A count of frames received that contain a valid SLD
field in a OLT, as defined in [802.3ah] clause
65.1.3.3.1, and pass the CRC-8 check, as defined in
[802.3ah] clause 65.1.3.3.3, and contain the ONU's LLID
as defined in [802.3ah] clause 65. This attribute is
mandatory for an ONU and mandatory for an OLT (a
counter per LLID).