DVRs & NVRs: Get It Straight
by Ron Nelson
Will network cameras overload your client’s network? Can you use analog cameras with a network video recorder? Find out what’s hogwash and what’s not, as
SDM’s video expert sets the record straight about the capabilities of DVRs and NVRs.
There are many misconceptions about digital video systems, mostly due to the relative newness of the equipment and lack of understanding of exactly how digital systems operate compared with analog systems.
When installing a stand-alone analog system, dealers could specify and install equipment as necessary without any thought of the impact of their system; but because digital systems have network connections and utilize network bandwidth, dealers and technicians must consider the impact of many external factors when designing and installing a system. In a facts-and-fiction format, this section addresses some of the more common misconceptions about system design and installation.
FICTION!
You Cannot Use Analog Cameras with an NVR
Although NVRs are designed to communicate only with IP-based cameras, you can add analog cameras by using a device called a video server. These devices digitize the video from an analog camera and send it over an IP-based network either in real time or on demand. Video servers are a good choice when you want to replace an existing analog VCR or DVR and do not want to rewire the entire system and replace all of the cameras.
To understand how they operate it is important for you to understand exactly what a video server does. First it takes the analog video signal from a traditional analog CCTV camera and then digitizes it. The digitized signal is then compressed using a compression algorithm and sent over a network.
Some video servers also may include a serial data port for pan-tilt-zoom (PTZ) control, alarm inputs that can be used to cause the video server to send images over the network, and alarm outputs that can be used to activate other devices. The server may also contain an image buffer to store images for pre-alarm transmission. Video servers can operate over a standard wired LAN, wireless network, Internet, or even a standard modem. You can even use any existing analog monitors with an IP-based video system by installing video encoders, which connect to the network and convert the digital signals to standard analog signals that can be displayed on a standard video monitor.
FACT!
Digital Video Cameras Can Provide a Higher Image Quality than Analog
Analog video cameras are limited to approximately 0.4 megapixel resolution by the NTSC/PAL standards. Digital cameras have no such limitation; it is common to see digital video cameras with a resolution of greater than 1 megapixel. In addition, the quality of an analog video image can be adversely affected by long cable runs, interference from outside electrical stimuli, and repeated copying of the images. Digital video cameras have no such cable problems and because the video image is completely digital, repeated copying has no affect on the quality of the image. As technology and market demands evolve, the quality of network cameras will increase and the cost of the cameras will decrease as their availability increases.
FICTION!
NVRs and DVRs Are Basically the Same
Nothing could be further from the truth. A DVR is basically a digital replacement for an analog VCR, while an NVR is at the heart of a totally new type of video surveillance system. In a DVR, analog video signals from the cameras are digitized, compressed and then stored on some type of mass storage media, such as a hard disk. The DVR performs the digitizing, compression, and storage functions just as a VCR does.
In an NVR the video images are digitized and compressed at the camera, or video server, and the resulting video data is then sent over any standard network configuration to the NVR, which stores the data for real-time viewing or retrieval of past events. In addition, due to cable restrictions, DVRs have to be located near the analog cameras while NVRs can be located anywhere on the network, on site across the street, or around the world. Because the video information is completely digital and standard network devices are used, location is not a consideration.
FACT!
IP-Based Video Systems Are Reliable
Companies use their networks for the most critical and sensitive business applications, such as e-mail, purchasing, billing and sales. Given the importance of these functions to the day-to-day operation of any company, a great deal of money and effort is expended in configuring a data network that is robust and as reliable as possible, because any outage can result in significant loss of revenue. Redundant servers, storage devices, switches, links, and UPS power are often incorporated into a data network, providing a very resilient, fault-tolerant transmission path.
Adding video to this existing infrastructure is simply a good use of resources and provides a great deal of flexibility for system expansion. The reliability of these systems is evident by the increasing number of IP-based systems being proposed, installed, and the number of manufacturers offering IT-based video equipment.
Another major advantage of IP-based systems is the ability to use redundant data storage techniques. In an analog VCR system a problem with the recording heads or tape can result in the loss of all video information. Because an IT-based system is capable of using standard data storage devices, redundancy can be achieved by using mirrored drives, or RAID. This will help ensure that a failure of a single disk will not result in the loss of any video information. The argument also can be made that by employing encryption algorithms, video signals transmitted over a network are more secure than analog video signals transmitted over a coaxial cable. With analog systems it is quite possible for an unauthorized individual to tap into the system for the purpose of viewing images or possibly feeding a false video stream into the system.
FICTION!
Network Cameras Will Overload a Network
This is a common misconception even among security dealers. The fact is that a well-designed network can support numerous cameras by using the intelligence that is built into the network camera. These devices can have the capacity to alter the data stream based upon motion, specific event, or time, so that the camera is not constantly sending high frame rate/resolution video images unless it is necessary to do so.
You also can locate the NVRs on the same segment of a network as the cameras, limiting the network segments that will carry the video information. If the existing network does not have the capacity to handle all of the cameras involved, then you also can install a parallel Gigabyte data network specifically for the video system and merge it into the existing data network for remote viewing and access to live or recorded images.
As with any system that will operate over an existing data network it is very important to speak to the IT manager before designing the system so that any issues of bandwidth and hardware utilization can be addressed early, preventing unexpected complications as the installation progresses.
FICTION!
IP-based Video Systems Are always more Expensive
The total cost for a video system has many components such as cameras, cables, recorders and labor. Despite the higher cost of the cameras, when comparing the cost for a total system frequently an IP-based system can be lower than a conventional analog system.
There are many reasons for this:
- CAT 5E (or better) cable is lower in cost than quality coaxial cable.
- Using POE (Power over Ethernet) eliminates the need for separate power cables to the cameras.
- PTZ commands can be sent over the same cable as the video and power for IP-based systems while most analog CCTV systems require a separate cable for these functions.
- The cost of an NVR is typically lower than a DVR.
Add to this the labor savings in running a single cable, or better yet using the existing network cables and it is easy to see how the final cost to install an IP-based system can be lower than an analog system. Another factor to consider is changes to the system layout and future additions. With an analog system, moving or adding a camera requires a new home run for video, power, and PTZ, while with an IP-based system all you need to do is run one cable to the nearest network switch/hub.
February 1, 2007 -- (Reprinted with permission from SDM magazine, Copyright 2007) |
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