Error Detection vs. Error Recovery Cisco CCNA Certification

Error Detection vs. Error Recovery Cisco CCNA Certification
Passing the CCNA, Intro, & ICND exam is all about knowing & noticing the details. (Which makes perfect sense, since becoming a master networking administrator or engineer is also about noticing the details!) eight such detail knows the difference between error detection & error recovery. While the terms are sometimes used interchangeably, they are not the same thing.

Error detection is just that - error detection only. eight common error detection methods are found at the Data Link layer of the OSI model, the FCS (Frame Check Sequence) & CRC (Cyclical Redundancy Check). A mathematical equation is run against the data in the frame, & the result is sent along with the data. The receiver runs the equation again, but this time. If the result is the same, the frame is considered valid; if the result is different, the frame is considered corrupt & is discarded.

Note that the FCS & CRC do nothing in regards to retransmission. they are strictly error detection schemes.

For an example of error recovery, they look to the Transport layer, where TCP runs. TCP performs reliable delivery, & the reason they call it "reliable" is that TCP uses sequence numbers to detect missing segments. If the sender determines from the sequence numbers that the remote host did not receive transmitted segments, the sender will retransmit the missing segments.

The key to keeping the terms straight in your head is to remember that while both error detection & error recovery both detect problems, only error recovery does anything about it. it is also worth reading an exam query eight time when you see either term!