58. What are the two classes of hardware building blocks?
Answer: Nodes and Links.
59. What are the types of errors?
Answer: There are mainly 2 types of error. They are:
a. Single-Bit error: In a single-bit error, only one bit in the data unit is changed from 1 to 0 or from 0 to 1.
b. Burst Error: A Burst error means that two or more bits in the data have changed from 1 to 0 from 0 to 1.
60. Explain the function of line discipline?
Answer: Line discipline is used in the data link layer which coordinates hop to hop data delivery. The hop can be a computer or a network controller. It also coordinates the half duplex transmission on data communication network. Acknowledgment discipline is used for simple networks, and poll/select is used for centrally controlled data networks.
61. What is Redundancy?
Answer: In general, it refers to duplicate devices that are used for backup purposes to prevent or recover from the failure of a specific component or system.. This technique is called redundancy. We usually used the secondary hard drive to backup our data, because if a hard drive fails, it may not be possible to recover personal data.
In Networking industry, it is very important to implement redundancy because if one system goes down, the connection between other systems will not be broken. We can take an example of, an FDDI network which has a duplicate data “ring” that is used automatically when the primary data path is interrupted.
62. What is Vertical Redundancy Check (VRC)?
Answer: Vertical redundancy check (VRC) is an error-checking method used on an eight-bit ASCII character. It is the most common and least expensive mechanism for Error Detection. This method is considered to be somewhat unreliable because If an odd number of bits are distorted, the check will not detect the error.
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.
63. What is longitudinal redundancy check – LRC?
Answer: In short, it is an error detection and checking method used to verify the accuracy of stored or transmitted data. LRC verifies the accuracy of stored and transmitted data using parity bits. It is a redundancy check applied to a parallel group of bit streams. This term is also known as a horizontal redundancy check. In LRC a redundant data unit follows n data units.
64. What is Cyclic Redundancy Check (CRC)?
Answer: CRC is based on binary division. In CRC, a special number is appended to a block of data in order to detect any changes introduced during storage (or transmission). Cyclic redundancy checks are quite simple to implement in hardware and can be easily analyzed mathematically. This technique was invented by W. Wesley Peterson in 1961 and further developed by the CCITT (Comité Consultatif International Telegraphique et Telephonique).
The CRC is recalculated on retrieval (or reception) and compared to the value originally transmitted, which can reveal certain types of error. For example, a single corrupted bit in the data results in a one-bit change in the calculated CRC, but multiple corrupt bits may cancel each other out.
CRC is more powerful than VRC and LRC in detecting errors because it is not based on binary