The maximum transmission unit is the largest size of IP datagram which may be transferred using a specific data link connection The MTU value is a design parameter of a LAN and is a mutually agreed value (i.e. both ends of a link agree to use the same specific value) for most WAN links. The size of MTU may vary greatly between different links (e.g. from 128 B up to 10 KB).
http://www.erg.abdn.ac.uk/users/gorry Date: 10/11/1995 Revised: 7/10/2003