This is the device-wide total number of SCTP chunks discarded. Discarded chunks usually mean malformed, out-of-window, or otherwise unprocessable data arrived, so a rising count on an otherwise healthy link is an early warning of a peer running an incompatible SCTP stack version, or of corruption on the path. This counter jumping right after a peer's software upgrade would point to a protocol-compatibility issue introduced by that upgrade rather than a network problem.