YEAR105

I. [50%] ( 2 25 )

1. The phenomenon where many autonomous peers join or leave simultaneously is called (A) Torrent (B)

Tit-for-tat (C) Peer Churn (D) DHT

2. For file distribution, the P2P model is expected to perform better than the client-server model by

utilizing (A) server download bandwidth (B) server upload bandwidth (C) peer download bandwidth

(D) peer upload bandwidth

3. Which is NOT supported by TCP? (A) error control (B) flow control (C) congestion control (D) delay

control

4. Which is NOT supported by UDP? (A) connectionless (B) best effort (C) multiple processes (D) in

order

5. Which is NOT supported by IPv4? (A) packet retransmission (B) packet fragmentation and reassembly

(C) packet routing (D) error detection by checksum

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

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

UDP port number

7. 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) source TCP port number (C) destination IP address (D) destination TCP port number

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

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

9. In a NAK-free protocol, when a receiver detects packet #n corrupted, it will respond (A) ACK #n (B)

NAK #n (C) ACK #(n-1) (D) NAK #(n-1)

10. 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

11. 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

12. Which of the following segment of the three-way handshake makes TCP vulnerable to a denial-of

service attack? (A) SYN (B) SYNACK (C) ACK (D) FIN

13. Which is a layer-4 device? (A) hub (B) bridge (C) NAT box (D) router

14. Which protocol checksum must be checked by the router for error detection? (A) Ethernet (B) IP (C)

TCP (D) UDP

15. The technique that a sender sends one packet then waits for its receivers response is called (A) store

and-forward (B) stop-and-wait (C) pipelining (D) retransmission

16. Which must have a buffer to receive out-of-order data? (A) Go-Back-N (B) Selective Repeat (C) TCP

(D) stop-and-wait

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

grows exponentially? (A) AIMD (B) Fast retransmit (C) Fast recovery (D) Slow start

18. Which approach increases transport rate linearly and cuts the rate in half after loss event? (A) AIMD

(B) Fast retransmit (C) Fast recovery (D) Slow start

19. Which approach transmits the missing segment again before the segments timer expires? (A) AIMD

(B) Fast retransmit (C) Fast recovery (D) Slow start

20. Which of the following field in the UDP header is NOT found in the TCP header? (A) source port (B)

destination port (C) checksum (D) length

21. Which is the state of a TCP server lifecycle when it receives FIN and sends ACK? (A) TIME_WAIT

(B) FIN_WAIT_2 (C) CLOSE_WAIT (D) LAST_ACK 22. Which of the following fields in the TCP header is designed for flow control? (A) Send window (B)

Receive window (C) Sliding window (D) Congestion window

23. Which is used by hosts and routers to communicate network-level information? (A) ICMP (B) NAT

(C) CIDR (D) DHCP

24. Which is the IPv4 address assignment strategy that supports address aggregation and splitting? (A)

ICMP (B) NAT (C) CIDR (D) DHCP

25. Which kind of switching models can switch multiple packets simultaneously (A) Switching via

crossbar? (B) Switching via bus (C) Switching via memory (D) Switching via token

II. [50%] ( 50 )

1. (12%) Consider Peer 51 wants to send a query to Peer 140 in complete circular DHTs of N peers, with

identities from 0 to n - 1.

(i) What are the relay peers (in order) and (ii) how many messages are required for

(a). a simple circular DHT and

(b). a circular DHT with shortcuts to neighbors of 2k distance?

2. (8%/10%) For reliable data transfer, the sender usually retransmits the packet after timeout without

receiving the ACK.

(a). Draw the message flow with a scenario of premature timeout for RDT 3.0 in action.

(b). Explain how TCP sets the timeout interval.

3. (12%) Consider Host A with IP address 140.127.208.129.

(a) If Host A connects to a /24 subnet. What are its subnet ID and netmask?

(b) If Host A connects to a /25 subnet. What is its subnet ID?

(c) If Host A connects to a /26 subnet. What is its netmask?

4. (8%) Which protocol field is present in IPv4 but absent in IPv6? Show at least two fields and explain

why to be removed in IPv6.