Ah the reliability of a link - so very dependent on the medium.
The most unreliable is radio and the characteristics of the link vary depending on the frequency. There are many sources of interference from natural and man-made radio sources, some frequencies get absorbed by air and water, there are reflections and obstacles.
Next is a copper wire, this is affected by poor connections, water or humidity and interference from adacent wires and wire can act as antennae becoming a source of radio interference.
All these arabesque modulation techniques and clever codec standards are intended to deal with these problems and get the maximum data throughput. You only have to look at digital terrestial TV to see how over ambitious modulation schemes result often result poor quality reception of some channels.
Best of all is optical fibre. There are some issues with repeating the signal over very long distances and switching. Connecting fibre has to be done very exactly, but it is a highly reliable medium, capable of very high throughput. 72 Terabits is the current laboratory record. The highest speed you can buy at the moment is the new 100Gb standard. So optical technology has quite a lot of potential. Most of the worlds telecoms networks (where it is practical to lay cables in the ground or undersea) use fibre running at muti-gigabit speeds. The limit of optical transmission has not been reached yet, one limiting factor is the capacity of the electronic conversion at each end. The signal processors and computers need to catch up.
I would be quite happy with a 100Gb fibre to my home and look forward to devices that can operate over the the whole 100Gz of radio spectrum.
Real soon, now. 