DSL: How To Calculate Your Download Speed Starting From BandWidth

How can you calculate an ADSL or xDSL line download speed when you only know the provider speed and the available minimum guaranteed band?

Many are DSL operators inefficiencies, and sometimes you just need a little bit more knowledge to avoid any useless stress. Here you can get some further information in order to verify whether your ADSL is really a slow one or you just made a possible wrong estimation.

Photo Credit: cerae

Differences between asynchronous (ADSL) and synchronous (SDSL) DSL

Asymmetric Digital Subscriber Line is a wide band line with an upload speed lower than its download one. For private and not business use ADSL is the most common one as there is no need to send too many data, for there are many more incoming data than outgoing ones. On the contrary symmetric DSL (SDSL) guarantees you the same speed, for both kind of data.

Megabit and Megabyte: how to understand lines real speed

For a 4 Mbps (Megabit per second) line people think of a 4 Mb/sec (Megabyte per second) download speed. Be careful: one byte corresponds to 8 bits; one kilobyte corresponds to 1024 bytes; one megabyte corresponds to 1024 kilobytes. Such a high quantity of speed measures variables usually generates a sort of confusion, created on purpose by the commercial system.

Here you have a list of an hypothetical 4Mbps line, which is translated in bit, bytes and megabytes:

• A Mbps line downloads no more than:

• 4 Megabit per second
• 500 Kbyte per second
• 0,5 MegaByte per second

So, a 100 Mb file, with a 4 Mbps line, should need 200 seconds time download, with a browser indicating a 500kb/sec download speed.

The minimum guaranteed band

Therefore, all operators guarantee a really minimum speed much lower than the one in force in all commercial networks. For a more detailed idea of ADSL lines performances, you must calculate as done before, considering the minimum guaranteed band and not the commercialized speed.

Anyway, take care: the minimum guaranteed band is often indicated in kilobit! But your PC can show a kilobyte speed where 1 kilobyte corresponds to 8 kilobit. Is that clear? You should divide the minimum guaranteed band for 8 and the result will be the value that should be then shown in your PC during the download (in case it shows it in kilobytes).

Let’s take a 10Mb file, that must be downloaded on a PC, and let’s give a glance to the maximum download speed supposed to be as the guaranteed band varies:

• 128 Kilobit/sec.-> 11 minutes download at the maximum, with a transfer speed of 16 Kilobyte/sec.
• 256 Kilobit/sec.-> 5,5 minutes download at the maximum, with a transfer speed of 32 Kilobyte/sec.
• 512 Kilobit/sec.-> 2,5 minutes download at the maximum, with a transfer speed of 64 Kilobyte/sec.

How to calculate your real ADSL download speed

1. Connect here and check your line download speed
2. Mark Kbps (kilobit per second) speed
3. Check which is the minimum speed guaranteed specified in your subscription and, first of all, if it is in Kilobit (it should be so)
4. Connect here, insert your value in the text box and then the speed is converted in other measurements standards (Kilobyte, Megabyte, etc).

In conclusion: too many people are still confused by kilobit and kilobytes, as there is no clearness on the subject.

I hope I didn’t do any serious mistake…if so…please tell me !!!