2. Q1. What is the Nyquist theorem and Shannon capacity? What purpose do they
have in communications? Explain in details.
Ans:
In data communication how data send is faster in bit per second is very important.there are two basic
theory for calculating data rate of data communication i.e.
1.Nyquist theorm:- Nyquist theorm is for calculating data rate for noiseless channel,according to
formulae
Bit Rate = 2 *bandwidth * log2 L
Here bandwith is bandwidth of noiseless channel,and L is the length of noiseless channel,and bite rate
measure in bit per second.
2.shannon theorm:-shannon capcity is for calculating data rate for noisy channel,according to formulae
capacity=bandwidth*log2(1+SNR)
here bandwidth is bandwidth of noisy channel ,SNR is Signal to noise ratio,and capacity is measure in
bit per second.This theorm was proposed in 1944 by claude Shannon.
Purpose:-Both of them are used for data transmission or in other way for sending data in bit per
second.
Q2. What is piggybacking? Explain the sliding window flow control technique
using piggybacking concept.
Ans:
Piggybacking:- In piggybacking when the receiver receives a dat segment,it checks the sequence
number and if sequence number is matches the next segment which receiver does expect,then the data
is received in order.the acknowledgement can be piggy-backed to normal trafific rather than wait for a
response every time. If data is not receive in order then data packet is dropped or send a
acknowledgement of data missing.
Sliding window flow control technique:-
With the use of multiple frames for a single message, the stop-and-wait protocol does not perform
well. Only one frame at a time can be in transit. In stop-and-wait flow control, if frame > 1, serious
inefficiencies result. Efficiency can be greatly improved by allowing multiple frames to be in transit
at the same time. Efficiency can also be improved by making use of the full-duplex line.
3. Sliding window has two types:-
1.sender sliding window(ssw)
2.receiver sliding window(rsw)
In the second types of sliding window we use the piggybacking concept because in rsw The receiver
always maintains a window of size 1 If it receives any other frame (out of order), it is discarded and
it needs to be resent. However, the receiver window also slides by one as the specific frame is
received and accepted.
Q3. What is data rate and signal rate? An analog signal has a bit rate of 8000 bps
and a baud rate of 1000 baud. How many data elements are carried by each signal
element? How many signal elements do we need?
Ans:-
Data rate:-Data rate is rate of transffering number of data elements from source to destination.it is
measure in bit per second.
Signal rate:Signal rate is rate of transferring number of signal elements from source to destination in
per second.it’s unit is baud.
N=8000bps
S=1000baud
R=N/S
R=8 bit/baud
L=2r=28=256 signal elements are required
Q4. Explain the basis of DSL technology. Which technique of multiplexing is
used in it.
Ans:-
Dsl:-Digital subscriber line technology is a modem technology that uses existing twisted-pair telephone
lines to transport high bandwidth data,such as multimedia and video,to service subscribers. DSL
technology is one of the most promosing for supporting high-speed digital communication over the
existing local loops.
There are various DSL technology available.for example ADSL,VDSL,SDSL,HDSL
4. 1.ADSL:The first technology in the set is asymmetric DSL(ADSL).ADSL,like a 56k modem ,provides higher
speed in downstream direction than in the upstream direction.that is the reason it is called asymmetric.
Time division multiplexing(TDM) is used in ADSL.
2.VDSL:-It provides a range of bit rate25 to 55 mbps for upstream communication at distances of 3000
to 10000ft.frequency division multiplexing(FDM) is used in VDSL.
3.HDSL:-Data rate of 1.544 Mbps sometimes 2Mbps can be achived without repeaters up to a diatance
of 12000 ft.
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