I found the definition of ipSystemInOctets:
The total number of octets received in input IP datagrams, including those received in error. Octets from datagrams counted in ipSystemStatsInReceives MUST be counted here.
Are all switch/router-octets counted system-wide or only those going in and out the Management IP-Interface? (our S,K and 7100 Series deliver quite low values in the kbs range, our new test summits deliver none)