A primer on wireless network topologies for video surveillance

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


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.