9-5
9 Socket Service
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
9-2 Basic Knowledge on Protocols
9
9-2-2 Fragmenting of Send Data
Data in TCP communications is delivered to the user program in a fragmented form, as shown
above. The number of bytes of data that is received must be checked to confirm all data was
received before the next receive request is made. (You can use the RecvDataSize output variable of
the socket receive request instruction to check the received data.)
Additional Information
If TCP is used to send data to a different segment, the data is separated into 536-byte frag-
ments.
Built-in
EtherNet/IP port
User program
(5) Receives remaining 976 bytes.
(6) Receive request
(request for 2,000 bytes)
(3)
Data A and
data B are
sent in
succession.
(2) Fragmenting
(4) Receive request
Receiving node
2,000 bytes
2,000 bytes
1,024 bytes
1,024 bytes
976 bytes 976 bytes
Data AData A Data A
Data BData B Data B
Original data
User program
2,000 bytes
(1) Send request
Sending node (Controller) Receiving node (host computer)
Ethernet line
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