basic data and voice communication

Topics: OSI model, Data transmission, Transmission Control Protocol Pages: 13 (1046 words) Published: September 25, 2013
STRATHMORE UNIVE
ERSITY
FACULT OF INFO
TY
ORMATION TECHNOLOGY
ACHELOR O SCIENC IN TELEC
OF
CE
COMMUNIC
CATIONS
BA
BTC 120 Basic Dat and Voice Communica
02:
ta
ations
DATE: 13th March 20
3
012
Instructio
ons:
Answer q
question 1 and any other t questions
d
two
s
All Quest
tions carry 20 marks each

HRS
TIME: 2 H

QUESTIO 1 (COMPULSORY)
ON
a. Match the followin functions t a layer of th OSI model
h
ng
to
he
i.
ii.
iii.
iv.
v.

(5 Marks)

Reliable pr
rocess-to-process message delivery
e
Route sele
ection
Defines fra
ames
Provides user services s
u
such as e-mai and file tran
il
nsfer
Transmission of bit stre across ph
eam
hysical mediu
um

wer
wing multiple c
choice questions:
b. Answ the follow
i.

The _____ is the phy
___
ysical path over which a me
essage travels
s.
A. Protocol B. Medium
P

ii.
iii.

iv.

h
rk)
(Each carries 1 mar

C. Signal

D. All

Which of the OSI layers is represent by frames?
t
ted
A. Session B. Datalink
t
ork
C. Transport D. Netwo
The proces
ss-to-process delivery of th entire message is the responsibility o the ______ he
of
__
layer.
N
on
cal
A. Network B. Transport C. Applicatio D. Physic
Before dat can be trans
ta
smitted, they must be trans
sformed to __
_______.
A. Periodic signals
P

tromagnetic s
signals
B. Elect

C.
C Aperiodic s
signals

D . Low frequen sine wave
ncy
es
v.

ncy
,
________.
As frequen increases, the period _
A. Decreases B. Increases
D

vi.

D.
D Doubles

Unipolar, bipolar, and p
b
polar encodin are types of _______ encoding.
ng
f
A. Line
L

vii.

C. Remains t same
the

B. Block

C. N
NRZ

D.
D Manchester
r

PCM is an example of _______ conversion.
i
e
A. Digital-to-Digital B. Digit
D
tal-to-Analog
g

C. Analog
g-to-Analog

D. Analog-to-

Digital
D
viii.

AM and FM are examp of ______ conversio
M
ples
___
on.


 

A. Digital-to-Digital B. Digital-to-Analog

C. Analog-to-Analog

D. Analog-to-

Digital
ix.

The sharing of a medium and its link by two or more devices is called _______. A. Modulation

x.

C. Line discipline

D. Multiplexing

Which multiplexing technique transmits analog signals?
A. FDM

xi.

B. Encoding

B. TDM

C. WDM

D. (A) and (C)

In ________, we combine signals from different sources to fit into a larger bandwidth. A. Spread spectrum

B. Line coding

C. Block coding

D.

None of the above
xii.

In modulo-2 arithmetic, we use the ______ operation for both addition and subtraction. A. XOR

xiii.

B. OR

C. AND

ARQ stands for _______.
A. Automatic repeat quantization
retransmission request

xiv.

D. None of them

B. Automatic Repeat Request

C. Automatic

D. Acknowledge repeat request

________ is a type of transmission impairment in which the signal loses strength due to the resistance of the transmission medium.
A. Attenuation

xv.

B. Distortion

C. Noise

D. Decibel

A _________ sine wave is not useful in data communications; we need to send a _______ signal.
A. Composite; single-frequency

B. single-frequency; composite

single-frequency; double-frequency
Total

C.

D. None of the above
(20 Marks)

QUESTION 2
a. Why does impulse noise have more effect on digital signals rather than on analog signals? (4 marks)
b. What is the result of scrambling this sequence 11100000000000 using B8ZS? Assume the last most recent preceding 1 was positive.

(4 marks)

c. What does dB measure? Let the energy strength at point 2 is 1/50th with respect to the point 1. Find out the attenuation in dB.
(5 marks)
d. Two neighboring nodes (A and B) use a sliding window protocol with a 3-bit sequence number. As the ARQ mechanism, go-back-N is used with a window size of 4. Assuming A is transmitting and B is receiving, show the window positions for following succession of events: 2 

 

i.
ii.
iii....
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