the fussing I've been doing over our Internet connection and the microcell lately, I came to discover that the latency on our connection had suddenly become about 40 ms, where it used to be much, much lower than that.

This happened after I had swapped out the Netopia modem/router combo for a separate Speedstream 5100 modem and a Linksys E1000 router.

I just couldn't believe that a separate PPPoE router would add that sort of latency to the connection. In trying to figure it out, I put an Ethernet switch in between the modem and router so I could conveniently connect a laptop simultaneously up to that segment to talk to the modem to get its current line quality metrics and such.

Well, long story short, over the weekend, our link not only had the high latency but started dropping 3-5% of the packets. That's enough packet loss to make the connection seem like EDGE. It was horrible.

Well, we had AT&T come out to check the line, and the technician reported that when he plugged his own laptop in, he saw the latency (as I did), but the packet loss went away.

Turns out the home-made Ethernet cable I had made to go between the modem and router was bad.

That's the one piece of equipment in the mix that I never tested and assumed was good.


The latency, it turns out, was caused by the DSLAM putting us in interleaved mode rather than fast-path. So the tech changed that up. Our first-hop latency when the connection is not being used is now an astonishing 7 milliseconds (from quack).

So big ups to AT&T - at least the part of AT&T that runs our DSL line. The Microcell folks... well, the jury is still out...

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