Subject: Data Communication -Unit-1, 2 & 3
Unit – I - Data
Communication and Networking
PART A
1. Define the term
Computer Network.
A Computer network is a number of
computers interconnected by one or more transmission paths. The transmission
path often is the telephone line, due to its convenience and universal
preserve.
2. Define Data Communication.
Data communication is the exchange
of data (in the form of 0s and 1s) between two devices via some form of
transmission medium (such as a wire cable).
3. What is the fundamental
purpose behind data communication?
The purpose of data communication is
to exchange information between two agents.
4. List out the types of data
communication.
Data communication is considered
Local – if the communicating device
are in the same building.
Remote – if the device are farther
apart.
5. Define the terms data and
information.
Data : is a representation of facts,
concepts and instructions presented in a formalized manner suitable for
communication, interpretation or processing by human beings or by automatic
means.
Information : is currently assigned
to data by means by the conventions applied to those data.
6. What are the fundamental
characteristics on which the effectiveness of data communication depends on?
The effectiveness of a data
communication system depends on three characteristics.
1. Delivery: The system must
deliver data to the correct destination.
2. Accuracy: The system must
deliver data accurately.
3. Timeliness: The system
must deliver data in a timely manner.
7. Give the components of
data communication.
1. Message – the message is
the information to be communicated.
2. Sender – the sender is the
device that sends the data message.
3. Receiver – the receiver is
the device that receives the message.
4. Medium – the transmission
medium is the physical path by which a message travels from sender to receiver.
5. Protocol – A protocol is a
set of rules that govern data communication.
8. Define Network.
A network is a set of devices
(nodes) connected by media links. A node can be a computer, printer, or any
other devices capable of sending and / or receiving data generated by other nodes
on the network.
9. What are the three criteria
necessary for an effective and efficient network?
1. Performance
2. Reliability
3. Security.
10. Define PROTOCOL.
A protocol is a set of rules
(conventions) that govern all aspects of data communication.
11. Give the key elements of
protocol.
* Syntax : refers
to the structure or format of the data, meaning the order in which they are
presented.
* Semantics :
refers to the meaning of each section of bits.
* Timing : refers
to two characteristics.
1. when data should be sent
and
2. how fast they can be sent.
12. Define Standard.
A standard provides a model for
development that makes it possible for a product to work regardless of the
individual manufacturer.
13. Define line configuration and
give its types.
-
Line configuration refers to the way
two or more
communication devices attach to a
link.
- There are two
possible line configurations:
i. Point to point and
ii. Multipoint.
14. Define topology and mention the
types of topologies.
Topology defines the physical or
logical arrangement of links in a network
Types of topology :
- Mesh
- Star
- Tree
- Bus
- Ring
15. Define Hub.
In a star topology, each device has
a dedicated point to point link only to a central controller usually called a
hub.
16. Give an advantage for each type
of network topology.
1. Mesh topology:
* Use of
dedicated links guarantees that each connection can carry its own data load,
thus eliminating traffic problems.
* Robust and
privacy / security.
2. Star topology:
* Less expensive
than mesh.
* Needs only one
link and one input and output port to connect it any number of others.
* Robustness.
3. Tree topology:
* same as those
of a star.
4. Bus topology:
* Ease of
installation.
* Uses less
cabling than mesh, star or tree topologies.
5. Ring topology:
* A ring is
relatively easy to install and reconfigure.
* Each device is
linked only to its immediate neighbors.
* Fault isolation
is simplified.
17. Define transmission mode and its
types.
Transmission mode defines the
direction of signal flow between two linked devices.
Transmission modes are of three
types.
-
Simplex
-
Half duplex
-
Full duplex.
18. Define Peer to peer processes.
The processes on each machine that
communicate at a given layer are called peer to peer processes.
19. What is half duplex mode?
A transmission mode in which each
station can both transmit and receive, but not at the same time.
20. What is full duplex mode?
A transmission mode in which both
stations can transmit and receive simultaneously.
21. What is internet?
* When two or
more networks are connected they become an internetwork or internet.
* The most
notable internet is called the Internet.
22. List the layers of OSI model.
- Physical
- Data Link
- Network
- Transport
- Session
- Presentation
- Application.
23. Define OSI model.
The open system Interconnection model
is a layered framework for the design of network system that allows for
communication across all types of computer systems.
24. Which OSI layers are the network
support layers?
- Physical
- Data link
- Network layers.
25. Which OSI layers are the user
support layers?
- Session
- Presentation
- Application.
26. What are the responsibilities of
physical layer, data link layer, network layer, transport layer, session layer,
presentation layer, application layer.
(i) Physical layer
– Responsible for transmitting individual bits from one node to the next.
(ii) Data link layer –
Responsible for transmitting frames from one node to the next.
(iii) Network layer –
Responsible for the delivery of packets from the original source to the final
destination.
(iv) Transport layer –
Responsible for delivery of a message from one process to another.
(v) Session layer – To
establish, manage and terminate sessions.
(vi) Presentation layer
– Responsible to translate, encrypt and compress data.
(vii) Application layer –
Responsible for providing services to the user. To allow access to network
resources.
27. What is the purpose of dialog
controller?
The session layer is the network
dialog controller. It establishes, maintains and synchronizes the interaction
between communicating systems.
28. Name some services provided by
the application layer.
Specific services provided by the
application layer include the following.
- Network virtual
terminal.
- File transfer, access
and management (FTAM).
- Mail services.
- Directory services.
29. Define the term transmission
medium.
The transmission medium is the
physical path between transmitter and receiver in a data transmission system.
The characteristics and quality of data transmission are determined both the
nature of signal and nature of the medium.
30. What are the types of
transmission media?
Transmission media are divided into
two categories. They are as follows:
(i) Guided
transmission media
(ii) Unguided
transmission media
31. How do guided media differ from
unguided media?
1. A guided media is
contained within physical boundaries, while an unguided medium is boundless.
32. What are the three major classes
of guided media?
Categories of guided media.
1. Twisted – pair
cable.
2.Coaxial cable.
3.Fiber – optic cable.
33. What is a coaxial cable?
A type of cable used for computer
network as well as cable television. The name arises from the structure in
which a metal shield surrounds a center wire. The shield protects the signal on
the inner wire from electrical interference.
34. A light beam travels to a less
dense medium. What happens to the beam in each of the following cases:
1.
The incident angle is less than the critical angle.
2.
The incident angle is equal to the critical angle.
3.
The incident angle is greater than the critical angle.
The incident angle is less than the
critical angle.: Then the ray refracts and moves closer to the surface.
The incident angle is equal to the
critical angle. : Then the light bends along the interface.
The incident angle is greater than
the critical angle.: Then the ray reflects and travels again in the denser
substance.
35. What is reflection?
When the angle of incident becomes
greater than the critical angel, a new phenomenon occurs called reflection.
36. Discuss the modes for
propagation light along optical channels.
There are two modes for propagating
light along optical channels.
Single mode and multimode.
Multimode can be implemented in two
forms: step index or graded index.
37. What is the purpose of cladding
in an optical fiber? Discuss its density relative to the core.
A glass or plastic is surrounded by
a cladding of less dense glass or plastic.
The difference in density of the two
materials must be such that a beam of light moving through the core is
reflected off the cladding instead of being refracted into it.
38. Name the advantage of optical
fiber over twisted pair and coaxial cable.
Higher bandwidth.
Less signal attenuation.
Immunity to electromagnetic
interference.
Resistance to corrosive materials.
More immune to tapping.
Light weight.
39. What does the term modem stands
for ?
Modem stands for modulator /
demodulator.
40. What is the function of a
modulator and a demodulator?
A modulator converts a digital
signal into an analog signal using ASK, FSK, PSK or QAM.
A de modulator converts an analog
signal into a digital signal.
41. What is an Intelligent modems?
Intelligent modems contain software
to support a number of additional functions such as automatic answering and
dialing.
42. What are the factor that affect
the data rate of a link?
The data rate of a link depends on
the type of encoding used and the bandwidth of the medium.
43. Define Line coding.
Line coding is the process of
converting binary data, a sequence of bits, to a digital signal.
44. What is CODEC?
A device that encodes analog voice into a
digital ISDN link is called a CODEC, for coder / decoder.
45.What are the different encoding
techniques?
· NRZ ·
NRZI · Manchester · 4B / 5B
46. Define Digital-to-analog
conversion process and methods employed
Digital-to-analog conversion is the
process of changing one of the characteristics of an analog signal based on the
information in digital data.
There are three mechanisms for
modulating digital data into an analog signal: amplitude shift keying (ASK),
frequency shift keying (FSK), and phase shift keying (PSK). In addition, there
is a fourth (and better) mechanism that combines changing both the amplitude
and phase, called quadrature amplitude modulation (QAM).
47. Discuss Analog To Analog
Conversion Techniques
Analog-to-analog
conversion, or analog modulation, is the representation of analog information
by an analog signal. Modulation is needed if the medium is bandpass in nature
or if only a bandpass channel is available to us.
Analog-to-analog conversion can be
accomplished in three ways:
Amplitude Modulation (AM)
Frequency
Modulation (FM)
Phase Modulation (PM)
48. Different Scrambling
Techniques for Data
Transfer:
Long sequence of Os upsets the
synchronization. If we can find a way to avoid a long sequence of Os in the
original stream. One solution to this is called as scrambling. Two
common scrambling techniques are B8ZS and HDB3. Bipolar with 8-zero
substitution (B8ZS) is commonly used in North America. In this technique, eight
consecutive zero-level voltages are replaced by the sequence OOOVBOVB. The
V in the sequence denotes violation; this is a nonzero voltage that breaks an
AMI rule of encoding (opposite polarity from the previous). The B in the
sequence denotes bipolar which means a nonzero level voltage in accordance with
the AMI rule.
