Differences Between Tcp And Udp; Opening Tcp Sockets - Omron CS1W-ETN01 Operation Manuals

Overview

6-1-5 Differences between TCP and UDP

TCP Communications
1, 2, 3...
Send
request
made.
Local node
UDP Communications
Send
request
made.
Local node

6-1-6 Opening TCP Sockets

88
Some port numbers over 1024 may be reserved on some workstations (for ex-
ample, the X-window server is port #6000). Do not use port numbers that are
already reserved for other processes.
The setting status of the UNIX workstation port numbers can be checked in /etc/
services.
There are differences in the socket services between TCP and UDP.
The following procedure is followed each time data is transmitted to ensure that
the data arrives normally at the remote node:
1. The remote node returns ACK when data is received normally.
2. The local node sends the next data after it receives ACK, or it resends the
same data if ACK is not returned within the specified time.
Transmitted data
ACK (acknowledge)
Resent data
With the TCP protocol, the remote IP address and remote TCP port number are
specified when an open request is made for a socket. When a send request is
made, the number of bytes to send and the send data are specified. When a re-
ceive request is made, the number of bytes to receive is specified.
With the TCP protocol, communications with another remote device are not pos-
sible until the socket that was opened has been closed.
Data is simply sent to the remote. Unlike TCP, the reception of data is not
checked and data is not resent. To increase communication reliability, data
resends must be programmed by the user in user application.
Transmitted data
ACK (acknowledge: only when
processed by application)
With the UDP protocol, the remote IP address and remote TCP port number are
not specified when an open request is made for a socket. When a send request
is made, the remote IP address, the remote TCP port number, the number of
bytes to send, and the send data are specified. When a receive request is made,
the number of bytes to receive is specified (the IP address and UDP port number
from which data was received are provided in the response data).
With the UDP protocol, communications with another remote device are pos-
sible even if the socket that was opened is not closed.
To achieve highly reliable data communications, TCP establishes a virtual com-
munications circuit between the two nodes before starting data transmissions.
The virtual communications circuit is known as a "connection."
Section
Receive
request
made.
Remote node
Receive
request
made.
Remote node
6-1