Ethernet transport fundamentals

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Ethernet Transport Fundamentals

For people who have done Carrier Ethernet - Overview, this module goes more in depth. It describes the Ethernet protocol in detail and key concepts Ethernet is based on. It also gives in depth explanation of some of the features Ethernet offers. Telecom Grade Ethernet is also presented here.

In this course we are going to discuss the following:
•An introduction to Ethernet
• Ethernet Loop Avoidance
• Ethernet Resiliency
• Ethernet Ring Protection
• Telecom Grade Ethernet Features


The original Etherenet standard was developed in the 70’s for frame transmission across LAN. The word Ethernet was used in the past to describe a medium that all waves could pass trough.

In the Ethernetstandard, the ether was the name given to the physical medium that all hosts connected to, to form a network. Thus the name ETHER-NET.

The original Ethernet was built around the use of thick coaxial cables which would run through a building. Hosts that wished to connect to this cable segment, typically using a Bayonet Neil-Concelman (or BNC connector).

Ethernet frames would then be transmittedwith source and destination addresses (commonly known as MAC addresses). These would be sent to this segment with all transmission delivered to all users.

When a device received a frame destined for another host the frame was dropped. The correct destination would receive the frame and process accordingly.

This topology is sometimes referred to as a shared segment. Although Ethernettopologies have advanced considerable from this many of the understanding principles of the original Ethernet still exist.


As Ethernet developed, different physical cables become more popular, especially the Unshielded Twisted Pair cable which had been used in telephone networks.

In order to use these cables a different physical topology was needed. This involved theuses of a Multi-port repeater commonly know as hub. This device could connect to multiple hosts using an unshielded twisted pair cable.

The hub is a simple physical layer device which takes in an incoming signal and repeats it out all other ports. This ensured that while the physical topology changed the logical Ethernet topology remained the same.

Ethernet Evolution

Ethernet was originallydesigned as a LAN transmission protocol. This meant all Ethernet networks where consigned to certain area such as a building or campus. Because of its success as a LAN protocol, Ethernet has evolved to be a viable protocol for carrier Networks spanning much larger areas, and Ethernet is now seen as a telecommunications technology.

Using Ethernet in carrier Networks has introduced newrequirements such as QoS, guarantees and fast recovery from failures. This is to allow Ethernet to be used as a viable protocol for real time traffic such as voice. Gaming and television over Carrier Networks.

Ethernet and OSI

As far as the OSI model is concerned, the Ethernet standard spans the physical and data link layers. Recall that the physical layer is connected with the physical transmissionof bits and the cables and connecter required. In the case of Ethernet this could be copper or fiber.

The data link layer is responsible for transmitting data across one hop on a network and can be broken up into two sub layers the MAC (Media Access Controller) and LLC (Logical link controller).

The Media access control layer is responsible for deciding when a host should transmit and thelogical link control layer is responsible for setting up and controlling the link.

In the specification of Ethernet, the IEEE defined to standards. IEEE802.2 for the logical link controller and IEEE802.3 for the physical and MAC layer. Over the years Ethernet has evolved many different variations exist, many of these carried over different physical cables. This means that there are a number of...
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