ScalabilityScalabilityrefers to how much growth a network design must support. For many enterprise network design customers, scalability is a primary goal. Many large companies addusers, applications, additional sites, and external network connections at a rapid rate. Thenetwork design you propose to a customer should be able to adapt to increases in network usage and scope.26 Top-Down Network DesignPlanning for ExpansionYour customer should help you understand how much the network will expand in thenext year and in the next 2 years. (Ask your customer to analyze goals for growth in thenext 5 years also, but be aware that not many companies have a clear 5-year vision.)You can use the following list of questions to analyze your customer’s short-term goalsfor expansion:■ How many more sites will be added in the next year? The next 2 years?■ How extensive will the networks be at each new site?■ How many more users will access the corporate internetwork in the next year? Thenext 2 years?■ How many more servers will be added to the internetwork in the next year? Thenext 2 years?Expanding Access to DataChapter 1, “Analyzing Business Goals and Constraints,” talked about a common businessgoal of expanding access to data for employees who use enterprise networks. Managersempower employees to make strategic decisions that require access to sales, marketing,engineering, and financial data. In the 1970s and early 1980s, this data was stored onmainframes. In the late 1980s and the 1990s, this data was stored on servers in departmental LANs. Today, this data is again stored on centralized mainframes and servers.In the 1990s, networking books and training classes taught the 80/20 rule for capacityplanning: 80 percent of traffic stays local in departmental LANs, and 20 percent of trafficis destined for other departments or external networks. This rule is no longer universaland is rapidly moving to the other side of the scale. Many companies have centralizedservers residing in data centers. In addition, corporations increasingly implementintranets that enable employees to access centralized web servers using Internet Protocol(IP) technologies.At some companies, employees can access intranet web servers to arrange business travel,search online phone directories, order equipment, and attend distance-learning trainingclasses. The web servers are centrally located, which breaks the classic 80/20 rule.As Chapter 1 also mentioned, there has been a trend of companies connecting internetworks with other companies to collaborate with partners, resellers, suppliers, and strategic customers. The term extranetis sometimes used to describe an internal internetworkthat is accessible by outside parties. If your customer has plans to implement an extranet,you should document this in your list of technical goals so that you can design a topology and provision bandwidth appropriately.In the 1980s and 1990s, mainframes running Systems Network Architecture (SNA) protocols stored most of a company’s financial and sales data. In recent years, the value ofmaking this data available to more than just financial analysts has been recognized. The
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