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The communications procedure is shown below for communications between
an FA computer and PC Card Unit using a TCP socket.
FA computer
(server)
Passive OPEN
PC Card Unit
(client)
Connection request
Active OPEN
Establish connection
Transmitted data
Send data
Receive data
ACK
Send next data
Establish connection
Establish connection
Receive data
Send next data
Send data
Close
Close
Transmitted data
ACK
10-1-5 Socket Services Port Numbers
Port numbers up to 1023 on a UNIX workstation can be used by the superuser
only. Port numbers 0 to 255 are reserved for well-known ports. Consequently,
port numbers from 1024 to 65535 should be used for socket services. The PC
Card Unit does not support port #0.
For FINS communications, the 9600 port is used as the default. Also, some port
numbers over 1024 may be reserved on some workstations (for example, the
X-window server is port #6000). Do not use port numbers that are already
reserved for other processes.
The setting status of the UNIX workstation port numbers can be checked in /etc/
services.
10-1-6 Fragmentation of Transmitted Data
The PC Card Unit fragments data for TCP transmission into units of 1,024 bytes
and data for UDP transmission into units of 1,472 bytes. TCP requires one
reception request to receive each unit of data. UDP, however, restores the origi-
nal data before passing it to the user process, allowing all the data in a single
transmission to be received with one reception request. Examples of these are
given next.
Cautions when Using TCP
An example of the fragmentation and transmission of data using the TCP is
shown in the following illustration.
1, 2, 3...
1. The transmission user program sends a request to send 1,982 bytes of data.
2. The PC Card Unit fragments the transmission data into Data A with 1,024
bytes and Data B with 958 bytes.
3. Data A and Data B are sent consecutively.
4. The receiving user program sends a request to receive 1,982 bytes of data.
However, only data A is sent in the first packet; data B is not received.
TCP Communications
Procedure
About Socket Services
Section 10-1
Summary of Contents for SYSMAC C200HW-PCS01-EV1
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