The communication protocol, therefore, can't exploit any hardware functionality, and any handshake must be performed in software. The time line of a PLIP transmission is depicted in figure 2, which details the steps involved in the transmission of a single byte of information. The image is available as PostScript here Internet Datagrams As far as the kernel proper is concerned, the PLIP device is just like any other network device. When a datagram must be transmitted through a network interface, it is passed to the transmission function of the device driver. The difference with PLIP is that although it receives a data packet which already includes an Ethernet header, the driver adds its own haeader.
Transmission is headed by the length of the data packet, in bytes.
The cound is transmitted as a 16-bit number and it doesn't include the count itself nor the final checksum byte. An ethernet header. These fourteen bytes are almost useless, but they are still there for backward compatibility. IP data directly follow the header, just like what happens with real ethernet interfaces. A checksum byte.