Yarmouk University
Hijjawi Faculty for Engineering Technology
Computer Engineering Department
CPE-562: Computer Networks
Second Midterm Exam: A
Date: 27/11/11
Student Name
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Student Number:------------------------------------------------------------------------------------------
INSTRUCTIONS (please read carefully)
1.
2.
3.
4.
5.
TURN OFF YOUR CELL PHONE NOW
Time allowed 60 minutes
Provide your answers on this page. Answers elsewhere will not be looked at.
Return all pages.
Provide only one answer to each question. Giving more than one answer for the same
question will result in zero credit for that question.
6. Mark the right answer with (×).
A
1|4
B
C
D
E
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B
C
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1.
2.
3.
4.
2|4
Which of the following statements is wrong?
a.
Skype is inherently a P2P application
b. Skype is a public application-layer protocol
c.
Skype uses a hierarchical overlay with super
nodes
d. Skype Index maps usernames to IP
addresses
e. Skype peers communicate through NATs via
relay
In BitTorent, a peer pulls chunks from _________
trading partners.
a.
one
b. two
c.
three
d. four
e. five
Which of the following choices has correct statements?
a.
The alternating-bit protocol (stop-and-wait
protocol) is the same as the Go-back-N
protocol with a sender and a receiver size of
1. The alternating-bit protocol (stop-andwait protocol) is the same as the SelectiveRepeat protocol with a sender and a
receiver size of 1.
b. The alternating-bit protocol (stop-and-wait
protocol) is not the same as the Go-back-N
protocol with a sender and a receiver size of
1. The alternating-bit protocol (stop-andwait protocol) is not the same as the
Selective-Repeat protocol with a sender and
a receiver size of 1.
c.
The alternating-bit protocol (stop-and-wait
protocol) is the same as the Go-back-N
protocol with a sender and a receiver size of
1. The alternating-bit protocol (stop-andwait protocol) is not the same as the
Selective-Repeat protocol with a sender and
a receiver size of 1.
d. The alternating-bit protocol (stop-and-wait
protocol) is not the same as the Go-back-N
protocol with a sender and a receiver size of
1. The alternating-bit protocol (stop-andwait protocol) is the same as the SelectiveRepeat protocol with a sender and a
receiver size of 1.
e. None of the given choices
Suppose that the ASCII characters
BDLZPXWKJANCSPUGVTKEG9T represent the
application data (message) of a UDP segment. What
value will the Length field of this segment have?
a.
9
b. 23
c.
31
d. 248
e. Impossible to know from the given
information
5.
6.
7.
8.
9.
Consider a fully-connected mesh overlay network with
N peers. How many messages are sent to know the
immediate successor of a key?
a.
1
b. N – 1
c.
N
d. N2
e. 𝑙𝑜𝑔2𝑁
Consider Selective-Repeat mechanism. Suppose the
sender sends pkt 0. The receiver receives pkt 0
correctly and sends ACK 0, which is correctly received
by the sender. Suppose then that the receiver receives
pkt 1, pkt 2, pkt 3, pkt 5. Which of the following
statements is correct?
a.
pkt 1, pkt 2, pkt 3 will be buffered. pkt 5 will
be discarded
b. pkt 1, pkt 2, pkt 3 will be discarded. pkt 5
will be buffered
c.
pkt 1, pkt 2, pkt 3, pkt 5 will be buffered
d. pkt 1, pkt 2, pkt 3 will be delivered. pkt 5
will be discarded
e. pkt 1, pkt 2, pkt 3 will be delivered. pkt 5
will be buffered
What does SNMP stand for?
a.
Simple Network Management Protocol
b. Source Network Message Protocol
c.
Service Network Management Point
d. Service Network Message Provider
e. Service Node Mail Protocol
In BitTorent, how many “optimistically unchoked”
peers does a peer have?
a.
1
b. 2
c.
3
d. 4
e. 5
Which of the following statements is correct?
a.
In connectionless demultiplexing, IP
datagrams with different source IP
addresses and/or source port numbers are
directed to same socket
b. In connectionless demultiplexing, IP
datagrams with different source IP
addresses and/or source port numbers are
directed to different sockets
c.
In connection-oriented demultiplexing, web
servers use one socket for all connecting
clients
d. In connection-oriented demultiplexing,
receiving host can direct segments to the
appropriate socket using source and
destination port numbers
e. Multiplexing at the receiving host works by
delivering received segments to the correct
socket
10. Consider distributing a file of 10 Gbits to 100 peers.
The server has an upload rate of 20 Mbps, and each
peer has a download rate of 1 Mbps and an upload
rate of 200 kbps. What is the minimum distribution
time for client-server distribution?
a.
10,000 s
b. 5,000 s
c.
50,000 s
d. 100,000 s
e. 60,000 s
11. The UDP segment header consists of _________
octets.
a.
4
b. 8
c.
32
d. 64
e. Variable number of octets as it may contain
options
12. Which of the following services does UDP provide?
a.
Bandwidth guarantees
b. Flow control
c.
Connection setup
d. Congestion control
e. Best-effort
13. Suppose you installed and compiled the Java programs
TCPClient and UDPClient on one host and TCPServer
and UDPServer on another host. Which of the
following choices has correct statements?
a.
It is ok. To run UDPClient before you run
UDPServer. It is ok. To run TCPClient before
you run TCPServer.
b. It is not ok. To run UDPClient before you
run UDPServer. It is not ok. To run TCPClient
before you run TCPServer.
c.
It is ok. To run UDPClient before you run
UDPServer. It is not ok. To run TCPClient
before you run TCPServer.
d. It is not ok. To run UDPClient before you
run UDPServer. It is ok. To run TCPClient
before you run TCPServer.
e. It is ok. If you use different port numbers
for the client and server sides.
14. Consider DHT with n = 4 and peers 1, 3, 4, 5, 8, 10, 12,
14. To which peer is the key 7 assigned?
a.
1
b. 5
c.
8
d. 14
e. 15
15. Which of the following may represent a valid UDP port
number?
a.
98456
b. 81002
c.
85328
d. 74105
e. 61970
3|4
16. Consider Go-back-N mechanism. Suppose the sender
sends pkt 0. The receiver receives pkt 0 correctly and
sends ACK 0, which is correctly received by the sender.
Suppose then that the receiver receives pkt 1, pkt 2,
pkt 4, pkt 5. Which of the following statements is
correct?
a.
pkt 1, pkt 2, pkt 4, pkt 5 will be delivered
b. pkt 1, pkt 2, pkt 4, pkt 5 will be discarded
c.
pkt 1, pkt 2 will be delivered. pkt 4, pkt 5
will be discarded
d. pkt 1, pkt 2 will be discarded. pkt 4, pkt 5
will be delivered
e. ACK5 will be sent
17. Consider peer churn in a “Circular DHT”. Which of the
following statements is correct?
a.
A peer does not need to know the IP
address of any other peer
b. Each peer needs to know the IP address of
its immediate successor only
c.
Each peer needs to know the IP address of
its second successor only
d. Each peer needs to know the IP addresses
of its immediate and second successor only
e. Each peer needs to know the IP address of
every other peer
18. Consider Go-back-N mechanism. What is the maximum
window size if 5-bit sequence numbers are used?
a.
31
b. 32
c.
15
d. 16
e. 4
19. Comparing “Circular DHT” and “Circular DHT with
shortcuts”. Which of the following statements is
correct?
a.
A peer has fewer neighbors in “Circular
DHT” but fewer query messages are sent
b. A peer has fewer neighbors in “Circular DHT
with shortcuts” but fewer query messages
are sent
c.
A peer has more neighbors in “Circular
DHT” and fewer query messages are sent
d. A peer has more neighbors in “Circular DHT
with shortcuts” and fewer query messages
are sent
e. “Circular DHT” and “Circular DHT with
shortcuts” have the same performance in
terms of the number of neighbors and
number of sent query messages
20. Consider distributing a file of 10 Gbits to 100 peers.
The server has an upload rate of 20 Mbps, and each
peer has a download rate of 1 Mbps and an upload
rate of 200 kbps. What is the minimum distribution
time for P2P distribution?
a.
10,000 s
b. 500 s
c.
25,000 s
d. 40,000 s
e. 35,500 s
21. Calculate the checksum for the following two 16-bit
values:
1000 0001 1010 1011
1101 1100 0000 1010
a.
1010 0010 0100 1010
b. 0101 1101 1011 0110
c.
1010 0010 0100 1001
d. 1001 0011 0100 0111
e. 0110 1100 1011 1000
22. Consider the stop-and-wait mechanism. Suppose that
the sender sends pkt 1, which is correctly received by
the receiver. The receiver sends ACK1 which is then
lost in the way. What happens next?
a.
The receiver resends ACK1
b. The receiver sends ACK0
c.
The sender continues normally by sending
pkt 0
d. The sender times out and sends pkt 0
e. The sender times out and resends pkt 1
23. Which of the following statements is wrong?
a.
In socket programming with UDP, sender
explicitly attaches IP address and port of
destination to each packet
b. In socket programming with UDP, server
must extract IP address and port of sender
from received packet
c.
In socket programming with TCP, client TCP
establishes connection to server TCP
d. In socket programming with TCP, client
creates client-local datagram socket
e. In socket programming with TCP, both input
and output streams are attached to sockets
24. Consider the stop-and-wait mechanism. Suppose a link
of 500 Mbps between the sender and the receiver, 5
ms propagation delay, and 2000-byte packet. What is
the utilization at the sender?
a.
0.0032
b. 0.0064
c.
0.0004
d. 0.0008
e. 0.017
4|4
25. Which of the following choices has correct statements?
a.
Network layer provides logical
communication between hosts. Transport
layer provides logical communication
between processes
b. Network layer provides logical
communication between processes.
Transport layer provides logical
communication between hosts
c.
Network layer provides physical
communication between hosts. Transport
layer provides physical communication
between processes
d. Network layer provides physical
communication between processes.
Transport layer provides physical
communication between hosts
e. Network layer provides physical
communication between hosts. Transport
layer provides logical communication
between processes