NETWORKING Interview Question ANSWERS 2

NETWORKING Interview Question ANSWERS 2

41. What are the categories of Transmission media?

a. Guided Media

i. Twisted - Pair cable

1. Shielded TP

2. Unshielded TP

ii. Coaxial Cable

iii. Fiber-optic cable

b. Unguided Media

i. Terrestrial microwave

ii. Satellite Communication

42. What are the types of errors?

a. Single-Bit error

In a single-bit error, only one bit in the data unit has changed

b. Burst Error

A Burst error means that two or more bits in the data have changed.

43. What is Error Detection? What are its methods?

Data can be corrupted during transmission. For reliable communication errors must be deducted and

Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for

detecting errors at the destination. The common Error Detection methods are

a. Vertical Redundancy Check (VRC)

b. Longitudinal Redundancy Check (VRC)

c. Cyclic Redundancy Check (VRC)

d. Checksum

44. What is Redundancy?

The concept of including extra information in the transmission solely for the purpose of comparison.

This technique is called redundancy.

45. What is VRC?

It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is

added to every data unit so that the total number of 1s becomes even for even parity. It can detect all

single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.

46. What is LRC?

In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It

can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions

in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant

data unit follows n data units.

47. What is CRC?

CRC, is the most powerful of the redundancy checking techniques, is based on binary division.

48. What is Checksum?

Checksum is used by the higher layer protocols (TCP/IP) for error detection

49. List the steps involved in creating the checksum.

a. Divide the data into sections

b. Add the sections together using 1's complement arithmetic

c. Take the complement of the final sum, this is the checksum.

50. What are the Data link protocols?

Data link protocols are sets of specifications used to implement the data link layer. The categories of

Data Link protocols are 1. Asynchronous Protocols

2. Synchronous Protocols

a. Character Oriented Protocols

b. Bit Oriented protocols

51. Compare Error Detection and Error Correction:

The correction of errors is more difficult than the detection. In error detection, checks only any error

has occurred. In error correction, the exact number of bits that are corrupted and location in the

message are known. The number of the errors and the size of the message are important factors.

52. What is Forward Error Correction?

Forward error correction is the process in which the receiver tries to guess the message by using

redundant bits.

53. Define Retransmission?

Retransmission is a technique in which the receiver detects the occurrence of an error and asks the

sender to resend the message. Resending is repeated until a message arrives that the receiver

believes is error-freed.

54. What are Data Words?

In block coding, we divide our message into blocks, each of k bits, called datawords. The block coding

process is one-to-one. The same dataword is always encoded as the same codeword.

55. What are Code Words?

"r" redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are

called codewords. 2n - 2k codewords that are not used. These codewords are invalid or illegal.

56. What is a Linear Block Code?

A linear block code is a code in which the exclusive OR (addition modulo-2) of two valid codewords

creates another valid codeword.

57. What are Cyclic Codes?

Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a codeword is

cyclically shifted (rotated), the result is another codeword.

58. Define Encoder?

A device or program that uses predefined algorithms to encode, or compress audio or video data for

storage or transmission use. A circuit that is used to convert between digital video and analog video.

59. Define Decoder?

A device or program that translates encoded data into its original format (e.g. it decodes the data).

The term is often used in reference to MPEG-2 video and sound data, which must be decoded before it

is output.

60. What is Framing?

Framing in the data link layer separates a message from one source to a destination, or from other

messages to other destinations, by adding a sender address and a destination address. The

destination address defines where the packet has to go and the sender address helps the recipient

acknowledge the receipt.

61. What is Fixed Size Framing?

In fixed-size framing, there is no need for defining the boundaries of the frames. The size itself can be

used as a delimiter.

62. Define Character Stuffing?

In byte stuffing (or character stuffing), a special byte is added to the data section of the frame when

there is a character with the same pattern as the flag. The data section is stuffed with an extra byte.

This byte is usually called the escape character (ESC), which has a predefined bit pattern. Whenever

the receiver encounters the ESC character, it removes it from the data section and treats the next

character as data, not a delimiting flag.

63. What is Bit Stuffing?

Bit stuffing is the process of adding one extra 0 whenever five consecutive Is follow a 0 in the data, so

that the receiver does not mistake the pattern 0111110 for a flag.

64. What is Flow Control?

Flow control refers to a set of procedures used to restrict the amount of data that the sender can send

before waiting for acknowledgment.

65. What is Error Control ?

Error control is both error detection and error correction. It allows the receiver to inform the sender of

any frames lost or damaged in transmission and coordinates the retransmission of those frames by

the sender. In the data link layer, the term error control refers primarily to methods of error detection

and retransmission.

66. What Automatic Repeat Request (ARQ)?

Error control is both error detection and error correction. It allows the receiver to inform the sender of

any frames lost or damaged in transmission and coordinates the retransmission of those frames by

the sender. In the data link layer, the term error control refers primarily to methods of error detection

and retransmission. Error control in the data link layer is often implemented simply: Any time an error

is detected in an exchange, specified frames are retransmitted. This process is called automatic repeat

request (ARQ).

67. What is Stop-and-Wait Protocol?

In Stop and wait protocol, sender sends one frame, waits until it receives confirmation from the

receiver (okay to go ahead), and then sends the next frame.

68. What is Stop-and-Wait Automatic Repeat Request?

Error correction in Stop-and-Wait ARQ is done by keeping a copy of the sent frame and retransmitting

of the frame when the timer expires.

69. What is usage of Sequence Number in Relaible Transmission?

The protocol specifies that frames need to be numbered. This is done by using sequence numbers. A

field is added to the data frame to hold the sequence number of that frame. Since we want to

minimize the frame size, the smallest range that provides unambiguous communication. The sequence

numbers can wrap around.

70. What is Pipelining ?

In networking and in other areas, a task is often begun before the previous task has ended. This is

known as pipelining.

71. What is Sliding Window?

The sliding window is an abstract concept that defines the range of sequence numbers that is the

concern of the sender and receiver. In other words, he sender and receiver need to deal with only part

of the possible sequence numbers.

72. What is Piggy Backing?

A technique called piggybacking is used to improve the efficiency of the bidirectional protocols. When

a frame is carrying data from A to B, it can also carry control information about arrived (or lost)

frames from B; when a frame is carrying data from B to A, it can also carry control information about

the arrived (or lost) frames from A.

73. What are the two types of transmission technology available?

(i) Broadcast and (ii) point-to-point

74. What is subnet?

A generic term for section of a large networks usually separated by a bridge or router.

75. Difference between the communication and transmission.

Transmission is a physical movement of information and concern issues like bit polarity,

synchronisation, clock etc.

Communication means the meaning full exchange of information between two communication media.

76. What are the possible ways of data exchange?

(i) Simplex (ii) Half-duplex (iii) Full-duplex.

77. What is SAP?

Series of interface points that allow other computers to communicate with the other layers of network

protocol stack.

78. What do you meant by "triple X" in Networks?

The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The

standard protocol has been defined between the terminal and the PAD, called X.28; another standard

protocol exists between hte PAD and the network, called X.29. Together, these three

recommendations are often called "triple X".

79. What is frame relay, in which layer it comes?

Frame relay is a packet switching technology. It will operate in the data link layer.

80. What is terminal emulation, in which layer it comes?

Telnet is also called as terminal emulation. It belongs to application layer.