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FINS/TCP Method Section 8-3
• After a FINS/TCP connection (connection number, remote IP address)
has been set in the FINS/TCP Tab Page of the Network Configurator’s
Edit Parameters Dialog Box, it can be dynamically changed from the lad-
der program using a FINS command (i.e., FINS/TCP CONNECTION
REMOTE NODE CHANGE REQUEST).
FINS/TCP Frame Format The following diagram shows the structure of a TCP packet sent over an
Ethernet network.
As the diagram shows, a nested structure is used with the FINS/TCP method,
i.e., Ethernet Ver. 2, IP frame, TCP frame, FINS/TCP header frame, and FINS
frame. A TCP data section (FINS/TCP header + FINS frame) that exceeds the
segment size (default setting of 1,024 bytes in the EtherNet/IP Unit or built-in
EtherNet/IP port, with automatic adjustment for optimum values between the
nodes) is split into TCP packets for transmission. The split TCP data is then
joined automatically at the remote node's TCP/IP protocol layer. The TCP/IP
protocol layer, however, cannot determine where the data has been split, so
the TCP data sections from multiple packets are all joined together. Therefore,
when using the FINS/TCP method, FINS/TCP headers must be added at the
beginning of FINS frames in order to serve as FINS frame delimiters. The
length of the data in the following FINS frame is stored in the header, allowing
the frame to be separated out by the remote node. With the EtherNet/IP Unit
or built-in EtherNet/IP port and FinsGateway (Ver. 2003 or higher) the appro-
priate frames are separated out automatically, so there is normally no need to
be pay attention to it at the application layer.
TCP Port Number for
FINS/TCP
The TCP port number is the number for TCP to identify the application layer
(i.e., the FINS communications service in this case). When communications
are executed using TCP/IP, this port number must be allocated for the com-
munications service.
The default setting for the TCP port number (i.e., the TCP port number of the
EtherNet/IP Unit or built-in EtherNet/IP port) is 9600. To set another number,
make the setting for the FINS/TCP port on the FINS/TCP Tab Page of the CX-
Programmer’s Edit Parameters Dialog Box.
The FINS/TCP port number set in the FINS Configuration Tab Page is used by
the FINS/TCP server's TCP socket. The FINS/TCP client's TCP socket uses
any TCP port number that can be used at that node. (With the EtherNet/IP
Unit or built-in EtherNet/IP port and FinsGateway (Ver. 2003 or higher), an
unused TCP port is automatically detected and utilized.)
At the EtherNet/IP Unit or built-in EtherNet/IP port, a TCP/IP frame that is
received is recognized as a FINS frame, according to the remote TCP port
number in the frame.
FINS/TCP Connection
Numbers
FINS/TCP allows up to 16 FINS/TCP connections to be established simulta-
neously, and these 16 connections are managed at the EtherNet/IP Unit or
built-in EtherNet/IP port by connection numbers. When setting FINS/TCP con-
nection settings in the FINS/TCP Tab Page of the Network Configurator’s Edit
Parameters Dialog Box, set them individually using these connection num-
bers.
Ethernet Ver. 2 IP TCP FINS frame FCSFINS/TCP header
TCP packet