Code: AC12 /
AT10
Subject: DATA COMMUNICATION & NETWORKS
Time: 3 Hours Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose the correct or best alternative in the following: (2x10)
a. What is the main function of the transport layer
(A) Node-to-node delivery
(B) Process-to-process delivery
(C) Synchronization
(D) Updating and maintenance of routing tables
b. As the data packet moves from the lower to the upper layers, headers are
(A) added (B) subtracted
(C) rearranged (D) modified
c. If a symbol is composed of 3 bits, there are ___________ data levels.
(A) 2 (B) 4
(C) 8 (D) 16
d. Which encoding type uses only one voltage level?
(A) Polar (B) Bipolar
(C) Unipolar
(D)
e. In TDM, for n signal sources of the same data rate, each frame contains _________ slots.
(A) n (B) (n+1)
(C) (n–1) (D) 0 to n
f. A traditional telephone line has a bandwidth of ___________.
(A) 2000 Hz (B) 3000 Hz
(C) 4000 Hz (D) 4000 MHz
g. If the data unit is 111111 and the divisor 1010, remainder 110, what is the dividend at the receiver?
(A) 111111011 (B) 111111110
(C) 1010110 (D) 110111111
h. In ________ ARQ, if a NAK is received, only the specific damaged or lost frame is retransmited.
(A) Stop-and-wait (B) Go back-N
(C) Selective repeat (D) Both (A) and (B)
i. An 80 stations conventional Ethernet is divided into four collision domains. This means that a maximum of ________ stations contend for medium access at any one time.
(A) 320 (B) 80
(C) 76 (D) 20
j. An IP address consists of _______ bits
(A) 4 (B) 8
(C) 128 (D) 32
Answer any FIVE Questions out of EIGHT Questions.
Each question carries 16 marks.
Q.2 a. Describe the ISO-OSI reference model of a computer network; Discuss the function of each layer. (8)
b. Explain peer-to-peer communication across a peer interface. (4)
c. Given a channel with an intended capacity of 20Mbps, the bandwidth of the channel of 3MHz. What signal to noise ratio is required to achieve this capacity? (4)
Q.3 a. Discuss digital transmission of analog signal with the help of a block diagram and a uniform quantizer. (8)
b. Explain SONET system and its frame structure for STS-1. (8)
Q.4 a. If the generator polynomial is x4+x+1 and the message bits are 1101101, obtain the CRC code. (5)
b. How is the inefficiency of stop-and-wait ARQ overcome in Go-Back-N ARQ? Discuss with suitable diagrams. (7)
c. Why and how is bit stuffing used in framing? Explain with an example. (4)
Q.5 a. For the ALOHA random access scheme, prove that the maximum throughput happens at G = 0.5 where G is the number of attempts per packet time. (7)
b. Find the length of three bytes token for 16Mbps token ring LAN. The speed of propagation is 2/3 the velocity of light. (4)
c. What is ALOHA? Explain how slotted ALOHA scheme reduces collision? (5)
Q.6 a. Discuss virtual circuit and datagram packet switching with suitable diagrams showing the delays. . (8)
b. Explain the Dijkstra’s routing algorithm to find the shortest paths from the source node to other nodes. (8)
Q.7 a. Describe the structure of IPv4 IP packet. (8)
b. Find the subnetwork address of the following;
(i) IP address; 125.34.12.56 Mask; 255.255.0.0
(ii) IP address; 141.181.80.16 Mask; 255.255.224.0 (4)
c. Explain the UDP datagram format. (4)
Q.8 a. Draw the structure of TCP segment and brief the function of each field. (8)
b. A TCP connection has 65,535 bytes windows sent over 1Gbps channel. The channel has a round trip delay of 20 millisecs.
Find (i) Maximum achievable throughput
(ii) Line efficiency (4)
c. Define CTD, PCR, CBR, ABR as applied to ATM. (4)
Q.9 a. Explain how fields in the ATM header are used to identify network connections. (6)
b. With a block schematic of router model, explain integrated services IP. (6)
c. Briefly describe SIP message exchange. (4)