Материал: m012900e

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Glossary • 317

Client

A system that requests the services of another. With the aid of the service request, the client can access objects (data) on the server. The service is provided by the server.

Coaxial cable

This cable contains a single wire and a radial shield to transmit information.

CSMA/CD

Carrier Sense Multiple Access with Collision Detection. When a collision is detected, all subscribers back off. After waiting a random delay time, the subscribers attempt to re-transmit the data.

Data bus

see Bus.

Deterministic ETHERNET

The ETHERNET data is transferred at a defined time constant. The ETHERNET network can be defined and calculated. A Switched ETHERNET architecture makes this possible.

DHCP

Dynamic Subscriber Configuration Protocol. This protocol allows the automatic network configuration of a computer.

Driver

Software code which communicates with a hardware device. This communication is normally performed by internal device registers.

ETHERNET

Specifies a Local Area Network (LAN), which was developed by Xerox, Intel and DEC in the 70’s. The bus access process takes place according to the

CSMA/CD method.

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ETHERNET Standard

In 1983 ETHERNET was standardized by IEEE 802.3 10Base-5. ISO took over the standardization in the ISO Standard 8802/3. The essential differences between ETHERNET and the IEEE standard are to be found in the frame architecture and treatment of pad characters.

Fieldbus

System for serial information transmission between devices of automation technology in the process-related field area.

Firewall

Collective term for solutions which protect LANs connection to the Internet from unauthorized access. They are also able to control and regulate the traffic from the LAN into the Internet. The crucial part of firewalls are static routers which have an access control list used to decide which data packets can pass from which subscriber.

Frame

Unit of data transferred at the Data-Link layer. It contains the header and addressing information.

FTP

(File Transfer Protocol) A standard application for TCP/IP which allows users on one machine to transfer files to/from another.

Function

Module that always returns the same result (as a function value), prerequisite being identical input values; it has no local variables that store values beyond an invoke.

Function block

Module that delivers one or more values when being executed. They can be stored as local variables („Memory“).

Gateway

Device for connecting two different networks. It converts the different protocols.

H

Glossary • 319

Hardware

Electronic, electrical and mechanic components of a module/subassembly.

Header

A portion of the data packet, containing, among others, the address information of the receiver.

Host computer / Subscriber

Originally used to describe a central mainframe computer accessed from other systems. The services provided by the subscriber can be called up by means of local and remote request. Today, this term is also used to refer to simple computers which provide particular central Services (i.e. UNIXSubscribers on the Internet).

HTML

Abbreviation of hypertext markup language

HTML is the description language for documents on the World Wide Web. It contains language elements for the design of hypertext documents.

HTTP

(Hyper Text Transfer Protocol) client server TCP/IP protocol which is used on the Internet or Intranets for exchanging HTML documents. It normally uses port 80.

Hub

A device which allows communication between several network users via twisted pair cable.

Similar to a repeater, but with many outputs, a hub is used to form a star topology.

Hypertext

Document format used by HTTP. Hypertext documents are text files which allow links to other text documents via particularly highlighted keywords.

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Intranet

A network concept with private network connections over which data can be exchanged within a company.

IP

Internet Protocol. The connectionless network layer, which relies on upper protocols to provide reliability.

ISA

Industry Standard Architecture. Offers a standard interface for the data exchange between CPU and periphery.

ISO/OSI reference model

Reference model of the ISO/OSI for networks with the objective of creating open communication. It defines the interface standards of the respective software and hardware requirements between computer manufacturers. The model treats communication removed from specific implementations, using seven layers.

LAN

Local Area Network.

Library

Compilation of modules available to the programmer in the programming tool WAGO-I/O-PRO 32 for the creation of a control program according to IEC 61131-3.

Manchester encoding

In this encoding system, a 1 is encoded as a transition from low to high and a 0 as a transition from high to low.

Modules

Functions, function blocks and programs are modules.

Each module has a declaration part and a body, the latter being written in one of the IEC programming languages IL (instruction list), ST (structured text), SFC (sequential flow), FBD (function block diagram) or LD (ladder diagram).