(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)