Header Error
Control (HEC)
8
7
6
5
4
3
2
1
GFC* / VPI
VPI
VPI
VCI
VCI
VCI
PTI
HEC
CLP
Only bit errors in ATM cell header are checked, not bit errors in
cell payload
At the transmitting side, the checksum is
calculated over the four first header bytes. The result is inserted into the HEC
field.
At the receiving side, the HEC byte may be used for
error control and cell
delineation
purposes.