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CS601 Final Term Solved Papers Mega Mega 03 ZIP Folders

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FINALTERM  EXAMINATION

Spring 2010

CS601- Data Communication

Time: 90 min

Marks: 60

 Student Info Student ID: Center: Exam Date:

 For Teacher's Use Only Q No. 1 2 3 4 5 6 7 8 Total Marks Q No. 9 10 11 12 13 14 15 16 Marks Q No. 17 18 19 20 21 22 23 24 Marks Q No. 25 26 27 28 29 30 31 32 Marks Q No. 33 34 35 36 37 38 39 40 Marks

Question No: 1      ( Marks: 1 ) - Please choose one

__________representation of links that connect nodes is called as physical topology.

► geometrical

► logical

► physical

Question No: 2      ( Marks: 1 ) - Please choose one

The internet model consists of _________ layers.

► three

► two

► five

seven

Question No: 3      ( Marks: 1 ) - Please choose one

Encryption and encoding are the same terms.

► True

False

Question No: 4      ( Marks: 1 ) - Please choose one

The amplitude of a digital signal depends upon the________ to represent a bit.

► phase

► voltage

► wavelength

Question No: 5      ( Marks: 1 ) - Please choose one

The inversion of the level at 1 bit is called as __________

► NRZ-L

NRZ-I

► RZ

Question No: 6      ( Marks: 1 ) - Please choose one

Modulation of an analog signal can be accomplished through changing the ___________ of the carrier signal.

► amplitude

► frequency

► phase

all of the given

Question No: 7      ( Marks: 1 ) - Please choose one

If FCC regulations are followed, the carrier frequencies of adjacent AM radio stations are ____________ apart.

► 5 KHz

► 10 KHz

► 200 KHz

► 530 KHz

Question No: 8      ( Marks: 1 ) - Please choose one

Category 5 UTP cable is used for data transmission of upto__________.

100 Mbps

► 200 Mbps

► 250 Mbps

► 400 Mbps

Question No: 9      ( Marks: 1 ) - Please choose one

The RG number gives us information about ________.

Twisted pairs

Coaxial cables

► Optical fibers

► all of the given

Question No: 10      ( Marks: 1 ) - Please choose one

The inner core of an optical fiber is __________ in composition.

Glass plastic

Copper

► Bimetallic

► Liquid

Question No: 11      ( Marks: 1 ) - Please choose one

All of popular Fiber optic connectors are ___________ shaped.

► Conical

► Barrel

► Circular

► Rectangular

Question No: 12      ( Marks: 1 ) - Please choose one

The VLF and LF bands use _________ propagation for communications.

► Ground

► Sky

► Line of sight

► Space

Question No: 13      ( Marks: 1 ) - Please choose one

Multiplexing is the set of techniques that allows simultaneous TX of multiple signals across  ___________ data link

► Single

► Multi

► Single and Multi

► none of the given

Question No: 14      ( Marks: 1 ) - Please choose one

A portion of the path that carries TX b/w a given pair of devices is known as __________.

► Node

► Bridge

Channel

► Gateway

Question No: 15      ( Marks: 1 ) - Please choose one

Which error detection method involves polynomials?

► Checksum

► Two-dimensional parity check

► CRC

► Simple parity check

Question No: 16      ( Marks: 1 ) - Please choose one

If the ASCII character G is sent and the character D is received, what type of error is this?

Single-bit

► Multiple-bit

► Burst

► Recoverable

Question No: 17      ( Marks: 1 ) - Please choose one

Which error detection method involves the use of parity bits?

► Simple parity check & two dimensional parity check

► CRC

► Two-dimensional parity check

Simple parity check

Question No: 18      ( Marks: 1 ) - Please choose one

Which error detection method can detect a single-bit error?

► Simple parity check

► Two-dimensional parity check

► CRC

► All of the given

Question No: 19      ( Marks: 1 ) - Please choose one

The Hamming code is a method of __________

► Error detection

Error correction

► Error ecapsulation

► Error detection & Error encapsulation

Question No: 20      ( Marks: 1 ) - Please choose one

Sliding window requires that data frames be transmitted _______________

Sequentially

► Frequently

► Synchronously

► Asynchronously

Question No: 21      ( Marks: 1 ) - Please choose one

In selective-reject ARQ, only the specific damaged or lost frame is_____________.

► Retransmitted

► Forwarded

► Selected

► Rejected

Question No: 22      ( Marks: 1 ) - Please choose one

Which of the following sublyer, resolves the contention for the shared media

► MAC

► LLC

► Physical

Question No: 23      ( Marks: 1 ) - Please choose one

The PDU  has no flag fields, no CRC, and no station address

► TRUE

► FALSE

Question No: 24      ( Marks: 1 ) - Please choose one

IEEE divides the base band category into  ______ standards.

5

► 4

► 3

► 6

Question No: 25      ( Marks: 1 ) - Please choose one

Like 10 Base 5, 10 Base 2 is a _________ topology LAN

► Ring

► Mesh

► Star

Bus

Question No: 26      ( Marks: 1 ) - Please choose one

Check sum method is used for _______________ layers.

► Physical

► Application

► Transport

Question No: 27      ( Marks: 1 ) - Please choose one

Repeater works on __________     layer.

Physical

Network

► Application

Question No: 28      ( Marks: 1 ) - Please choose one

Trunks are transmission media such as _________ that handle the telephone to the nearest end office.

► Twisted-pair & Fiber-optic

► Twisted-pair

► Fiber-optic

Question No: 29      ( Marks: 1 ) - Please choose one

Which of the following ___________ uses a series of filters to decompose multiplexed signal into its constituent signals.

► MUX

► DEMUX

► Switch

► Bridge

Question No: 30      ( Marks: 1 ) - Please choose one

In Fast Ethernet, data rate can be increased by _______________ collisions.

► Increasing

► Decreasing

► Keeping Constant

► None of the given

Question No: 31      ( Marks: 2 )

What are the advantages of a multipoint connection over a point-to-point connection?

Point-to-point connection is limited to two devices, where else more than two devices share a single link in multipoint connection. Multipoint connection can be used for fail-over and reliability.

Question No: 32      ( Marks: 2 )

What's the name of the telephone service in which there is no need of dialing.

DSS (digital data service)   is the telephone service in which there is no need of dialing.

Question No: 33      ( Marks: 2 )

Which type of frames are present in BSC frames?

There are two types of frames that are present in BSC.

1. 1.      Control Frames and
2. 2.      Data Frames

Question No: 34      ( Marks: 2 )

What methods of line discipline are used for peer to peer and  primary secondary communication?

Line discipline is done in two ways:

1. ENQ/ACK      (Enquiry Acknowledgement)

This is used for peer to peer communication.

1. Poll/ Select

This method is used for primary secondary communication.

Question No: 35      ( Marks: 3 )

How does the checksum checker know that the received data unit is undamaged? [3]

Checksum Checker or generator:

The sender subdivides data units into equal segments of ‘n’ bits(16 bits)

1. These segments are added together using one’s complement.
2. The total (sum) is then complemented and appended to the end of the original data unit as redundancy bits called CHECKSUM.
3. The extended data unit is transmitted across the network.
4. The receiver subdivides data unit and adds all segments together and complement the result.
5. If the intended data unit is intact, total value found by adding the data segments and the checksum field should be zero.
6. 6.      If the result is not zero, the packet contains an error & the receiver rejects it.

Question No: 36      ( Marks: 3 )

A bridge has more overhead than a repeater. A bridge processes the packet at two

layers ; a repeater processes a frame at only one layer. A bridge needs to search a

table and find the forwarding port as well as to regenerate the signal; a repeater

only regenerates the signal. In other words, a bridge is also a repeater (and more); a

repeater is not a bridge.

Question No: 37      ( Marks: 3 )

Write down disadvantages of Ring Topology.

Unidirectional Traffic

A break in a ring that is a disabled station can disable the entire network

Can be solved by using:

Dual Ring or

A switch capable of closing off the Break

Question No: 38      ( Marks: 3 )

How parity bits are counted in VRC error detection method technique in case of odd parity generator?

For example:

We want to TX the binary data unit 1100001

Adding together the number of 1’s gives us 3, an odd number

Before TX, we pass the data unit through a parity generator, which counts the 1’s and appends the parity bit (1) to the end

The total number of 1’s is now 4, an even number

The system now transfers the entire expanded across the network link

When it reaches its destination, the RX puts all 8 bits through an even parity checking function

If the RX sees 11100001, it counts four ones, an even number and the data unit passes

When the parity checker counts the 1’s, it gets 5 an odd number

The receiver knows that an error has occurred somewhere and therefore rejects the whole unit

Some systems may also use ODD parity checking

The principal is the same as even parity

Question No: 39      ( Marks: 5 )

How are lost acknowledgment and a lost frame handled at the sender site? [5]

At some error rates (16%-20%) the protocol hung up in an infinite loop, while it worked fine for other error rates. On examining the code it was determined that this problem resulted from improper variable initialization. On these certain error rates the pseudo-random number generator caused the very first frame sent to be lost or damaged. The receiver used a variable to keep track of the last in sequence frame received. This was erroneously initialized to 0. Therefore if the first frame got lost (sequence no 0), when the receiver received the second frame (sequence number 1) it sent an acknowledgment for the last in sequence frame  received, which had been initialized to 0. Therefore the sender received an acknowledgement for sequence number 0 and moved its window up accordingly. It caused everything to get out of synch, and caused the protocol to go into infinite loop.  This was resolved by initializing the variable to remember the last in sequence frame received to an out of range sequence number.

Question No: 40      ( Marks: 5 )

Explain Protocol Data Unit (PDU)?

Protocol data unit (PDU) is an OSI term that refers generically to a group of information added or removed by a particular layer of the OSI model. In specific terms, an LxPDU implies the data and headers defined by layer x. Each layer uses the PDU to communicate and exchange information. The PDU information is only read by the peer layer on the receiving device and then stripped off, and data is handed over to the next upper layer.

FINALTERM  EXAMINATION

Spring 2009

CS601- Data Communication

Ref No: 656191

Time: 120 min

Marks: 80

 For Teacher's Use Only Q No. 1 2 3 4 5 6 7 8 Total Marks Q No. 9 10 11 12 13 14 15 16 Marks Q No. 17 18 19 20 21 22 23 24 Marks Q No. 25 26 27 28 29 30 31 32 Marks Q No. 33 34 35 36 37 38 39 40 Marks Q No. 41 42 43 44 45 46 47 48 Marks Q No. 49 50 Marks

Question No: 1      ( Marks: 1 ) - Please choose one

Which is not an element of protocol

► semantics

timing

► communication service module

Question No: 2      ( Marks: 1 ) - Please choose one

Layers 5, 6 and 7 also called as network support layers.

► True

► False

Question No: 3      ( Marks: 1 ) - Please choose one

Fourier transform tells us that any digital signal can be decomposed into infinite number of periodic signals

► True

► False

Question No: 4      ( Marks: 1 ) - Please choose one

Time domain plot show changes in signal phase with respect to time.

► True

► False

Question No: 5      ( Marks: 1 ) - Please choose one

Analog to digital conversion is also termed as modulating an analog signal.

► True

► False

Question No: 6      ( Marks: 1 ) - Please choose one

DC component is also termed as Direct current component or a component with non-zero frequency.

► False

► True

Question No: 7      ( Marks: 1 ) - Please choose one

Manchester is a type of ____________encoding.

► biphase

► polar

► biphase & polar

► none of the given

Question No: 8      ( Marks: 1 ) - Please choose one

The inversion of the level at 1 bit is called as __________

► NRZ-L

► NRZ-I

► RZ

Question No: 9      ( Marks: 1 ) - Please choose one

PCM is the first process of PAM.

► True

► False

Question No: 10      ( Marks: 1 ) - Please choose one

In 4PSK each phase change represents ______bits.

► 3

► 6

► 2

► 4

Question No: 11      ( Marks: 1 ) - Please choose one

In RS 422 Balanced mode two lines carry ________ signals which are not identical to each other.

► same

► different

► digital

► analog

Question No: 12      ( Marks: 1 ) - Please choose one

A ______________ converts an analog signal into a digital signal.

► Demodulator

► Modulator

► Digital-to-analog converter

Question No: 13      ( Marks: 1 ) - Please choose one

Which of the following is an example of ITU-T modem standards:

► T-series

► X-series

► N-series

► V-series

Question No: 14      ( Marks: 1 ) - Please choose one

► 26.6 Kbps

► 33.6 Kbps

► 36.6 Kbps

► 46.6 Kbps

Question No: 15      ( Marks: 1 ) - Please choose one

Which of the following primarily uses guided media

► Cellular telephone system

► Local telephone system

► Satellite communications

Question No: 16      ( Marks: 1 ) - Please choose one

When a beam of light travels through media of two different densities, if the angle of incidence is greater than the critical angle, ____________occurs.

► Reflection

► Refraction

► Incidence

► Criticism

Question No: 17      ( Marks: 1 ) - Please choose one

When we talk about unguided media, usually we are referring to _________.

► Metallic wires

► Nonmetallic wires

► The air

► Water

Question No: 18      ( Marks: 1 ) - Please choose one

Optical fibers are defined by the ratio of the ___________ of their core to the diameter of their cladding.

► Diameter

► Length

► Width

Question No: 19      ( Marks: 1 ) - Please choose one

All of popular Fiber optic connectors are ___________ shaped.

► Conical

Barrel

► Circular

► Rectangular

Question No: 20      ( Marks: 1 ) - Please choose one

Radio wave transmission utilizes ___________ different types of propagation.

► Four

► Three

► Two

► Five

Question No: 21      ( Marks: 1 ) - Please choose one

dB is ____________ if a signal is amplified.

► Negative

► Positive

► Null

► Zero

Question No: 22      ( Marks: 1 ) - Please choose one

A prism can deflect the light depending upon the angle of ____________ and the frequency.

► Deviation

► Incident

► Refraction

► Reflection

Question No: 23      ( Marks: 1 ) - Please choose one

Asynchronous TDM is efficient only when the size of the time slot is kept relatively _______________

► Large

► Small

► Medium

► None of the given

Question No: 24      ( Marks: 1 ) - Please choose one

The local loop has ___________ cable that connects the subscriber telephone to the nearest end office.

► Twisted-pair

► Coaxial

► Fiber-optic

► None of the given

Question No: 25      ( Marks: 1 ) - Please choose one

Data from a computer are ____________; the local loop handles _________ signals.

► Analog; analog

► Analog; digital

► Digital; digital

► Digital; analog

Question No: 26      ( Marks: 1 ) - Please choose one

Which error detection method uses ones complement arithmetic?

► Simple parity check

► Two-dimensional parity check

► CRC

► Checksum

Question No: 27      ( Marks: 1 ) - Please choose one

Flow control is needed to prevent ____________

► Bit errors

► Overflow of the sender buffer

► Overflow of the receiver buffer

► Collision between sender and receiver

Question No: 28      ( Marks: 1 ) - Please choose one

____________ coordinates the amount of data that can be sent before receiving acknowledgment

► flow control

► error control

► data control

Question No: 29      ( Marks: 1 ) - Please choose one

Error control is both error _________ and error ___________

► detection; correction

► detection; deletion

► detection; avoidance

► detection; forwarding

Question No: 30      ( Marks: 1 ) - Please choose one

Addressing is not needed in _______________ configuration.

Point to Point

► Multipoint

► Point to point and multipoint

Question No: 31      ( Marks: 1 ) - Please choose one

In a Go-Back-N ARQ, if the window size is 63, what is the range of sequence number?

► 0 to 63

► 0 to 64

► 1 to 63

► 1 to 64

Question No: 32      ( Marks: 1 ) - Please choose one

A timer is set when ___________ is sent out.

► A data frame

► An ACK

► A NAK

Question No: 33      ( Marks: 1 ) - Please choose one

Sliding window requires that data frames be transmitted _______________

► Sequentially

► Frequently

► Synchronously

► Asynchronously

Question No: 34      ( Marks: 1 ) - Please choose one

In Y-MODEM Multiple files can be sent simultaneously

► True

► False

Question No: 35      ( Marks: 1 ) - Please choose one

BLAST stands for :

► Blocked asynchronous transmission

► Blocked synchronous transmission

► Barrel asynchronous transmission

► Below asynchronous transmission

Question No: 36      ( Marks: 1 ) - Please choose one

HDLC is an acronym for ______________.

► High-duplex line communication

► Host double-level circuit

Question No: 37      ( Marks: 1 ) - Please choose one

The HDLC ___________ field defines the beginning and end of a frame.

► Flag

► Control

► FCS

Question No: 38      ( Marks: 1 ) - Please choose one

_________ is the access protocol used by traditional Ethernet.

► CSMA/CD

► CSMA/CA

► Token Ring

► CSMA

Question No: 39      ( Marks: 1 ) - Please choose one

Bridges can divide a large ________ into smaller segments

► Network

► Packet

► Frame

Question No: 40      ( Marks: 1 ) - Please choose one

Like VRC, LRC and CRC, Checksum is also based on _______________.

► Redundency

► Decimal Division

► Encryption

► Encoding

Question No: 41      ( Marks: 2 )

What are the conditions for the polynomial used by the CRC generator?

CRC generator:

CRC generator (the divisor) is most often represented not as a1’s and 0’s but as an algebraic polynomial.

conditions for the polynomial:

it should have following properties:

It should not be divisible by “x”.

It should not be divisible by “x+1”.

The first condition guarantees that all burst error of a length equal to degree of the polynomial is detected.

The 2nd condition guarantees that all burst error affecting an odd number of bits are detected.

Question No: 42      ( Marks: 2 )

What are intelligent modems?

Intelligent modems:

A modem that responds to commands and can accept new instructions during online transmission. It was originally developed by Hayes.

Example:

• Dialing etc.

Question No: 43      ( Marks: 2 )

What is the basic purpose of Router?

Basic purpose of Router:

"A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path. They connect networks together;

a LAN to a WAN for example, to access the Internet.
"A more precise definition of a router is a computer networking device that interconnects separate logical subnets."

Question No: 44      ( Marks: 3 )

What are the fractional T Lines?

The fractional T Lines:

Many subscribers don’t need the entire capacity of the T-line.

For example,

A small business may need only one-fourth of the capacity of T-line. if four business of same size lie in the same building, they can share  T-line.DSU/CSU allow the capacity of T-line to be interleaved in to four channels

Question No: 45      ( Marks: 3 )

What are the light sources used for optic fiber?

• light sources used for optic fiber:
• The light source can weather be an LED or ILD
• LED (Light emitting diode) cheaper but provide unfocused light that strikes the boundaries of channel at uncontrollable angles.
• Limited to short distance use.
• LASSER
• Can be focused to a narrow range allowing control over angle of incidence.

Question No: 46      ( Marks: 3 )

What is Multi Access Unit (MAU) in Token Ring?

Multi Access Unit (MAU) in Token Ring:

• Individual automatic switches are combined in to a hub
• One MAU can support up to 8 stations.
• Although it looks like a star, it is in fact a ring.

Question No: 47      ( Marks: 5 )

Give characteristics of Dual Ring, if necessary then draw the diagram. [5]

Characteristics of Dual Ring:

A network topology in which two concentric rings connect each node on a network instead of one network ring that is used in a ring topology. Typically, the secondary ring in a dual-ring topology is redundant. It is used as a backup in case the primary ring fails. In these configurations, data moves in opposite directions around the rings. Each ring is independent of the other until the primary ring fails and the two rings are connected to continue the flow of data traffic.

 Node

 Node

 Node

 Node

 Node

Question No: 48      ( Marks: 5 )

What the receiver will receive if the checksum method is applied to the following

bit.

10101001  00111001

Ans:

the receiver will receive the checksum method is applied to the following bit.

10101001  00111001

10101001  00111001

Sum of 2 bits are

10101001

00111001

-------------------

11100010

00011101       1's complement

1

--------------

00011110        2's complement

-----------

10101001      00111001    ==>  00011110

So the data transmitted which will receiver get:
10101001 00111001 00011110

Question No: 49      ( Marks: 5 )

What is rafraction in terms of optic fiber? Give one example.

Refraction:

Light travels in a straight line as long as it is moving through a single uniform structure If a ray of light traveling through one substance enters another (more or less dense) substance, its speed changes abruptly causing the ray to change direction. This phenomenon is called Refraction.

Refraction in terms of optic fiber:

the propagation of light in an optical fiber which in its simplest form consists of a circular core of uniform refractive index surrounded by a cladding of slightly lower refractive index. The light is launched into the entrance face of the fiber.

The light is propagated by the total internal reflection at the interface between core and cladding. However the rays incident at angles larger than a certain angle, called the cut-off angle, suffer both refraction and reflection at the interface between the core and the cladding.

They, therefore, are not guided. Due to this the optical fiber has a numerical aperture. The numerical aperture is given by the square root of (n12-n22). Typical values of numerical aperture lie between 0.1 and 0.3.

The refractive indices of the core and the cladding are n1 and n 2 respectively. The fiber is normally in air (n0=1) but could also be in a medium of refractive index n0.

Question No: 50      ( Marks: 10 )

What are the asynchronous protocols in data link layer? Discuss in detail with examples.  [10 marks]

Asynchronous protocols in data link layer:

Asynchronous communication at the data link layer or higher protocol layers is known as statistical multiplexing or packet mode communication,

For example :

Asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets,

Async protocols in Data link layer is called statistical multiplexing. for example ATM cells.

The opposite is circuit switched communication, which provides constant bit rate, for example ISDN and SONET/SDH.

The packets may be encapsulated in a data frame, with a frame synchronization bit sequence indicating the start of the frame, and sometimes also a bit synchronization bit sequence, typically 01010101, for identification of the bit transition times. Note that at the physical layer, this is considered as synchronous serial communication.

Examples of packet mode data link protocols that can be/are transferred using synchronous serial communication are the

• HDLC,
• Ethernet,
• PPP and
• USB protocols.

question No: 1 ( Marks: 1 ) - Please choose one
Which is not an element of protocol
► semantics
► timing
communication service module

Question No: 2 ( Marks: 1 ) - Please choose one
Layers 5, 6 and 7 also called as network support layers.

► True
► False

Question No: 3 ( Marks: 1 ) - Please choose one
Fourier transform tells us that any digital signal can be decomposed into infinite number of periodic signals

True
► False

Question No: 4 ( Marks: 1 ) - Please choose one
Time domain plot show changes in signal phase with respect to time.

True
► False

Question No: 5 ( Marks: 1 ) - Please choose one
Analog to digital conversion is also termed as modulating an analog signal.

► True
False

Question No: 6 ( Marks: 1 ) - Please choose one
DC component is also termed as Direct current component or a component with non-zero frequency.

► False
True

Question No: 7 ( Marks: 1 ) - Please choose one
Manchester is a type of ____________encoding.

biphase
► polar
► biphase & polar
► none of the given

Question No: 8 ( Marks: 1 ) - Please choose one
The inversion of the level at 1 bit is called as __________

► NRZ-L
► NRZ-I
► RZ

Question No: 9 ( Marks: 1 ) - Please choose one
PCM is the first process of PAM.

► True
False

Question No: 10 ( Marks: 1 ) - Please choose one
In 4PSK each phase change represents ______bits.

► 3
► 6
2
► 4

Question No: 11 ( Marks: 1 ) - Please choose one
In RS 422 Balanced mode two lines carry ________ signals which are not identical to each other.

same
► different
► digital
► analog

Question No: 12 ( Marks: 1 ) - Please choose one
A ______________ converts an analog signal into a digital signal.

Demodulator
► Modulator
► Digital-to-analog converter

Question No: 13 ( Marks: 1 ) - Please choose one
Which of the following is an example of ITU-T modem standards:

► T-series
► X-series
► N-series
► V-series

Question No: 14 ( Marks: 1 ) - Please choose one

► 26.6 Kbps
33.6 Kbps
► 36.6 Kbps
► 46.6 Kbps

Question No: 15 ( Marks: 1 ) - Please choose one
Which of the following primarily uses guided media

► Cellular telephone system
Local telephone system
► Satellite communication

Question No: 16 ( Marks: 1 ) - Please choose one
When a beam of light travels through media of two different densities, if the angle of incidence is greater than the critical angle, ____________occurs.

Reflection
► Refraction
► Incidence
► Criticism

Question No: 17 ( Marks: 1 ) - Please choose one
When we talk about unguided media, usually we are referring to _________.

► Metallic wires
► Nonmetallic wires
The air
► Water

Question No: 18 ( Marks: 1 ) - Please choose one
Optical fibers are defined by the ratio of the ___________ of their core to the diameter of their cladding.

Diameter
► Length
► Width

Question No: 19 ( Marks: 1 ) - Please choose one
All of popular Fiber optic connectors are ___________ shaped.

► Conical
Barrel
► Circular
► Rectangular

Question No: 20 ( Marks: 1 ) - Please choose one
Radio wave transmission utilizes ___________ different types of propagation.

► Four
► Three
► Two
► Five

Question No: 21 ( Marks: 1 ) - Please choose one
dB is ____________ if a signal is amplified.

► Negative
► Positive
► Null
► Zero

Question No: 22 ( Marks: 1 ) - Please choose one
A prism can deflect the light depending upon the angle of ____________ and the frequency.

Deviation
► Incident
► Refraction
► Reflection

Question No: 23 ( Marks: 1 ) - Please choose one
Asynchronous TDM is efficient only when the size of the time slot is kept relatively _______________

Large
► Small
► Medium
► None of the given

Question No: 24 ( Marks: 1 ) - Please choose one
The local loop has ___________ cable that connects the subscriber telephone to the nearest end office.

► Twisted-pair
► Coaxial
► Fiber-optic
► None of the given

Question No: 25 ( Marks: 1 ) - Please choose one
Data from a computer are ____________; the local loop handles _________ signals.

► Analog; analog
► Analog; digital
► Digital; digital
Digital; analog

Question No: 26 ( Marks: 1 ) - Please choose one
Which error detection method uses ones complement arithmetic?

► Simple parity check
► Two-dimensional parity check
► CRC
► Checksum

Question No: 27 ( Marks: 1 ) - Please choose one
Flow control is needed to prevent ____________

► Bit errors
Overflow of the sender buffer
► Overflow of the receiver buffer
► Collision between sender and receiver

Question No: 28 ( Marks: 1 ) - Please choose one
____________ coordinates the amount of data that can be sent before receiving acknowledgment

flow control
► error control
► data control

Question No: 29 ( Marks: 1 ) - Please choose one
Error control is both error _________ and error ___________

detection; correction
► detection; deletion
► detection; avoidance
► detection; forwarding

Question No: 30 ( Marks: 1 ) - Please choose one
Addressing is not needed in _______________ configuration.

Point to Point
► Multipoint
► Point to point and multipoint

Question No: 31 ( Marks: 1 ) - Please choose one
In a Go-Back-N ARQ, if the window size is 63, what is the range of sequence number?

0 to 63
► 0 to 64
► 1 to 63
► 1 to 64

Question No: 32 ( Marks: 1 ) - Please choose one
A timer is set when ___________ is sent out.

► A data frame
An ACK
► A NAK

Question No: 33 ( Marks: 1 ) - Please choose one
Sliding window requires that data frames be transmitted _______________

Sequentially
► Frequently
► Synchronously
► Asynchronously

Question No: 34 ( Marks: 1 ) - Please choose one
In Y-MODEM Multiple files can be sent simultaneously

True
► False

Question No: 35 ( Marks: 1 ) - Please choose one
BLAST stands for :

► Blocked asynchronous transmission
► Blocked synchronous transmission
► Barrel asynchronous transmission
► Below asynchronous transmission

Question No: 36 ( Marks: 1 ) - Please choose one
HDLC is an acronym for ______________.

► High-duplex line communication
► Host double-level circuit

Question No: 37 ( Marks: 1 ) - Please choose one
The HDLC ___________ field defines the beginning and end of a frame.

Flag
► Control
► FCS

Question No: 38 ( Marks: 1 ) - Please choose one
_________ is the access protocol used by traditional Ethernet.

CSMA/CD
► CSMA/CA
► Token Ring
► CSMA

Question No: 39 ( Marks: 1 ) - Please choose one
Bridges can divide a large ________ into smaller segments

Network
► Packet
► Frame

Question No: 40 ( Marks: 1 ) - Please choose one
Like VRC, LRC and CRC, Checksum is also based on _______________.

Redundency
► Decimal Division
► Encryption
► Encoding

Question No: 41 ( Marks: 2 )
What are the conditions for the polynomial used by the CRC generator?

CRC generator:
CRC generator (the divisor) is most often represented not as a1’s and 0’s but as an algebraic polynomial.
conditions for the polynomial:
it should have following properties:
It should not be divisible by “x”.
It should not be divisible by “x+1”.
The first condition guarantees that all burst error of a length equal to degree of the polynomial is detected.
The 2nd condition guarantees that all burst error affecting an odd number of bits are detected.

Question No: 42 ( Marks: 2 )
What are intelligent modems?
Intelligent modems:

A modem that responds to commands and can accept new instructions during online transmission. It was originally developed by Hayes.
Example:
• Dialing etc.

Question No: 43 ( Marks: 2 )
What is the basic purpose of Router?

Basic purpose of Router:
"A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path. They connect networks together;
a LAN to a WAN for example, to access the Internet.
"A more precise definition of a router is a computer networking device that interconnects separate logical subnets."

Question No: 44 ( Marks: 3 )
What are the fractional T Lines?

The fractional T Lines:
Many subscribers don’t need the entire capacity of the T-line.
For example,
A small business may need only one-fourth of the capacity of T-line. if four business of same size lie in the same building, they can share T-line.DSU/CSU allow the capacity of T-line to be interleaved in to four channels

Question No: 45 ( Marks: 3 )
What are the light sources used for optic fiber?

• light sources used for optic fiber:
• The light source can weather be an LED or ILD
• LED (Light emitting diode) cheaper but provide unfocused light that strikes the boundaries of channel at uncontrollable angles.
• Limited to short distance use.
• LASSER
• Can be focused to a narrow range allowing control over angle of incidence.

Question No: 46 ( Marks: 3 )
What is Multi Access Unit (MAU) in Token Ring?
Multi Access Unit (MAU) in Token Ring:
• Individual automatic switches are combined in to a hub
• One MAU can support up to 8 stations.
• Although it looks like a star, it is in fact a ring.

Question No: 47 ( Marks: 5 )
Give characteristics of Dual Ring, if necessary then draw the diagram. [5]

Characteristics of Dual Ring:
A network topology in which two concentric rings connect each node on a network instead of one network ring that is used in a ring topology. Typically, the secondary ring in a dual-ring topology is redundant. It is used as a backup in case the primary ring fails. In these configurations, data moves in opposite directions around the rings. Each ring is independent of the other until the primary ring fails and the two rings are connected to continue the flow of data traffic.

Question No: 48 ( Marks: 5 )
What the receiver will receive if the checksum method is applied to the following
bit.
10101001 00111001

Ans:
the receiver will receive the checksum method is applied to the following bit.
10101001 00111001
10101001 00111001
Sum of 2 bits are
10101001
00111001
-------------------
11100010
00011101 1's complement
1
--------------
00011110 2's complement
-----------
10101001 00111001 ==> 00011110

So the data transmitted which will receiver get:
10101001 00111001 00011110

Question No: 49 ( Marks: 5 )
What is rafraction in terms of optic fiber? Give one example.

Refraction:
Light travels in a straight line as long as it is moving through a single uniform structure If a ray of light traveling through one substance enters another (more or less dense) substance, its speed changes abruptly causing the ray to change direction. This phenomenon is called Refraction.

Refraction in terms of optic fiber:

the propagation of light in an optical fiber which in its simplest form consists of a circular core of uniform refractive index surrounded by a cladding of slightly lower refractive index. The light is launched into the entrance face of the fiber.
The light is propagated by the total internal reflection at the interface between core and cladding. However the rays incident at angles larger than a certain angle, called the cut-off angle, suffer both refraction and reflection at the interface between the core and the cladding.
They, therefore, are not guided. Due to this the optical fiber has a numerical aperture. The numerical aperture is given by the square root of (n12-n22). Typical values of numerical aperture lie between 0.1 and 0.3.

The refractive indices of the core and the cladding are n1 and n 2 respectively. The fiber is normally in air (n0=1) but could also be in a medium of refractive index n0.

Question No: 50 ( Marks: 10 )
What are the asynchronous protocols in data link layer? Discuss in detail with examples. [10 marks]
Asynchronous protocols in data link layer:
Asynchronous communication at the data link layer or higher protocol layers is known as statistical multiplexing or packet mode communication,
For example :
Asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets,
Async protocols in Data link layer is called statistical multiplexing. for example ATM cells.
The opposite is circuit switched communication, which provides constant bit rate, for example ISDN and SONET/SDH.
The packets may be encapsulated in a data frame, with a frame synchronization bit sequence indicating the start of the frame, and sometimes also a bit synchronization bit sequence, typically 01010101, for identification of the bit transition times. Note that at the physical layer, this is considered as synchronous serial communication.
Examples of packet mode data link protocols that can be/are transferred using synchronous serial communication are the
• HDLC,
• Ethernet,
• PPP and
• USB protocols.

Question No: 1      ( Marks: 1 ) - Please choose one

An unauthorized user is a network ___________ issue.

► Performance

► Reliability

► Security

► All of the given

Question No: 2      ( Marks: 1 ) - Please choose one

Which is not an element of protocol

► semantics

► timing

► communication service module

Question No: 3      ( Marks: 1 ) - Please choose one

_______ is a multipoint topology.

► Ring

► Mesh

► Tree

► Bus

Question No: 4      ( Marks: 1 ) http://www.vustudents.net- Please choose one

Unidirectional traffic movement is overcome by dual ring technology.

► True

► False

Question No: 5      ( Marks: 1 ) - Please choose one

Physical layer define characteristics of interface between device and _________

► transmission medium

► another device

► another peer physical layer at other side

► modem

Question No: 6      ( Marks: 1 ) - Please choose one

________ layer deals with syntax and semantics of information exchange.

► presentation

► session

► application

► physical

Question No: 7      ( Marks: 1 ) - Please choose one

► application layer

► physical layer

► network layer

Question No: 8      ( Marks: 1 ) - Please choose one

Time domain plot show changes in signal phase with respect to time.

► True

► False

Question No: 9      ( Marks: 1 ) - Please choose one

In 8QAM each signal shift or one baud represents ______.

► 4 bits

► 2 bits

► 5 bits

► 3 bits

Question No: 10      ( Marks: 1 ) - Please choose one

Modulation of an analog signal can be accomplished through changing the ___________ of the carrier signal.

► amplitude

► frequency

► phase

► all of the given

Question No: 11      ( Marks: 1 ) - Please choose one

EIA 449 provides much better functionality than EIA ________

► 232

► 223

► 262

► 222

Question No: 12      ( Marks: 1 ) - Please choose one

Which of the following is an example of ITU-T modem standards:

► T-series

► X-series

► N-series

► V-series

Question No: 13      ( Marks: 1 ) - Please choose one

Traditional modems are wide spread now to a data rate of __________.

► 56 Kbps

► 72 Kbps

► 42 Kbps

► 96 Kbps

Question No: 14      ( Marks: 1 ) - Please choose one

In case of uploading at the switching station, data is converted to digital signal using ___________.

► TCP

► PCM

► ICP

► TDM

Question No: 15      ( Marks: 1 ) - Please choose one

The RG number gives us information about ________.

► Twisted pairs

► Coaxial cables

► Optical fibers

► all of the given

Question No: 16      ( Marks: 1 ) - Please choose one

The _________ is an association that sponsors the use of infrared waves.

► IrDA

► EIA

► FCC

► PUD

Question No: 17      ( Marks: 1 ) - Please choose one

Optical fibers are defined by the ratio of the ___________ of their core to the diameter of their cladding.

► Diameter

► Length

► Width

Question No: 18      ( Marks: 1 ) - Please choose one

The section of EM spectrum defined as Radio Communication is divided into _____ ranges called BANDS.

► 8

► 10

► 5

► 6

Question No: 19      ( Marks: 1 ) - Please choose one

Radio wave transmission utilizes ___________ different types of propagation.

► Four

► Three

► Two

► Five

Question No: 20      ( Marks: 1 ) - Please choose one

The VLF and LF bands use _________ propagation for communications.

► Ground

► Sky

► Line of sight

► Space

Question No: 21      ( Marks: 1 ) - Please choose one

In __________ propagation, low-frequency radio waves hug the earth.

► Ground

► Sky

► Line of Sight

► Space

Question No: 22      ( Marks: 1 ) - Please choose one

dB is ____________ if a signal is amplified.

► Negative

► Positive

► Null

► Zero

Question No: 23      ( Marks: 1 ) - Please choose one

Distortion occurs in a ___________ signal.

► Rectified

► Composite

► Amplified

► none of the given

Question No: 24      ( Marks: 1 ) - Please choose one

There are ________ basic categories of multiplexing.

► 3

► 4

► 2

► 5

Question No: 25      ( Marks: 1 ) - http://www.vustudents.net Please choose one

In bit ____________, MUX adds extra bits to a device.

► Stuffing

► Multiplication

► Exchanging

Question No: 26      ( Marks: 1 ) - Please choose one

The local loop has ___________ cable that connects the subscriber telephone to the nearest end office.

► Twisted-pair

► Coaxial

► Fiber-optic

► None of the given

Question No: 27      ( Marks: 1 ) - Please choose one

FTTC stands for _____________

► flexible to the curb

► fiber to the curb

► fiber to the cable

► fiber to the center

Question No: 28      ( Marks: 1 ) - Please choose one

If the ASCII character G is sent and the character D is received, what type of error is this?

► Single-bit

► Multiple-bit

► Burst

► Recoverable

Question No: 29      ( Marks: 1 ) - Please choose one

Which error detection method can detect a single-bit error?

► Simple parity check

► Two-dimensional parity check

► CRC

► All of the given

Question No: 30      ( Marks: 1 ) - Please choose one

Flow control is needed to prevent ____________

► Bit errors

► Overflow of the sender buffer

► Overflow of the receiver buffer

► Collision between sender and receiver

Question No: 31      ( Marks: 1 ) - Please choose one

In data link layer, communication requires at least ___________ devices working together

► 3

► 2

► 4

► 5

Question No: 32      ( Marks: 1 ) - Please choose one

Data link control is composed of ____________ important functions.

► 2

► 3

► 4

► 5

Question No: 33      ( Marks: 1 ) - Please choose one

____________ coordinates the amount of data that can be sent before receiving acknowledgment http://www.vustudents.net

► flow control

► error control

► data control

Question No: 34      ( Marks: 1 ) - Please choose one

Primary device uses ____________ to receive transmission from the secondary devices.

► ACK

► ENQ

► POLL

Question No: 35      ( Marks: 1 ) - Please choose one

In a Go-Back-N ARQ, if the window size is 63, what is the range of sequence number?

► 0 to 63

► 0 to 64

► 1 to 63

► 1 to 64

Question No: 36      ( Marks: 1 ) - Please choose one

Data link protocols can be divided into ______________ sub-groups.

► two

► three

► four

► five

Question No: 37      ( Marks: 1 ) - Please choose one

XMODEM is a ______________ protocol designed for telephone-line communication b/w PCs.

► file transfer

► hardware

► software

► application exchange

Question No: 38      ( Marks: 1 ) - Please choose one

YMODEM uses ITU-T CRC-_____  for Error Checking

► 16

► 32

► 8

► 4

Question No: 39      ( Marks: 1 ) - Please choose one

In Y-MODEM Multiple files can be sent simultaneously

► True

► False

Question No: 40      ( Marks: 1 ) - Please choose one

HDLC is an acronym for ______________.

► High-duplex line communication

► Host double-level circuit

Question No: 41      ( Marks: 1 ) - Please choose one

What is present in all HDLC control fields?

► P/F bit

► N(R)

► N(S)

► Code bits

Question No: 42      ( Marks: 1 ) - Please choose one

Which of the following sublyer, resolves the contention for the shared media

► MAC

► LLC

► Phyical

Question No: 43      ( Marks: 1 ) - Please choose one

Ethernet LANs can support data rates between _____________

► 1 and 100 Mbps

► 1 and 200 Mbps

► 1 and 500 Mbps

► 1 and 100 Gbps

Question No: 44      ( Marks: 1 ) - Please choose one

In FDDI, Token Passing is used as Access method.

► True

► False

Question No: 45      ( Marks: 1 ) - Please choose one

Bridges can divide a large ________ into smaller segments

► Network

► Packet

► Frame

Question No: 46      ( Marks: 1 ) - Please choose one

Like VRC, LRC and CRC, Checksum is also based on _______________.

► Redundency

► Decimal Division

► Encryption

► Encoding

Question No: 47      ( Marks: 1 ) - Please choose one

Check sum method is used for _______________ layers.

► Physical

► Application

► Transport

Question No: 48      ( Marks: 1 ) - Please choose one

Which of the following ___________ uses a series of filters to decompose multiplexed signal into its constituent signals.

► Bridge

► MUX

► DEMUX

► Switch

Question No: 49      ( Marks: 1 ) - Please choose one

We need ____________ to decompose a composite signal into its components.

► fourier transform

► nyquist theorem

► shannon capacity

Question No: 50      ( Marks: 1 ) - Please choose one

Data from computer is in ____________ form and the local loop handles _________ signals.

► Analog; analog

► Analog; digital

► Digital; digital

► Digital; analog

MC060400684

Q#1 what are the conditions for the polynomial used by the CRC generator? [2]

Q#2 writes down names of the control frames in XMODEM? [3]

Q#3 defines frequency Modulation? [3]

Q#4 what is ETX in data frames of data link layer? [3]

Q#5 what are three types of digital service? [3]

Q#6 what is selective Reject ARQ in slicing window? [5]

Q#7 Give methods of Analog to Analog conversion? [2]

Q#8 whether in Asynchronous or Synchronous TDM, addressing in used?

Q#9 what is the basic purpose of Router?

Q#10 what are the possible consequences of replacing a bridge with a routes?

### ________ ARQ, if a NAK is received, only the specific damaged or lost frame is retransmitted.   Select correct option:   Stop and Wait  Go-Back-N  Selective repeat           Stop-and-wait & Go-back-N

Why do we need Inverse Multiplexing? [5]

Data & Video can be broken into smaller portions using Inverse Multiplexing and TX. An inverse multiplexer (often abbreviated to "inverse mux" or "imux") allows a data stream to be broken into multiple lower data rate communication links. An inverse multiplexer differs from a demultiplexer in that each of the low rate links coming from it is related to the others and they all work together to carry their respective parts of the same higher rate data stream. By contrast, the output streams from a demultiplexer may be completely independent from each other and the demultiplexer does not have to understand them in any way.

This is the opposite of a multiplexer which creates one high speed link from multiple low speed ones.

It can lease a 1.544 Mbps line from a common carrier and only use it fully for

sometime

Or it can lease several separate channels of lower data rates

Voice can be sent over any of these channels

Question No: 58      ( Marks: 5 )

Describe method of checksum briefly?

The sender subdivides data units into equal segments of ‘n’ bits(16 bits).These segments are added together using one’s complement. The total (sum) is then complemented and appended to the end of the original data unit as redundancy bits called CHECKSUM. The extended data unit is transmitted across the network. The receiver subdivides data unit as above and adds all segments together and complement the result. If the intended data unit is intact, total value found by adding the data segments and the checksum field should be zero. If the result is not zero, the packet contains an error & the receiver rejects it

Question No: 59      ( Marks: 10 )

Explain Asynchronous Time Division Multiplexing in detail? Also discuss its advantages over synchronous TDM?

Asynchronous time-division multiplexing (ATDM) is a method of sending information that resembles normal TDM, except that time slots are allocated as needed dynamically rather than preassigned to specific transmitters. ATDM is more intelligent and has better bandwidth efficiency than TDM.

Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel. After the last sub-channel the cycle starts all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1, etc.

asynchronous time-division multiplexing comprising receive circuits (CRl/i) supplying cells received via input links, transmit circuits (CTl/j) transmitting retransmitted cells on output links, a buffer memory (MT) storing the received cells and delivering the cells to be retransmitted and a buffer memory addressing device (SMT) including a write address source (SAE) and a read address source (fsl/j).

The switching unit further comprises a write disabling circuit (pi) conditioned by a signal (adl) derived from the content of at least one received cell or a signal (tle) derived from the absence of any received cell and supplying a disabling signal (spi) and the address source includes a disabling device (pac, pal) influenced by the disabling signal (spi) so that no memory location is then occupied in the buffer memory (MT).

In asynchronous TDM, the timeslots are not fixed. They are assigned dynamically as needed.

In order to reduce the communications costs in time-sharing systems and multicomputer communication systems, multiplexing techniques have been introduced to increase channel utilization. A commonly used technique is Synchronous Time Division Multiplexing (STDM). In Synchronous Time Division Multiplexing, for example, consider the transmission of messages from terminals to computer, each terminal is assigned a fixed time duration. After one user's time duration has elapsed, the channel is switched to another user. With synchronous operation, buffering is limited to one character per user line, and addressing is usually not required. The STDM technique, however, has certain disadvantages. As shown in Figure 1, it is inefficient in capacity and cost to permanently assign a segment of bandwidth that is utilized only for a portion of the time. A more flexible system that efficiently uses the transmission facility on an "instantaneous time-shared" basis could be used instead. The objective would be to switch from one user to another user whenever the one user is idle, and to asynchronously time multiplex the data. With such an arrangement, each user would be granted access to the channel only when he has a message to transmit. This is known as an Asynchronous Time Division Multiplexing System (ATDM). A segment of a typical ATDM data stream is shown in Figure 2. The crucial attributes of such a multiplexing technique are:

1. An address is required for each transmitted message, and

2. Buffering is required to handle the random message arrivals.

Question No: 1      ( Marks: 1 ) - Please choose one

An unauthorized user is a network ___________ issue.

► Performance

► Reliability

► Security

► All of the given

Question No: 2      ( Marks: 1 ) - Please choose one

Which is not an element of protocol

► semantics

► timing

► communication service module

Question No: 3      ( Marks: 1 ) - Please choose one

_______ is a multipoint topology.

► Ring

► Mesh

► Tree

► Bus

Question No: 4      ( Marks: 1 ) - Please choose one

Unidirectional traffic movement is overcome by dual ring technology.

► True

► False

Question No: 5      ( Marks: 1 ) - Please choose one

Physical layer define characteristics of interface between device and _________

► transmission medium

► another device

► another peer physical layer at other side

► modem

Question No: 6      ( Marks: 1 ) - Please choose one

________ layer deals with syntax and semantics of information exchange.

► presentation

► session

► application

► physical

Question No: 7      ( Marks: 1 ) - Please choose one

► application layer

► physical layer

► network layer

Question No: 8      ( Marks: 1 ) - Please choose one

Time domain plot show changes in signal phase with respect to time.

► True

► False

Question No: 9      ( Marks: 1 ) - Please choose one

In 8QAM each signal shift or one baud represents ______.

► 4 bits

► 2 bits

► 5 bits

► 3 bits

Question No: 10      ( Marks: 1 ) - Please choose one

Modulation of an analog signal can be accomplished through changing the ___________ of the carrier signal.

► amplitude

► frequency

► phase

► all of the given

Question No: 11      ( Marks: 1 ) - Please choose one

EIA 449 provides much better functionality than EIA ________

► 232

► 223

► 262

► 222

Question No: 12      ( Marks: 1 ) - Please choose one

Which of the following is an example of ITU-T modem standards:

► T-series

► X-series

► N-series

► V-series

Question No: 13      ( Marks: 1 ) - Please choose one

Traditional modems are wide spread now to a data rate of __________.

► 56 Kbps

► 72 Kbps

► 42 Kbps

► 96 Kbps

Question No: 14      ( Marks: 1 ) - Please choose one

In case of uploading at the switching station, data is converted to digital signal using ___________.

► TCP

► PCM

► ICP

► TDM

Question No: 15      ( Marks: 1 ) - Please choose one

The RG number gives us information about ________.

► Twisted pairs

► Coaxial cables

► Optical fibers

► all of the given

Question No: 16      ( Marks: 1 ) - Please choose one

The _________ is an association that sponsors the use of infrared waves.

► IrDA

► EIA

► FCC

► PUD

Question No: 17      ( Marks: 1 ) - Please choose one

Optical fibers are defined by the ratio of the ___________ of their core to the diameter of their cladding.

► Diameter

► Length

► Width

Question No: 18      ( Marks: 1 ) - Please choose one

The section of EM spectrum defined as Radio Communication is divided into _____ ranges called BANDS.

► 8

► 10

► 5

► 6

Question No: 19      ( Marks: 1 ) - Please choose one

Radio wave transmission utilizes ___________ different types of propagation.

► Four

► Three

► Two

► Five

Question No: 20      ( Marks: 1 ) - Please choose one

The VLF and LF bands use _________ propagation for communications.

► Ground

► Sky

► Line of sight

► Space

Question No: 21      ( Marks: 1 ) - Please choose one

In __________ propagation, low-frequency radio waves hug the earth.

► Ground

► Sky

► Line of Sight

► Space

Question No: 22      ( Marks: 1 ) - Please choose one

dB is ____________ if a signal is amplified.

► Negative

► Positive

► Null

► Zero

Question No: 23      ( Marks: 1 ) - Please choose one

Distortion occurs in a ___________ signal.

► Rectified

► Composite

► Amplified

► none of the given

Question No: 24      ( Marks: 1 ) http://www.vustudents.net- Please choose one

There are ________ basic categories of multiplexing.

► 3

► 4

► 2

► 5

Question No: 25      ( Marks: 1 ) - Please choose one

In bit ____________, MUX adds extra bits to a device.

► Stuffing

► Multiplication

► Exchanging

Question No: 26      ( Marks: 1 ) - Please choose one

The local loop has ___________ cable that connects the subscriber telephone to the nearest end office.

► Twisted-pair

► Coaxial

► Fiber-optic

► None of the given

Question No: 27      ( Marks: 1 ) - Please choose one

FTTC stands for _____________

► flexible to the curb

► fiber to the curb

► fiber to the cable

► fiber to the center

Question No: 28      ( Marks: 1 ) - Please choose one

If the ASCII character G is sent and the character D is received, what type of error is this?

► Single-bit

► Multiple-bit

► Burst

► Recoverable

Question No: 29      ( Marks: 1 ) - Please choose one

Which error detection method can detect a single-bit error?

► Simple parity check

► Two-dimensional parity check

► CRC

► All of the given

Question No: 30      ( Marks: 1 ) - Please choose one

Flow control is needed to prevent ____________ http://www.vustudents.net

► Bit errors

► Overflow of the sender buffer

► Overflow of the receiver buffer

► Collision between sender and receiver

Question No: 31      ( Marks: 1 ) - Please choose one

In data link layer, communication requires at least ___________ devices working together

► 3

► 2

► 4

► 5

Question No: 32      ( Marks: 1 ) - Please choose one

Data link control is composed of ____________ important functions.

► 2

► 3

► 4

► 5

Question No: 33      ( Marks: 1 ) - Please choose one

____________ coordinates the amount of data that can be sent before receiving acknowledgment

► flow control

► error control

► data control

Question No: 34      ( Marks: 1 ) - Please choose one

Primary device uses ____________ to receive transmission from the secondary devices.

► ACK

► ENQ

► POLL

Question No: 35      ( Marks: 1 ) - Please choose one

In a Go-Back-N ARQ, if the window size is 63, what is the range of sequence number?

► 0 to 63

► 0 to 64

► 1 to 63

► 1 to 64

Question No: 36      ( Marks: 1 ) - Please choose one

Data link protocols can be divided into ______________ sub-groups.

► two

► three

► four

► five

Question No: 37      ( Marks: 1 ) - Please choose one

XMODEM is a ______________ protocol designed for telephone-line communication b/w PCs.

► file transfer

► hardware

► software

► application exchange

Question No: 38      ( Marks: 1 ) - Please choose one

YMODEM uses ITU-T CRC-_____  for Error Checking

► 16

► 32

► 8

► 4

Question No: 39      ( Marks: 1 ) - Please choose one

In Y-MODEM Multiple files can be sent simultaneously

► True

► False

Question No: 40      ( Marks: 1 ) - Please choose one

HDLC is an acronym for ______________.

► High-duplex line communication

► Host double-level circuit

Question No: 41      ( Marks: 1 ) - Please choose one

What is present in all HDLC control fields?

► P/F bit

► N(R)

► N(S)

► Code bits

Question No: 42      ( Marks: 1 ) - Please choose one

Which of the following sublyer, resolves the contention for the shared media

► MAC

► LLC

► Phyical

Question No: 43      ( Marks: 1 ) - Please choose one

Ethernet LANs can support data rates between _____________

► 1 and 100 Mbps

► 1 and 200 Mbps

► 1 and 500 Mbps

► 1 and 100 Gbps

Question No: 44      ( Marks: 1 ) - Please choose one

In FDDI, Token Passing is used as Access method.

► True

► False

Question No: 45      ( Marks: 1 ) - Please choose one

Bridges can divide a large ________ into smaller segments

► Network

► Packet

► Frame

Question No: 46      ( Marks: 1 ) - Please choose one

Like VRC, LRC and CRC, Checksum is also based on _______________.

► Redundency

► Decimal Division

► Encryption

► Encoding

Question No: 47      ( Marks: 1 ) - Please choose one

Check sum method is used for _______________ layers.

► Physical

► Application

► Transport

Question No: 48      ( Marks: 1 ) - Please choose one

Which of the following ___________ uses a series of filters to decompose multiplexed signal into its constituent signals.

► Bridge

► MUX

► DEMUX

► Switch

Question No: 49      ( Marks: 1 ) - Please choose one

We need ____________ to decompose a composite signal into its components.

► fourier transform

► nyquist theorem

► shannon capacity

Question No: 50      ( Marks: 1 ) - Please choose one

Data from computer is in ____________ form and the local loop handles _________ signals.

► Analog; analog

► Analog; digital

► Digital; digital

► Digital; analog

Question No: 51      ( Marks: 2 )

What is the formula to calculate the number of redundancy bits required to correct a bit error in a given number of data bits? [2]

Messages(frames) consist of m data (message) bits, yielding an n=(m+r)-bit codeword.

Question No: 52      ( Marks: 2 )

What is R G rating of coaxial cable?

Different coaxial cable designs are categorized by their Radio government (

RG ) ratings

Each cable defined by RG rating is adapted for a specialized function:

RG-8

• Used in Thick Ethernet

RG-9

• Used in Thick Ethernet

RG-11

• Used in Thick Ethernet

RG-58

• Used in Thin Ethernet

RG-59

• Used for TV

Question No: 53      ( Marks: 2 )

What are the advantages of thin ethernet?

The advantages of thin Ethernet are :

• reduced cost and
• ease of installation

Because the cable is lighter weight and more flexible than that used in Thicknet

Question No: 54      ( Marks: 3 )

What is the difference between a unicast, multicast, and broadcast address? [3]

Three methods can be used to transmit packets over a network: unicast, multicast, and broadcast.

Unicast involves communication between a single sender and a single receiver. This is a type of point-to-point transmission; since the packet is transmitted to one destination at a time.

Multicast is used to send packets to a group of addresses, represented by a "group address." In this case, packets are transmitted from a single sender to multiple receivers. Since the same data packet can be sent to multiple nodes by sending just one copy of the data, the load of the sender and the overall load of the network are both reduced.

Broadcast involves sending packets to all nodes on a network simultaneously. This type of transmission is used to establish communication with another host, and for DHCP type methods of assigning IP addresses.

Question No: 55      ( Marks: 3 )

T lines are designed for Digital data how they can be used for Analog Transmission ?

T Lines are digital lines designed for digital data however; they can also be used for analog transmission (Telephone connections). Analog signals are first sampled and the Time Multiplexed.

Question No: 56      ( Marks: 3 )

What are the three types of Guided Media?

Guided Media, are those media that provide a conduit from one device to another. Three types are

1. Twisted pair cable
2. Coaxial cable
3. Fiber-optic Cable

Question No: 57      ( Marks: 5 )

Why do we need Inverse Multiplexing? [5]

Data & Video can be broken into smaller portions using Inverse Multiplexing and TX. An inverse multiplexer (often abbreviated to "inverse mux" or "imux") allows a data stream to be broken into multiple lower data rate communication links. An inverse multiplexer differs from a demultiplexer in that each of the low rate links coming from it is related to the others and they all work together to carry their respective parts of the same higher rate data stream. By contrast, the output streams from a demultiplexer may be completely independent from each other and the demultiplexer does not have to understand them in any way.

This is the opposite of a multiplexer which creates one high speed link from multiple low speed ones.

It can lease a 1.544 Mbps line from a common carrier and only use it fully for

sometime

Or it can lease several separate channels of lower data rates

Voice can be sent over any of these channels

Question No: 58      ( Marks: 5 )

Describe method of checksum briefly?

The sender subdivides data units into equal segments of ‘n’ bits(16 bits).These segments are added together using one’s complement. The total (sum) is then complemented and appended to the end of the original data unit as redundancy bits called CHECKSUM. The extended data unit is transmitted across the network. The receiver subdivides data unit as above and adds all segments together and complement the result. If the intended data unit is intact, total value found by adding the data segments and the checksum field should be zero. If the result is not zero, the packet contains an error & the receiver rejects it

Question No: 59      ( Marks: 10 )

Explain Asynchronous Time Division Multiplexing in detail? Also discuss its advantages over synchronous TDM?

Asynchronous time-division multiplexing (ATDM) is a method of sending information that resembles normal TDM, except that time slots are allocated as needed dynamically rather than preassigned to specific transmitters. ATDM is more intelligent and has better bandwidth efficiency than TDM.

Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel. After the last sub-channel the cycle starts all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1, etc.

asynchronous time-division multiplexing comprising receive circuits (CRl/i) supplying cells received via input links, transmit circuits (CTl/j) transmitting retransmitted cells on output links, a buffer memory (MT) storing the received cells and delivering the cells to be retransmitted and a buffer memory addressing device (SMT) including a write address source (SAE) and a read address source (fsl/j).

The switching unit further comprises a write disabling circuit (pi) conditioned by a signal (adl) derived from the content of at least one received cell or a signal (tle) derived from the absence of any received cell and supplying a disabling signal (spi) and the address source includes a disabling device (pac, pal) influenced by the disabling signal (spi) so that no memory location is then occupied in the buffer memory (MT).

In asynchronous TDM, the timeslots are not fixed. They are assigned dynamically as needed.

In order to reduce the communications costs in time-sharing systems and multicomputer communication systems, multiplexing techniques have been introduced to increase channel utilization. A commonly used technique is Synchronous Time Division Multiplexing (STDM). In Synchronous Time Division Multiplexing, for example, consider the transmission of messages from terminals to computer, each terminal is assigned a fixed time duration. After one user's time duration has elapsed, the channel is switched to another user. With synchronous operation, buffering is limited to one character per user line, and addressing is usually not required. The STDM technique, however, has certain disadvantages. As shown in Figure 1, it is inefficient in capacity and cost to permanently assign a segment of bandwidth that is utilized only for a portion of the time. A more flexible system that efficiently uses the transmission facility on an "instantaneous time-shared" basis could be used instead. The objective would be to switch from one user to another user whenever the one user is idle, and to asynchronously time multiplex the data. With such an arrangement, each user would be granted access to the channel only when he has a message to transmit. This is known as an Asynchronous Time Division Multiplexing System (ATDM). A segment of a typical ATDM data stream is shown in Figure 2. The crucial attributes of such a multiplexing technique are:

1. An address is required for each transmitted message, and

2. Buffering is required to handle the random message arrivals.

Question No: 1      ( Marks: 1 ) - Please choose one

__________representation of links that connect nodes is called as physical topology.

► geometrical

► logical

► physical

Question No: 2      ( Marks: 1 ) - Please choose one

The internet model consists of _________ layers.

► three

► two

► five

► seven

Question No: 3      ( Marks: 1 ) - Please choose one

Encryption and encoding are the same terms.

► True

► False

Question No: 4      ( Marks: 1 ) - Please choose one

The amplitude of a digital signal depends upon the________ to represent a bit.

► phase

► voltage

► wavelength

Question No: 5      ( Marks: 1 ) - Please choose one

The inversion of the level at 1 bit is called as __________

► NRZ-L

► NRZ-I

► RZ

Question No: 6      ( Marks: 1 ) http://www.vustudents.net- Please choose one

Modulation of an analog signal can be accomplished through changing the ___________ of the carrier signal.

► amplitude

► frequency

► phase

► all of the given

Question No: 7      ( Marks: 1 ) - Please choose one

If FCC regulations are followed, the carrier frequencies of adjacent AM radio stations are ____________ apart.

► 5 KHz

► 10 KHz

► 200 KHz

► 530 KHz

Question No: 8      ( Marks: 1 ) - Please choose one

Category 5 UTP cable is used for data transmission of upto__________.

► 100 Mbps

► 200 Mbps

► 250 Mbps

► 400 Mbps

Question No: 9      ( Marks: 1 ) - Please choose one

The RG number gives us information about ________.

► Twisted pairs

► Coaxial cables

► Optical fibers

► all of the given

Question No: 10      ( Marks: 1 ) - Please choose one

The inner core of an optical fiber is __________ in composition.

► Glass plastic

► Copper

► Bimetallic

► Liquid

Question No: 11      ( Marks: 1 ) - Please choose one

All of popular Fiber optic connectors are ___________ shaped.

► Conical

► Barrel

► Circular

► Rectangular

Question No: 12      ( Marks: 1 ) - Please choose one

The VLF and LF bands use _________ propagation for communications.

► Ground

► Sky

► Line of sight

► Space

Question No: 13      ( Marks: 1 ) - Please choose one

Multiplexing is the set of techniques that allows simultaneous TX of multiple signals across  ___________ data link

► Single

► Multi

► Single and Multi

► none of the given

Question No: 14      ( Marks: 1 ) - Please choose one

A portion of the path that carries TX b/w a given pair of devices is known as __________.

► Node

► Bridge

► Channel

► Gateway

Question No: 15      ( Marks: 1 ) - Please choose one

Which error detection method involves polynomials?

► Checksum

► Two-dimensional parity check

► CRC

► Simple parity check

Question No: 16      ( Marks: 1 ) - Please choose one

If the ASCII character G is sent and the character D is received, what type of error is this?

► Single-bit

► Multiple-bit

► Burst

► Recoverable

Question No: 17      ( Marks: 1 ) - Please choose one

Which error detection method involves the use of parity bits?

► Simple parity check & two dimensional parity check

► CRC

► Two-dimensional parity check

► Simple parity check

Question No: 18      ( Marks: 1 ) - Please choose one

Which error detection method can detect a single-bit error?

► Simple parity check

► Two-dimensional parity check

► CRC

► All of the given

Question No: 19      ( Marks: 1 ) - Please choose one

The Hamming code is a method of __________

► Error detection

► Error correction

► Error ecapsulation

► Error detection & Error encapsulation

Question No: 20      ( Marks: 1 ) - Please choose one

Sliding window requires that data frames be transmitted _______________

► Sequentially

► Frequently

► Synchronously

► Asynchronously

Question No: 21      ( Marks: 1 ) - Please choose one

In selective-reject ARQ, only the specific damaged or lost frame is_____________.

► Retransmitted

► Forwarded

► Selected

► Rejected

Question No: 22      ( Marks: 1 ) - Please choose one

Which of the following sublyer, resolves the contention for the shared media

► MAC

► LLC

► Physical

Question No: 23      ( Marks: 1 ) - Please choose one

The PDU  has no flag fields, no CRC, and no station address

► TRUE

► FALSE

Question No: 24      ( Marks: 1 ) - Please choose one

IEEE divides the base band category into  ______ standards.

► 5

► 4

► 3

► 6

Question No: 25      ( Marks: 1 ) - Please choose one

Like 10 Base 5, 10 Base 2 is a _________ topology LAN

► Ring

► Mesh

► Star

► Bus

Question No: 26      ( Marks: 1 ) - Please choose one

Check sum method is used for _______________ layers.

► Physical

► Application

► Transport

Question No: 27      ( Marks: 1 ) - Please choose one

Repeater works on __________     layer.

► Physical

► Network

► Application

Question No: 28      ( Marks: 1 ) - Please choose one

Trunks are transmission media such as _________ that handle the telephone to the nearest end office.

► Twisted-pair & Fiber-optic

► Twisted-pair

► Fiber-optic

Question No: 29      ( Marks: 1 ) - Please choose one

Which of the following ___________ uses a series of filters to decompose multiplexed signal into its constituent signals.

► MUX

► DEMUX

► Switch

► Bridge

Question No: 30      ( Marks: 1 ) - Please choose one

In Fast Ethernet, data rate can be increased by _______________ collisions.

► Increasing

► Decreasing

► Keeping Constant

► None of the given

Question No: 31      ( Marks: 2 )

What are the advantages of a multipoint connection over a point-to-point connection?

Point-to-point connection is limited to two devices, where else more than two devices share a single link in multipoint connection. Multipoint connection can be used for fail-over and reliability.

Question No: 32      ( Marks: 2 )

What's the name of the telephone service in which there is no need of dialing.

DSS (digital data service)   is the telephone service in which there is no need of dialing.

Question No: 33      ( Marks: 2 )

Which type of frames are present in BSC frames?

There are two types of frames that are present in BSC.

1. 1.      Control Frames and
2. 2.      Data Frames

Question No: 34      ( Marks: 2 )

What methods of line discipline are used for peer to peer and  primary secondary communication?

Line discipline is done in two ways:

1. ENQ/ACK      (Enquiry Acknowledgement)

This is used for peer to peer communication.

1. Poll/ Select

This method is used for primary secondary communication.

Question No: 35      ( Marks: 3 )

How does the checksum checker know that the received data unit is undamaged? [3]

Checksum Checker or generator:

The sender subdivides data units into equal segments of ‘n’ bits(16 bits)

1. These segments are added together using one’s complement.
2. The total (sum) is then complemented and appended to the end of the original data unit as redundancy bits called CHECKSUM.
3. The extended data unit is transmitted across the network.
4. The receiver subdivides data unit and adds all segments together and complement the result.
5. If the intended data unit is intact, total value found by adding the data segments and the checksum field should be zero.
6. 6.      If the result is not zero, the packet contains an error & the receiver rejects it.

Question No: 36      ( Marks: 3 )

A bridge has more overhead than a repeater. A bridge processes the packet at two

layers ; a repeater processes a frame at only one layer. A bridge needs to search a

table and find the forwarding port as well as to regenerate the signal; a repeater

only regenerates the signal. In other words, a bridge is also a repeater (and more); a

repeater is not a bridge.

Question No: 37      ( Marks: 3 )

Write down disadvantages of Ring Topology.

Unidirectional Traffic

A break in a ring that is a disabled station can disable the entire network

Can be solved by using:

Dual Ring or

A switch capable of closing off the Break

Question No: 38      ( Marks: 3 )

How parity bits are counted in VRC error detection method technique in case of odd parity generator?

For example:

We want to TX the binary data unit 1100001

Adding together the number of 1’s gives us 3, an odd number

Before TX, we pass the data unit through a parity generator, which counts the 1’s and appends the parity bit (1) to the end

The total number of 1’s is now 4, an even number

The system now transfers the entire expanded across the network link

When it reaches its destination, the RX puts all 8 bits through an even parity checking function

If the RX sees 11100001, it counts four ones, an even number and the data unit passes

When the parity checker counts the 1’s, it gets 5 an odd number

The receiver knows that an error has occurred somewhere and therefore rejects the whole unit

Some systems may also use ODD parity checking

The principal is the same as even parity

Question No: 39      ( Marks: 5 )

How are lost acknowledgment and a lost frame handled at the sender site? [5]

At some error rates (16%-20%) the protocol hung up in an infinite loop, while it worked fine for other error rates. On examining the code it was determined that this problem resulted from improper variable initialization. On these certain error rates the pseudo-random number generator caused the very first frame sent to be lost or damaged. The receiver used a variable to keep track of the last in sequence frame received. This was erroneously initialized to 0. Therefore if the first frame got lost (sequence no 0), when the receiver received the second frame (sequence number 1) it sent an acknowledgment for the last in sequence frame  received, which had been initialized to 0. Therefore the sender received an acknowledgement for sequence number 0 and moved its window up accordingly. It caused everything to get out of synch, and caused the protocol to go into infinite loop.  This was resolved by initializing the variable to remember the last in sequence frame received to an out of range sequence number.

Question No: 40      ( Marks: 5 )

Explain Protocol Data Unit (PDU)?

Protocol data unit (PDU) is an OSI term that refers generically to a group of information added or removed by a particular layer of the OSI model. In specific terms, an LxPDU implies the data and headers defined by layer x. Each layer uses the PDU to communicate and exchange information. The PDU information is only read by the peer layer on the receiving device and then stripped off, and data is handed over to the next upper layer.

Ppr Cs601

2010

Shifa Zahra

Question#1

What are the Asynchronous protocols in data communication layer? ………….Marks (10)

Question#2

What is Frequencly division multiplexing ?.......Marks (5)

Question#3

Find the binary equivalent  ………….Marks (5)

Question#4

What is stop and wait ARQ in error control ?....Marks (3)

Question#5

What is Interleaving ?........Marks (3)

Question#6

What is DSU in terms of digital services?.........Marks (3)

Question#7

Which architecture of Ethernet developed by ITU_T and

ANSI?........... Marks (2)

Question#8

What is a spike in noise term?.........Marks (2)

Question#9

What is even parity generator in  VRC error detection mechanism?...........Marks (2)

1

2

3

4

5

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