Omron CS1W-ETN21 operation manual TCP Port Number for, FINS/TCP Connection Numbers

FINS/TCP Method Section 6-3

•Once a FINS/TCP connection (connection number, remote IP address) has been set in the Unit Setup, it can be dynamically changed from the ladder 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.

Ethernet Ver. 2

IP

TCP

FINS/TCP header

FINS frame

FCS

TCP packet

TCP Port Number for

FINS/TCP

FINS/TCP Connection Numbers

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: 1,024 bytes, 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 Unit and FinsGateway Ver. 2003 the appropriate frames are separated out automatically, so there is normally no need to be pay attention to it at the application layer.

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 FINS/TCP local TCP port number (i.e., the Ethernet Unit's TCP port number) is 9600. To set another number, make the setting for the FINS/TCP port using the Setup Tab in the Unit Setup.

The FINS/TCP port number set in the Unit Setup 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 Unit and FinsGate- way Ver. 2003, an unused TCP port is automatically detected and utilized.)

At the Ethernet Unit, 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 allows up to 16 FINS/TCP connections to be established simulta- neously, and these 16 connections are managed at the Ethernet Unit by con- nection numbers. When setting connections by means of the FINS/TCP settings in the CX-Programmer's Unit Setup, set them individually using these connection numbers.

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