This counts data-plane payload packets transmitted specifically over the EOBC out-of-band path for operations like ISSU. An admin cares because bulk data transfer over the lower-bandwidth EOBC path would be much slower than over the main VSL, so heavy reliance on this path could explain an unusually slow upgrade. For example, an ISSU image transfer showing significant traffic on this counter rather than the main VSL data counter would suggest the transfer is happening over the slower out-of-band path.