16-02-2013, 02:05 PM
QUESTION & ANSWERS FOR MULTIPLEXING
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Q. 1. Define multiplexing.
Ans.Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. Q. 2. State the importance of multiplexing.Ans.To make efficient use of high speed telecommunications lines, some form of multiplexing is used. Multiplexing allows several transmission sources to share a larger transmission capacity. A common application of multiplexing is in long-haul communications. Trunks on long-haul networks are high capacity fiber, coaxial or microwave links. These links can carry large numbers of voice and data transmission simultaneously using multiplexing.
Q. 3. What are the types of multiplexing?Ans.Multiplexing can be classified as
1. Analog2. Digital
Q.4.What is FDM?
Ans.Frequency-division multiplexing (FDM) is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted. In FDM signal generated by each sending device modulate different carrier frequencies. These modulated signals are then combined into a single composite signal that can be transported by the link.
Q.5. Write a short note on WDM
Ans.Wave division multiplexing (WDM) is designed to use the high data rate capability of fiber optic cable. The optical fiber data rate is higher than the data rate of metallic transmission cable. WDM is conceptually the same as FDM, except that the multiplexing and demuitiplexing in value optical signals transmitted through fibre optic channels. Following fig. gives the conceptual view of a WI)M multiplexer and demultiplexer very narrow bands of light from different sources are combined to make a wider band of light. At the receiver, the signals are separated by the demultiplexer.One application of WDM is the SONET network in which multiple optical fiber lines are multiplexed ad demultiplexed. A new method called DWDM (dense WDM), can multiplex a very large number of channels by spacing channels closer to one another. It achieves even greater efficiency.
Q. 7. Explain the two types of TDM implementation and how do they differ from each other
Ans.There are two methods
(1) TDM(2) INVERSE TDM(1) TDM: - Time Division Multiplexing (TDM) is a digital process that allows several connections to chare the high bandwidth of a link. Instead of sharing a portion of the bandwidth as in FDM, time is shared. Each Connection occupies a portion of time in the link. Figure gives a conceptual view of ‘1DM. Note that the same link is used as in FDM: here, however, the link is shown sectioned by time rather than by frequency. In the figure portion of signals 1, 2, 3 and 4 occupy the link sequentially.
Q. 8. What is Bit Padding?
Ans. In bit padding, the multiplexer adds extra bits to a device is source stream to force the speed relationships among the various devices into integer multiples of each other. When speeds are not multiples of each other, they can be made to behave as if they were, by the technique called bit padding
Q.9. What is interleaving?Ans.in multiplexing side, as the switch opens in front of connection, that connection has the opportunity to send a unit onto path. This process is called interleaving.
Q. 10. Is bit padding is technique for FDM or TDM? Is the framing bit used in FDM or TDM?
Ans. Bit padding is a technique for TDM. TDM is the digital way of multiplexing.Framing bits are used in TDM to make synchronization between sender and receiver,
Q.11. Define the difference between switched arid leased lines.Ans. In switched line communications, a link that is established in a switched network, such as the international dial-up telephone system.A leased line is a symmetric dedicated service (the same upstream and downstream bandwidth) creating a permanent connection between your premises and the Internet.
Q. 12. What are switched communications networks?Ans. In the switched communications networks data entering the network from a station are routed to the destination by being switched from node to node. For example in the fig. data from station A intended for station F are send to node 4. They may then be routed via nodes 5 and 6 or nodes 7 and 6 to the destination. This is called switched communication networks.