ok my understanding of what bandwidth is how much "Electricity" can you transmit though a pipeline of copper or optical fibers... small bandwidth = small cables... right? this is my theory..
if i get a 1mm in Diameter of a pure copper pole and than isolate it in a "inner dielectric insulator" have the excess "current" shielded off from a weaved copper surrounding the insulation and than have a plastic coating over it and than :
--------6mm in Di-------|--[converted to a normal RG6 coax]--------> modem or what ever...
i would image that doing this would kinda make like a "pool" of current and when it reaches the the smaller connection it than kinda increases the overall momentum of the electrical current... (a DAM with a tiny hole... get what im trying to explain?). but than again i would also image that do this could cause a collision of current (2 cars cant fit in on lane road so they crash) this would cause data lose or am i wrong?
If your referring to computer network it is best that you use the software to tweak the hardware involve not tampering with the hardware side, this is quite safe. There are lots to consider with the design but if you insist then you can go to electronics designing books or site.
Assume you have two buckets of water at two different heights.
The bandwidth can be considered as the amount of water filling the lower bucket.
If we use pipe A the rate of filling the lower bucket is lesser than the rate of filling if we use pipe B
Bandwith here = Rate of Filling. i.e. the amount of data that can be send per unit of time.
Like kbps, Mbps or Gbps.
For your internet connection this cannot be changed by you. Cause you'll have replace the existing physical layer, which is the tel. lines, the switching devices at the ISP etc.....