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Reminders
• Course final review with Q&A on Dec 15th
• Final exam on Dec 22th 10:30AM ~ 12:30PM
• Final score available before Dec 29th
HW1, HW2, HW3, Mid-term: accumulative percentage
20% A, 20% A-, 34% B , 13% C, 10% less than C
Work HarderGoodJob
More on Final Exam “Comprehensive”, emphasis on
material covered after mid-term Everything in lecture notes Section 1.1 – 1.7 (1.8 excluded) Section 2.1 – 2.8 (2.9 excluded) Section 3.1 – 3.7.1 (3.7.2 excluded) Section 4.1 – 4.8 Section 5.1~5.7 (section 5.8 excluded) Section 6.1 ~ 6.8
Hints for last-minute preparation
• Jeopardy Game Question (20%)
• Sample Final Exam (20%)
• Lecture notes (20%)
• Homework (20%)
• Textbook (20%)
CSCI 4211Introduction to Computer Networks
Jeopardy Review
Rules • Three/Four students form a group.
• After the questions show up, the team raises the # card first to get called on and MUST start to answer the question when TA calls on them with in 10 seconds (otherwise lost points)
• Each team gets one AND ONLY ONE answer per question
Difference from normal Jeopardy! game• Questions are given, you provide the answer.
(not vise versa)
• The group that answers correctly has the exclusive right to answer the next question.
• At most answer two questions in a row for a group. After that, all groups are allowed to compete for the next question.
• Only The Jeopardy Round and Final Jeopardy round
Other logistics
• Pengkui is charge of book keeping on white board (one score per group)
• To ensure the smoothness of the game, lecturer makes the FINAL decision whether an answer is correct or not, we can resolve disagreement later.
• Some questions would be related to the final
Trophies at stake
– The winning team wins 5$ star-buck card per member. You can enjoy together after class.
Click to begin.
Click here for Final Jeopardy
Category AApplication
Category BTransport
Category DNetwork II
Category EDL/Wireless
Level
100 $
200 $
300 $
400 $
500 $
100 $ 100 $ 100 $ 100 $Easy
200 $ 200 $ 200 $ 200 $Medium
300 $
400 $
500 $
300 $ 300 $ 300 $Hard
400 $ 400 $ 400 $Daunting
500 $ 500 $ 500 $ Impossible
Category CNetwork I
Category AApplication
Category BTransport
Category DReliableProtocols
Category ETCP
CongestionControl
Level
100 $
200 $
300 $
400 $
500 $
100 $ 100 $ 100 $ 100 $Easy
200 $ 200 $ 200 $ 200 $Medium
300 $
400 $
500 $
300 $ 300 $ 300 $Hard
400 $ 400 $ 400 $Daunting
500 $ 500 $ 500 $ Impossible
Category CTCP Connection
Management
Question 1aThe name of an internet application that listens to the port number 80.
Answer 1a
HTTP
Question 2aA special application layer protocol that is essential to the operation of the Internet.
Answer 2aDNS
Domain Name System
Question 3a
Name three protocols commonly used for sending and receiving
emails
Answer 3a
SMTP
IMAP
POP3
Question 4aSuppose a user at m.a.com types in www.b.com, if no DNS information is cached at any level of DNS hierarchy. How many DNS requests will be issued by m.a.com?
Answer 4a1
Question 5aHow many DNS requests are needed to resolve the domain name www.b.com iteratively
Answer 5a4
m.a.com
www.b.com
root DNS server
local DNS serverDns.a.com
1
23
4
5
6
authoritative DNS serverdns.b.com
78
TLD DNS server.com
Question 1bHow many sockets are created totally at both client and server sides, when 11 users query a DNS server at the same time?
Answer 1b1 socket at the server side, 11
sockets at the client side, totally 12.
Question 2bName at least four key techniques needed for reliable data transfer
Answer 2bError Detection
ACK/NACK/Retransmission
Sequence Number
Timer
Question 3bName at least four key functions provided by TCP
Answer 3bReliable transfer, flow control, congestion control and multiplexing.
Question 4bWhy the TCP header has a header
length field, while UDP doesn’t
Answer 4bUDP has a fixed header of 8 bytes
The length of a TCP header is 20 bytes + Options
Length is needed to indicate how long the options are
Question 5bWhy TCP avoids measuring the Sample-RTT for retransmitted
segments?
Answer 5bThe source will mistakenly take an old (delayed) acknowledgment as the acknowledgment for retransmitted packet and calculate an incorrect (smaller) value of Sample-RTT.
Question 1c In a CIDR format 192.168.2.0/12
What is the meaning of 12?
Answer 1cThe length of network prefix
Question 2c How many subnets are below?
Answer 2c8
Question 3c
A widely used technique for alleviating the IPv4 address shortage
Answer 3cNAT
Network Address Translation
mapping mulitple intranet IP addresses to a single internet IP address using
different port numbers
Question 4c How many Class C Internet addresses
would an organization need in order to number 2000 hosts ( classful addressing)?
Answer 4c2^8-2 = 254 hosts each Class C address.
2000/254 = 7.87 8.
Question 5c How many packets are needed for RPF
A
B
D
E
c
F
Answer 5cTotally 11
A
B
D
E
c
F
3
2
2
1
2
1
Question 1dHow long An IPv6 address is
(in number of bits)
Answer 1d128 bits
Question 2dHow many packets is needed for Spanning Tree based Flooding
A
B
D
E
c
F
Answer 2d5
Question 3d
Name A Link-State Protocol
Answer 3d
OSPF
Open Shortest Path First
Question 4dThe name of the technique that
encapsulates a Multicast IP packet into a Unicast IP packet
(IP-in-IP)
Answer 4dMulticast Tunneling
Question 5d
How the BGP Protocol detects routing loops?
Answer 5dBGP use Path Vector: A sequence of
AS numbers
If the same AS number appears more than once, there is a loop.
Question 1eWhat is the name of the layer-1 device that repeats the signal
Answer 1eNetwork Hub/Repeater
Question 2e
Name the media access control protocol that can guarantee no collision and with
low management overhead
Answer 2eChannel Partition Protocols
Such as
TDMA, FDMA and CDMA
Question 3eSuppose switch tables are all empty (assume ARP is up-to-date). If Host A sends a packet to Host B. How many frames are sent in the network?
Host AHost B
Answer 3e8
Host AHost B
Question 4eIf Host B replies to Host A right away,
how many frames are sent?
Host AHost B
Answer 4e3
Self Learning
Question 5eIn mobile IP indirect routing scenario, who assigns a care-of address (COA)?
(1) Mobile device, (2) Correspondent, (3) Home agent, (4) Foreign agent, or (5) DNS server?
Answer 5eA care-of-address is the one its gets when it is visiting a foreign network. The COA is assigned by the foreign agent (which can be the edge router in the foreign network or the mobile node itself).
TCP-Related Questions
Question 1fWhat is the main problem using the Stop-&-Wait protocol on a 1Gbps link with a propagation delay of 15 ms (and maximum packet size of 1 KB)?
Answer 1f
Question 2fIn the Go-Back-N protocol, if 4 bits are used for the sequence numbers, what is the maximum number of packets that can be transmitted in one-round without acknowledgment?
Answer 2f
Question 3fIn the Selective Repeat protocol, if 4 bits are used for the sequence numbers, what is the maximum number of packets that can be transmitted in one-round without acknowledgment?
Question 4fSuppose a TCP sender is currently in the slow-start phase. It transmits 4 segments (each 1500 bytes) in the current round, and the sequence no. carried in the last segment is 6000. When it receives an acknowledgement with ack. no =7501, what value will it set its Congestion Window to?
Question 5fSuppose a TCP sender is currently in the congestion avoidance phase, and its CongWin is set = 10000 bytes. After it has transmitted 8 segments (each 1500 bytes), a time-out event happens. What will it set its “threshold” variable to?
What value will it set its CongWin to?
Answer 2f
Question 3f
Answer 3f
Question 4f
Answer 4f
Question 5f
Answer 5f
Make your wager up to what you have
Write down the wager along with the answer on the back of the index card.
Finish in 3 minutes!!!
Final Question
Suppose initially all ARP tables and switching tables are empty. Suppose now host A sends an IP data packet to host C. How many Ethernet frames are sent?
A
D
S3
B C
S2 S1
Switch Host
Formal Class Evaluation Lecturer: Tian HeTA: Pengkui LuoTA: Jaehoon Paul JeongTerm: Fall Current Year: 2009Course ID: 24513 Section: 001
Your positive feedback is very important to me and TAs! Thank you
Final Answer
14 frames
6 frames for the ARP request4 frames for the ARP reply
4 frames for data