Computer Networks questions and answers

The following texts are the property of their respective authors and we thank them for giving us the opportunity to share for free to students, teachers and users of the Web their texts will used only for illustrative educational and scientific purposes only.

All the information in our site are given for nonprofit educational purposes

The information of medicine and health contained in the site are of a general nature and purpose which is purely informative and for this reason may not replace in any case, the council of a doctor or a qualified entity legally to the profession.

Computer Networks questions and answers

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 path by which a
message travels from sender to receiver.
Protocol   : A protocol is a set of rules that governs data 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 a periodic signal?
               Periodic signal                                       A periodic signal
      1.A periodic signal completes a pattern          1.A periodic 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. Which type of plot shows the components of a composite signal?
           Frequency domain plot shows the components of a composite signal.
The frequency domain plot shows changes in signal amplitude with
respect to frequency.

20.Which type of plot shows the amplitude of a signal at a given time?
Time domain plot shows the amplitude of a signal at a given time.
The Time domain plot shows changes in signal amplitude with respect to time.

21. How is the bandwidth of the signal related to spectrum?
The width of a single spectrum is called as the bandwidth. The range of
frequency that a medium can pass is called its bandwidth. Bandwidth is the
difference between the highest and the lowest frequency of the spectrum.

22. How composite signal will decompose into an individual frequency?
Composite signal will decompose into an individual frequency by Fourier
analysis. According to Fourier analysis , any composite signal can be represented as
a combination of simple sine waves with different frequencies, phases and
amplitudes.

23. 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.

24.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

25. The sine wave completes one cycle in 4seconds.What is its frequency?
Answer in Hz.

Given T = 4 seconds
f = ¼ =0.25 Hertz.

26. 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

27. 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.

28.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.

29. 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.

30. 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.

31. 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.

32. Name the advantages of optical fiber over twisted pair and coaxial cable?
The advantages of optical fiber over twisted pair and coaxial cable are

Noise resistance.
Less signal attenuation.
Higher bandwidth.

33. What are the disadvantages of optical fiber as a transmission medium?
The disadvantages of optical fiber are

Very expensive.
Installation and maintenance is difficult.
Fragility.

34. What are the methods used to propagate radio waves?
The methods used to propagate radio waves are

Surface propagation.
Tropospheric propagation.
Ionospheric propagation.
Line of sight propagation.
Space propagation.

35. What is a handoff in cellular telephone?
If the mobile moves from one cell to another cell during conversation
then handoff occurs. When the mobile moves from one cell to another the signal
may become week, to solve this problem the MTSO monitors the level of the signal
every few seconds. If the strength of the signal decreases, the MTSO seeks a new cell
that can accommodate the communication better.

36. 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.

37. What are the criteria used to evaluate transmission medium?
The criteria used to evaluate transmission medium are

Throughput
Propagation speed
Propagation time
Wavelength

38. 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.

39. Explain cross talk and what is needed to reduce it?
Effect of one wire on the another is called as cross talk. One wire will be
the sending antenna and the other wire will be the receiving antenna. We can use the
shielded twisted pair cable or coaxial cable for transmission, which contains metal
foil to reduce cross talk.

40. How does ionospheric propagation work? What are the uses for this type of
propagation?
The high frequency signals radiate upwards towards ionosphere where
they are reflected back to earth. The density difference between the troposphere and
ionosphere causes each radio waves to speed up and change direction bending back
to earth.

UNIT – II

PART – A Questions & Answers

1. 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.

2. 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.

3. 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.

4. 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.

5. 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:

Physical characteristics of interfaces and media.
Representation of bits.
Data rate.
Synchronization of bits.
Line configuration.
Physical topology & Transmission mode.

6. 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:

Framing.
Physical addressing.
Flow control.
Error control.
Access control

7. 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:

Logical addressing.
Routing.

8. 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:

Service-point addressing.
Segmentation and reassembly.
Connection control.
Flow control.
Error control

9. 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:

Connection establishment
Data transfer
Connection release.

10. 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.

11. 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:

Dialog control
synchronization

12. 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.

13. Name some services provided by the application layer
The services provided by the application layer include the following:

Network virtual terminal.
File transfer, access, and management.
Mail services
Directory services.

14. What is data transparency in BSC protocol?
BSC was designed to transport only textual images. For a protocol to be
useful it must be transparent ie. it must be able to carry any combination of bit as
data without confused with the control information. Data transparency means, ability
to send any combination of bits as data.

15. What is the difference between the information field in HDLC I- frame and
U- frame?

Information field in HDLC I-frame	Information field in HDLC U-frame
In an I-frame the information field contains the user data.	In an U-frame the information field contains the network management information.

16. How the asynchronous protocols are primarily used?
The asynchronous protocols are primarily used as modems, future start and
stop bits and variable length gap between characters.
UNIT – III

PART – A Questions & Answers

What are the objectives of Frame Relay?

The objectives of frame relay are:

higher data rate at lower cost
Bursty data transmission
Less overhead due to improved transmission media.

What are the advantages of Frame Relay?

Operates at higher data rate ( 1.544 Mbps and 44.376Mbps)
Operates just in Physical and data link layer which means that it acts as a backbone network to provide services to protocol that already have a network layer protocol.
Frame relay allows bursty data.
Frame relay is less expensive.

What are the disadvantages of Frame Relay?

The data rate is not high enough to the protocols with higher data rate

( B – ISDN)

Frame relay allows variable length frames. This may create varying delays for different users.
Because of varying delays, frame relay is not suitable for sending delay sensitive data such as real-time video or audio.

How a virtual circuit is identified in Frame relay network?

A virtual circuit is identified by a number called Data link connection identifier(DLCI). When a virtual circuit is established by the network, A DTE is given a DLCI number that it can use to access the remote DTE. The local DTE uses this DLCI to send frames to the remote DTE.

How a PVC connection is established in Frame relay?

A permanent Virtual Connection(PVC) is established between two DTEs by the network provider. The two DTEs are connected permanently through a virtual connection. Two DLCIs are assigned to the UNI interfaces at both ends of connection.

What is the role of DLCI?

DLCI defines the virtual path connection between the local DTE & DCE and between remote DTE & DCE. It also define the virtual circuit between two DCEs inside the network.

What are the frame relay layers?

The frame relay layers are:
Physical Layer – contain the protocols recognized by ANSI
Data Link layer – employs a simplified version of HDLC called core LAPF

When a congestion occur?

Congestion in a network may occur, if users send data into the network at a rate greater than that allowed by network resources. For example, congestion may occur because the switches in a network have a limited buffer size to store arrived packets before processing.

How a congestion can be avoided?

A congestion can be avoided in two ways. First, the frame relay protocol uses two bits in the frame to explicitly warn the source and destination of the presence of congestion. The two bits are: Backward Explicit Congestion Notification(BECN) & Forward Explicit Congestion Notification(FECN) bits. Second, the users are notified of the congestion implicitly when the upper layer protocols find that some frames have not reached the destination.

What are the attributes of traffic control?

The attributes are:

Access rate
Committed Burst Size
Committed Information Rate
Excess Burst Size.

What are the objectives of ATM networks?

The objectives of ATM networks are:

need for a transmission system to optimize the use of high data rate transmission media.
Need for a system that can interface with existing system and to provide connection between them without reducing their effectiveness.
Need for a design that can be implemented inexpensively
Ability to work with and support the existing telecommunication hierarchies.
The new system must be connection-oriented to ensure accurate and predictable delivery.
To eliminate many of the software functions by hardware functions so that increasing the data rate.

What is a cell? What are its advantages?

A cell is defined as a small fixed-size block of information. The advantages of cells are:

the cells from two lines are interleaved so that none suffers a long delay
Despite interleaving, cells from each line arrive at their respective destinations in an approximation of a continuous stream.

How a connection is established in ATM network?

Connection between two end points is accomplished through transmission path(TP), Virtual path(VP) and the virtual circuit(VC).
TP – physical path between an end point and switch or between two switches.
VP – set of connections between two switches
VC – Logical path between the endpoints.

What are the layers of ATM?

The ATM defines three layers: They are the Application Adaptation Layer, the ATM layer and the Physical layer.

What are the service classes defined by ATM?

The service classes defined by ATM are:

Constant Bit Rate(CBR)
Variable Bit Rate(VBR)
Available Bit Rate(ABR)
Unspecified Bit Rate(UBR)

How a virtual circuit is identified in ATM?

In ATM, virtual circuit is identified by Virtual Path Identifier(VPI) – defines the specific VP and a Virtual Circuit Identifier(VCI) – defines a particular VC inside the VP. ie. A virtual connection is defined by a pair of numbers: the VPI and the VCI.

What is the use of switching? What type of switches does ATM use?

Switches are used to route all the incoming cells from a source endpoint to the destination end point. The two types of switches supported by ATM are:

VP switch – route the cell using only VPI
VPC switch – route the cells using VPI & VCI.

What are the two sub layers of AAL? Mention its functions.

The two sub-layers of AAL are:

Convergence Sub layer – divides the bit stream into 47-byte segments and passes them to the SAR sub-layer below.
Segmentation & Reassembly Layer – accepts a 47-byte payload from the CS and adds a one-byte header and pass them to the ATM layer.

What are the functions of ATM layer?

The ATM layer provides routing, traffic management, switching, and multiplexing services. It processes outgoing traffic by accepting 48-byte segments from the AAL sub-layers and transforming them into 53-byte cells by the addition if a 5-byte header.

What is Quality of Service?

The QoS defines a set of attributes related to the performance of the connection. For each connection, the user can request a particular attribute. Each service class is associated with a set of attributes.

UNIT – IV

PART – A Questions & Answers

1. What is LAN? What are the dominating architectures?
A Local Area Network (LAN) is a data communication system that allows a number of independent devices to communicate directly within a limited geographical area. LANs are dominated by four dominating architectures,

Ethernet
Token Bus
Token ring
Fiber Distributed Data Interface

2. With a neat diagram explain the relationship of IEEE Project to the OSI model?

Other layers

Network

Data link

Physical

Other layers

Network

Logical Link Control

Media Access Control

Physical

The IEEE has subdivided the data link layer into two sub layers:
* Logical link control (LLC)
* Medium access control (MAC)
LLC is non-architecture specific. The MAC sub layer contains a number
of distinct modules ,each carries proprietary information specific to the LAN
product being used.

3. What are the functions of LLC?
The IEEE project 802 model takes the structure of an HDLC frame and divides it into 2 sets of functions. One set contains the end user portion of the HDLC frame - the logical address, control information, and data. These functions are handled by the IEEE 802.2 logical link control(LLC) protocol.

4. What are the functions of MAC?
MAC sub layer resolves the contention for the shared media. It contains synchronization, flag, flow and error control specifications necessary to move information from one place to another, as well as the physical address of the next station to receive and route a packet .

5. What is protocol data unit?
The data unit in the LLC level is called Protocol Data Unit (PDU). It contains four fields.

Destination Service Point Address (DSAP)
Source Service Access Point
Control field
Information field

DSAP

SSAP

Control

Information

6. What are collisions? What are the mechanisms that can be used to avoid collisions?
Whenever multiple users have unregulated access to a single line, there is a danger of signals overlapping and destroying each other. Such overlaps, which turn the signals into unusable noise are called collisions. The access mechanism used to coordinate traffic, minimize the number of collisions occur, and maximize the number of frames that can be delivered successfully is Carrier Sense Multiple Access with collision detection (CSMA\CD).

7. What is thick Ethernet?
The first of the physical standards defined in the IEEE 892.3 model is called 10Base5,thick Ethernet, or thicknet. This is a bus topology LAN that uses base band signaling and has a maximum segment length of 500 meters. The data rate is 10MBPS.To reduce collisions the bus should not exceed 2500meters(5 segments).

8. What are advantages and disadvantages of thin Ethernet over thicknet?
The advantages are

Reduced cost
Ease of installation

The disadvantages are

Shorter range (185meters)
Smaller capacity

9. What is twisted pair Ethernet?
Twisted pair Ethernet is a star topology LAN using unshielded twisted pair cable (UTP) instead of coaxial cable. It supports a data rate of 10MBPS and has a maximum length of 100meters.

10. What is Token Bus?
Token Bus is a physical bus that operates as a logical ring using tokens. Here stations are logically organized into a ring. A token is passed among stations. If a station wants to send data, it must wait and capture the token. Like Ethernet, station communicates via a common bus.

11. What is token passing?
Stations may attempt to send data multiple times before a transmission makes it onto a link. This redundancy may create delays of indeterminable length if the traffic is heavy. Token ring resolves this uncertainty by requiring that stations take turns sending data. Each station may transmit only during its turn and may send only one frame during each turn. The mechanism that coordinates this rotation is called token passing.

12. What is FDDI?
Fiber Distributed Data Interface (FDDI) is a local area network protocol standardized by ANSI and the ITU-T. It supports data rates of 100MBPS and provides a high-speed alternative to Ethernet and Token Ring. It uses Fiber Optic cable.

13. What are the configurations in which wireless LANs can operate?
Wireless LANs can operate in two configurations. They are,

With base band station
Without base band station

14. What is BSS?
The smallest building block of a wireless LAN is a Basic Service Set (BSS), which consists of some number of stations executing the same MAC protocol and competing for access to the same shared medium.

15. What is an ESS?
An Extended Service Set is one which consists of two or more BSS interconnected by a distributed system. The ESS appears as a single logical LAN to the LLC level.

16. What are the types of stations defined by 802.11 standard?
802.11 standard defined three types of stations based on the mobility,
No transition: A station of this type is either stationary or moves only within the direct communication range of the communication stations of a single BSS.
BSS transition: This is defined as a station movement from one BSS to another BSS within the same ESS.
ESS transition: This is defined as a station transition from a BSS in one ESS to a BSS within Another ESS.

17. What is the transmission schemes defined in the current 802.11 standard?
The transmission schemes defined in the current 802.11 standard are,
Infrared: At 1 Mbps and 2Mbps operating at a wavelength between 850 and 950 nm
Direct Sequence Spread Spectrum: Operating in the 2.4GHz ISM band. Up to 7 channels, each with a data rate of 1Mbps or 2 Mbps, can be used.
Frequency Hopping Spread Spectrum: operating in the 2.4GHz ISM band, with data rate of 1 Mbps or 2 Mbps.

18. What is ATM LAN? What are its types?
An ATM LAN implies the use of ATM, as a data transport protocol somewhere within the local premises. The types of ATM LANs are,
Gateway to ATM WAN: An ATM switch acts as a router and traffic concentrator for linking a premises network complex to ATM WAN.
Backbone ATM switch: Either a single ATM switch or a local network of ATM switches interconnect other LANs.
Workgroup ATM: High performance multimedia workstations and other end systems connect directly to an ATM switch.

19. Name some random access protocols?
Some random access protocols are

ALOHA
Slotted ALOHA
CSMA (Carrier Sense Multiple Access)

20. How data transmission occurs using ALOHA protocol?
With ALOHA, when a station has a frame to send, it does so .The station then listens for an amount of time equal to the maximum possible round trip propagation delay on the network plus a small fixed time increment. If the station hears an acknowledgement during that time, fine; otherwise it resends the frame. If the station fails to receive an acknowledgement after repeated transmissions, it gives up.

UNIT – V

PART – A Questions & Answers

Discuss the functions of session layer?

Services of the session layer are:

To coordinate connection & disconnection of dialogs b/w application .
To provide synchronization points for data exchange
To coordinate who sends & when

Define the term graceful close?

Graceful close represents that the data exchange is complete before the session begins.

What are the differences between minor & major synchonization points?

MAJOR SYNCHRONIZATION MINOR SYNCHRONIZATION

      * These points must be confirmed.           * These points don’t need to be
confirmed.
* if there is an error control can go           * if there is an error control can go
back to last major synchronization           back 1 or more minor synchonization
points.                                                        Points.

Discuss the functions of presentation layer?

The functions performed in this layer include translation, authentication,
Encryption/decryption and compression.

What is the translation method recommended by OSI? What is the role of ANS.1?

The translation method recommended by OSI is ANS.1.The role of ANS.1
is to provide a mechanism for defining data types in an implementation –
independent format.

What are the 2 categories of encryption/decryption methods& what are the

methods of character –level encryption?
2 categories of encryption/decryption methods are

Character –level encryption
Bit level encryption

Methods of character –level encryption are

Substitutional
Tranpositional

7. What sort of operations can be performed on bit level encryption?
The sorts of operations that can be performed on bit level encryption are
Encoding/decoding, permutation, substitution, product, exclusive OR & rotation.

What is the goal of data compression?

The goal of data compression is to reduce the number of transmitted Bits.

What is the use of sliding window?

Sliding window is used to make data transmission more efficient as well as to control data flow so that receiver does not become overwhelmed .The sliding window used at the transport layer are byte –oriented.

What is the concept behind monoalphabetic encryption & decryption algorithm?

The concept behind monoalphabetic encryption algorithm is that it simply adds the number to the ASCII code of the character.
The concept behind monoalphabetic encryption algorithm is it simply subtracts the same number from the ASCII code.

Why polyalphabetic encryption technique is used?

The polyalphabetic encryption technique is used to find the position of
Character in the text & use that value as the key.

Contrast straight, compressed & expanded permutation

In straight permutation the number of bits in the i/p & o/p are preserved;
Only the positions are changed.
In compressed permutation the number of bits is reduced.
In expanded permutation the number of bits is increased.

What is authentication?

Authentication means verifying the identity of a sender. In other words
Authentication tries to verify that a message is coming from a authentic sender
and not from an imposter.

What are the 3 stages that a connection _oriented transmission undergoes?

The 3 stages that a connection _oriented transmission undergoes are

Connection establishment
Data transfer
Connection termination

What is statistical compression?

Statistical compression method is one type of loss-less compression.
This method uses short codes for frequent symbols and long codes for infrequent
symbols.

What are the types of encoding system?

Types of encoding system are

Morse code
Huffman encoding, Huffman decoding
Lempel-Ziv-Welch encoding.

What is the use of JPEG &MPEG?

The Joint Photographic Experts Group is used to compress pictures & graphics. The Motion Picture expert Group is used to compress video.

Name 5 standard application protocols:

5 standard application protocols are:

Mail handling system - protocol for E-mail & store-and-forward

Handling.

File transfer access & management (FTAM) - transfers, accesses, and manages files. FTAM uses virtual files.
Virtual terminal - allows dissimilar terminals or machines to

communicate with one another.

Directory service - An application program that allows users

access to databases

Common management information protocol - implements an OSI

Management service.

What is meant by translation?

Changing the internal representation of data from one form to another is
Called translation.

What are the objectives of CMIS?

The objectives of CMIS are:

Fault management
Accounting management
Configuration and name management
Performance management
Security management

Source : http://www.niceindia.com/qbank/computer_networks.doc

Web site link to visit: http://www.niceindia.com/

Google key word : Computer Networks questions and answers file type : doc

Author : not indicated on the source document of the above text

If you are the author of the text above and you not agree to share your knowledge for teaching, research, scholarship (for fair use as indicated in the United States copyrigh low) please send us an e-mail and we will remove your text quickly.