Ex/MCSE/4251/30/2004
M. C. S. E. EXAMINATION, 2004 1st Semester
COMPUTER COMMUNICATION NETWORK Time : Three hours
Full Marks : 100 Answer any five questions.
Answer should be brief and to the point. 1
a)
What is a subnet? “A WAN subnet has a 2-level hierarchy” — explain. 4
b)
Explain the meaning of each of the following terms in the context of the OSI Reference Model : Layer, service, protocol, peer process, interface, SDV, PDU, ICI. 8
c)
State what is meant by a A/B/m/K/M queueing system. 4
d)
Assuming that packets whose lengths are exponentialIy distributed with a mean of 500 m bytes arrive in a poisson manner at a concentrator (modelled as a M/M/1 queueing system) at the rate of 150 packets/sec. Assuming the capacity of the outgoing link to be 1 Mbps, determine, the mean queueing delay and the mean time (total time) spent in the concentrator.
4
[Turn Over]
(2) 2.
a)
Explain why synchronous communication of data is more efficient than asynchronous communication. 3
b) What is data-transparent communication? How is it achieved? 4 c)
Assuming the generator polynomial to the x3 + x + 1 and the incoming frame data to be 1001101110, determine whether the receiver will accept or reject the frame. 4
d) Computer A sends 1000 byte frames (including all nondata or overhead bytes) to computer B over a 200 Km, 1 Mbps channel, using a stop-and-wait protocol. The efficiency of the protocol is .78, neglecting frame retransmissions time for transmission of Ack frames and frame processing delays at the two computers. Assuming the signal propagation velocity to be 2.0 × 105 Km/sec, determine the number of overhead bytes in the frame.
3
e)
How will you view or characterize the “go back n” and the “selective repeat” protocols as sliding window protocols? 3
a)
Clearly explain the concepts of “CSMA”, “CD” and “1-persistent” in the ethernet protocol. 5
b) Why do collisions occur in the ethernet inspite of carrier sensing? 3
(3)
c)
How does the collision detect feature improve the ethernet protocol efficiency?
d) Explain the roles of the Preamble and the Pad fields in the ethernet frame format. 4 c)
4.
a)
50 computers are connected in a 10 Mbps token ring LAN. The average distance between two neighbouring computers is 20 metres. Each station captures a passing token with a probability of .3 and holds it for 3 msec on the average. Assuming the signal propagation velocity to be 2.0 × 105 km/sec, determine the walk time and the average scan time. What is B-ISDN? What is ATM? Why is ATM more suitable than STM (synchronous transfer mode) for building a B-ISDN network?
b) What are the important advantages of ATM over IP? 3 c)
5
What are the different layers and sub-layers in the ATM network? Briefly discuss their functions. 8
d) Explain the use of VPI and VCI in the forwarding of ATM cells. a) Describe the salient features of a cellular wireless network. 6 b) In an infinite population slotted ALOHA network, time is slotted in units of 10 msec and the total average load on the system is 80 packets/sec. [Turn Over]
(4) i)
What is the throughput of the system?
4
ii) What is the chance of success in the third attempt? 2
6.
c)
Explain the communication.
principle
of
spread
spectrum 8
a)
Out line the basic functions of a Repeater, a Hub, a Bridge and a Ethernet Switch. 8
b) Briefly explain the principle of operation of a Transparent Bridge. 8
7
c)
Explain why architecture of the Internet is called “quasihierarchical”.
a)
Briefly describe the nature of services received (not provided) by each layer in the Internet.
6
b) “CIDR-ized addressing and IPv6 addressing respectively provides a short-term and a long-term solution to the IP address scarcity problem”— explain clearly. 5 c)
Determine the net-id for the CIDR-ized address 25.18.33.7/20 and 35.27.65.1 1/18. 2
d) Explain the concepts of port and socket. e)
2
Outline the special problems encountered in implementing the sliding window protocol in the TCP compared to those encountered in the data link layer. 5
(5) 8.
Write short notes on any four
5×4
i) CDMA principle ii) Link stale routing iii) Differences between FDDI. LAN and token ring LAN iv) Routing in the Internet v) vi)
DHCP NAT
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