A look at the network-specific issues associated with multi-site video systems
Much has been speculated recently about the shift away from traditional CCTV systems to fully networked solutions. While there is little doubt that systems with all cameras connected directly to a digital video network will become increasingly common, it is nevertheless not cost-effective to implement such solutions for the majority of applications today. Examples cited by proponents of full networking tend to be few in number, and they tend to be based on large-scale local CCTV systems where the customer requirements include multiple viewing points and complete flexibility in configuration. Despite the hype surrounding such ‘new technology solutions’, most current CCTV projects will not show cost or performance advantages by embracing the fully networked vision. And this is likely to remain true for some years.
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Networking best use
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There are however two classes of CCTV applications where it is clearly advantageous to make use of some networking technologies ‘ namely remote video alarm verification and remote access to digital recording systems. Both these applications can use a variety of networking technologies to improve the cost-effective management of multiple facilities by providing remote access to on-site video systems. Remote video alarm verification has made sound economic sense for some time, as it can allow a few operators to manage security on hundreds of sites. The success of this approach is clearly evidenced by the tens of thousands of installed systems. Remote access digital recording systems may also be used to provide central management of site security needs. A key difference to the requirements for alarm verification may be the provision of access to stored information from multiple review locations. Such systems do not make the jump into full networking. Rather, they apply the engineering maxim of the simplest solution being the best by blending a sensible mix of non-networked and networked technologies. They run analogue video connections from the cameras to a local video recording or transmission system, which then connects to a network to provide remote site access and control.
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Remote alarm verification
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Remote alarm verification systems have been installed worldwide The most successful applications are typically those on high-value sites, where on-site guards are an alternative. In these instances the potential cost savings have been large enough to allow well-engineered solutions to be applied while still seeing payback periods of less than 12 months. For such remote electronic guarding systems to show labour savings and hence cost benefits, the remote system must automatically report suspicious activity and send the associated video imagery to the monitoring centre. Operators can then assess the situation and instigate appropriate actions ranging from issuing verbal warnings to calling mobile guards or the police. Early warning of a potential site intrusion can add value by offering the possibility of intervention before damage. This is best provided by a continuously active perimeter sensing system that triggers alarm image captures from the verification cameras. Such a covert system usually proves much harder to defeat than on-site guard patrols as intruders can see the times at which the guards are absent from a part of the perimeter, and hence gain unchallenged entry or exit. The effectiveness of remote video alarm verification products is determined by the quality of the transmitted images, storage and transmission of multiple images from multiple alarms, the ability to conduct two-way audio conversations to the remote site and the reliability of the system. Live video transmission capability, remote camera control and remote site control capabilities may also add significant value to the system in applications such as remote access control, lone worker safety monitoring and other surveillance applications. But all of this is of little value if the system is not supported by quality central station monitoring software that integrates properly into the general alarm monitoring environment. Installers designing systems for remote alarm verification should also be aware of the requirements of the forthcoming standard BS8418 (installation and remote monitoring of detector activated CCTV) and ensure that the alarm verification allows for compliance.
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Remote access recorders
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The ability to provide remote access to stored video information is a second clear-cut need for networking video communications between multiple sites. The management of identity fraud, such as false usage of credit cards or cheques, is one major application area. In these instances significant cost savings and improved customer service can be offered by allowing virtually instantaneous retrieval of stored information from both a central investigation location and from multiple customer service centres. In such applications the key system requirements include reliable unattended operation, high image quality, evidential integrity of the images presented for prosecution, ease of access to the recorded information from multiple locations, automatic search of images based on transaction number and a recording capacity of up to 90 days. To make the most of the finite storage capacity available it is best to choose a system that compresses the video signals very efficiently. This means selecting equipment using either MPEG or H.26x compression technologies, which store only the changing portions of the images, rather than full frame compression technologies such as JPEG, MJPEG or Wavelet which store each image in its entirety. This selection criteria applies also to alarm verification systems as it reduces the operator interaction times quite dramatically and can even allow effective camera and site control over relatively slow speed data links.
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Remote video management
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Telecommunications service suppliers offer a range of options for network connectivity between sites based on leased lines, circuit switched networks or packet switched networks. Leased line systems provide a fixed point-to-point connection and so are often the least suitable for the class of application where multiple site connectivity is required. However, they may be used in some very high reliability applications where there is a justifiable cost of extra equipment provided to make the system appear as one homogeneous network. Circuit switched systems are ones in which data can only flow between sites when a physical connection is established through a switching system. Common examples are the Public Switched Telephone Network (PSTN) and the Integrated Services Data Network (ISDN). PSTN provides data capability over voice networks through the use of modems, but is limited to data rates below 56 Kilobits per second. ISDN gives direct access to digital data transmission and at data rates of 64 Kilobits per second and higher. Packet Switched networks maintain a permanent physical connection between all sites. Data is passed between sites in packets, each packet containing the information to define its destination address in addition to the included data for that address. Examples of packet switched networks include ones operating the old X.25 protocol and Internet Protocols (IP networks). X.25 networks are typically limited to less than 10 Kilobits per second and are not normally considered for new systems. IP networks are available with a wide range of data rates. The choice of network type for interconnecting the sites is primarily dictated by the integrity or guaranteed availability of a network connection, the availability of a backup signalling path, the data carrying capacity (bandwidth) of the network and the cost to use the network.
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Network reliability
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The inter-site networking requirements for video alarm verification and remote access digital recording differ due to the required level of integrity or guaranteed availability of the network. Reliability is critical for alarm verification. It may even be necessary to have both continuous monitoring for network failure and also a backup communications path over a separate network. Many remote access recording applications can meet their operational requirements without having to resort to backup network options and can be used over lower reliability networks.
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Network capacity
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In an ideal world, high-speed data connections would be used to allow instantaneous retrieval of stored alarm images and live viewing of cameras from the remote site. But in most instances this is neither affordable nor strictly necessary. By using the most efficient video compression technologies, live video of reasonable quality can be transmitted over links with bandwidths of a few hundred kilobits per second. Several images per second can be obtained over standard telephone lines, which is sufficient for alarm verification and remote access to stored event images, although marginal for control of PTZ cameras and general site surveillance.
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Network costs
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Network costs vary significantly but tend to be based on a combination of capacity and reliability. Low cost options sometimes considered include the use of the Internet or piggybacking on existing IT infrastructures. But both, as outlined below, often have significant limitations.
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Using the internet
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Using the internet to provide low-cost multi-site connectivity is one option often considered, but this does have some serious limitations in relation to the capabilities of a network whose traffic is unregulated, and for which no quality of service can be guaranteed. The most common options for connecting to the internet are to use a PSTN modem, to connect via ISDN or to use the recently available Assymetrical Digital Subscriber Line (ADSL) connectivity. Other options may include cable, wireless or satellite connectivity. The first two do offer the advantage of connection to multiple sites by a single call. However, it should be noted that the data carrying capacity accessed will at best be that of the PSTN modem or ISDN link, and often much less depending on network availability and traffic. On paper, ADSL offers a much faster connection to the internet. However the caveats of unpredictable throughput still apply. It should also be noted that most popular offerings of ADSL for internet access are based on the assumption that not all users will require all the bandwidth they have paid for all the time. Typically this bandwidth is shared between up to 20 or 50 users, depending on the service selected. Early adopters of ADSL may well see excellent speed of data transfer but should expect their average speeds to drop down as more users come on line. For occasional access to stored video this may be quite acceptable, but for multi-channel live surveillance it is likely to be unsatisfactory. If the internet is used for security applications it is wise to have backup communications via a more reliable network, and to select equipment that can automatically revert to this network.
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Piggybacking on an IT data network
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At first glance this seems a most attractive proposition as it may amount to ‘free communications’ if the infrastructure in place has excess capacity. Yet this is not always the case, and even if it is true there will often be issues associated with the perceived potential for the new video system to disrupt, or lower the performance of the activities for which the network was originally established. Complications may arise if the network is managed by an IT out-sourcing contractor who provides performance guarantees on the applications which use it. In this instance the network is highly unlikely to be made available.
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Practical choices
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So what are the realistic alternatives’ Unless the applications can justify the high and ongoing communications costs of high capacity network connections, the current options are still most likely to be ISDN and PSTN. These do not offer the capacity to provide multiple channels of high quality live video, but are perfectly useable for video alarm verification or event query searching from digital video recorders. ISDN is the most logical choice for most video alarm verification applications as it has an excellent reliability specification, is almost universally available and is competitively priced for the data carrying capacity that it provides.<br>
For remote access digital recording, the generally lower network reliability criteria coupled with cost constraints may see a wider range of ‘less optimal’ solutions including PSTN, corporate network piggybacking or the use of the internet. In choosing equipment to provide the alarm verification or recording functions it is wise to consider products which make the best use of the available bandwidth and which support a wide range of network connection options.
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The future
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Networking of digital video is here to stay, but its adoption rates will grow most rapidly in areas where the benefits are clear and the price is right. From the rapid uptake of remote video alarm verification and remote access digital recording it is clear that both have a bright future. Until recently these two functions were considered separate, as the majority of digital recorders had been designed purely as local surveillance tools for evidence gathering. A new breed of recorders which can make efficient use of limited bandwidth network connections and which can meet the forthcoming standards for remote monitoring of detector-activated CCTV, will offer an elegant system solution for sites requiring remote access recording and remote guarding. Such combined solutions are likely to simplify the installation and offer a lower systems solution cost to customers. The choice of network between sites to best support these applications is likely to change as the telecommunications providers finally move their remaining network capabilities away from voice to data. To design systems to best capitalise on these changes it’s important that installers work with equipment which supports a wide range of physical connectivity. It is also crucial to work with equipment suppliers with proven track records for product reliability and support, who can provide expert guidance on network connectivity and systems design.
