75
Figure 9.1d An existing system can be upgraded with PoE functionality using a midspan and splitter.
The midspan, which adds power to an Ethernet cable, is placed between the network switch and
the powered devices. To ensure that data transfer is not affected, it is important to keep in mind
that the maximum distance between the source of the data (e.g., switch) and the network video
products is not more than 100 m (328 ft.). This means that the midspan and active splitter(s)
must be placed within the distance of 100 m.
A splitter is used to split the power and data in an Ethernet cable into two separate cables,
which can then be connected to a device that has no built-in support for PoE. Since PoE or High
PoE only supplies 48 V DC, another function of the splitter is to step down the voltage to the
appropriate level for the device; for example, 12 V or 5 V.
PoE and High PoE midspans and splitters are available from Axis.
9.2
The Internet
To send data between a device on one local area network to another device on another LAN,
a standard way of communicating is required since local area networks may use different types
of technologies. This need led to the development of IP addressing and the many IP-based pro-
tocols for communicating over the Internet, which is a global system of interconnected com-
puter networks. (LANs may also use IP addressing and IP protocols for communicating within a
local area network, although using MAC addresses is sufficient for internal communication.)
Before IP addressing is discussed, some of the basic elements of Internet communication such
as routers, firewalls and Internet service providers are covered below.
Routers
To forward data packages from one LAN to another LAN via the Internet, a networking equip-
ment called a network router must be used. A router routes information from one network to
Network switch
Uninterruptible
Power Supply
(UPS)
3115
Midspan
Network camera
with built-in PoE
Network camera
without built-in
PoE
Active splitter
Power
Ethernet
Power over Ethernet
NETWORk TECHNOLOGIES - CHAPTER 9
