ORNL TCP Bandwidth tester

This is a java applet (deprecated, see above) to test inbound and outbound TCP bandwidth (Kilobits/sec) from your browser to this web server. Each test takes about 10 seconds. Click on "start" to start tests. Speeds may vary as server and network traffic loads vary. Links that do compression may give unreasonably high data rates since we send the same packet over and over. The applet connects to two non-http ports on the web server, if your browser is behind a firewall, such connections may be denied. Since this is an experimental service, it may also happen that the "bandwidth server" is not running at the time of your test. Your browser's "Java console" may provide additional clues.

• microsoft's bandwidth tester
• dslreports upload/download tester and speed result archive
• bt2kfast browser/throughput tester
• our ORNL web100 bandwidth tester, experimental (not always available)
• our UT web100 bandwidth tester, experimental (not always available)

You can see the hops (routers) that your packets pass through from your machine to a target Internet site with the traceroute command (for Windows, use tracert in DOS/command prompt window). The route can actually vary from packet to packet, test to test, and the reverse route (return path) may not be the same. There are several traceroute servers around the world that can show you the route back to your browser. I also have traceroute servers at ORNL and at UT.

Throughput can be limited by both client and server OS's TCP window size. The rule is, windowsize = bandwidth * RTT For @home to ORNL, RTT is 200 ms, default windowsize for Windows is 9KBytes, which implies the max bandwidth you can get to ornl is about 360 Kbs. Most UNIX's allow the application to increase the windowsize with a setsockopt(). For Win95/98 you'll need to mess with the registry:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP
"DefaultRcvWindow"="32767"
Max window used to be 64KB, but newer OS's now support window scaling, so you may be able to request more than 64 KB. (The remote server for this test uses a window of 64,000 bytes, and the network interface is 10 Mbps.) For more info on TCP tuning, visit cable/dsl tuning or dslreports.com tweaks or UNIX and Windows TCP/IP tuning tips. You can measure round-trip times with the ping command.

Throughput is also affected by packet loss due to congestion. Visit my cable modem testing page to learn more about the effect of packet loss on TCP performance. For a Windows graphical network performance speedometer, try netpersec