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- From: Philip.Blundell@pobox.com (Phil Blundell)
- Newsgroups: comp.sys.acorn.networking,comp.sys.acorn.announce,comp.answers,news.answers
- Subject: comp.sys.acorn.networking Frequently Asked Questions
- Supersedes: <csan_919798559@kings-cross.london.uk.eu.org>
- Followup-To: comp.sys.acorn.networking
- Date: 4 Jun 1999 21:27:52 +0100
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- Xref: senator-bedfellow.mit.edu comp.sys.acorn.networking:24473 comp.sys.acorn.announce:3843 comp.answers:36455 news.answers:159521
-
- Archive-name: acorn/networking/faq
- Posting-Frequency: monthly
- Last-modified: 1998-04-19
- URL: http://www.tazenda.demon.co.uk/phil/csan-faq
- Maintainer: Phil Blundell <Philip.Blundell@pobox.com>
- Version: 1.32
-
- This file tries to collect together some of the accumulated wisdom to
- do with networking of Acorn computers, in order to reduce the number
- of times the same questions are asked in the comp.sys.acorn.networking
- newsgroup. Although the traffic in c.s.a.networking is not high, and
- the signal-to-noise ratio is normally quite good, there are some
- questions that tend to crop up repeatedly, and it gets a little
- tedious for the regular readers to answer them every time. Please
- read this FAQ before posting.
-
- Despite what the above paragraph might imply, not every question
- answered in this document has necessarily been frequently asked. Some
- of the information has cropped up on the newsgroup only a few times,
- or not at all, but still seemed interesting enough to be worthy of
- inclusion.
-
- This FAQ is divided into five parts. If you're not interested in a
- section, you can search for '**' to skip to the next one.
-
- I am working on a pretty HTML version of the FAQ. Until this is done,
- it's only in plain text, and may not look too great in web browsers.
- Also, updates may be sporadic (and the table of contents is missing)
- since I have two copies to worry about right now.
-
- This FAQ is posted monthly to comp.sys.acorn.networking and
- comp.sys.acorn.announce, as well as news.answers and comp.answers.
-
-
- ** Section A: General stuff **
-
- Q. What's comp.sys.acorn.networking?
-
- A. This group is for discussion related to networking of Acorn machines.
- This includes both connecting your own machine to the Internet and
- running a local-area network of machines.
-
-
- Q. Are there any other newsgroups I ought to read?
-
- A. Yes. You might like to check out comp.dcom.lans.ethernet,
- comp.dcom.cabling and comp.protocols.tcp-ip for a start. Many of the
- people who know Ethernet bridges inside out, for example, don't read
- comp.sys.acorn.networking.
-
- If you're having trouble connecting to the Internet that may be
- specific to your ISP, look to see if they have local support groups
- first.
-
- Of course, the other comp.sys.acorn.* newsgroups are the place to go
- for Acorn discussion that isn't necessarily networking-related.
-
- Several of these groups have their own FAQs, and you should check them
- out as well.
-
-
- Q. Is there other good stuff available on the net?
-
- A. Yes. Many vendors have their own web sites; see below.
-
- There is a pile of LAN information, including the FAQ for
- comp.dcom.lans.ethernet, at <http://web.syr.edu/~jmwobus/lans/>.
-
- Acorn's ftp site has a pile of stuff, including online versions of
- their Application Notes (nos 228, 231, 261, 264, 283 & 296 may be of
- particular interest) and circuit diagrams for some of their hardware,
- including Econet interfaces. This can all be found at
- <ftp://ftp.acorn.co.uk/pub/documents>.
-
- Education people might like to look at
- <http://sunsite.unc.edu/cisco/noc/> as well.
-
- Kevin F. Quinn used to maintain a seperate FAQ containing information
- on using Acorn machines for Internet access. This document is quite
- old now and has not been maintained for some time. However, it may
- still contain useful information. You can get it from
- ftp.demon.co.uk:/pub/archimedes/FAQ-Using-Acorns-For-Internet-Access.txt.
-
-
- Q. This FAQ is awful! Whose fault is it?
-
- A. Phil Blundell <Philip.Blundell@pobox.com> put the FAQ together,
- and he would appreciate comments and suggestions for improvement.
- Many of the answers were provided by the amassed intelligence of
- comp.sys.acorn.networking posters, of whom there are too many to list
- them all individually. Andrew Gordon provided a lot of the
- information in, and checked the technical accuracy of, the Econet
- section. George Hawes, Dom Latter and others at i-cubed ltd provided
- lots of useful information about Ethernet and AUN.
-
-
- Q. I'm an educational user. What I really need to make my life of
- drudgery more bearable is some sort of guide to Ethernet.
-
- A. You're in luck! i-cubed limited have a document for just such an
- eventuality. You can find it on the Web (start from
- <http://www.i-cubed.co.uk/> and follow the links through "Support").
- Alternatively, if you need a paper copy, send email to
- <support@i-cubed.co.uk> and ask nicely.
-
-
- Q. Can I ask people here to help me set up a network?
-
- A. By all means. But remember to take advice you get with a pinch of
- salt. Networking can be a complex subject, and you ought to make sure
- that the person who advises you knows what they're talking about
- (which, sadly, isn't true of all Usenet posters) before you take their
- advice too seriously (and particularly before you spend any money).
-
-
- Q. Who makes or sells Acorn networking equipment?
-
- A. Here is a partial list of suppliers with brief contact details.
- Don't construe the inclusion of a company here as a recommendation.
- If your company has been left out and feels hurt, send me email.
-
- i-cubed Ltd. <http://www.i-cubed.co.uk>
- Xemplar Education. <http://www.xemplar.co.uk>
- Atomwide Ltd. <http://www.atomwide.co.uk>
- ANT Ltd. <http://www.ant.co.uk>
-
-
- Q. What's an `intranet'?
-
- A. Whatever you want it to be. This question gets asked on the
- newsgroup an awful lot, and usually provokes uninteresting rants from
- a nunber of quarters. If you post this question again, expect a
- hostile response.
-
- For those who really want an answer, there are some who believe an
- `intranet' is any network on which TCP/IP protocols are used and that
- is not part of the global Internet. However, there is an alternative
- school of thought that holds that an `intranet' must span many
- continents, consist of many thousands of machines, and be owned by at
- least five major world powers, and that anything less is merely a LAN
- with aspirations. And thirdly there are those who feel the word is a
- vile piece of marketing-speak and that anybody accused of uttering it
- should be shot on sight.
-
-
- ** Section B: TCP/IP and Ethernet **
-
- Q. What's IEEE 802.3?
-
- A. It's the standard document that defines Ethernet. If you want the
- last word on what is and is not allowed by the specification then this
- is the place to look. You can buy a copy from your local IEEE agent -
- in the UK this is BSI. It's quite expensive, but worth it if you do a
- lot of work with Ethernet.
-
-
- Q. I want to run TCP/IP on my machine. What do I need?
-
- A. Before anything else, you need a "protocol stack". There are two
- options here, Acorn's own Internet suite and Tom Hughes' FreeNet.
- These days there probably isn't very much to choose between the two;
- FreeNet has more features, but more people seem to use the Acorn
- version.
-
- Some useful URLs are:
-
- <ftp://ftp.acorn.co.uk/pub/riscos/networking>. (Acorn TCP/IP)
- <http://www.compton.demon.co.uk/> (FreeNet)
-
- Once you've got the stack, you need a hardware driver for whatever
- interface you want to use. This might be an Ethernet card, or it
- might be a serial line (with or without a modem) or it might be
- something even more strange. If you're lucky, your card will have one
- in ROM (look for a module with a name like "Ether1" for an Ethernet
- card). If not, you may be able to find one on the net, or you may
- have to talk to your vendor. Then you should read the rest of the
- questions in this section.
-
-
- Q. What's DCI?
-
- A. DCI is the Driver Control Interface, a way for protocol modules
- (eg the Internet TCP/IP suite) to talk to the drivers for your
- hardware (eg an Ethernet card). DCI-2 was the first widely-released
- version, and DCI-3 is to all intents and purposes the same. DCI-4 is
- a more recently developed replacement, which provides better
- performance and increased functionality. DCI-2 and DCI-4 are not at
- all compatible; you must make sure that your protocol stack and your
- hardware drivers are trying to use the same version of DCI.
-
- Both FreeNet (from version 2) and Acorn Internet (from version 3) use
- DCI-4. DCI-2 is essentially obsolete now.
-
- If you use !BootNet or !Gateway, you need to make sure you are using
- the correct version to match the rest of your system - both DCI-2 and
- DCI-4 versions exist.
-
-
- Q. Would it be possible to write a converter to make DCI-2 drivers
- work with DCI-4 (or vice versa)?
-
- A. In theory yes. However, this would only be a useful thing to do
- if you're stuck with old hardware and no new driver. As far as I know
- nobody has actually written such a beast, but post to the newsgroup if
- you're desperate and maybe someone will help you out. Probably a
- better plan, though, would be to find someone to write a new driver
- for your card.
-
-
- Q. I want to write a network device driver. Where can I get
- information on DCI-4?
-
- A. Theoretically, this is freely available from Acorn. In practice,
- as with much of Acorn's technical documentation, it can be something
- of a challenge to get hold of it. There are two documents you need,
- the DCI4 specification itself and the MbufManager programming
- details.
-
- To make matters worse, the "official" electronic version of the DCI-4
- specification at Acorn now seems to be an Impression document, and the
- person who imported it didn't take enough care to stop Impression
- chewing up the C structure definitions (it has a habit of eating
- anything starting with a '{' character, unless very carefully
- restrained). Intact versions of the document do exist, but it may
- be even more difficult to get hold of one. Acorn were apparently able
- to ship the mangled specification for two years without anybody
- complaining.
-
-
- Q. My Ethernet card has a driver in ROM (or I'm soft-loading one),
- but Internet doesn't recognise it!
-
- A. You may be trying to mix DCI-2 and DCI-4. Talk to your vendor to
- see if you can get a ROM upgrade or soft-loadable replacement driver.
- There are some updated driver modules included with the Internet
- distribution on Acorn's ftp site. The "EtherR" card by Risc
- Developments needs a new ROM (costing ú10) - no soft-loading drivers
- are available.
-
- As far as I'm aware, DCI-4 drivers exist for most Ethernet cards that
- have been made for Acorn machines. The Atomwide/ANT "Pocket Ethernet"
- adapter and all Digital Services cards are DCI-2 only. If you're
- using an A4, it looks like you're stuck with DCI-2 for the time being.
- The Ether1 driver is apparently only of beta quality, but I haven't
- heard of any problems with it other than its apparently incompatibility
- with Internet 5.xx.
-
-
- Q. Do all the machines on my network have to use the same stack?
-
- A. No. The protocols that your hosts talk on the wire is, at least
- in theory, completely independent of the network stack, DCI and driver
- versions that you're using. If you're installing new machines, it's
- probably a good idea to use the same stack on them all as far as
- possible to make maintenance easier, but there's no pressing need from
- a technical point of view.
-
- Some people have reported problems when DCI-2 and DCI-4 stacks are
- mixed on the same network. There doesn't seem to be any evidence to
- back this up,
-
-
- Q. How do I use TCP/IP over my modem (or null-modem link)?
-
- A. You need a SLIP driver. There is one included with FreeNet; it
- will work equally well with Acorn Internet.
-
-
- Q. Can I run TCP/IP over Econet?
-
- A. Yes. You need a module called "EconetA", which provides an "ec0"
- interface. A new DCI-4 version of this module has just been released
- by Xemplar, and can be obtained from their FTP site. Note that this
- module uses a different protocol over the wire to older EconetA
- modules and so the two will not interwork, though they can coexist on
- a network without interfering.
-
- You can get a free DCI-2 version, including source, from
- <http://www.tazenda.demon.co.uk/phil/>.
-
-
- Q. Does that work for Nexus Virtual Econet as well?
-
- A. Yes. NexusVE behaves just like real Econet as far as TCP/IP is
- concerned - you need the same EconetA module.
-
-
- Q. Can I run TCP/IP on a BBC micro?
-
- A. Strangely enough, yes (after a fashion). Phil Blundell has some
- software to allow you to use Econet-equipped BBCs as telnet
- terminals. If you have a roomfull of old machines and would like to
- use them to talk to your Unix hosts, send email to
- <Philip.Blundell@pobox.com> and ask for a copy.
-
-
- Q. I have more than one interface in my machine. Can it act as a
- gateway, relaying packets from one to the other?
-
- A. Yes, but this is disabled by default. To turn it on, investigate
- the *InetGateway command (for DCI-4 versions of Acorn Internet) or the
- "ip forwarding" variable in !FreeUser.Files.Config (for FreeNet).
-
-
- Q. What's AUN? Isn't that the same as TCP/IP?
-
- A. AUN has two distinct meanings. Primarily it is Acorn's networking
- strategy (Acorn Universal Networking), and in this sense it covers the
- full range of Acorn networking products which will work across
- Ethernet networks
-
- A second usage of AUN is to refer to the protocols used to access a
- Level 4 file server, and to run a number of other network programs,
- across an Ethernet network. In effect, this involves implementing the
- protocols written for the older Econet network hardware on an
- Ethernet.
-
- While the two uses of AUN is confusing, no other term exists for the
- `Econet over Ethernet' protocols and so in practice we are stuck with
- AUN. In this second sense, AUN is implemented on top of UDP/IP. Each
- machine on an AUN network is, by default, given a non-standard IP
- address of the form 1.x.n.s, where n.s are the network and station
- numbers respectively. The station number is configured in CMOS RAM,
- using the SetStation utility.
-
- If there are no stations on the network running the !Gateway
- application then the network number will be 128, and the second byte
- of the IP address will be 0, giving a typical IP address of 1.0.128.32
- (station 32).
-
- If any stations are running !Gateway then the network number is
- configured within !Gateway, and the second byte of the IP address is
- determined by the network's position in !Gateway's list of networks (1
- for the first entry, 2 for the second, etc). Typical IP addresses
- would then be:
-
- 1.1.128.32 Station 32 on network 128
- 1.3.129.36 Station 36 on network 129
-
- Network numbers under AUN must be greater than 128; those between 1
- and 127 are reserved for 'real' Econet.
-
- Yes, it's a bit of a shame that Acorn chose to use 1.0.0.0 as the AUN
- network number, but IP addresses like this should never go anywhere
- near the real Internet anyway.
-
-
- Q. What about Access/Access+?
-
- A. These are Acorn's Peer to Peer networking products; Access is the
- DCI-2 release, while Access+ is the DCI-4 version and has additional
- features. They allow computers to share files across an Ethernet
- network. Any computer can export any directory, including $, on any
- filing system, across the Ethernet network. The exported directory and
- its sub-directories will then be available to all other computers
- which have Access/Access+ software. Access+ also provides printer
- sharing, although a computer with a shared printer must have a local
- copy of !Scrap. This normally means it must have its own hard disc,
- although it is possible for it to have a RAM disc set up with a copy
- of !Scrap.
-
- Access(+) is implemented using UDP/IP as its lower-level protocols; by
- default it uses its own non-standard IP addressing scheme, where:
-
- First byte: Always 1
- Second byte: Related to the make of the network card;
- 104 (&68) for i-cubed cards
- Third and fourth bytes: Last two bytes of the network card's MAC address.
-
- The netmask used is 255.0.0.0.
-
- It is possible to use Access(+) with AUN/Ethernet networking
- (described above), in which case Access(+) uses the IP address set up
- by AUN. It is also possible to use Access(+) with 'standard' IP
- addressing, in much the same way as described for AUN
- networking. (Note that if you are using Access(+) without AUN
- networking you run !Internet to set up the required IP address and
- netmask but DO NOT need to run !Bootnet.)
-
- When using Access+, the system variable inet$localaddr is set to the
- IP address in use, but with the order of the bytes reversed.
-
- The command *FWShow gives information about the set-up of the
- Access(+) network, with stations ("Holders") being identified by their
- IP addresses. In this output lines marked with a * refer to the local
- station.
-
-
- Q. What's masquerading?
-
- A. Masquerading is a way to allow machines to access (a limited
- subset of) Internet services without having to have real IP addresses
- assigned to them. You may want to do this both for technical reasons
- (if you've only been assigned one IP address, say for a dial-up
- account, but you have a whole roomfull of machines you want to be able
- to use) or for administrative reasons (you don't want your machines to
- be able to have unfettered access to the Internet due to security
- concerns).
-
- To use masquerading, you need one firewall machine. This must be able
- to talk to the real Internet (so it needs a proper IP address) and to
- the client machines that hide behind it, and are typically on a
- private Ethernet. Masquerading works by having the firewall rewrite
- the headers on datagrams that pass through it from the hidden clients
- to the outside world, so they look like they came from the firewall
- machine itself. When reply datagrams come back, the firewall
- remembers where the original connection comes from, rewrites the
- headers again, and forwards them to the appropriate client station.
-
- All this means that masquerading is only good for outgoing
- connections. You can't telnet _in_ to a masqueraded machine from the
- outside world. This also means that FTP sessions will usually fail
- from masqueraded machines - you must select passive mode first.
-
-
- Q. Can I do masquerading on my RISC OS machine?
-
- A. Yes, if you use the FreeNet stack. Acorn's Internet module has no
- support for masquerading.
-
-
- Q. What's proxying, then?
-
- A. Proxying is the technique of having outgoing requests (eg for web
- pages) passed to a 'proxy server', which performs the request on
- behalf of the original client and then forwards the results. This can
- be useful both if the clients can't be given direct access to the
- Internet, and because it allows the proxy server to perform caching
- and reduce the external bandwidth needed. FTP, HTTP and gopher are
- easy to proxy, given suitable clients. Telnet is virtually impossible
- to proxy transparently.
-
-
- Q. Now I'm confused! It sounds like proxying and masquerading are
- pretty much the same.
-
- A. To some extent they do the same thing, yes. The difference is a
- bit like that between routing and bridging. Masquerading works at a
- low level in the network stack; the datagrams are simply rewritten as
- they pass through the gateway. Proxying requires that you talk to a
- server, which then talks to the outside world on your behalf.
-
-
- Q. What Ethernet cards are available?
-
- A. Several have been produced, though I'm not sure which are still
- available these days. A partial list is:
-
- Ether1: an Acorn card based on the Intel 82586. Also known as the
- AKA25. Has 10base2 and AUI (somewhat spuriously labelled
- "10base5") connectors. This card has no real on-board ROM,
- so it's no use for diskless operation.
-
- Ether2: another Acorn card. This uses an National Semiconductors
- 8390 chipset. Full details of the Ether1 and Ether2 cards can
- be found in the A500/R200 technical reference manual.
-
- Ether3: an Atomwide card based on a SEEQ chipset, available in both
- 10baseT and 10base2 versions. Acorn-badged versions of this
- were marked AEH54.
-
- EtherB: an ANT card, available in both 10baseT and 10base2 versions.
-
- EtherH: i-cubed's Ethernet card. Equipped with both 10base2 and
- 10baseT connectors, and available in flavours for standard
- Archimedes podules, A3000 mini-podule slots and RiscPC NIC
- slots. Acorn-badged versions are marked AEH62 for the AUN
- version, and AEH78 for the Access+ version; they use a PROM
- for the firmware rather than the flash ROM found on i-cubed's
- own cards.
-
- EtherO: Oak's Ethernet card; 10base2 only, uses a Fujitsu chipset.
-
- EtherP: the "Pocket Ethernet" adaptor by Atomwide. It has a BNC
- connector and plugs into the parallel port, deriving its power
- from the mouse socket.
-
- EtherR: Risc Developments / Beebug cards. Available with 10base2,
- 10baseT and AUI connectors, for all models of machines.
-
- EtherM: a RiscPC 'ethernet' socket card (ie not a full width podule,
- but designed for RiscPC only) by ANT. Otherwise known as a
- 'Myson' card, equipped with 10baseT(RJ45) and 10base2 connectors.
- Driver supposedly has problems with Internet 5, but in reality
- appears to work fairly well (EtherM 0.39, 10-Apr-1997).
-
- A variety of other cards exist. If you have a card that is not listed
- here, or more information about one that is, please send email to the
- FAQ maintainer.
-
-
- Q. I want to change to 10baseT cabling, but I have a huge investment
- in old cards with no RJ45 connectors. Help!
-
- A. If your old cards have AUI connectors (look for a 15-pin D type
- socket, which may be labelled "AUI", "10base5", "Transceiver" or
- something even weirder) then you can plug in an external transceiver.
- These cost around 20ukp, and will let you use a 10baseT network
- connection. If the only connector on your card is the BNC for
- 10base2, then I'm afraid you're out of luck. Media converters do
- exist, but you're probably better off either keeping enough 10base2
- segments to handle the old cards or replacing them with new ones.
-
- You may find that installing a number of cheap hubs is the way
- forward; this will allow you to use small 10base2 segments for your
- old machines and connect them to a twisted-pair infrastructure. Be
- careful that you don't exceed the Ethernet limitations on repeater
- count, however.
-
-
- Q. I fitted an Ether1 to my machine, but *Podules doesn't show it!
-
- A. The Ether1 has no ROM. This means that *Podules has no way to
- identify the card, and it will show up as a blank line (note that a
- slot that is actually empty will show 'No installed podule'). Another
- effect of this is that the Ether1 driver must always be softloaded,
- unlike other cards which usually have the driver in firmware.
-
-
- Q. I'm trying to use my Ether1 card with Internet 5.xx, but I've come
- to a sticky end. Everything seems to be set up correctly but it just
- doesn't work.
-
- A. There is a mysterious problem with Ether1 cards and newer versions
- of the Internet module, which seems to result in no received frames
- ever reaching the protocol stack. As far as I know the only fix is to
- go back to an older (4.xx) version of the Internet module. The Ether1
- driver has been unsupported for some time so it seems unlikely that a
- fix will be forthcoming.
-
-
- Q. I want to use AUN networking but need to use IP addresses which fit
- in with the non-Acorn computers on my site.
-
- A. This is quite straightforward in principle. If you are using the
- Acorn Internet stack then you run the !Internet application; this
- allows complete freedom of choice of IP address and netmask (but
- conversely requires you to understand IP addressing and netmasking).
-
- Having set the required IP address in this way, you run the !Bootnet
- application. This replaces the Net module with the NetI module, which
- is aware of 'full' IP addressing. The !Bootnet application has to be
- configured to map the true IP addresses you are using onto the Acorn
- net.station addressing convention.
-
- The problem here is that stations which have run !Internet/!Bootnet
- can not communicate with stations which are in the default
- configuration. Consequently running !Internet/!Bootnet from a network
- server is quite difficult, and means that you will no longer be able
- to communicate with that server once the applications have been run.
- There are no such problems running !Internet/!Bootnet from a local
- disc.
-
-
- Q. Aren't there any 100Mbps Fast Ethernet cards?
-
- A. No. The expansion bus in current Acorn machines is too slow to
- keep up with a 100Mbps card. This doesn't mean that Fast Ethernet
- cards would be useless, as you'd still have 100Mbps of bandwidth to
- share between your clients, even if no single station could use it
- all, but it does reduce the attractiveness a bit. So far, no company
- has seemed willing to invest the development effort to build a 100Mbps
- card.
-
-
- Q. Why are Acorn network cards so expensive? I can buy one for my PC
- for ú20.
-
- A. That's true. Cheap ISA network cards are made in vast quantities,
- so they gain advantage from economies of scale, and require fairly
- little development effort on the part of the vendor (they use a
- standardised chipset optimised for the ISA bus, so no drivers need to
- be written and very little board design is needed). Acorn cards enjoy
- none of these advantages, and the result is that the cost is higher.
- The same is true for some ISA cards as well - the 3Com Etherlink III
- (3C509), for example, uses custom components and needs its own
- drivers, and costs about the same as a card for an Acorn system.
-
-
- Q. I want to connect two computers together with 10baseT. Do I need a hub?
-
- A. No. You can connect two (but no more) machines "back to back",
- with a special cross-cover cable. Consult the comp.dcom.lans.ethernet
- FAQ for details of the wiring.
-
-
- Q. I'm trying to use 10baseT networking with a "combo" card but it doesn't
- seem to work. What could be wrong?
-
- A. Some combo cards, notably the i-cubed Etherlan 600 series, will
- only switch to 10baseT mode if they detect a valid signal at the RJ45
- connector. This "link good" signal is generated by all hubs and
- network cards, but you can run into trouble if you are trying to
- connect two auto-sensing cards "back to back" as mentioned above -
- neither card will switch to 10baseT mode until it sees a "link good"
- signal from the other, and neither will generate "link good" signals
- unless they are in 10baseT mode. If you use a hub then this problem
- will not occur. The best solution is probably to replace one of the
- cards with one that can be manually switched to 10baseT mode (or
- indeed a 10baseT-only model) - if this is not possible then you can
- use a loopback plug to fool one of the cards at startup.
-
-
- Q. I'd like to connect two machines using their parallel ports. Is there
- a PLIP driver for RISC OS?
-
- A. A few years ago somebody was working on one, but it seems to have sunk
- without trace. If anybody knows different, please say so.
-
-
- ** Section : Disk sharing, etc **
-
- Q. I want to use disks and printers that are connected to Unix
- machines. Can I do it?
-
- A. Yes, though not for free. You need an NFS client. The full Acorn
- TCP/IP suite (which is a commercial product, unlike the stack itself
- which is freeware) includes an NFS client, and ANT's OmniClient
- software also includes NFS support.
-
- Once you've obtained the necessary client software, you need to make
- sure that your Unix machines are running the right servers. You may
- need to run "pcnfsd" or something similar in addition to your standard
- NFS daemons to allow access from RISC OS machines.
-
- The best way to share printers is currently with NFS. If you don't
- have NFS, and don't want to fork out for it just to print
- occasionally, there is an lpr client for RISC OS available. This only
- works from the command line, and doesn't integrate with !Printers.
- Get it at <ftp://ftp.demon.co.uk/pub/archimedes/utils/lpr010.zip>.
-
-
- Q. Okay, so the Unix people are happy. But I use Windows for
- Workgroups and/or Windows 95 and/or Windows NT. Can I do the same
- thing?
-
- A. Yes.
-
- Microsoft systems use a protocol called SMB to share files and
- printers. This is carried on top of a system known as NetBIOS, which
- in turn sits on top of _another_ protocol, which is either TCP/IP or
- NetBEUI, the latter being a proprietary Microsoft protocol.
-
- Two SMB clients are currently available for RISC OS, Omniclient and
- RMLogon.
-
-
- Q. Hey! I've got an SMB server for my Unix machine and I'm using it
- to share files with my Windows machines. But my RISC OS computers
- can't talk to it! What's the deal?
-
- A. Sadly, the SMB system isn't as simple as you might hope. SMB sits
- on top of a protocol called NetBIOS, which in turn sits on top of
- another protocol. This low-level transport protocol can either be
- TCP/IP or NetBEUI, the latter being a proprietary Microsoft protocol.
- Windows for Workgroups can only speak NetBEUI, though there is an
- upgrade available to add TCP/IP support. Windows 95 and NT can both
- speak NetBEUI and TCP/IP equally well.
-
- So far, so good. Unfortunately, because NetBEUI is proprietary, it
- _isn't_ supported by the servers you can run on Unix machines.
- Normally this isn't a problem, because Windows will use TCP/IP to talk
- to the Unix hosts. However, Omniclient I has the opposite problem (it
- can _only_ speak NetBEUI) and so it can't communicate with a Unix host
- even though they're both running the same sharing system.
-
- Omniclient II supports TCP/IP and so upgrading should solve your
- problem. Otherwise, you have to either use NFS to talk to Unix
- machines, or find an NT machine to re-export the disks from the Unix
- server. Windows 95 won't do here, because irritatingly it seems not
- to let you re-export a remote filesystem or printer.
-
-
- Q. What about Novell? My PCs and Macs are happily talking to my
- server - can my RiscPC do the same?
-
- A. Not directly. To produce a Novell client for RISC OS the
- protocols would have to be licensed from Novell (at great expense and
- under non-disclosure) and nobody has seemed keen to do this. If you
- have an NT machine on hand, though, it should be able to talk to the
- Novell server and re-export the filesystems with SMB. You may be able
- to pull the same trick with a Linux machine and ncpfs as well, though
- this may not be so reliable.
-
-
- Q. Or AppleTalk? Surely there must be _some_ hope for the Mac?
-
- A. Again, RISC OS machines can't talk directly to Macs, and there's
- no immediate prospect of them being able to (though apparently
- AppleTalk support is planned for a future release of Omniclient).
- However, again, there is a partial solution available. If you have a
- FreeBSD or Linux server, installing the `netatalk' package will allow
- it to talk to the Macs and access AppleTalk drives and printers; it
- can then re-export them to the RISC OS world using NFS.
-
-
- Q. I'm running Acorn Access. Is there any way I can share files over
- a serial link? I have SLIP set up, and I can ping one machine from
- the other with no problems, but I can't see its disks.
-
- A. Not easily. The problem is that the Freeway module refuses to use
- any interface that it thinks isn't "broadcast capable" - and a
- point-to-point link, such as a SLIP interface, doesn't fall into this
- category.
-
- People have talked of modifying Freeway to remove this restriction,
- but as far as I know nobody has actually done so yet. Aside from the
- 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 <http://www.tazenda.demon.co.uk/phil/>.
-
-
- 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
- <http://www.freebsd.org/> and <http://www.linux.org.uk>.
-
- 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.
-