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Overview Section 6-1
quently, port numbers 1024 and above should be used for socket services.
The Ethernet Unit does not support port #0.
Some port numbers over 1024 may be reserved on some workstations (for
example, 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.
6-1-5 Differences between TCP and UDP
There are differences in the socket services between TCP and UDP.
TCP Communications The following procedure is followed each time data is transmitted to ensure
that the data arrives normally at the remote node:
1,2,3... 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.
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 receive request is made, the number of bytes to receive is specified.
With the TCP protocol, communications with another remote device are not
possible until the socket that was opened has been closed.
UDP Communications 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.
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. (In addition to the
received data, the source IP address and source UDP port number are stored
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.
Local node
Transmitted data
ACK (acknowledge)
Resent data
Remote node
Send
request
made.
Receive
request
made.
Local node Remote node
Transmitted data
ACK (acknowledge: only when
processed by application)
Send
request
made.
Receive
request
made.