Cyprus Message Switching Systemby

Graham Smith, December 2017

Introduction

The Cyprus Message Switching System was developed for the CyprusTelecommunications Authority (CyTA) in the late 1960s and went live in 1970. Itprovided store and forward message handling and routing facilities for both theAeronautical Fixed Telecommunication Network (AFTN) and the public telegram networkin Cyprus. It replaced the manual torn tape systems that were then in use.

The system comprised 2 Myriad II computers, each with a single hard disc drive, togetherwith switching panels etc. There was also a control room equipped with a number ofteleprinters. It was located next to Nicosia International Airport although I believe that itwas re-located to Larnaca after the partition of the country in 1974. Nicosia airport is stillunused and is derelict.

For the AFTN network, the system had teleprinter communication channels to a number ofthe nearby countries in the eastern Mediterranean plus channels to the Control Tower etc.The ICAO address designation for Nicosia was LCNC (if I remember correctly). For thepublic telegram network, there were channels to several nearby countries plus longdistance ones to both London and Canada; there were also local channels to the telegramoffices in Nicosia and all the other major towns on the island. The system could support amaximum of 128 channels which included a number of local control & reporting channels.A few destinations operated with two or even three channels on that route; Athens I believewas one of these.

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Nicosia International Airport terminal building circa 1970

All traffic used the 5-unit CCITT No. 1 alphabet with one start bit and one and a half stopbits. Most of the channels operated at 50 baud (bits per second) or 6 & 2/3

characters per

second, a few were faster at 75 baud (10 cps) and a few were ARQ error corrected. Thechannel to Canada operated at three-quarter speed (5 cps). I think most of the channelswere cable (underwater where necessary) but I seem to remember that one or two weretropospheric scatter links and a couple of others were (HF) radio.

Development work had just started in 1966 when the author joined the team in Septemberof that year straight from college as a trainee computer programmer. All the software wasdeveloped at Great Baddow by members of the Central Automation Systems Department(CASD for short) which was part of Automation Division; Arthur Young was thedepartment manager, Alan Bartrup was my section manager and Brian Hammans was theteam leader. There were also a couple of people on the team from Lines Division atWrittle which was the lead organisation on the project. I think Eric Rose was thesalesman, Florian Lapinsky was chief designer and the engineer in charge in Cyprus wasBrian Guest. Other members of the software development team included Graham Smith,Mary Harries, Myra McKinley, John Rowe and Archie Dickson (CASD) and DickMuggeridge and John Selby (Lines).

The System

As stated above, the system had two Myriad II computers that acted as a dual replicatedsystem, both processed all the incoming messages and commands. One computer acted asthe main and the other as a hot standby; there was a parallel interconnection link. Themain computer performed all the output and the standby continually monitored the mainand could take over instantly in case of a failure; the roles could be changed over by asuitable supervisor command. The system could operate with a single computer and there

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The Ops building where our equipment was installed

was a supervisor command (“resync”) to bring the second computer back on-line as thestandby. This took time as it meant copying all the messages that were received duringsingle mode plus any configuration changes to the new standby across the interconnectionlink.

Each computer was fitted with a32k word core store (24 bit wordswere used on Myriads) and eacha l s o h a d a C o n t r o l D a t aCorporation (CDC) disk drive unitfitted with a single 5 platterremovable disk; the disk controllerwas a Marconi designed unit. Thedisk he ld a l l the messages(typically a few days worth oftraffic) together with all thes o f t w a r e a n d t h e s y s t e mconfiguration data. Only one diskpack was needed for each computerand was permanently fitted; therewere a few spares.

The default formatting for the disksprovided for 8 sectors each of 128words on a track plus a small indexsector (sector 0). This, we decided,was inefficient for our use asmessages could be quite small andarrived slowly. So we read thesmall print in the disk controllerhandbook. The format we designedhad about 30 small sectors of 33words each for the traffic and onesingle large sector per track (about1100 words) for the software.There were other formats for them e s s a g e i n d e x e s a n d t h econfiguration data.

In order to optimise the resync process we interleaved the message sectors in the order 1,11, 21, 2, 12 etc. We read the complete track in one go taking one revolution of the diskbut wrote the sectors in order. By interleaving them there was time to issue the next writecommand before for sector passed under the read/write head; thus we only took 3revolutions to write all 30 sectors.

Backup power supply was provided by a standby diesel generator and a motor flywheelalternator.

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Two views of the computer room showing the twoMyriads and their disc drives with the disc controllers

cabinets in the background

Operation

In the operations room there were a number of teleprinters. Each printer had a papercollector above it and a Temporary Out Of Service switch that an operator could toggle ifhe needed to change the paper roll or conduct any other maintenance on the printer.

The Supervisor position was flanked by the Report printer and the Alarm printer. TheSupervisor monitored the system, made any configuration changes and could send andreceive messages addressed to the station. The Alarm printer was used to tell thesupervisor of any significant event on the system whilst the Report printer was normallyused to print Supervisor requested reports of the system such as the state of the channelsand the lengths of the output queues.

There were four Journal printers which recorded all the traffic, one each for receivedmessages and one for transmitted messages on each network.

There were also two Intercept positions for dealing with messages that were receivedcorrupted or in error. There was one position for each network, each being provided withtwo teleprinters, one for receiving the corrupt message and one for retransmitting thecorrected message.

In the computer room there were also two other printers, the Engineering printers, one foreach computer and they worked independently of each other.

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The supervisor position. The guy on the left is examining one of the journals

Development, Installation & Commissioning

All the software development work was done at Baddow where the team had a number ofoffices in C Block (the old demountable building). Next door in A block a small testsystem was set up; this used Myriad I computers and no disc drive. The plan was that wewould deliver Phase 1 in the autumn of 1968 which would handle only the AFTN traffic tobe followed in early 1970 by the full system including discs.

The customer equipment was installed in A Block and we transferred our testing to that inmid 1968 promptly to discover a problem. In the interrupt area of the Myriad we had apair of instructions – ENTR and SETP. If we swopped the order of these two it allworked. We had been told that there were no differences between Myriad I and Myriad IIso we consulted Brian Partridge who pronounced it a “feature”. A few months later in thenext amendment to the Myriad User Code Programming Manual this feature wasdocumented – it said do not do this.

The customer equipment was packed up and sent to Cyprus for installation in late Summerand in September 1968 we went to Cyprus to test and commission Phase 1. There were afew problems with the hardware so testing was not very productive. And then the CyTAstaff went on strike so it was decided that we should abandon Phase 1 and return to the UKafter just 6 weeks on site.

Phase 2 development continued at Baddow with testing conducted on a test systeminstalled at Writtle. So in early 1970 we were off to Cyprus again to install andcommission the full system. There were 3 software engineers (Brian Hammans, the authorand John Rowe) and 2 hardware engineers together with the engineer in charge (BrianGuest). Two of software engineers left after a month or two leaving the author on site for4 months.

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In the foreground is one of the two intercept positions; the other is at the far end

Once installed the system shadowed the torn tape system, receiving all messages andoutputting them to locally fitted printers. During this period the operators gainedexperience in using the system and a few bugs were ironed out.

In the latter stages of commissioning the system we often had problems with the resyncprocess which failed leaving the new standby computer running as main in a singlecomputer system. After several weeks of hard debugging the fault was tracked down totwo instructions being in the wrong order, one of which was of course SETP. This gaverise to Graham's Maxim of software debugging – “The time taken to fix a fault is inverselyproportional to the time taken to detect it.”

In early May the AFTN system went live. This happened at 2 am local time i.e. midnightGMT. Just beforehand all the output channels were shut down followed by a greatunplugging and replugging of the switchboards to connect our outputs to the real channels.The operators then checked each channel before opening it once again to traffic output.All went well and after few hours of hard work by the operators the full AFTN system wasworking live. Success.

A week later we had a big celebration in a local restaurant with all the bigwigs fromMarconi & CyTA present. Shortly after that the Marconi staff left the island.

Miscellany

As Mothering Sunday approached that year the author sent a greetings telegram to hismother in the UK. Later that day, one of his colleagues was monitoring some of theshadow output channels and spotted a telegram addressed to the author and told him aboutit. He recalled a copy of it to the report printer and thereby got his own copy many hoursbefore he got the official copy. It was from his mother thanking him for his own earliertelegram to her.

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Brian Hammans, John Rowe and Graham Smith

By August 1970 the public telegram network had gone live and we heard that on the 13 th

the system crashed. It was President Makarios's birthday and he received so manytelegrams that the system could not cope – it just filled up and collapsed into a small heap.Oh dear. What they should have done was to have installed an extra channel or two to theNicosia central telegram office instead of just the one – maybe they did afterwards.

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The Averof Hotel where I stayed for 4 months. It's me by the entrance

The Ledra Palace Hotel where I stayed on the short trips

Over the next year, the author made 3 or 4 short trips to Nicosia either to install a patch orpossibly to do a bit of flag waving. As far as I can remember the system remained patchedthroughout its whole life. I don't recall ever rebuilding the software.

I believe the system remained operational until the early 1990s. By that time I hadtransferred to Marconi Communications Systems at New Street and it occurred to me thatthe company might have bid for its replacement as it was still into message switchingsystems. It decided not to.

I thoroughly enjoyed my time on the project, seeing it right through from start to finish. Itwasn't all hard work though as when I was not on call, Sunday usually saw me on a beachsomewhere possibly after having a good lunch by Kyrenia Harbour. On other days Iexplored the island, visiting Famagusta, the Troodos mountains and Limassol; I evenremember driving through Ayia Napa when it was just a small fishing village.

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The plane home