Documentation/networking/plip.rst

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Documentation/networking/plip.rst
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.. SPDX-License-Identifier: GPL-2.0

================================================
PLIP: The Parallel Line Internet Protocol Device
================================================

Donald Becker (becker@super.org)
I.D.A. Supercomputing Research Center, Bowie MD 20715

At some point T. Thorn will probably contribute text,
Tommy Thorn (tthorn@daimi.aau.dk)

PLIP Introduction
-----------------

This document describes the parallel port packet pusher for Net/LGX.
This device interface allows a point-to-point connection between two
parallel ports to appear as a IP network interface.

What is PLIP?
=============

PLIP is Parallel Line IP, that is, the transportation of IP packages
over a parallel port. In the case of a PC, the obvious choice is the
printer port.  PLIP is a non-standard, but [can use] uses the standard
LapLink null-printer cable [can also work in turbo mode, with a PLIP
cable]. [The protocol used to pack IP packages, is a simple one
initiated by Crynwr.]

Advantages of PLIP
==================

It's cheap, it's available everywhere, and it's easy.

The PLIP cable is all that's needed to connect two Linux boxes, and it
can be built for very few bucks.

Connecting two Linux boxes takes only a second's decision and a few
minutes' work, no need to search for a [supported] netcard. This might
even be especially important in the case of notebooks, where netcards
are not easily available.

Not requiring a netcard also means that apart from connecting the
cables, everything else is software configuration [which in principle
could be made very easy.]

Disadvantages of PLIP
=====================

Doesn't work over a modem, like SLIP and PPP. Limited range, 15 m.
Can only be used to connect three (?) Linux boxes. Doesn't connect to
an existing Ethernet. Isn't standard (not even de facto standard, like
SLIP).

Performance
===========

PLIP easily outperforms Ethernet cards....(ups, I was dreaming, but
it *is* getting late. EOB)

PLIP driver details
-------------------

The Linux PLIP driver is an implementation of the original Crynwr protocol,
that uses the parallel port subsystem of the kernel in order to properly
share parallel ports between PLIP and other services.

IRQs and trigger timeouts
=========================

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