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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.

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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

 

       ► Datalink



 

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

 

 

Repeater works on __________     layer.

 

       ► Data Link

 

       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.

 

       ► Satellite links

 

       ► 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?

Answer:

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.

 

Answer:

 

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?

 

Answer:

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?

Answer:

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]

 

Answer:

 

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 )

 

 

Which one has more overhead, a repeater or a bridge? Explain your answer. [3]

 

Answer:

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.

 

Answer:

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?

 

Answer:

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]

 

Answer:

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)?

 

 

Answer:

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.

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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

 

 

The maximum data rate in the uploading direction is still ____________.

 

 

       ► 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

 

       ► Radio broadcasting



 

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

 

       ► Radius

 

       ► 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

 

       ► High-level data link control

 

       ► Half-duplex digital link combination

 

       ► Host double-level circuit



 

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

 

 

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

 

 

       ► Flag

 

       ► Address

 

       ► 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

 

       ► Address



 

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:

  • Automatic answering,
  • 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
The maximum data rate in the uploading direction is still ____________.


► 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
► Radio broadcasting



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
► Radius
► 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
 High-level data link control
► Half-duplex digital link combination
► Host double-level circuit



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


 Flag
► Address
► 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
► Address



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:
• Automatic answering,
• 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

 

 

To allow access to network resources is the function of ___________

 

       ► 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

 

       ► Radius

 

       ► 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

 

       ► Adding

 

       ► 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

 

       ► High-level data link control

 

       ► Half-duplex digital link combination

 

       ► 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

 

       ► Address



 

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

 

       ► Datalink



 

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? 

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

Single Bit

Multiple Bit 

Burst

Recoverable

 

The number of bit positions in which two code words differ is called

Checksum distance

Hamming Distance

CRC distance

Parity distance

 

Which error detection method cannot detect a burst error?

VRC

LRC

CRC

Hamming Code


If odd parity is used for ASCII error detection, the number of 0's per 8 - bit symbol is

Even

ODD

Indeterminate

42

 

If the data unit is 111111,the divisor 1010,what is the dividend a the transmitter?

111111000

1111110000

111111 

1111111010

 

If the data unit is 111111, the divisor 1010, and the reminder 110, what is the dividend at the receiver?

111111011

11111110

1010110

110111111

 

If source machine sends independent frames to destination machine without having acknowledgment, this service is _ _ _ _ _ _ _

Unacknowledged connection oriented   

Unacknowledged connection less

Acknowledged connection oriented 

Acknowledged connection less

 

A path which connects DLL and Network layer on source to DLL and Network layer on the destination is _ _ _ _ _ _ _ _ _ _ path

Actual

Critical

Vertical Virtual

 

When the receiver sees five consecutive incoming '1' bits followed by a '0' bit it automatically dyestuffs _ _ _ _ _ _ _ _ _ in bit stuffing

'1' bit 

'0' bit

'01' bit

'10' bit   

 

In the data link layer, each frame begins and ends with a special bit pattern _ _ _ _ _ _ _ _, called a flag byte

01110110

01111110

01011010

10101010

 

The data link layer must use the service provided to it by the _ _ _ _ _ _ _ _ layer

Data Link

Physical

Transport

Session

 

 

 

 

 

 

Each frame begins and ends with a special bit pattern called _ _ _ _ _

Char Stuffing

Flag

Bit Stuffing

Char Count

 

 

Unacknowledged connection less service is adopted when _ _ _ _

Error is very low   

Error rate is very high

Long length is required

Error rate is very high

 

____ Technique requires more redundancy bits.
Select correct option:

Error detection
Error correction
Both of the given
None of the given

 

Error control in the data link layer is based on _______________.
Select correct option:

automatic repeat request
automatic repeat acknowledgment
automatic send acknowledgment
automatic send request

 

Question # 5 of 10 ( Start time: 11:27:46 PM )  Total Marks: 1  
CRC must have ____ qualities to be valid.  
Select correct option:  




Which error detection method involves polynomials?
Select correct option:

Simple parity check
Two-dimensional parity check
CRC
Checksum

 

In Go-Back-N ARQ, if frames 4, 5 and 6 are received successfully, the receiver may send an ACK _________ to the sender.  
Select correct option:  




Any of the given 

 

VRC and LRC are based on?
Select correct option:
Addition
Multiplication
Subtraction
Division

 

If the primary wants to receive data, it asks the second-arise if they have anything to send, this is called  
Select correct option:  

POLLING 
SELECTING 

 

 

________ 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).

 

Advantages asynchronous TDM:

 

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

 

 

To allow access to network resources is the function of ___________

 

       ► 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

 

       ► Radius

 

       ► 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

 

       ► Adding

 

       ► 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

 

       ► High-level data link control

 

       ► Half-duplex digital link combination

 

       ► 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

 

       ► Address



 

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

 

       ► Datalink



 

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).

 

Advantages asynchronous TDM:

 

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

 

       ► Datalink



 

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

 

 

Repeater works on __________     layer.

 

       ► Data Link

 

       ► 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.

 

       ► Satellite links

 

       ► 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?

Answer:

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.

 

Answer:

 

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?

 

Answer:

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?

Answer:

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]

 

Answer:

 

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 )

 

 

Which one has more overhead, a repeater or a bridge? Explain your answer. [3]

 

Answer:

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.

 

Answer:

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?

 

Answer:

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]

 

Answer:

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)?

 

 

Answer:

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)

 

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