their acknowledge lines to indicate that the read or write operation has been performed. As a result, each host has to wait for a toggle from the other host before proceeding with a new operation. As an example, the transfer of nibble proceeds as follows: t->r lines r->s lines operation 00010 0xxxx transmitter sets data lines to 0010 10010 0xxxx transmitter toggle ACK line receiver detects toggle and reads 0010 10010 1xxxx receiver toggle ACK line transmitter detects toggle When the transmitter detects the toggle, this procedure is repeated for the next nibble. Internet Protocol packets are sent over the line after encapsulating them into PLIP packets before transmission over the line. The encapsulated packet has the following structure: packet length: 2 bytes, little endian ethernet header (mostly used for backward compatibility) the IP packet checksum: 1 byte, sum modulo 256 of bytes in the packet The length and checksum are calculated over the second and third field only, so that the actual total length of the packet is three more than the length as reported in the first two bytes of the packet. Similar methods An analogous feature for serial communications ports is the Serial Line Internet Protocol (SLIP), using null-modem cables, but allows transfer of four bits at a time rather than one. It generally works at higher bitrates. The method is based on the "Crynwr" standard devised by Russ Nelson. Ethernet may also be used as a direct computer-to-computer communications method using an Ethernet crossover cable. Other point-to-point connections, such as USB host-to-host bridges or cables are also used to transfer files between two computers where a network is not necessary or available. See also PPP Point-to-Point Protocol Direct cable connection Serial Line Internet Protocol (SLIP) References External links PLIP explanation PLIP install how-to PLIP-Install-HOWTO A description of the PLIP protocol by Alessandro Rubini Internet protocols Link protocols