The Nuances of Network Video Recorders

Welcome to our new “Consultant’s Notebook” series. In each part of this series, we will take a specific electronic security technology – in this case, network video recorders (NVRs) – review the benefits and drawbacks, and present several hypothetical case studies to illustrate the material. It is designed to give the reader insight into where this technology is appropriate and where it is not.

We will also generalize somewhat about the technology being described. For the most part, this information accurately describes what is currently available on the majority of products offered in this area. Certain manufacturers and products break away from the pack, particularly when new and evolving technologies are being discussed. We will mention these areas where we feel they are trends but may not cover all variants available on the market.

Packaging Is Primarily What Distinguishes NVRs From DVRs
An NVR is a system component that takes digital video streams and stores them on an array of hard drives. It also presents these images for later playback, archiving and manipulation. While this may seem like the function of all digital recording systems, there is a distinction between a NVR and a DVR.

All digital video systems can be divided into four distinct areas: image acquisition; analog to digital encoding; storage; and image retrieval. In fact, the key difference between systems is the packaging of these subsystems.

A DVR packages everything but the imaging device (camera) in one box, with analog (BNC) inputs, software to view and retrieve the images, and hard drive storage generally in the same chassis. Sure, you can often add storage in the form of additional hard drives (either internally or externally) and use additional software clients for remotely accessing the video, but it’s essentially a one-box solution.

NVR-based systems retain the same functionality, but the packaging is different. An NVR requires a digital stream that it can accept from two different sources. If the system is using conventional analog cameras, they are fed to an encoder that converts the stream to an IP stream the NVR can record.

These encoders vary in density, with some manufacturers offering single-channel encoders that have one input (analog) and one output (Ethernet). Others combine multiple analog channels to provide an encoder with several inputs and a single output. There are manufacturers that offer both types, and there are reasons for and against both types.

The second source is a camera and encoder combined in a single unit. These are referred to as IP cameras, and the flavors can vary. Some units provide additional inputs to allow a single IP camera to encode signals from external analog cameras in addition to their own image. IP cameras are more expensive than analog cameras, larger because of the additional functionality and associated circuitry, and are not available in as many aesthetically pleasing configurations as conventional analog cameras.

These differences are shrinking with market acceptance of the IP camera, but it is anybody’s guess when industry volume and the associated economies of scale will erase the cost and size differential. Make no mistake, these differences will ultimately go away. For proof, you only need to look at the difference in price between color and monochrome cameras 10 years ago and today.

It is important to note that NVRs do not care where the signal originates – an encoder is an encoder, whether it is a standalone box or built into an IP camera. It is possible to mix and match IP cameras and legacy cameras (digitized through a standalone encoder) in the same system, as long as the encoder or IP camera is sending out an IP stream that the NVR can read. And that’s a pretty big “if.” For the most part, encoders and NVRs must be matched to ensure they will work together. While there are a few exceptions, most systems are still somewhat closed and compatibility is not a given.

In many ways, the protocols used to send IP signals to NVRs today are where dome telemetry protocols were several years ago. These systems were also extremely proprietary, and the end user needed to purchase the same brand dome and matrix switch to ensure full compatibility, or deal with a host of protocol translator boxes. Today, a few standard dome protocols have emerged, and interoperability is less of a challenge. This is the direction that IP protocols are heading, although we’re not there yet.

NVRs Found at Low, High Ends of Market
Interestingly, NVRs appear at both the top and bottom end of the market. Enterprise systems such as those from Honeywell and Pelco are encoder/NVR systems and have become the standard for high-end gaming applications, widely considered the most critical and performance intensive. However, many smaller systems are built using IP cameras and software that is loaded onto a conventional PC that turns the PC into an NVR.

Either application can benefit from the use of an NVR, and we will explore this further in the case studies later in this article. For the most part, the mainstream market today belongs to the DVR. With embedded and PC-based solutions available (see the February 2006 “Enterprising Solutions” column for an analysis of embedded vs. PC-based DVRs), these units are extremely cost effective and usually easier to configure than NVRs. The variety of analog camera configurations available makes them compelling for many users. So why would you consider a separate Encoder/NVR system?

Placement, Storage, Fewer Failures Are Among Pluses
Because of their distributed nature, NVR-based systems allow a great deal of flexibility in configuration. In many larger applications, it means the recorder can be placed in a location that is more centralized and secure than can be easily achieved in a DVR-based system.

For example, at the Mystic Lake Casino (profiled in SSI’s March issue), an encoder/NVR system is used. This allows the NVRs to be located in a centralized, secure rack room in the main building, while some encoders are located at a remote facility more than a half-mile away. This flexibility allowed them to digitally record all signals from the remote facility without worrying about the increased power and air conditioning requirements that digital video incurs.

In fact, NVR systems can record to multiple locations. It is possible to send the digital video stream to multiple NVRs, either live or after the fact. Live allows a camera to stream to two or more DVRs for true data redundancy, while scheduled backup allows signals to be pulled off of an NVR from another NVR, generally done when an off-site backup is required.

NVRs also allow a level of storage pooling that is not available on DVRs. Since each NVR is capable of handling multiple video streams, the system can be configured to ensure that storage space is maximized. This allows the system to provide a predetermined time limit on video storage without wasting hard drive space.

NVR-based systems can also efficiently handle failures. If an NVR fails, many systems will reroute the IP data streams to a backup unit until the first unit is restored to operation. Coupled with the reliability inherent in RAID-based storage systems, available dual-redundant power supplies from many manufacturers, and controlled environments allowed by this distributed architecture of an NVR-based system, it is easy to see why this is the design of choice for high-end enterprise digital video systems.

NVR Disadvantages Include Bandwidth, Cost, Complexity
No system is perfect, and there are some disadvantages to NVR-based systems. The first is bandwidth.

Unless there is some level of data storage in the field device (which really makes the field device a DVR), the system is always consuming bandwidth. If the network link from the encoder or IP camera to the NVR goes down, recording will stop. This almost necessitates a separate network for the digital video system and creates numerous opportunities for sabotage or other system failures.

One proposed solution is to distribute the NVRs, locating them closer to the field devices, but that makes the system look, smell and act more like a conventional DVR system. This brings up the second disadvantage: cost.

Systems with NVRs are generally more expensive, unless they require one or more of the features that are listed as advantages. If centralized storage is required, it is frequently less costly to place encoders in the field than it is to run each camera back to a central point. If storage-intensive video recording is required, either because of resolution, frame rate or retention time, the pooled storage nature of NVR systems may significantly decrease costs.

High reliability, the ability to record to multiple locations and other architecturedependant features also swing the balance toward NVRs, but for many systems, the lower entry cost and modular nature of conventional DVRs is more appropriate.

The complexity of NVR systems can also be a factor. With a DVR, you simply add additional DVRs when more inputs are required. NVRs require more complex calculations of the number of video streams that can be handled by a server, the amount of hard drive space available, frame rate, compression and other factors. These attributes often must be plugged into a spreadsheet to determine which part(s) of the system must be expanded if additional cameras are added.

NVRs Suitabie for Applications Like Casinos, Offices, Schools

Casinos – With the high camera count, demanding video quality and long image retention requirements that are typical of a casino, these applications are prime candidates for NVRbased systems. Security personnel in these environments are looking to centralize data storage for security reasons and can benefit from storage pooling.

Redundancy is often critical, and the budgetary requirements often pale when compared to the costs associated with a system failure. Such a failure can potentially cause the casino to close until the problem is fixed, which can cost millions of dollars in lost revenue.

Because of this natural selection, many NVR system manufacturers ensure their systems are tailored to the particular requirements of gaming applications. From integration with point-of-sale systems to specialized image logging and playback tools, special attention is paid to this particular industry, and the resulting products further cement the relationship.

Unless the facility is extremely small or has already made a significant investment in conventional DVRs, NVR systems are the clear choice.

Office buildings – Office buildings, on the other hand, are an application that can benefit from either technology, but NVRs are frequently a better fit. Smaller buildings may benefit from the ability to feed all cameras to a few strategically located DVRs. However, a building has to be fairly small for this to make sense. Larger facilities generally benefit more from NVRs due primarily to the widely disbursed nature of the camera systems used in these complexes.

If DVRs are used in closets around the facility, there will frequently be open inputs on the DVRs as the number of cameras in a given area rarely meshes with the number of inputs available on the nearest DVR. The broad array of available encoders – including IP-based cameras with built-in encoders – allows the system designer to include the precise number of inputs required in each area, while routing the signals across a network to a centralized storage area with pooled storage.

Schools – Looking at schools, because of the range of applications within a school district, there is a wide range of solutions that require further study before determining which approach is best. On the surface, in much the same way as an office building, this is an NVR application. Cameras are widely disbursed, and the variety of encoders available makes them a more cost-effective choice than leaving open inputs in closet-mounted DVRs.

But there are other factors that make DVRs more attractive to schools. For one, their modularity is appealing. Schools frequently phase in their systems, and the ease of buying a DVR and plugging in cameras appeals to school officials. While the risk that DVR inputs will go unused is there, there are usually enough cameras that can be routed to a choice of data closets depending on where the nearest open input is located.

Bandwidth is another factor in school buildings and districts. Closet-mounted DVRs connected via a local area network (LAN) allow remote viewing with recording maintained in the event of a LAN failure. While this may not be a factor within buildings (although with open LAN ports in each classroom and plenty of curious fingers and minds, there are ample security risks), bandwidth between facilities is often limited. Further, there isn’t always room for added boxes in the IT room, making disbursed systems a better option in terms of footprint.

NVRs Figure to Proliferate, but Don’t Count DVRs Out

One side effect of the proliferation of digital video systems is the sheer number of options available in the market. The increasing reliability and ease of installation for NVR-based systems allows them to be viable candidates for applications that may have been too complex to consider a few years ago.

With the speed and reliability of networks ever increasing, it makes sense to consider systems that utilize the network as an integral part of their DNA. This doesn’t mean that the DVR is going away any time soon. It does mean that the DVR is transforming into a variety of form factors, one of which is the NVR.

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