Parallel Line Internet Protocol: Difference between revisions

Revision as of 07:42, 12 July 2009

Revision as of 10:12, 9 October 2009

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==Description==

The [[laplink cable|null-printer cable]] connects five output pins of a parallel port to five input pins on the other port, and vice versa. Due to the lack of an internal timing in the parallel ports, synchronization is done via software handshaking: of the five input or output pins, four are used for data transfer and one is used for synchronization. The logical values at these pins can be read and written directly by the software via an io instruction.

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Every IP packet is sent over the line by first encapsulating it into a plip packet, which is then sent using the above protocol. The encapsulated packet is as follows:

* 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 for example the actual total length of the packet is three more than the length as reported in the first two bytes of the packet.

==See also==

* [[Serial line internet protocol]]

* [[Point-to-point protocol]]

* [[Direct cable connection]]

==External links==

* [[TLDP]]: [http://www.tldp.org/HOWTO/PLIP-Install-HOWTO.html PLIP-Install-HOWTO]

* [http://www.linux.it/~rubini/docs/plip/plip.html A description of the PLIP protocol] by Alessandro Rubini

[[Category:Internet protocols]]

[[Category:Link protocols]]

[[zh:并行线IP协议]]