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1-7
Section
IP Addresses
8
ability are not performed for UDP communications, i.e., there is no way of guar-
anteeing normal communications without programming special measures to do
so into the user’s application program.
TCP
Transmission Control Protocol: Performs communications after establishing a
connection (i.e., a virtual circuit) with the target node to provide a highly reliable
communications method.
FINS
Factory Interface Network Service: A protocol that sends messages between
PCs on any of various OMRON FA networks. The user must provide measures
such as retry processing to ensure that transmitted messages arrive at the des-
tination node.
SMTP
Simple Mail Transfer Protocol: A communications protocol for sending e-mail by
TCP/IP.
FTP
File Transfer Protocol: Transfers data files.
1-7
IP Addresses
Ethernet networks use IP addresses for communications. IP addresses (Inter-
net addresses) identify both the Ethernet network and the node (host computer,
Ethernet Unit, etc.) on the Ethernet network. IP addresses must be set and con-
trolled so that they are not duplicated.
1-7-1 IP Address Configuration
IP addresses are made up of 32 bits of binary data divided into four 8-bit fields
called octets. These four octets provide the network number (net ID) and host
number (host ID). The network number identifies the network and the host num-
ber identifies the node (or host) on the network.
The network numbers in an IP addresses are divided into three classes, A, B,
and C, so that the address system can be selected according to the scale of the
network. (Classes D and E are not used.) The configuration of the IP address for
each of these classes is shown in the following diagram.
Class A
Bit 31
0
Network number (7 bits)
Host number (24 bits)
23
00
Class B
Bit 31
1
Network number (14 bits)
Host number (16 bits)
15
00
0
Class C
Bit 31
1
Network number (21 bits)
Host number (8 bits)
7
00
1
0
Class D
Bit 31
Class E
Bit 31
Multicast address
Test address
(Cannot be used.)
1
1
1
0
00
1
1
1
1
00
(Cannot be used.)
The number of networks in each class and the number of nodes possible on the
network differ according to the class.