Advanced Computer Networks: Lecture 7. This lecture will cover the following: error detection and correction; digital error detection techniques; cyclic redundancy check (CRC); two-dimensional parity; internet checksum algorithm; topics already covered; detecting transmission errors;...
CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 7 Error Detection and Correction +15 voltage 15 • • ? (erasure) Possible binary voltage encoding symbol Neighborhoods and erasure region • • Possible QAM symbol • Neighborhoods in green All other space results in erasure Input to digital level: valid symbols or erasures Error Detection: How ? • How to detect error ? – Add redundant information to a frame to determine errors • Transmit two complete copies of data – n redundant bits for nbit message – Error at the same position in two copies go undetected Error Detection: How ? • We want only k redundant bits for an nbit message, where k