CHAPTER CHAPTER

Mainframe/Mini Mainframe/Mini Related Related

Communication Communication EquipmentEquipment

Chapter Objectives

• Present mainframe and minicomputer related communication hardware that has not been presented elsewhere– Front-end processors, concentrators, protocol

converters etc.

• Describe the different types of terminals such as the ASCII and EBCDIC terminals, smart terminals etc.

• Present examples of the use of the above equipment in practice

Chapter Modules

• Mainframe Data Communication Equipment: Front End Processor and Concentrator

• Minicomputer Data Communication Equipment: Communication Controllers

• Protocol Converters• Data Terminal Equipment

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MODULE

Mainframe Communication Equipment: Front End

Processor and Concentrator

Definition of DCE and DTE

• DCE– Data Communication Equipment

• DTE– Data Terminal Equipment

DCE and DTE in the Real World

MainframeComputer

DCE

DCE

DTE

DTE

Front End Processors, Concentrators, Protocol Converters etc.

Printers,Terminal etc.

Some Mainframe Communication

Equipment• Front End Processors

– Manages the network traffic in a mainframe environment

• Multiplexers– Discussed in an earlier chapter in

detail

• Communication controllers– Controllers, concentrators etc.

Mainframe Communication Equipment (Cont.)

• Protocol converters– Used for linking devices that operate

under a different protocol - different from the mainframe protocol

Overview of Communication

Controllers• Used extensively in mainframes

– 3270 controllers for IBM mainframes

• Level of sophistication– On one end of the spectrum is the front end

processor– On the other end is the communication

controller– There are also the other intermediate

communication controllers and devices that are grouped under the 3270 family of communication equipment

Front End Processors (FEPs)

• Computers by themselves• Connected to a mainframe for the

purpose of managing the network traffic• FEPs reduce the load on the CPU

– Enable the CPU to perform its primary task of running applications

• FEP is a comprehensive DCE – Minicomputers, modems, LANs etc. can be

attached to the mainframe through the FEP

A Front End Processor Connection

Mainframe

Front End ProcessorMini-Computer

Term. Term. PCPC

Concentrator

LAN

ModemServer

Ter.

External Lines

Gateway

Ter.

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MODULE

Minicomputer Data Communication Equipment:

The Communication Controller

Communication Controllers for Minicomputers

• In the case of the minicomputer, the controllers can be of the internal or external type

• If they are internal controllers, they are installed in the expansion slot of the minicomputers

• Manages the network traffic among the host, DTE and DCE

Controllers for AS 400

• Known as the 5250 controllers– Fall under the 5250 family of DCE

• Compare this with the mainframe’s 3270 family of DCE

Connecting DTE to a Communication Controller

ASCIIPrinter

ASCIITerminal

HP Plotter

Modem

AS 400

5250CommunicationController

AS/400 Connection to Terminal Equipment

AS/400 withBuilt-in Communication

Controller

AS/400 Terminal Equipment

Source: Black Box

AS/400 LAN Connection

AS 400

Server

PC

PC

Plotter

Modem PoolPrinter

OS/400

OS/2

AS 400 LAN Connection Practical Example

Remote AS 400Central Unit

LAN

Source: Black Box

In Summary

• Two different ways by which a minicomputer can be connected to other devices including the DTE

• Connect the terminal equipment directly to the minicomputer through its communication controller

• Link the mini to its terminal equipment over a LAN

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MODULE

Protocol Converter

Definition and Use

• A protocol converter can be defined as an equipment used for interfacing systems working under different protocols

• Protocol converters are most widely used for connecting peripheral devices to hosts– An example is the connection of ASCII

terminals to IBM mainframes

ASCII and EBCDIC Terminals

• EBCDIC terminals– Standard terminals used with the IBM

mainframe

• Code conversion difference is present between the EBCDIC and ASCII terminals

• A protocol converter is required when an ASCII terminal is to be linked to an IBM mainframe

ASCII Terminal Link to an IBM Mainframe

IBM 3274

Controller

ProtocolConverter

ToIBMMainframe (FEP) ASCII Terminal

PSTN

Modem

Use of Protocol Converter to Connect ASCII Equipment to

IBM Mainframe

Protocol Converter

ASCII Printer PC (ASCII) Terminal

Source: Black Box

Mainframe Modem Connection

To IBM Mainframe

Unix ComputerRemote PC

Source: Black Box

Protocol Converter Used in Mini Computer Connection

AS 400

ASCIIPrinter

ASCIITerminal

HP Plotter

Modem

TwinaxMulti-portProtocolConverter

Protocol Converters:AS/400 to

ASCII Connection

Source: Black Box

Protocol Converter: AS400 to LAN and Printer

Connection

Source: Black Box

Preferred AS 400 Connection to a LAN

AS 400

PC

Network Interface Card LAN

In Summary

• Frequent Usage– Connecting ASCII equipment to

computers that operate under a different protocol

• Utilized for connecting DTE to the mini and mainframe computers

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MODULE

Data Terminal Equipment (DTE)

EBCDIC and ASCII Terminals

• EBCDIC– IBM mainframes

• ES 9000 series

– IBM minis • AS 400 series

• ASCII– Popular in the Unix environment

• IBM RS 6000 Unix computer• DEC computers running the Unix OS

– Most recognizable ASCII terminal is the VT 100 terminal

Initial (Dumb) Terminals

Mainframe DumbTerminals

Only involved in conveying the information betweenthe mainframe and the terminal.

Smart Terminals

• Smart terminals are likely to incorporate reasonably powerful processors within themselves

• They are able to perform local processing such as the local editing of information on the screen

Dumb Terminals

• Do not have processors for local processing

• They rely on the host to perform most operations

• Overloading the CPU is not a desirable course of action

• The use of dumb terminals is on the decline

Microcomputer as a Terminal

• There are two methods by which a microcomputer can be connected to a mainframe to act as a terminal

• One involves a direct connection to a concentrator – Terminal emulation hardware and software are

required for terminal emulation

• The alternative method is to connect a LAN consisting of microcomputers to the mainframe

Micro as a Terminal: Direct Connection

IBM Cluster

Controller.

Micro

To IBMMainframe (FEP)

Terminal EmulationBoard

Terminal EmulationSoftware

IBM Terminal Emulation

Source: Black Box

LAN Based Connection

PC

PC

PCFEP

MainFrame

PC

Gateway or similar device

Terminal Emulation Software

RS 6000: Native ASCII Connection

AIX (Unix) Computer

Terminals

Source: Black Box

In Summary

• Two major types– ASCII and EBCDIC

• Smart and Dumb terminals• Smart terminals engage in local

processing• Microcomputers are increasingly

being used to emulate the terminals

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