University of Delhi 2009-2nd Sem M.C.A DATA COMMUNICATON AND COMPUTER NETWORKS - Question Paper

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Your Roll No

6128

MCA/1I Sem.

Paper MCA-204 - Data Communication and Computer Networks (Admissions of 2009 and onwards)

Maximum Marks 50

(Write your Roll No on the top immediately on receipt of this question paper )

All quest tom are compulsory

Attempt all parts of a question together

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1 Consider the following tree for a part of DNS name space

Show all the steps (path) to resolve each of the following queries

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(a) ahc eng du ac in to xvz cs du ac in fb) xvz cs du ac in to uvr cs utd ernet m

2    Aditya has an internet connection at home provided by his ISP comsat Hr uses gmail to send his mails On Monda\ at 11 pm, when he is sleeping and computer in oft, his friend s* nds him a mail Next day, he gets up .starts his computer, logs into his gmail account and

his mail there Explain procedure step-wise, how does he get to read his mail even though his computer was off when his friend sent him the mail    6

3    Suppose that the clock-dnven scheme for generating initial sequence numbers is used with a 15-bit wide clock counter The clock ticks every 100 m sec, and the maximum packet lifetime is 60 sec How often need resynchronization take place

<a) In the worst case ⁰ Give justification

(b) When the data consumes 240 sequence numbers/

mm (hve justification

4 Token bui ket algorithms is used to regulate a network working at 10 Mbps The token bucket is filled at a rate of 2 Mbps Initially the bucket is filled with capacity 12 megabits How long can the computer transmit at

full network speed ⁹

5 Suppose a host A is connected to another host B through routers K, and R₂ m that order Suppose A wants to

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send a TCP message consisting of 1000 bytes of data and 16 b>tes of header Assume that the link between A and R, can support a maximum frame size of 1000 bytes including 20 byte header The link between Rj and R> can support a maximum frame size of 500 bytes including 10 byte header and the hnk between R₂ and B can support a maximum frame size of 500 bytes including 15 byte header Show the total length, identification (assume), DF, MF and fragment offset field of the IP header m each packet transmitted over the three links    8

6    Why do we need to have error control in the data link layer, when we are doing it at the transport layer any way ⁹ Explain with example    3

7    In the working of NAT, local IP address is mapped to global IP address before sending out the packet on the internet Will it work if simply the source address (local IP) of the network header is replaced by the global IP address ⁹ If yes how ⁹ Jf not, why not ⁹    4

8    A large number of consecutive IP addresses are available starting at 198 160 0 Suppose four organizations A, B. C and D request 4000 2000, 4000 and 8000 addresses respectively and m that order Give a table showing, foi each of these, the first IP address assigned, the last IP address assigned and the mask m the w x y z/s notation

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9    Compare the maximum data rate of a noiseless 4-kHz channel using

(a)    Analog encoding Q AM-64 with 1 bit use for error control

(b)    Tl PCM system

What is the maximum achievable data rate if the signal to noise ratio is 15 db What is the maximum number of signal levels one must have for such a noisy channel ⁷    6

10    Can there be a network which uses FDM and TDM at the same time ⁷ If yes, give an example of one such network with justification If no, explain why not⁹ 3

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