The Evolution of CICS

The Evolution of CICS: TCAM - Message Switching and More (1971)

A current generation may have difficulty understanding "how we got here". The concept of message switching is quite old, at least going back to the "torn tape" days of the 1930-1950 era. I suppose we could go back even further and talk about the Indians sending smoke signals from one location to another, but let's just assume torn tape as a reference point in the evolution of information systems.

The telegraph came into being in the mid-1800s and served the nation well for the transmission of information (messages). In the first half of the twentieth century, torn tape came into being as a more automated way of routing messages to many destinations. In addition to displaying message data on keyboard/printer types of devices, the teletype also had the ability to 'punch' data on paper tape. Paper tape devices could read or 'write' data on paper tape, often one inch wide, with six or eight holes (literally) punched in a row across the width of the tape, to represent one character of information.

For the purpose of illustration, let's assume a company (maybe a railroad) had offices in Los Angeles, Chicago, New York and Miami. Instead of all offices having direct communication links to all other offices, the concept of a message switching center came into being. All offices would send their messages to a central point, let's say St.Louis, and St.Louis would forward the message to its final destination. St.Louis would have paper tape punches to receive data from each of the company's offices, and paper tape readers to send data to each of its offices. So a message from LA to St.Louis would arrive on one paper tape punch, the paper tape was torn (literally), and inserted into the paper tape reader to transmit the message to (say) Miami as its final destination. Today, that seems a bit antiquated, but at the time, it got the job done.

With the advent of computers, IBM saw an opportunity to apply new technology to the need for message switching. In the early 1960s, IBM marketed computer-like devices such as the 7740 and 7750 message switching systems. Good idea, but bad timing. What the information technology sector was looking for in the mid-1960s was a solution to what we now refer to as transaction management. Message switching was relegated to being as subset of transaction management.

As we well know, the IBM System/360 was announced in April 1964 and with it came communication access methods such as BTAM and QTAM (Basic and Queued Telecommunications Access Methods). In the late 1960s, still another communication access method became available and it was known as TCAM, the Telecommunications Access Method. TCAM offered its users a more advanced form of message switching or message routing. TCAM was widely accepted, especially in the financial and brokerage industries.

In the late 1960s, transaction management systems came into being, each trying to achieve a leadership position in the industry. Within IBM, CICS and IMS were chosen as strategic products to address the need for transaction management. Within both CICS and IMS, each had its version of message switching, IMS being a front-end queued system and CICS having its Transient Data facility as the possible basis for message switching.

As CICS established itself as a popular transaction management system in the 1968-1971 timeframe, those users who had adopted TCAM for its message handling capabilities, now wanted a combined use of TCAM with CICS. In December 1971, IBM announced CICS support of TCAM as part of the CICS/OS-Standard product, to be delivered in December 1972. For interested customers, this enabled them to use TCAM for its message handling strengths and also have TCAM-connected terminals or computers interface with CICS online applications.

In January 1973, TCAM continued to be supported by CICS/OS-Standard Version 2.3. However, TCAM support was omitted from the initial release of CICS/VS, announced in February 1973 and delivered in June 1974. Needless to say, many CICS-TCAM customers were not happy with that product direction.

With considerable pressure from CICS-TCAM customers, the CICS support of TCAM was reinstated in the CICS/VS 1.1 product, as of September 1974. In addition to the previous DCB support, with this reinstatement of TCAM support, CICS began to support TCAM access via VTAM, also known as the ACB support. CICS TCAM ACB support was discontinued as of the CICS/ESA Version 3 product in 1990.

In 1992, IBM announced a new product family called MQSeries. Unlike TCAM, which was limited to communications among IBM systems, MQSeries had an architecture which enabled heterogenous systems to communicate with each other (e.g. IBM, HP, Sun, Tandem, etc). MQSeries can be used with CICS systems to send and receive data to/from any other MQ-eligible system. MQSeries can be used to initiate work in a CICS system or a CICS transaction can initiate work in another CICS or non-CICS system. MQSeries supports well over 35 different environments and has become the leading message switching/routing product in the industry. CICS support TCAM DCB support continues, but the use of MQSeries is predominant.