代写网络作业，了解 Medium Access Control
(MAC) 协议，实现Bozon Channel Access协议.
Learning Objectives
The purpose of this assignment is to learn about Medium Access Control (MAC)
protocols. Along the way, you will also learn how to develop and use a simple
discrete-event simulation for the performance analysis of network protocols.
Background Scenario
The “Planet of the Jumping Bozons” is a wonderful place, and you are delighted
that the Bozons have invited you there on an all-expenses-paid trip as a
network protocol performance consultant. The Bozons are curious but friendly
creatures who spend all of their lives alternating between two states:
sleeping and yodeling. Other needs, such as nourishment and waste elimination,
occur magically during the sleeping state, by osmosis with the planet’s
nutrient-rich atmosphere. The durations of the sleep periods are independent
and identically distributed (iid) random variables drawn from an exponential
distribution with a mean of S time units (e.g., S = 8.5 hours). The durations
of the yodeling periods are iid random variables drawn from an exponential
distribution with a mean of Y time units (e.g., Y = 1.2 hours). Bozons live in
colonies of size M. In such a colony, there are M beds laid out in a perfectly
straight line, with all of the beds exactly one meter apart. Each Bozon has a
designated bed, which is used as the home base for all of its activities. When
sleeping, the Bozon is horizontal on the bed and silent. When it is time to
yodel, the Bozon awakes instantly, leaps high into the air, and emits a
melodious yodel (song). Once the (randomly chosen) duration of the yodeling
period has elapsed, the Bozon lands gently back on the bed and instantly falls
asleep. Bozons are so fascinating that bus-loads of tourists come from miles
around just to watch them. In fact, tourism is the main source of revenue for
the Bozon planet. The complication that arises is the following: if more than
one Bozon yodels at the same time, the result is an ear-piercing screech that
drives all tourists away This screechy sound is in stark contrast to the
melodious sound savoured by the tourists when a single Bozon is yodeling, and
the peaceful night air when all Bozons are sleeping. To further complicate
matters, the planet is shrouded in eternal darkness (thus the Bozons cannot
see which other Bozons are awake) and all Bozons are tone-deaf (and thus
cannot hear each other yodeling). The leader of the Bozons has proposed
building larger and larger colonies to really draw in the tourists. Other
Bozons are concerned about the scalability of the random channel access
protocol, and that is why they have brought you here. They want your
recommendations in this regard.
Your Tasks
Your task in this assignment is to study the performance of the Bozon channel
access protocol. Rather than staying up all night observing and recording the
yodeling and screeching in different Bozon colonies, you will write a simple
computer simulation program in C or C++ to study this problem. Specifically,
write a computer simulation program (in C or C++) that can model (i.e.,
simulate) the channel access protocol used in a Bozon colony, and determine
the average channel performance. For assessing “channel performance”, you
should identify the (average) percentage of the time that the channel is
silent (i.e., not very interesting to tourists), melodious (i.e., very
interesting to tourists), and screechy (i.e., intolerable to tourists). Your
program should also report the number of attempted yodels, and the percentage
of attempted yodels that were perfect. A “perfect yodel” is one that was
melodious from start to finish, without any interruption by other Bozons.
(Hint: Tracking this information will be very helpful for debugging your
program.) Your program should be easily parameterizable for different values
of M, S, and Y (as command line arguments). You will use these parameters to
explore several Bozon configuration scenarios listed below. You may assume
that all the Bozons are initially asleep at time zero. Remember that
transitioning from sleeping to yodeling takes no time at all. When you are
finished, please submit your solution in electronic form via D2L. Your
submission should include the source code for your Bozon protocol simulator, a
very brief user manual, and your simulation results (in graphical and/or
tabular form).
Grading Scheme
The proposed grading scheme for the assignment is as follows:
- 20 marks for the design and implementation of a credible simulator for the Bozon channel access protocol
- 4 marks for a brief user manual describing how to compile and use your simulator, and a brief description of your testing
- 4 marks for simulation results evaluating the channel performance for a small Bozon colony, where M = 5, S = 100.0 time units, and Y = 10.0 time units. Show the average percentages achieved for each of the performance metrics stated above, from a “long enough” observation period to have some statistical confidence in your result (e.g., 1,000,000.0 simulated time units).
- 4 marks for simulation results to determine the optimal colony size M when S = 100.0 and Y = 10.0. That is, use your program to determine the maximum “melodious” percentage that can be achieved, as a function of M. State this percentage value, as well as the value(s) of M at which it is achieved.
- 4 marks for simulation experiments to assess the scalability of Bozon colonies when S = 200.0 time units, and Y = 10.0 time units. Produce a graph or table (or both) that clearly shows the percentages achieved for each of the performance metrics above, as a function of M, using M = 1, 2, 4, 8, 16, 32, 64, and 128. Make sure to indicate the highest “melodious” value achieved, and the value of M at which it occurs.
- 4 marks for a short summary (at most 1 page) of your results and observations about the Bozon protocol
Bonus (optional)
The Bozon parliament is considering the establishment of a standardized
“national yodel” of fixed time duration 10.0 time units.
If each Bozon emitted this standardized yodel during their wake period, rather
than a random (i.e., exponentially distributed) duration, would the channel
performance be better, worse, or the same? Use your simulator to explore this
scenario. Show your results (4 marks), and explain them as best you can (4
marks).
Tips
When debugging your code, use a small network topology (e.g., M = 4, or
smaller). When you are sure your results make sense, scale up the network size
and do your final runs.
If you want a test case for comparison, try this one:
M = 10, S = 50.000, and Y = 25.000
Total time observing channel: 1000000.000
Idle time on the channel: 17311.017 1.731%
Melodious time on channel: 87547.472 8.755%
Screech time on the channel: 895141.511 89.514%
In C, a convenient way to generate exponentially-distributed random numbers
with a mean of mu is indicated below. Note that exponential random variables
are continuous (i.e., floating point) values, and not discrete (i.e., integer)
values. Please do not round off these values to the nearest integer.
/* Parameters for random number generation. /
#define MAX_INT 2147483647 / Maximum positive integer 2^31 - 1 /
/ Generate a random floating point number uniformly distributed in [0,1] /
double Uniform01()
{
double randnum;
/ get a random positive integer from random() /
randnum = (double) 1.0 * random();
/ divide by max int to get something in the range 0.0 to 1.0 /
randnum = randnum / (1.0 * MAX_INT);
return(randnum);
}
/ Generate a random floating point number from an exponential /
/ distribution with mean mu. */
double Exponential(double mu)
{
double randnum, ans;
randnum = Uniform01();
ans = -(mu) * log(randnum);
return(ans);
}
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