3 Basics | LXM32M |
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3.1.3Client / server model
Request | Indication |
Modbus Client | Modbus Server |
Confirmation | Response |
Figure 2: Client / server model
The Modbus messaging service implements client/server communica- tion between devices connected by means of a TCP/IP network. Mod- bus TCP does not use an object dictionary.
The client/server model is based on 4 types of messages:
•Request: Message sent by the client to initiate a transaction.
•Indication: Request as received by the server.
•Response: Response message to the request sent by the server.
•Confirmation: Response as received by the client.
A communication cycle consists of the request from the client (request from the fieldbus master) and a response from the server (response from the fieldbus slave). Modbus request and Modbus response have the same structure. If an error occurs on receipt of the Modbus request or if the slave cannot execute the action, the slave sends an error message in the Modbus response.
The product analyzes the Modus requests received. Depending on the Modbus request, the product triggers actions or provides requested data.
3.1.4Network service SNMP
The Internet community has developed the SNMP standard "Simple Network Management Protocol" to support the management of differ- ent network devices by means of a single system.
The Network Management System can exchange data with SNMP devices. The tasks of the network management system comprise monitoring, control and configuration of network components as well as error detection and error messaging.
SNMP agent ConneXview The product supports SNMP version 1.0. An SNMP agent must be used to monitor a network with SNMP. Schneider Electric offers the tool ConneXview for such purposes.
0198441113843, V1.01, 01.2012
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