56.6.23.2.3 Support for FRER Redundancy Tag and Sequence Number Identification

To identify duplicate frames, a sequence number must be extracted from the incoming frame.

IEEE 802.1CB defines a new optional redundancy tag field that will immediately follow either the MAC source address field or the VLAN tag fields of the frame. This redundancy tag is identified by a new Ethertype with a value of 0xF1C1.

GMAC supports Draft 2.5 of the IEEE 802.1CB standard (see sub-clause 7.8). Thus the length of the redundancy tag is 6 bytes:

• The first two bytes are for the Ethertype (F1C1)
• The second two bytes are reserved and are set to zero
• The final two bytes are the 16-bit sequence number.