In computer networking, the term Maximum Transmission Unit
(MTU) refers to the size (in bytes) of the largest packet
that a given layer of a communications protocol can pass
onwards. MTU parameters usually appear in association with a
communications interface (NIC, serial port, etc.). The MTU
may be fixed by standards (as is the case with Ethernet) or
decided at connect time (as is usually the case with
point-to-point serial links). A higher MTU brings higher
bandwidth efficiency. However large packets can block up a
slow interface for some time, increasing the lag on other
packets. For example a 1500 byte packet, the largest allowed
by Ethernet (and hence most of the Internet), would block up
a 14.4k modem for about one second.