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I have used dial-up and/or broadband services from many service providers (in India) and one thing I noted is that the upload bandwidth is lower than the download bandwidth.

Is there any reason for this?

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6 Answers

up vote 14 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:

There are both technical and marketing reasons why ADSL is in many places the most common type offered to home users. On the technical side, there is likely to be more crosstalk from other circuits at the DSLAM end (where the wires from many local loops are close to each other) than at the customer premises. 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. It therefore makes technical sense to have the DSLAM transmit at a higher bit rate than does the modem on the customer end. Since the typical home user in fact does prefer a higher download speed, the telephone companies chose to make a virtue out of necessity, hence ADSL. On the marketing side, limiting upload speeds limits the attractiveness of this service to business customers, often causing them to purchase higher cost Leased line services instead. In this fashion, it segments the digital communications market between business and home users.

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Oh, no! Jon Skeet! –  Daniel C. Sobral Jul 15 '09 at 11:47
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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
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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.

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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
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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).

Of course, the ISPs may be imposing some kind of extra cap. :)

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

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I believe it is because under normal usage, it was found that people download more data than they upload. Thus, ISPs tweak their systems to allow more download speeds than upload speeds.

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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.

Even allowing for the odd media file upload, the aggregate size of all the text, images, audio, ... you download is far greater.

Therefore the engineers who designed ADSL chose to make it asymmetric with more data in one direction.

Of course if you want to run servers it is the wrong approach, but then contact a hosting organisation with fat symmetric pipes.

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