Sorry if it's irrelevant for this forum, but I couldn't find any good answers online.
I know that "Internet speed" isn't a stable thing, and the rate of getting a something online, for example loading a video, is a mixture of many factors.
But when an ISP claims that it provides me surfing speed of "100 Mbps", what does it actually mean? Does it mean that it will connect me to the Internet with a link that's capable of transferring 100 Mb per second?

  • Doesn't your business have a contract with the ISP that explains what you are getting?
    – Ron Maupin
    Commented Dec 13, 2017 at 21:45
  • normally the speed provided by an ISP is a theoretical max. Speed so it is what they configure your connection to be. But as you say there are many factors which influence the actual speed so most ISP use something like a Best Effort clause where they say that your speed can be variable an there they sometimes write down what your actual minimum granted speed is. Some ISP‘s don‘t even garantie a minimum.
    – konqui
    Commented Dec 14, 2017 at 13:31

2 Answers 2


An ISP provides an uplink to the Internet with a specific line speed. That speed is the maximum bandwidth you can use for the very last part of a connection to another node anywhere on the Internet. Your link limits any transfer speed you can get (as does any link in between) but it doesn't guarantee any speed.

The actual "Internet speed" you get depends on a large number of factors. In a nutshell, the slowest or most congested link on the path to the destination node will determine the usable speed.


Usually, you can expect it to be a capped to a maximum speed, but you always get less. For *DSL, it depends on distance from the DSLAM, and for fiber, it is usually constant. If you have 100mbit/s, expect 90-95mbit/s on TCP, since there’s overhead on error correction etc.

If you wish to test a connection, and wish to know e.g. speed for a single TCP connection, download a large file from a fast server - e.g. ftp.funet.fi . The speed is derived from a download lasting more than 60 seconds, from several capable hosts, so OKLAs SpeedTest is a bit misleading.

To see packetloss to various nodes, use MyTraceroute (for windows, linux, etc). It has various types of trace IIRC.

Some routers are stunted in the number of connections they can manage (it’s mainly a memory issue, test for this malady by downloading some large files over bittorrent), so try a commercial grade router as well.

Of course, test from a wired connection.

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