next up previous contents
Next: Internet Service Model Up: Problems with the Previous: Problems with the

Performance Parameters

There are three key parameters to worry about in the network, and these are important if you intend using a part of the Internet to deliver commercial or dependable WWW services:

  1. Errors

    Transmission technology is NEVER perfect. Even glass fiber has occasional errors. These are when what is received is not what was sent. (Imagine you send a letter by airmail, and the plane crashes at sea, and the postbags are recovered but water damaged - it happens!).

  2. Delay or Latency

    A network is not infinitely fast. In fact, now that we are building a global society, the speed of light limit that Einstein was so keen on, is rearing its pretty head. Also, busy networks run slower. Picture the difference between a space shuttle and a canal boat. A canal boat runs at 4 miles an hour, while the shuttle runs at around 7 miles a second. So the time to get there and back is much less on the shuttle. However, there is a limit.

  3. Throughput.

    Different networks are built for different amounts of traffic. The canal system above can carry around 200 tons per boat, while the shuttle can only carry around 1 ton. So while you may have lower latency on some networks, you may also have lower throughput. Normally, though, latency and throughput are largely unconnected.

    Typically, throughput is a feature of how much you pay, while latency is a feature of the distance you are communicating over, plus the busyness of the net.

Jon Crowcroft
Wed May 10 11:46:29 BST 1995