The IT Stuff

NAT can take a single IP address and distribute it for use of many users by creating a Local Area Network (LAN).The LAN will share a single globally recognized IP address.
Disadvantages:

Translation sometime complex (e.g. FTP, VOIP).
Apps using dynamic ports (UPnP).
Does not scale (today avg. of 500 active sessions per user).
Introduce states inside the network:
Multi-homed networks
Breaks [...]

Transmission medium
Topology
Medium Access tecniques

The  transmission medium  used in local area networks are:

Coaxial cable
Twisted pair
Fibre optics
Wireless

.It is also necessary to set a standard access method between computers, so that they know how the computers are exchanging data, especially when more than two computers are sharing the same physical support. This access method is called a logical topology. [...]