

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer


Is there any reason for this?

share|improve this question
up vote 19 down vote accepted

Most broadband services use ADSL: asymmetric digital subscriber line.

The "asymmetric" bit of that refers to the asymmetric bandwidth, i.e. the upload bandwidth isn't the same as the download bandwidth.

From the referenced wikipedia article:


share|improve this answer
From the same article, what is the logic behind this - Thus the upload signal is weakest at the noisiest part of the local loop, while the download signal is strongest at the noisiest part of the local loop? The tone of the passage suggests that it is very obvious but I dont understand why. – Lazer Sep 24 '11 at 15:30
@Lazer - "noisiest part of the local loop" is at the DSLAM in the central office. Because of line attenuation (e.g. resistance) the signal sent by the user is weakest at this end. To compensate for this weak upload signal, it should have reduced speed so that it's more immune to noise. The DSLAM is the origin of the download signal, so this signal is strongest at this point, and can tolerate some noise even if its speed is high. IOW a stronger signal or lower data rate is required for noise immunity. – sawdust Feb 10 at 22:14

I think the majority comes down to the fact that the main part of people using internet connections will need more download rather than upload.

For the most part we use upload to tell servers what we want (HTTP protocol as an example) and through download is where the heavy lifting comes.

The thing is, that if you run a server then you want a good upload - but most of the time it will be companies running servers - so they get to pay extra for this - and it's a brilliant way to charge extra where it can be done (mainly this is done by selling them a completely different technology though).

Of course there's the limitation of ADSL as well - and the ISPs want to give their customers the best experience, which is done through good download and not too good upload.

All in all a certain ratio needs to be kept for the massive download to be worth anything - and normally (at least in Denmark where I live) you get a little higher upload as you get better download.

share|improve this answer
In fact, most consumer/home ISP services actually forbid running servers of any kind on the connection in the EULA and force you to subscribe to their (much more expensive) business services if you want to run a server (ie upload more than just a little). So like kastermester said, it’s a (sneaky? selfish?) way of making money. – Synetech Jun 12 '11 at 0:48

This is a limitation of ADSL broadband - the A stands for "Asymmetric". The ISPs have no control over this - I hear cable/fibre-optic is much better, but I can't get that where I live (rural Scotland).


share|improve this answer
Not asynchronous - asymmetric. – Jon Skeet Jul 15 '09 at 11:15
Yes! Damn it! :) – Lucas Jones Jul 15 '09 at 11:26

In addition to the technical reasons mentioned above, there are also political/economic reasons that ISPs want it this way. For one, it places control of content distribution in the hands of centralized service providers, and prevents their replacement by peer-to-peer content distribution systems (which would require symmetric bandwidth to enable all nodes to contribute resources at the same rate that they consume them). This is an especially strong motivator for companies like Comcast who are in the business of selling and distributing content, and want to push out smaller competitors. And second, it enables telecom companies to charge exorbitant rates for "business" internet services to anyone who wants to run a server.

share|improve this answer

You can also get SDSL connections, where the two speeds are comparable.

But most of the time, unless you are running some sort of server (or you actually seed), you download much more than you upload, so ADSL works fine.

share|improve this answer


share|improve this answer

The amount of data that can go down POTS (Plain Old Telephone System") wiring is limited by the materials and state of the conductors. But, in most user scenarios, you download far more data from the internet then you send.




share|improve this answer


share|improve this answer

Your Answer


