President Lee Coone has asked you to continue planning for an integrated corporate NDAS network. Ultimately, this network will link all the offices with the Tampa head office and become the foundation on which to build a sophisticated voice, video, and data communication network that includes LANs at most NDAS sites. President Coone is still not completely convinced that NDAS needs video capabilities, but he wants you to include that in your plan. As a first step, President Coone wants you to examine the current information flow within NDAS. Case Figure 3–1 shows the movement of invoice information. In reality, it shows the number of packages that are transferred between offices, but each package also requires an invoice. These averages were compiled from a 2-week survey of each office. The average length of each invoice is 750 characters. Use this statistic as the basis for your computations. Every number in the figure represents the number of packages (each of which requires an invoice) that move from the city of origin to a destination city for delivery in the latter city’s delivery zone. Local deliveries are indicated in situations in which the origins and destinations are the same. For example, the intersection of the Atlanta column and the Atlanta row shows 500 local deliveries.
Invoice information is transmitted from the origin to the destination. In addition, a copy of all invoice information is transmitted to the home office in Tampa for billing. For example, every day, Los Angeles ships 150 packages to Memphis, and each one requires an invoice. This means that Los Angeles will transmit 150 750-character invoices to both Memphis and Tampa every day.
Exercises
1. President Coone is baffled about how digital information from a computer can be sent over a network connection. Prepare a brief position paper for management explaining the way information is transferred from one computer to another over digital lines. Keep it simple. Be sur to describe the types of devices used in data transmission. Include comments on the role of data compression in increasing transmission rates. Justify the observation that as a general rule, it is best to purchase the fastest devices your communications lines can support.
2. As you begin thinking about the redesign of the network, you realize that there are various types of media to choose from. Which media will you use in the network and where will you utilize these types?
3. Using the network that is being redesigned will certainly speed data transfers considerably. President Coone is amazed to see that an email message with a large attachment can be sent in a matter of seconds. He reflects back on the time when data was primarily transmitted via modems:
a. Compute each office’s number of bits sent per day (origin to destination) on the basis of the data provided in Case Figure 3–1. Use 10 bits per character to keep computations simple and assume all transmissions are error free. Hint: Bits per day = Packages × 750 × 10 × 2.
b. How many minutes will it take for each city’s modem to transmit its invoices? Use the bits per day calculated in question 2 and assume that the V.34 modems transmit at an average rate of 28,800 bps.
c. Previously, you calculated the transmission time in minutes per day, based on a 28,800-bps modem and 10 bits per character. Now calculate the file transfer time for Atlanta to transmit all of its invoices to Tampa at the end of the workday. Why is this answer different from the time calculated for Atlanta previously?
d. Could all the NDAS offices transmit their invoices to Tampa between 5:00 P.M. and 6:00 P.M. each evening? How would they achieve this goal?
4. Would it be better to transmit all invoice information from the origin to Tampa and for Tampa to send the information to the destination? Why?
5. With the addition of a network that can handle voice, video, and data, what other uses and benefits can NDAS derive from the new network?