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Remote control

decimal numbers separated by points (e.g. 192.168.15.1).

Each decimal number is represented by a binary number

of 8 bits. IP addresses are divided into public and private

address ranges. Public IP addresses will be able to route

by the Internet and an Internet service Provider (ISP) can to

be made available. Public IP addresses can be reached di-

rectly over the Internet to directly exchange internet data.

Private IP addresses are not routed by the Internet and are

reserved for private networks. Network elements with pri-

vate IP addresses cannot be reached directly over the Inter-

net so no data can be directly exchanged over the Internet.

To allow network elements with a private IP address to ex-

change data over the Internet, they require a router for IP

address conversion (English NAT; Network address trans-

lation), before connection to the Internet. The attached ele-

ments can then data exchange over this router, which pos-

sesses a private IP address (LAN IP address) and also a pu-

blic 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rst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 catego-

risation from IP addresses is for the assignment of public

IP address ranges of importance and essentially depends

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x

(statically) or variable (dynamically) to be assigned.

IfIPaddressesinanetworkareassignedx,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Congura-

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 addres ses 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rst3numbers)andhost

class adress range net quota host quota max. number of networks max. number of hosts

A 0.0.0.1 - 127.255.255.255 8 Bit 24 Bit 126 16.777.214

B 128.0.0.1 - 191.255.255.255 16 Bit 16 Bit 16.384 65.534

C 192.0.0.1 - 223.255.255.255 24 Bit 8 Bit 2.097.151 254

D 224.0.0.1 - 239.255.255.255 Reserved for multicast applications

E 240.0.0.1 - 255.255.255.255 Reserved for special applications

Table 13.2: Classes of IP adresses

adress range subnetz mask CIDR way of writing number of possible host adresses

10.0.0.0 –10.255.255.255 255.0.0.0 10.0.0.0/8 2

−2=16.777.214

172.16.0.0 –172.31.255.255 255.240.0.0 172.16.0.0/12 2

−2=1.048.574

192.168.0.0 –192.168.255.255 255.255.0.0

255.255.255.0

192.168.0.0/16

192.168.0.0/24

−2=65.534

−2=254

Table 13.1: Private IP adress ranges