Editing Maximum transmission unit (section)

==Applicability==
MTUs apply to [[communications protocol]]s and [[network layer]]s. The MTU is specified in terms of [[byte]]s or [[Octet (computing)|octets]] of the largest PDU that the layer can pass onwards. MTU parameters usually appear in association with a communications interface ([[network interface card|NIC]], [[serial port]], etc.). Standards ([[Ethernet]], for example) can fix the size of an MTU; or systems (such as point-to-point serial links) may decide MTU at connect time.

Underlying [[data link layer|data link]] and [[physical layer]]s usually add overhead to the network layer data to be transported, so for a given maximum frame size of a medium, one needs to subtract the amount of overhead to calculate that medium's MTU. For example, with Ethernet, the maximum [[Ethernet frame#Structure|frame]] size is 1518 bytes, 18 bytes of which are overhead ([[Ethernet frame#Header|header]] and [[frame check sequence]]), resulting in an MTU of 1500 bytes.