Part A: Multiple Choice and True/False

Question 1

Suppose we run simulation experiments to estimate some network metric of interest (say, delay). From a large number N of samples, we are able to calculate the average and 90% confidence interval. How should we interpret these results?

(Hint: Check Credibility of simulation results in Module 2

All the options are correct.

If we calculate 90% confidence interval from independently obtained sets of N samples, we should expect 90% of those intervals to contain the true mean delay.

If N is large enough, we expect the collected samples to follow a Gaussian distribution.

If we repeat the experiment and collect an additional M samples, we should expect 90% of those M samples to fall into the calculated confidence interval.

If we repeat the experiment once and measure delay, the measured value has a 0.9 probability of falling in the calculated confidence interval.

Question 2

The picture shows a Linksys WiFi access point being sold at Amazon.com.

Linksys WAP300N IEEE 802.11n 300 Mbps Wireless Access Point

Two antennas are used:

To have a backup antenna in case one fails

For allowing dual frequency operation

To connect to two different wireless LANs

For frequency hopping

For spatial diversity

Question 3

Which of the following is true regarding fixed TDM (time division multiplex) wireless networks?

It is an efficient technique for handling bursty traffic

Delays can be infinite due to the rigid, slotted nature of communication

All the options are correct.

Synchronization is not an issue because nodes will defer transmission if they sense another node transmitting

Bandwidth is generally fixed because nodes can usually only transmit during their timeslot

Question 4

Which of the following components of delay is typically probabilistic and depends on the packet arrival process?

Queuing delay

Propagation delay

Processing delay

Transmission delay

Packetization delay

Question 5

Due to obstacles and reflectors in the wireless propagation channel, a transmitted signal may arrive at the receiver from various directions. This comprises an unpredictable set of reflections and/or direct waves, each with its own degree of attenuation and delay. This phenomenon, which can cause distortions to the received signal, is known as

Collision

Path loss

Multipath fading

Shadowing

Interference

Question 6

If a random variable describing wait time has a exponential distribution (aka, follows a Poisson process), which of the following is true?

Wait time is fixed, so you would know exactly how much longer you must wait

Wait time is independent of the time you have already waited

The longer you have waited, the sooner you would expect to be done

The longer you have waited, the longer you expected future waiting time will be

Question 7

The session initiation protocol (SIP) ...

Is adopted by several voice of IP applications

Is an example of mobility support at the application layer

All the options are correct.

Defines mechanisms for communication between end systems and proxy servers

Question 8

When analyzing packet sizes in observed Internet traffic, which of the following is true?

Packet size is bursty, making Internet traffic extremely hard to analyze mathematically

Packet size follows a uniform distribution

Packet size is mutli-modal, with a high percentage of header-only packets and large packets bounded by the maximum transmission unit of the network link

Packet size follows a light-tailed, Pareto distribution