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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 aected, 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 dierent 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 sucient for internal communication.)
Before IP addressing is discussed, some of the basic elements of Internet communication such
as routers, rewalls 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 TECHNOLOGIES - CHAPTER 9