CS601 Final Term Solved Subjective with References by Moaaz

CS601-Data Communication

Latest Solved subjective from Final term Papers

May 08,2011 · Latest subjectives · SPRING 2011

What is the difference between guided and unguided media?

Guided Media are those media that provide a conduit from one device to another. Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path while Unguided Transmission Media consists of a means for the data signals to travel but nothing to guide them along a specific path. It passes through a vacuum; it is independent of a physical pathway.

Write Commercial advantage and characteristics of token bus

Answer: (Page 232)

•  Other LANs are not suitable for this purpose
•  Token Bus has no commercial application in data communications
•  Token Ring allows each station to send one frame per turn
•  Access method: Token passing

What is the difference between FDM and TDM

1. FDM-Frequency division multiplexing where as TDM mean Time division

Multiplexing.

2. In FDM spectrum is divided into frequency whereas in TDM divided into time slot.
3. FDM is used in 1st generation analog system whereas TDM is used in 2nd generation analog system.

Write the types transmission noise

Answer: (Page 143) Thermal Noise: Due to random originally sent by TX Induced Noise: Comes from sources like Motors and Appliances Crosstalk: Effect of one wire on another Impulse Noise: Spike (A signal with high energy in a very short period of timepower lines, lightening etc.

What is power bandwidth

The power bandwidth of an amplifier is sometimes taken as the frequency range (or, rarely, the upper frequency limit) for which the rated power output of an amplifier can be maintained (without excessive distortion) to at least half of the full rated power. OR

Power Bandwidth

Answer: (Page 67) Frequency band in which 99% of the total power resides.

What does the CRC generator append to data unit? [2]

Answer: (Page 175) Appending it to the end of the data must make the resulting bit sequence exactly divisible by the divisor

How much bandwidth for modem is required in case of FSK? [2]

Answer: BW required for FSK is equal to the Baud rate of the signal plus the frequency shift. Because of the limitations of voice-grade telephone lines, these modems are restricted to a bandwidth of about 3 kHz

What is even parity generator in VRC error detection mechanism? [2]

Answer: (Page 172)

What is the difference between angle of incident and angle of reflection? [2]

Answer: (Page 126) The difference between them is that Angle of refraction passes from less dense to denser medium whereas angle of incidence passes from more dense to less dense medium.

What is daisy chaining in 1Base 5 star Lan? [2]

Answer: (Page 229) Slower speed in star lan can be increase by the use of DAISY CHAINING.

What is the responsibility of Application layer? [3]

Answer: Page 53 Enables the user either human or software to access the network It provides user interface and support for the services such as Electronic mail, Remote File access and Transfer, Shared Database Management and other services

What is critical angle?

Answer: (Page 127) We have a beam of light moving from a more dense to a less dense medium. We gradually increase the angle of incidence measured from vertical axis. As angle of incidence increases, so does the angle of refraction. The angle at which refracted line lies on the horizontal axis is called Critical Angle

Hamming code-Redundancy bit (5 marks Q)

Answer: (Page 181) Redundancy Bits (r)

•  r must be able to indicate at least m+r+1 states
•  m+r+1 states must be discoverable by r bits
•  Therefore, 2r ≥ m+r+1
•  If m=7, r=4 as 24 ≥ 7+4+1

Tree topology advantages (3 or 5 marks)

Answer: (Page 31)

•  Because of Secondary Hub, More devices can be attached to a Central Hub and therefore increase the distance a signal can travel
•  Enables Differentiated Services: Allows to prioritize communication, e.g. computers attached to one secondary hub can be given priority over others
•  Therefore, TIME SENSITIVE data will not have to wait for access to the network
•  Rest of the advantages are almost the same as STAR

Q41. Whether VRC error detection method is used for single bit error or burst error. (2)

Answer: (Page 173) VRC can detect all single bit errors Can also detect Burst errors as long as the total number of bits changed is ODD

Q42. Which modem was first developed commercially in 1970? (2)

Answer: (Page 114)

–First commercial modems by Bell Telephone Co. –Developed in early 1970s

Q45. Consider a major telecom company using RZ encoding for its signals

conversion. What will be the major problem faced by using such type of

encoding? (2)

Answer: (Page 75) Any time, data contains long strings of 1’s or 0’s, Rx can loose its timing. The only problem with RZ encoding is that it requires two signal changes to encode one bit and therefore occupies more BANDWIDTH

Q47. Geosynchronous Satellite? (3)

Answer: (Page 139)

•  Line of sight propagation requires the sending and receiving antennas must be locked into each other
•  To ensure continuous communication, satellites must move with the same speed as earth. So that they seem fixes w.r.t earth
•  These satellites are called Geosynchronous Satellites