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TcpSpeed Online Help


TcpSpeed is the first public utility which measures the bandwidth of any TCP/IP connection. This is useful for Internet users, as well as for users of an internal TCP/IP corporate network.


No installation routine has been provided since it's so easy to do a manual installation. (Plus, it helps to keep down the size of the file that you must download.) Here's how to install TcpSpeed:
  1. Get the TCPSPEED.ZIP file (or TCPSPD.ZIP on CompuServe).
  2. Unzip the files into the desired directory. If you are running a Windows 95 system we would recommend that you create a directory called C:\Program Files\Maximized Software\TcpSpeed.
  3. After you have unzipped the files you can delete TCPSPEED.ZIP.
  4. That's all! You're ready to run TCPSPEED. You may want to drag the executable to your Windows 95 Start menu (or put it somewhere deeper in the menu), or create an icon in the Windows 3.1 Program Manager.

To uninstall TcpSpeed, simply delete the following files:
  • IPP20.VBX
  • TCPSPEED.INI (in your Windows directory)

There's a small bug!
Oops! There's a small bug in TcpSpeed 1.01. The bug is that if the first host that you try to connect to doesn't work, then subsequent hosts will not work at all.

The workaround is to make sure that you always meter a known, reliable host first, then try other hosts. Otherwise, you will need to exit TcpSpeed and then restart it in order to reset it.

Basic Concepts

In the world of TCP/IP, the word host just refers to a computer. For example, when you are connected to the Internet your computer is considered to be a host. TcpSpeed measures the throughput between two hosts on the Internet: your computer (host), and another computer that you specify.

The most challenging part of using TcpSpeed is finding another host which can be metered. For more information see the section below titled Finding A Host To Meter.

Once you've found a host to meter, TcpSpeed will measure the throughput between the two computers. If you are connecting to a host that is far away then the data will have to travel a much longer distance, and will most likely travel along many different segments of the Internet. It is important to note that the throughput will always be limited by the slowest segment! The slowest segment effectively acts as a choking point, and you will never get higher throughput than that link allows. (It's like a pipe carrying water.) For home users, it is likely that the slowest link will be their modem.

Keep in mind that using TcpSpeed sucks up all available bandwidth, so use it sparingly. That's why there is a 12-second time limit built in. That also is the reason that we do not provide a list of suggested sites to meter: because if we did then these sites would be constantly bombarded with TcpSpeed activity, thus using up all of their bandwidth (not cool!) as well as increasing the chance that your readings won't be as accurate because someone else may also be connecting to the same host. So please try to find new and different hosts to meter so that the common hosts don't get overloaded. And please don't over-use TcpSpeed, since too many simultaneous high-throughput users can adversely affect the performance of the Internet.

How To Use TcpSpeed

Using TcpSpeed is very simple. Just make sure that you have a live connection to the Internet, then follow these steps:
  1. Type the name of a host that you want to meter into the Host Name edit field.
  2. Click on the Start Metering button, or just press Enter.
  3. TcpSpeed will attempt to connect to this host and meter the bandwidth between your computer and the other host. If it cannot connect then you will see an error message. If it can connect, then TcpSpeed will begin to measure the throughput between the two computers.
  4. After 12 seconds have passed the test run will be stopped. You may also stop it at any point before the 12 seconds have elapsed.

If you want to operate TcpSpeed through a firewall, your firewall needs to pass TCP packets on ports 62901 and 19.

Understanding The Statistics

TcpSpeed performs relatively simple math: it divides the total number of bytes received by the time it took to receive them. This is the basis for all of its calculations. The following three numbers are provided:
  1. Avg Kbits/sec: This indicates how many thousands of bits were transferred per second. This number is similar to the speed ratings for modem. The user of a 14.4 modem might expect to see a number like 14 or 15. The user of an ISDN line might see numbers as high as 128. Higher numbers indicate higher throughput.
  2. (max): This is the highest value that Avg Kbits/sec (above) has had during the current test run. You will see it change as new high values are reached.
  3. Avg Bytes/sec: This reports the average number of bytes received per second during the test run.

It is important to note that the statistics are updated only when data is being transferred. Thus, if the data stream pauses for a while the statistics won't be updated. This can lead to potentially misleading numbers unless you understand the numbers. For example, consider the case where as soon as you start the test 100 bytes are transferred immediately. The window will update to show 100 bytes/sec. Then if nothing else happens during the rest of the test, the window will not update again, so when the test is done it will look like an average of 100 bytes/sec bandwidth. But in fact, that number is only valid up until the point that it stopped receiving data. If you were to average the bytes over the total time then you would get a number more like: 100 bytes / 12 seconds = 8 bytes/sec.

In general, this shouldn't be a problem for most hosts that you meter, since they usually have pretty decent throughput.

Reading The Graph

The blue bar indicates the amount of throughput currently measured. At the far right of the graph is the maximum Avg Kbits/sec value that has happened during this trial run, and the blue bar is filled in proportion to the current value of Avg Kbits/sec. Higher numbers are better because they indicate higher throughput.

If you get a situation where the maximum value is very high but the blue bar drops well below the maximum value, then that means that the packet traffic between the computers is "bursty".

Finding A Host To Meter

Not every computer on the Internet can be metered. There's no good way to find hosts which can be metered without just trying some common locations. Here are some suggestions to help you on your way:
  1. When entering a host name, do not include any leading protocol string, such as http://. For example, if you are curious about the bandwidth coming from Netscape's web site (, you would specify just the host name ( instead of the web site's full url ( (Please note that this is only an example; the Netscape home page cannot be metered.)
  2. The first host that you should try is your Internet access provider. For example, if you are a home user and have an Internet account with an access provider whose domain is then you might want to try metering the hosts,, and
  3. If you are a user connected to an internal LAN, try connecting to your main server. For example,
  4. Try a local university. These often have host names like
  5. Try a university located far away. This often provides a good comparison of how much longer it takes data to move across long distances.
  6. Popular web sites and FTP sites can often be metered. Also try the servers of popular computer companies.
  7. If you know of a domain such as but find that it cannot be metered, don't forget to try other derivatives of that name, such as and

Most of these suggestions are available from the Help / Finding Hosts menu command.

If you specify a host name which doesn't exist, it may look like your computer is hung for up to 30 seconds (while your TCP/IP stack figures out that the host doesn't exist). If this happens, just wait a while and control will be returned to you soon.

Modem Compression And High Numbers

Unfortunately, the data that TcpSpeed uses to measure bandwidth is highly compressible. In fact, the compression rate may go as high as 98%! Therefore, users connected to the Internet via a modem with compression (V.42bis, MNP, etc) may see bandwidth numbers that look much too high. For example, one home user with a 14.4 modem reported an Avg Kbits/sec ranging from 20 to 30!

At this point the best solution for this problem is to disable modem compression in your TCP/IP stack's dialer program, and then try TcpSpeed while no compression is going on.

We are looking for ways to improve the situation, and will let everyone on our mailing list know if we put out any new solutions.

Registering TcpSpeed

TcpSpeed is freeware, but we do request that you register your copy after 10 uses. You can register at any time by choosing the File / Register command. If you have not registered after 10 uses then the registration dialog box will pop up the next time you start TcpSpeed.

Please note when registering that you are asked whether or not you would like to be on our mailing list. If you decide to be on the list then we will keep you informed of major events at Maximized Software that might be of interest to you. But we promise not to bombard you with junk mail!

The Help / About Dialog Box

TcpSpeed provides a Help / About menu command. If you choose this menu command you will discover that there are two links at the bottom of the dialog box. Clicking on them with your mouse will have your copy of Netscape jump to the Maximized Software web site, or will pop up a Netscape mail window so that you can send e-mail to us.

This feature requires you to be running Netscape Navigator 1.1 or greater at the time that you click on the link!

Error Messages

Host Cannot Be Metered

This message indicates that the specified host was found on the Internet, but is not properly configured to allow you to measure the bandwidth between it and your computer. There's nothing that you can do about this problem; you must simply try to find another host to meter.


This vague error message indicates that the specified host name does not exist. There's no way to fix this; you must simply try to find another host to meter.

Other error message

If any other error message appears in the Status field, it will be an error returned by your Winsock implementation (i.e., TCP/IP stack). You may find the message useful, but there may be nothing that you can do to solve the problem. The message is provided merely for your information.

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