GCN Update June 2006

June 9, 2006

Hotmail and Banking Sites now working properly with acceleration.

This morning our satellite modem manufacturer, in cooperation with our upstream Internet provider, has solved a long-running problem that dial-up users were having with the Gustavus Community Network. As of about 11:15 a.m. "acceleration" (also known as "spoofing") is enabled on our satellite modem and dial-up users are able to view Hotmail attachments and banking sites. Since our cutover to the new satellite modem in January the attachments and some banking sites were not working for dial-up users when acceleration was enabled. We disabled acceleration most of the time since then to accommodate dial-up users but this meant much slower performance for broadband users.

As of now,

• Hotmail attachments and banking sites are working for dial-up users and 
• Performance is much better for broadband users.

Performance testing

The following used Vonage's speed test.

Dial-Up

At the library, where my modem reports a connect speed of 53.2 Kbps (about the maximum possible with an analog modem operating over plain phone lines anywhere), I get the following results:

Given satellite latency and protocol overhead, this is reasonable throughput for a modem connection to the Internet in Gustavus. I repeated the test several times, getting similar results:

Broadband

All GCN Broadband customers should have performance very similar to the following now. Performance does vary from time to time, however, depending on how heavily the shared system is being used. Note that this is a huge improvement over the results I was getting when acceleration was off. Then I was seeing results consistently in the 90-120 Kbps range for downloads and 120-260 Kbps range for uploads (note the odd reverse asymetry).

Technical Background

A technology known variously as acceleration or spoofing is required to overcome the latency buildup that otherwise limits the speed of satellite data communications using the TCP/IP protocol. The problem we were having is that our satellite modem expected the bottleneck to be the satellite connection but for dial-up users the bottleneck was their analog modem connection. Here is how IDirect, the satellite modem manufacturer, explains the problem and the fix that resolved it today:

The satellite network is considerably faster than the Dial up LAN connections. When downloading a file from a PC behind the dialup link, the remote modem ends up buffering a large amount of data that it is slowly distributing to the PC. In the meantime, the server thinks the download is complete, and decides to reset the connection. In the current code design, when the reset is received the session is cleaned up, the still-pending portion of the download is lost, and is never received by the PC.

The above workaround build will allow a configurable setting(through custom keys)on the PP to suppress the cleanup of the session in this case, and allow the download to continue.