Wireless mesh is a new network architecture that makes use of ‘AovNv=intelligent’ wireless transmitters, thus providing reliability and flexibility for high-end surveillance applications.
In a wireless mesh network, every mesh unit not only transmits data packets received from the cameras directly attached to it, but it can also forward packets arriving from other mesh units, via an optimal path.
These mesh networks have been a very active field of academic research in the last two decades. Indeed, their initial application was mobile and nomadic communication in the battlefield, or in hostile environments. Many defence-related applications of mesh networks involve highly mobile and battery-powered units, creating challenging technical problems whose solutions are yet to mature. However, mesh networks for data transmission, video-streaming, or temporary communications in the event of natural disasters, are a reality today.
Self-forming and self-healing
Nodes in a wireless mesh network are powerful devices that run advanced mesh routing algorithms, designed to evaluate and select the optimal path for every transmitted packet in real time. The dynamic mesh routing algorithm allows the routing of packets and video-streams around obstacles, sources of interference or low-quality links, therefore increasing reliability and flexibility at the same time.
The devices are completely auto-configurable: the routing protocol takes care of finding other mesh devices nearby and the location of the base units attached to the wired network. In the event of a link going down, the connection points (nodes) in the network will not only immediately notice that a failure exists but they will change their preferred path to avoid the failed link. This absence of any single point of failure makes mesh architecture a reliable network topology where many-to-many communications are required – without having to rely on any layered architecture, in which data moves from one defined level of processing to another. In a mesh network, every node is a peer, i.e. providing the same functionality as other nodes, so there is no higher layer or controlling node that can be destroyed in order to bring down the entire network.
Routing in a wireless environment is conceptually similar to routing in the Internet, but it presents several differences in terms of evaluating the quality of a particular path. While Internet routing is based on minimal hop count – the number of point-to-point links in a transmission path – in a mesh network the quality of wireless links is of crucial importance.
Researchers at the Massachusetts Institute of Technology (MIT) recently discovered that minimum hop count is not effective for wireless routing. Rather, a metric involving link-quality measurements is required to create reliable wireless mesh networks. This discovery broke most of the layered abstractions developed by the ‘AovNv=inventors’ of the Internet in the 1980s and 90s, and established a fresh school of thought about wireless routing.
The importance of link quality in a wireless environment should not be understated. Wireless links tend to have a high packet-loss rate and the transmitter needs to resend the lost packets several times, wasting valuable bandwidth and increasing delays. Therefore, in a mesh network, it is often preferable to take a longer, yet more reliable path to the end point.
By continuously probing the different wireless links, every mesh node builds and updates statistics regarding every link available. These link-quality tables are then employed by the routing protocol to compare every possible path and pick the optimal route at any point in time.
Video-streaming challenges
Video-streaming and video surveillance have been one of the latest additions to the list of possible applications for mesh technology. But high-resolution video-streaming over a mesh network presents several technical challenges, bandwidth being one. When one deals with high-resolution video, bandwidth is often scarce, and a multi-hop transmission may decrease usable bandwidth and increase delay. For example, a video packet that goes through three hops absorbs three times the bandwidth compared to a video packet that is only one hop away from its destination.
However, advanced mesh products can solve these challenges by operating multiple radios at the same time. In this way the video stream can use many different channels to create high-bandwidth and low-delay paths. Operating multiple radios allows bandwidth to be increased, by not only spreading the transmissions on multiple non-overlapping channels but by decreasing the delay of the network. At every hop the packets go through, the mesh transmitter can choose the best frequency to reach the following node, therefore optimising not only the path but the frequency spectrum usage as well.
All that said, routing in a multi-hop, multi-radio mesh network requires advanced routing algorithms and powerful processors embedded in the transmitter. In terms of computations, the optimisation work is expensive and the processor needs to continuously crunch and solve complex optimisation problems in real time.
Video surveillance: why mesh?
Mesh architecture can be the solution to several problems faced by security system integrators when they work on wireless video-surveillance systems. Firstly, being auto-configurable, mesh devices are able to decide how to transmit packets based on the present conditions of the channels, rather than on predetermined configuration values.
Secondly, unpredictable sources of interference do not need to be predicted. Instead, the network will identify the position of the source of interference and start routing packets around these low-quality links.
Airports and seaports are typical locations where mesh architecture can solve several problems at once. Aircraft taxing on the ground are often unpredictable and moveable sources of interference. But during the design and the installation of a mesh-based CCTV system, it won’t be necessary to identify every possible position where a plane can interfere with the video-streaming quality. Instead, the mesh network will automatically find alternative paths.
Similarly, using traditional wireless technology in commercial seaports is very challenging because loaded container ships are almost ‘AovNv=moving buildings’, making the design of a traditional static wireless network virtually impossible. However, using a mesh-based architecture, video-streams will change their path in the event that a container ship docks in the middle of a wireless link, impeding transmission through that particular path.
Using traditional point-to-point solutions, large obstacles like hills, buildings or forests require the installation of high towers or poles, in order to create line of sight between the antennas. This is in contrast to a mesh-based approach, in which video-streams can simply be routed around such obstacles. It is necessary only to connect to the next node in the mesh network, which will then relay the stream to the following node and so on, until the packets reach the base station.
Temporary and mobile applications
The flexibility and ease of installation of mesh-based video surveillance systems create the opportunity for new applications for video surveillance, particularly when mobility and speed during the installation process are required.
In such applications, a new node can be easily added to the network without needing to change the configuration or the settings of the rest of the system. This enables police departments, for example, to easily move or add new cameras for temporary events, such as summit meetings, public demonstrations, strikes and sports events.
Mesh units can also be installed on police cars or vans to create mobile cameras for special events. And temporary networks can be quickly installed in case of emergency or natural disaster, creating a moveable and easily deployable wireless infrastructure to transmit critical data, video and voice information.
Moreover, the large use of omni-directional antennas in mesh networks allows quick installations, with no need for time-consuming antenna alignments, because the network will automatically reconfigure itself.
Summary
Mesh topology’s intrinsic reliability and flexibility offers a step forward in wireless networking when applied to video surveillance applications. Every node in the network is an ‘AovNv=intelligent’ router, able to forward packets received from nearby units, and deciding in real time the optimal path based on the channel and network conditions. Mesh networks also enable the installation of wireless CCTV systems where other wireless solutions would struggle, such as in the presence of moveable obstacles or sources of interference, or in cases where frequent repositioning of the cameras is necessary.
Umberto Malesci is president and co-founder of Fluidmesh Networks.