Mesh: The next step for wireless

Mesh technology allows new wireless networks to be created, or existing WLANs to be extended, without needing a wired connection to each base station

In late February 2004, emergency agencies responded to a catastrophe at San Francisco's landmark Golden Gate Bridge. First to the scene was the Marin County Office of Emergency Services, followed by the San Francisco Fire Department, and ultimately other agencies, including the National Park Service, California Highway Patrol and US Coastguard.

All these agencies use a variety of different radio systems which usually can't communicate. But this time they were equipped with a new type of data link allowing them to coordinate on laptops, PDAs and tablet PCs with video links, real-time resource maps and multimedia messaging, among other applications.

The three-hour session was a simulation by the Golden Gate Safety Network, comprised of 11 California emergency bodies, trialling an emerging wireless networking technique known as mesh. In this case, technology from PacketHop, a Silicon Valley start-up, set up an ad-hoc broadband wireless network linking workers with different varieties of off-the-shelf equipment on the bridge, on land and on the water. There was no central server, no single point of failure, and the nodes were able to maintain their network connections without being in range of an access point -- each node acted as a repeater and router for the nodes around it.

The next step for wireless
Tech industry heavyweights such as Cisco and Intel believe mesh techniques are the logical next step for the wireless networks that are increasingly ubiquitous in offices, homes and public places. Enterprises could use mesh to quickly create new wireless networks or extend existing WLANs without needing a wired connection to each base station. Mesh-enabled base stations are good at load balancing because they can choose the most efficient path for data. Industrial users can quickly deploy networks of sensors and controllers with embedded wireless mesh radios.

Start-ups and established vendors are selling modified wireless local-area network (WLAN) kit incorporating mesh ideas. Standards groups are working on building mesh into the families of standards in use today, such as 802.11, and those coming down the line, such as 802.16 (also known as WiMax). On the embedded side, mesh technologies are feeding into nascent standards like ZigBee.

A fine mesh
In essence mesh is something very familiar -- wireless mesh networks are really just applying the basic principles of the wired Internet to the wireless world, says Scott Burke, vice president of engineering for PacketHop: "The fixed Internet we have today can be thought of as a large fixed mesh network."

Each device on a mesh network receives and transmits its own traffic, while acting as a router for other devices; intelligence in each device allows it to automatically configure an efficient network, and to adjust if, for example, a node becomes overloaded or unavailable. The advantages include ease of setup, the ability to spread wireless access over a wide area from a single central wired connection, and the inherent toughness of such networks.

Perhaps not surprisingly, wireless mesh got an initial kick-start from the Defense Advanced Research Projects Agency (DARPA), the central research and development organisation for the US' Department of Defense, the same agency that helped develop the Internet in the first place. Early work on PacketHop's technology, for example, was carried out for DARPA at the Stanford Research Institute, and focused on creating on-the-fly wireless data networks for soldiers going into the field. The technology of Florida-based start-up MeshNetworks was originally developed under DARPA-directed programmes.

The military and security agencies are still seen as the most immediate markets for mesh products. "That's a market that is happening right now," says Burke.

Mesh in the enterprise
Enterprises may have a lot to gain from mesh-enabled WLANs, according to Nortel and a handful of start-ups targeting corporate networks. Nortel is launching a Wi-Fi mesh product in the first half of this year, the Wireless 7200 Series, although a planned London trial with BT has been put off.

"Whereas in a traditional WLAN solution every access point is connected to the backbone, in our solution we have eliminated the need for a wired backbone," says Peter Zwinkels, EMEA business development manager for wireless mesh networks. "This will make it possible to deploy wireless in areas where it was difficult or not cost-effective in the past."

These areas include large areas, either indoor or outdoor, such as a warehouse or a golf course. The catch with Nortel's solution is that a power source has to be present, although this could be a traffic light or streetlamp; but Nortel admits that customers in situations where traditional wired networks are available or could be easily installed would be better off with traditional power-over-Ethernet access points.

One of Intel's planned mesh trials at Dartmouth College, New Hampshire, will link students living in areas around the campus to the university network. The campus itself is already wired up, but many in the surrounding area have had to rely on dial-up connections; the trial, scheduled to go live this spring or summer, will give them broadband connections with no need for expensive telco or cable company infrastructure.

Such projects point to what could become a major application for mesh: wide-area broadband wireless. Currently coffee shops, railway stations, airports and other public places are rushing to set up Wi-Fi hot spots, with Starbucks recently promising to more than double the size of its Wi-Fi network. Wireless ISPs and telcos believe they can attract business subscribers by offering access to extensive networks of Wi-Fi hot spots, increasingly often marketed as an add-on to Internet, standard mobile phone or 3G access. Mesh techniques could greatly simplify things and accelerate the trend: instead of myriad T1 or ADSL lines, each with an attached hot spot, a single high-bandwidth wired-link could be made to blanket an entire city area with wireless. Nortel calls the concept a "hotzone", and says running such a system would be cheaper and offer better coverage than the current hodgepodge of hot spots.

Enter the hotzone
Some cities are already rolling out similar services, though they tend to provide access to city workers rather than latte-sippers (see case study). Verge Wireless is one exception, running hotzone-type mesh services in Baton Rouge and New Orleans.

Some ISPs are looking to wireless last-mile standards such as WiMax to provide broadband in hard-to-reach areas, but Nortel argues its Wi-Fi-based mesh technology could be better suited. "In areas where DSL has not been deployed, this could provide broadband to 100-200 houses in a small village," says Zwinkels. WiMax would require special equipment at the user end, while with a Wi-Fi solution users could plug into the network with a standard PMCIA card.

BT actually ran a rural mesh radio trial covering an 80-square-kilometre area around Pontypridd, South Wales, in 2002, using a 28GHz fixed-wireless setup from Cambridge-based Radiant Networks. The trial ended without result, however; BT says the technology was "not appropriate", and Radiant has gone into insolvency administration.

Sensors, sensors everywhere
Embedded mesh takes some of the ideas behind RFID and goes a step further; instead of fixed scanning apparatus, all the sensors and controllers talk to one another and feed the information back to wherever it is needed, over a wireless or Internet link. Boston, Massachusetts-based Ember, which makes mesh RF chips, is pitching its technology to cargo carriers as a simple way of keeping an eye on their shipping containers. Its sensors are designed to be scattered all over a container, where they sense dangerous materials and keep detailed records of everything that happens to the cargo during transit. Anyone using US ports will soon have to use such wireless monitoring systems, for anti-terrorism purposes, or face slow, expensive manual customs inspections.

"There is a network inside the container, and then you can have each container act as a node within a bigger mesh network," says Ember's EMEA business development director Jim Schoenberger. "Because the containers themselves form the network, you don't need antennae all over a ship or a port. It's an infrastructure-less communications system."

Embedded mesh could also be used to simplify the collection of utility meter data in houses, or be built into light switches as a more flexible alternative to electrical wiring. Ember is working with the emerging ZigBee standard and is contributing parts of its EmberNet technology to ZigBee.

A mesh standard?
A host of other start-ups, including BelAir Networks, Tropos, FireTide and Strix Systems are all beginning to announce mesh products and customers. Currently different companies' systems all use proprietary technology bolted onto standards such as Wi-Fi, meaning the different types of equipment can't work together, a problem being addressed by standards groups.

Pressed by Intel, Cisco, MeshNetworks and others, the IEEE has formed a study group that could eventually build mesh into wireless LAN specifications; its first meeting was held in January. Critics say a standard could end up being a lowest-common-denominator approach lacking the efficiency of proprietary protocols. In the meantime, MeshNetworks has repackaged its mesh special sauce as licensable libraries aimed at wireless equipment manufacturers; these will be available in the second quarter of this year.

Mesh has its sceptics, who point out that it only makes sense in special circumstances. "I'm not sure enough people will pay for it for it to be built into equipment as standard," says Richard Mironov, vice president of marketing for wireless security firm AirMagnet. "If you're in a building with the capability for Ethernet wiring, mesh is not needed."

But mesh is not going away, Intel argues. "It lowers the barriers to deploying a network, and that can be applied to a lot of different scenarios," says researcher Lakshman Krishnamurthy. "Unlicensed spectrum usage allows wireless networks to be everywhere, and mesh is one element to that larger revolution."

Case study: City of Garland, Texas
Garland, located 15 miles northeast of Dallas and with a population of 221,000, is in the process of replacing the cellular-based communications system it uses for public safety workers such as police officers, fire fighters and medical emergency teams. Lockheed Martin Space Operations Division was awarded the contract last September and chose mesh technology from NexGen City, a system integrator using technology licensed from MeshNetworks. The new system will cover 57 square miles, and is touted as the largest mobile mesh network in the world. It is scheduled for completion in the second quarter of this year, initially providing mobile data, with the option of adding video and voice later on.

Mesh technology promises to greatly simplify things for Garland, while offering 50 times the bandwidth. "We eliminate expensive towers, subscriber fees, and zoning issue headaches associated with our old system," notes city telecommunications manager Darrell McClanahan. The mesh system supports sustained throughput of 1Mbps with bursts of up to 6Mbps.

Its components include PC cards, wireless repeaters, gateways, geo-location software, administration servers for command and control centres, and modified PocketPC handhelds (though these won't be in production until mid-2004). The repeaters and gateways are built into buildings, streetlights or traffic lights; they only need to provide enough power to communicate with the next device or repeater, so can operate at lower power than a cellular tower. The PC cards and PDAs also act as repeaters and routers, adding further nodes to the network and making the network more fault-tolerant. The geo-location software provides latitude, longitude and elevation information without the need for GPS. The system supports industry-standard TCP/IP, DHCP, and SNMP protocols.

Garland chose the scheme after NexGen City completed a test phase across a five-square-mile area along Texas' Highway 190 in 2003. In a demonstration, two networked vehicles travelling faster than 60 miles per hour in opposite directions exchanged real-time streaming video, voice over IP calls and data throughput of up to 1.5Mbps.

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