An essential characteristic of frames is the frame length, which can be varied between minimum and maximum length. This is particularly important for asynchronous applications or for real-time applications, for high-speed transfer or mass transfer.
The variable packet length varies between a few bytes and a few 1000 bytes depending on the system and the transmission speed. In cell-oriented systems such as ATM, it is constant.
Ethernet has a minimum frame length of 64 bytes and a maximum of 1,518 bytes, Token Ring has 13 bytes or 4,500 bytes in the 4-Mbit/s version, 13 bytes or 17,800 bytes in the 16-Mbit/s version, FDDI has 12 bytes as minimum frame length and 4,500 bytes as maximum frame length, and in Fibre Channel the Maximum Transmission Unit (MTU) is 2,112 bytes. ATM uses fixed frames, or cells, which are 53 bytes long. With Ethernet, the frame length directly affects Ethernet performance. The more stations want to transmit and the smaller the frame length, the lower the channel efficiency.