1. Identify the components of data communication system?
Message : The message is the information to be communicated.
Sender :The sender is the device that sends the data message.
Receiver : The receiver is the device that receives the message.
Medium : The transmission medium is the physical a message travels from sender to receiver.
Protocol : A protocol is a set of rules that governs ata communications.
2. What are the advantages of distributed processing?
* Security/Encapsulation.
* Distributed database.
* Faster-problem solving.
* Security through redundancy.
* Collaborative processing.
3 . What are the fundamental three characteristics that determine the effectiveness of data communication system?
Delivery : The system must deliver data to the correct destination.
Accuracy : The system must deliver the data accurately.
Timeliness : The system must deliver data in a timely manner.
4. Why protocols are needed?
A protocol is a set of rules that governs data communications. Without a protocol, two devices may be connected but they cannot communicate with each other.
A protocol defines what is communicated, how and when it is communicated.
5. Why standards are needed?
* Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes.
* They provide guidelines to manufacturers, vendors, government agencies and other service providers to ensure the kind of interconnectivity necessary in today’s marketplace and in international communications.
6. Difference between de facto and de jure standard?
De facto De jure
1.Meaning “by fact” or “by convention” 1.Meaning “by law” or “by regulation”
2.Standards that have not been approved 2.Those that have been legislated by an by an organized body but have been officially recognized body are de jure standards. adopted as standards through widespread use are de facto standards.
7. Write the formula to find the number of links in mesh topology?
The number of links in mesh topology = n (n – 1) /2, Where n is the number of devices.
8.Describe the three characteristics of sine wave?
The three characteristics of sine wave are:
Amplitude: Amplitude represents the height of the signal either in positive or negative direction.
Frequency and period: Period refers to the amount of time a signal needs to complete one cycle.
Frequency refers to the number of periods in one second.
Phase: Phase describes the position of the waveform relative to time zero.
9. What is a spectrum of a signal?
The spectrum of a signal consists of the sine waves that make up the signal. The description of a signal using the frequency domain and containing all its components is called the frequency spectrum of that signal.
10. Difference between information and signal?
Information Signal
1.Information means the data to be 1.The data to be transmitted are send in the transmitted from sender to receiver. form of signals through the transmission media.
2.The data usable to a application are 2. The transmission media accept the not in a form that can be transmitted information in the form of signals. over a network.
11. Give two examples for analog and digital information?
Analog information: Eg) Human voice. Sine wave.
Digital information: Eg) Data stored in computer memory. Square wave.
12. Compare analog with digital signal?
Analog signal Digital signal
1.Analog signals can have an infinite 1.Digital signals can have only a limited number of values in a range. number of values.
2.Signal that varies continuously with time 2. Signal that have values only at discrete is called analog signal instance of time is called digital signal
13. Compare periodic and aperiodic signal?
Periodic signal Aperiodic signal
1.A periodic signal completes a pattern 1.Aperiodic signal changes without within a measurable time frame called exhibiting a pattern or cycle that period and repeats that pattern over repeats over time subsequent identical periods.
2.In data communication we use periodic 2. In data communication we use a
analog signals. periodic digital signals
14.Give the relationship between period and frequency?
$ Period refers to the amount of time a signal needs to complete one cycle.
$ Frequency refers to the number of periods in one second.
$ Period is the inverse of frequency and frequency is the inverse of period.
f = 1/ T and T = 1/ f
f = frequency in hertz, T = period in second.
15. What are the units of period and frequency?
Period is expressed in seconds and frequency is expressed in hertz.
TABLE: Units of period and frequency.
Unit Equivalent
Unit Equivalent
Seconds
1s
Hertz
1 Hz
Milliseconds
10-3 s
Kilohertz
103 Hz
Microseconds
10-6 s
Megahertz
106 Hz
Nanoseconds
10-9 s
Gigahertz
109 Hz
Picoseconds
10-12 s
Terahertz
1012 Hz
16.Difference between high frequency signal and low frequency signal?
High frequency signal Low frequency signal
1.If the value of the signal changes 1.If the value of the signal changes over
over a very short span of time ,then a long span of time, then the signal
the signal is called as high is called as low frequency signal
frequency signal. .
17. What do the amplitude, frequency and phase of the signal measure?
The amplitude, frequency and phase of the signal measure the
characteristics of the sine wave.
Amplitude is measured in volts.
Frequency is measured in hertz.
Phase is measured in degrees or radians.
18. Difference between simple periodic and composite periodic signal?
Simple periodic Signal composite periodic signal
1.Simple periodic signal consists of 1.Composite signal consists of multiple
only one frequency. Frequencies.
2.Simple signals are periodic which cannot 2.Composite signals are periodic which
be decomposed into number of sine waves can be decomposed into a collection of
sine waves.
19. What is the bit rate and bit interval? How are they related?
Bit interval: It is the time required to send one single bit.
Bit rate: It is the number of bit intervals per second. It is measured in bits per
second.
Bit rate = 1/ Bit interval.
20.A sine wave has a frequency of 6Hz. What is its period?
f = 1/ T and T = 1/ f
f = frequency in hertz.
T = period in seconds.
Given f = 6 Hz
T= 1/6
=0.167 seconds
21. The sine wave completes one cycle in 4seconds.What is its frequency?
Answer in Hz.
Given T = 4 seconds
f = ¼ =0.25 Hertz.
22. The sine wave completes one cycle in 25micro seconds. What is its frequency?
Answer in KHz.
Given T = 25 micro seconds.
f = 1/(25 *10-6 )
= 40000 Hz
= 40 KHz
23. Which parts of the electromagnetic spectrum are used for communication?
The section of electro magnetic spectrum defined as radio waves and
microwaves that ranges from 3 kHz to 300 GHz is used for communication. This
section is divided into eight ranges called bands.
24. How are the guided media differ from unguided transmission media?
Guided transmission media Unguided transmission media
1.Guided indicate, medium is contained 1.Unguided medium does not have
any within physical boundary Physical boundary
2.Transmission takes place through wire. 2.It is a wireless transmission.
25. Why is coaxial cable superior to twisted pair cable?
Coaxial cable carries signals of higher frequency ranges than twisted pair
cable. Coaxial cable provides high bandwidth and high data rate. Because of these
reasons coaxial cable is superior to twisted pair cable.
26. What happens to a beam of light as it travels to a less dense medium?
If a ray of light traveling through one substance suddenly enters another
medium the ray changes direction. If the angle of incidence is equal to the critical
angle the light bends along the interface. If the angle of incidence is greater than the
critical angle the ray reflects and travels again in the same medium. If the angle of
incidence is less than the critical angle the ray refracts.
27. What is reflection?
Reflection means the ray takes a turn and travels in the same medium.
If the angle of incidence is greater than the critical angle the ray reflects and travels
again in the same medium.
28. Name the advantages of optical fiber over twisted pair and coaxial cable?
The advantages of optical fiber over twisted pair and coaxial cable are
v Noise resistance.
v Less signal attenuation.
v Higher bandwidth.
29. What are the disadvantages of optical fiber as a transmission medium?
The disadvantages of optical fiber are
v Very expensive.
v Installation and maintenance is difficult.
v Fragility.
30.What does a decibel measure?
To check whether a signal has loosed or gained strength we use the
concept decibel. Decibel measures the relative strength of two signals or a signal at a
two different points. Decibel is negative if a signal is attenuated and positive if a
signal is amplified.
31. What are the criteria used to evaluate transmission medium?
The criteria used to evaluate transmission medium are
v Throughput
v Propagation speed
v Propagation time
v Wavelength
32. Give the relationship between propagation speed and propagation time?
Propagation time = distance / propagation speed
The time required for a signal or a bit to travel from one point to another is
called propagation time.
Propagation speed is the distance, a signal or a bit travel through a
medium in one second.
33.What are the network support layers and the user support layers?
Network support layers:
The network support layers are Physical layer, Data link layer and
Network layer. These deals with electrical specifications, physical connection,
transport timing and reliability.
User support layers:
The user support layers are: Session layer, Presentation layer,
Application layer. These allow interoperability among unrelated software system.
34. What is the difference between network layer delivery and the transport layer
delivery?
Network layer delivery
Transport layer delivery
The network layer is responsible for the the source-to-destination delivery of packet
across multiple network links.
The transport layer is responsible for source-to-destination delivery of the entire message.
35. What is a peer-to-peer process?
When a message travels from A to B, it may pass through many
intermediate nodes, which contains only the first three layers. Within a single
machine, each layer gets the service from the below layer. Layer X on one machine
communicates with layer X on another machine by a set of rules and conventions
called as protocols. The processes on each machine that communicate at a given layer
are called peer-to- peer process.
36. What are headers and trailers and how do they get added and removed?
The control data added to the beginning of a data is called headers. The
control data added to the end of a data is called trailers. At the sending machine, when
the message passes through the layers each layer adds the headers or trailers. At the
receiving machine, each layer removes the data meant for it and passes the rest to the
next layer.
37. What are the concerns of physical layer?
The physical layer coordinates the functions required to transmit a bit
stream over a physical medium. The physical layer is concerned with the following:
v Physical characteristics of interfaces and media.
v Representation of bits.
v Data rate.
v Synchronization of bits.
v Line configuration.
v Physical topology & Transmission mode.
38. What are the responsibilities of data link layer?
The data link layer is responsible for delivering data units from one station
to the next without errors. The specific responsibilities of data link layer include the
following:
v Framing.
v Physical addressing.
v Flow control.
v Error control.
v Access control
39. What are the responsibilities of network layer?
The network layer is responsible for the source-to-destination delivery of
Packet across multiple network links. The specific responsibilities of network layer
include the following:
v Logical addressing.
v Routing.
40. What are the responsibilities of transport layer?
The transport layer is responsible for source-to-destination delivery of the
entire message. The specific responsibilities of transport layer include the following:
v Service-point addressing.
v Segmentation and reassembly.
v Connection control.
v Flow control.
v Error control
41. The transport layer creates the connection between source and destination.
What are the three events involved in the connection?
For security , the transport layer may create a connection between the two
end ports. A connection is a single logical path between the source and destination that
is associated with all packets in a message. Creating a connection involves three steps:
v Connection establishment
v Data transfer & Connection release.
42. What is the difference between service point address, logical address and
physical address?
Service point addressing
Logical addressing
Physical addressing
The transport layer header includes a type of address called a service point address or port address, which makes a data delivery from a specific process on one computer to a specific process on another computer.
If a packet passes the network boundary we need another addressing to differentiate the source and destination systems. The network layer adds a header, which indicate the logical address of the sender and receiver.
If the frames are to be distributed to different systems on the network, the data link layer adds the header, which defines the source machine’s address and the destination machine’s address.
43. What are the responsibilities of session layer?
The session layer establishes, maintains and synchronizes the interactions
between communicating devices. The specific responsibilities of session layer
include the following:
v Dialog control
v synchronization
44. What is the purpose of translation by presentation layer?
The processes in two systems are usually exchanging information in the
form of character strings, numbers, and so on. The information should be changed to
bit streams before being transmitted. Because different computers use different
encoding systems, the presentation layer is responsible for interoperability between
these different encoding methods. The presentation layer at the sender changes the
information from its sender-dependent format into a common format. The
presentation layer at the receiving machine changes the common format into its
receiver-dependent format.
45. Name some services provided by the application layer
The services provided by the application layer include the following:
v Network virtual terminal.
v File transfer, access, and management.
v Mail services
v Directory services.
No comments:
Post a Comment