Prof. Boerner's Explorations

by Gerald Boerner

Ethernet has become the standard for Local Area Networking. But is was not always so; in the early days of networking, mainframe computers would use this technology, but it was expensive, slow and not supported by a major vendor. IBM was pushing its Token Ring technology while office networks often used ARCNet because it was less expensive. But 3Com developed this technology into a viable player, who has become the dominant technology in this area.

The old saying when dealing with networks is this: “In a network, you need to consider speed, cost, and reliability. But you can only have two!” Ethernet provides an inexpensive network that transfers data reliably. In recent specifications, it has also achieved speeds into the Gbit/second range.

Be aware that this technology was the enabling technology for Local Area Networks which today pervades our offices and homes. The topic is so large that this is the first installment of four parts.  GLB

“Its dedicated Ethernet. The POPs are held together by native, Layer 2, dedicated Ethernet.”
— Alan Davis

“There is an enormous market for feature-rich, value-priced Fast Ethernet switches at the edge of today’s next-generation networks,”
— Tom Burns

“Token ring was a very elegant way of sharing bandwidth on a LAN, …What killed it was LAN switching because all that matters there is price per port. Ethernet was simpler and supported by more vendors, so it was cheaper to build Ethernet chip sets.”
— David Passmore

“Although Ethernet has existed for more than 25 years, it does not have an industry voice that represents the spectrum of IEEE 802 Ethernet standards developments and serves the IEEE 802 Ethernet industry as a whole.”
— Brad Booth

“The Ethernet Alliance is pleased to have Sun Microsystems as one of our founders. Sun Microsystems has a long history of involvement in IEEE 802.3 and in the formation of various past alliances for promoting of Ethernet technologies.”
— Brad Booth

“Although Ethernet has existed for more than 25 years, it does not have an industry voice that represents the spectrum of IEEE 802 Ethernet standards developments and serves the IEEE 802 Ethernet industry as a whole. With the strong support of our founding members, the Ethernet Alliance will be that voice, and we will move aggressively to accelerate the growth and expansion of IEEE 802 Ethernet technologies.”
— Brad Booth

“Whether for entertainment, business or personal communications, video is becoming a crucial application for our customers, and distance learning and video conferencing are natural extensions of our expertise in transporting video as part of the triple play to cable subscribers, … We’ve built our video transport market leadership on carrier-grade optical Ethernet platforms that ensure reliability, performance and manageability – because best-effort is not good enough in the video world.”
— Steve Alexander

Wizards of the Internet: Ethernet, Part 1

Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model, through means of network access at the Media Access Control protocol (a sub-layer of Data Link Layer), and a common addressing format.

Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from around 1980 to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET.

History

Ethernet was developed at Xerox PARC between 1973 and 1975. In 1975, Xerox filed a patent application listing Robert Metcalfe, David Boggs, Chuck Thacker and Butler Lampson as inventors, U.S. Patent 4,063,220 “Multipoint data communication system (with collision detection)”. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper.

The experimental Ethernet described in the 1976 paper ran at 3,000,000 bits per second (3 Mbit/s) and had eight-bit destination and source address fields, so the original Ethernet addresses were not the MAC addresses they are today. By software convention, the 16 bits after the destination and source address fields specified a “packet type”, but, as the paper says, “different protocols use disjoint sets of packet types”. Thus the original packet types could vary within each different protocol, rather than the packet type in the current Ethernet standard which specifies the protocol being used.

Metcalfe left Xerox in 1979 to promote the use of personal computers and local area networks (LANs), forming 3Com. He convinced DEC, Intel, and Xerox to work together to promote Ethernet as a standard, the so-called “DIX” standard, for “Digital/Intel/Xerox”; it specified the 10 megabits/second Ethernet, with 48-bit destination and source addresses and a global 16-bit type field. The first standard draft was first published on September 30, 1980 by the Institute of Electrical and Electronics Engineers (IEEE). It competed with two largely proprietary systems, Token Ring and Token Bus.

To get over delays of the finalization of the Ethernet “Carrier sense multiple access with collision detection” (CSMA/CD) standard due to the difficult decision processes in the “open” IEEE, and due to the competitive Token Ring proposal strongly supported by IBM, support of CSMA/CD in other standardization bodies (i.e. ECMA, IEC and ISO) was instrumental to its success. The proprietary systems soon found themselves buried under a tidal wave of Ethernet products. In the process, 3Com became a major company. 3COM built the first 10 Mbit/s Ethernet adapter (1981). This was followed quickly by DEC’s Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, reaching over 10,000 nodes by 1986, far and away the largest then extant computer network in the world.

The advantage of CSMA/CD was that, unlike Token Ring and Token Bus, all nodes could “see” each other directly. All “talkers” shared the same medium – a single coaxial cable – however, this was also a limitation; with only one speaker at a time, packets had to be of a minimum size to guarantee that the leading edge of the propagating wave of the message got to all parts of the medium before the transmitter could stop transmitting, thus guaranteeing that collisions (two or more packets initiated within a window of time which forced them to overlap) would be discovered. Minimum packet size and the physical medium’s total length were thus closely linked.

Through the first half of the 1980s, Digital’s ethernet implementation utilized a coaxial cable about the diameter of a US nickel (5¢ coin) which became known as “thick wire ethernet” when its successor, “thin wire ethernet” was introduced. Thin-wire ethernet was in essence a high-quality version of the cable used on closed-circuit television of the era. The emphasis was on making the physical routing of cable easier, less costly, and, whenever possible, utilize existing wiring. The observation that there was plenty of excess capacity in unused “twisted pair” (sometimes “twisted copper”) telephone wiring already installed in commercial buildings provided another opportunity to expand the installed base and thus twisted-pair ethernet was the next logical development.

Twisted-pair Ethernet systems were developed in the mid 1980s, beginning with StarLAN, and become widely known with 10BASE-T. These systems replaced the coaxial cable on which early Ethernets were deployed with a system of hubs linked with unshielded twisted pair (UTP), ultimately replacing the CSMA/CD scheme in favor of a switched full duplex system offering higher performance.

Standardization

Notwithstanding its technical merits, timely standardization was instrumental to the success of Ethernet. It required well-coordinated and partly competitive activities in several standardization bodies such as the IEEE, ECMA, IEC, and finally ISO.

In February 1980 IEEE started a project, IEEE 802 for the standardization of Local Area Networks (LAN).

The “DIX-group” with Gary Robinson (DEC), Phil Arst (Intel) and Bob Printis (Xerox) submitted the so-called “Blue Book” CSMA/CD specification as a candidate for the LAN specification. Since IEEE membership is open to all professionals including students, the group received countless comments on this brand-new technology.

In addition to CSMA/CD, Token Ring (supported by IBM) and Token Bus (selected and henceforward supported by General Motors) were also considered as candidates for a LAN standard. Due to the goal of IEEE 802 to forward only one standard and due to the strong company support for all three designs, the necessary agreement on a LAN standard was significantly delayed.

In the Ethernet camp, it put at risk the market introduction of the Xerox Star workstation and 3Com’s Ethernet LAN products. With such business implications in mind, David Liddle (General Manager, Xerox Office Systems) and Metcalfe (3Com) strongly supported a proposal of Fritz Röscheisen (Siemens Private Networks) for an alliance in the emerging office communication market, including Siemens’ support for the international standardization of Ethernet (April 10, 1981). Ingrid Fromm, Siemens representative to IEEE 802 quickly achieved broader support for Ethernet beyond IEEE by the establishment of a competing Task Group “Local Networks” within the European standards body ECMA TC24. As early as March 1982 ECMA TC24 with its corporate members reached agreement on a standard for CSMA/CD based on the IEEE 802 draft. The speedy action taken by ECMA decisively contributed to the conciliation of opinions within IEEE and approval of IEEE 802.3 CSMA/CD by the end of 1982.

Approval of Ethernet on the international level was achieved by a similar, cross-partisan action with Fromm as liaison officer working to integrate IEC TC83 and ISO TC97SC6, and the ISO/IEEE 802/3 standard was approved in 1984.

General description

Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. The methods used show some similarities to radio systems, although there are fundamental differences, such as the fact that it is much easier to detect collisions in a cable broadcast system than a radio broadcast. The common cable providing the communication channel was likened to the ether and it was from this reference that the name “Ethernet” was derived.

A 1990s network interface card.
This is a combination card that
supports both coaxial-based
using a 10BASE2 (BNC connector,
left) and twisted pair-based
10BASE-T, using an RJ45 (right).

From this early and comparatively simple concept, Ethernet evolved into the complex networking technology that today underlies most LANs. The coaxial cable was replaced with point-to-point links connected by Ethernet hubs and/or switches to reduce installation costs, increase reliability, and enable point-to-point management and troubleshooting. StarLAN was the first step in the evolution of Ethernet from a coaxial cable bus to a hub-managed, twisted-pair network. The advent of twisted-pair wiring dramatically lowered installation costs relative to competing technologies, including the older Ethernet technologies.

Above the physical layer, Ethernet stations communicate by sending each other data packets, blocks of data that are individually sent and delivered. As with other IEEE 802 LANs, each Ethernet station is given a single 48-bit MAC address, which is used to specify both the destination and the source of each data packet. Network interface cards (NICs) or chips normally do not accept packets addressed to other Ethernet stations. Adapters generally come programmed with a globally unique address, but this can be overridden, either to avoid an address change when an adapter is replaced, or to use locally administered addresses.

Despite the significant changes in Ethernet from a thick coaxial cable bus running at 10 Mbit/s to point-to-point links running at 1 Gbit/s and beyond, all generations of Ethernet (excluding early experimental versions) share the same frame formats (and hence the same interface for higher layers), and can be readily interconnected.

Due to the ubiquity of Ethernet, the ever-decreasing cost of the hardware needed to support it, and the reduced panel space needed by twisted pair Ethernet, most manufacturers now build the functionality of an Ethernet card directly into PC motherboards, eliminating the need for installation of a separate network card.

CSMA/CD Shared Medium Ethernet

Ethernet originally used a shared coaxial cable (the shared medium) winding around a building or campus to every attached machine. A scheme known as carrier sense multiple access with collision detection (CSMA/CD) governed the way the computers shared the channel. This scheme was simpler than the competing token ring or token bus technologies. When a computer wanted to send some information, it used the following algorithm:

Main Procedure…

1. Frame ready for transmission.
2. Is medium idle? If not, wait until it becomes ready and wait the interframe gap period (9.6 µs in 10 Mbit/s Ethernet).
3. Start transmitting.
4. Did a collision occur? If so, go to collision detected procedure.
5. Reset retransmission counters and end frame transmission.

Collision Detected Procedure…

1. Continue transmission until minimum packet time is reached (jam signal) to ensure that all receivers detect the collision.
2. Increment retransmission counter.
3. Was the maximum number of transmission attempts reached? If so, abort transmission.
4. Calculate and wait random backoff period based on number of collisions.
5. Re-enter main procedure at stage 1.

This can be likened to what happens at a dinner party, where all the guests talk to each other through a common medium (the air). Before speaking, each guest politely waits for the current speaker to finish. If two guests start speaking at the same time, both stop and wait for short, random periods of time (in Ethernet, this time is generally measured in microseconds). The hope is that by each choosing a random period of time, both guests will not choose the same time to try to speak again, thus avoiding another collision. Exponentially increasing back-off times (determined using the truncated binary exponential backoff algorithm) are used when there is more than one failed attempt to transmit.

Varieties of Ethernet

The following lists detail the diversity of cabling methods over which Ethernet has or is being used, including some of the technologies of the future. It is not critical that you understand these cabling media in detail; they are included here for reference. In the second part of our coverage of Ethernet we will explore the details of the configuration of these cabling varieties in more detail. At this point, the important consideration is that you realize that the Ethernet Standard is NOT tied to a given wiring schema or a given speed, but that it is a method of placing a packet of data on this cabling within the Local and/or Wide Area Network.

For more detail, please check out the Wikipedia article on “Ethernet.”

Early Varieties [Antiquated]

• 10BASE5:
  Original standard uses a single coaxial cable into which you literally tap a connection by drilling into the cable to connect to the core and screen. Largely obsolete, though due to its widespread deployment in the early days, some systems may still be in use. Was known also as Thick-Ethernet.
• 10BROAD36:
• 10BASE2 (also called ThinNet or Cheapernet):
  50 Ω coaxial cable connects machines together, each machine using a T-adaptor to connect to its NIC. Requires terminators at each end. For many years this was the dominant Ethernet standard 10 Mbit/s.
• 1BASE5:

10 MBit/s Ethernet

• 10BASE-T:
  Runs over four wires (two twisted pairs) on a Category 3 or Category 5 cable. An active hub or switch sits in the middle and has a port for each node. This is also the configuration used for 100BASE-T and gigabit Ethernet.
• FOIRL:
• 10BASE-F:
  A generic term for the new family of 10 Mbit/s Ethernet standards: 10BASE-FL, 10BASE-FB and 10BASE-FP. Of these only 10BASE-FL is in widespread use.
  • 10BASE-FL:
    An updated version of the FOIRL standard.
  • 10BASE-FB:
    Intended for backbones connecting a number of hubs or switches, it is now obsolete.

Fast Ethernet

The following define the varieties of 100 Mbit/sec Ethernet:

• 100BASE-T:
  A term for any of the three standard for 100 Mbit/s Ethernet over twisted pair cable. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2. As of 2009, 100BASE-TX has totally dominated the market, and is often considered to be synonymous with 100BASE-T in informal usage.
  • 100BASE-TX:
  • 100BASE-T4:
  • 100BASE-T2:
• 100BASE-FX:
  100 Mbit/s Ethernet over fiber.

Gigabit Ethernet

The following define the varieties of 1 Gbit/sec Ethernet:

• 1000BASE-T:
• 1000BASE-SX:
• 1000BASE-LX:
• 1000BASE-CX:

10-gigabit Ethernet

The 10 gigabit Ethernet family of standards encompasses media types for single-mode fibre (long haul), multi-mode fibre (up to 300 m), copper backplane (up to 1 m) and copper twisted pair (up to 100 m). It was first standardized as IEEE Std 802.3ae-2002, but is now included in IEEE Std 802.3-2008.

• 10GBASE-SR:
• 10GBASE-LX4:
• 10GBASE-LR and 10GBASE-ER:
• 10GBASE-SW, 10GBASE-LW and 10GBASE-EW.
• 10GBASE-T: 

As of 2009, 10 gigabit Ethernet is predominantly deployed in carrier networks, where 10GBASE-LR and 10GBASE-ER enjoy significant market shares.

40 Gigabit Ethernet and 100 Gigabit Ethernet

As of 2009, 40 Gigabit Ethernet and 100 Gigabit Ethernet (100GbE) standards are still in draft status.

[ End of Part 1 of 4 ]

References:

Katie Hafner & Matthew Lyon. (1998) Where Wizards Stay Up Late: The Origins of the Internet. Simon & Schuster

Background and biographical information is from Wikipedia articles on:

Wikipedia: ARPANet… 
http://en.wikipedia.org/wiki/ARPAnet

Wikipedia: The Internet…
http://en.wikipedia.org/wiki/The_Internet

Wikipedia: Ethernet…
http://en.wikipedia.org/wiki/Ethernet

Wikipedia: Robert Metcalfe…
http://en.wikipedia.org/wiki/Robert_Metcalfe

Web Sites and Blogs:

About.com: Inventors of the Modern Computer — The Invention of Ethernet and Local Area Networks…
http://inventors.about.com/library/weekly/aa111598.htm

IdeaFinder.com: Ethernet…
http://www.ideafinder.com/history/inventions/ethernet.htm

ThinkExist.com: Ethernet Quotes…
http://thinkexist.com/search/searchQuotation.asp?search=Ethernet

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