• Does the test ever overestimate speed?
• Why are there speed tests that claim to be more reliable
• kilobit = 1000 bits per second
• Assuming my connection is running properly, what else may impact my speed

No. It is impossible for this Java-based speed test to overestimate speed. It can, however, underestimate due to prevailing "Internet weather" between you and the test site (which is why, if you are most interested in your last mile speed, finding a nearby test site is important), but it can never overestimate.

If you try a few different test servers, including some of the third-party ones that also use our Java test applet, then the highest speed reported is closest to your last mile speed.

Don't forget that protocol overhead will mean that you never reach the actual speed advertised by your ISP. In some cases, especially PPPoE connections, you can lose almost 15% of advertised speed in protocol overhead.

In response to this problem, certain ISPs have set the actual sync rate of consumer broadband connections higher to provide a buffer against the overhead. The idea is a 15% up in advertised speed is worth less people calling into support and complain about lack of advertised throughput.

edited by Mike
last modified: 2013-02-17 16:01:06

Speed tests are simply how fast it is to get from Point A to Point Z. However, slow downs can occur between your computer and the host. These real world speed tests provide results that are not reproducible from inside your ISP's network.

If your ISP is prepared to locate a speed test server inside its network, then it will give you the most accurate measure for last mile speed. Having a very fast connection within your ISP's network is nice (and is what you're paying for as a customer) but that doesn't mean much in real world usage.

Either way, we have a large selection of Java and Flash based speed tests located both in ISPs and elsewhere on our speed test list. If your ISP is one of those, then you will probably be able to test last mile speed the best by using their local test server. If you are interested in real world test results, then pick another well-connected server. It is your choice.

edited by Mike
last modified: 2013-02-17 15:54:47

For the purposes of presenting speed test results, we adopt the data communications convention of k = 1000, not k = 1024. For example, 28.8k modems ran at 28800 bits per second, and 56k modems ran at 56000 bits per second.

The transfer rate expressed as kilobytes per second is based on 1024 as per data storage conventions.

Feedback received on this FAQ entry:

• Be clear. Label the Kb on the main screen to be Kilobits or Kilobytes. I'm still not clear which you mean. The 1024 vs 1000 is a detail in this context.

  2011-09-23 18:32:36

• FYI : Kb = kilo bit KB = kilo byte Mb = mega bit MB = mega byte

  2012-01-16 09:24:13

• lower case b means bits, upper case B means bytes. So Kb is always kilobits. Kilobyte would be KB

  2012-02-22 16:27:32

• Just for information, "k" meaning "kilo" should be always low case - "k", never "K". Upper case is simbol of "Kelvin", unit for absolute temperature.

  2012-02-24 08:15:33

• The computer industry has tried to standardize the meanings of binary prefixes. There is ambiguity in how the old nomenclature is used. There is now a more precise standard that is more precise when describing bit and byte quantities. Kibibyte = 2^10 bytes = 1024 bytes Mebibyte = 2^20 bytes = 1048576 bytes and others http://en.wikipedia.org/wiki/Binary_prefix which is part of http://en.wikipedia.org/wiki/IEC_60027 This standard attempts to overcome ambiguity. Yes it is change and is annoying but it's very specific and guarantees what you write is what others will read.

  2012-03-24 21:44:57 (mrmeval )

• Per ISO and NIST a lower case 'k' is the proper prefix for the 1000s multiplier kilo. The upper case 'K' does not represent kilo (http://physics.nist.gov/cuu/Units/prefixes.html). As was previously posted, the Kibi (Ki) prefix is used to represent 2^10, or 1024 decimal as a multiplier (http://physics.nist.gov/cuu/Units/binary.html). Also, technically "bit" is the proper abbreviation for "binary digit", not 'b', whereas 'B' is generally - but not always - understood to be an 8-bit byte. A kilobyte per second would be 1000 x 8 bits/byte = 8000 bits per second, whereas a Kibibyte per second would be 1024 x 8 bits/byte = 8192 bits per second.

  2012-11-29 01:01:22 (viasatguy )

edited by Mike
last modified: 2012-02-24 09:35:40

Outside of any end to end congestion issues, there are a number of things which may negatively impact speedtest results:

1. Physical distance. You have likely noticed that downloading from a local server location is faster than a distant one. This is because the TCP window (e.g. HTTP transfers) is not optimized for the increased latency that comes from an increase in physical distance the bits have to travel. HTTP is bound by the TCP congestion window which determines how many packets can be sent at one time before an acknowledgment. The larger the window size, the higher the TCP throughput.

2. Firewalls, wireless, Local LAN, PC and modem issues. There are many localized issues which may negatively impact speedtest results. The best (but not perfect) PC test environment is to have a high end PC capable of delivering the provisioned speeds, directly attached to the modem.

3. Capacity issues with intermediate ISPs between the server and the user. There are some speedtest servers on ISPs with poor interconnect relationships or capacity issues. The path between the user and the server factors into any results. Local, on-net, speedtest servers are best to measure your provisioned speed.

4. Tuning of the Speedtest server with parallel TCP streams. This is not well known, but does have a direct impact to higher broadband speeds. Most speedtest servers open multiple TCP streams to more accurately account for single stream TCP limitations. How many simultaneous TCP streams a server opens is important as with 4 streams a server is accurate to up to 50Mbps testing on an average PC. Some speedtest servers are configured for even fewer streams and therefor are less accurate at higher speeds.

5. Asymmetric test environments - High end commercial connections with symmetric speeds often ask why they get asymmetric results from most speedtest servers. This is because most speedtest software / servers are configured for residential broadband testing. They are normally configured for 2-4 simultaneous download streams / test, but only 1-2 upload streams. This will inaccurately give results of asymmetric bandwidth even when you have symmetric speeds. Those with higher end work connections can simulate this.

by ccneteng edited by Mike
last modified: 2010-11-09 19:29:33