9 Socket Service
9-4
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
The receive buffer for the built-in EtherNet/IP port is a maximum of 9,000 bytes per handle. Up to 16
handles can be used at the same time. If any data that is larger than 9,000 bytes is received, any data
over 9,000 bytes is discarded. Up to 2,000 bytes can be received for a single request. In this case, the
data is sent in fragments as described below.
The conditions shown in the following figure occur when data is sent in fragments in TCP 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 1,024 bytes in data A and
976 bytes in data B.
(3) Data A and data B are sent in sequence by the sending node.
(4) After data A is received, the remaining data B is received.
9-2-2 Fragmenting of Send Data
Using TCP
Socket interface
Packets sent by higher layers
Packets sent by the TCP/IP layer
Socket
FIN
ACK
ACK
ACK
SYN ACK
SYN
Send
Close
Connect
Socket
Bind
Listen
Accept
Recv
Client Server
SktTCPAccept Instruction
• Execution of Socket Functions
Socket(), Bind(), Listen(), and
Accept()
• Timeout monitoring until Connect is
completed
The connection is established by the
normal completion of the SktTCPAc-
cept instruction.
SktTCPRcv Instruction
• Execution of Socket Function
Recv()
• Timeout monitoring until data is
received from the remote node
Writing the received data to the variable
is completed by the normal completion
of the SktTCPRcv instruction.
SktTCPConnect Instruction
• Execution of the Socket Function
Connect()
The connection is established by
the normal completion of the
SktTCPConnect instruction.
SktTCPSend Instruction
• Execution of the Socket Function
Send()
The data is stored in the send
buffer by the normal completion of
the SktTCPSend instruction.
Instruction
completed.
Instruction
completed.
Instruction
completed.
Instruction
completed.
SktClose Instruction
• Execution of the Socket Function
Close()
The acknowledgment (ACK) of
FIN from the remote node is
received by the normal comple-
tion of the SktClose instruction.
However, RST (not FIN) is sent if
the Linger Option is specified.
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