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Assignment
PROGRAM BCA(REVISED FALL 2012)
SEMESTER 3
SUBJECT CODE & NAME BCA 3040– DATA COMMUNICATION
CREDIT 4
BK ID B1644
MAX.MARKS 60
1. What is modulation? Explain why modulation is required?
Answer : Modulation is the addition of information (or the signal) to an electronic or optical signal
carrier. Modulation can be applied to direct current (mainly by turning it on and off), to alternating
current, and to optical signals. One can think of blanket waving as a form of modulation used in
smoke signal transmission (the carrier being a steady stream of smoke). Morse code, invented for
telegraphy and still used in amateur radio, uses a binary (two-state) digital code similar to the code
used by modern computers. For most of radio and telecommunication today, the carrier is
alternating current (AC) in a given range of frequencies. Common modulation methods include:
2. Write short note on:
1. Ground Wave Propagation
Answer : Ground Wave propagation is a method of radio frequency propagation that uses the area
between the surface of the earth and the ionosphere for transmission. The ground wave can
propagate a considerable distance over the earth's surface particularly in the low frequency and
medium frequency portion of
2. Sky Wave Propagation
Answer : Sky wave propagation: The sky waves have frequency range between 2MHz to 30MHz.
These radio waves have the ability to pass through earth’s atmosphere. The ionosphere of our earth
reflects these rays very efficiently. When these rays move along the atmosphere then their
movement is from transmitter towards the receiver antenna. This is called as sky wave propagation
of the waves. In the above figure, b is the name assigned to the path of the sky wave propagation.
These waves can have medium as well as

2. 3. Briefly explain Nyquist theorem with mathematical representation.
Answer : The Nyquist–Shannon sampling theorem, which has been named after Harry Nyquist and
Claude Shannon, is a fundamental result in the field of information theory, in particular
telecommunications and signal processing. Sampling is the process of converting a signal (for
example, a function of continuous time or space) into a numeric sequence (a function of discrete
time or space). Shannon's version of the
4. What is Time-division multiplexing (TDM)? Explain.
Answer : TDM is a common form of sending multiple signals or streams of information on a carrier at
the same time in the form of a single, complex signal and then recovering the separate signals at the
receiving end. In this scheme, several low speed channels are multiplexed into a single high speed
channel for transmission over a network.
5. Write short note on:
1. Least-Cost Algorithms
Answer : In practice, the majority of Internet routing methods are based on least-cost algorithms. In
such algorithms, a link cost is proportional to the links's current traffic load. However, the link cost
may not always be proportional to the current load. The link cost is defined on both directions
between each pair of nodes. Several least-cost-path algorithms have been developed for packet-switched
networks. In particular, Dijkstra's algorithm and the Bellman-Ford algorithm are the most
effective and widely used algorithms.
2. Dijkstra’s Algorithm
Answer : Dijkstra's algorithm, conceived by computer scientist Edsger Dijkstra in 1956 and published
in 1959,[1][2] is a graph search algorithm that solves the single-source shortest path problem for
a graph with non-negative edge path costs, producing ashortest path tree. This algorithm is often
used in routing and as a subroutine in other graph algorithms.
For a given source vertex (node) in the
6. What are the requirements of Wirelesses LAN? Explain briefly
Answer : A wireless LAN must meet the same sort of requirements typical of any LAN, including high
capacity, ability to cover short distances, full connectivity among attached stations, and broadcast
capability. In addition, a number of requirements are specific to the wireless LAN environment. The
following are among the most important requirements for wireless LANs:

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