Editing Frame check sequence (section)

== Purpose ==
All frames and the bits, bytes, and fields contained within them, are susceptible to errors from a variety of sources. The FCS field contains a number that is calculated by the source node based on the data in the frame. This number is added to the end of a frame that is sent. When the destination node receives the frame the FCS number is recalculated and compared with the FCS number included in the frame. If the two numbers are different, an error is assumed and the frame is discarded.

The FCS provides error detection only. Error recovery must be performed through separate means. [[Ethernet]], for example, specifies that a damaged frame should be discarded and does not specify any action to cause the frame to be retransmitted. Other protocols, notably the [[Transmission Control Protocol]] (TCP), can notice the data loss and initiate retransmission and error recovery.<ref>{{cite book |last1=Odom |first1=Wendell |title=CCNA 200-301 Official Cert Guide, Volume 1 |date=2019-10-10 |publisher=Cisco Press |isbn=9780135792735 |url=https://books.google.com/books?id=LyCtDwAAQBAJ}}</ref>