(MTU) The largest number of bytes of "payload" data a frame can carry, not counting the frame' s header and trailer. A frame is a SIngle unit of transportation on the {data link layer}. It conSIsts of header data plus data which was passed down from the network layer (e.g. an IPdatagram) plus sometimes trailer data. An Ethernet (V2) frame has a MTU of 1500 bytes but the SIze of the frame can be up to 1526 bytes (22 byte header, 4 byte CRC trailer). See also fragmentation. (2000-10-07)