mark bit (M bit)
- InX.25, the M bit, D bit, and Q bit were used for control functions. The M bit was bit five of the third octet in the Packet Type Identifier( PTI), which identified the packet type. It indicated whether the data packet was logically connected to the subsequent data packet. The M-bit procedure was used to concatenate data packets together to allow longer contiguous data sets to be transmitted.
- In 802-LANs, the M-bit is a bit in the 48-bit MAC address that indicates whether it is a unicast or multicast address. For multicast addresses, the M bit must be 1 and the L bit, the universal/local bit, must be 0.