This Counter64, in bytes, tracks the total amount of data the CDMA modem itself has transmitted across all calls, which the MIB notes is distinct from bytes transmitted through the router's logical interface. An admin comparing this to interface-level transmit counters can spot discrepancies caused by modem-level retransmissions or protocol overhead not visible at the interface layer. For example, if this modem-level counter grows much faster than the corresponding WAN interface's output byte counter, it may point to excessive retransmissions at the radio link layer.