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