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Chapter 1: The Need for SwithcingTo fully understand the need for switches on a network, you must have a clear understanding of how networks have evolved from their beginnings to where they are now.This chapter will discuss this history, and will show the limitations that exist with traditional local area networks (LANs). We will also examine some of the methods that network designers used to overcome the constraints of these older network topologies. Although traditional network architectures are still being used in corporations all over the world, highbandwidth applications such as video, voice, and the Internet have forced networks to adapt to meet today's challenges. We will also cover the components of the network in depth in this chapter, from repeaters to hubs, routers, and switches. The advantages and disadvantages of each device will be discussed, as well as when they should be used in the network. Last, we will show the different types of switches in use in today's networks. We will describe the various types of switching used on these devices and discuss the challenges involved with this technology.
The first LANs began as a result of the introduction of PCs into the workplace. As more computers were used, a need arose for sharing resources, such as printers or files. These early networks were simple, with a handful of computers and printers and not much more. Before long, however, the increasing numbers of computers, along with applications that could take advantage of the network, pointed out the weaknesses in traditional network designs.
The limitations of traditional Ethernet technology brought forth a number of innovations to the Ethernetprotocol-such as full-duplexing, Fast Ethernet, and Gigabit Ethernet-that have made possible a transition to switches from shared hubs. Because of the limitations to the way networks operated in a shared environment, alternative methods had to be designed to permit the use of bandwidth-intensive applications such as video and voice. Switches are one of these alternative methods. In many respects, switches are relatively simple devices. By design, they require very little configuration to get them up and running. To properly use these devices in your network, though, it's important to have an in-depth knowledge of the issues involved when using switches. This includes knowing the basics of Ethernet technology. To effectively do your job, you need a good grasp of the technology and how it works, as well as the constraints of each type of device you may use in the network. We will cover the basics of Ethernet technology in depth.
The types of devices you use in the network have important implications for network performance. For example, bridges and routers are both devices that network administrators use to extend the capabilities of their networks. Both of them have advantages and disadvantages. Bridges, for example, can easily solve distance limitations and increase the number of stations you can have on a network, but they can have real problems with broadcast traffic. Routers can be used to prevent this problem, but they increase the time it takes to forward the traffic.
This has been the pattern throughout the history of networking. A new product is introduced. Problems are found that limit the product's usefulness. Innovations are made to the product to make it perform better.As we will see in upcoming sections, this pattern began in the earliest days of networking and continues to this day.
Traditional Network Architectures
From the beginning of networking, designers of networks were faced with the limitations of the LAN topologies they were using. Modern-day corporate networks use LAN topologies such as Ethernet,Token Ring, and Fiber Distributed Data Interface (FDDI) to provide network connectivity. Network designers try to deploy a design that uses the fastest functionality that can be applied to the physical cabling. Although networks have been designed using all these methods, Ethernet LANs have won the battle for market share and remain the dominant type of network in most corporations.
A few years ago, many analysts saw a competing technology, Token Ring, as a technically superior product and a viable alternative to Ethernet. Many installations still have Token-Ring networks, but very few new installations are being done. This is due in part to the fact that Token Ring was basically an IBM product with little support from other vendors, and prices were substantially higher than for its Ethernet counterparts.
FDDI networks share some of the same limitations ofToken Ring. Like Token Ring, it offers excellent benefits in the areas of performance and redundancy. Unfortunately, it has the same limitations of high equipment costs and limited vendor support. FDDI has been used in many organizations to provide a highspeed backbone that could withstand the problems that happen to networks. However, it was not widely embraced by the networking community due to its complexity and high costs.
Ethernet networks, by contrast, are open-standards-based, cost-effective, and have a large base of vendors supporting the products. In addition, a huge number of professionals understand how Ethernet works. Even IBM now recognizes the hold that Ethernet LANs have on the market and supports the technology...