YEAR 107

I. [50%] ( 2 25 )

1. 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

2. 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

3. 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

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

control

6. 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

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

selective repeat

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

(D) stop-and-wait

9. Which of the following fields in the TCP header is designed for flow control? (A) receive window (B)

send window (C) congestion window (D) sliding window

10. Which header field is included in UDP but not in TCP? (A) source port number (B) destination port

number (C) checksum (D) length

11. Which is NOT related to the set of TCP timeout interval? (A) estimated RTT (B) sampled RTT (C)

sampled timeout (D) sampled deviation

12. Which event will trigger RDT 3.0 sender to resend a packet? (A) timeout (B) corrupt (C) isNAK (D)

isACK

13. Which protocol field is present in IPv6 but absent in IPv4? (A) hop limit (B) length (C) checksum

(D) flow label

14. Which is used by reliable transfer protocols to detect if a received packet is duplicate? (A) timeout

(B) length (C) checksum (D) sequence number

15. In a NAK-free protocol, when a receiver detects packet #n corrupted, it will respond (A) ACK #(n-1)

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

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

(B) TIME_WAIT (C) CLOSE_WAIT (D) FIN_WAIT_2

17. Which is the state of a TCP client lifecycle to let it resend the final acknowledgment in case the

ACK is lost? (A) LAST_ACK (B) TIME_WAIT (C) CLOSE_WAIT (D) FIN_WAIT_2

18. Which host is NOT within the network of 192.168.0.0/23? (A) 192.168.2.1 (B) 192.168.1.254 (C)

192.68.0.1 (D) 192.168.0.254 19. 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

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

(B) fast recovery (C) fast retransmit (D) slow start

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

(B) fast recovery (C) fast retransmit (D) slow start

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

(C) CIDR (D) DHCP

23. Which device always needs to examine the transport-layer header of an incoming packet? (A) hub

(B) bridge (C) router (D) NAT box

24. Which is NOT true about the distance-vector routing algorithm? (A) asynchronous (B) global (C)

iterative (D) distributed

25. Which doesnt a TCP receiver send an acknowledgement?

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

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

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

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

II. [50%] ( 50 )

1. (4%/4%/4%/4%) Consider transport-layer services.

(a). What is the main distinction of the services provided by the network layer and by the transport

layer? ($3.1, p.216-217)

(b). How does the transport layer support its main service mentioned above? ($3.2, p.221)

(c). How is a UDP socket fully identified? What about a TCP socket? ($3, R3, p.315)

(d). How do UDP and TCP view the transported data? ($3.3.1, p.232; $3.5.2, p.266)

2. (6%/6%) Consider network-layer services.

(a). We made a distinction between the forwarding function and the routing function performed in the

network layer. What are the key differences between routing and forwarding? ($4, R3, p.390)

(b). How does generalized forwarding differ from destination-based forwarding? ($4, R32, p.392)

3. (12%) Consider a router of prefix 140.127.208.0/24 that interconnects three subnets: Subnet 1, Subnet

2, and Subnet 3. Suppose that Subnet 1 is required to support up to 120 interfaces, and Subnets 2 and

3 are each required to suppose up to 60 interfaces. Provide three network addresses (of the form

a.b.c.d/x) in order and subnet masks that satisfy these constraints.

4. (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 a 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.

c

b

d

e

f

6 5

2 4

1 3

12

8

a

7

5