Specifications

9.3 VLANs

When a network video system is designed, there is often a desire to keep the network separate

from other networks, both for security as well as performance reasons. At rst glance, the obvious

choice would be to build a separate network. While the design would be simplied, the cost of

purchasing, installing and maintaining the network would often be higher than using a technology

called virtual local area network (VLAN).

VLAN is a technology for virtually segmenting networks, a functionality that is supported by

most network switches. It can be achieved by dividing network users into logical groups. Only

users in a specic group are capable of exchanging data or accessing certain resources on the

network. If a network video system is segmented into a VLAN, only the servers located on that

VLAN can access the network cameras. VLANs normally provide a better and more cost-ecient

solution than a separate network. The primary protocol used when conguring VLANs is IEEE

802.1Q, which tags each frame or packet with extra bytes to indicate which virtual network the

packet belongs to.

Figure 9.3a In this illustration, VLANs are set up over several switches. First, each of the two dierent LANs are seg-

mented into VLAN 20 and VLAN 30. The links between the switches transport data from dierent VLANs. Only members

of the same VLAN are able to exchange data, either within the same network or over dierent networks. VLANs can be

used to separate a video network from an oce network.

9.4 Quality of Service

Since dierent applications—for example, telephone, e-mail and surveillance video—may be

using the same IP network, there is a need to control how network resources are shared to fulll

the requirements of each service. One solution is to let network routers and switches operate

dierently on dierent kinds of services (voice, data, and video) as trac passes through the

network. By using Quality of Service (QoS), dierent network applications can co-exist on the

same network without consuming each other’s bandwidth.

VLAN 20

VLAN 30

VLAN 20

CHAPTER 9 - NETWORK TECHNOLOGIES