Setting up bandwidth throttling for ADSL with linux

Question

I'm going to set up a new linux router for a company, and have to set up bandwidth throttling.
They have an unlimited ADSL internet connection which will be shared between 2 businesses, one being them.
I will need to set it up so their connection will never be slowed down by the other business.
They will both be connected to the same NIC, but will be on different subnets.
How would I go about doing this?

Answer 1

The LARTC will teach you everything you need to know about tc and QoS.

Answer 2

The LARTC link is a good starter.
Here is a UbuntuForums link that dicusses an example,

Limiting upload speed for non-local connections

I'm looking for a way to limit the upload speed on my Ubuntu machine, so that my upload link doesn't get saturated. However, I don't want to limit traffic within my LAN, so I can FTP/Samba locally with full speed.

^{goes on to reach a tc solution script in two pages}