PC Hardware published the third article in the "Master a Network" series, this is helpful for anyone wishing to know about a network and how the whole lot works, while not taking a 4 year degree course like I did :]
This one is about OSI Layer 2 Data Link and covers MAC addresses, network topologies, standards, encapsulation, specifications and layer 2 devices like bridges and switch. Heres a quote:
"As data from the Application layer travels down the Layer stack, it is broken down into smaller units and each unit receives additional information (headers and trailers). These units have particular names, one for each layer that encapsulates data. The Layer 2 encapsulated data is called a frame. The extra bytes in the header and trailer identify the source and the destination of transmitted data and also help in finding erroneous packets, thus ensuring reliable network communications."