5.7.13
Instruction manual UNIGATE
®
IC - Ethernet V. 2.9
45
Deutschmann Automation GmbH & Co. KG
Representation of the data in Ethernet
15 Representation of the data in Ethernet
Each Ethernet-Client processor with TCP/IP network-protocol in a 10 Mbaud Ethernet can
exchange data with the gateway.
15.1 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.
15.2 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 configu-
ration. A Client processor is in the position to open a TCP/IP connection with the gateway under
the port determined in the configuration. After a successful connecting, data can be exchanged.
15.3 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 responsible for the control of the data flow as well as for the backup of
the data.
15.3.1
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 net-
work 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 UNIGATE-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
UNIGATE-server and the application on the TCP/IP-station anyhow.
15.4 TCP/IP-deviations from the standard
Deviations of the TCP/IP-stack from the conventions from RFC 791, RFC 792 and RFC 793:
1) Deviation from RFC 793 (Multiplexing)
Only an active TCP-session is possible. Depending on the configuration:
a) A new connection is not permitted.
Gateway is not responding to new SYN-packets.
b) In case of an already existing connection a new one is made.
The existing connection in not further serviced.
This connection, however, is not closed either.
