Comp 443 Computer Networks Final Exam Study Guide
The exam will cover material in the following sections. Some of the
midterm study topics appear here, but some do not (and will thus not be
on the final).
Chapter 2
2.5: sliding windows (only as it applies to TCP)
Chapter 4
4.1: basic IP
4.2: routing
4.3: subnets, supernets (CIDR), and the Internet
Global routing issues: provider-based, etc
(omit 4.3.5, on IPv6)
BGP and the SPF algorithm will not be on the exam
Chapter 5
5.1: UDP
5.2: TCP
State diagrams
Timers
TCP scenarios
5.3: RPC: not covered at all
Chapter 6
6.1: general info
6.3: TCP congestion control mechanisms
Slow Start
Congestion Avoidance phase - linear increase
Sawtooth graph (p 467, 471, 474)
Fast retransmit
Fast recovery (general overview)
Fairness
Two TCPs with same RTT
Two TCPs with different RTTs
6.4.1: DECbit
RED
TCP Vegas
Basics of TCP Westwood (not in the book)
Here are some relevant exercises from the text. Numbering is (5th edition)/(4th edition). I will post selected answers .
You should definitely read all these exercises, even if you don't work through them in detail.
Solutions to most problems are here.
Chapter 4:
Note that the 5th edition moved some of these exercises to chapter 3. Where applicable, I've numbered those as 3.N.
3.40/4.8: What is the maximum bandwidth at which an IP host can send
576-byte packets without having the Ident field wrap around within 60
seconds?
3.45/4.14: Suppose an iP implementation adheres literally to the following algorithm....
3.48/4.17: For the network given in ..., show how the link-state agorithm builds the routing table
3.64/4.30: Suppose the nodes in the networkshown participate in link-state routing, and C receives contradictory LSPs....
4.1/4.31: Consider the network shown in ..., in which horizontal lines represent transit providers....
4.3/3.33: Let A be the number of Autonomous Systems on the Intenet, and let D be the maximum AS-path length....
3.65b/4.34b: Suppose IP routers learned about IP networks the way Ethernet bridges learn about hosts ....
3.51/4.39: bridge-router problem (based on experience at Loyola!)
3.72/4.45: Table ... is a routing table using CIDR ... (a) C4.5E.13.87
4.5/4.47: Suppose P, Q and R are networks service providers ....
4.6/4.48: In the previous problem, ... suppose customer PA switches to provider Q ...
4.11/4.54: Suppose network N iwthin a larger organization A acquires its own direct connection to an ISP...
Chapter 5:
5/5: When closing a TCP connection, ....
20/20: The Nagle algorithm ....
22/22: Explain why TIME_WAIT is a somewhat more serious problem if ...
33/33: One of the purposes of TIME_WAIT ...
36ab/36ab: TCP is a very symmetric protocol, but the client/server model is not.
39/39: When TCP sends a ⟨SYN,SEQ=x⟩ or ⟨FIN,SEQ=x⟩, ...
Chapter 6:
5/5: Is it possible for TCP/Reno to reach a state ...
13/13: Two users, one using Telnet and oen sending files with FTP, ....
16/16 (do for both RWS=1MB and RWS=10MB) Assume that TCP implements an extension ...
17/17: Consider a simple congestion-control algorithm ....
21/21: Suppose that between A and B there is a router R.
23/23: Suppose that the R--B link in the previous exercise ...
26/26: Defeating TCP congestion-control mechanisms ....
27/27: Consider the TCP trace in ...
30/30: Suppose two TCP connections share a path through a router R.
33/33: Discuss the relative advantages and disadvantages of marking a packet ...
43a/42a: Consider the following two causes of a 1-second network delay:
Extra:
Suppose the window size (cwnd) is 40, and packet 1001 is lost. Packet
1000 will be ACKed normally. Packets 1001-1040 will be sent, and
1002-1040 will each trigger a duplicate ACK[1000].The sender's goal will be to reduce cwnd to 20.
(a) What actual data packets trigger the first three dupACKs?
(b) Just after the third dupACK[1000], how many packets/ACKs does the sender estimate are in flight?
At this point, the sender uses fast retransmit to retransmit packet 1001. When it arrives, ACK[1040] will be sent back.
(c) As the dupACKs arrive, consider them to be numbered with the actual
data packet that triggered them (as would be the case with SACK TCP).
If the sender is using fast recovery, at what point does it begin transmitting new data? (The next new data packet is 1041.)
(d) What is the first Data[N] sent for which the response is ACK[N], for N>1000?
(e) What is the first Data[N+20] send in response to ACK[N] (that is, we are back to having a normal window size of 20)?