This counts instances where the reserved field in a SIP3 header was found to contain a non-zero or otherwise invalid value on frames received on this interface, one of the SIP3-level validation checks as opposed to the DXI2-level ones above. An admin treats this as evidence of a non-conformant SMDS implementation somewhere upstream sending this interface traffic, since properly conformant equipment should always leave reserved fields at their defined value. For example, a spike in lportSmdsCntSip3RsvdInvalids coinciding with a carrier network change upstream might indicate an interoperability issue introduced by new equipment in the SMDS cloud, not a local CPE problem.