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8 APPENDIXES
8.1.5 Subnet mask
In compliance with the FL-net protocol, the subnet mask is fixed at 255.255.255.0. The FL-net
user must always use a subnet mask setting of 255.255.255.0. This value has the same network
address section and host address section as for Class C.
8.1.6 TCP/IP and UDP/IP communication protocols
TCP, UDP, and IP are important protocols that Ethernet uses.
IP corresponds to the communication protocol's network layer and controls the flow of
communications data.
TCP and UDP correspond to the transport layer. They both use IP as a network layer but greatly
differ in the contents of services.
TCP offers highly reliable services without causing a higher layer to be aware of data segments.
UDP, on the other hand, functions to transmit a datagram (one pack or unit of information) from
IP to a higher layer, but does not guarantee the delivery of data to a transmission destination. It
lets a higher layer perform data acknowledgment, retransmission, and other processes.
UDP is not as reliable as TCP. However, it offers communication services with a minimum of
overhead.
The FL-net uses UDP. The reason is that TCP's complicated data verification/retransmission
procedure is redundant for the FL.NET. The FL-net provides an increased data exchange speed
by skipping such a complicated procedure and having the FL-net protocol layer on a higher level
perform token-based transmission right management, multiple-frame division/synthesis, and other
relevant processes.
8.1.7 Port numbers
For the FL-net, the following port numbers are predetermined to ensure that services are
implemented by the FL-net protocol layer, which is positioned higher than the transport layer.
Note, however, that the FL-net user does not have to set these port numbers with parameters or
the like.
Cyclic transmission port number
Message communication port number
Enter request frame port number
Transmission port number
Table 8-3 FL-net Port Numbers
Name
8-4
Port number
55000 (fixed)
55001 (fixed)
55002 (fixed)
55003 (fixed)
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