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another based on IP addresses. It forwards only data packages that are to be sent to another
network. A router is most commonly used for connecting a local network to the Internet. Tradi-
tionally, routers were referred to as gateways.
Firewalls
A firewall is designed to prevent unauthorized access to or from a private network. Firewalls
can be implemented in both hardware and software, or a combination of both. Firewalls are
frequently used to prevent unauthorized Internet users from accessing private networks that are
connected to the Internet. Messages entering or leaving the Internet pass through the firewall,
which examines each message, and blocks those that do not meet the specified security criteria.
Internet connections
In order to connect a LAN to the Internet, a network connection via an Internet service provider
(ISP) must be established. When connecting to the Internet, terms such as upstream and down-
stream are used. Upstream describes the transfer rate with which data can be uploaded from the
device to the Internet; for instance, when video is sent from a network camera. Downstream is the
transfer speed for downloading files; for instance, when video is received by a monitoring PC.
In most scenarios—for example, a laptop that is connected to the Internet—downloading infor-
mation from the Internet is the most important speed to consider. In a network video application
with a network camera at a remote site, the upstream speed is more relevant since data (video)
from the network camera will be uploaded to the Internet.
9.2.1 IP addressing
Any device that wants to communicate with other devices via the Internet must have a unique
and appropriate IP address. IP addresses are used to identify the sending and receiving devices.
There are currently two IP versions: IP version 4 (IPv4) and IP version 6 (IPv6). The main differ-
ence between the two is that the length of an IPv6 address is longer (128 bits compared with
32 bits for an IPv4 address). IPv4 addresses are most commonly used today.
9.2.1.1 IPv4 addresses
IPv4 addresses are grouped into four blocks, and each block is separated by a dot. Each block
represents a number between 0 and 255; for example, 192.168.12.23.
Certain blocks of IPv4 addresses have been reserved exclusively for private use. These private IP
addresses are 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255 and 192.168.0.0 to
192.168.255.255. Such addresses can only be used on private networks and are not allowed to be
forwarded through a router to the Internet. All devices that want to communicate over the Internet
must have its own individual, public IP address. A public IP address is an address allocated by an
Internet service provider. An ISP can allocate either a dynamic IP address, which can change during
a session, or a static address, which normally comes with a monthly fee.
CHAPTER 9 - NETWORk TECHNOLOGIES
