Documentation/networking/arcnet-hardware.rst - linux/kernel/git/klassert/ipsec - Git at Google

 .. SPDX-License-Identifier: GPL-2.0

 ===============
 ARCnet Hardware
 ===============

 :Author: Avery Pennarun <apenwarr@worldvisions.ca>

 .. note::

    This file is a supplement to arcnet.rst.  Please read that for general
    driver configuration help.

 Because so many people (myself included) seem to have obtained ARCnet cards
 without manuals, this file contains a quick introduction to ARCnet hardware
 and some cabling tips. If you have any other information, do not hesitate to
 :ref:`send an email to netdev <arcnet-netdev>`.


 Introduction to ARCnet
 ======================

 ARCnet is a network type which works in a way similar to popular Ethernet
 networks but which is also different in some very important ways.

 First of all, you can get ARCnet cards in at least two speeds: 2.5 Mbps
 (slower than Ethernet) and 100 Mbps (faster than normal Ethernet).  In fact,
 there are others as well, but these are less common.  The different hardware
 types, as far as I'm aware, are not compatible and so you cannot wire a
 100 Mbps card to a 2.5 Mbps card, and so on.  From what I hear, my driver does
 work with 100 Mbps cards, but I haven't been able to verify this myself,
 since I only have the 2.5 Mbps variety.  It is probably not going to saturate
 your 100 Mbps card.  Stop complaining. :)

 You also cannot connect an ARCnet card to any kind of Ethernet card and
 expect it to work.

 There are two "types" of ARCnet - STAR topology and BUS topology.  This
 refers to how the cards are meant to be wired together.  According to most
 available documentation, you can only connect STAR cards to STAR cards and
 BUS cards to BUS cards.  That makes sense, right?  Well, it's not quite
 true; see below under "Cabling."

 Once you get past these little stumbling blocks, ARCnet is actually quite a
 well-designed standard.  It uses something called "modified token passing"
 which makes it completely incompatible with so-called "Token Ring" cards,
 but which makes transfers much more reliable than Ethernet does.  In fact,
 ARCnet will guarantee that a packet arrives safely at the destination, and
 even if it can't possibly be delivered properly (ie. because of a cable
 break, or because the destination computer does not exist) it will at least
 tell the sender about it.

 Because of the carefully defined action of the "token", it will always make
 a pass around the "ring" within a maximum length of time.  This makes it
 useful for realtime networks.

 In addition, all known ARCnet cards have an (almost) identical programming
 interface.  This means that with one ARCnet driver you can support any
 card, whereas with Ethernet each manufacturer uses what is sometimes a
 completely different programming interface, leading to a lot of different,
 sometimes very similar, Ethernet drivers.  Of course, always using the same
 programming interface also means that when high-performance hardware
 facilities like PCI bus mastering DMA appear, it's hard to take advantage of
 them.  Let's not go into that.

 One thing that makes ARCnet cards difficult to program for, however, is the
 limit on their packet sizes; standard ARCnet can only send packets that are
 up to 508 bytes in length.  This is smaller than the Internet "bare minimum"
 of 576 bytes, let alone the Ethernet MTU of 1500.  To compensate, an extra
 level of encapsulation is defined by RFC1201, which I call "packet
 splitting," that allows "virtual packets" to grow as large as 64K each,
 although they are generally kept down to the Ethernet-style 1500 bytes.

 For more information on ARCnet networks, visit the "ARCNET Resource Center"
 WWW page at:

 	https://www.arcnet.cc


 Cabling ARCnet Networks
 =======================

 This section was rewritten by

 	Vojtech Pavlik     <vojtech@suse.cz>

 using information from several people, including:

 	- Avery Pennraun     <apenwarr@worldvisions.ca>
 	- Stephen A. Wood    <saw@hallc1.cebaf.gov>
 	- John Paul Morrison <jmorriso@bogomips.ee.ubc.ca>
 	- Joachim Koenig     <jojo@repas.de>

 and Avery touched it up a bit, at Vojtech's request.

 ARCnet (the classic 2.5 Mbps version) can be connected by two different
 types of cabling: coax and twisted pair.  The other ARCnet-type networks
 (100 Mbps TCNS and 320 kbps - 32 Mbps ARCnet Plus) use different types of
 cabling (Type1, Fiber, C1, C4, C5).

 For a coax network, you "should" use 93 Ohm RG-62 cable.  But other cables
 also work fine, because ARCnet is a very stable network. I personally use 75
 Ohm TV antenna cable.

 Cards for coax cabling are shipped in two different variants: for BUS and
 STAR network topologies.  They are mostly the same.  The only difference
 lies in the hybrid chip installed.  BUS cards use high impedance output,
 while STAR use low impedance.  Low impedance card (STAR) is electrically
 equal to a high impedance one with a terminator installed.

 Usually, the ARCnet networks are built up from STAR cards and hubs.  There
 are two types of hubs - active and passive.  Passive hubs are small boxes
 with four BNC connectors containing four 47 Ohm resistors::

 	   |         | wires
 	   R         + junction
 	-R-+-R-      R 47 Ohm resistors
 	   R
 	   |

 The shielding is connected together.  Active hubs are much more complicated;
 they are powered and contain electronics to amplify the signal and send it
 to other segments of the net.  They usually have eight connectors.  Active
 hubs come in two variants - dumb and smart.  The dumb variant just
 amplifies, but the smart one decodes to digital and encodes back all packets
 coming through.  This is much better if you have several hubs in the net,
 since many dumb active hubs may worsen the signal quality.

 And now to the cabling.  What you can connect together:

 1. A card to a card.  This is the simplest way of creating a 2-computer
    network.

 2. A card to a passive hub.  Remember that all unused connectors on the hub
    must be properly terminated with 93 Ohm terminators (or something else if you
    don't have the right ones), although the network may work without
    terminators.

 3. A card to an active hub.  Here there is no need to terminate the unused
    connectors except some kind of aesthetic feeling.  But, there may not be
    more than eleven active hubs between any two computers.  That of course
    doesn't limit the number of active hubs on the network.

 4. An active hub to another.

 5. An active hub to passive hub.

 Remember that you cannot connect two passive hubs together.  The power loss
 implied by such a connection is too high for the network to operate reliably.

 An example of a typical ARCnet network::

 	   R                     S - STAR type card
     S------H--------A-------S    R - Terminator
 	   |        |            H - Hub
 	   |        |            A - Active hub
 	   |   S----H----S
 	   S        |
 		    |
 		    S

 The BUS topology is very similar to the one used by 10BASE2 Ethernet.  The only
 difference is in cable and terminators: they should be 93 Ohm. 10BASE2 Ethernet
 uses 50 Ohm impedance. You use T connectors to put the computers on a single
 line of cable, the bus. You have to put terminators at both ends of the
 cable. A typical BUS ARCnet network looks like::

     RT----T------T------T------T------TR
      B    B      B      B      B      B

   B - BUS type card
   R - Terminator
   T - T connector

 But that is not all! The two types can be connected together.  According to
 the official documentation, the only way of connecting them is using an active
 hub::

 	 A------T------T------TR
 	 |      B      B      B
      S---H---S
 	 |
 	 S

 The official docs also state that you can use STAR cards at the ends of a
 BUS network in place of a BUS card and a terminator::

      S------T------T------S
 	    B      B

 But, according to my own experiments, you can simply hang a BUS type card
 anywhere in middle of a cable in a STAR topology network.  And more - you
 can use the bus card in place of any star card if you use a terminator. Then
 you can build very complicated networks fulfilling all your needs!  An
 example::

 				  S
 				  |
 	   RT------T-------T------H------S
 	    B      B       B      |
 				  |       R
     S------A------T-------T-------A-------H------TR
 	   |      B       B       |       |      B
 	   |   S                 BT       |
 	   |   |                  |  S----A-----S
     S------H---A----S             |       |
 	   |   |      S------T----H---S   |
 	   S   S             B    R       S

 A completely different cabling scheme is used with Twisted Pair cabling. Each
 of the TP cards has two RJ (phone-cord style) connectors.  The cards are
 then daisy-chained together using a cable connecting every two neighboring
 cards.  The ends are terminated with RJ 93 Ohm terminators which plug into
 the empty connectors of cards on the ends of the chain.  An example::

 	  ___________   ___________
       _R_|_         _|_|_         _|_R_
      |     |       |     |       |     |
      |Card |       |Card |       |Card |
      |_____|       |_____|       |_____|


 There are also hubs for the TP topology.  There is nothing difficult
 involved in using them; you just connect a TP chain to a hub on any end or
 even at both.  This way you can create almost any network configuration.
 The maximum of 11 hubs between any two computers on the net applies here as
 well.  An example::

     RP-------P--------P--------H-----P------P-----PR
 			       |
       RP-----H--------P--------H-----P------PR
 	     |                 |
 	     PR                PR

     R - RJ Terminator
     P - TP Card
     H - TP Hub

 Like any network, ARCnet has a limited cable length.  These are the maximum
 cable lengths between two active ends (an active end being an active hub or
 a STAR card).

 		========== ======= ===========
 		RG-62       93 Ohm up to 650 m
 		RG-59/U     75 Ohm up to 457 m
 		RG-11/U     75 Ohm up to 533 m
 		IBM Type 1 150 Ohm up to 200 m
 		IBM Type 3 100 Ohm up to 100 m
 		========== ======= ===========

 The maximum length of all cables connected to a passive hub is limited to 65
 meters for RG-62 cabling; less for others.  You can see that using passive
 hubs in a large network is a bad idea. The maximum length of a single "BUS
 Trunk" is about 300 meters for RG-62. The maximum distance between the two
 most distant points of the net is limited to 3000 meters. The maximum length
 of a TP cable between two cards/hubs is 650 meters.


 Setting the Jumpers
 ===================

   - Every ARCnet card has its own "unique" network address from 0 to 255.
     Unlike Ethernet, you can set this address yourself with a jumper or switch
     (or on some cards, with special software).  Since it's only 8 bits, you can
     only have 254 ARCnet cards on a network.  DON'T use 0 or 255, since these
     are reserved (although neat stuff will probably happen if you DO use them).
     By the way, if you haven't already guessed, don't set this the same as any
     other ARCnet device on your network!

   - There may be ETS1 and ETS2 settings.  These may or may not make a
     difference on your card (many manuals call them "reserved"), but are
     used to change the delays used when powering up a computer on the
     network.  This is only necessary when wiring VERY long range ARCnet
     networks, on the order of 4km or so; in any case, the only real
     requirement here is that all cards on the network with ETS1 and ETS2
     jumpers have them in the same position.  Chris Hindy <chrish@io.org>
     sent in a chart with actual values for this:

 	======= ======= =============== ====================
 	ET1	ET2	Response Time	Reconfiguration Time
 	======= ======= =============== ====================
 	open	open	74.7us		840us
 	open	closed	283.4us		1680us
 	closed	open	561.8us		1680us
 	closed	closed	1118.6us	1680us
 	======= ======= =============== ====================

     Make sure you set ETS1 and ETS2 to the SAME VALUE for all cards on your
     network.

 LED Indicators
 ==============

 Many cards have red and green LEDs, which have the following meanings:

 	=============== =============== =====================================
 	Green           Red             Status
 	=============== =============== =====================================
 	OFF             OFF             Power off
 	OFF             Short flashes   Cabling problems (broken cable or not
 					terminated)
 	OFF (short)     ON              Card init
 	ON              ON              Normal state - everything OK, nothing
 					happens
 	ON              Long flashes    Data transfer
 	ON              OFF             Never happens (maybe when wrong ID)
 	=============== =============== =====================================
	.. SPDX-License-Identifier: GPL-2.0

	===============
	ARCnet Hardware
	===============

	:Author: Avery Pennarun <apenwarr@worldvisions.ca>

	.. note::

	This file is a supplement to arcnet.rst. Please read that for general
	driver configuration help.

	Because so many people (myself included) seem to have obtained ARCnet cards
	without manuals, this file contains a quick introduction to ARCnet hardware
	and some cabling tips. If you have any other information, do not hesitate to
	:ref:`send an email to netdev <arcnet-netdev>`.


	Introduction to ARCnet
	======================

	ARCnet is a network type which works in a way similar to popular Ethernet
	networks but which is also different in some very important ways.

	First of all, you can get ARCnet cards in at least two speeds: 2.5 Mbps
	(slower than Ethernet) and 100 Mbps (faster than normal Ethernet). In fact,
	there are others as well, but these are less common. The different hardware
	types, as far as I'm aware, are not compatible and so you cannot wire a
	100 Mbps card to a 2.5 Mbps card, and so on. From what I hear, my driver does
	work with 100 Mbps cards, but I haven't been able to verify this myself,
	since I only have the 2.5 Mbps variety. It is probably not going to saturate
	your 100 Mbps card. Stop complaining. :)

	You also cannot connect an ARCnet card to any kind of Ethernet card and
	expect it to work.

	There are two "types" of ARCnet - STAR topology and BUS topology. This
	refers to how the cards are meant to be wired together. According to most
	available documentation, you can only connect STAR cards to STAR cards and
	BUS cards to BUS cards. That makes sense, right? Well, it's not quite
	true; see below under "Cabling."

	Once you get past these little stumbling blocks, ARCnet is actually quite a
	well-designed standard. It uses something called "modified token passing"
	which makes it completely incompatible with so-called "Token Ring" cards,
	but which makes transfers much more reliable than Ethernet does. In fact,
	ARCnet will guarantee that a packet arrives safely at the destination, and
	even if it can't possibly be delivered properly (ie. because of a cable
	break, or because the destination computer does not exist) it will at least
	tell the sender about it.

	Because of the carefully defined action of the "token", it will always make
	a pass around the "ring" within a maximum length of time. This makes it
	useful for realtime networks.

	In addition, all known ARCnet cards have an (almost) identical programming
	interface. This means that with one ARCnet driver you can support any
	card, whereas with Ethernet each manufacturer uses what is sometimes a
	completely different programming interface, leading to a lot of different,
	sometimes very similar, Ethernet drivers. Of course, always using the same
	programming interface also means that when high-performance hardware
	facilities like PCI bus mastering DMA appear, it's hard to take advantage of
	them. Let's not go into that.

	One thing that makes ARCnet cards difficult to program for, however, is the
	limit on their packet sizes; standard ARCnet can only send packets that are
	up to 508 bytes in length. This is smaller than the Internet "bare minimum"
	of 576 bytes, let alone the Ethernet MTU of 1500. To compensate, an extra
	level of encapsulation is defined by RFC1201, which I call "packet
	splitting," that allows "virtual packets" to grow as large as 64K each,
	although they are generally kept down to the Ethernet-style 1500 bytes.

	For more information on ARCnet networks, visit the "ARCNET Resource Center"
	WWW page at:

	https://www.arcnet.cc


	Cabling ARCnet Networks
	=======================

	This section was rewritten by

	Vojtech Pavlik <vojtech@suse.cz>

	using information from several people, including:

	- Avery Pennraun <apenwarr@worldvisions.ca>
	- Stephen A. Wood <saw@hallc1.cebaf.gov>
	- John Paul Morrison <jmorriso@bogomips.ee.ubc.ca>
	- Joachim Koenig <jojo@repas.de>

	and Avery touched it up a bit, at Vojtech's request.

	ARCnet (the classic 2.5 Mbps version) can be connected by two different
	types of cabling: coax and twisted pair. The other ARCnet-type networks
	(100 Mbps TCNS and 320 kbps - 32 Mbps ARCnet Plus) use different types of
	cabling (Type1, Fiber, C1, C4, C5).

	For a coax network, you "should" use 93 Ohm RG-62 cable. But other cables
	also work fine, because ARCnet is a very stable network. I personally use 75
	Ohm TV antenna cable.

	Cards for coax cabling are shipped in two different variants: for BUS and
	STAR network topologies. They are mostly the same. The only difference
	lies in the hybrid chip installed. BUS cards use high impedance output,
	while STAR use low impedance. Low impedance card (STAR) is electrically
	equal to a high impedance one with a terminator installed.

	Usually, the ARCnet networks are built up from STAR cards and hubs. There
	are two types of hubs - active and passive. Passive hubs are small boxes
	with four BNC connectors containing four 47 Ohm resistors::

	\| \| wires
	R + junction
	-R-+-R- R 47 Ohm resistors
	R
	\|

	The shielding is connected together. Active hubs are much more complicated;
	they are powered and contain electronics to amplify the signal and send it
	to other segments of the net. They usually have eight connectors. Active
	hubs come in two variants - dumb and smart. The dumb variant just
	amplifies, but the smart one decodes to digital and encodes back all packets
	coming through. This is much better if you have several hubs in the net,
	since many dumb active hubs may worsen the signal quality.

	And now to the cabling. What you can connect together:

	1. A card to a card. This is the simplest way of creating a 2-computer
	network.

	2. A card to a passive hub. Remember that all unused connectors on the hub
	must be properly terminated with 93 Ohm terminators (or something else if you
	don't have the right ones), although the network may work without
	terminators.

	3. A card to an active hub. Here there is no need to terminate the unused
	connectors except some kind of aesthetic feeling. But, there may not be
	more than eleven active hubs between any two computers. That of course
	doesn't limit the number of active hubs on the network.

	4. An active hub to another.

	5. An active hub to passive hub.

	Remember that you cannot connect two passive hubs together. The power loss
	implied by such a connection is too high for the network to operate reliably.

	An example of a typical ARCnet network::

	R S - STAR type card
	S------H--------A-------S R - Terminator
	\| \| H - Hub
	\| \| A - Active hub
	\| S----H----S
	S \|
	\|
	S

	The BUS topology is very similar to the one used by 10BASE2 Ethernet. The only
	difference is in cable and terminators: they should be 93 Ohm. 10BASE2 Ethernet
	uses 50 Ohm impedance. You use T connectors to put the computers on a single
	line of cable, the bus. You have to put terminators at both ends of the
	cable. A typical BUS ARCnet network looks like::

	RT----T------T------T------T------TR
	B B B B B B

	B - BUS type card
	R - Terminator
	T - T connector

	But that is not all! The two types can be connected together. According to
	the official documentation, the only way of connecting them is using an active
	hub::

	A------T------T------TR
	\| B B B
	S---H---S
	\|
	S

	The official docs also state that you can use STAR cards at the ends of a
	BUS network in place of a BUS card and a terminator::

	S------T------T------S
	B B

	But, according to my own experiments, you can simply hang a BUS type card
	anywhere in middle of a cable in a STAR topology network. And more - you
	can use the bus card in place of any star card if you use a terminator. Then
	you can build very complicated networks fulfilling all your needs! An
	example::

	S
	\|
	RT------T-------T------H------S
	B B B \|
	\| R
	S------A------T-------T-------A-------H------TR
	\| B B \| \| B
	\| S BT \|
	\| \| \| S----A-----S
	S------H---A----S \| \|
	\| \| S------T----H---S \|
	S S B R S

	A completely different cabling scheme is used with Twisted Pair cabling. Each
	of the TP cards has two RJ (phone-cord style) connectors. The cards are
	then daisy-chained together using a cable connecting every two neighboring
	cards. The ends are terminated with RJ 93 Ohm terminators which plug into
	the empty connectors of cards on the ends of the chain. An example::

	___________ ___________
	_R_\|_ _\|_\|_ _\|_R_
	\| \| \| \| \| \|
	\|Card \| \|Card \| \|Card \|
	\|_____\| \|_____\| \|_____\|


	There are also hubs for the TP topology. There is nothing difficult
	involved in using them; you just connect a TP chain to a hub on any end or
	even at both. This way you can create almost any network configuration.
	The maximum of 11 hubs between any two computers on the net applies here as
	well. An example::

	RP-------P--------P--------H-----P------P-----PR
	\|
	RP-----H--------P--------H-----P------PR
	\| \|
	PR PR

	R - RJ Terminator
	P - TP Card
	H - TP Hub

	Like any network, ARCnet has a limited cable length. These are the maximum
	cable lengths between two active ends (an active end being an active hub or
	a STAR card).

	========== ======= ===========
	RG-62 93 Ohm up to 650 m
	RG-59/U 75 Ohm up to 457 m
	RG-11/U 75 Ohm up to 533 m
	IBM Type 1 150 Ohm up to 200 m
	IBM Type 3 100 Ohm up to 100 m
	========== ======= ===========

	The maximum length of all cables connected to a passive hub is limited to 65
	meters for RG-62 cabling; less for others. You can see that using passive
	hubs in a large network is a bad idea. The maximum length of a single "BUS
	Trunk" is about 300 meters for RG-62. The maximum distance between the two
	most distant points of the net is limited to 3000 meters. The maximum length
	of a TP cable between two cards/hubs is 650 meters.


	Setting the Jumpers
	===================

	- Every ARCnet card has its own "unique" network address from 0 to 255.
	Unlike Ethernet, you can set this address yourself with a jumper or switch
	(or on some cards, with special software). Since it's only 8 bits, you can
	only have 254 ARCnet cards on a network. DON'T use 0 or 255, since these
	are reserved (although neat stuff will probably happen if you DO use them).
	By the way, if you haven't already guessed, don't set this the same as any
	other ARCnet device on your network!

	- There may be ETS1 and ETS2 settings. These may or may not make a
	difference on your card (many manuals call them "reserved"), but are
	used to change the delays used when powering up a computer on the
	network. This is only necessary when wiring VERY long range ARCnet
	networks, on the order of 4km or so; in any case, the only real
	requirement here is that all cards on the network with ETS1 and ETS2
	jumpers have them in the same position. Chris Hindy <chrish@io.org>
	sent in a chart with actual values for this:

	======= ======= =============== ====================
	ET1 ET2 Response Time Reconfiguration Time
	======= ======= =============== ====================
	open open 74.7us 840us
	open closed 283.4us 1680us
	closed open 561.8us 1680us
	closed closed 1118.6us 1680us
	======= ======= =============== ====================

	Make sure you set ETS1 and ETS2 to the SAME VALUE for all cards on your
	network.

	LED Indicators
	==============

	Many cards have red and green LEDs, which have the following meanings:

	=============== =============== =====================================
	Green Red Status
	=============== =============== =====================================
	OFF OFF Power off
	OFF Short flashes Cabling problems (broken cable or not
	terminated)
	OFF (short) ON Card init
	ON ON Normal state - everything OK, nothing
	happens
	ON Long flashes Data transfer
	ON OFF Never happens (maybe when wrong ID)
	=============== =============== =====================================