9-7
9 Socket Service
NJ-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
9-2 Basic Knowledge on Protocols
9
9-2-3 Data Reception Processing
z UDP Receive Processing
With UDP communications, the receive data that is stored in the receive buffer cannot be separated
and received. (The receive buffer holds up to 9,000 bytes.) Therefore, the data that is sent for each
send request must be received with one receive request. Because of this, attention must be given to
the following at the receiving node when data is received.
• When the Size of the Variable Specified in the Receive Request Is Smaller Than the Data Size
Sent with the Send Request
The received data that exceeds the size of the variable that is specified in the receive request is
discarded. All of the receive data is received if there is less data in the receive buffer than the size
of the variable that was specified in the receive request.
Example 1: Receive Request for 1,000 Bytes when 2,000 Bytes of Data Was Received
1. The data that was sent from the sending node in two sends is stored in the receive buffer.
2. If a receive request is made for 1,000 bytes for the first send data, the remaining 1,000 bytes is
discarded.
3. If the next receive request is for 2,000 bytes, all of the send data for the second send is received.
1st send
request
2nd send
request
Receiving node
Original data
Original data
User program
1,000 bytes
2,000 bytes
Original data
Original data
3,000 bytes
Sending node (Controller)
Receiving node (host computer)
Receive buffer
(9,000 bytes)
User program
Original data
Original data
1st receive request
(request for 2,000 bytes)
2nd receive request
(request for 2,000 bytes)
Ethernet line
(1) Data received to
receive buffer.
(2) The data is received in
two sections.
1st send
request
2nd send
request
Receiving node
Original data
User program
2,000 bytes
Original data
2,000 bytes
Original data
Original data
4,000 bytes
Sending node (Controller)
Receiving node (host computer)
Receive buffer
(9,000 bytes)
User program
Original data
Ethernet line
Original data
(1) Data received to
receive buffer.
(2) 1st receive
request (request
for 1,000 bytes)
(3) 2nd receive
request (request
for 2,000 bytes)
The remaining
data is discarded.
1,000 bytes
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