DVRs Are Driving CCTV to New Heights
With the International Security Conference (ISC West) upon us, security professionals will be spending a great deal of time standing in front of manufacturers’ displays and seeking information on digital video recorders (DVRs). Some will do so because they are merely curious about the hoopla surrounding digital CCTV, while others will want to see how digital can actually benefit their customers.
However, with more than 235 different vendors vying for a piece of this rapidly expanding market, attendees’ minds as well as their plastic travel bags figure to be overtaxed. The following information will help seasoned veterans as well as first-time buyers navigate through the new, bold world of digital recorders and remote video access.
DVR Features Leave Analog VCRs in the Dust
In order to understand why there is so much interest in digital recording and an ever-growing population of manufacturing competitors, we should first review the advantages DVRs offer compared to analog VCRs.
The most obvious difference is that VCRs use standard two-hour magnetic VHS tape, while digital information can be stored on digital audiotape (DAT), digital versatile disc (DVD), hard disk drive (HDD), or any combination of these mediums.
Digital recorders have the ability to search for recorded information based on time/date/second as well as camera input, allowing for much faster retrieval times. Instead of wading through countless frames of video information, digital machines can obtain the desired images in fractions of a second.
Another one of the many advantages of digital recording is image quality. Digital recorders – due to the use of digital storage devices – can save images that have very little background picture noise and higher stability, and are generally of higher quality. With digital recording, the image quality does not deteriorate during long-term storage or frequent accessing of the recorded image.
On the service side, gone are the days of high machine maintenance, and head and tape replacement. DVRs still require some maintenance such as cleaning fan entry points and, on DAT machines, heads. But in the long run, very little time and money is required to keep digital recording devices operational.
Digital recorders offer many additional features – such as remote video retrieval, integral multiplexing, pre- and post-image enhancements, and networking capabilities – that would be next to impossible for any standard analog tape machine to match.With so many different additional features, which ones should be part of the selection process? To help answer that question, let’s take a closer look at the different types of DVRs.
DVRs Can Be Basic, Multiplexed or Multichannel
Digital recorders can be placed into three basic groups: basic, multiplexed and multichannel.
Many dealers and integrators view the basic form of DVR as a direct replacement for traditional VCRs, as well as an inexpensive way to evaluate the overall performance of today’s digital recorders. They are typically single-channel devices capable of recording up to one or two weeks. These digital units offer little or no setup parameters. The recorder usually determines the playback quality, storage capacity, and reviewing characteristics.
The second group of digital recorders combines multiplexed video inputs and a recording unit. This group is the largest of the three and can cause some confusion in both selection and setup.
Multiplexed DVRs combine an eight- or 16-channel multiplexing unit with the digital recording device. The time-sharing of video inputs operates the same way as standalone video multiplexers. The advantages of this combination are that installers no longer have to worry about interface wiring and compatibility of individual setup programs.
The last group is multichannel digital recorders. For many, this form of digital recording is designed for high-end applications. Requirements such as monthlong storage, real-time video recording (60 images per second) of all video inputs and unlimited video channels can be provided by multichannel DVRs.
Many of the same features offered by multiplexed DVRs can be found in multichannel units. However, there are some notable differences between the two.
First, multichannel recorders allow all 60 images per camera to be recorded, whereas, in a multiplexed unit, video inputs are divided between the 60 images. This division, or time-sharing of images, is what causes the jerky motion during playback (this occurs when the image rate per camera falls below 15 images per second).
Secondly, multiplexed recorders usually have a maximum storage capacity of 480GB to 600GB, which is based on the type of storage devices available at that particular time. Multichannel units incorporate expandable storage devices that range from DAT in jukebox configurations to a redundant array of independent disks (RAID), each with the capability of supplying many terabytes of memory.
Different RAID levels are utilized for different applications, depending on the fault tolerance, speed of access required or average size of the files being stored. The most common RAID formats found in the CCTV industry are RAID-0, -1 and -5.
Digital Recording Is Well Suited for Remote Viewing
More companies are turning to remote viewing of their video systems and are considering incorporating LANs, WANs and Web-based systems.
One major advantage of an IP-addressed network is the ability to receive video signals anywhere using equipment ranging from a simple Internet browser to special client-based application software. Another appealing aspect is that it eliminates the need to run new cabling and provides easier solutions for future system expansion.
Many security experts agree that, through system integration and networks, the job of command and control by remote security operators can be made more effective and efficient. Network configurations vary greatly, depending on the number and type of sites being monitored, the available bandwidth of the network and the number of users in the system.
Networked Systems Need Bandwidth Management
The most important question to consider before attempting remote viewing over a network is whether the video is to be interfaced with existing networks and, if so, what the available bandwidth is for the remote video signal.
The impact of bandwidth utilization must be understood when remote video application traffic is requested from a client on LAN or WAN systems. The network bandwidth demands can be reduced if image quality and number of sessions are also reduced.
In an intranet, IP address assignments as well as network parameters are controlled by the in-house network manager. It is important to regulate the maximum network bandwidth that will be consumed by streaming multicast or unicast multimedia in order to protect existing applications. Controls are generally available within the application to set bandwidth limits at the server-to-network interface.
Transmission Medium Affects Frame Rate
Many of today’s DVRs are triplex, as opposed to duplex, in design, meaning they facilitate live, recorded and remote video monitoring. For many, remote view monitoring means access from a Web browser connected to the Internet. This requires a local Internet service provider (ISP) to connect to the outside world.
Because Internet connection speeds vary, understanding different types of transmission lines can explain the differences found in remote quality.
Cellular is the slowest transmission method and, presently, not widely used in the CCTV market. However, for remote areas or areas that offer no telephone service, this is the only way to offer remote surveillance. The speed of such systems is 9.6Kbps, but, like everything else, that is increasing.
G3 technology, which is starting to appear
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