Ethernet

see also:  Ethernet How To     IEEE 802.3 Ethernet        Charles Spurgeon's Ethernet Site

Ethernet was developed in 1971, and rocketed into the most dominant LAN technology in the world.  Ethernet is an open standard with many competing companies providing it.  Today it represents well over 90% of all Local Area Networks.

Here we will display the important aspects of Ethernet, and attempt to create something that apparently does not exist - a simple Table listing all of the Ethernet protocols along with their Identifiers !!  I have found plenty of small, incomplete tables listing the main protocol standards, but nothing that is even close to complete.

The only real competitor to Ethernet used to be IBM's Token Ring architecture.  15 years ago, LAN's were about 60% Ethernet, and 40% Token Ring, and there are still a lot of token ring LAN's.  But in May, 2003, IBM announced a $100 million program to tear out token rings inside of IBM and replace them with Ethernet. That's a sign that you could declare it dead. Although Token Ring has been dead for some time, that was the final blow. 

A Quick List of the dominant Ethernet Technologies

More Links:

http://www.10gea.org (10 Gbps Ethernet)
http://www.metroethernetforum.org/whitepapers.htm
http://www.i-cubed.co.uk/ethnet.html
 

Ethernet Standard, it's Supplements (Clauses), and Identifiers

As Ethernet standards were developed, they were assigned numerical references by IEEE.  They all begin with 802.3, and the supplements (called "clauses" by IEEE) add one or two letters onto that, such as 802.3a, 802.3j, 802.3ac, etc.  The industry needed a name for these supplements to clarify what they actually are.  For example, 802.3j defines Ethernet over Fiber-optic links.  The identifier is 10BASE-FL, and unlike "802.3j" which says nothing about the underlying technology, the identifier defines the basic parameters of the standard:

 10BASE-FL  =  10 Mbps BASEband - Fiber-optic Link

Communications about Ethernet

Too many people, books, websites, etc - reference Ethernet networks by using only the standard, or the identifier.  To laymen and technicians alike, this causes confusion.  To describe any given Ethernet network accurately, you must include which Ethernet standard it is based on - but also describe the basic details.  Very few people have these standards memorized !!

For example, if you are presenting ans say "we are running an Ethernet 802.3i network", for the vast majority - that measn nothing to them.  If you go on to tell them "it is 10BASE-T" then most will at least guess it uses Twisted Pair.  But to let them know exactly what network you are running, go ahead and state the details :

"We are running an 802.3i, 10BASE-T network, at 10 Mbps over CAT5 unshelded twisted pairs."

Development of Ethernet Standards

Ethernet is by far the most common LAN technology worldwide.  It was thought to be headed to an early grave, but several speed enhancements by a factor of 10 have solidified it as the number one set of standards.  It went from 10 Mbps, to 100 Mbps, and now 10 Gbps is being feverishly developed.  

To understand the formats you need to see the frames - so we will dive right in and list the frame types.  Novell and Cisco use different designations as shown below (the first diagram shows layer 2 Ethernet frames, and the next shows Cisco encapsulated Novell Ethernet frames (Novell uses IPX, which Cisco must encapsulate in IP) with the IP headers removed.

    

DIX Ethernet  (DEC-Intel-Xerox Ethernet)

Formal specifications for Ethernet were published in 1980 by a multi-vendor consortium that created the DEC-Intel-Xerox (DIX) standard. This effort turned the experimental Ethernet into an open, production-quality Ethernet system that operates at 10-Mbps. 

DIX vs IEEE 802.3  -  In IEEE bits 13-14 are used to indicate the length of the data field whereas is DIX they used as an Ethertype. The reason for this change in Frame Header format lies in differences at the data-link layer. 802.3 specifies two distinct sublayers to the data-link layer, (LLC) Logical Link Control and (MAC) Media Access Control. LLC is a separate standard (IEEE 802) and is also found in other types of network such as the 802.5 Token Ring Network. It was the inclusion of LLC in 802.3 that forced the change in bits 13-14 of the Frame Header.

IEEE 802.3 Ethernet

Ethernet technology was then adopted for standardization by the LAN standards committee of the Institute of Electrical and Electronics Engineers (IEEE 802).

The IEEE standard was first published in 1985, with the formal title of "IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications." The IEEE standard has since been adopted by the International Organization for Standardization (ISO), which makes it a worldwide networking standard.

The IEEE standard provides an "Ethernet like" system based on the original DIX Ethernet technology. All Ethernet equipment since 1985 is built according to the IEEE 802.3 standard, which is pronounced "eight oh two dot three." To be absolutely accurate, then, we should refer to Ethernet equipment as "IEEE 802.3 CSMA/CD" technology. However, most of the world still knows it by the original name of Ethernet, and that's what we'll call it as well.

The 802.3 standard is periodically updated to include new technology. Since 1985 the standard has grown to include new media systems for 10-Mbps Ethernet (e.g. twisted-pair media), as well as the latest set of specifications for 100-Mbps Fast Ethernet.