Specifications

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(2) Comparison between TCP and UDP
The request level for the network differs depending on the user application.
However, it is difficult to create each unique protocol for many requests.
Then, TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)
are developed as minimally-required basic services.
TCP .............Fixes connection to the destination at first and performs bidirectional
1:1 communication with high reliability.
UDP.............Performs one-way communication to transfer the data given from an
application to the designated destination.
This is a high speed communication as data are directly sent using
IP.
The following table compares the characteristics of TCP and UDP.
Item TCP UDP Remarks
Reliability High Low
(Processing) Speed Low High
No. of target devices 1:1 1:1 or 1:n
Unicast (1:1 communication)
Multicast (1:n communication)
(*1)
Guarantee to reach
destination
Guaranteed Not guaranteed
Operation when send
error occurs
Resends automatically
(depending on setting)
No resending (packet
disposal)
Communication
connection
establishment
Required Not required
Reaches in order of sending
packets for TCP.
Transfer type
Stream type (Instructions
and data are sent with
character strings)
Datagram type
(Sent in fixed format)
Datagram transfer can be
performed in the application level
even for TCP.
Flow control Available Not available
Sending side controls the send
data amount depending on the
buffer size of the receiving side.
Congestion control
(Resend control) (*2)
Available Not available
Send packet amount is controlled
depending on the congestion
degree of the network.
Target device change
during an open
connection
Not possible Possible (*3)
Refer to Section 2.3 for
connection.
TCP is suitable for assured data transfer.
UDP is suitable for real time monitoring by the PC display.
*1 The "n" of multicast (1:n communication) represents multiple devices
belonging to one group on the same Ethernet.
*2 The buildup of communication packets on the network is called "congestion".
*3 Target device change during an open connection may cause communication
troubles.
Do not change the target device while a connection is open.