Equipment
The equipment required consists of a communications receiver, an
antenna, an interface unit/software and a computer.
Communications receiver - This is the name given to a good quality
high frequency receiver. Suitable models can be obtained,
second-hand, at around £100; new receivers cost upwards of £175.
There is no point is buying a radio simply designed to pick up
shortwave broadcasts which will lack the sensitivity, selectivity and
resolution necessary. A minimum specification would be:
Coverage 500 kHz--30 MHz
Resolution >100 Hz
** Page 100
Modes AM, Upper Side Band, Lower Side Band,
CW (Morse)
Tuning would be either by two knobs, one for MHz, one for kHz, or
by keypad. On more expensive models it is possible to vary the
bandwidth of the receiver so that it can be widened for musical
fidelity and narrowed when listening to bands with many signals close
to one another.
Broadcast stations transmit using AM (amplitude modulation), but
in the person-to-person contacts of the aeronautical, maritime and
amateur world, single-side-band-suppressed carrier techniques are
used--the receiver will feature a switch marked AM, USB, LSB, CW etc.
Side-band transmission uses less frequency space and so allows more
simultaneous conversations to take place, and is also more efficient
in its use of the power available at the transmitter. The chief
disadvantage is that equipment for receiving is more expensive and
must be more accurately tuned. Upper side band is used on the whole
for voice traffic, and lower side band for data traffic. (Radio
amateurs are an exception: they also use lower side-band for voice
transmissions below 10 MHz.) Suitable sources of supply for
communications receivers are amateur radio dealers, whose addresses
may be found in specialist magazines like Practical Wireless, Amateur
Radio, Ham Radio Today.
Antenna - Antennas are crucial to good shortwave reception--the sort
of short 'whip' aerial found on portable radios is quite insufficient
if you are to capture transmissions from across the globe. When using
a computer close to a radio you must also take considerable care to
ensure that interference from the CPU and monitor don't squash the
signal you are trying to receive. The sort of antenna I recommend is
the 'active dipole', which has the twin advantages of being small and
of requiring little operational attention. It consists of a couple of
1-meter lengths of wire tied parallel to the ground and meeting in a
small plastic box. This is mounted as high as possible, away from
interference, and is the 'active' part. From the plastic box descends
coaxial cable which is brought down to a small power supply next to
the receiver and from there the signal is fed into the receiver
itself. The plastic box contains special low-noise transistors.
It is possible to use simple lengths of wire, but these usually
operate well only on a limited range of frequencies, and you will
need to cover the entire HF spectrum. Active antennas can be obtained
by mail order from suppliers advertising in amateur radio
magazines--the Datong is highly recommended.
** Page 101
Interface The 'interface' is the equivalent of the modem in landline
communications; indeed, advertisements of newer products actually refer to
radio modems. Radio tele-type, or RTTY, as it is called, is traditionally
received on a modified teleprinter or telex machine; and the early interfaces
or terminal units (TUs) simply converted the received audio tones into 'mark'
and 'space' to act as the equivalent of the electrical line conditions of a
telex circuit. Since the arrival of the microcomputer, however, the design
has changed dramatically and the interface now has to perform the following
functions:
1 Detect the designated audio tones
2 Convert them into electrical logic states
3 Strip the start/stop bits, convert the Baudot code into ASCII
equivalents, reinsert start/stop bits
4 Deliver the new signal into an appropriate port on the computer.
(If RS232C is not available, then any other port, e.g. Game, that
is)
A large number of designs exist: some consist of hardware
interfaces plus a cassette, disc or ROM for the software; others
contain both the hardware for signal acquisition and firmware for its
decoding in one box.
Costs vary enormously and do not appear to be related to quality
of result. The kit-builder with a ZX81 can have a complete set-up for
under £40; semi-professional models, including keyboards and screen
can cost in excess of £1000.
The kit I use is based on the Apple II (because of that model's
great popularity in the USA, much hardware and software exists); the
interface talks into the game port and I have several items of
software to present Baudot, ASCII or Morse at will. There is even
some interesting software for the Apple which needs no extra
hardware--the audio from the receiver is fed direct into the cassette
port of the Apple, but this method is difficult to replicate on other
machines because of the Apple's unique method of reading data from
cassette.
** Page 102
Excellent inexpensive hard/firmware is available for many Tandy
computers, and also for the VlC20/Commodore 64. On the whole US
suppliers seem better than those in the UK or Japan-- products are
advertised in the US magazines QST and 73.
Setting Up Particular attention should be paid to linking all the
equipment together; there are special problems about using sensitive
radio receiving equipment in close proximity to computers and VDUs.
Computer logic blocks, power supplies and the synchronising pulses on
VDUs are all excellent sources of radio interference (rfi). RFI
appears not only as individual signals at specific points on the
radio dial, but also as a generalised hash which can blank out all
but the strongest signals.
Interference can escape from poorly packaged hardware, but also
from unshielded cables which act as aerials. The remedy is simple to
describe: encase and shield everything, connecting all shields to a
good earth, preferably one separate from the mains earth. In
practice, much attention must be paid to the detail of the
interconnections and the relative placing of items of equipment. In
particular, the radio's aerial should use coaxial feeder with a
properly earthed outer braid, so that the actual wires that pluck the
signals from the ether are well clear of computer-created rfi. It is
always a good idea to provide a communications receiver with a proper
earth, though it will work without one: if used with a computer, it
is essential.
Do not let these paragraphs put you off; with care excellent
results can be obtained. And bear in mind my own first experience:
ever eager to try out same new kit, I banged everything together with
great speed--ribbon cable, poor solder joints, an antenna taped
quickly to a window in a metal frame less than two meters from the
communications receiver--and all I could hear from 500 kHz to 30
MHz, wherever I tuned, was a great howl-whine of protest...
Where to listen
Scanning through the bands on a good communications receiver, you
realise just how crowded the radio spectrum is. The table in Appendix
VI gives you an outline of the sandwich-like fashion in which the
bands are organised.
The 'fixed' bands are the ones of interest; more particularly, the
following ones are where you could expect to locate news agency
transmissions (in kHz):
** Page 103
3155 -- 3400 14350 -- 14990
3500 -- 3900 15600 -- 16360
3950 -- 4063 17410 -- 17550
4438 -- 4650 18030 -- 18068
4750 -- 4995 18168 -- 18780
5005 -- 5480 18900 -- 19680
5730 -- 5950 19800 -- 19990
6765 -- 7000 20010 -- 21000
7300 -- 8195 21850 -- 21870
9040 -- 9500 22855 -- 23200
ggoo -- 9995 23350 -- 24890
10100 -- 11175 25010 -- 25070
11400 -- 11650 25210 -- 25550
12050 -- 12330 26175 -- 28000
13360 -- 13600 29700 -- 30005
13800 -- 14000
In addition, amateurs tend to congregate around certain spots on the
frequency map: 3590, 14090, 21090, 28090, and at VHF/UHF: 144.600,
145.300, MHz 432.600, 433.300.
Tuning In
Radio Teletype signals have a characteristic two-tone warble sound
which you will hear properly only if your receiver is operating in
SSB (single-side-band) mode. There are other digital tone-based
signals to be heard: FAX (facsimile), Helschcrieber (which uses a
technique similar to dot-matrix printers and is used for Chinese and
related pictogram-style alphabets), SSTV (slow scan television, which
can take up to 8 seconds to send a low-definition picture), and
others.
But with practice, the particular sound of RTTY can easily be
recognised. More experienced listeners can also identify shifts and
speeds by ear.
You should tune into the signal watching the indicators on your
terminal unit to see that the tones are being properly captured--
typically, this involves getting two LEDs to flicker simultaneously.
The software will now try to decode the signal, and it will be up
to you to set the speed and 'sense'. The first speed to try is 66/7
words per minute, which corresponds to 50 baud, as this is the most
common. On the amateur bands, the usual speed is 60 words per minute
(45 baud); thereafter, if the rate sounds unusually fast, you try 100
words per minute (approximately 75 baud).
** Page 104
By 'sense' or 'phase' is meant whether the higher tone corresponds
to logical 1 or logical 0. Services can use either format; indeed
the same transmission channel may use one 'sense' on one occasion and
the reverse 'sense' on another. Your software can usually cope with
this. If it can't, all is not lost: you retune your receiver to the
opposite, side-band and the phase will thereby be reversed. So, if
you are listening on the lower side-band (LSB), usually the
conventional way to receive, you simply switch over to USB (upper
side-band), retune the signal into the terminal unit, and the sense'
will have been reversed.
Many news agency stations try to keep their channels open even if
they have no news to put out: usually they do this by sending test
messages like: 'The quick brown fox....' or sequences like
'RYRYRYRYRYRY...' such signals are useful for testing purposes, if
a little dull to watch scrolling up the VDU screen.
You will discover many signals that you can't decode: the
commonest reason is that the transmissions do not use European
alphabets, and all the elements in the Baudot code have been
re-assigned--some versions of Baudot use not one shift, but two, to
give the required range of characters. Straightforward en- crypted
messages are usually recognisable as coming in groups of five
letters, but the encryption can also operate at the bit- as well as
at the character-level -- in that case, too, you will get
gobbleydegook.
A limited amount of ASCII code as opposed to Baudot is to be
found, but mostly on the amateur bands.
Finally, an error-correction protocol, called SITOR, is
increasingly to be found on the maritime bands, with AMTOR, an amateur
variant, in the amateur bands, SITOR has various modes of operation
but, in its fullest implementation, messages are sent in blocks which
must be formally acknowledged by the recipient before the next one is
despatched. The transmitter keeps trying until an acknowledgement is
received. You may even come across, on the amateur bands, packet
radio, which has some of the features of packet switching on digital
land lines. This is one of the latest enthusiasms in amateur radio
with at least two different protocols in relatively wide use.
Discussion of SITOR and packet radio is beyond the scope of this
book, but the reader is referred to BARTG (the British Amateur Radio
Teletype Group) and its magazine Datacom for further information. You
do not need to be a licensed radio amateur to join. The address is:
27 Cranmer Court, Richmond Road, Kingston KT2 SPY.
Operational problems of radio hacking are covered at the end of
Appendix I, the Baudot code is given Appendix IV and an outline
frequency plan is to be found in Appendix VI.
** Page 105
The material that follows represents some of the types of common
transmissions: news services, test slips (essentially devices for
keeping a radio channel open), and amateur. The corruption in places
is due either to poor radio propagation conditions or to the presence
of interfering signals.
REVUE DE LA PRESSE ITALIENNE DU VENDREDI 28 DECEMBRE 1984
LE PROCES AUX ASSASSINS DE L~ POIELUSZKO, LA VISITE DE
M. SPADOLINI A ISRAEL, LA SITUATION AU CAMBODGE ET LA GUER-
ILLA AU MOZAMBIQUE FONT LES TITES DES PAGES POLITIQUES
MOBILISATION TO WORK FOR THE ACCOUNT OF 1985
- AT THE ENVER HOXHA AUTOMOBILE AND
TRACTOR COMBINE IN TIRANA 2
TIRANA, JANUARY XATA/. - THE WORKING PEOPLE OF THE ENVER HOXH~/
AUTOMOBILE AND TRACTOR COMBINE BEGAN THEIR WORR WITH VIGOUR
AND MOBILISATION FOR THE ACCOUNT OF 1985. THE WORK IN THIS
IMPROVOWNT CENTER FOR MECHANICAL INDUSTRY WAS NOT INTERRUPTED
FOR ONE MOMENT AND THE WORKING PEOPLE 8~S ONE ANOTHER FOR
FRESHER GREATER VICTORIES UNDER THE LEADERSHIP OF THE PARTY
WITH ENVER HOXHA AT THE HEAD, DURING THE SHIFTS, NEAR
THE FURNANCES~ PRESSES ETC.. JUST LIKE SCORES OF WORKING COLLE-
CTIVES OF THE COUNTRY WHICH WERE NOT AT HOME DURING THE NEW
YEAR B
IN THE FRONTS OF WORK FOR THE BENEFITS OF THE SOCI-
ALIST CONSTRUCTION OF THE COUNTRY.
PUTTING INTO LIFE THE TEACHINGS OF THE PARTY AND THE INSTRU-
CTIONS OF COMRADE ENVER HOXHA, THE WORKING COLLECTIVE OF THIS
COMBINE SCORED FRESH SUCCESSES DURING 1984 TO REALIZE THE
INDICES OF THE STATE PLAN BY RASING THE ECEONOMIC EFFECTIVE-
NESS. THE WORKING PEOPLE SUCCESSFULLY REALIZED AND OVERFUL
FILLED THE OBJECTIVE OF THE REVOLUTIONARY DRIVE ON THE HIGHER
EFFECTIOVENESS OF PRODUCTION, UNDERTAKEN IN KLAIDQAULSK SO~
WITHIN 1984 THE PLANNED PRODUCTIVITY, ACCORDING TO THE INDEX
OF THE FIVE YEAR PLAN, WAS OVERFULFILLED BY 2 PER CENT.
MOREOVER, THE FIVE YEAR PLAN FOR THE GMWERING OF THE COST OF
PRODUCTION WAS RAISED 2 MONTHS AHEAD OF TIME, ONE FIVE YEAR
PLAN FOR THE PRODUCTION OF MACHINERIES LAND EQUIPMENT AND
THE PRODUCTION OF THE TRACTORS WAS OVER-
FULFILLED. THE NET INCOME OF THE FIVE YEAR PLAN WAS REALIZED
WITHIN 4 YEARS. ETCM
YRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRY
RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYR
** Page 106
YRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRY
YRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRY
RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYR~ u UL ~v_.~v
GJ4YAD GJ4YAD DE G4DF G4DF
SOME QRM BUT MOST OK. THE SHIFT IS NORMAL...SHIFT IS NORMAL.
FB ON YOUR RIG AND NICE TO MEET YOU IN RTTY. THE WEATHER HERE
TODAY IS FINE AND BEEN SUNNY BUT C9LD. I HAVE BEEN IN THIS MODE
BEFORE BUT NOT FOR A FEW YEARS HI HI.
GJ4YAD GJ4YAD DE G4DF G4DF
PSE KKK
G4ElE G4EJE DE G3IMS G3IMS
TNX FOR COMING BACk. RIG HERE IS ICOM 720A BUT I AM SENDING
AFSk; NOT FSk'. I USED TO HAVE A CREED BUT CHUCKED IT OUT IT WAS
TOO NOISY AND NOW HAVE VIC2D SYSTEM AND SOME US kIT MY SON
BROUGHT ME HE TRAVELS A LOT.
HAD LOTS OF TROUBLE WITH RFI AND HAVE NOT YET CURED IT. VERTY BAD
QRM AT MOMENT. CAN GET NOTHING ABOVE 1CI MEGS AND NOT MUCH EX-G ON
S(:). HI HI. SUNSPOT COUNT IS REALLY LOW.
G4EJE G4EJE DE G3IMS G3IMS
~I.Of;KKKk'KKKK
RYRYRYRYRYRYRYRYRYR
~K~fk'KKKKKKK
G3IMS G3IMS DE G4EJE G4EJE
FB OM. URM IS GETTING WORSE. I HAVE ALWAYS LIk.ED ICOM RIGS BUT
THEY ARE EXEPENSIVE. CAN YOU RUN FULL 1QCI PER CENT DUTY CYCLE ON
RTTY OR DO YOU HAVE TO RUN AROUND 50 PER CENT. I GET OVER-HEATING
ON THIS OLD YAESU lQl. WHAT SORT OF ANTENNA SYSTEM DO YOU USE.
HERE IS A TRAPPED VERTICAL WITH 8CI METERS TUNED TO RTTY SPOT AT
~;59(:1.
I STILL USE CREED 7 THOUGH AM GETTING FED UP WITH MECHANICAL
BREAK- W WN AND NOISE BUT I HAVE HEARD ABOUT RFI AND HOME
COMPUTER5. MY NEPHEW HAS A SPECTRUM, CAN YOU GET RTTY SOFTWARE
FOR THAT/.
G3IMs G3IMS DE G4EJE G4EJE
** Page 107
CHAPTER 10
Hacking: the Future
Security is now probably the biggest single growth area within the
mainstream computer business. At conference after conference,
consultants compete with each other to produce the most frightening
statistics.
The main concern, however, is not hacking but fraud. Donn Parker,
a frequent writer and speaker on computer crime based at the Stanford
Research Institute has put US computer fraud at $3000 million a year;
although reported crimes amount to only $100 million annually. In
June 1983 the Daily Telegraph claimed that British computer-related
frauds could be anything between £500 million and £2.5 billion a
year. Detective Inspector Ken McPherson, head of the computer crime
unit at the Metropolitan Police, was quoted in 1983 as saying that
within 15 years every fraud would involve a computer. The trouble is,
very few victims are prepared to acknowledge their losses. To date,
no British clearing bank has admitted to suffering from an
out-and-out computer fraud, other than the doctoring of credit and
plastic ID cards. Few consultants believe that they have been immune.
However, to put the various threats in perspective, here are two
recent US assessments. Robert P Campbell of Advanced Information
Management, formerly head of computer security in the US Army,
reckons that only one computer crime in 100 is detected; of those
detected, 15 per cent or fewer are reported to the authorities, and
that of those reported, one in 33 is successfully prosecuted--a
'clear-up' rate of one in 22,000.
And Robert Courtney, former security chief at IBM produced a list
of hazards to computers: 'The No 1 problem now and forever is errors
and omissions'. Then there is crime by insiders, particularly
non-technical people of three types: single women under 35; 'little
old ladies' over 50 who want to give the money to charity; and older
men who feel their careers have left them neglected. Next, natural
disasters. Sabotage by disgruntled employees. Water damage. As for
hackers and other outsiders who break in, he estimates it is less
than 3 per cent of the total.
** Page 108
Here in the UK, the National Computing Centre says that at least
90 per cent of computer crimes involve putting false information into
a computer, as opposed to sophisticated logic techniques; such crimes
are identical to conventional embezzlement: looking for weaknesses
in an accounting system and taking advantage. In such cases the
computer merely carries out the fraud with more thoroughness than a
human, and the print-out gives the accounts a spurious air of being
correct.
In the meantime, we are on the threshold of a new age of
opportunities for the hacker. The technology we can afford has
suddenly become much more interesting.
The most recent new free magazines to which I have acquired
subscriptions are for owners of the IBM PC, its variants and clones.
There are two UK monthlies for regular users, another for corporate
buyers and several US titles.
The IBM PC is only partly aimed at small business users as a
stand-alone machine to run accounting, word processing, spread- sheet
calculation and the usual business dross; increasingly the marketing
is pitching it as an executive work-station, so that the corporate
employee can carry out functions not only local to his own office,
but can access the corporate mainframe as well--for data, messaging
with colleagues, and for greater processing power.
In page after page, the articles debate the future of this
development--do employees want work-stations? Don't many bosses still
feel that anything to do with typing is best left to their secretary?
How does the executive workstation relate to the mainframe? Do you
allow the executive to merely collect data from it, or input as well?
If you permit the latter, what effect will this have on the integrity
of the mainframe's files? How do you control what is going on? What
is the future of the DP professional? Who is in charge?
And so the articles go on. Is IBM about to offer packages which
integrate mainframes and PCs in one enormous system, thus effectively
blocking out every other computer manufacturer and software publisher
in the world by sheer weight and presence?
I don't know the answers to these questions, but elsewhere in
these same magazines is evidence that the hardware products to
support the executive workstation revolution are there--or, even if
one has the usual cynicism about computer trade advertising ahead of
actual availability, about to be.
The products are high quality terminal emulators, not the sort of
thing hitherto achieved in software--variants on asynchronous
protocols with some fancy cursor addressing--but cards capable of
supporting a variety of key synchronous communications, like 327x
(bisynch and SDLC), and handling high-speed file transfers in CICs,
TSO, IMS and CMS.
** Page 109
These products feature special facilities, like windowing or
replicate aspects of mainframe operating systems like VM (Virtual
Machine), giving the user the experience of having several different
computers simultaneously at his command. Other cards can handle IBM's
smaller mini- mainframes, the Systems/34 and /38. Nor are other
mainframe manufacturers with odd-ball comms requirements ignored:
ICL, Honeywell and Burroughs are all catered for. There are even
several PC add-ons which give a machine direct X.25; it can sit on a
packet-switched network without the aid of a PAD.
Such products are expensive by personal micro standards, but it
means that, for the expenditure of around £8000, the hacker can call
up formidable power from his machine. The addition of special
environments on these new super micros which give the owner direct
experience of mainframe operating systems--and the manuals to go with
them--will greatly increase the population of knowledgeable computer
buffs. Add to this the fact that the corporate workstation market, if
it is at all succesful, must mean that many executives will want to
call their mainframe from home --and there will be many many more
computer ports on the PTSN or sitting on PSS.
There can be little doubt that the need for system security will
play an increasing role in the specification of new mainframe
installations. For some time, hardware and software engineers have
had available the technical devices necessary to make a computer
secure; the difficulty is to get regular users to implement the
appropriate methods--humans can only memorise a limited number of
passwords. I expect greater use will be made of threat monitoring
techniques: checking for sequences of unsuccessful attempts at
logging in, and monitoring the level of usage of customers for
extent, timing, and which terminals or ports they appear on.
The interesting thing as far as hackers are concerned is that it
is the difficulty of the exercise that motivates us, rather than the
prospect of instant wealth. It is also the flavour of naughty, but
not outright, illegality. I remember the Citizens Band radio boom of
a few years ago: it started quietly with just a handful of London
breakers who had imported US sets, really simply to talk to a few
friends. One day everyone woke up, switched on their rigs and
discovered overnight there was a whole new sub-culture out there,
breathing the ether. Every day there were more and more until no
spare channels could be found. Then some talented engineers found out
how to freak the rigs and add another 40 channels to the original 40.
And then another 40. Suddenly there were wholesalers and retailers
and fanzines, all selling and promoting products the using or
manufacturing of which was illegal under British law.
** Page 110
Finally, the government introduced a legalised CB, using different
standards from the imported US ones. Within six months the illegal
scene had greatly contracted, and no legal CB service of comparable
size ever took its place. Manufacturers and shop- keepers who had
expected to make a financial killing were left with warehouses full
of the stuff. Much of the attraction of AM CB was that it was
forbidden and unregulated. There is the desire to be an outlaw, but
clever and not too outrageous with it, in very many of us.
So I don't believe that hacking can be stopped by tougher
security, or by legislation, or even by the fear of punishment.
Don't get me wrong: I regard computers as vastly beneficial. But
they can threaten our traditional concepts of freedom, individuality
and human worth I like to believe hacking is a curious
re-assertion of some of those ideas.
The challenge of hacking is deeply ingrained in many computer
enthusiasts; where else can you find an activity the horizons of
which are constantly expanding, where new challenges and dangers can
be found every day, where you are not playing a visibly artificial
'game', where so much can be accessed with so little resource but a
small keyboard, a glowing VDU, an inquisitive and acquisitive brain,
and an impish mentality?
** Page 111
APPENDIX I
Trouble Shooting
The assumption is that you are operating in the default mode of
300/300 baud asynchronous using CCITT tones, 7 bits, even parity, one
stop bit, full-duplex/echo off, originate. You have dialled the
remote number, seized the line and can hear a data tone. Something is
not working properly. This is a partial list of possibilities.
The screen remains blank.
* A physical link has failed -- check the cables between computer,
modem and phone line.
* The remote modem needs waking up--send a <cr> or failing that, a
ENQ (<ctrl>E), character.
* The remote modem is operating at a different speed. Some modems
can be brought up to speed by hitting successive <cr>s; they usually
begin at 110 baud and then go to 300,so two successive <cr>s should
do the trick.
* The remote modem is not working at V21 standards, either because
it is a different CCITT standard, e.g. V22, V22 bis, V23 etc or
operates on Bell (US) tones.
* Since different standards tend to have different 'wake-up' tones
which are easily recognised with practice, you may be able to spot
what is happening. It shouldn't need to be said that if you are
calling a North American service you should assume Bell tones.
* Both your modem and that of the remote service are in answer or in
originate and so cannot 'speak' to each other. Always assume you are
in the originate mode.
* The remote service is not using ASCII/International Alphabet No 5.
The screen fills with random characters
* Data format different from your defaults--check 7 or 8 bit
characters, even/odd parity, stop and start bits.
* Mismatch of characters owing to misdefined protocol--check
start/stop, try alternately EOB/ACK and XON/XOF.
* Remote computer operating at a different speed from you-- try, in
order, 110, 300, 600, 1200, 75.
** Page 112
* Poor physical connection--if using an acoustic coupler check
location of handset, if not, listen on line to see if it is noisy or
crossed.
* The remote service is not using ASCII/International Alphabet No 5.
Every character appears twice
* You are actually in half-duplex mode and the remote computer as
well as your own are both sending characters to your screen--switch
to full-duplex/echo off.
All information appears on only one line, which is constantly
overwritten.
* The remote service is not sending line feeds--if your terminal
software has the facility, enable it to induce line feeds when each
display line is filled. Many on-line services and public dial-up
ports let you configure the remote port to send line feeds and vary
line length. Your software may have a facility to show control
characters, in which case you will see <ctrl>J if the remote service
is sending line feeds.
Wide spaces appear between display lines.
* The remote service is sending line feeds and your software is
inducing another one simultaneously--turn off your induced carriage
return facility. In 'show control character' mode, you will see
<ctrl>Js.
Display lines are broken awkwardly
* The remote service is expecting your screen to support more
characters than it is able. Professional services tend to expect 80
characters across whilst many personal computers may have less than
40, so that they can be read on a tv screen. Check if your software
can help, but you may have to live with it. Alternatively, the
remote computer may let you reconfigure its character stream.
Most of the display makes sense, but every so often it becomes
garbled
* You have intermittent line noise--check if you can command the
remote computer to send the same stream again and see if you get the
garbling.
* The remote service is sending graphics instructions which your
computer and software can't resolve.
** Page 113
The display contains recognisable characters in definite groupings,
but otherwise makes no sense The data is intended for an intelligent
terminal, which will combine the transmitted data with a local
program so that it makes sense.
* The data is intended for batch processing.
* The data is encrypted Although the stream of data appeared
properly on your vdu, when you try to print it out, you get
corruption and over-printing
* Most printers use a series of special control characters to enable
various functions--line feeds, back-space, double- intensity, special
graphics etc. The remote service is sending a series of control
characters which, though not displayed on your screen, are
'recognised' by your printer, though often in not very helpful ways.
You may be able to correct the worst problems in software, e.g. by
enabling line-feeds; alternatively many printers can be re-configured
in hardware by appropriate settings of DIL switches internally.
When accessing a viewdata service, the screen fills with squares.
* The square is the standard display default if your viewdata
terminal can't make sense of the data being sent to it.
* Check physical connections and listen for line noise.
* The viewdata host does not work to UK viewdata standards-- French
viewdata uses parallel attributes and has a number of extra features.
The CEPT standard for Europe contains features from both the UK and
French systems and you may be able to recognise some of the display.
North American videotex is alpha-geometric and sends line drawing
instructions rather than characters.
* The viewdata host has enhanced graphics features, perhaps for
dynamically redefined character sets, alphageometric instructions, or
alpha-photographic (full resolution) pictures. If the host has some
UK standard-compatible features, you will be able to read them
normally. If the cursor jumps about the screen, the host has dynamic
graphics facilities. If the viewdata protocol is anything at all like
the UK standard, you should see regular clear-screens as each new
page comes up; however, advanced graphics features tend to work by
suppressing clear-screens.
** Page 114
* The service you have dialled is not using viewdata. PSS is
accessible at 75/1200, as are one or two direct-dial services. In
this case you should be seeing a conventional display or trying one
of the other suggestions in this appendix. It is usual to assume that
any subscriber dialling into a 75/1200 port has only a 40 character
display.
You can't see what you are typing
* The remote computer is not echoing back to you--switch to
half-duplex. If the remote computer's messages now appear doubled;
that would be unusual but not unique; you will have to toggle back to
full-duplex for receive.
Data seems to come from the remote computer in jerky bursts rather
than as a smooth stream.
* If you are using PSS or a similar packet-switched service and it
is near peak business hours either in your time zone or in that of
the host you are accessing, the effect is due to heavy packet
traffic. There is nothing you can do--do not send extra commands to
'speed things up' as those commands will arrive at the host
eventually and cause unexpected results.
* The host is pausing for a EOB/ACK or XON/XOF message-- check your
protocol settings--try sending ctrl-Q or ctrl-F.
You have an apparently valid password but it is not accepted.
* You don't have a valid password, or you don't have all of it.
* The password has hidden control characters which don't display on
the screen. Watch out for <ctrl>H -- the back-space, which will
over-write an existing displayed character.
* The password contains characters which your computer doesn't
normally generate--check your terminal software and see if there is a
way of sending them.
Most of the time everything works smoothly, but you can't get past
certain prompts
* The remote service is looking for characters your computer doesn't
normally generate. Check your terminal software and see if there is a
way of sending them.
A list or file called up turns out to be boring--can you stop it?
* Try sending <ctrl>S; this may simply make the remote machine
pause, until a <ctrl>Q is sent--and you may find the list resumes
where it left off. On the other hand it may take you on to a menu.
* Send a BREAK signal (<ctrl>1). If one BREAK doesn't work, send
another in quick succession.
** Page 115
You wish to get into the operating system from an applications
program.
* Don't we all? There is no standard way of doing this, and indeed
it might be almost impossible, because the operating system can only
be addressed by a few privileged terminals, of which yours (and its
associated password) is not one. However, you could try the
following:
* Immediately after signing on, send two BREAKs (<ctrl>1).
* Immediately after signing on, try combinations of ESC, CTRL and
SHIFT. As a desperate measure, send two line feeds before signing
on--this has been known to work!.
* At an options page, try requesting SYSTEM or some obvious
contraction like SYS or X. If in the Basic language, depending on the
dialect, SYSTEM or X in immediate mode should get you the operating
system.
You are trying to capture data traffic from a short-wave radio and are having
little success
* Your computer could be emitting so much radio noise itself that
any signal you are attempting to hear is squashed. To test: tune your
radio to a fairly quiet short-wave broadcast and then experiment
listening to the background hash with the computer switched first
on, then off. If the noise level drops when you turn off the
computer, then you need to arrange for more rf suppression and to
move the computer and radio further apart. Another source of rf noise
is the sync scan in a tv tube.
* If you can hear the two-tones of rtty traffic but can't get
letters resolved, check that your terminal unit is locking on to the
signal (often indicated by LEDs); you should then at least get some
response on your screen, if it doesn't make immediate sense.
* Once you have letters on screen, try altering the speed at which
you are receiving (see chapter 10); check also that you are reading
in the right 'sense', ie that mark and space have not been reversed.
* In addition to signals sent with the conventional International
Telegraphic Code No 2 (Baudot), variants exist for foreign letter
sets, like Cyrillic, which your software may not be able to resolve.
* There are other data-type services which sound a little like RTTY,
but are not: they include FAX (facsimile) hellschreiber ( a form of
remote dot-matrix printing), SITOR (see chapter 10) and special
military/diplomatic systems.
** Page 116
APPENDIX II
Glossary
This glossary collects together the sort of name, word, abbreviation
phrase you could come across during your network adventures
and for which you may not be able to find a precise definition
ACK
Non--printing character used in some comms protocols to indicate that
a block has been received and that more can be sent; used in
association with EOB.
ANSI
American National Standards Institute--one of a number of standards
organizations.
Answer mode
When a modem is set up to receive calls--the usual mode for a host.
The user's computer will be in originate.
ARQ
Automatic Repeat Request--method of error correction.
ASCII
American Standard Code for Information Interchange--alternate name
for International Telegraph Alphabet No 5: 7-bit code to symbolise
common characters and comms instructions, usually transmitted as
8-bit code to include a parity bit.
ASR
Automatic Send Receive--any keyboard terminal capable of generating a
message into off-line storage for later transmission; includes
paper-tape telex machines as well as microcomputers.
Asynchronous
Description of communications which rely on 'start' and 'stop' bits
to synchronise originator and receiver of data--hence asynchrnous
protocols, channels, modems, terminals etc.
** Page 117
Backward channel
Supervisory channel, not used as main channel of communication; in
viewdata the 75 baud back from the user to the host.
Baud
Measure of the signalling rate on a data channel, number of
signalling elements per second.
Baseband
Modulation is direct on the comms line rather than using audio or
radio frequencies; used in some local area networks. A baseband or
'short-haul' modem can be used to link computers in adjacent offices,
but not over telephone lines.
Baudot
5-bit data code used in telegraphy, telex and RTTY--also known as
International Telegraph Alphabet No 2.
Bell
(1) non-printing character which sounds a bell or bleep, usually
enabled by <ctrl> G; (2) Common name for US phone company and, in
this context, specifiers for a number of data standards and services,
e.g. Bell 103a, 202a, 212a, etc--see Appendix V
Bit Binary digit
value 0 or 1.
Broadband
Broadband data channels have a wider bandwidth than ordinary
telephone circuits--12 times in fact, to give a bandwidth of 48kHz,
over which may simultaneous high-speed data transfers can take place.
Broadcast service
Data service in which all users receive the same information
simultaneously, without the opportunity to interrogate or query;
e.g. news services like AP, Reuters News, UPI etc. See also on-line
service.
Bisynchronous
IBM protocol involving synchronous transmission of binary coded data.
** Page 118
BLAISE
British Library Automated Information Service-- substantial
bibliographic on-line host.
BREAK
Non-printing character used in some data transmission protocols and
found on some terminals--can often be regenerated by using <ctrl> 1.
BSC
Binary Synchronous Communications--see bisynchronous.
I Byte
Group of bits (8) representing one data character.
Call accept
In packet-switching, the packet that confirms the party is willing to
proceed with the call.
Call redirection
In packet-switching, allows call to be automatically redirected from
original address to another, nominated address.
Call request
In packet-switching, packet sent to initiate a datacall.
CCITT
Comite Consultatif International Telephonique et Telegraphique
--committee of International Telecommunications Union which sets
international comms standards. Only the US fails to follow its
recommendations in terms of modem tones, preferring 'Bell' tones. The
CCITT also sets such standards as V21, 24, X25 etc.
Character terminal
In packet-switching, a terminal which can only access via a PAD.
Cluster
When two or more terminals are connected to a data channel at a
single point.
Common Carrier
A telecommunications resource providing facilities to the public.
** Page 119
Connect-time
Length of time connected to a remote computer, often the measure of
payment. Contrast with cpu time or cpu units, which measures how
much 'effort' the host put into the communication.
CPS
Characters Per Second.
Cpu Time
In an on-line session, the amount of time the central processor
actually spends on the interaction process, as opposed to connect-
time; either can be used as the basis of tariffing.
CRC
Cyclic Redundancy Check--error detection method.
CUG
Closed User Group--group of users/terminals who enjoy privacy with
respect to a public service.
Datacall
In packet-switching, an ordinary call, sometimes called a 'switched
virtual call'.
Dataline
In packet-switching, dedicated line between customer's terminal and
packet-switch exchange (PSE).
DCE
Data Circuit-terminating Equipment--officialese for modems.
DTE
Data Terminal Equipment--officialese for computers.
EBCDIC
Extended Binary Coded Decimal Interchange Code--IBM's alternative to
ASCII, based on an 8-bit code, usually transmitted synchronously. 256
characters are available.
Emulator
Software/hardware set-up which makes one device mimic another, e.g. a
personal computer may emulate an industry-standard dumb terminal like
the VT100. Compare simulator, which gives a device the attributes of
another, but not necessarily in real time, e.g. when a large mini
carries a program making it simulate another computer to develop
software.
** Page 120
Euronet-Diane
European direct access information network.
Datel
BT's name for its data services, covering both the equipment and the
type of line, e.g. Datel 100 corresponds to telegraph circuits, Datel
200 is the usual 300/300 asynchronous service, Datel 400 is for
one-way transmissions e.g. monitoring of remote sites, Datel 600 is
a two- or four-wire asynchronous service at up to 1200 baud, Datel
2400 typically uses a 4-wire private circuit at 2400 baud
synchronous, etc. etc.
DES
Data Encryption Standard--a US-approved method of encrypt- ing data
traffic, and somewhat controversial in its effectiveness.
Dialog
Well-established on-line host available world-wide covering an
extensive range of scientific, bibiographic and news services. Also
known as Lockheed Dialog.
Dial-up
Call initiated via PTSN, no matter where it goes after that; as
opposed to service available via permanent leased line.
Duplex
Transmission in two directions simultaneously, sometimes called
full-duplex; contrast half-duplex, in which alternate transmissions
by either end are required. NB this is terminology used in data
communications over land-lines. Just to confuse matters, radio
technology refers to simplex, when only one party can transmit at a
time and a single radio frequency is used; two-frequency-simplex or
half-duplex when only one party can speak but two frequencies are
used, as in repeater and remote base working; and full-duplex, when
both parties can speak simultaneously and two radio frequencies are
used, as in radio-telephones.
Echo
(1) When a remote computer sends back to the terminal each letter as
it is sent to it for confirming re-display locally. (2) Effect on
long comms lines caused by successive amplifications
--echo-suppressors are introduced to prevent disturbance caused by
this phenomenon, but in some data transmission the echo- suppressors
must be switched off.
** Page 121
EIA
Electronic Industries Association, US standards body.
ENQ
Non-printing character signifying 'who are you?' and often sent by
hosts as they are dialled up. When the user's terminal receives ENQ
it may be programmed to send out a password automatically.
Corresponds to <esc> E.
EOB
End Of Block--non-printing character used in some protocols, usually
in association with ACK.
Equalisation
Method of compensation for distortion over long comms channels.
FDM
Frequency Division Multiplexing--a wide bandwidth transmission
medium, e.g. coaxial cable, supports several narrow band- width
channels by differentiating by frequency; compare time division
multiplexing.
FSK
Frequency Shift Keying--a simple signalling method in which
frequencies but not phase or amplitude are varied according to
whether '1' or '0' is sent--used in low-speed asynchronous comms both
over land-line and by radio.
Handshaking
Hardware and software rules for remote devices to communicate with
each other, supervisory signals such as 'wait', 'acknowledge',
'transmit', 'ready to receive' etc.
HDLC
In packet-switching, High Level Data Link Control procedure, an
international standard which detects and corrects errors in the
stream of data between the terminal and the exchange--and to provide
flow control. Host The 'big' computer holding the information the
user wishes to retrieve.
** Page 122
Infoline
Scientific on-line service from Pergamon.
ISB
see sideband.
ISO
International Standards Organisation.
LAN
Local Area Network--normally using coaxial cable, this form of
network operates at high speed over an office or works site, but no
further. May have inter-connect facility to PTSN or PSS.
LF
Line Feed--cursor moves active position down one line--usual code is
<ctrl>J; not the same as carriage return, which merely sends cursor
to left-hand side of line it already occupies. However, in many
protocols/terminals/set-ups, hitting the <ret> or <enter> button
means both <lf> and <cr>.
Logical Channel
Apparently continuous path from one terminal to another.
LSB
see sideband.
KSR
Keyboard Send Receive--terminal with keyboard on which anything that
is typed is immediately sent. No off-line preparation facility, e.g.
teletypewriter, 'dumb' terminals.
Macro software
Facility frequently found in comms programs which permits the
preparation and sending of commonly-used strings of information,
particularly passwords and routing instructions.
Mark
One of the two conditions on a data communications line, the other
being 'space'; mark indicates 'idle' and is used as a stop bit.
** Page 123
Message switching
When a complete message is stored and then forwarded, as opposed to a
packet of information. This technique is used in some electronic mail
services, but not for general data transmission.
Modem
Modulator-demodulator.
Multiplexer
Device which divides a data channel into two or more independent
channels .
MVS
Multiple Virtual Storage--IBM operating system dating from mid-70s.
NUA
Network User Address, number by which each terminal on a
packet-switch network is identified (character terminals don't have
them individually, because they use a PAD). In PSS, it's a 10-digit
number.
NUI
Network User Identity, used in PSS for dial-up access by each user.
Octet
In packet-switching, 8 consecutive bits of user data, e.g. 1
character.
On-line service
Interrogative or query service available for dial-up. Examples
include Lockheed Dialog, Blaise, Dow Jones News Retrieval, etc;
leased-line examples include Reuters Monitor, Telerate.
Originate
Mode-setting for a modem operated by a user about to call another
computer.
OSI
Open Systems Interconnect--intended world standard for digital
network connections--c.f. SNA. Packet terminal Terminal capable of
creating and disassembling packets, interacting with a
packet-network, c.f. character terminal.
** Page 124
PAD
Packet Assembly/disassembly Device--permits 'ordinary' terminals to
connect to packet switch services by providing addressing, headers,
(and removal), protocol conversion etc.
Parity checking
Technique of error correction in which one bit is added to each data
character so that the number of bits is always even (or always odd).
PDP/8 & /11
Large family of minis, commercially very sucessful, made by DEC. the
PDP 8 was 12-bit, the PDP 11 is 16-bit. The LSI 11 have strong family
connections to the PDP 11, as have some configurations of the
desk-top Rainbow.
Polling
Method of controlling terminals on a clustered data network, where
each is called in turn by the computer to see if it wishes to
transmit or receive.
Protocol
Agreed set of rules.
PSE
Packet Switch Exchange--enables packet switching in a network.
PTSN
Public Switched Telephone Network--the voice-grade telephone network
dialled from a phone. Contrast with leased lines, digital networks,
conditioned lines etc.
PTT
jargon for the publicly-owned telecommunications authority/ utility
PVC
Permanent Virtual Circuit--a connection in packet switching which is
always open, no set-up required.
** Page 125
Redundancy checking
Method of error correction.
RS232C
The list of definitions for interchange circuit: the US term for
CCITT V24--see Appendix III.
RSX-ll
Popular operating system for PDP/11 family.
RTTY
Radio Teletype -- method of sending telegraphy over radio waves.
RUBOUT
Back-space deleting character, using <ctrl>H.
Secondary channel
Data channel, usually used for supervision, using same physical path
as main channel; in V23 which is usually 600 or 1200 baud
half-duplex, 75 baud traffic is supervisory but in viewdata is the
channel back from the user to the host, thus giving low-cost full
duplex.
Segment
Chargeable unit of volume on PSS.
Serial transmission
One bit at a time, using a single pair of wires, as opposed to
parallel transmission, in which several bits are sent simultaneously
over a ribbon cable. A serial interface often uses many more than two
wires between computer and modem or computer and printer, but only
two wires carry the data traffic, the remainder being used for
supervision, electrical power and earthing, or not at all.
Sideband
In radio the technique of suppressing the main carrier and limiting
the transmission to the information-bearing sideband. To listen at
the receiver, the carrier is re-created locally. The technique, which
produces large economies in channel occupany, is extensively used in
professional, non-broadcast applications. The full name is single
side-band, supressed carrier. Each full carrier supports two
sidebands, an upper and lower, USB and LSB respectively; in general,
USB is used for speech, LSB for data, but this is only a
convention--amateurs used LSB for speech below 10 MHz, for example.
ISB, independent side-band, is when the one carrier supports two
sidebands with separate information on them, usually speech on one
and data on the other. If you listen to radio teletype on the 'wrong'
sideband, 'mark' and 'space' values become reversed with a consequent
loss of meaning.
** Page 126
SITOR
Error-correction protocol for sending data over radio-path using
frequent checks and acknowledgements.
SNA
System Network Architecture-- IBM proprietary networking protocol,
the rival to OSI.
Space
One of two binary conditions in a data transmission channel, the
other being 'mark'. Space is binary 0.
Spooling
Simultaneous Peripheral Operation On-Line--more usually, the ability,
while accessing a database, to store all fetched information in a
local memory buffer, from which it may be recalled for later
examination, or dumped to disc or printer.
Start/Stop
Asynchronous transmission; the 'start' and 'stop' bits bracket each
data character.
Statistical Multiplexer
A statmux is an advanced multiplexer which divides one physical link
between several data channels, taking advantage of the fact that not
all channels bear equal traffic loads.
STX
Start Text--non-printing character used in some protocols.
SVC
Switched Virtual Circuit--in packet switching, when connection
between two computers or computer and terminal must be set up by a
specific call.
** Page 127
SYN
Non-printing character often used in synchronous transmission to tell
a remote device to start its local timing mechanism.
Synchronous
Data transmission in which timing information is super-imposed ~,n
pure data. Under this method 'start/stop' techniques are not used
and data exchange is more efficient, hence synchronous channel,
modem, terminal, protocol etc.
TDM
Time Division Multiplex--technique for sharing several data channels
along one high-grade physical link. Not as efficient as statistical
techniques.
Telenet
US packet-switch common carrier.
Teletex
High-speed replacement for telex, as yet to find much commercial
support.
Teletext
Use of vertical blanking interval in broadcast television to transmit
magazines of text information, e.g. BBC's Ceefax and IBA's Oracle.
Telex
Public switched low-speed telegraph network.
TOPIC
The Stock Exchange's market price display service; it comes down a
leased line and has some of the qualities of both viewdata and
teletext.
Tymnet
US packet-switch common carrier.
V-standards
Set of recommendations by CCITT--see Appendix III.
VAX
Super-mini family made by DEC; often uses Unix operating system.
** Page 128
Viewdata
Technology allowing large numbers of users to access data easily on
terminal based (originally) on modified tv sets. Information is
presented in 'page' format rather than on a scrolling screen and the
user issues all commands on a numbers-only keypad. Various standards
exist of which the UK one is so far dominant; others include the
European CEPT standard which is similar to the UK one, a French
version and the US Presentation Level Protocol. Transmission speeds
are usually 1200 baud from the host and 75 baud from the user.
Viewdata together with teletext is known jointly as videotex(t).
Virtual
In the present context, a virtual drive, store, machine etc is one
which appears to the user to exist, but is merely an illusion
generated on a computer; thus several users of IBM's VM operating
system each think they have an entire separate computer, complete
with drives, discs and other peripherals--in fact the one actual
machine can support several lower-level operating systems
simultaneously.
VT52/100
Industry-standard general purpose computer terminals with no storage
capacity or processing power but with the ability to be locally
programmed to accept a variety of asynchronous transmission
protocols--manufactured by DEC. The series has developed since the
VT100
X-standards
Set of recommendations by CCITT--see Appendix III.
XON/XOF
Pair of non-printing characters sometimes used in protocols to tell
devices when to start or stop sending. XON often corresponds to
<ctrl>Q and XOF to <ctrl>S.
80-80
Type of circuit used for telex and telegraphy--mark and space are
indicated by conditions of--or + 80 volts. Also known in the UK as
Tariff J. Usual telex speed is 50 baud, private wire telegraphy (news
agencies etc) 75 baud.
** Page 129
APPENDIX III
Selected CCITT Recommendations
V series: Data transmission over telephone circuits
V1 Power levels for data transmission over telephone lines
V3 International Alphabet No S (ASCII)
V4 General structure of signals of IA5 code for data
transmission over public telephone network
V5 Standardisation of modulation rates and data signalling
rates for synchronous transmission in general switched
network
V6 Ditto, on leased circuits
V13 Answerback simulator
V15 Use of acoustic coupling for data transmission
V19 Modems for parallel data transmission using telephone
signalling frequencies
V20 Parallel data transmission modems standardised for
universal use in the general switched telephone network
V21 200 baud modem standardised
V22 1200 bps full-duplex 2-wire modem for PTSN
V22bis 2400 bps full-duplex 2-wire modem for PTSN
V23 600/1200 bps modem for PTSN
V24 List of definitions for interchange circuits between data
terminal equipment and data circuit-terminating equipment
V25 Automatic calling and/or answering equipment on PTSN
V26 2400 bps modem on 4-wire circuit
V26bis 2400/1200 bps modem for PTSN
V27 4800 bps modem for leased circuits
V27bis 4800 bps modem (equalised) for leased circuits
V27 4800 bps modem for PTSN
V29 9600 bps modem for leased circuits
V35 Data transmission at 48 kbits/sec using 60-108 kHz band
circuits
** Page 130
X series: recommendations covering data networks
X1 International user classes of services in public data networks
X2 International user facilities in public data networks
X3 Packet assembly/disassembly facility (PAD)
X4 General structure of signals of IA5 code for transmission
over public data networks
X20 Interface between data terminal equipment and data
circuit-terminating equipment for start-stop transmission
services on public data networks
X20bis V21-compatible interface
X21 Interface for synchronous operation
X25 Interface between data terminal equipment and data
circuit-terminating equipment for terminals operating in
the packet-switch mode on public data networks
X28 DTE/DCE interface for start/stop mode terminal equipment
accessing a PAD on a public data network
X29 Procedures for exchange of control information and user
data between a packet mode DTE and a PAD
X95 Network parameters in public data networks
X96 Call progress signals in public data networks
X121 International addressing scheme for PDNs
** Page 131
APPENDIX IV
Computer Alphabets
Four alphabets are in common use for computer communications:
ASCII, also known as International Telegraphic Alphabet No 5; Baudot,
used in telex and also known as International Telegraphic Alphabet No
2; UK Standard videotex, a variant of ASCII; and EDCDIC, used by IBM.
ASCII
This is the standard, fully implemented character set. There are a
number of national variants: # in the US variant is £ in the UK
variant. Many micro keyboards cannot generate all the characters
directly, particularly the non-printing characters used for control
of transmission, effectors of format and information separators. The
'keyboard' column gives the usual method of providing them, but you
should check the firmware/software manuals for your particular
set-up. You should also know that many of the 'spare' control
characters are often used to enable special features on printers.
HEX DEC ASCII Name Keyboard Notes
00 0 NUL Null ctrl @
01 1 SOH Start heading ctrl A
02 2 STX Start text ctrl B
03 3 ETX End text ctrl C
04 4 EOT End transmission ctrl D
05 5 ENQ Enquire ctrl E
06 6 ACK Acknowledge ctrl F
07 7 BEL Bell ctrl G
08 8 BS Backspace ctrl H or special key
09 9 HT Horizontal tab ctrl I or special key
OA 10 LF Line feed ctrl J
OB 11 VT Vertical tab ctrl K
0C 12 FF Form feed ctrl L
** Page 132
OD 13 CR Carriage return ctrl M or special key
OE 14 SO Shift out ctrl N
OF 15 Sl Shift in ctrl O
10 16 DLE Data link escape ctrl P
11 17 DC1 Device control 1 ctrl Q also XON
12 18 DC2 Device control 2 ctrl R
13 19 DC3 Device control 3 ctrl S also XOF
14 20 DC4 Device control 4 ctrl T
15 21 NAK Negative acknowledge ctrl U
16 22 SYN Synchronous Idle ctrl V
17 23 ETB End trans. block ctrl W
18 24 CAN Cancel ctrl X
19 25 EM End medium ctrl Y
1A 26 SS Special sequence ctrl Z spare
1B 27 ESC Escape check manuals to
transmit
1C 28 FS File separator
1D 29 GS Group separator
1E 30 RS Record separator
1F 31 US Unit separator
20 32 SP Space
21 33 ~
22 34 "
23 35 # £
24 36 $
25 37 %
26 38 &
27 39 ' Apostrophe
28 40 (
29 41 )
2A 42 ~
2B 43 +
2C 44 , Comma
2D 45 -
2E 46 . Period
2F 47 / Slash
30 48 0
31 49 1
32 50 2
33 51 3
34 52 4
35 53 5
36 54 6
37 55 7
** Page 133
38 56 8
39 57 9
3A 58 : Colon
3B 59 ; Semicolon
3C 60 <
3D 61
3E 62 >
3F 63 ?
40 64 @
41 65 A
42 66 B
43 67 C
44 68 D
45 69 E
46 70 F
47 71 G
48 72 H
49 73 1
4A 74 J
4B 75 K
4C 76 L
4D 77 M
4E 78 N
4F 79 O
50 80 P
51 81 Q
52 82 R
53 83 S
54 84 T
55 85 U
56 86 V
57 87 W
58 88 X
59 89 Y
5A 90 Z
5B 91 [
5C 92 \ Backslash
5D 93 1
5E 94 ^ Circumflex
5F 95 _ Underscore
60 96 Grave accent
61 97 a
62 98 b
** Page 134
63 99 c
64 100 d
65 101 e
66 102 f
67 103 9
68 104 h
69 105 i
6A 106 j
6B 107 k
6C 108 l
6D 109 m
6E 110 n
6F 111 o
70 112 p
71 113 q
72 114 r
73 115 s
74 116 t
75 117 u
76 118 v
77 119 w
78 120 x
79 121 y
7A 122 z
7B 123 {
7C 124
7D 125 }
7E 126 ~ Tilde
7F 127 DEL Delete
Baudot
This is the telex/telegraphy code known to the CCITT as International
Alphabet No 2. It is essentially a 5-bit code, bracketed by a start
bit (space) and a stop bit (mark). Idling is shown by 'mark'. The
code only supports capital letters, figure and two 'supervisory'
codes: 'Bell' to warn the operator at the far end and 'WRU'--'Who are
you?' to interrogate the far end 'Figures' changes all characters
received after to their alternates and 'Letters' switches back. The
letters/figures shift is used to give the entire character set.
** Page 135
Viewdata
This is the character set used by the UK system, which is the most
widely used, world-wide. The character-set has many features in
common with ASCII but also departs from it in significant ways,
notably to provide various forms of graphics, colour controls,
screen-clear (ctrl L) etc. The set is shared with teletext which in
itself requires further special codes, e.g. to enable sub-titling to
broadcast television, news flash etc. If you are using proper
viewdata software, then everything will display properly; if you are
using a conventional terminal emulator then the result may look
confusing. Each character consists of 10 bits:
Start binary 0
7 bits of character code
Parity bit even
Stop binary 1
ENQ (Ctrl E) is sent by the host on log-on to initiate the
auto-log-on from the user's terminal. If no response is obtained, the
user is requested to input the password manually. Each new page
sequence opens with a clear screen instruction (Ctrl L, CHR$12)
followed by a home (Ctrl M, CHR$14).
Some viewdata services are also available via standard asynchronous
300/300 ports (Prestel is, for example); in these cases, the graphics
characters are stripped out and replaced by ****s; and the pages will
scroll up the screen rather than present themselves in the
frame-by-frame format.
** Page 136
*** Original contains a diagram of Viewdata Graphic Character Set.
** Page 137
If you wish to edit to a viewdata system using a normal keyboard,
or view a viewdata stream as it comes from a host using
'control-show' facilities, the table below gives the usual
equivalents. The normal default at the left-hand side of each line is
alphanumeric white. Each subsequent 'attribute', i.e. if you wish to
change to colour, or a variety of graphics, occupies a character
space. Routing commands and signals to start and end edit depend on
the software installed on the viewdata host computer: in Prestel
compatible systems, the edit page is *910#, options must be entered
in lower case letters and end edit is called by <esc>K.
esc A alpha red esc Q graphics red
esc B alpha green esc R graphics green
esc C alpha yellow esc S graphics yellow
esc D alpha blue esc T graphics blue
esc E alpha magenta esc U graphics magenta
esc F alpha cyan esc V graphics cyan
esc G alpha white esc W graphics white
esc H flash esc I steady
esc L normal height esc M double height
esc Y contiguous graphics esc Z separated graphics
esc ctrl D black background esc-shift M new background
(varies)
esc J start edit esc K end edit
EBCDIC
The Extended Binary Coded Decimal Interchange Code is a 256-state
8-bit extended binary coded digit code employed by IBM for internal
purposes and is the only important exception to ASCII. Not all 256
codes are utilised, being reserved for future expansion, and a number
are specially identified for application- specific purposes. In
transmission, it is usual to add a further digit for parity checking.
Normally the transmission mode is synchronous, so there are no
'start' and 'stop' bits. The table shows how EBCDIC compares with
ASCII of the same bit configuration.
** Page 138
IBM control characters:
EBCDIC bits Notes
NUL 0000 0000 Nul
SOH 0000 0001 Start of Heading
STX 0000 0010 Start of Text
ETX 0000 0011 End of Text
PF 0000 0100 Punch Off
HT 0000 0101 Horizontal Tab
LC 0000 0110 Lower Case
DEL 0000 0111 Delete
0000 1000
RLF 0000 1001 Reverse Line Feed
SMM 0000 1010 Start of Manual Message
VT 0000 1011 Vertical Tab
FF 0000 1100 Form Feed
CR 0000 1101 Carriage Return
SO 0000 1110 Shift Out
Sl 0000 1111 Shift In
DLE 0001 0000 Data Link Exchange
DC1 0001 0001 Device Control 1
DC2 0001 0010 Device Control 2
TM 0001 0011 Tape Mark
RES 0001 0100 Restore
NL 0001 0101 New Line
BS 0001 0110 Back Space
IL 0001 0111 Idle
CAN 0001 1000 Cancel
EM 0001 1001 End of Medium
CC 0001 1010 Cursor Control
CU1 0001 1011 Customer Use 1
IFS 0001 1100 Interchange File Separator
IGS 0001 1101 Interchange Group Separator
IRS 0001 1110 Interchange Record Separator
IUS 0001 1111 Interchange Unit Separator
DS 0010 0000 Digit Select
SOS 0010 0001 Start of Significance
FS 0010 0010 Field Separator
0010 0011
BYP 0010 0100 Bypass
LF 0010 0101 Line Feed
ETB 0010 0110 End of Transmission Block
** Page 139
EBCDIC bits Notes
ESC 0010 0111 Escape
0010 1000
0010 1001
SM 0010 1010 Set Mode
CU2 0010 1011 Customer Use 1
0010 1100
ENQ 0010 1101 Enquiry
ACK 0010 1110 Acknowledge
BEL 0010 1111 Bell
0011 0000
0011 0001
SYN 0011 0010 Synchronous Idle
0011 0011
PN 0011 0100 Punch On
RS 0011 0101 Reader Stop
UC 0011 0110 Upper Case
EOT 0011 0111 End of Transmission
0011 1000
0011 1001
0011 1010
CU3 0011 1011 Customer Use 3
DC4 0011 1100 Device Control 4
NAK 0011 1101 Negative Acknowledge
0011 1110
SUB 0011 1111 Substitute
SP 0100 0000 Space
** Page 140
APPENDIX V
Modems and Services
The table below shows all but two of the types of service you are likely to
come across; V-designators are the world-wide 'official names given by the
CCITT; Bell-designators are the US names:
Service Speed Duplex Transmit Receive Answer
Designator 0 1 0 1
V21 orig 300(*) full 1180 980 1850 1650 -
V21 ans 300(*) full 1850 1650 1180 980 2100
V23 (1) 600 half 1700 1300 1700 1300 2100
V23 (2) 1200 f/h(**) 2100 1300 2100 1300 2100
V23 back 75 f/h(**) 450 390 450 390 -
Bell 103 orig 300(*) full 1070 1270 2025 2225 -
Bell 103 ans 300(*) full 2025 2225 1070 1270 2225
Bell 202 1200 half 2200 1200 2200 1200 2025
(*)any speed up to 300 baud, can also include 75 and 110 baud
services
(**)service can either be half-duplex at 1200 baud or asymmetrical
full duplex, with 75 baud originate and 1200 baud receive (commonly
used as viewdata user) or 1200 transmit and 75 receive (viewdata
host)
The two exceptions are:
V22 1200 baud full duplex, two wire
Bell 212A The US equivalent
Both these services operate by detecting phase as well as tone.
British Telecom markets the UK services under the name of Datel as
follows--for simplicity The list covers only those services which use
the PTSN or are otherwise easily accessible--4-wire services, for
example are excluded.
** Page 141
Datel Speed Mode Remarks
100(H) 50 async Teleprinters, Baudot code
100(J) 75-110 async News services etc, Baudot code
50 async Telex service, Baudot code
200 300 async full duplex, ASCII
400 600 Hz async out-station to in-station only
600 1200 async several versions exist--for 1200
half-duplex; 75/1200 for viewdata
users; 1200/75forviewdata hosts; and
a rare 600 variant. The 75 speed is
technically only for supervision but
gives asymetrical duplex
BT has supplied the following modems for the various services-- the
older ones are now available on the 'second-user' market:
Modem No Remarks
1200 half-duplex--massive
2 300 full-duplex--massive
11 4800 synchronous--older type
12 2400/1200 synchronous
13 300 full-duplex--plinth type
20(1) 1200 half-duplex--'shoe-box' style
(2) 1200/75 asymetrical duplex--'shoe-box' style
(3) 75/1200 asymetrical duplex--'shoe-box' style
21 300 full-duplex--modern type
22 1200 half-duplex--modern type
24 4800 synchronous--modern type (made by Racal)
27A 1200 full duplex, sync or async (US made &
modified from Bell 212A to CCITT tones)
27B 1200 full duplex, sync or async (UK made)
You should note that some commercial 1200/1200 full duplex modems
also contain firmware providing ARQ error correction protocols;
modems on both ends of the line must have the facilities, of course.
** Page 142
BT Line Connectors
Modems can be connected directly to the BT network ('hard- wired')
simply by identifying the pair that comes into the building. Normally
the pair you want are the two outer wires in a standard 4 x 2 BT
junction box. (The other wires are the 'return' or to support a
'ringing' circuit.)
A variety of plugs and sockets have been used by BT. Until
recently, the standard connector for a modem was a 4-ring jack, type
505, to go into a socket 95A. Prestel equipment was terminated into a
similar jack, this time with 5 rings, which went into a socket type
96A. However, now all phones, modems, viewdata sets etc, are
terminated in the identical modular jack, type 600. The corresponding
sockets need special tools to insert the line cable into the
appropriate receptacles.
Whatever other inter-connections you see behind a socket, the two
wires of the twisted pair are the ones found in the centres of the
two banks of receptacles. North America also now uses a modular jack
and socket system, but not one which is physically compatible with UK
designs...did you expect otherwise?
** Page 143
APPENDIX VI
The Radio Spectrum
The table gives the allocation of the radio frequency spectrum up
30 MHz. The bands in which radio-teletype and radio-data traffic are
most common are those allocated to 'fixed' services, but data traffic
is also found in the amateur and maritime bands.
LF,MF,HF, RADIO FREQUENCY SPECTRUM TABLE
9 -- 14 Radionavigation
14 -- 19.95 Fixed/Maritime mobile
20 Standard Frequency & Time
20.05 -- 70 Fixed & Maritime mobile
70 -- 90 Fixed/Maritime mobile/Radionavigation
90 -- 110 Radionavigation
110 -- 130 Fixed/Maritime mobile/Radionavigation
130 -- 148.5 Maritime mobile/Fixed
148.5 -- 255 Broadcasting
255 -- 283.5 Broadcasting/Radionavigation(aero)
283.5 -- 315 Maritime/Aeronautical navigation
315 -- 325 Aeronautical radionavigation/Maritime
radiobeacons
325 -- 405 Aeronautical radionavigation
405 -- 415 Radionavigation (410 = DF)
415 -- 495 Aeronautical radionavigation/Maritime mobile
495 -- 505 Mobile (distress & calling) > 500:cw&rtty
505 -- 526.5 Maritime mobile/Aeronautical navigation
526.5 -- 1606.5 Broadcasting
1606.5 -- 1625 Maritime mobile/Fixed/Land mobile
1625 -- 1635 Radiolocation
1635 -- 1800 Maritime mobile/Fixed/Land mobile
1800 -- 1810 Radiolocation
1810 -- 1850 Amateur
1850 -- 2000 Fixed/Mobile
** Page 144
2000 -- 2045 Fixed/Mobile
2045 -- 2160 Maritime mobile/Fixed/Land mobile
2160 -- 2170 Radiolocation
2170 -- 2173.5 Maritime mobile
2173.5 -- 2190.5 Mobile (distress & calling) >2182--voice
2190.5 -- 2194 Maritime & Mobile
2194 -- 2300 Fixed & Mobile
2300 -- 2498 Fixed/Mobile/Broadcasting
2498 -- 2502 Standard Frequency & Time
2502 -- 2650 Maritime mobile/Maritime radionavigation
2650 -- 2850 Fixed/Mobile
2850 -- 3025 Aeronautical mobile (R)
3025 -- 3155 Aeronautical mobile (OR)
3155 -- 3200 Fixed/Mobile/Low power hearing aids
3200 -- 3230 Fixed/Mobile/Broadcasting
3230 -- 3400 Fixed/Mobile/Broadcasting
3400 -- 3500 Aeronautical mobile (R)
3500 -- 3800 Amateur/Fixed/Mobile
3800 -- 3900 Fixed/Aeronautical mobile (OR)
3900 -- 3930 Aeronautical mobile (OR)
3930 -- 4000 Fixed/Broadcasting
4000 -- 4063 Fixed/Maritime mobile
4063 -- 4438 Maritime mobile
4438 -- 4650 Fixed/Mobile
4650 -- 4700 Aeronautical mobile (R)
4700 -- 4750 Aeronautical mobile (OR)
4750 -- 4850 Fixed/Aeronautical mobile (OR)/
Land mobile/Broadcasting
4850 -- 4995 Fixed/Land mobile/Broadcasting
4995 -- 5005 Standard Frequency & Time
5005 -- 5060 Fixed/Broadcasting
5060 -- 5450 Fixed/Mobile
5450 -- 5480 Fixed/Aeronautical mobile (OR)/Land mobile
5480 -- 5680 Aeronautical mobile (R)
5680 -- 5730 Aeronautical mobile (OR)
5730 -- 5950 Fixed/Land mobile
5950 -- 6200 Broadcasting
6200 -- 6525 Maritime mobile
6525 -- 6685 Aeronautical mobile (R)
6685 -- 6765 Aeronautical mobile ~OR)
6765 -- 6795 Fixed/lSM
7000 -- 7100 Amateur
7100 -- 7300 Broadcasting
7300 -- 8100 Maritime mobile
** Page 145
8100 -- 8195 Fixed/Maritime mobile
8195 -- 8815 Maritime mobile
8815 -- 8965 Aeronautical mobile (R)
8965 -- 9040 Aeronautical mobile ~OR)
9040 -- 9500 Fixed
9500 -- 9900 Broadcasting
ggoo -- 9995 Fixed
9995 -- 10005 Standard Frequency & Time
10005 -- 10100 Aeronautical mobile (R)
10100 -- 10150 Fixed/Amateur(sec)
10150 -- 11175 Fixed
11175 -- 11275 Aeronautical mobile (OR)
11275 -- 11400 Aeronautical mobile (R)
11400 -- 11650 Fixed
11650 -- 12050 Broadcasting
2050 -- 12230 Fixed
12230 -- 13200 Maritime mobile
13200 -- 13260 Aeronautical mobile (OR)
13260 -- 13360 Aeronautical mobile (R)
13360 -- 13410 Fixed/Radio Astronomy
13410 -- 13600 Fixed
13600 -- 13800 Broadcasting
13800 -- 14000 Fixed
14000 -- 14350 Amateur
14350 -- 14990 Fixed
14990 -- 15010 Standard Frequency & Time
15010 -- 15100 Aeronautical mobile (OR)
15100 -- 15600 Broadcasting
15600 -- 16360 Fixed
16360 -- 17410 Maritime mobile
17410 -- 17550 Fixed
17550 -- 17900 Broadcasting
17900 -- 17970 Aeronautical mobile (R)
17970 -- 18030 Aeronautical mobile (OR)
18030 -- 18052 Fixed
18052 -- 18068 Fixed/Space Research
18068 -- 18168 Amateur
18168 -- 18780 Fixed
18780 -- 18900 Maritime mobile
18900 -- 19680 Fixed
** Page 146
19680 -- 19800 Maritime mobile
19800 -- 19990 Fixed
19990 -- 20010 Standard Frequency & Time
20010 -- 21000 Fixed
21000 -- 21450 Amateur
21450 -- 21850 Broadcasting
21850 -- 21870 Fixed
21870 -- 21924 Aeronautical fixed
21924 -- 22000 Aeronautical (R)
22000 -- 22855 Maritime mobile
22855 -- 23200 Fixed
23200 -- 23350 Aeronautical fixed & mobile (R)
23350 -- 24000 Fixed/Mobile
24000 -- 24890 Fixed/Land mobile
24890 -- 24990 Amateur
24990 -- 25010 Standard Frequency & Time
25010 -- 25070 Fixed/Mobile
25070 -- 25210 Maritime mobile
25210 -- 25550 Fixed/Mobile
25550 -- 25670 Radio Astronomy
25670 -- 26100 Broadcasting
26100 -- 26175 Maritime mobile
26175 -- 27500 Fixed/Mobile (CB) (26.975-27.2835 ISM)
27500 -- 28000 Meteorological aids/Fixed/Mobile (CB)
28000 -- 29700 Amateur
29700 -- 30005 Fixed/Mobile
Note: These allocations are as they apply in Europe, slight variations occur
in other regions of the globe.
** Page 147
APPENDIX VII
Port-finder Flowchart
This flow-chart will enable owners of auto-diallers to carry out
an automatic search of a range of telephone numbers to determine
which of them have modems hanging off the back.
It's a flow-chart and not a program listing, because the whole
exercise is very hardware dependent: you will have to determine what
sort of instructions your auto-modem will accept, and in what form;
you must also see what sort of signals it can send back to your
computer so that your program can 'read' them.
You will also need to devise some ways of sensing the phone line,
whether it has been seized, whether you are getting 'ringing', if
there is an engaged tone, a voice, a number obtainable tone, or a
modem whistle. Line seizure detect, if not already available on your
modem, is simply a question of reading the phone line voltage; the
other conditions can be detected with simple tone decoder modules
based on the 567 chip.
The lines from these detectors should then be brought to a A/D
board which your computer software can scan and read.
