Part A: Multiple Choice and True/False Question 1 Suppose we run simulation expe
ID: 3736646 • Letter: P
Question
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
Explanation / Answer
1)
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.
A confidence interval is how much uncertainty there is with any particular statistic. Confidence intervals are often used with a margin of error.
2) Spatial Diversity
The picture shows a Linksys WiFi access point being sold at Amazon.com.
Acees Pponts with dual antennas, use "space diversity". This works on the principle that both are unlikely to be in a dead spot. If one antenna can't receive the signal, the other likely can.
Two or more antennas to improve the quality and reliability of a wireless link.
3)All the options are correct.
Time-division multiplexing (TDM) is a method of putting multiple data streams in a single signal by separating the signal into many segments, each having a very short duration.
In fixed rate TDM for wireless networks data connections are "bursty"-they need a large amount of bandwidth at times, and very little at other times.
4) Queuing Delay
The time required to examine the packet's header and determine where to direct the packet is part of the processing delay.
The queuing delay of a specific packet will depend on the number of other, earlier-arriving packets that are queued and waiting for transmission across the link. So this delay is probabilistic and depends on packet arrival process.
Transmission dealay is the amount of time required to transmit all of the packet's bits into the link. Also known as packetization delay.
The time required to propagate from the beginning of the link to router is the propagation delay.