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14. Representation of the data in Ethernet-TCP/IP
Each Ethernet-Client processor with TCP/IP network-protocol in a 10/100 Mbaud Ethernet can exchange data with the Gateway.
14.1 Network-addresses, network-connections
After switching on, the Gateway is waiting for data communication with a network-participant. In this case the Gateway is always
prepared to react to ICMP messages (e. g.
PING
Request and Reply). The functions of the ARP-protocol are also available.
14.2 TCP-connection setup
In the characteristic application in the TCP/IP-protocol, after switching on, the Gateway is in the state "Passive Open" under an
IP-address and port number that was determined in the configuration. A Client processor is in the position to open a TCP/IP con-
nection with the Gateway under the port determined in the configuration. After a successful connecting, data can be exchanged.
14.3 Data exchange
At the protocol TCP/IP, a full duplex data connection is available after establishing a connection between the Gateway and the
attached Ethernet-Client. The data stream is protected by the TCPI/IP-protocol in both directions.
When operating with UDP/IP-protocol, no connection is established before data is transferred. In this case the application is res-
ponsible for the control of the data flow as well as for the backup of the data.
14.3.1 TCP or UDP?
TCP is a connection-oriented protocol: Here a fixed logical connection between Client and Server exists in the course of the data
communication. TCP features all mechanisms, that are required, in order to open a connection and to guarantee a flawless data
transfer across the network and then again close the connection. For that reason the protocol software creates and administers
own buffers for each connection. In case a lot of Fieldbus Gateway-servers are to be addressed from one processor at the same
time, storage limits in the processor might result in an extreme case.
In contrast to TCP, UDP does not have mechanisms available to repeat data packets or to check them on their completeness. The
data communication with UDP is to be recommended if a parent protocol guarantees a flawless transmission between the terminal
device at the Fieldbus Gateway-server and the application on the TCP/IP-station anyhow.
14.4 Data exchange mode
The Gateway has to be in the data exchange mode, so that a data exchange between the RS-side of the Gateway and the field-
bus is possible. As long as the Gateway is not in the configuration mode or the test mode, the data exchange mode is active. In
the data exchange mode the Gateway will carry out the Script with those parameters preset through WINGATE and in the Script.
There are 4 communication channels.
For the channels the following adjustments in the Script in each case have to be made:
* The port numbers (Destination-Port and Source-Port)
* At client operation TCP or at UDP the destination-IP-address
* The mode or the protocol of the channel:
0 = TCP-server,
1 = TCP-client,
2 = UDP,
3 = Channel not used (closed)
WIthout these settings a connection to the Gateway cannot be set up via the Ethernet. Only ICMP-data traffic (PING) is possible.
