This second part of the Digital Network Camera Surveillance
School covers the various components of a network and a brief
description of their function, written in an easy to understand way.
Standing alone it can work as a useful glossary for anybody who
comes across technical terms not fully understood. It is also useful
for a better understanding of the coming lessons of the Digital
Network Camera Surveillance School.
TCP/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, lowcost
equipment.
In a modern office, computers are most likely to use TCP/IP and are connected via an Ethernet network,
either in a LAN (Local Area Network), or in a Wireless LAN.
Ethernet gives a fast network 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 in three different speeds: 10 Mbps, 100 Mbps and 1,000 Mbps. For home
and small office use, 100 Mbps is recommended.
A typical configuration of networked surveillance cameras. All cameras are accessible from any
computer connected to the network. In addition remote control of cameras is possible from a
computer in the home or elsewhere.
This chapter of the Network School contains basic information about network components.
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 to 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 more
expensive than normal hubs, switches provide much better capacity and are generally recommended.
Switches can interface between 10, 100 and 1000 Mbps.
“A switch manufactured by Cisco. Other major switch manufacturers are HP and 3com”.
As an example, you may 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 may use a hub or a switch, which interconnects the cameras and only need 200 meters
of 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 network systems compared to analog technology.
Bridges
If more than 255 devices are connected to the same network, the network needs to be divided into
several segments. A router must be placed between segments. Alternatively, a bridge can be used. Switches
sometimes have built-in router functions. As an example, an airport with two buildings 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.
Patch panel
In a modern office, each room is often fitted with at least two network cables that are connected to
a server room. In an office with several floors, the network cables on each floor end up in one or
more patch panels. These panels, together with hubs, switches, gateways and other communication
equipment, make it possible for the network administrator to decide how the network should be
physically connected. If a company chooses a modern, network-based security solution, the existing
cables can be used. (If there are two network outlets in a room but more are needed, a hub can be
placed in the room.) Using the patch panel, the network administrator can then connect all the security
devices in a physically separate network, which can be accessed via a bridge from other parts
of the office network. Having the security devices on a separate network ensures that the devices do
not place a burden on the normal office network.
Gateways
Gateways provide a convenient way to create a local network. This product works as a combined router
or switch and is available from various manufacturers, for example D-Link, Cisco and 3Com. Gateways
make it possible to create a protected security network that is accessible via the company’s Internet
or intranet.
Server
A server is a computer or software application that provides services to other computers connected via a
network. The most common example is a file server that has a local disk and handles requests from
clients to read and write files on this disk. A server is commonly located together with other network
equipment in a separate room. In big companies, the room is usually locked with limited personnel access.
The room would have its own backup power supply in case of a power failure, as well as a separate
humidity and temperature control system. Normally, all information on a server is automatically backed
“An example showing a typical office using a PC as a gateway to the Internet. The PC operates
as a router with two IP addresses: one for the internal network and one for the Internet”.
DHCP Servers
If there are many devices on a network, a DHCP server can be used to help reduce the time in administering
the devices’ IP addresses and keep the number of IP addresses to a minimum. This type of server automatically
issues network devices with IP addresses when they connect to the network. This is normally
not a good solution for security devices since you do not want them to change addresses every
time they are reconnected after, for example, a service break or power failure.
Domain Name Servers
In larger networks, a Domain Name Server (DNS) is included. This is literally a ‘name’ server that
associates and remembers given names to corresponding IP addresses. For example, a network camera
monitoring a door is more easily remembered and accessed with the word ‘door’ than with its IP
address, e.g. 192.36.253.80.
Firewalls
All networks connecting to the Internet should be protected against hackers. An Internet ‘firewall’ is a
device that ensures that only authorized users can access devices connected in a LAN. In larger
networks, it is common to use a PC to perform the combined functions of a NAT, DHCP server
and firewall. This PC may also be used as an e-mail server, name server, or for storing images.
Remote modem
In many cases, it may be interesting to be able to control, for instance, a security system remotely
from the home. With a remote modem, you can connect to a remote location via the ordinary
phone network. phone network.
IP addresses
Each device on a LAN must have a unique address. This is commonly called the IP address, and is
occasionally referred to as the Ethernet address. An IP address consists of four numbers separated by
a dot “.”, each number is in the range of 0 to 255. For example, the address could be
192.36.253.80. The first three groups of digits will be common to all devices connected to the
same segment, i.e. in the previous example, all units within the same segment will have a common address
beginning with 192.36.253.
It is important to remember that every camera or other security device connected in a network has
a unique IP address, similar to a unique telephone number. More information about IP addresses
will be covered in a coming section of the Detektor Network School.
Data Packets
All data is sent within a data packet, and all packets are labeled with the address of the destination.
In an Ethernet network, a packet is transmitted approximately every 0.1 millisecond. This
means that up to 10,000 packets can be transmitted every second. Since modern computers and network
devices have a high capacity, they can communicate simultaneously with several units. A modern
network camera can send images to at least five computers simultaneously.
