88 Ethernet module User’s Manual
Chapter 6 Socket Interface Communication
6
6.1 Overview
This section describes the functions and positioning of the socket interface, and the
differences between the UDP socket interface and the TCP socket interface.
(1) Positioning and functionality
The socket interface is a programming interface that allows user programs to use the
TCP/IP and UDP/IP functions. Socket interface communication is a communication
technique that has become standard on engineering workstations (EWS) and others.
The socket interface can be used for communication between host application
programs and user programs running on the S controller.
The EN311 socket interface provides eight sockets, and the communication protocol
(TCP/IP or UDP/IP) used with the remote destination can be specified for each
socket. User programs on the S controller use the USEND_T and URCV_T function
blocks to use the socket interface.
TCP/IP (Transmission Control Protocol/Internet Protocol)
UDP/IP (User Datagram Protocol/Internet Protocol)
Figure 6-1 shows the positioning of the socket interface.
Figure 6-1 Positioning of the socket interface
(2) Differences between the UDP socket interface and the TCP socket interface
(a) UDP socket interface (See Figure 6-2.)
• Provides an in/out port (socket) for data communication between a transmis-
sion source node and a transmission destination node.
• Data for the transmission source and transmission destination (IP addresses
and port numbers) is specified in the send/receive data.
• Since the transmission source and transmission destination are specified in
each data item, a UDP socket can communicate with multiple remote UDP
sockets.
• The UDP socket interface provides no control functionality such as reception
verification using, e.g. ACK (acknowledge) responses, or retransmission pro-
cessing to assure transmission reliability. Therefore, reliability must be
assured by higher level protocols implemented by user programs.
EWS S controller + EN311
Application program S controller user program
System USEND_T
calls /URCV_T
OS(UNIX) S controller firmware
Socket interface Socket interface
UDP/TCP UDP/TCP
IP IP
CSMA/CD CSMA/CD
Data send/receive
TCP or UDP 10BASE5/10BASE2
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