9 Socket Service
9-6
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
The conditions shown in the following figure occur when data is sent in fragments in UDP communica-
tions.
(1) A send request is sent from the user program at the sending node. It specifies a vari-
able with a data length of 2,000 bytes.
(2) The built-in EtherNet/IP port separates the send data into 1,472 bytes in data A and
528 bytes in data B.
(3) Data A and data B are sent in sequence by the sending node.
(4) Data A and data B are joined to restore the original send data, and the data is passed
to the user program.
Because UDP communications are performed in datagram units as shown above, send data is
returned to the original data format before it is passed to the user program.
This section describes data reception processing for TCP and UDP.
z TCP Receive Processing
With TCP communications, the receive data that is stored in the receive buffer can be separated and
received. (The receive buffer holds up to 9,000 bytes.) This can be used to receive data that
exceeds the size that can be received with one data request (2,000 bytes), i.e., more than one
receive request is used to receive all of the data. Also, all of the receive data can be received if there
is less data in the receive buffer than the size of the variable that was specified in the receive
request.
Example: Receiving 3,000 Bytes of Receive Data in Two Sections
1. The data that was sent from the sending node in two sends is stored in the receive buffer.
2. Two receive requests are used to receive all of the send data.
Using UDP
9-2-3 Data Reception Processing
Built-in
EtherNet/IP port
User program
(3)
Data A and
data B are
separated
and sent.
(2) Fragmenting
Receiving node
1,472 bytes
528 bytes
Data A
Data B
Original data
User program
2,000 bytes
(1) Send request
Sending node (Controller) Receiving node (host computer)
(4) Receive request
2,000 bytes
Data A Data B
Ethernet line
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