Ethernet 101

June 10, 2009
Ethernet is a local area networking (LAN) technology that has become the most widely use computer networking method of all time.

Ethernet is a local area networking (LAN) technology that has become the most widely use computer networking method of all time.  While it is the most wide spread LAN used in business and industry, its more recent versions have made it a practical metropolitan area network (MAN) technology and it beginning to be considered an option in wide area networks (WANs) replacing Sonet/SDH.  It is also widely used in other special applications where networking is used.


Ethernet was invented in 1972 by Robert Metcalfe and his associates.  The original was a coax bus topology with a bit rate of 2.94 Mb/s.  During the next ten years it evolved into a 10 Mb/s coax bus and a frame format and protocol emerged.  In 1983, this 10 Mb/s version was standardized by the IEEE as 802.3.

During the early years of its use as a LAN, Ethernet competed with several other technologies most prominently ARCNET a token coax bus and IBM’s Token Ring of twisted pair.  But Ethernet’s proponents kept making improvements and additions that continued to make it popular for a wide range of networking applications.  The big change came with the 1987 version 802.3j that specified low cost unshielded twisted pair (UTP) as the medium. 

Another big breakthrough came in 1995 with the 802.3u standard that defined three versions of a 100 Mb/s data rate technology.  The 100BASE-TX version soon became the mainstay of enterprise LANs everywhere.  It used CAT5 UTP and this so-called 10/100 version of Ethernet is still the anchor of the technology.  But Ethernet was not through yet.  Faster smaller semiconductors and other technologies soon made it possible to go way beyond 10/100.  A 1 Gb/s version was developed and standardized in 1998 as 802.3z.  This was a fiber version that was supplemented by a UTP version in 1999 as 802.3ab and dubbed as 1000BASE-T.

Since then the technology improvements have continued.  Today the latest versions of Ethernet run at a 10 Gb/s rate.  There are multiple fiber and UTP versions as well as coax and backplane versions.  And there are other developments that have kept Ethernet the technology to beat.  Currently, it is without doubt the only remaining LAN technology in use.  And because of its high speed and other improvements, its use is rapidly extending into the metropolitan and wide area networks that in the past have been implemented with ATM over T1 and DS3 lines as well as Sonet/SDH fiber networks.

The table below summarizes some of the latest standards of interest.  One of the most exciting is the next speed increment to 40 and 100 Gb/s.

Figure 2           Summary of some of the more recent and significant Ethernet standards.

IEEE Standard

Ratification Date




Frame size increased to 1522 bytes to allow tagging for virtual LANs and establishing data priority.



10 Gb/s standard, multiple versions over fiber.



Power over Ethernet (PoE).  DC power distribution over the UTP medium to power wireless access points up to 15 watts.



10 Gb/s over UTP.



1 Gb/s and 10 Gb/s over PCB backplanes



PoE enhancements and isolation.  Power boost to the 30-45 watt range.



10 Gb/s Ethernet Passive Optical Network (EPON)



40/100 Gb/s over fiber.

Most Recent Ethernet Applications and Developments

 Roll out of the 10 Gb/s standard.  Now that prices have moderated, the 10 Gb/s version is being widely adopted in data centers to connect servicers, in some of the larger LANs and in some more geographically widespread MANs.  Most versions are based on a fiber optic medium but a twisted pair version is also available for short distances (<100 meters).
  • Rapid development of the 40 and 100 Gb/s standard.  Work continues toward a version of the standard that can replace MANs and WANs not using the more expensive and not-compatible Sonet/SDH fiber standard.  A final standard is not expected until 2010.
  • The emergence of carrier Ethernet.  Carrier Ethernet is a creation of the Metro Ethernet Forum (MEF) and its members.  It defines a set of standards and implementation agreements for a carrier-class service and network that distinguishes it from LAN Ethernet.  Carrier Ethernet is for mission critical applications where quality of service (QoS) is mandatory. 
  • Adoption in storage area networks.  Fibre Channel is the most widely used SAN networking technology.  However it is expensive and it has been discovered that Ethernet can replace it in some applications.  A lower cost alternative solution called Internet Small Computer Systems Interface (iSCSI or I-scuzzy) has been developed.  The iSCSI option is a serial version of the widely used older SCSI parallel connections and protocol used with hard drives.  It uses Ethernet as the networking medium to tunnel SCSI commands and data.  As a result, it is much lower in cost and can run in parallel with existing Ethernet networks. 
  • Increasing use in industrial networks.  Industrial Ethernet is the use of standard Ethernet in place of other special networks developed for the harsh and critical nature of industry.  These networks have to operate with high levels of noise and in extreme environments of temperature variations and corrosive atmospheres.
  • Adoption for instrumentation.  LXI (LAN eXtensions for Instrumentation) is the relatively new instrumentation communications standard designed to replace the GPIB (general purpose instrumentation bus) so widely used in test systems over the years.  It is designed to connect test instruments, PCs and the Internet for any combination of testing, measuring, recording, storing and accessing data.  The basis of LXI is the use of Ethernet because of its low cost and wide availability.
  • Growing use in passive optical networks (PONs).  There is work being done on a 10 Gb/s version of Ethernet designed for PONs that are widely used in metro networks for delivery of digital TV and Internet access services.  PONs use low cost fiber to distribute video and other services to homes and businesses without the need for costly repeaters or other active intermediary hardware in the field.  PONs are widely deployed in cable TV and telecomm infrastructures to provide higher speeds and quality video. 
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