User`s manual

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5.2 Private MIB
The private MIB can be found in product CD. Compile the private MIB file by
your SNMP tool. The private MIB tree is the same as the web tree. This is easier
to understand and use. If you are not familiar with standard MIB, you can
directly use private MIB to manage /monitor the switch, no need to learn or
find where the OIDs of the commands are.
5.3 Modbus TCP /IP
The Modbus TCP/IP is very similar to Modbus RTU, but transmits data within
TCP/IP Data packets. It was developed in 1979 for industrial automatic
communication system and have becomes a standard protocol for industrial
communication for the transfer discrete analogy I/O devices or PLC systems. It
defines a simple protocol data unit independent of the underlying data link
layer. The modbus TCP packet includes 3 parts - MBAP header, function code
and data payload, the MBAP header is used on TCP/IP header to identify the
Modbus application Data Unit and provides some differences compared to the
MODBUS RTU application data unit used on serial line. The MBAP header also
includes unit identifier to recognize and communicate between multiple
independent modbus end units.
The modbus devices communicate using a master (client) /slave (server)
architecture, only one device can initiate transaction and the others respond to
the master/client. The other devices (slave/server) respond by supplying the
requested data to the master/client, or by taking the action requested in the
query. The slave/server can be any peripheral device (DSC unit, PLC unit,
Volt/Current Transducer, network communication switch) which process
information and sends the output data to the master using modbus TCP
protocol. Westermo MDI-110 Switch operating as slave/server devices, while a
typical master/client device is host computer running appropriate application
software, like as SCADA / HMI system. The transaction architecture like as the
drawing following.