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.
- 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.
- 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.
- 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
- 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
- Using three different looking glass sites (other than Cogent),
determine the AS path to Columbia University (18.104.22.168). Name the
- 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 22.214.171.124 and
- 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?
- 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?
- 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
- (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?
- 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.