Another benefit of Ethernet cabling is Power over Ethernet (PoE), which powers devices through the network cables. This eliminates the need to install power outlets at camera locations and enables a more continuous power supply.
Sometimes a non-wired solution is beneficial, particularly for buildings where cable installation will damage the interior, or where cameras will be regularly moved. Another common use of wireless technology is to bridge two buildings or sites without expensive and complex ground works. Wireless LANs are available in a number of well-defined standards that allow for vendor neutrality. The most common standard is 802.11g, which provides higher transfer rates at greater distances than 802.11a and 802.11b.
New or Existing Network?
With all of these networking options available, it is sometimes difficult to determine whether to run IP surveillance on an existing network or to build a new network dedicated to security and surveillance needs.
Today's LANs typically offer plentiful bandwidth, with network switches providing 100 Mbit for each device connected on the network. Since network cameras can consume anywhere from 0.1Mbit to 8 Mbit, some precaution is needed to ensure the network video system will operate as intended. Depending on the number of cameras and required frame rate, three options are available:
1. Dedicated Network. Professional surveillance applications may benefit from a dedicated network in which the IP surveillance system has its own dedicated switches that are connected to a high-capacity backbone (see Figure 1). Dedicated networks handle video traffic more efficiently, without slowing down other general-purpose network applications like voice over IP or file sharing. In addition, keeping the surveillance network separate and disconnected from the Internet will make it as secure as-or more secure than-any local CCTV system. Dedicated networks are preferable in very sensitive applications, like those in casinos or airports, and for systems requiring high frame rates and more than 50 cameras.
2. Combination Network. In some cases, it might make sense to implement a dedicated IP surveillance network in conjunction with a general-purpose network. Video can be recorded locally and isolated to the dedicated network, except when a viewer on the general-purpose network wants to access it, or when an event triggers video to be sent to a user on the general-purpose network (see Figure 2). Because access to video using the general-purpose network (and the extra load it causes) is temporary, it makes sense to have the two networks work in combination.
3. Existing Network. When there is enough capacity on the network and the application doesn't require heavy security, you may simply add network video equipment onto the existing network. You can further optimize your network using technologies such as virtual local area networks (VLAN) and quality-of-service (QoS) levels.
A VLAN uses the existing LAN infrastructure but separates the surveillance network from the general-purpose network. The router/switch is configured to provide a range of IP addresses with assigned features. In Figure 3, the router/switch manages the IP addresses, bandwidth and security allocated to users on VLAN A (with access to video) and VLAN B (general purpose traffic). No matter where users might physically be, all those on VLAN A will have access to the video while those on VLAN B will not.
QoS ensures that bandwidth will be available for surveillance equipment on the general-purpose network by setting priority levels for specific ports on a switch. Connections to network cameras and storage servers can be set at high priority, while desktops can be set for low priority to ensure that bandwidth is always available for critical surveillance video.
Once your network layout is established and your devices are connected, information will be transmitted over the network. Transmission Control Protocol/Internet Protocol (TCP/IP) is the most common way to transmit all types of data. It is the protocol used for nearly every application that runs over a network, including the Internet, e-mail and network video systems.