What is SNA/RJE?
Introduction to IBM 3770 SNA/RJE Communications
Who Uses 3770 SNA/RJE Communications Today?
What Did 3770 SNA/RJE Terminals Look Like?
What is SNA/RJE?
3770 SNA/RJE Communications Frequently Asked Questions
3770 SNA/ RJE Communications Glossary
Things to Consider When Purchasing 3770 SNA/RJE Emulation
|SNA is an acronym for "Systems Network
Architecture". SNA was introduced by
IBM in 1974 as a strategic architecture to
unify its teleprocessing systems and products
under a single set of protocols. Under SNA,
IBM has designed a flexible, ever expanding
networking system to provide interconnection
between mainframes, mini-computers (i.e.,
IBM System 36s, System 38s, and AS400s),
PCs, data terminals, and other devices such
as ATM machines. SNA has continued to evolve
over the years but it now being challenged
by TCP/IP and the Internet.
RJE is an acronym for "Remote Job Entry". The term was usually applied to a type of data terminal (i.e, an RJE terminal) used during the early days of SNA and before. These terminals, generally called IBM Modem 3770 data terminals, used punch cards and consisted of a card reader, up to two diskette drives (known as the exchange device), a card punch, and a line printer. 3770 terminals operated in an SNA environment, specifically using the Synchronous Data Link Communications (SDLC) protocol, to transmit and receive data with an IBM mainframe computer, over dial-up or leased telephone lines using 2400 bps Bell 201C modems, and later 4800 bps Bell 208B modems.
RJE was how programs, often referred to as jobs, were submitted to be run on mainframe computers back in the 1970s and earlier. That was the era of keypunch machines and punched cards. The statements for a computer program, usually COBOL or FORTRAN, and the input data for the programs were punched onto cards using a keypunch machine. The resulting card deck was carried, often wheeled over on carts, to an RJE terminal, placed into a card reader hopper, a button was pushed, and the card images were transmitted to the mainframe.
An immediate response may have come back to printer, exchange, or card punch devices of the terminal. This output might have been the result of program just submitted, or from some previous run. Very frequently, the program and data were held at the mainframe for execution at a later time. This is known as batch processing.
RJE terminals did not originate with SNA. Earlier IBM terminals, the Model 2780 and Model 3780 data terminals, used the binary synchronous communications (BSC or bisync) protocol. Bisync was ultimately superseded by SNA.
While it is true that few, if any, original IBM 3770 data terminals exist outside of museums now, the SNA connection used by these terminals to submit jobs to IBM mainframes is still in use today. There remains a great many IBM mainframe computers throughout the world that utilize SNA/RJE emulation to connect with remote systems such as PCs and other computers.
RJE is just a small subset of the types of transactions that occur over an SNA network. One of the largest applications was support for huge networks of interactive display terminals -- in the IBM world these are known as 3270 and 5250 terminals. Undoubtedly, just about every adult in the United States and much of the industrialized world has directly or indirectly been in contact with a 3270 or 5250 terminal in their lifetimes. Insurance claims, driver's license renewals, card catalog inquiries in libraries, purchasing of automobile part, and countless other routine computer activities take place by way of 3270 or 5250 terminals daily.
Use of SNA networks is slowly being replaced by TCP/IP and the Internet. IBM has not manufactured 3770 RJE terminals in many, many years. RJE connectivity has been completely taken over by products that emulate these old terminals. The evolution of the PC has opened the door for specialty companies, like Serengeti Systems, to expand into the niche market of providing 3770 SNA/RJE emulation solutions.
To some, it is remarkable that any computer-related technology first used nearly thirty years ago could still be in use today, but there is no doubt that SNA, and SNA/RJE specifically, is still a vital link in the chain of the world's computer infrastructure.
The following IBM publications may be helpful if you need to explore 3770 SNA/RJE communications in more depth:
SNA Format and Protocol: Architecture Logic (IBM publication: SC30-3112)
SNA Technical Overview (IBM publication: SC30-3073)
SDLC Concepts (IBM publication: GA27-3093)
Component Description for the IBM 3776 and 3777 Communications Terminals (IBM publication: GA27-3145-2)
IBM 3770 SNA Installation Guide (IBM publication: GC30-3064-0)
|E-mail For More Info||For more information on SNA, may we suggest the excellent book SNA: Architecture, Protocols, and Implementation by Atul Kapoor which was one of the reference sources used for this page.|
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