Data Link Layer

So far, all that has been mentioned is that information has been sliced up by the higher layers into ‘packets’ . But in fact each packet needs to be broken up into the most basic form of data i.e. data ‘bits’.

A ‘bit’ has two values – a ‘high’ or a ‘low’. Each packet is converted into a series of bits:

This is the job of the data link layer.

It converts the outgoing packets into the correct series of bits. It also converts incoming bits back into complete packets.

Fixing errors

Bits can be corrupted as they travel along the network i.e. a bit can be flipped into the wrong state so a ‘high’ bit may become a ‘low’ bit and vice versa.

The DATA LINK layer tries to spot these reversals and fix them.

To summarise:

	The DATA LINK layer talks to the NETWORK layer above it and the PHYSICAL layer below it.
	It converts outgoing packets into bits and incoming bits back into the correct packets.
	It tries to correct any errors it encounters so that the transfer of information is as effective as possible.