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Note that Figure 1.13 is by no means comprehensive. For example, the role of facilities in obtaining power, cooling, and space has not been presented, nor has the process of locating vendorsand the roles that contracts and requests for proposals (RFPs) play in that processbeen introduced. Also note that the ordering process has not been included. (This step could easily enter into the flow at any point following the requirements analysis; however, some installations may find that some components must be ordered well in advance.) This flow chart concentrates solely on the technical aspects. Keeping that in mind, lets examine each step in more detail.
FIGURE 1.14 The three-tier (hierarchal) network
FIGURE 1.15 The three-tier network with IP addressing and DNS names
Lets walk through a simple network design process. Do not be concerned if you are unfamiliar with the specific technologies noted in this scenariothe actual details are unimportant. However, a good designer should always have a list of technologies to research and learn, and you may wish to add the unfamiliar components to your list.
The Sales department has requested a DSL-based solution for their team. One of the senior sales executives has read articles touting the benefits of DSL, which has led to this request. Users will want access to corporate data and the Internet at high speeds. In addition, users may be at home, at a clients site, or in a hotel. The budget for the project is undefined; however, you are told that there will be funding for whatever it takes.
Stop for a moment and consider the different factors and issues associated with this request. List some of the questions that should be answered.
Here is a short list of preliminary questions:
Note that some of these questions will not have an answer, or the answer will be vague.
The designer will have to make some interesting decisions at this point. The requirement for high-speed access from client sites and hotels is one issue. DSL requires a pre-installed connection. It is not widely available, unlike POTS (plain old telephone service), and is either configured as private (similar to Frame Relay in which companies share switches and other components, while PVCs keep traffic isolated) or public, which usually connects to an ISP and the Internet. An immediate red flag would be the lack of DSL availability in remote locations. Note that the request specified DSL. Why? Is it because the technology is needed or because it is perceived as newer, better, and faster?
Depending on the answers, it may still make sense to use DSL for the home. However, the design will still fail to address the hotel and customer sites. Perhaps a VPN (Virtual Private Network) solution with POTS, ISDN, and DSL technologies would work. This solution may include outsourcing or partnering with an ISP (Internet Service Provider) in order to implement the design. Note that at no point in the process have routing protocols, hardware components, support, or actual costs been discussed. These factors should be considered once the objectives for the project have been defined.
Network Design in the Real World: Nontechnical Solutions
Network designers should not be afraid to suggest nontechnical solutions in response to requests. For example, consider a request to install a Frame Relay T1 for a connection to another company. There will be a large data transfer every month of approximately 100Mb. The data is not time sensitive, and no additional data is anticipated (i.e., neither the frequency of the data nor the volume of data is expected to increase.)
This problem begs a nontechnical solution, especially since the costs for a technical solution, even for Frame Relay, would be very high. As a variation on SneakerNet, why not propose FedExNet? (SneakerNet was one of the most popular network technologies ever usedusers simply walked floppies and files to recipients.) It is important to consider the alternativesin this case the requirements did not mandate a technical solution, just a solution. A CD-ROM or tape would easily contain the data, and, at current tariffs, the cost would be less than 1/20th the technical solution. It may not appear as glamorous, but it is secure and reliable. Note these last two points when considering an Internet-based solution, which would also be cheaper than private Frame Relay.
This chapter has already touched upon cost as a significant factor in network design, and the majority of these costs are associated with the telecommunications tariff. The tariff is the billing agreement used, and, like home phone service, most providers charge a higher tariff for long-distance and international calls than they do for local ones. Designers should always consider the distance sensitivity and costs associated with their solutions Frame Relay is typically cheaper than a leased line, for example.
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