Assignment 3

The assignment is due Wednesday, April 29, 5 pm EDT, to be submitted via CourseWorks.

Some of the questions below are research questions, where you are asked to find information about a particular issue. You may use the Engineering Library, any text books you have, one of the paper from the class readings, or the web to come up with answers. Be sure to cite your sources. Generally, a paragraph or two should be sufficient to answer the question. There is no need to write a tutorial.


  1. Measure the audio frequency transmission range for telephony and Skype. Using a tone generator, generate a set of tones at increasing frequencies and transmit them via a landline or cellphone as well as FaceTime or Skype. To avoid measuring the acoustic transmission path, set up the sender and receiver in different rooms. Measure (using a loudness meter) which frequencies get transmitted at both the low end (below 300 Hz) and higher frequencies (3 kHz and above). Show the amplitude vs. frequency curve. Document your measurement setup (including any screen shots or photos for illustration), the Skype/FaceTime configuration and any limitations you encountered. Frequency generators and loudness meters are available for Android, IOS, MacOS and Windows. You can either pick up the received sound with a microphone or directly couple the receiving application to the measurement system using a headphone (3.5 mm) cable. For this problem, you may, but do not have to, work in teams of two; indicate your team mate on your assignment.

  2. Touch tones (the tones generated when you press the digit or #/* buttons on a phone keypad) consist of two tones. Using a frequency analyzer tool (any platform), see if you can identify the tones for two digits and if your measurement corresponds to the published values. To generate the tones, you can call a VoIP application with your phone. Also, applications such as Skype or Hangout may allow you to generate tones during a call. Document your experimental setup.
  3. Both yellow cabs (taxis) and Uber transport people for a fee. Typically, taxis are considered common carriers, but Uber and limousine services are not. Apply the tests that determine common carrier status to the two transportation options. Does the distinction make sense? Why or why not?
  4. US telecommunication law distinguishes between telecommunications and information services. Apply the definitions to categorize backbone IP transport, MPLS, CDN, a DNS service (like OpenDNS), Starbucks Wi-Fi Internet access and residential Internet access. Justify your answers, citing the characteristics from the definition of the two services that apply in each case. You can refer to the Open Internet order if needed.
  5. Using three different looking glass sites (other than Cogent), determine the AS path to Columbia University ( Name the carriers.
  6. Assume that the CS department within Columbia University has its own Internet connection through Level3, in addition to the regular CU connectivity, but does not have its own ASN. What routes would be advertised to reach CUCS? (Columbia CS uses and
  7. What are the fiber spectral windows typically used for transmitting data? How much bandwidth (in Hz) do they offer? Does this differ between singlemode and multimode fiber?
  8. Using the Spectrum dashboard or other sources, compute which fraction of the spectrum between 1 and 2 GHz is used for licensed cellular (broadband), fixed wireless, mobile radio, radar, satellite, unlicensed and other uses. For the 1755 to 1850 MHz band, what is band called and what is the maximum allowed power?
  9. Using a Wi-Fi exploration tool on your laptop, determine the usage of the 2.4 and 5 GHz spectrum in percent. Outside of the Columbia campus (e.g., in a coffee shop or park), count the number of Wi-Fi access points. Which ones can you connect to, even if just to be prompted for a password? List the SSIDs, frequencies (channels) and status (e.g., open access point, password protected, connection timed out).
  10. (a) Could you place a geostationary satellite in an orbit that circled the north and south pole? If not, why not? (b) Can you determine how many geostationary satellites there are? (c) What is the physical separation of these satellites in orbit?
  11. Programming problem (audio): Build a very simple unicast audio sender and receiver. Your program should read short blocks (no more than 100 ms) of audio data (sampling rate 8 kHz, mono, G.711 (mu-law) or 16-bit) from the sound device, e.g., from a microphone connected to your PC, and then send it, via UDP unicast to to the receiver, designated by a host name or IP address on the command line. For this assignment, you can simply put some number of samples (say, 100) into one packet. The receiver should play back the audio.

    Audio data needs to be read when ready, not at nominally fixed intervals. For this assignment, you should play out the audio packet as soon as it arrives at the receiver. If necessary, you can find routines to convert to and form mu-law format online or here.