A primer on wireless network topologies for video surveillance

Reviewing the pros and cons of mesh, point-to-point and point-to-multipoint technologies


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.