--------------CED977BBD89F0FFDBC293BEB
Content-Type: text/plain; charset=gb2312; name="reading5.txt"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename="reading5.txt"
Week 5 Review
Analysis and Simulation of a Fair Queueing Algorithm
------------------------------------------------------
It is pretty interesting to read about this fair queueing
issues and think about its effectiveness. It states that fair
queueing has several advantages over the FCFS queueing algorithms.
1. Fair allocation of bandwidth
2. Lower delay for sources using less than their full share of
bandwidth
3. protection from ill-behaved sources.
Regarding fairness, it's really hard to define. The paper
said an allocation is fair if
1. no user receives more than its request
2. no other allocation scheme satisfying condition 1 has a
higher minimum allocation, and
3. condition 2 remains and reduce the total resource accordingly.
At the first glance, the definition seems to be good enough
and the algorithm may seems to solve the problem.
Thinking about this more, even though we defined the rule of
fairness, the problem still remains. The algorithm only holds
when all processes have the same priority. That means, no matter
how much bandwidth you needed, each process is allocated the same.
This doesn't really work for the real world when a user have
many processes. Then he is granted more bandwidth. Another situation
is: there are some sources, (say NFS) deserves more bandwidth than
others, but there is no mechanism to get that knowledge. Hence,
they are treated equally. Probably there are more problems that I
cannot think of at this moment. So, fairness still rises lots of
rhetorical questions.
As a conclusion, it is nice to see the effort and difficulties
in allocating bandwidth, promptness, and buffer space in
the fair queueing algorithm for congestion control. I think
that resources allocation will not be fair in this always changing
and not standarized environment. This could be the reasons for all
the problems.
--------------CED977BBD89F0FFDBC293BEB--