This counts frames that were not transmitted because they hit the maximum configured number of collisions. The description notes this counter should only increment when the network is heavily saturated with traffic, so a rising count here on a link that is not otherwise busy would point to a duplex mismatch or a faulty cable or switch port rather than genuine congestion. This counter climbing steadily even during a period of light traffic would suggest a half-duplex/full-duplex mismatch between the modem's cdmipEthernetSpeed setting and the connected switch port, rather than actual network saturation.