Telecommunications Management

90-768

Answers to MidTerm 1, 1997

The answers to the questions have annotated by Sumit.

    1. Q1
      1. What is an analog signal?

        A signal where strength (amplitude) varies continuously in time.
        Common Mistakes
        Continuous flow of information (as opposed to discrete flow of information), Where the signal is sinusoidal, it goes on and on (as opposed to on and off) etc.

      2. Give an example of an analog information source.

        Human Voice

      3. Can analog data be transmitted digitally? What device is needed to make this possible? Use the answer to b. to illustrate.

        Yes. Codec. A codec can be used to digitize human voice.
        Common Mistake
        PCM - Pulse code modulator - Well there is nothing called a pulse code modulator. PCM is a modulation technique called pulse code modulation. It is not a device. Almost everybody made this mistake. Some had PMC, PDM etc. i don't know what that is.

      4. What is a digital signal?

        A signal whose strength changes discretely in time.
        Common Mistakes
        See Analog signal mistakes

      5. Give an example if an information source which generates digital signals?

        Computer or a sensor.
        Common Mistakes
        Text, image..... these are not digital information sources.

      6. Can digital data be transmitted using analog transmission? What device is needed to make it possible? Use answer e. to illustrate.

        Yes. You need to encode using a modem.

      7. What is the fundamental difference between analog transmission and digital transmission?

        Analog transmission is not aware of signal content when signal attenuate, they are boosted using amplifiers. Digital transmission takes signal content into account. The digital data is recovered using repeaters.

      8. Data from an analog information source needs to be transmitted over a satellite microwave network using digital transmission. How should the data be encoded to make this possible?

        Analog source => Digitized using a modem => Modulated onto wave for transmission.

      9. Give an example of an everyday service that uses analog transmission.

        Cable, TV, PSTN.

      10. Give an example of an everyday service that uses digital transmission.

        Direct satellite broadcast, ISDN.

    2. State three services that a data link protocol supplies to sending and receiving devices to help them coordinate and communicate.
      1. Flow control
      2. Error control
      3. Synchronization

      Common Mistakes
      Too many to list here

    3. Q3
      1. What is a key characteristic of a voice and video transmission which distinguish them from data transmission?

        Voice and video are streaming data. Data is bursty.

      2. What impact does this difference have on planning communication network infrastructure?

        When data is bursty, it is hard to anticipate bandwidth and plan for peak capacity. When data is stream, one has a much better idea what bandwidth is required.

      3. The Internet is a network originally designed to transmit data. However, is being used to deliver other types of information, including voice and video. Typically the problem has been the delay associated with downloading audio and video files. Name a product that has addressed this problem to deliver audio and video over low bandwidth connections to the Internet.

        Real Audio, real Video

    4. Q4 A video signal with a frame resolution of 360 x 280 pixels needs to be transmitted.
      1. if the signal is color with 12bit/pixel encoding and 30 frames/sec, what is bandwidth required to transmit the signal?

        360 * 280 = 100,800

        360 * 280 * 30 * 12 = 36,288,000

      2. How many bits would be needed to transmit the same signal if the signal is a black and white signal?

        B/w image uses 1 bit per pixel
        360 * 280 * 30 = 3,024,000
        Common Mistakes
        People have used 2 bit per pixel, or 4 bits per pixel. You have lost only 2 points overall for this mistake if rest of your anawers are consistent.

      3. You have available a T1 line with 1.544 Mbs of bandwidth. What is maximum number of frames per second that can be supported with a black and white signal assuming you would like to have the same resolution?

        360 * 280 * F = 1.544 x 106

        F = 1.544 x 106 / (360 * 280)= 15.3

      4. Given the same T1 line with 1.533Mbs, if I wanted 15 frame/second, what is the compression required to transmit the black and white signal?

        360 * 280 * 15 * Compression factor = 1.544 x 106

        Compression factor = 1.544 x 106/ (260* 280 * 15) = no compression

    5. Q5

      1. Rank order the following media in terms of bandwidth that can be supported by assigning numbers between 1 and 4. Let 1 denote the media with the lowest bandwidth and 4 denote the media with the highest bandwidth.
        1. twisted pair
        2. coaxial cable
        3. microwave
        4. optical fiber
      2. Give an example of an application where each of these media is the preferred choice.
        1. twisted pair - telephone local loop
        2. optical fiber - backbone networks
        3. microwave - bypass, satellite
        4. coaxial cable - cable TV
    6. Q6

      1. Give two examples where wireless media would be preferred over wireline media.
        remote access - cost of wiring

        congested areas with right of way - bypass application


        Common Mistakes
        Many of the students mentioned Satellite or cellular as examples but these are inherently wireless technologies. These are not applications where you have a choice of media. In cellular or satellite you have no option but to go wirless. You are asked for an application where you would use cellular over landline or satellite over wireline. Same problem for the next answer.

      2. Give two examples where wireline media would be preferred over wireless media.
        1. security is better with wireline than with wireless especially with fiber
        2. Environmental effects - wireless media is affected more by weather than wireless media.
    7. Q7 You would like to set up information service from which a person could obtain the latest weather for cities in the U.S.
      1. what are two alternative public network infrastructures that could be used to host this service?
        1. PSTN
        2. Internet
      2. For any one of your alternatives, summarize the fundamental business process underlying the provisioning of this service using the framework discussed in class.
        1. Customers: external - consumer, internal - service providers
        2. Information - weather + duration of call, queries about which info was requested.
        3. IT - PSTN + Computer-telephony infrastructure
        4. participants - consumer + service providers updating weather database
        5. Business process (billing by the telephone company)- call info number, punch in city ID based on voice prompt, obtain info.
      3. Compare the alternative ways of provisioning this service in terms of reach, range, and responsiveness.
        Reach - PSTN has higher reach then Internet now. More ubiquitous access devices. Range - very limited range of media as telephones now. But could change responsiveness near real rime.
      4. Ho would you generate the revenues required to provide the service under the options identified n a.

        The call charges are an excellent way of generating. The PSTN bills a from the customer. They pay you, the information provider.

    8. Q8
      1. Why is 1984 a landmark date in US telecommunication history? What happened to the telecommunications industry after 1984 with respect to provision of telephony?


        Break up of AT&T into local RBOC'S and local distance service providers. RBOC'S could only provide local service. IXC'S could only provide long distance.

      2. Since 1984, Long Distance companies are required to an access charge to local loop companies to complete long distance calls on the local network. This access charge increases long distance charges. What have organizations dome to avoid paying this access charge? Give an example of a service or a technology which has enabled them to do so.


        Bypass. Alternative Access or Comprehensive access providers enable bypass to IXC POP. Wireless technology like microwave towers on buildings can be used for bypass.
        Common Mistakes
        Satellitle is not used not local bypass. VSAT was a common answer but unfortunately no where in the world VSAT is used for local bypass. It is used for WANs or private networks. Satellite technology is far too expensive for bypass. FOr example a satellite call $3 per minute. I am ignoring other mistakes.

      3. What was the principal objective of telecommunications Act of 1996?


        To open up the local service to competition. Allow various plyers (Cable TV, Long Distance and TELCOs) to compete in each others territory. It had the violence and decency clauses in it and also guidelines for investment in different markets.

    9. Q9 Consider Internet push technology such as Pointcast. What is the principal benefit of this technology to an information consumer and an information provider?

      1. Information consumer?

        The information comes to you. Id needed you can get additional details by "pulling" more information from the web.

      2. Information provider?

        No change to what needs to be done. Point cast is a way of getting consumer 's attention in a crowded information space.

      3. Give an example of the potential use of this technology within an organization?

        Intranet - based dissemination of organizational documents based on interest profile supplied by info. consumers.