A Short History of Ethernet


Ethernet was originally developed at Xerox PARC (Palo Alto Research Center) Laboratories in the 1970s. Robert Metcalfe was charged with the responsibility of networking a group of computers that could all use a new laser printer that Xerox had developed. Xerox also had just developed what was probably the first personal workstation, and had a need to network more than the usual two or three computers that you would find in a single building during that time.

The original Ethernet standard was developed over the next few years, and this resulted in a paper, "Ethernet: Distributed Packet-Switching for Local Computer Networks," written by Metcalfe and David Boggs (Communications of the ACM, Vol. 19, No. 5, July 1976, pp. 395404). This paper gives credit to the ALOHA project that had been done in Hawaii with packet radio transmissions into the "ether," noting that scientists once thought that electromagnetic radio signals traveled through a substance known as "ether." In this first Ethernet experimental network described in the paper, the network covered a distance of 1 kilometer, ran at 3Mbps, and had 256 stations connected to it. For its time, this was an accomplishment.

Note

The Metcalfe and Boggs paper anticipated many other innovations that would appear in the next few years in the arena of networking. They recognized the limits of a local area network using a shared medium. They also anticipated the use of bridges (repeaters with packet filters) and of higher-level protocols that would have an expanded address space that would allow for additional fields that could be used for routing purposes. Another interesting thing to note is that, similar to IBM when it created the now-famous personal computer that has become a standard, Metcalfe and Boggs also chose to use "off the shelf" parts for the network transmission medium: ordinary CATV coaxial cables and the taps and connectors used with them. This made it even cheaper to think about creating a commercial version of Ethernet. An online copy of this paper can be found at www.acm.org/classics/apr96.


Later, a consortium of three companiesDigital Equipment Corporation, Intel, and Xeroxfurther developed the Ethernet II standard, sometimes referred to in older literature as the DIX standard, based on the first initials of the participating corporations. These companies used the technology to add networking capabilities to their product lines. For example, at one time Digital Equipment Corporation had the largest commercial network in the world, using DECnet protocols connecting Ethernet LANs. Today the dominant protocol used with Ethernet is TCP/IP.

The idea of networking hundreds, and thousands, of PCs into a LAN would have sounded pretty optimistic back when Ethernet was first developed. Yet, in part because of its simplicity and widespread support among manufacturers, Ethernet has adapted over the years to grow and survive, running on newer devices and network media. You can now run an Ethernet network on wired media such as coaxial cable, twisted-pair wiring (shielded and unshielded), and fiber-optic cabling. Ethernet obviously also functions with wireless technologies as well, as discussed in Part V of this book, "Wireless Networking Protocols."

Variations on a Theme: How Many Kinds of Ethernet Are There?

In 1985, the IEEE standard 802.3 "Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications" was published. These specifications made it easy for vendors to create hardware, from cabling to LAN cards, which could interoperate. The many different Ethernet standards you will need to know about are all identified by a name that includes "IEEE 802." followed by a number and possibly a letter or two.

The IEEE 802 LAN/MAN Standards Committee is responsible for creating standards for local and wide area networking. This committee was formed in February of 1980 and was originally called the Local Network Standards Committee. The name has been changed to reflect the evolutionary development of some of the committee's standards to MAN (metropolitan area network) speeds. Chapter 12, "The IEEE LAN/MAN Committee Networking Standards," contains short descriptions of some of the more relevant standards that were defined for LAN/MAN networks.

Note

It's safe at this point to say that we all know LAN stands for local area network. It's also common knowledge that WAN stands for wide area network. So what, then, is a MAN? It's a metropolitan area networksmaller than a WAN but larger than a LANgenerally used to refer to a network that connects a group of smaller related networks within a city or regionalized geographic area. Other acronyms used to describe specific networks are PANs (personal area networks created by Bluetooth devices), CANs (which stand for Campus Area Networkscontained only within a campus environment, such as a college university), and SANs (which are dedicated to high-speed storage area networks). Make sure that you do not get confused when you are discussing network types.

You can learn more about the activities of the IEEE 802 LAN/MAN Standards Committee and the different working groups that concentrate on specific network standards by visiting the website at http://ieee802.org/. You can also download many of the standards developed by the 802 LAN/MAN committee from this website, though printing all of them will require a lot of paper!


The committee is made up of various working groups and technical advisory groups. For example, IEEE 802.3 is the working group for standard Ethernet CSMA/CD technology, whereas IEEE 802.3z is the standard for Gigabit Ethernet, which is an updated, faster version of the original 802.3.

Different forms of Ethernet are also referred to using a naming scheme that links the network speed, the word "BASE" (for baseband signaling), and an alpha or numeric suffix that specifies the network media used. An example of this is 10BASE-T, which is broken down like this:

10 = Ethernet, running at a speed of 10Mbps

BASE = baseband signaling

T = over twisted-pair (T) wiring

Today there is a wide assortment of Ethernet solutions from which to choose. Originally, Ethernet used coaxial cable (10BASE-5) that was "tapped" into when a new workstation was added to the bus network. Later, thinnet (10BASE-2) was developed and allowed a smaller, more flexible coaxial cable to be used to connect the network. With thinnet, BNC connectors were introduced, making it unnecessary to "tap" into the coaxial cable. The most recent versions of Ethernet use twisted-pair wiring and fiber-optic cables and centralized wiring concentrators, such as hubs and switches.

The original Ethernet II network operated at a blazingly fast speed of 10Mbps. The most recent standard that is integrated into desktop systems is Gigabit Ethernet, now that it has been standardized. And as if that weren't enough, the 10Gigabit Ethernet standard has been finished, and products are readily available for high-speed networks.

These are the most common standards-based Ethernet solutions from the past to the present:

  • 10BASE-5 Often called "thickwire" or "thicknet," this standard uses thick coaxial cable. The 10 in this name indicates the speed of the network, which is 10 megabits/second (Mbps). As mentioned earlier, the term "Base" references the technology used, which is Baseband. The number 5 in the name indicates that the maximum length allowed for any segment using this topology is 500 meters. 10BASE-5 networks used thick coaxial cable. To install a node on the network, it is necessary to use what is commonly referred to as a "vampire tap." That is, you attach a connector to the backbone thicknet coaxial cable by punching into the wire. A drop cable is then run to the workstation that is being added to the network. If you are still using this technology, it's time to upgrade because you will find it very difficult to find parts and support for this outdated technology.

  • 10BASE-2 Often called "thinwire" or "thinnet," this Ethernet standard runs at the same speed as a 10BASE-5 network (10Mbps) but uses a smaller, more flexible cable. The number 2 in the name indicates a maximum segment length of 200 meters. This is a bit misleading, because it is actually rounded up from the true maximum segment length of 185 meters, but it sure was easier than calling it 10BASE-1.85. It is common to see older networks composed of multiport repeaters, with each port using thinnet cables to connect one or multiple computers. Each repeater is joined using a 10BASE-5 thicknet cable. Using a BNC T-connector, it is possible to create a simple daisy-chain bus using 10BASE-2. Again, if you are still using this technology, you are living in the past! It is easier to find parts and support for this older technology, but with the inception of Twisted Pair cabling, you will find it very hard to find coaxial-based networks, whether Thick or Thinnet based.

  • 10BASE-36 This rarely used Ethernet specification uses broadband instead of baseband signaling despite the fact that the name implies the use of baseband. The coaxial cable for this technology uses a coaxial cable that has three sets of wires, each for a separate channel, and each channel operates at 10Mbps and can extend over a distance of about 3,600 meters.

  • 10BASE-T The network connection is made from workstations to a central hub or switch (also known as a concentrator), using a physical star topology. The use of twisted-pair wiring (hence the "T" in the name), which is cheaper and much more flexible than earlier coaxial cables, makes routing cables through ceilings and walls a much simpler task. Centralized wiring also makes it easier to test for faults and isolate bad ports or move users from one area to another. If you are still using this technology, you can get by, but you'd find your job a lot easier if you upgraded to at least 100BASE-T.

    The topologies used by various forms of Ethernet are discussed in Chapter 2, "Overview of Network Topologies."


  • 10BASE-FL This version of Ethernet also operates at 10Mbps, but instead of using copper wires, fiber-optic cables (FL) are usedspecifically, multimode fiber cable (MMF), with a 62.5 micron fiber-optic core and a 125 micron outer cladding. Separate strands of fiber are used for transmit and receive functions, allowing full-duplex to operate easily across this kind of link. This technology has also been relegated to history, although it's very common to find this technology on most legacy networks today.

  • 100BASE-TX Uses Category 5 wiring (see Chapter 6, "Wiring the NetworkCables, Connectors, Concentrators, and Other Network Components") to allow a distance of up to 100 meters between the workstation and the hub. Four wires (two pairs) in the cable are used for communications. This technology is still used widely today, and will probably be around for a while until applications mandate the necessity of upgrading your network to use Gigabit Ethernet to the desktop.

  • 100BASE-T4 Uses Category 3 or Category 5 wiring to allow for a distance of up to 100 meters (328 feet) between the workstation and the hub. Four wires (two pairs) in the cable are used for data communications. This is another 100Mbps technology that was used to provide an upgrade path for installations that had not yet upgraded to Category 5 cabling (or better). If you still use this technology, it's time to consider an upgrade if you find that network congestion and excessive errors are occurring.

  • 100BASE-FX Uses multimode fiber-optic cables to allow for a distance of up to 412 meters between the workstation and the hub. One strand of the cable is used for transmitting data while the other is used for receiving data.

  • 1000BASE-SX The 802.3z IEEE standards document, approved in 1998, defines several Gigabit Ethernet networking technologies. 1000BASE-SX is intended to operate over fiber links using multimode fiber, operating with lasers that produce light at approximately 850 nanometers (nm). The "S" in the name implies a short wavelength of light. The maximum length for a segment of 1000BASE-SX is 550 meters.

  • 1000BASE-LX This fiber-based standard defines Ethernet when used with single-mode or multimode fiber. The "L" in the name implies a longer wavelength of light, from 1,270 to 1,355 nanometers. The maximum length for a single segment of 10BASE-LX is 550 meters using multimode fiber, and up to 5,000 meters using single-mode fiber.

  • 1000BASE-CX This standard allows for Gigabit Ethernet across shielded copper wires. It is designed primarily for connecting devices that are only a short distance away25 meters or less.

  • 1000BASE-T The IEEE standard 802.3ab added to the Physical layer of Gigabit Ethernet Category 5 unshielded twisted-pair wire cables. The maximum distance for any segment using 1000BASE-T is 100 meters.

It's important to remember that when working with network cabling, you need to make sure you are using the correct type. Category 5, 5e, and 6 are the most commonly used cable types today. Note that you need to use Category 5-rated cable or higher with Gigabit Ethernet technologies. To learn more, please see Chapter 6, "Wiring the NetworkCables, Connectors, Concentrators, and Other Network Components."




Upgrading and Repairing Networks
Upgrading and Repairing Networks (5th Edition)
ISBN: 078973530X
EAN: 2147483647
Year: 2006
Pages: 411

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