Example A = 01000001
Parity
(error checking)
Parity a way of checking to see if the signal has been corrupted (for example, a voltage spike on the line might shift all 0s to 1s).
Even parity an extra bit is added to make the total number of 1s an even number.
Odd parity an extra bit is added to make the total number of 1s odd.
An A with even parity would be 010000010 there are two ones in A, so it is already an even number.
An A with odd parity would be 010000011 there are two ones in A, so an additional 1 is added to come to an odd number three.
If the receiving computer expects even parity, and finds an odd number of 1s, it knows there was a transmission problem.
A start and stop bit are usually added to show where the letter begins and ends, so the complete packet for a letter A with even parity would be:
10100000101

Strength 
Problems 
Twisted pair (STP and UTP)

Cheap to install, and large established base 
Attenuation, cross talk, eavesdropping 
Coax 
Good speeds, easy to work with 
Bulky and only moderate bandwidth 
Optical
fiber 
Best bandwidth 
Connections are difficult 
microwave 
Good bandwidth, crosses land that might be expensive to trench 
Weather interference, eavesdropping 
satellite 
Good speeds, and great footprint 
Expensive to install and repair 
Radio
(wifi) 
No need for wires 
Eavesdropping, limited speed, still limited availability 
Attenuation weakening. Signals lose energy over time, and the voltage levels that show a 1, can lower enough to look like 0s.
EMI electromagnetic interference. Surrounding equipment throws off an electromagnetic field. This field generates a current that can interfere with other systems. This is a common problem in factories with larger electrical motors.
Corsstalk. If two wires are right next to each other, the current on one may induce a current on the other. We usually experience this as hearing some strangers voice on our phone.