CS 118 Homework 8


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Problem 1
In this problem, you will put together much of what you have learned about Internet protocols. Suppose
you walk into a room, connect to Ethernet, and want to download a Web page. What are the protocol steps
that take place, starting form powering on your PC to getting the Web page? Assume there is nothing in
our DNS or browser caches when you power on your PC. Explicitly indicate in your steps how you obtain
the IP and MAC addresses of a gateway router.
Write your solution to Problem 1 in this box
Problem 2
Suppose there are two ISPs, providing WiFi access in a particular caf´e, with each ISP operating its own AP
and having its own IP address block.
(a) Further suppose that by accident, each ISP has configured its AP to operate over channel 11. Will the
802.11 protocol completely break down in this situation? Discuss what happens when two stations,
each associated with a different ISP, attempt to transmit at the same time.
(b) Now suppose that one AP operates over Channel 1 and the other over Channel 11. How do your
answers change?
Write your solution to Problem 2 in this box
Problem 3
In Mobile IP, what effect will mobility have on end-to-end delays of datagrams between the source and
Write your solution to Problem 3 in this box
Problem 4
Consider the hierarchical network in Slide 6-84 and suppose that the data center needs to support email and
video distribution among other applications. Suppose four racks of servers are reserved for email and four
racks are reserved for video. For each of the applications, all four racks must lie below a single tier-2 switch
since the tier-2 to tier-1 links do not have sufficient bandwidth to support the intra-application traffic. For
the email application, suppose that for 99.9 percent of the time only three racks are used, and that the video
application has identical usage patterns.
(a) For what fraction of time does the email application need to use a fourth rack? How about for the
video application?
(b) Assuming email usage and video usage are independent, for what fraction of time do (equivalently,
what is the probability that) both applications need their fourth rack?
Write your solution to Problem 4 in this box
Problem 5
Answer the following questions:
(a) What is the role of the “core network” in the 3G cellular data architecture?
(b) What is the role of the RNC in the 3G cellular data network architecture?
(c) What role does the RNC play in the cellular voice network?
Write your solution to Problem 5 in this box
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