legal issues and the fact that recent versions of Freeway can't be
soft-loaded, there is an additional complication in that SLIP doesn't
have any way to distinguish different types of traffic passing over
it, and so you may come to grief if you try to run TCP/IP and Access
simultaneously on the same line. PPP doesn't suffer from this
limitation.
Q. I see Acorn are shipping Freeway in ROM with newer RISC OS
revisions. Does that mean it's freely distributable now?
A. No. As with any other part of RISC OS, it's still commercial
software and you're still not allowed to copy it. This means that,
for example, you aren't allowed to take the module from a new machine
and soft-load it (or blow it into an expansion card ROM) on old
machines.
** Section D: Econet **
Q. We had a thunderstorm last night, and now my Econet doesn't work.
A. One or more of your machines has probably had its interface
toasted by surges induced on the cable by lightning strikes. Finding
out which ones is just a matter of trial and error - go round
unplugging stations until things start working again. Don't forget
that it's not only client machines that can be damaged - your clock
and fileserver may have been taken out as well.
Once you've identified the afflicted stations, repairing them is
usually quite easy. Econet interfaces use two line receiver chips and
one line driver. Most machines use LM319 dual comparators as the line
receivers (except bridges, which use 26LS34s). These are reputedly
fairly robust, and are protected by resistors from the full impact of
surges, so are less likely to fail than the line drivers. The drivers
vary from machine to machine - BBCs and most SJ equipment use 75159s,
whereas Master, Archimedes machines and bridges use 26LS30s.
Unfortunately, these chips are often not socketed, so you may need to
do some soldering. It's well worth taking the extra moment it takes
to fit a socket when you change one, as they can die quite frequently.
It's also worth changing, or at least testing, all three chips if you
suspect that one may be faulty. One of the LM319s recovers the
incoming clock and data signals, and is needed for the interface to
work at all; the other is used for collision detection. Without this
second receiver the machine will appear to work, but will have an
adverse effect on the reliability of the network. You can also get
various bizarre effects from chips that have been damaged but not
destroyed - partial failure of a 75159, for example, can lead to a
machine working fine when it's switched on, but jamming the network
when turned off.
New Econet modules use surface-mounted components that can be
difficult to replace by hand. By cutting some tracks on the board you
can disable these and fit ordinary DIL versions in the spaces provided.
If you find this happens to you an awful lot, or if you have long runs
of exposed cable, you may want to invest in some surge suppressors
(basically just some hefty diodes between the signal lines and ground)
to try to eat the surges before they eat your machines. Another idea
that was floating around at one time, but as far as I know never
implemented, was to add opto-isolators onto one side of a bridge to
provide more complete protection from electrical accidents. However,
before worrying about suppressors and particularly if you get through
a lot of drivers for no apparent reason, you should check that all
your electrical outlets are properly grounded. Particularly in
schools, this is often not the case. Make sure that you unplug all
your computers before testing the sockets, as otherwise you can get
earthing effects through your network that fool your socket tester
into thinking all is well.
Q. I have an bridge on my network. Sometimes my Archimedes and
Master machines don't seem to be able to find out their network number
(and default to 0) - what could be wrong?
A. Make sure that the network on the other side of the bridge isn't
getting disconnected. Acorn bridges will go dead to the world if
there is a fault on either of the two networks they're bridging
between.
It's also possible your network is just unreliable. When a machine
starts, it broadcasts a single "interrogate bridge" message, and
listens for the response. If the broadcast is lost, there will be no
response. See the next question for what the problem might be.
Q. My Econet doesn't seem to be reliable. What might be wrong?
A. Most Econet transactions take place using a "four-way handshake",
and will be retried if something goes wrong. This means that the
underlying network can become quite unreliable before operations start
to go obviously wrong. The first symptom that all isn't well may be
that things take longer than they should, broadcasts go missing, or
you find that you have certain files that refuse to be sent over the
network even though others are fine. If you inspect the traffic with
a packet monitor, you may well see lots of repeated frames, and very
possibly a high number of "Aborted" or "CRC error" messages.
If the problems seem to be local to one machine, suspect its network
hardware or (more likely) the drop cable connecting it to the network.
If they're more widespread, there are several possible causes. One or
both of your terminators may be faulty or missing - if you're using SJ
plug-in terminators in ordinary socket boxes it's quite likely
somebody has unplugged one. You may have a fault in the network
cabling - a broken drain wire can cause various insidious reliability
problems, mostly because it upsets the characteristics of the
terminators. You may have exceptionally high levels of electrical
noise on the line (though Econet's differential transmission lines are
usually very good at coping with this - check with an oscilloscope).
Check to make sure that you don't have any excessively long drop-leads
or spurs on the network - 2 or 3 metres is about the longest you ought
to use. Finally, it may simply be that you're running the network too
fast - try slowing the clock down and see if matters improve.
Q. I'm getting cryptic error messages from my Econet software. What
do they mean?
A. The Acorn "standard" error messages aren't always particularly
self-explanatory. They are:
- No clock. This means that your machine is not seeing the clock
signal on the Econet line. Probably your machine is not plugged in,
or the clock box is broken, or you have a faulty cable or machine
somewhere. If only one machine gives this error and others are fine,
either its drop cable or its Econet hardware is probably at fault.
In an emergency, you can try swapping the 75159 chips between a BBC
and a clock box. The 75159 is actually a dual driver, and the two
machines use opposite sides of it, so this trick can sometimes get you
going again if one driver has been toasted.
- Not listening. This means that the destination machine completely
ignored all the packets you sent to it. Most likely it is switched
off, or disconnected from the network. You may also have a faulty
cable or bad termination. The remote machine may be accessing its
floppy disk or doing something else that locks out the network for a
long time. If you get this error when you try to perform an immediate
operation, it probably means that the remote machine has the
protection bits set.
- Net error. This means that the destination machine acknowledged
the first frame of the packet (the 'scout frame') but failed to
acknowledge the data frame. If this happens with your own code, you
may be transmitting more data than the remote has buffer space to
handle. Otherwise, it probably means that you have electrical noise,
bad cabling or a faulty terminator on the network.
- Line jammed. This means that your machine was unable to gain
access to the Econet wire for a long time, because it appeared to be
permanently busy. Almost always this happens because of a faulty
cable or terminator.
- No reply. Your packet was received by the remote machine, but its
reply didn't make it back to your station. This may happen if a
server is running abnormally slowly for some reason, or because of any
of the general reasons above (bad cabling etc).
- Station not present. This is really a special case of 'not
listening', and occurs for the same reasons.
Q. I'm trying to read files from %TAPE (or ~TAPE) on my SJ server,
but I get "No reply" errors every time!
A. When you access the %TAPE pseudo-directory, the tape drive is
being used as a very slow read-only disk (MDFS tape drives, unlike
most, can actually do this). It can often take several minutes for
the tape to be wound to the right place to find your file, during
which time the client times out.
If the server is lightly loaded, you may be able to just repeat the
command a few times - eventually all the data will be cached in the
MDFS's memory, and it can be returned straight away without waiting
for the tape. If the server is busy this may not work, as it will be
constantly throwing away your data to make room for files other users
have requested. Alternatively, on Master series and RISC OS machines
you can increase the time for which your machine will wait for a
reply. Under RISC OS, this is done with the SWI NetFS_SetFSTimeouts;
the following bit of BASIC increases the reply timeout to 10 minutes.
SYS "NetFS_ReadFSTimeouts" TO txC%,txD%,mpC%,mpD%,rD%,bD%
SYS "NetFS_SetFSTimeouts",txC%,txD%,mpC%,mpD%,60000,bD%
Q. Are there any network monitors available for the Archimedes?
A. Yes. Acorn have one, called "NetMonitor", which behaves much the
same as *NETMON on the BBC did (it gives you a dump of the packets in
hex). I'm not sure if this is currently available.
Phil Blundell also has one of his own which is a bit more like SJ's
Ecomon - it tries to decode the packets into a more human-friendly
form. You can get it from .
Q. Can I build my own clock?
A. Yes. An Econet clock is a fairly simple device - it just has to
generate a steady square-wave on the two clock lines. There is an
old circuit diagram in the back of the Econet Advanced User Guide,
and a more modern one (for the Level 3 clock) in the Econet Design &
Installation Guide.
Be warned, though, that if you use self-powered terminators the clock
has to provide a common-mode voltage to drive them. A very simple
clock may require you to use powered terminators.
If you have an old issue 3 BBC, you can arrange for it to generate a
clock signal (and/or provide termination) by fitting a few extra
components to the motherboard. This may not be a good idea, though,
because the Econet interfaces on those machines are slightly marginal
even at the best of times.
Q. How fast does Econet go?
A. Not very. The exact speed you can get depends on what machines
you have connected - Archimedes and SJ MDFSs are comparitively fast,
whereas BBCs and older SJ servers are slower - and on the length of
the cable, and quality (or presence, for that matter) of termination.
Some theoretical maximum figures are:
Archimedes 500Kb/sec (that's kilo*bits*), up to 25m
MDFS (v1.06+) 300Kb/sec, up to 120m
BBC 'B' 200Kb/sec, up to 275m
You can trade off increased speed for reduced length, and vice versa,
but exceeding these limits is likely to make your network unreliable.
Q. I was told I need terminators, but my network seems fine without.
A. You may get away with this, or you may not - it depends what
machines you're using, and on other characteristics of your network.
An Econet should have exactly two terminators, one at each end, and
you will get better performance if you stick to this rule.
Econet terminators do two things - they bias the data lines when
they're not being driven, and they absorb reflections at the end of
the cable. If your network is short enough and your clock speed is
low enough, you may be able to live with the reflections and so the
second property is unnecessary. Also, newer machines
(Master/Archimedes series) stand a reasonable chance of working
without the data lines being correctly biassed; BBC series and SJ
servers are a lot more sensitive in this respect.
It's also possible you have terminators without realising it.
Old-style SJ socket boxes (the square white ones that soldered on to
the cable) had a space inside for you to plug in a hidden terminator.
SJ also made seperate "secure terminator boxes" to go with the newer
black IDC-style sockets, though these are rather easier to spot.
Finally, you may have an old BBC doing duty as a terminator (see "Can
I build my own clock?" above).
Q. I added a terminator, and now my network doesn't work! I thought
they were supposed to be good!
A. Maybe it's faulty. Also, terminators are only good in moderation.
An Econet is supposed to be (electrically) a single bus in a straight
line, with no branches. Some people seem to think that they can add
as many spurs as they like, so long as they terminate the ends - this
isn't true, and the extra termination will probably make things worse.
If you _need_ a T-junction, you will have to use a bridge. If you
added a SJ self-powering terminator (or Acorn 'Level 3' passive
terminator) and your network was on the edge before, it's possible
that the extra load on the clock lines has pulled it far enough out of
tolerance to stop altogether. A terminator combined with a broken
drain wire (see the earlier "My Econet isn't reliable" section) is a
particular recipe for disaster.
Q. I found this old cream-coloured server with a black front panel.
It says "SJ" on the front and weighs about a ton. What is it?
A. It's an HDFS, the original self-contained SJ fileserver. It's
probably a collector's item now. It had an internal hard drive,
giving 20MB of online storage, and there was an optional tape streamer
for backup, which used DC600 tapes. The other main notable feature of
its design is that it has two independent CPUs.
Q. I found another cream-coloured server with "SJ" on the front.
This one isn't quite so old, and it's much smaller. There's a single
button on the front, labelled "Remove Discs", and connectors on the
back for two floppy drives.
A. It's an FDFS, the little brother to the HDFS. It, also, is
probably a collector's item. You may also, conceivably, come across
FDFSs being used in applications other than file servers - it was
possible to load different software into the unit to make it act as a
serial gateway, for example. It takes two standard dual floppy
drives, giving you a total of 3200k of online storage at any given
time with its own disk format.
Q. I've found an old fileserver, but I don't know what station number
it is. Help!
A. The traditional station number for a fileserver is 254, so try
that first. In any case, if the server has been sitting unused for a
long time its battery may have gone flat, and it should default to 254
when it comes back up. If it seems to be stuck on some weird number
and you have another machine to hand, you can use *STATIONS or *FSLIST
to try to track it down. Holding down the button when you switch on
may also reset it to 254.
If all else fails, you can change the station number of an SJ server
from Utility Mode. If you turn the keyswitch straight from "off" to
"system" (on MDFS and HDFS machines), the server should start up in
utility mode. On an FDFS, turn the server on and then push the button
while all the drives are empty. You should now be able to connect a
terminal to the serial port, and talk directly to the fileserver's
firmware.
Q. My SJ server keeps flashing its "printing" lights, and refuses to
respond to the network. And I'm not even printing anything!
A. The printer buffer is probably full of system messages. This
might be because you've turned logging on, or it might be because the
server is unhappy for some reason (it may be getting disk errors, for
example). The server will stop until the buffer drains.
Q. When I type "*USERS" on my SJ server, I see this strange user at
the bottom called "SYSTEM" (and maybe his friend, "SPOOL"). What's
going on?
A. These are special psuedo-users that the fileserver uses
internally. Some versions of the fileserver software (as far as I
know, all FDFS and HDFS versions, and early MDFSs) would actually let
you log them out, which usually brought the fileserver to a sticky
end. often corrupting the disk in the process.
Q. My MDFS tape drive is faulty! Can I get a spare?
A. Not easily. The MDFS used a bizarre species of tape drive that
pretended to be a direct-access device. It's almost certainly easier
to find some other way to back up your files. Some people have had
luck connecting other devices in place of the tape; Design IT are
apparently the people to talk to about this.
Q. I've lost the system password for my SJ server! How can I get back
in?
A. Use the original boot disk that came with the server. If you don't
have it then you need to read the manual, which explains what to do in
these dire situations. Please don't ask the group for help; people will
be reluctant to give it you, lest you turn out to be a malefactor trying to
break into somebody else's server.
Q. Can I connect my PC to an Econet network?
A. Not easily. Once upon a time there was a card called the
"Ecolink" to do this. However, few were made, they weren't always
completely reliable, and the drivers only work with MS-DOS 3.3. An
Ecolink is probably not something you want to install, except for
historical interest value.
If all you want to do is be able to talk TCP/IP with machines on the
Econet, you can use an Archimedes equipped with Econet and some other
interface (Ethernet, serial line, ...) as a gateway.
There have been rumours of a PCI-bus Econet card but nothing concrete has
emerged yet. Work is ongoing to add support to Linux for Econet hardware.
Q. Okay, so can I connect my PC to an Ethernet network and run AUN?
A. Again no (though see earlier sections for other ways to share
files between PCs and Acorn machines). Phil Blundell has some
experimental patches for Linux to add support for AUN-over-UDP
protocols.
Q. When I switch on my Archimedes, it complains that the "configured
station number is invalid". What's up?
A. All Acorn computers since the Master have had their Econet station
number stored in the first byte of CMOS RAM. If the battery goes
flat, or you reset the CMOS RAM, it will get cleared to zero - this
isn't a legal station number. Archimedes machines notice this and
default to being station number 1 instead. If your station numbers
are getting reset when you do a delete power-on, you need a newer
version of SetStation.
You need a program to change the station number. Location 0 is
protected, so the normal OSBYTE call to write CMOS RAM won't affect
it. The Archimedes program is called "SetStation", and may be
available from Acorn's ftp site.
Note that station 1 is actually an illegal value for AUN, and it's a
good idea to avoid it in any case to reduce the risk of duplicate
station numbers if a machine has its CMOS RAM reset.
** Section E: Cabling **
Q. I've heard that my 10base2 network has to be earthed! It isn't -
is this important?
A. The latest IEEE standard specifies that 10base2 networks, like
10base5, have to be earthed at a single point (usually one of the
terminators). If you're installing new cabling you ought to take note
of this, but there's probably no immediate cause for alarm if you've
got an existing (and working) network that isn't earthed.
Q. Can I install my own Econet or Ethernet cabling?
A. Yes, if you feel competent to do so - it can often be a lot
cheaper than paying a contractor to do it, though obviously you have
no comeback if you make a mistake. It's not particularly difficult,
though it can be time-consuming. You should probably take a trip to
comp.dcom.cabling if you have questions about the precise ins and outs
of installation.
Q. How do I attach Econet or 10baseT cable to the socket boxes?
A. You need a special insulation-displacement ("tonking") tool. You
can buy one from RS; their order code is 470-128. The IDC connectors
are the same that are used in some telephone sockets, and so the same
tool will work - and indeed if you're only installing one or two
sockets you can probably make do with the plastic tool that usually
comes with telephone extension kits. If you're installing a lot of
sockets, though, you probably want the proper metal version.
Q. I want to make my own 10baseT drop leads. Can I?
A. Yes. You need some category 5 UTP cable, some RJ45 plugs, and a
special crimp tool to fix one to the other. The wiring is "straight
through", so pin 1 connects to pin 1 and so on. Be warned though that
you can't just connect wires to pins at random - things have to be
arranged so that one pair is on pins 1/2, one is on 3/6, one is on 4/5
and the last is on 7/8. It doesn't matter which pair is which. Note
that some of the cables you can buy off the shelf are actually wired
incorrectly in this regard, and may cause you problems.
Making your own leads as a way to save money may be a false economy.
It's quite a fiddly and time-consuming business, and you can probably
expect a significant failure rate (the plugs are single-use, so if you
get one wrong you have to cut it off and try again). On the other
hand, it can be worth keeping the supplies you need in case you do
ever need a drop-lead in a hurry, or you need one that's slightly
longer than your supplier can provide.
Note that the cable used for connecting socket boxes to patch panels
is solid-core, whereas the cable used for drop leads is stranded.
It's not a very good idea to use off-cuts of solid core to make up
drop leads; not only is the cable more brittle and prone to fail when
flexed, but you need a different design of RJ45 plug to make a
reliable connection with solid core cable.
Q. I have a 10base2 network, and it doesn't work. Is there any way
to trace the fault, other than checking each cable individually?
A. If you can shut down the entire network (not difficult if it's
broken anyway) and you have a multimeter at your disposal, you can
check for gross faults fairly quickly. Disconnect the cable at some
convenient point by removing a T-piece; you should be left holding two
BNC plugs, one connected to each half of your network segment. For
each one, measure the resistance between the centre pin and the
outside body of the plug. If all is well, you should get a reading of
50 ohms, give or take a few. If the resistance is significantly lower
than this, you may well have a short circuit somewhere on the line -
maybe a bad connector, or maybe somebody stuck a pin through the
cable. If it's significantly higher, you probably have an open
circuit at large - perhaps somebody undid one of the BNC twist-locks,
or perhaps a cable has broken internally (this happens more often than
you might think). By repeating this procedure at strategically-chosen
points along the network, you should be able to narrow down the area
of the fault fairly quickly. See also the next question for a
possible alternative approach.
If all else fails, throw the whole lot away and replace it with
10baseT cabling. Then, next time a fault happens, you can just look
at the lights on the hub and know straight away which link is to
blame.
Q. I have a long run of cable, and there's a break or short somewhere
in it. Is there any way to pinpoint the fault?
A. Yes. The main reason that network cables need to be terminated is
to avoid reflections, and it is possible to turn this fact to your
advantage. If there is a break or short-circuit in the cable, it will
no longer be terminated with its characteristic impedance, and
waveforms will "bounce off" the end. By injecting a pulse into the
cable and timing how long it takes for the reflection to come back,
you can gauge the distance to the fault quite accurately - this is
handy if you have a long run of buried cable, for example, and don't
want to have to dig up the whole lot to fix it.
This procedure can't quite be done with normal household items, but it
doesn't require anything particularly exotic - if you're in a school,
your physics department should be able to furnish you with everything
you need. Essentially, you need some source of regular sharp pulses,
and a fast oscilloscope to watch the action with. You should find,
once you've adjusted the scope correctly, that you see the pulse
you're injecting onto the wire, and then a short time later a smaller
pulse which is the returning reflection. The polarity of the
returning pulse will depend on whether the fault in question is an
open or short circuit. The time between the original pulse and its
reflection is the time the waveform takes to make the round trip to
the fault and back, so the distance to the fault is given by half that
time multiplied by the velocity of the signal (which is a property of
the cable - usually around 70% of the speed of light).
You can buy devices known as time-domain reflectometers (TDRs) to do
this automatically. These used to be very expensive, but are now
sufficiently affordable that one might be within your budget,
especially if it saves you from the prospect of paying to have
hundreds of metres of cable dug up and replaced. Some Ethernet cards,
for example the Acorn Ether1, also have on-board TDRs - these are less
accurate than stand-alone units, but may still be able to give you a
useful clue as to where the fault lies.
Q. Can I use my old Econet cables for Ethernet?
A. Yes, for Base-T point-to-point links. Econet cable is superior to
Cat-5, but it has only four wires and is more expensive: it has also
not yet been tested at 100 Mbits/sec. You can tonk the ends straight
into the IDC connections on the backs of the RJ-45 outlets. For
standard SJ cable connect
(Clock -, DIN 5) Blue to 1 (white/orange)
(Clock +, DIN 3) Yellow to 2 (orange)
(Data -, DIN 4) Red to 3 (white/green)
(Data +, DIN 1) Green to 6 (green)
This cable will certainly work to well over 150 metres, but not if
there are a string of Econet outlets attached to it. If you are using
this on a large site, you will find that Base-T hubs are a lot more
resistant to lightning damage than Econet line drivers.
Such an installation is not in any way marginal; this cable conforms
to the IEEE 802.3 requirements for 10baseT links and so will be as
good as the more standard UTP cable.
** Section F: Internet Servers **
Q. I've heard that Unix machines are better for running servers than
RISC OS. Is that true?
A. In general, yes. The state of the art in server technology is
usually more advanced for Unix than for RISC OS. If you have
requirements for mail handling, for example, beyond anything very
simple then you will probably have trouble under RISC OS. The same
applies if you want to run your own news server, or provide ftp access
for multiple users with flexible access controls.
Q. But isn't a Unix machine really expensive? Aren't its commands
really arcane and difficult to use?
A. Not necessarily. There are now a number of free "Unix clones",
such as FreeBSD and Linux. Given a copy of one of these, and
virtually any PC machine (for example, an old 386 or 486 that's been
retired from duty as a Windows machine), you can build your own Unix
server at pretty minimal cost. Take a look at
and .
It's also not true that Unix is inherently difficult to use. It can
be a bit daunting at first, but there are plenty of books available to
teach you the basics. Given one of these, a machine to practice on,
and a bit of time and determination it's remarkably easy to pick up -
and once you start to learn the system, people tend to find that it's
far more intuitive and easy to use than DOS.
** The End **
Here endeth the comp.sys.acorn.networking FAQ.
