[GreenKeys] re Question regarding TWX and Dial TWX...

[wa3frp at aol.com]

Let me try to fill in some of the blanks.
 
AT&T was in the TWX business and Western Union was in the Telex business.  TWX was used in North America only and at the end was composed of both baudot (3 row) and ASCII (4 row) machines. Telex was a worldwide network that was built to CCITT standards. 
 
Since these two networks, TWX and Telex, started differently, there were integration issues. TWX did not require answerback mechanisms. Telex required that each machine have a unique answerback message.  At the beginning of the message, the sender would transmit a WRU (Who aRe yoU) code usually FIGS D, and the recipient machine would automatically initiate a response which was encoded in a rotating drum with pegs. The position of the pegs sent an unambiguous identifying code to the sender, so the sender could verify connection to the correct recipient. The WRU code would also be sent at the end of the message, so a correct response would confirm that the connection had remained unbroken during the message transmission.
 
In addition, the baudot versions used a slightly different speed.  TWX used 60 WPM (45.45 baud) just like Amateur Radio RTTY uses today. Telex was just a little faster at 66 WPM (50 baud).
 
TWX used the public switched telephone network. In addition to having separate Area Codes (510, 610, 710 and 810) for the TWX service, the TWX lines were also set up with a special Class of Service to prevent connections to and from POTS to TWX and vice versa. 
 
By the time that I became involved in TWX, all of the loops were analog versus the 120 /240  VDC loops that Western Union had in place until the mid 1970s. 
 
Telex used a network and switches that were built and dedicated specifically for Telex.  This statement is true for the Western Union and CNCP portions of the network in the States and Canada but it is probably true for the rest of the world.
 
The Western Union Telex loops came in two flavors: The first option, sometimes called local or loop service, provided a 60 milliampere loop circuit from the exchange to the customer teleprinter. The second option, sometimes called long distance or polar was used when a 60 milliampere connection could not be achieved, provided a ground return polar circuit using 35 milliamperes on separate send and receive wires. By the mid 1970s, and under pressure from the Bell operating companies wanting to modernize their cable plant and lower the adjacent circuit noise that these Telex circuits sometimes caused, Western Union migrated customers to a third option called F1F2. This F1F2 option replaced the DC voltage of the local and long distance options with modems at the exchange and subscriber ends of the Telex circuit.
  
Western Union started offering connections from Telex to the AT&T Teletypewriter eXchange (TWX) system in May 1966 via its New York Information Services Computer Center. These connections were limited to those TWX machines that were equipped with automatic answerback capability per CCITT standard.
 
Western Union purchased the TWX system from AT&T in January 1969. See Western Union News Volume II, No. 4, January 15, 1969. The TWX system and the special area codes (510, 610, 710 and 810) continued right up to 1981 when Western Union completed the conversion to the Western Union Telex II system. Any remaining "3-row" baudot customers were converted to Western Union Telex service during the period 1979 to 1981.
 
Telex was very profitable for Western Union as it was making a margin of over 40% on revenues of 450M USD during the 1970s.  This was a higher profit margin than private wire which was basically break even and the telegram service which made some profit but nothing like 40%.
 
Deskfax was already on its way out by the mid to late 1960s when Telex was introduced. It also had limited use.  This was not typically a subscriber to subscriber service but a Western Union to subscriber service and a way for Western Union to get a printed telegram to a subscriber without manual physical delivery.
 
The Western Union involvement in Telex and Telex II service ended in July 1990 when WU reached agreement to sell its Business Services (Telex and EasyLink) unit to AT&T for $180 million cash.
 
Western Union had a virtual monopoly on Telex service in the USA but it did not have direct lines to other countries based on a 1939 agreement. Companies such as RCA Global Communications (Globecom), ITT World Communications (Worldcomm), Tropical Radio Telecommunications (TRT) and others provided gateway services for Telex traffic to and from other parts of the world. In addition, these International Record Carriers (IRCs) had the right to offer Telex service in the cities where they operated.  This was basically in New York City for Globecom, Worldcom and Miami for TRT. 
 
As Manager of Circuit Switching Systems, I was a part of the team that converted Delaware, New Jersey and Pennsylvania from TWX to Telex II in addition to my responsibilities for designing, implementing and operating the Telex network in those states. It was great to walk through a Telex exchange as it sounded like thousands of crickets and you knew that all of the "doorbell circuits" were working correctly just by the sounds of the exchange in operation. Bell System employees who worked in Number Five Crossbar know that I'm talking about.
 
73 de Russ WA3FRP