9-2
Basic Knowledge on Protocols
9-2-1
Differences between TCP and UDP
The TCP and UDP functions used on socket services differ as shown below.
TCP Communications
The following operations are performed each time data is sent to ensure that it reaches the destination
node.
The destination node returns an acknowledgment (ACK) when data is received normally.
The sending node sends the next data after ACK is returned. It resends the same data if ACK is not
received within a certain length of time.
Destination node
Receive
request
Sending node
Resend data
If ACK is not returned
Acknowledgement (ACK)
Send data
Send
request
In TCP, the remote IP address and the remote TCP port number are specified when a request is made
to open a socket. The variables that store the data to send are specified when the send request is
made.
UDP Communications
Data is simply sent to the destination node, and neither acknowledgment nor resends are performed
like they are for TCP
.
To increase the reliability of communications, some user application must be used to perform data re-
send processing.
Destination node
Acknowledgement (AC
K)
(When ACK processing is performed by user application)
Sending node
Send
request
Receive
request
Send data
In UDP, the remote IP address and the remote UDP port number are not specified when a request is
made to open a socket. The variables that store the remote IP address, the remote UDP port number
,
and the data to send are specified when the send request is made.
(The send data includes information on the IP address and UDP port number of the sending node.)
9 Socket Service
9-3
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
9-2 Basic Knowledge on Protocols
9
9-2-1 Differences between TCP and UDP
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