Why upload rates are lower than download rates in normal internet connections?

"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."

"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. :)"

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.

"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."

Download is faster than upload due to downloading having more channels of networking than upload in a DSL cable. DSL has a wire that can split the signals in three, phone, data upload, and data download. Phone has the least due to less data usage than both, while upload is not expected to be used in large amounts.