Teleprocessing(network Structures)

Teleprocessing Teleprocessing refers to a large variety of data processing applications in which data is received from or sent to a central data processing system over communication lines, including ordinary telephone lines.  Usually the source or destination of the data is remote from the central processing system, although it can be in the same building.  In any event, the source or destination points of the data are often called terminals or (for some applications) work stations. 

General Types of Applications DATA COLLECTION  MESSAGE SWITCHING  REMOTE JOB PROCESSING  TIME SHARING  ONLINE PROBLEM SOLVING  INQUIRY AND TRANSACTION PROCESSING 

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DATA COLLECTION  Data Collection is a teleprocessing application in which data is

received by a central processing system from one or more remote terminals and is stored for later processing. Depending on the specific application, the transfer of data may be initiated either at the terminal or by the central processing system.

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MESSAGE SWITCHING  Message switching is a type of teleprocessing application in

which a message received by the central computing system from one remote terminal is sent to one or more other remote terminals

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REMOTE JOB PROCESSING  Remote job processing is a type of application in which data

processing jobs, like those that are entered into the system locally, are received from one or more remote terminals and processed by the operating system.

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TIME SHARING Time sharing is a teleprocessing application in which

a number of users at remote terminals can concurrently use a central computing system.

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ONLINE PROBLEM SOLVING Online problem solving is a form of time sharing that

has a great many potential applications in the fields of education, engineering, and research.

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INQUIRY AND TRANSACTION PROCESSING Inquiry and transaction processing is a teleprocessing

application in which inquiries and records of transactions are receive from a number of remote terminals and are used to interrogate o update one or more master files maintained by the central computing system

Message Control and Message Processing Programs  Message

The traditional name for unit information. May consist of one or more segments.

 Two

parts of a single-segment message:

Message header; followed by, Message text.

 Message

Header – contains control information concerning the message, such as the source or destination code of the message, message priority, and the type of message.  Message Text – consists of the actual information that is routed to a user at a terminal or to a program in the central computing system that is to process it.

 MESSAGE

CONTROL PROGRAMS The main function of a message control program is to control the transmission of information between an application program in the central computing system and I/O devices at remote terminals. Access method routines – routines provided by the IBM for use in creating a message control program.

Three sets of access method routines: Queued Telecommunication Access Method

(QTAM) Telecommunications Access Method (TCAM) Basic Telecommunication Access Method (BTAM)

Queued Telecommunications Access Method  can be used to create message control program for a

variety of teleprocessing applications ranging from message switching or data collection to high volume inquiry and transaction processing.

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The message control program serves as an intermediary between the I/O devices at remote terminals and the application programs that process messages (Fig. 3). It enables the terminals to be referred to indirectly, in much the same way as local I/O devices are referred to, using such standard macro instructions as GET, PUT, OPEN, and CLOSE. It automatically performs detailed functions, such as sending or receiving messages, allocating buffers, translating message codes, formatting messages, and checking for errors.

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The message control program serves as an intermediary between the I/O devices at remote terminals and the application programs that process messages (Fig. 3). It enables the terminals to be referred to indirectly, in much the same way as local I/O devices are referred to, using such standard macro instructions as GET, PUT, OPEN, and CLOSE. It automatically performs detailed functions, such as sending or receiving messages, allocating buffers, translating message codes, formatting messages, and checking for errors.

Telecommunications Access Method The telecommunications access method

(TCAM) is similar to QTAM, but offers a wider range of device and program support. For remote terminals, TCAM supports both startstop and binary synchronous methods of data transmission; binary synchronous support permits the use of faster terminals than are available with QTAM. In fact, in TCAM, a terminal may be an independent computing system.

To take advantage of TCAM facilities, QTAM application programs can easily be converted to TCAM. TCAM facilities include: Online testing of teleprocessing terminals and

control units. Input/output error recording. Program debugging aids. Network reconfiguration facilities.

Basic Telecommunications Access Method The basic telecommunications access

method (BTAM) is designed for limited applications that do not require the extensive message control facilities or QTAM or TCAM, or for applications that require special facilities not normally found in most applications.

The BTAM facilities provide tools that would be required to design and construct almost nay teleprocessing application. These include facilities for creating terminal lists and performing the following operations: Polling terminals. Answering. Receiving messages. Allocating buffers dynamically. Addressing terminals. Dialing. Creating buffer chains. Changing the status of terminal lists.

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MESSAGE PROCESSING PROGRAMS A message processing program is an application program that processes or otherwise responds to messages received from remote terminals. In designing the program, all of the facilities of the operating system are available including the language translators, service programs, and the data, program, and task management facilities can be performed sequentially as a series of single tasks or more than one message can be processed concurrently.