This counts flow-control frames, both XOFF and XON, transmitted by the device to ask the far end to pause or resume sending. A rising count here means this modem's Ethernet interface is itself becoming a bottleneck and asking the connected switch to throttle back, a useful early sign that this side of the link, not necessarily the network beyond it, cannot keep up with the current traffic rate. Seeing this counter climb during periods of high LAN-side traffic would suggest the modem's Ethernet interface is the constraint, asking the switch to pause, rather than any issue with the satellite link itself.