Data Link Layer and IEEE

Long after the OSI model was laid down as the standard guideline from which manufacturers would make their products conform to, for the sake of multi-vendor compatibility, it was clear that certain manufacturers had produced products which had not adhered to the OSI guidelines. Something needed to be done. This is where the Institute of Electrical and Electronic Engineers (IEEE) came in.

They looked at the existing technology that had been built and came up with some new standards. Among these standards were IEEE 802.3 and IEEE 802.5, which we now know as Ethernet and Token Ring respectively. The IEEE decided that it was necessary to divide the data link layer into two separate parts.

The Media Access Control (MAC) and Logical Link Control (LLC) sublayers were born.

Logical Link Control (LLC) Sub Layer

The Logical Link (LLC) sublayer provides services to the Network layer above it and to the MAC sublayer below.

The Data Link layer communicates with upper layers through the LLC.

Media Access Control (MAC) Sublayer

The MAC sublayer uses a flat addressing scheme, which is unique to that device. The MAC sublayer uses framing to organise and group the data, and contains an algorithm which decides when to transmit data.

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