Introduction
I'll start out with a quote from a classic article from 1976, written by the "fathers" of Ethernet, Robert M. Metcalf and David R. Boggs. The article introduces us to a new shared communications mechanism: Ethernet. The authors stated:
Computer networking evolved from telecommunications terminal-computer communication, where the
object was to connect remote terminals to a central computing facility. As the need for computer-computer
interconnections grew, computers themselves were used to provide communication. Communication
using computers as packet switches and communication
among computers for resource sharing were both advanced by the development of the Arpa Computer
Network.
...
Just as computer networks have grown across continents and oceans to interconnect major computing facilities
around the world, they are now growing down corridors and between buildings to interconnect mini-computers
in offices and laboratories.
It is pretty obvious that as soon as there were multiple computing facilities, a need to interconnect computers arose. But what spurred the development of Local Area Networks was the growing number of computers that were in close proximity. A Local Area Network (henceforth, LAN) is a network that inherently has a distance limitation. Wide area technologies can be extended - well, perhaps not infinitely - but for extremely large distances, by use of repeaters, or by increasing the numbers of switches and the links that connect those switches. But local area technologies have physical distance limitations beyond which we cannot extend the network. For some local area technologies, the distance might not seem so short - several or even tens of kilometers, but relative to wide area technologies, a LAN is still restricted.
Other than the distance limitation, what characterizes a LAN is the fact that it is controlled by one administrative authority. LANs also have relatively high data rates, in comparison to WAN technologies. Though the speed of WANs today far exceeds the speed of the early LANs (e.g., 10 Mbps for the original Ethernet), in any given technology generation, the speed of LANs in that generation far outpaces that of WANs in that generation.
This portal will focus on a variety of LAN technologies, including those that have become the dominant and highly successful methods and also a few that had limited success or shorter-term success.
We will begin with a tutorial on Ethernet, the LAN technology that has undergone many changes, but has been amazingly resilient, robust, and ubiquitous. The Ethernet tutorial is followed by a link to a tutorial on virtual LANs, which are typically based on a switched-Ethernet infrastructure, and thus are an extension of the basic Ethernet technology.
Shortly into the tutorial on Ethernet, I will give a brief overview of the IEEE LAN standards. Though IEEE impacted Ethernet only partially (which will be discussed in the Ethernet tutorial), this is as good a place as any to introduce the LAN standardization efforts of IEEE.
Some other IEEE standardized LANs have come and gone, but the wireless LANs that we commonly use are IEEE standards (as are some other currently in-use network standards). The wireless LAN could be pointed to as the one LAN technology that has come along in a long time to challenge Ethernet in the realm of its application and ease of use, and it is probably the only one that has ever competed in popularity and low cost. Just as, for years, every computer had a built-in Ethernet interface, more and more computers now have a built-in wireless LAN interface. And there are now many devices - especially smaller ones that are meant to be portable, that have only a wireless LAN interface, but no Ethernet interface!
Though LANs based on token ring technology have not had the long-lasting success that Ethernet has, they use the sort of algorithms and protocols that are so clever that it could happen that token ring-based networks will show some kind of comeback. No, I'm not making any kind of prediction, but from many years of experience in the computer networking field, I've learned that certain good concepts do find new usefulness, which is why it is valuable to learn about these technologies. You never know where you might find application for these concepts in a new technology. And, I should note that the IBM Token Ring has not totally disappeared from the networking scene. It still has limited support and sales. (No, it is not my practice to advertise other vendors' products. The reason that I specifically name IBM is because by licensing the token ring patent, IBM Token Ring became synonymous with the IEEE 802.5 token ring standard. There were other, proprietary token ring implementations that were not standardized and had some short-lived marketing success.)
There are also some types of LANs that have had some success in their heyday, but will not be so honored with much attention in this portal. These include the Token Bus (which will only get a brief mention in the overview on IEEE LAN standards), and ARCNET. When I first used ARCNET (it was the first LAN that I was connected to), it was clear that it was installed where I was working because it used the same cabling that was used for terminal-mainframe communications. When the terminals were replaced with PCs and the organization wanted to install a LAN, the cabling that was in place served as the LAN cabling, which was very neat, and therefore required minimal additional investment. ARCNET never made it to the IEEE LAN Standards and I was actually pretty surprised to find that it is still alive and kicking (since 1977), as indicated on the ARCNET Resource Center website.
Thank you for visiting RAD University. We hope that this portal will be helpful and fun, and we
welcome your comments.
Debby Koren, "Dean" RAD University
