Ethernet Technologies Overview

Ethernet is a family of networking technologies used in local area networks (LAN), which are defined under IEEE 802.2 and 802.3 standards. It is the most widely used LAN technology family used today.

Ethernet and the OSI model

The ethernet family of protocols operates at both layer 2 (data link layer) and layer 1 (physical layer) of the OSI model. They are defined in the IEEE 802.2 and 802.3 standards.

LLC sublayer

The LLC sublayer is used to communicate with the upper protocol layers of the OSI model. It takes the protocol data units (PDUs) from the upper layers, which are typically IPv4 packets and adds control information to help deliver the data to its destination.

LLC sublayer is implemented in software, and its implementation is hardware agnostic. An example of the LLC can be considered the network driver software of a server's NIC. The NIC driver is a software program that interacts directly with the NIC hardware and passes the data between the MAC sublayer and the physical media.

MAC sublayer

MAC constitutes the lower sublayer of the data link layer. MAC sublayer is implemented in hardware, typically in the server's NIC. The Ethernet MAC sublayer has two primary functions:

·       Data Encapsulation and Decapsulation

o   Frame Delimiting

o   Addressing

o   Error detection

·       Media Access Control

o   Control of media access

o   Media recovery

Data Encapsulation

The data encapsulation process includes forming the frame, adding Ethernet Header and Trailer, and decapsulation of the frame upon receiving. It provides three primary functions:

·       Frame delimiting - This process provides bit-level synchronization between the sending and receiving nodes. It also signals the receiving node about the start of a new frame.

·       Addressing - This process adds an Ethernet Header to the frame. The header contains the physical addresses (MAC addresses) that are used by the network devices

·       Error detection -  Every frame has a trailer with a cyclic redundancy check (CRC) of the frame contents. The receiving node calculates again the CRC sum and compares it to the one in the frame. If these two CRC calculations match, the frame must have been received without error.

-Ashitosh Ghate