Mesh networks are wireless links which allow data connections between nodes by hopping from node to node.   Each node can act as both an network Access Point and a Network Client and can support multiple paths.  This means that in the event of a node failure (eg due to a power outage) the data will be sent via a different route.

Connectivity

Mesh networks support IP connectivity. This means they are suitable for use in UTMC communication networks (eg. connecting variable message signs, counters etc) and traffic signal controllers provided they have IP-compatible OTUs ( Outstation Transmission Units) such as the Siemens Gemini and Peek Chameleon products. One of the key advantages to a Local Authority UTC operator of moving to IP connectivity is the ability to deploy UTC traffic control at a distance from the UTC instation where this would have been prohibitively expensive using BT circuits. In Cumbria we installed a mesh network over 60 miles from the UTC instation. By using existing Local Authority backhaul we deployed UTC with zero operating costs and performance which exceeded the BT circuits adjacent to the instation.

Using mesh for Traffic Signals

Traffic signal installations which run UTC (urban traffic control) require frequent communication with the UTC instation. Traditionally these communication links have been provided by leased analogue BT circuits - such as multipoint EPS42 circuits. There has been much discussion over the years about the long-term viability of these circuits and a proposal to withdraw them in the mid-1990s led to the establishment of the UTMC initiative by the UK Department for Transport. 

The UTMC initiative recognised that the world was moving towards an IP-based communications environment.  The outcome was a series of open standard definitions for the interface between roadside equipment and instations which have enabled open and competitive procurement exercises which help Local Authority purchasers avoid supplier 'lock-in'.

The complexity of UTC operation has meant that IP-enabled OTUs took a little longer to be developed but suitable products are now available from both Siemens and Peek. Other suppliers may soon identify the opportunities that are opening in this area.

A Mesh network can provide a good communications medium for IP data traffic. For a Local Authority this means that the OTUs and instation need to IP-capable; in most cases this means deploying new OTUs with consequent implications for capital. It is, however, worth bearing in mind that some existing signal installations using leased circuits can cost as much to run over 12 months as the cost of a replacement communications network.

IDT has deployed nearly 200 mesh-enabled junctions and, with our experience of traffic signals and UTMC, are well-placed to assist with weighing up the relative merits. Please don't hesitate to ask.

Network design and monitoring

Mesh networks need to be designed carefully with a sense of engineering pragmatism as any wireless network will be subject to interference during operation. Our experience of the physics of radio engineering and the realities of roadside deployment have helped us overcome some of the challenges of deployment and we always recommend an initial survey to determine the feasibility of a network.

The network design must also take into account the availability of other communication networks which may assist, for example, in the provision of backhaul (the communications circuit to link the roadside with the instation or datacentre).

A simple network schematic is shown below (click the drawing to expand).  This drawing shows an xDSL backhaul link from the instation terminating at a car park counter.  A mesh link from the counter to CCTV mast then hops on to a car park VMS and two sets of traffic signals.

IDT's mesh network router has 3 layers of security to which a fourth layer can be added.