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CSC358 Tutorial 8 Notes

Below are some notes and sample solutions to the tutorial questions. These
notes are only meant to provide the necessary amount of information for you to
verify your own work and to help you recall the discussions in the tutorial.
Simply reading these solutions does NOT convey the same learning experience as
attending a tutorial (not even close). The tutorial materials are a mandatory
and important component of this course, so don't miss any of them!
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Question 1

(a) NEXT-HOP is used
(b) AS-PATH is used to avoid loops
(c) Not redundant because packets can be dropped at the network layer 

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Question 2

From w's point of view

w --- A --- B --- x
      |
      C --- y


From x's point of view

w --- A --- B --- x
                  |
                  C --- y


From y's point of view

w --- A --- C --- x
            |
            y

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Quesiton 3

Note: addition and subtraction are just bitwise XOR, no carry bit.

(a) R = 0100

(b) Add to D "mulitiple" of G, e.g.,

    D' = 1010101010 xor 10011 = 1010111001
    D' = 1010101010 xor 100110 = 1010001100

Note how CRC can detect error's of multiple bits and when it can't detect the
error, e.g., can't tell the difference between D and D'.

Practice a lot and use the web calculator to verify your answer!