This is a running count of HDLC header bytes received over the satellite interface, covering the control field, HDLC address, Flow ID, and CRC. Because HDLC framing overhead directly eats into the modem's usable satellite bandwidth, an admin trends this against cdmipWanFpgaRxHdlcPayLoadCount to judge whether overhead is disproportionately large relative to payload, which would suggest an excess of small frames. For example, seeing header bytes grow at nearly the same rate as payload bytes signals many small frames, worth investigating on an otherwise-idle link.