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Remote Control

able to route by the Internet and an Internet service Pro-
vider (ISP) can to be made available. Public IP addresses
can be reached directly over the Internet to directly ex-
change internet data. Private IP addresses are not rou-
ted by the Internet and are reserved for private networks.
Network elements with private IP addresses cannot be
reached directly over the Internet so no data can be di-
rectly exchanged over the Internet. To allow network ele-
ments with a private IP address to exchange data over the
Internet, they require a router for IP address conversion
(English NAT; Network address translation), before con-
nection to the Internet. The attached elements can then
data exchange over this router, which possesses a private
IP address (LAN IP address) and also a public IP address
(WAN IP address), via the Internet.

If network elements exchange data only over a local net-
work (without connection with the Internet), appropriate
use private IP addresses. Select in addition e.g. a private IP
address for the instrument and a private IP address for the
host (PC), with which you would like to control the instru-
ment. If you might connect your private network with the
Internet later via a router, the private IP addresses used in
your local network can be maintained. Since within each
IP address range the first IP address is used as network
IP address and the last IP address is used as Broadcast IP
address, in each case two IP addresses have to be taken
off from the “number of possible host addresses“ (see ta-
ble 1: Private IP address ranges). Apart from the organiza-
tion of IP addresses into public and private address ran-
ges, IP addresses are also divided into classes (Class: A,
B, C, D, E). Within the classes A, B, and C are also include
the private IP of address ranges described before. The ca-
tegorisation from IP addresses is for the assignment of pu-
blic IP address ranges of importance and essentially de-
pends on the size of a local network (maximum number of
hosts in the network), which is to be connected with the
Internet (see table 2: Classes of IP addresses). IP addresses
can fix (statically) or variable (dynamically) to be assigned.
If IP addresses in a network are assigned fix, an IP address
must be preset manually with each network element. If IP
addresses in a network are assigned to the attached net-
work elements automatically (dynamically), a DHCP ser-

ver (English DHCP becomes; Dynamic Host Configura-
tion Protocol) is required for the dispatching of IP addres-
ses. With a DHCP server an IP address range for the auto-
matic dispatching of IP addresses can be preset. A DHCP
server is usually already integrated in a router (DSL router,
ISDN router, Modem router, WLAN router, …) integrated.
If a network element (e.g. an instrument) is connected by
a network cable directly with a host (PC), the IP addresses
cannot be assigned to the instrument and the host (PC) au-
tomatically, since no network with DHCP server is present
here. They have to be preset therefore at the instrument
and at the host (PC) manually.

IP addresses are divided by using subnet mask into a net-
work quota and into a host quota, so similarly e.g. a te-
lephone number is divided in pre selection (land and lo-
cal area network number) and call number (user num-
ber). Subnet mask have the same form as IP addresses.
They are represented with four decimal numbers separa-
ted by points (e.g. 255.255.255.0). As is the case for the IP
addresses here each decimal number represents a binary
number of 8 bits. The separation between network quota
and host quota is determined by the subnet mask within
an IP address (e.g. the IP address 192.168.10.10 by the sub-
net mask 255.255.255.0 is divided into a network quota
192.168.10.0 and a host quota of 0.0.0.10). The allocation
takes place via the transformation of the IP address and
the subnet mask in binary form and afterwards a bit by bit
one logical AND operation between IP address and subnet
mask. The result is the network quota of the IP address.
The host quota of the IP address takes place via the bit by
bit logical NAND operation between IP address and sub-
net mask. By the variable allocation of IP addresses in net-
work quota and host quota via subnet masks, one can spe-
cify IP address ranges individually for large and small net-
works. Thus one can operate large and small IP networks
and connect if necessary to the Internet via a router. In
smaller local networks the subnet mask 255.255.255.0 is
mostly used. Network quota (the first 3 numbers) and host
quota (the last number) are simple here without much ma-
thematical expenditure to determine and it can with these
subnet mask up to 254 network elements (e.g. measuring
instruments, hosts/PC‘s...) in a network be operated at the