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All computer network Interview Questions
41.What do you mean by redundancy?
Ans: Redundancy is the concept of sending extra bits for use in error detection. Three common redundancy methods are parity check, cyclic redundancy check (CRC), and checksum.
42.Define parity check.
Ans: In parity check, a parity bit is added to every data unit so that the total number of 1s is even (or odd for odd parity).Simple parity check can detect all single bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.In two dimensional parity checks, a block of bits is divided into rows and a redundant row of bits is added to the whole block.
43. Define cyclic redundancy check (CRC).
Ans: C RC appends a sequence of redundant bits derived from binary division to the data unit. The divisor in the CRC generator is often represented as an algebraic polynomial.
44. What is hamming code?
Ans: The hamming code is an error correction method using redundant bits. The number of bits is a function of the length of the data bits. In hamming code for a data unit of m bits, we use the formula 2r >= m+r+1 to determine the number of redundant bits needed. By rearranging the order of bit transmission of the data units, the hamming code can correct burst errors.
45.What do you mean by flow control?
Ans: It is the regulation of sender’s data rate so that the receiver buffer doesn’t become overwhelmed.i.e. flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgement.
46.What do you mean by error control?
Ans: Error control refers primarily to methods of error detection and retransmission. Anytime an error is detected in an exchange, specified frames are retransmitted. This process is called automatic repeat request (ARQ).
47.Define stop and wait ARQ.
Ans: In stop and wait ARQ, the sender sends a frame and waits for an acknowledgement from the receiver before sending the next frame.
48.Define Go-Back-N ARQ?
Ans: In Go-Back-N ARQ, multiple frames can be in transit at the same time. If there is an error, retransmission begins with the last Unacknowledged frame even if subsequent frames arrived correctly. Duplicate frames are discarded.
49.Define Selective Repeat ARQ?
Ans: In Selective Repeat ARQ, multiple frames can be in transit at the same time. If there is an error, only unacknowledged frame is retransmitted.
50.What do you mean by pipelining, is there any pipelining in error control?
Ans: The process in which a task is often begun before the previous task has ended is called pipelining. There is no pipelining in stop and wait ARQ however it does apply in Go-Back-N ARQ and Selective Repeat ARQ.
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