June 1997

Question Paper of CS-09 – Data Communication & Network of June 1997 from IGNOU

1 (i) Sketch the differential Manchester encoding for the bit stream of 0001110101. Assume the line is initially in the low state. [3]

(ii) The following data fragment occurs in the middle of data stream for which the character-stuffing algorithm is used. [3] DLE, STX, A, DLE, B, DLE, ETX. What is output after stuffing?

(iii) Consider two host computers HC1 and HC4 connected via two switching nodes HC2 and HC3 in a store and forward network [HC1]- [HC2]- [HC3]- [HC4] Ignoring processing time in the hosts and switching nodes and assuming transmission rates of 10 k bits/s. Calculate the time to send a 3 K bit message from HC1 to HC4 in case a whole message is transmitted as a single block. [6]

(iv) Discuss the tradeoff, which have to be considered infixing a maximum message length within a communication system. [5]

(v) What is the advantage of frequency modulation over amplitude modulation and at what cost? [3]

(vi) Discuss the relative advantages and disadvantages of the following:

� Terrestrial links (switched and leased connection)
� Satellite links
� Radio links
� Optical fiber transmission [10]

2 (i) Define and discuss the importance of the following terms in data communication: � Band
� Bandwidth
� Wavelength [6]
(ii) Discuss the finite limits of a transmission path with Shannon�s and Nyquist�s formulae. [9]

3 (i) Discuss types of errors and how they are managed at DLL (Data Link Layers). [6]
(ii) What is HDLC ( High Level Data Link Control) protocol? Discuss its importance in data communication. What are the different types of frames? Discuss briefly. [9]

4 (i) Compare the effect of node failure in CSMA/CD and token passing ring. [7]

(ii) Why is an Ethernet not suitable for real time applications? Explain. Which of the LANs is most suitable for such a purpose and why? [8]

5 Compare the following:
� Connection oriented and connectionless gateways. [6]
� Transparent Bridge and Source Routing Bridge. [6]
� Virtual circuit service and Data gram service. [3]

6 (i) Give the speed of proposed Broadband and ISDN channel. [2]

(ii) List some features of ISDN that you think will be useful to you. [5]

(iii) What is ATM? What can ATM offer to reduced bandwidth bottlenecks that traditional LAN technologies cannot provide? [8]

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