Header check sequence

{{Short description|Error checking feature of some header data structures}}

{{technical|date=July 2018}}

A header check sequence (HCS) is an error checking feature for various header data structures, such as in the media access control (MAC) header of Ethernet. It may consist of a cyclic redundancy check (CRC) of the frame, obtained as the remainder of the division (modulo 2) by the generator polynomial multiplied by the content of the header excluding the HCS field.

The HCS can be one octet long, as in WiMAX,{{cite web|url=http://wirelessman.org/tgd/docs/80216d-03_01.pdf|title=Project 802.16d: Working Document (System Profiles for 2–11 GHz)|date=September 2004|archive-url=https://web.archive.org/web/20160305215558/http://wirelessman.org/tgd/docs/80216d-03_01.pdf|archive-date=March 5, 2016|url-status=live|accessdate=October 29, 2007}} or a 16-bit value for cable modems.{{cite web|url=http://www.cablelabs.com/specifications/SP-RFI-I01-970326.pdf|title=Data-Over-Cable Interface Specifications, Radio Frequency Interface Specification|date=March 26, 1997|archiveurl=https://web.archive.org/web/20110525094347/http://www.cablelabs.com/specifications/SP-RFI-I01-970326.pdf|archivedate=May 25, 2011|url-status=dead|accessdate=October 29, 2007}}