Transcript Jepardy - CSE Labs User Home Pages

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
Good
Job
Work Harder
20% A, 20% A-, 34% B , 13% C, 10% less than C
More on Final Exam
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“Comprehensive”, emphasis on material
covered after mid-term
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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 4211
Introduction 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
Level
Category A Category B Category C Category D Category E
Application Transport
Network I Network II DL/Wireless
Easy
100 $
100 $
100 $
100 $
100 $
Medium
200 $
200 $
200 $
200 $
200 $
Hard
300 $
300 $
300 $
300 $
300 $
Daunting
400 $
400 $
400 $
400 $
400 $
Impossible
500 $
500 $
500 $
500 $
500 $
Level
Category D Category E
Category
C
Category A Category B
TCP
Application
Transport
TCP Connection
Management
Reliable
Protocols
Congestion
Control
Easy
100 $
100 $
100 $
100 $
100 $
Medium
200 $
200 $
200 $
200 $
200 $
Hard
300 $
300 $
300 $
300 $
300 $
Daunting
400 $
400 $
400 $
400 $
400 $
Impossible
500 $
500 $
500 $
500 $
500 $
Question 1a
The name of an internet application
that listens to the port number 80.
Answer 1a
HTTP
Question 2a
A special application layer protocol
that is essential to the operation of
the Internet.
Answer 2a
DNS
Domain Name System
Question 3a
Name three protocols commonly
used for sending and receiving
emails
Answer 3a
SMTP
IMAP
POP3
Question 4a
Suppose 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 4a
1
Question 5a
How many DNS requests are needed to
resolve the domain name www.b.com
iteratively
root DNS server
2
3
Answer 5a
TLD DNS server
.com
4
5
local DNS server
Dns.a.com
1
8
4
7
6
authoritative DNS server
dns.b.com
m.a.com
www.b.com
Question 1b
How many sockets are created
totally at both client and server
sides, when 11 users query a DNS
server at the same time?
Answer 1b
1 socket at the server side, 11
sockets at the client side, totally
12.
Question 2b
Name at least four key techniques
needed for reliable data transfer
Answer 2b
Error Detection
ACK/NACK/Retransmission
Sequence Number
Timer
Question 3b
Name at least four key functions
provided by TCP
Answer 3b
Reliable transfer, flow control,
congestion control and multiplexing.
Question 4b
Why the TCP header has a header
length field, while UDP doesn’t
Answer 4b
UDP 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 5b
Why TCP avoids measuring the
Sample-RTT for retransmitted
segments?
Answer 5b
The 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 1c
The length of network prefix
Question 2c
How many subnets are below?
Answer 2c
8
Question 3c
A widely used technique for alleviating
the IPv4 address shortage
Answer 3c
NAT
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 4c
2^8-2 = 254 hosts each Class C address.
2000/254 = 7.87  8.
Question 5c
How many packets are needed for RPF
A
B
c
D
F
E
Answer 5c
Totally 11
A
3
2
B
c
2
D
1
F
E
2
1
Question 1d
How long An IPv6 address is
(in number of bits)
Answer 1d
128 bits
Question 2d
How many packets is needed for
Spanning Tree based Flooding
A
B
c
D
F
E
Answer 2d
5
Question 3d
Name A Link-State Protocol
Answer 3d
OSPF
Open Shortest Path First
Question 4d
The name of the technique that
encapsulates a Multicast IP packet into a
Unicast IP packet
(IP-in-IP)
Answer 4d
Multicast Tunneling
Question 5d
How the BGP Protocol detects routing
loops?
Answer 5d
BGP use Path Vector: A sequence of AS
numbers
If the same AS number appears more
than once, there is a loop.
Question 1e
What is the name of the layer-1 device
that repeats the signal
Answer 1e
Network Hub/Repeater
Question 2e
Name the media access control protocol
that can guarantee no collision and with
low management overhead
Answer 2e
Channel Partition Protocols
Such as
TDMA, FDMA and CDMA
Question 3e
Suppose 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 A
Host B
Answer 3e
8
Host A
Host B
Question 4e
If Host B replies to Host A right away,
how many frames are sent?
Host A
Host B
Answer 4e
3
Self Learning
Question 5e
In 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 5e
A 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 1f
What 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 2f
In 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 3f
In 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 4f
Suppose 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 5f
Suppose 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?
Switch
A
Host
S1
D
S2
S3
B
C
Formal Class Evaluation
Lecturer: Tian He
TA: Pengkui Luo
TA: Jaehoon Paul Jeong
Term: Fall Current Year: 2009
Course 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 request
4 frames for the ARP reply
4 frames for data