Chapter 3. Network Design Strategies

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

Planning a Logical Network Design 31

Planning and Design Components 36

The Physical Network 39

Planning Resources 40

Many types of networks were discussed in Chapter 1, "A Short History of Computer Networking," from ARPANET to TCP/IP. And in Chapter 2, "Overview of Network Topologies," you learned about the various topologies you can employ when designing and creating a local area network (LAN), and we also looked at some scenarios in which several networks were connected to form a wide area network (WAN). In this chapter, we will look at another aspect of creating a network: the network's logical and physical design. The physical aspects of your LAN will depend on the underlying physical transport technologyEthernet or Token-Ring, for example, or possibly ATM, which is supported as a LAN protocol in products such as Windows 2000/XP, Windows Server 2003, and Linux. Depending on which technology you use, there will be one or more LAN topologies from which to choose.

Note

Although there are other LAN technologies, such as ARCnet and Novell's IPX/SPX, these are basically legacy products that are no longer being deployed in newer networks. For example, ARCnet is now used mostly in vertical-market applications (such as on the factory floor, or for point-of-sale cash registers). If you don't need the features that TCP/IP provides, and don't need an Internet connection, then these older protocols may be a workable solution for your network. Novell's NetWare products, while allowing for backward compatibility with the IPX/SPX protocol, have finally caught up with the times, and new installations will more than likely use the IP protocol. Other protocols, such as Microsoft's LAN Manager and NetBEUI, are used only in older networks. If you are still using older proprietary protocols, you should consider upgrading to TCP/IP, which is now the de facto standard, from the worldwide Internet down to the LAN.

Before you can begin to design a physical network, however, you first must determine your needs. What services must you provide to your user community? What are the resources you'll need? If you have to compromise, what will it take to satisfy the most users or to provide the more important services? You then will have to take into account network protocols, applications, network speed, and, most important, network security issues; each of these figures into a network's logical design. Another important factor your management will probably force you to consider is costyou can't forget the budget. These factors make up the logical design for your network. You first should decide what you need and what it will take to provide for those needs.

If you are creating a new network and purchasing new applications, you will probably spend most of your time considering the licensing and other financial costs (training users, network personnel, and so on). If you are upgrading older applications, several other factors come into consideration. Many applications that were coded using COBOL, BASIC, FORTRAN, and other languages that helped jumpstart the computer age may have built-in network functionality based on older proprietary network protocols. If this is the case with your network, you have to consider several things. What will it cost to update thousands of lines of code (or more) to more modern versions of the same programming language? What will it cost to upgrade these programs to newer object-oriented languages? To save money, can you upgrade part of your network and use gateway hardware/software to connect to older network components?

Because of the costs associated with coding applications that were created many years ago, and the expenses that will be required to update them to modern programming languages, you may be forced to maintain legacy applications for a few years while replacement applications are designed and created. You may find a packaged application that can be used to replace older programs. This problem will apply mostly to proprietary computer architectures, instead of Windows or Unix platforms. If you can simply make minor changes and compile the source code so that it will run on a newer operating system, your costs will be much less than if you have to re-create the applications your users need from scratch. Another cost associated with upgrading to new programs is training users and help-desk personnel.