Interview Questions - Networking

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.

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.

"r" redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are called codewords. 2ⁿ - 2^k codewords that are not used. These codewords are invalid or illegal.

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