A primer on wireless network topologies for video surveillance

In recent years, there has been incredible growth in the video surveillance market due to an increased need to secure the world's ports, airports, cities and transportation infrastructure as well as schools, hospitals, government and other critical environments. This is a market whose growth has exploded over the past five years, and that ABI Research forecasts will be a $41 billion a year market by 2014.

Now more than ever, organizational demands have hastened the search for better, more cost-effective security applications, and in many instances, rapid deployment of security systems has become essential. But as critical as improved security has become, budgets to accomplish this goal are by no means unlimited.

Organizations of all kinds are being challenged to install video surveillance in areas that are too remote, too costly or even physically impossible to reach with additional wired cabling. As a result, wireless solutions have been a boon to the video surveillance market as they enable the ability to cost-effectively leap over these barriers, allowing a virtually unlimited number of video surveillance cameras to be deployed quickly, easily and affordably.

Though there are many wired video surveillance networks already in use today, the need to expand and scale those networks cost-effectively and in a timely manner introduces an opportunity for wireless solutions to take over where wire left off. And for new wireless video deployments -- such as the many new networks that are being deployed in the U.S. (which has only a fraction of the amount of cameras deployed as other areas of the world like the UK) -- the ease of initial deployment, flexibility, scalability and cost-effectiveness of wireless technology makes it the ideal candidate.

More importantly, beyond cost savings, scalability and ease of use, wireless has proven time and time again in real-world deployments to provide the necessary performance and reliability to ensure the ongoing operation of even the most mission-critical video surveillance networks. But the fact that wireless has proven itself as a reliable alternative to wired technologies is just the beginning. What wireless technology is best for wireless video, and what is the difference between systems?

Today, there are three predominant wireless technologies that are being utilized for the successful deployment of wireless video surveillance networks -- wireless mesh, point-to-point (P2P), and point-to-multipoint (P2MP). Each technology has its own merits, and each has its own place in the video surveillance ecosystem. What's important is to know the capabilities and limitations of each technology, and then make the determination on which technology is right for your particular network based on how well each technology delivers on the specific requirements of your deployments.

The following is a primer on these three primary wireless technologies, and how each of them stacks up as a solution for video surveillance networks.

Wireless/Wi-Fi Mesh

Wireless mesh technology refers to modified Wi-Fi radios that connect to each other in a daisy-chained or "multi-hop" fashion, enabling traffic to be passed from radio to radio en route to its final destination. Wireless mesh networks enable many cameras to be connected together via a wireless network that blankets an area, and does not require that a camera have a direct connection (wireless or wired) to the termination point (command center, network operations center, etc.).

Over the last few years, many wireless mesh companies have poured a lot of marketing dollars into establishing wireless mesh as the ideal wireless technology for video surveillance. Not all mesh technologies are alike, but in general, the same claims are made by all when talking about the fundamentals of wireless mesh -- and this includes the self-configuring, self-healing nature and the built-in redundancy/reliability of the multi-hop environment.

However, this topology can often prove to be problematic when it comes to the specific application of delivering video traffic. Latency, unpredictable/undesirable behavior, dynamic bottlenecks and the subsequent capacity shortages have been all too common when trying to support video on wireless mesh. Now, that is not to say that wireless mesh is incapable of delivering video traffic -- but several misconceptions and unrealistic expectations regarding the performance and ease of use have caused a great deal of confusion around wireless mesh.

Given the fact that wireless mesh radios (also called nodes) are designed to operate as both transmitters and repeater, these networks can be a convenient means of extending connectivity around obstacles that might otherwise prevent a direct line-of-sight link. This is referred to as providing non-line-of-sight (NLOS) operation. Given the use of omni-directional antennas on wireless mesh networks, however, overall system gain and increased reception of interference can often cause mesh units to have high outage and require more cycles to adapt to the environment. So, while NLOS capabilities can be recognized in ideal situations (environments with no other -- or very little -- radio noise or interference, which are rare), often times wireless mesh deployments can fall victim to the interference of the environments they are deployed in.

As appealing as the term "self-configuring" may be, any mission critical surveillance network should be carefully designed to operate to a specific availability and within parameters that are understood and agreed upon by all parties. With that said, dynamic and adaptive technologies are not specific, and regardless of which topology is used a good rule of thumb is to minimize the variables and have a very comprehensive understanding and documentation for how each device in a network is configured. The technology chosen should also provide enough management over these functions to keep the systems under control.

The "self-healing" trait touted as a strength in wireless mesh systems is also important to review. You must ask yourself -- why is the system in need of healing in the first place? A properly designed and installed wireless network with adequate signal should perform to 99.999 percent availability at the desired modulation required to support the video surveillance application.

So, while wireless mesh technologies certainly have their uses, in situations where high reliability and performance are necessary -- like in most video surveillance networks -- wireless mesh can present a few problems. For more information and to review the results of a performance test for mesh as a video transport, you can download a whitepaper from ZDNet.com.

Pros & Cons of Mesh:
Pros:

  • Establishes connections dynamically/automatically
  • Adds a degree of fault tolerance
  • Easy deployment for standard municipal wifi networks
  • Simplified sparing
  • Repeater function for avoiding obstacles

Cons:

  • Dynamic bottlenecks
  • Difficult to control
  • Increased latency
  • Shared capacity
  • Requires higher signal-to-noise ratio (SNR) due to use of omni-directional antennas

 

Point-to-Point (P2P)

Point-to-Point (P2P) technologies refer to wireless systems that provide a dedicated, high-performance link between two locations. This is fundamentally different from the wireless mesh technology discussed above, as the main goal for P2P wireless links in video surveillance networks is to provide an extremely reliable backhaul link. This could be a backhaul link connecting a single camera back to the wired backbone, or it could be a dedicated link that backhauls traffic from a single aggregation point (like the termination point in a mesh network) carrying all video traffic from a larger network back to the network operations center.

By providing a single, dedicated link, P2P eliminates many of the problems such as interference and noise that affect the wireless mesh technologies. Also, because it is not a multi-hop technology, it does not introduce increased latency that can hinder the performance of a video transmission. P2P links utilize higher-gain/narrower beam-width antennas which greatly increase Fade Margin and SNR while minimizing the reception of undesired interference from other systems.

Though the performance and reliability benefits of P2P over wireless mesh are undeniable, these direct links are more costly than wireless mesh links, which means they are not always feasible depending on the project budget. In addition, P2P links can provide a great deal more bandwidth than wireless mesh networks -- with some wireless P2P backhaul solutions providing as much as 1.25 Gbps links. So, depending on the link performance of the given P2P technology used, it could be overkill for the particular connection, leaving some bandwidth/throughput unused.

For these reasons, P2P technologies are often used to backhaul traffic from a single termination point (like the termination point in wireless mesh networks) where it can aggregate all the video traffic and then transport it to the command center or network operation center.

Pros & Cons of Point-to-Point (P2P)

Pros:

  • Dedicated access
  • Increased reception and transmission levels
  • Less vulnerable to interference
  • Lower latency than most shared mediums
  • Simplified troubleshooting

Cons:

  • Higher cost per end point
  • Sometimes more difficult to align
  • Excess/under-utilized capacity
  • Increased head-end equipment

Point-to-Multipoint (P2MP)

Point-to-Multipoint (P2MP) systems are often a cost-effective means of obtaining a balance between the advantages of wireless mesh and P2P systems. P2MP technologies implement central base station units (BSUs) that then connect to multiple subscriber units (SUs). This enables the deployment of separate, lower-cost SUs next to each video camera in the network, enabling SU to deliver the video traffic directly from the camera back to the BSU. The BSU acts as the aggregation point for the traffic from all SUs.

Unlike wireless mesh deployments, which can introduce detrimental latency based on the non-direct multi-hop nature of the technology, P2MP networks provide a series of direct connections from the many SUs back to the central BSU. This provides a balance between the dedicated connectivity needed to ensure the quality and performance needed for mission critical video surveillance networks and the cost-effectiveness of a distributed network (as opposed to many dedicated links).

The best P2MP networks for video will utilize a polling algorithm (like WiMAX) to provide an efficient and effective means of distributing bandwidth amongst the end points/SUs fairly and in a controlled manner. This helps to provide quality of service (QoS) in the wireless video surveillance network, and to ensure that each camera receives the bandwidth necessary to deliver a constant, reliable video stream.

Though traditionally a technology that required line-of-sight connectivity between SUs and the BSU, there are recent advances that have enabled NLOS functionality in some P2MP systems, which provides even great ease of use and configuration. For the best performance, though, line of sight operation among P2MP links still yields the greatest return.

Pros & Cons of Point-to-Multipoint

Pros:

  • Cost effective
  • Efficient means of sharing capacity
  • Decreased head-end footprint
  • Simplified alignment

Cons:

  • Wider antennas increase exposure
  • BSUs can provide a single point of failure for multiple SUs
  • Requires more attention to throughput planning

One Size Does Not Fit All

It is important to remember that -- though each of these technologies has its strengths and weaknesses in different scenarios -- the best technology is largely dependent on the individual needs of the particular video surveillance deployment in question. In some situations (with low noise or interference environments), wireless mesh can provide an acceptable solution. When the most important consideration is absolute link reliability and performance, P2P technologies can be ideal. And when looking to find a balance between the cost-effectiveness of wireless mesh and the performance/reliability of P2P, P2MP solutions are a solid decision.

It is also critical to understand that you do not need to commit to only one of these technologies. Any provider that only sells mesh will of course try to convince you that mesh is the best solution. Likewise, a provider that only sells P2P will try to convince you that you need dedicated links throughout your video network. As the saying goes -- when all you have is a hammer, then everything looks like a nail. But based on the individual needs of each application, you may need a multi-technology solution.

P2P systems can provide the backhaul for wireless mesh and P2MP networks, P2MP and wireless mesh networks can be deployed together to provide a balance of video backhaul and Wi-Fi connectivity, or all three can be utilized for a complete end-to-end wireless network. The important thing is to utilize whichever technology is best for your particular deployment.

About the author: Robb Henshaw, is director of marketing and communications for Proxim Wireless, a Silicon Valley-based developer of wireless radios and transceivers that are for business and municipal networking and often for campus-style and municipal video surveillance.

Editor's note: This is a guest column provided by an expert from a manufacturer. If you would like to dispute, debate or inquire about technical points made in this article, please use our comments area (below).

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