YEAR 109

I. ( 22 2 44 )

1. All UDP datagrams leaving a local network via a NAT box must have the same (A) source IP address

(B) destination IP address (C) source UDP port number (D) destination UDP port number

2. A browser establishes two parallel TCP connections to the same Web server. When the host running

the browser receives a segment from the server, which field of the segment is different? (A) source IP

address (B) destination IP address (C) source TCP port number (D) destination TCP port number

3. When a DNS server receives two queries from the same host, which field of the query message is

different? (A) source IP address (B) destination IP address (C) source UDP port number (D)

destination UDP port number

4. During TCP three-way handshake, which of the following segment does the server send initial

sequence number and buffer size with? (A) SYN (B) SYNACK (C) ACK (D) FIN

5. Which is the state of a TCP client lifecycle after it receives SYNACK? (A) LAST_ACK (B)

SYNSENT (C) SYNRCVD (D) ESTAB

6. Which is NOT the state of a TCP client lifecycle? (A) FIN_WAIT_1 (B) FIN_WAIT_2 (C) CLOSE_WAIT

(D) TIMED_WAIT

7. Which socket function is called by an application different from the other three functions? (A) accept()

(B) bind() (C) connect() (D) listen()

8. Using redundancy within images to decrease the number of bits used to encode image is called (A)

temporal coding (B) spatial coding (C) channel coding (D) network coding

9. Which does NOT use UDP? (A) SNMP (B) DNS (C) HTTP/3 (D) SSH

10. Which header field is included in UDP but not in TCP? (A) acknowledgement number (B) sequence

number (C) checksum (D) length

11. Which device is expected to examine the link layer header of an incoming packet? (A) NAT box (B)

bridge (C) router (D) hub

12. Which header field is NOT modified by a NAT for incoming datagrams? (A) checksum (B)

destination IP address (C) destination port (D) source port

13. Which host is NOT within the same network of subnet /23? (A) 192.168.2.253 (B) 192.68.3.254 (C)

192.168.3.1 (D) 192.168.4.1

14. What is the network mask for subnet /26? (A) 255.255.252.0 (B) 255.255.255.0 (C) 255.255.255.128

(D) 255.255.255.192

15. Which must have a buffer to receive out-of-order data? (A) go-back-N (B) selective repeat (C) TCP

(D) stop-and-wait

16. Which does NOT have the premature timeout problem? (A) RDT 2.0 (B) RDT 3.0 (C) go-back-N (D)

selective repeat

17. A RDT2.2 (NAK-free) sender is in the state of waiting for ACK 0. It will resend the data packet if it

receives (A) timeout (B) NAK 0 (C) ACK 0 (D) ACK 1

18. A RDT3.0 (channels with loss) sender is in the state of waiting for ACK 0. It will resend the data

packet if it receives (A) timeout (B) NAK 0 (C) ACK 0 (D) ACK 1

19. Considering TCP sequence number, the acknowledgement number for three-byte data transmitted

with seq 44 is (A) 44 (B) 45 (C) 46 (D) 47

20. An acknowledgment for a packet with sequence number n indicating that all packets with a sequence

number up to and including n have been correctly received at the receiver is called (A) negative

acknowledgement (B) selective acknowledgement (C) cumulative acknowledgement (D) duplicate

acknowledgement 21. Which is the mechanism applied when the congestion window is below the Threshold and the window

grows exponentially? (A) AIMD (B) fast recovery (C) fast retransmit (D) slow start

22. For the same expected seq #, which does a TCP receiver send the highest acknowledgement #?

(A) Arrival of in-order segment with expected seq #. All data up to expected seq # already ACKed.

(B) Arrival of in-order segment with expected seq #. One other segment has ACK pending.

(C) Arrival of out-or-order segment higher-than-expected seq #. Gap detected.

(D) Arrival of segment that partially or completely fills gap.

II. ( 56 )

1. (6%) Explain the following terms. (a) AS (B) OSPF (C) SDN

2. (10%) Consider socket programming. A client wants to send blocks of data to a server. If the client

sends the data with (i) UDP or (ii) TCP,

(a). What may happen for the transmission of the data and

(b). What actions does the server need to take for the cases of (a)?

3. (10%) Explain how TCP sets and manages the retransmission timeout interval.

4. (5%/5%) Consider network-layer services.

(a). Argue the efficiency of IPv4 and IPv6.

(b). What are included in the entry of the flow table in OpenFlow?

5. (10%) Consider the given network of six nodes, and assume that each node

initially knows the costs to each of its neighbors. Use Dijkstras algorithm

to compute the shortest path from node e to all the other network nodes.

Demonstrate how the algorithm works by computing a table step-by-step

and show the final forwarding table with paths and costs to the others.

6. (10%) Consider the given network of four nodes, and assume that each node

initially knows the costs to each of its neighbors. Use the distance vector algorithm

to compute the distance table of each node step-by-step. Besides, show the final

forwarding table with paths and costs to the others from node x.

a

d

e

b

c

6 4

2 9

1

3

10

8

f

5

7

a

d

e

b

c

6 4

2 9

1

3

10

8

f

5

7

w

y

z

x

2

1

3

6

5

w

y

z

x

2

1

3

6

5