First multicast mesh network in Darwin

Tuesday, 08 March, 2011

When NT police planned an $8.612 million closed-circuit television system to monitor trouble hotspots in Darwin, it deployed a self-healing wireless network designed by MIMP connecting solutions to manage 109 cameras covering 6 sq km of the city’s streets.

Project manager STS selected Adelaide-based network specialist MIMP to design and deploy what it claims is Australia’s first multicast mesh IP-based wireless network, with the ability to self-heal any points of failure and to survive lightning strikes.

Since the Darwin Street Camera wireless network was deployed in December 2009, it has successfully transported hundreds of gigabytes of video data each day without any major disruptions or outages.

“We chose MIMP based on their previous experience and the fact that they’d delivered similar projects elsewhere," said STS Managing Director Greg Ireland. "We also chose MIMP for a similar project in Alice Springs, which says a lot about what we think of them.”

In 2009, the Northern Territory Government and the Australian Government committed $8.612 million to establish a closed-circuit television system to enable NT police to monitor and reduce antisocial behaviour on the streets of Darwin.

After a competitive tender, the NT Police Fire and Emergency Services Department chose Darwin-based security company Security & Technology Services (STS) to deliver the project.

The project required STS to integrate 47 existing CCTV cameras deployed at ‘hotspots’ - mass passenger transport systems as well as bus interchanges - with 62 new pan, tilt and zoom cameras, installed at popular congregation points at Casuarina, Palmerston and Darwin.

Due to the prohibitive cost of connecting all the cameras with fibre-optic cable, STS needed a highly reliable wireless network to allow police to monitor the 109 cameras, control them remotely and record high-resolution vision of any incidents that are of a quality fit for use in a court.

Major challenges of transmitting high-definition video streams from the cameras to three police stations - plus a fourth remote storage facility - were to avoid network congestion from the large volume of data traffic and to eliminate the risk caused by single points of failure.

The demanding Top End environment delivered difficulties including high year-round heat and humidity plus thousands of lightning strikes a day during the turbulent wet season. Another issue was vandalism.

To meet the Darwin climate and operational challenges, MIMP decided the wireless network needed to be self-healing, so it would keep working if part of the network went offline and selected network equipment from Strix Systems, a US-based global leader in wireless mesh networking. The Strix Access/One Outdoor Wireless System is a modular, in-the-field upgradable system that delivers high throughput and low latency levels.

The technology provides high redundancy by using a multicast mesh structure with self-healing capabilities to optimise performance and availability. Multicast mesh is a highly distributed network model where any device can accept and pass on a data packet, even if it’s not on the shortest path from sender to receiver.

This maintains data delivery even when devices or even parts of the network become unavailable.

With 128-bit data encryption for security, the system also uses a multisubnet architecture to route video data streams over diverse data paths via multiple subnetworks. This design effectively created three stand-alone mesh networks with a fibre backbone.

MIMP general manager Allan Aitchison said the multicast mesh structure gave the Darwin wireless network both resilience and redundancy. “To our knowledge, this is the first multicast mesh network in Australia,” he said.

“A multicast mesh network provides the richest connectivity and is very robust, because it self-heals if devices disappear off the network. By designing the network so each device accepts messages, even if the device is not on the shortest path from a camera to the police station, it routes data around any disrupted areas, so there’s no single point of failure. Further robustness is added by the use of multiple subnets, so the second and third subnets can continue operating even if one area goes down.”

Aitchison said the Strix equipment also handled the demanding Darwin environment including heat, humidity, lightning and vandalism.

“Lightning is a huge issue in Darwin during the wet, when there are as many as 3000 strikes a day, which all tend to hit the top of buildings. As well as lightning protection in the antenna and the equipment itself, the wireless units have a heat shield over the radio unit, which also protects them from vandalism.”

MIMP designed, configured and tested the network at its Adelaide head office before sending it to Darwin where it was installed by STS. MIMP technicians then commissioned the network, which went live in December 2009.

The CCTV system is operated by a dedicated police monitoring team in a real-time CCTV control room at the Joint Emergency Services Communications Centre in Berrimah. As well as video data being recorded at this secure remote data storage facility, surveillance capabilities are available at police stations in Casuarina, Darwin and Palmerston.

Cameras are monitored 24 hours a day, seven days a week. Each day, the 109 cameras deliver hundreds of gigabytes of new vision for storage at two locations, one of which is a central repository with 30 terabytes of data storage. Most video data is destroyed after 30 days, although some is retained as evidence for police investigations and prosecutions.

NT police CCTV project administrator Shane Moten said the CCTV network had assisted police to more proactively manage and reduce antisocial behaviour on the streets of Darwin.

“Since the system has been live, we have generated hundreds of additional incidents that we might otherwise have missed,” he said.

“It has helped to solve problems that range from recovering stolen property, dealing with assaults and vandalism to identifying multiple persons on different occasions with concealed weapons, which enabled us to direct police to intercept these persons before incidents occurred.

“As the video operators become more experienced with identifying developing problems, they are able to proactively look for certain things at hotspots for antisocial behaviour and alert police to intervene before a situation becomes bigger.”


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