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In a modern ofﬁ ce, computers are most likely to be

connected through Ethernet, via a Local Area Network

(LAN), or a Wireless LAN. Ethernet gives a fast net work

at a reasonable cost. All modern computers are supplied

with an Ethernet connection or can easily accommodate

an Ethernet connection card. If you install an Internet

connection today (cable modem, xDSL, etc.) it will

probably have an Ethernet connector.

Ethernet is available over ﬁ xed or wireless networks

and is available in three different speeds: 10 Mbit/s, 100

Mbit/s and 1,000 Mbit/s. For home and small ofﬁ ce use

100 Mbit/s is recommended.

This chapter contains basic information about Ether net

network components and their relative protocols.

Hubs, switches and routers

Hubs are essentially used as connection boxes to allow

several pieces of equipment to share a single Ethernet

connection. Usually 5-24 devices can be connected to one

hub. If more devices are used, another hub can be added.

To speed up the network, you can use switched hubs,

switches or routers that allow several data packets to be

transmitted simultaneously. Although they are some what

more expensive than normal hubs, switches provide

much better capacity and are generally recommended.

Switches can interface between 10, 100 and 1,000 Mbps.

Example

You want to record images from six network cameras

connected to a server placed in a room 200 meters

away. Instead of using cables from each camera with

200 meters of cables (1.2 km cables in total), you could

use a hub or a switch, which interconnects the cameras

and only need one 200 meter cable. The cable used for

these kinds of connections, CAT-5, is also cheaper than

the coax cable used in analog installations. And since

the installation using a hub or a switch requires less

cabling, the overall cost will be kept to a minimum.

This is a huge advantage for IP network video systems

compared to analog technology.

Bridges

If more than 255 devices are connected to the same net-

work, the network needs to be divided into segments. A

router must be placed between segments. Alternatively,

a bridge can be used. Switches sometimes have built-in

router functions. For example, an airport with two buil-

dings using 170 cameras each needs to be connected to

the same security central several kilometers away. To

have access to all cameras simultaneously, you simply

divide the cameras into two networks and connect them

together with a bridge.

IP networks

IP is the most common computer communication protocol today. It is the

base protocol used for Internet, e-mail and almost every newly installed

network. One of the reasons for its popularity is its scalability. In other

words, it works equally well in very small installations as it does in very

large installations and is supported by an increasingly wide range of

high-performance, low-cost equipment.

This switch is manufactured by Cisco. Other major manufacturers include

D-Link and 3com.

N ETWORK BASICS

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Axis 2400+ Manuale Utente Pagina 40

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