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Mesh networks - Scaling the heights
WiFi networks have become a popular phenomenon, but in the right environments mesh networking could take them to a new level, says John Oliver
One of the best things about the Internet is its resilience. Designed to help protect wide area communications networks during wartime attacks, its biggest benefits were increased reliability and more efficient use of bandwidth. Now, as the world continues to embrace wireless data networking, we are beginning to apply the same principles there, too.
The conventional wired Internet uses a vast collection of routers that pass data packets along to each other en route to their final destination. Because routers have multiple connections to other routers, it becomes possible to route a packet around the network even if a piece of router equipment fails.
The introduction of mesh networking into WiFi wireless networks is a logical application of this idea. Single, autonomous WiFi access points are fine, as far as they go, which is about 100 metres. After that, you fall out of range. If another access point is nearby, you can rejoin the network, but of course that access point must also have a network cable connection to your LAN, or metropolitan area network. Therefore, building out such infrastructure becomes expensive, and the signal interruption caused by moving out of one hotspot's range and into another's could disrupt your use of an online application.
Routing concepts
Mesh wireless networking uses the routing concepts of the conventional Internet in a wireless context. Wireless access points are situated in range of each other so that ideally, no 'dead' radio areas exist in between them. A wireless access point no longer has to have a direct connection to the cable network, but can instead exchange its signals wirelessly with other access points, possibly passing through multiple points until it reaches one with a direct cable connection, at which point the signal can pass from the wireless layer to the wired infrastructure and out to the wider Internet.
Lower cost of deployment is therefore a major benefit of wireless mesh networking. Although the efficiency of the network will be increased with the number of cabled access points (or “cut-ins”), you can nevertheless extend the scope of the network by simply nailing up non-cabled wireless access points to get you into new areas.
Other benefits of the mesh concept are reliability and bandwidth. As you add more wireless access points within range of each other, the number of available routes through the network increases, meaning that more wireless access points can fail while still enabling the network to get your messages through. Increasing the number of access points also gives you more bandwidth by decreasing the potential bottlenecks in the system and giving the network more options to route traffic around already congested links.
WiFi movement
No wonder, then, that the nascent community WiFi movement, in which charitable neighbours co-operated to produce mostly unmeshed, open access wireless networks in certain neighbourhoods, has metamorphosed quickly into a municipal meshed WiFi movement. A recent study by ABI research indicated that citywide wireless networks could increase by a factor of ten in the next five years, and we are already seeing clear enthusiasm in cities. Philadelphia recently appointed EarthLink to operate its own wireless mesh network. City hall CIO Dianah Neff has been quoted as saying that the network will save the City $2m in communications costs in a single year.
Taiwan is turning Taipei into a “digital city” with a similar network, while the Republic of Macedonia wants to turn its whole 1000-plus square miles into a nationwide mesh network. And then, of course, there's Google. It recently won a contract with the city of Mountain View, California, to install as many as 400 transmitters on street lamps throughout the city. Such activities can revitalise urban infrastructures and increase their attraction for business visitors. In rural areas, meshed infrastructures can theoretically extend network coverage to reach small numbers of remote users that cannot take advantage of wired broadband networks.
Not without challenges
However, meshed WiFi is not without its challenges. For one thing, engineers must navigate the plethora of standards available to route packets across mesh networks. Protocols such as Hazy Sighted Link Stage, Optimised Link State Routing and Temporally-Ordered Routing Algorithm all vie for prominence in the mesh world.
Secondly, one of the biggest benefits of WiFi is also one of its biggest threats. Like its more modern 802.11g counterpart, 802.11b WiFi works in the unlicensed 2.4 GHz spectrum, meaning that it can be deployed freely, without licence applications. However, this unlicensed spectrum is muddied by interference from a myriad of electrical devices, including everything from microwave ovens through to cordless phones. The uncertainty surrounding levels of environmental interference makes it difficult to maintain a guaranteed level of service. This consequently makes it difficult for a service provider to offer a service level agreement (SLA), which could hinder the commercial viability of these networks.
The other concern for supporters of meshed municipal WiFi is WiMAX, the emerging long range wireless communications standard. Likely to target fixed network service provision to homes and businesses initially, it could also become a killer application for users of mobile consumer technology in urban areas, thanks to the inclusion of a mobile version of the standard – 802.16e.
One of the biggest advantages of WiMAX is its broader coverage; it has a range of kilometres, rather than metres, which would theoretically make deployment much easier and cheaper within an urban environment, especially as WiMAX base stations could potentially be fitted to existing cell towers, lowering the cost of implementation. Although discrete WiFi hotspots are deployed in their thousands around the world, the implementation of meshed WiFi technology is only slightly ahead of WiMAX, making the race a much closer one.
But blanket municipal coverage is not the only opportunity for mesh WiFi networks. The technology has a promising future both in enterprise and campus environments, and also in suitable industrial applications.
Consider, for example, specialist environments such as open pit mining sites, where it is difficult to dig ground up and lay cables because of iron ore in the ground, compacted by huge earth movers. Similarly, it is often difficult to deploy wired networks in construction sites because of the rapidly developing and changing infrastructure. A wireless mesh network can bring fast connectivity to mobile workers and vehicles in such environments, with a relatively low deployment cost.
In a campus environment, such as an academic institution or a business park, the use of meshed networks would make it possible for visitors, students, or workers to have always-on access, no matter where they were in the establishment. This would transform everything from business meetings through to student lectures and even telephone communications. As voice over IP continues to capture mind share in the business world, VoIP delivered to WiFi-compatible handsets could bring immense benefits to on-site personnel.
And again, in a commercial or academic campus environment, meshed WiFi can help to overcome infrastructural difficulties. It may not be possible to run wires through an older building with protected heritage status, for example, but network engineers could flood the building with radio points without damaging its walls, ceilings, or floors.
Such enterprise and campus mesh deployments are not pipe dreams. They are already happening, at a research and an operational level. MIT, for example, has been piloting both in-building and rooftop wireless meshed networks. Its release of the grid networking software in open source form is designed to promote further adoption by other wireless access point vendors. Mesh networks in the right environment could therefore grow organically, offering interesting opportunities for expanding coverage at very low cost.
Mesh networks are still relatively rare, but they are likely to make an increasing appearance both in wider urban areas and in enterprise environments. Their benefits – reliability, decreased network congestion and ubiquitous access within the network area – are too attractive to ignore. •
John Oliver, AlanDick, can be contacted via tel: +44 7753 968549; e-mail: john.oliver@alandick.co.uk
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