Note: This server is configured to handle multiple clients in parallel. So the throughput you get may be limited because of competition from other users. This should only be relevant if you have a very fast Internet connection.
Located at SWITCH's PoP at CERN, Meyrin, Geneva, Switzerland
1 Gbps Ethernet network connection with large-frame support
It can also identify 2 serious error conditions:
More information about NDT is available in our PERT knowledge base.
There are some well-known problems, please read before submitting a report:
It appears that the applet does not work with the Microsoft Java Virtual Machine. Sun's JRE 5 or above is recommended.
** Starting test 1 of 1 **
Server process not running: start web100srv process on remote server
(ndt.switch.ch:3001)
This error usually means that your local firewall is blocking
access to this server. Please make sure that connections to
TCP ports 3001, 3002, 3003 of ndt.switch.ch are permitted
before submitting a problem report.
** Starting test 1 of 1 **
unknown server
You may run into this problem if your computer connects to the
Internet through a Web proxy but is otherwise restricted to your
intranet. For this service to work, your computer needs to be
able to look up the address of ndt.switch.ch in the
global DNS and connect to it on TCP ports 3001, 3002 and 3003 (see
above).
A test takes about 20 seconds. Click on "start" to begin.
Report Problems Use "ctrl-C" to copy data onto the clipboard and then paste it into the email message.
The NDT performs 2 TCP throughput tests between your desktop computer and this NDT server. First, data is streamed for 10 seconds from your desktop to the server and then a second 10 second test is performed in the opposite direction. A Web100 modified linux kernel captures detailed statistics on these TCP data flows. This data is then analyzed to determine why the connection achieved the throughput results it reported.
The throughput an application achieves is dependant on the amount of buffer space available in the sending and receiving hosts, packet loss due to errors or congestion, packet size (usually limited to 1500 bytes by Ethernet), and the round trip time between the 2 hosts. If this test reports that the sender or receiver buffer size is the limiting factor, increase the buffer size by changing the default buffer size on your computer. Win 95/98/NT users can easily set and change their default buffer size by using the TCPtune application developed by the NLANR MOAT group. Windows users may find that they perfer the DrTCP tool from the dslreports.com web site.
If a large number of retransmissions occur, check the duplex and speed setting on your host and the network switch it attaches to (duplex mismatches are a serious problem due to broken autonegoation protocols). Extremely long round trip times (over 1 sec) ususally indicate that a network router or switch is congested leading to long queuing times. Contact your local network administrator for help in solving this problem.
The Bandwidth * Delay product is reported at the bottom of the "more details" page. Throughput limits for the NDT server's transmit buffer, your clients receive buffer, and the network infrastructure. You may use these numbers as a guide to determining what your client's receive buffer is currently set to. Divide the buffer size by the reported round trip time (RTT) to calculate the throughput value.
For more info on TCP tuning, visit cable/dsl tuning or dslreports.com tweaks or UNIX and Windows TCP/IP tuning tips.
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. Tom Dunigan at ORNL also has traceroute servers at ORNL and at UT.
The NDT server window size for this Java tester is 4MB. The maximum window size used to be 64KB, but newer OS's now support window scaling, so you may be able to request more than 64 KB.
The NDT software (source and compiled programs) is available at http://e2epi.internet2.edu/ndt/download.html.
This java applet was originally developed by ORNL and has been extensively modified
at ANL.
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