length field (LTH)
The Length Field (LTH) is a data field in the Ethernet frame according to IEEE 802.3.
It is a 2 byte long field that indicates the number of bytes that are in the following data field. In Ethernet frames, this data field is used as a type field that specifies the network protocol contained in the data field of the relevant data packet. Using this field as a length field provides an additional way to detect transmission errors.