Материал: m012900e

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MS-DOS

Operating system, which allows all applications direct access to the hardware.

Open MODBUS/TCP specification

Specification which establishes the specific structure of a MODBUS/TCP data packet. This is dependent upon the selected function code or from the selected function (readin/readout bit or register).

Operating system

Software which links the application programs to the hardware.

Ping command

When a ping command (ping <IP address>) is entered, the ping program ICMP generates echo request packets. It is used to test whether a node is available.

Port number

The port number, together with the IP address, forms an unambiguous connection point between two processes (applications).

Predictable ETHERNET

The delay time of a message on an ETHERNET network can be predicted. The measures which have been taken in predictable ETHERNET make it virtually possible to realize realtime requirements.

Proxy gateway

A proxy gateway (or proxy server, too) allows systems which do not have direct access to the Internet, indirect access to the network. These can be systems which are excluded from direct access by a firewall for security reasons.

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A proxy can filter out individual data packets between the Internet and a local network to increase security. Proxies are also used to limit access to particular servers.

In addition, proxy gateways can also have a cache function, in which case they check whether the respective URL address is already available locally and return it immediately, if necessary. This saves time and costs when there are multiple accesses. If the URL is not in the cache, the proxy forwards the request as normal.

The user should not notice the proxy gateway apart from the single configuration in the web browser. Most web browsers can be configured so that they use different or no proxy gateways per access method (FTP, HTTP).

Repeater

Repeaters are physical amplifiers without their own processing function. They refresh data without detecting damaged data and forward all signals. Repeaters are used for longer transmission distances or when the maximum number of nodes of 64 devices per twisted pair segment is exceeded. A request from a client to server is a provision to act on a serivce or funtion call.

Request

A service request from a client which requests the provision of a service from a server.

Response

The server’s reply to a client’s request.

RFC specifications

Specifications, suggestions, ideas and guidelines regarding the Internet are published in the form of RFCs (Request For Comments).

RJ45 connector

Also referred to as a Western connector. This connector allows the connection of two network controllers via twisted pair cables.

Router

Connects neighboring subnets, the router operating with addresses and protocols of the third ISO/OSI layer. As this layer is hardware independent, the routers allow transition to another transmission medium.

To transmit a message the router evaluates the logical address (source and destination address) and finds the best path if there are several possibilities. Routers can be operated as repeaters or bridges.

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Routing

Method of selecting the best path over which to send data to a distant network.

SCADA

Abbreviation for Supervisory Control and Data Acquisition. SCADA software is a program for the control and visualization of processes.

Segment

Typically, a network is divided up into different physical network segments by way of routers or repeaters.

Server

Device providing services within a client/server system. The service is requested by the Client.

Service

An operation targeted at an object (read, write).

Socket

Is a software interface introduced with BSD-UNIX for inter-process communication. Sockets are also possible in the network via TCP/IP. As from Windows 3.11, they are also available in Microsoft operating systems.

Structured cabling

This specifies the maximum permissible cable lengths (EIA/TIA 568, IS 11801) and gives recommendations for the different types topology for ground area, building and floor cabling.

Subnet

A portion of a network that shares the same network address as the other portions. These subnets are distinguished through the subnet mask.

Subnet mask

The subnet mask can be used to manipulate the address areas in the IP address room with reference to the number of subnets and subscribers. A standard subnet mask is, for example, 255.255.255.0.

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S-UTP

Screened unshielded twisted pair cable which only has one external shield. However, the twisted pair cables are not shielded from each other.

Switch

Switches are comparable to bridges, but with several outputs. Each output uses the full ETHERNET bandwidth. A switch switches a virtual connection between an input port and an output port for data transmission. Switches learn which nodes are connected and filter the information transmitted over the network accordingly. Switches are inteligent devices that learn the node connections and can transfer data at the switch and not have to send it back to the main server.

Switched ETHERNET

The segments of this type of ETHERNET are connected by switches. There are many applications for switching technologies. ETHERNET switching is becoming increasingly popular in local networks as it allows the realization of a deterministic ETHERNET.

TCP

Transport Control Protocol.

TCP/IP protocol stack

Network protocols which allow communication between different networks and technologies.

Telnet

The Telnet protocol fulfils the function of a virtual terminal. It allows remote access from the user’s computer to other computer systems on the network.

Twisted pair

Twisted pair cables (abbreviated to TP).

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UDP protocol

The user datagram protocol is a transport protocol (layer 4) of the ISO/OSIreference model which supports data exchange between computers without a connection. UDP runs directly on top of the underlying IP protocol.

URL

Abbreviation for uniform resource locator.

Address form for Internet files which are mostly applied within the World Wide Web (WWW). The URL format makes the unambiguous designation of all documents on the Internet possible by describing the address of a document or object which can be read by a web browser. URL includes the transmission type (http, ftp, news etc.), the computer which contains the information and the path on the computer. URL has the following format: Document type//Computer name/List of contents/File name.

WAGO-I/O-PRO 32

Uniform programming environment, programming tool from WAGO Kontakttechnik GmbH for the creation of a control program according to IEC 61131-3 for all programmable fieldbus controllers. Allows testing, debugging and the start-up of a program.

Web browser

Program for reading hypertext. The browser allows the various documents to be viewed in hypertext and navigation between documents.

Wide band

Transmission technology which operates with a high bandwidth, thereby permitting high transmission rates. This allows several devices to transmit simultaneously.

Opposite: Baseband.

Word-alignment

Set configuration of the fieldbus coupler/controller for the creation of a process image. Word-alignment is used to establish the process image word-by- word (2 bytes).

World Wide Web

HTTP server on the Internet.