A remote host asked PacBell to gracefully transfer their service to a new location. The result was random net.lossage.

It's a long story. The condensed version: High-speed service was disconnected before it ought to have been, and it eventually was replaced by a dedicated 56Kbps modem. Sometimes there's not enough bandwidth to go around, and that means isolated patches of color.

There's also a vertical line of 1's on the chart. My local machine probably did something silly like poll for e-mail.