Sample Questions and Answers: Midterm I

1. The US Postal Service has the sole authority to create postage stamps in the US. They may be viewed among other things, as a "manufacturers" of postage stamps. Assume you are an executive at the US Postal Service. You would like the Postal Service to distribute and sell postage stamps via ATM machines.
   • What are the principal steps involved in making this possible? You should consider the organizations that need to be involved to make this possible and consider flows of information as well as goods between the players.

     
     Players: US Postal Service, ATM Network Service Providers, and ATM owners (banks)

     Information Exhanged: Financial information needed to reconcile accounts between players, frequency of this exchange can be predetermined. Frequency can either be per transaction or aggregated at the end of the week/month. Given the average transaction for postage stamps, it is likely the frequency is of aggregate information.

     Goods Exchanged: Postage stamps between US Postal Service & organizations that own the ATM M/C's

   • Summarize the reach, range and responsiveness requirements for this telecommunications application.

     Reach: Only data, no other type of information is exchanged

     Range: Inter Organizational

     Responsiveness: immediate, real time dispensing of postage stamps

   • You have been told that the State of Maryland distributes welfare payments using ATM machines. What if any, is the difference between the State of Maryland's use of the ATM Networks and your planned use of it for the US Postal Service.

     Physical goods (postage stamps) need to be distributed to the ATM Machines working with the US Postal Service. It is more than just information being transferred as is the case with disbursing welfare payments.

2. What is the difference between
   • an analog signal and a digital signal

     An analog signal is a continuous signal. A digital signal is a discrete signal of high and low voltages.

3. a) Give two common examples of telecommunications which use unguided media.

   • celluar telephones

   • satellite

   b) Why is it the case that VSAT dishes are so much smaller than "regular" satellite (C-Band) dishes?

   VSAT transmits in 12/14 Ghz range. The higher the frequency the more directed the signal, thereby enabling smaller dishes.

   c) Give an example of an application in which a wireless media would be preferred over a wireline media.

   A bypass application or interconnectivity between buildings where rights of way are not available.

   d) Give an example of an application in which wireline media would be preferred over wireless media.

   Secure transmission as a requirement or a harsh environment like found in a M/C shop would make wireline the preferred choice.

4. Consider the following information sources

   (a) human voice

   (b) data stream from a computer

   For each of these sources answer the following questions.

   • Is the information generated by the source analog or digital?

     human voice - analog

     data stream - digital

   • Can human voice be transmitted digitally? If so, what technology is needed to enable it?

     Yes. You need a pulse code modulator (PCM)

   • Can a data stream from a computer be transmitted using analog transmission? If so, what technology is needed to enable it?

     Yes. You need a modem.

   • Given that telephone quality voice requires 4000Hz of bandwith, compute the data rate in bits per second need to transmit it. Assume 8 bit encoding.

     4000 * 2 * 8 = 64 Kbs

5. A TV signal requires 5Mhz for analog transmission. Using pulse code modulation, this TV signal is to be digitized.
   • What is the rate at which this signal should be sampled?

     5 *2 = 10 M samples/sec

   • Assume that each sample is encoded using 10 bits, what is the date rate required to transmit this signal.

     10 * 10 = 100 Mbs

   • The media that is to be used to transmit this signal has a bandwith of 10 Mhz and a signal to noise ratio of 15. Is it theoretically feasible to transmit this signal over the media?

     No. => C = 10 * log2(16) = 40 Mbs

   • If not, how much compression is required to transmit the signal?

     40%

   Bonus Question

6. What was the event that took place last week that shook the telecommunications industry?

   The voluntary break up of AT&T.

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