Most recently, the Gigabit Ethernet system was developed using both fiber optic and twisted-pair cabling. The supplement may consist of one or more entirely new clauses, and may also contain changes to existing clauses in the standard.
New supplements to the standard are evaluated by the engineering experts at various IEEE meetings and the supplements must pass a balloting procedure before being voted into the full standard. New supplements are given a letter designation when they are created.
Once the supplement has completed the standardization process, it becomes part of the base standard and is no longer published as a separate supplementary document.
On the other hand, you will sometimes see trade literature that refers to Ethernet equipment with the letter of the supplement in which the variety was first developed e. Table 1. The dates indicate when formal acceptance of the supplement into the standard occurred.
Access to the complete set of supplements is provided in Appendix A. This illustrates a common problem: innovation in the computer field, and especially in computer networking, always outpaces the more deliberate and slow-paced process of developing and publishing standards. One way you can do that is to insist on complete information from the vendor as to what standard the product complies with.
It may not be a bad thing if the product is built to a draft version of a new supplement. Draft versions of the supplements can be substantially complete yet still take months to be voted on by the various IEEE committees. When buying pre-standard equipment built to a draft of the specification, you need to ensure that the draft in question is sufficiently well along in the standards process that no major changes will be made.
One solution to this is to get a written guarantee from the vendor that the equipment you purchase will be upgraded to meet the final published form of the standard. Note that the IEEE forbids vendors to claim or advertise that a product is compliant with an unapproved draft. The specifications for the original DIX Ethernet standard were developed by the three companies involved and were intended to describe the Ethernet system—and only the Ethernet system.
The efforts aimed at creating a worldwide system of open standards had only just begun. Consequently, the IEEE made several technical changes required for inclusion in the worldwide standardization effort. This model was developed in by the International Organization for Standardization, whose initials derived from its French name are ISO. Headquartered in Geneva, Switzerland, the ISO is responsible for setting open, vendor-neutral standards and specifications for items of technical importance.
The ISO developed the OSI reference model to provide a common organizational scheme for network standardization efforts with perhaps an additional goal of keeping us all confused with reversible acronyms.
What follows is a quick, and necessarily incomplete, introduction to the subject of network models and international standardization efforts. The OSI reference model is a method of describing how the interlocking sets of networking hardware and software can be organized to work together in the networking world.
In effect, the OSI model provides a way to arbitrarily divide the task of networking into separate chunks, which are then subjected to the formal process of standardization. To do this, the OSI reference model describes seven layers of networking functions, as illustrated in Figure 1.
The lower layers cover the standards that describe how a LAN system moves bits around. The higher layers deal with more abstract notions, such as the reliability of data transmission and how data is represented to the user. The layers of interest for Ethernet are the lower two layers of the OSI model. In brief, the OSI reference model includes the following seven layers, starting at the bottom and working our way to the topmost layer:.
Standardizes the electrical, mechanical, and functional control of data circuits that connect to physical media. Establishes communication from station to station across a single link.
This is the layer that transmits and receives frames, recognizes link addresses, etc. The part of the standard that describes the Ethernet frame format and MAC protocol belongs to this layer. Establishes communication from station to station across an internetwork, which is composed of a number of data links. This layer provides a level of independence from the lower two layers by establishing higher level functions and procedures for exchanging data between computers across multiple links.
Standards at this layer of the model describe portions of the high-level network protocols that are carried over an Ethernet in the data field of the Ethernet frame. Protocols at this layer of the OSI model and above are independent of the Ethernet standard. Provides reliable end-to-end error recovery mechanisms and flow control in the higher level networking software. Provides mechanisms to support end-user applications such as mail, file transfer, etc. The Ethernet standard concerns itself with elements described in Layer 2 and Layer 1, which include the data link layer of the OSI model and below.
The Ethernet standards describe a number of entities that all fit within the data link and physical layers of the OSI model. While at first glance these extra layers might seem to be outside the OSI reference model, the OSI model is not meant to rigidly dictate the structure of network standards. Instead, the OSI model is an organizational and explanatory tool; sublayers can be added to deal with the complexity of a given standard.
Figure 1. Within these major sublayers there are even further sublayers defined for additional MAC functions, new physical signaling standards, and so on. The MAC layer defines the protocol used to arbitrate access to the Ethernet system. Both of these systems are described in detail in Chapter 3. At the physical layer, the IEEE sublayers vary depending on whether , , or Mbps Ethernet is being standardized.
Each of the sublayers is used to help organize the Ethernet specifications around specific functions that must be achieved to make the Ethernet system work. Understanding these sublayers can also help us understand the scope of the various standards involved. As such, it is functionally independent of the various physical layer media specifications and does not change, no matter which physical media variety may be in use.
To help make this clearer, the Ethernet-specific portions of the standard in Figure 1. In developing a technical standard, the IEEE is careful to include only those items whose behavior must be carefully specified to make the system work. Therefore, all Ethernet interfaces that operate in the original half-duplex mode described in Chapter 3 must comply fully with the MAC protocol specifications in the standard to perform the functions identically.
Otherwise, the network would not function correctly. At the same time, the IEEE makes an effort not to constrain the market by standardizing such things as the appearance of an Ethernet interface, or how many connectors it should have on it.
The intent is to provide just enough engineering specifications to make the system work reliably, without inhibiting competition and the inventiveness of the marketplace.
In general, the IEEE has been quite successful. Most equipment designed for use in an Ethernet system fully complies with the standard. Vendor innovation can sometimes lead to the development of devices that are not described in the IEEE standard, and that are not included in the half-duplex mode timing specs or the media specs in the standard. Some of these devices may work well for a small network, but might cause problems with signal timing in a larger network operating in half-duplex mode.
Further, a network system using equipment not described in the standard or included in the official guidelines cannot be evaluated using the IEEE half-duplex mode configuration guidelines. How much you should be concerned about all this is largely up to you and your particular circumstances.
For one thing, not all innovations are a bad idea. After all, the thin coaxial and twisted-pair Ethernet media systems started life as vendor innovations that later became carefully specified media systems in the IEEE standard. However, if your goal is maximum predictability and stability for your network given a variety of vendor equipment and traffic loads, then one way to help achieve that goal is by using only equipment that is described in the standard.
One way to decide how important these issues are is to look at the scope and type of network system in question. For an Ethernet that just connects a couple of computers in your house, you may feel that any equipment you can find that helps make this happen at the least cost is a good deal. The limited scope of your network makes it easier to decide that you are not all that worried about multi-vendor interoperability, or about your ability to evaluate the network using the IEEE configuration guidelines.
On the other hand, if you are a network manager of a departmental or campus network system, then the people using your network will be depending on the network to get their work done. The expanded scope changes your context quite a bit. Departmental and workgroup nets always seem to be growing, which makes extending networks to accommodate growth a major priority for you.
In addition, network stability under all sorts of traffic loads becomes another important issue. In this very different context, the issues of multi-vendor interoperability and compliance with the standard become much more important. Sometimes vendors may not tell you whether the component they are selling is included in the IEEE system configuration guidelines, and whether it is a piece of standard and interoperable equipment that is widely available from other vendors. Some components that are not included in the official standard or media system configuration guidelines include the 10 Mbps AUI port concentrator, media converters, and special media segments.
These components are described in later chapters and Appendix C. The IEEE has assigned shorthand identifiers to the various Ethernet media systems as they have been developed.
The three-part identifiers include the speed, the type of signaling used, and information about the physical medium. In the early media systems, the physical medium part of the identifier was based on the cable distance in meters, rounded to the nearest meters.
In the more recent media systems, the IEEE engineers dropped the distance convention and the third part of the identifier simply identifies the media type used twisted-pair or fiber optic. In roughly chronological order, the identifiers include the following set:.
This identifies the original Ethernet system, based on thick coaxial cable. The identifier means 10 megabits per second transmission speed, base band transmission, and the 5 refers to the meter maximum segment length. The word baseband simply means that the transmission medium, thick coaxial cable in this instance, is dedicated to carrying one service: Ethernet signals. The meter limit refers to the maximum length a given cable segment may be. Longer networks are built by connecting multiple segments with repeaters or switching hubs.
Also known as the thin Ethernet system, this media variety operates at 10 Mbps, in baseband mode, with cable segment lengths that can be a maximum of meters in length. The answer is that the identifier is merely a bit of shorthand and not intended to be an official specification.
The IEEE committee found it convenient to round things up to 2, to keep the identifier short and easier to pronounce. The original DIX Ethernet standard mentioned a point-to-point link segment that could be used between repeaters, but did not provide any media specifications. The specifications in the original FOIRL segment only provide for linking two repeaters together, one at each end of the link.
While waiting for a larger set of fiber optic specifications to appear, vendors extended the set of devices that are connected via fiber, allowing an FOIRL segment to be attached to a station as well. These changes were taken up and added to the newer fiber optic link specifications found in the 10BASE-F standard described later in this section.
This system was designed to send 10 Mbps signals over a broadband cable system. Broadband cable systems support multiple services on a single cable by dividing the bandwidth of the cable into separate frequencies, each assigned to a given service. Cable television is an example of a broadband cable system, designed to deliver multiple television channels over a single cable.
These days, the vast majority of sites use fiber optic media for covering large distances, and broadband Ethernet equipment is not widely available. This standard describes a 1 Mbps system based on twisted-pair wiring, which did not prove to be a very popular system. This variety of the Ethernet system operates at 10 Mbps, in baseband mode, over two pairs of Category 3 or better twisted-pair wires.
The category system for classifying cable quality is described in Chapter This includes a set of fiber optic link segment specifications that updates and extends the older FOIRL standard. Two of these specifications have not been widely deployed.
This is the IEEE shorthand identifier for the entire Mbps system, including all twisted-pair and fiber optic Fast Ethernet media systems. This variety of the Fast Ethernet system operates at Mbps, in baseband mode, over two pairs of high-quality, Category 5 twisted-pair cable. This is the most widely used variety of Fast Ethernet.
This variety of the Fast Ethernet system operates at Mbps, in baseband mode, over multi-mode fiber optic cable. This variety of the Fast Ethernet system operates at Mbps, in baseband mode, over four pairs of Category 3 or better twisted-pair cable. This variety of the Fast Ethernet system operates at Mbps, in baseband mode, on two pairs of Category 3 or better twisted-pair cable.
This variety was never developed by any vendor, and equipment based on the T2 standard is non-existent. This is the short wavelength fiber optic media segment for Gigabit Ethernet. This is the long wavelength fiber optic media segment for Gigabit Ethernet. This is a short copper cable media segment for Gigabit Ethernet, based on the original Fibre Channel standard.
This system is based on a different signal encoding scheme required to transmit gigabit signals over twisted-pair cabling.
A LAN has to be able to work with the widest variety of equipment possible to provide you with the greatest flexibility. For maximum utility, your LAN must be vendor-neutral: that is, capable of interworking with all types of computers without being vendor-specific. This was not the way things worked in the s when computers were expensive and networking technology was exotic and proprietary.
Bob Metcalfe understood that a revolution in computer communications required a networking technology that everyone could use. In he set out to make Ethernet an open standard, and convinced Xerox to join a multi-vendor consortium for the purposes of standardizing an Ethernet system that any company could use.
This DIX standard made the technology available to anyone who wanted to use it, producing an open system. As part of this effort, Xerox agreed to license its patented technology for a low fee to anyone who wanted it. In Xerox also gave up its trademark on the Ethernet name. The idea of sharing proprietary computer technology in order to arrive at a common standard to benefit everyone was a radical notion for the computer industry in the late s.
You can read about the entire process here. Metcalfe basically improved on this system by developing a way to detect collisions.
Stations would listen for activity before transmitting anything. Metcalfe basically improved this system by developing a way to detect collisions. He thought this was much like the old luminiferous ether was once thought to propagate electromagnetic waves through space. By TeleGeography Staff. By Kristin Lee. By Elizabeth Thorne. CC0 Public Domain. It all started on May 22,
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