Omron R6YXC1000, Руководство пользователя, Страница: 131 / 260

6
Exter
nal comm
unica
tion interf
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6-21
The host address can be set freely by each company (organization). However, when connecting to the Internet, it is
necessary to make an application to the NIC (JPNIC in Japan) for a network address to get the acquisition. Note that the
network address can also be set freely by each company (organization) in the environment where the network is not
connected to the Internet in the same manner as the host address.
In the environment where the network is not connected to the Internet, it is permitted to freely use the addresses
shown below. These addresses are called "private address".
10.0.0.0 to 10.255.255.255 (1 unit of class A)
172.16.0.0 to 172.31.255.255 (16 units of class B)
192.168.0.0 to 192.168.255.255 (256 units of class C)
An address acquired by making application to NIC on the other hand is referred to as a global address.
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Subnet mask
This subnet mask is used to separate the IP address into a network address part and host address part. The network
address bits are set to "1" and the host address bits are set to "0".
In the same manner as the IP address, the subnet mask is a 32bit-(4byte)-numeric value. The subnet mask is separated
1-byte by 1-byte by a dot (".") and expressed in decimal notation.
Therefore, when the subnet mask is "255.255.255.0", the network address part becomes 24 bits.
Generally, when making an application to the NIC for an IP address, only one network address is allocated to each
company (organization). Any of class A to class C is allocated depending on the scale of each company (organization).
For example, since the network length is 16 bits in class B, one network address that can connect up to 65533 units is
allocated. However, when using this network address as it is, the efficiency of the management or process becomes poor.
Normally, the subnet mask is set appropriately to separate the network into multiple networks.
For example, when a subnet mask of 255.255.255.0 is set for the class B network, 256 networks, each of which can
control up to 254 units, can be set.
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MAC address (Media Access Control Address)
This MAC address is also called "Ethernet address" and shows a hardware identification number (6-byte numeric value)
set for each network interface. Since the MAC address is set for each unit in the manufacture phase, users do not need to
set it.
The Ethernet system identifies the connected unit from this MAC address. That is, even when the communication is
performed using the TCP/IP protocols, the communication is performed while the IP address is automatically converted
into the MAC address.
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HUB
HUB is a device used to connect the personal computer and each unit. This is equipped with multiple ports to connect
the modular jacks. A unit is connected to this port using the twist pair cable with the modular jack.
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Router
A router is a device used to connect multiple networks with each other. This sends the external data transmitted from the
internal network to the external network or sends the data transmitted from the external network to the internal network.
Additionally, specific data is disposed of through the filtering process to ensure the network safety.
The IP address of the router is set for each network unit as a gateway address. As this setting is made, each unit can
correctly receive or send the data among the networks.