Caught in the mesh
Mesh WiFi has quickly become the darling of large-scale wireless projects. But is it the best solution?
- By William Jackson
- Mar 02, 2006
As more municipalities and government campuses look to build out large-scale wireless networks, so-called mesh technologies built around current 802.11 WiFi standards have become the dominant choice. But with many of these networks still in the building phases'and many more still to be planned'it's not too late to look at current wireless systems and determine whether one size fits all.
Although the 802.11 family of standards is still evolving, the hardware is fairly mature.
'It is an exciting, affordable and robust technology at this point,' said Paul Butcher, marketing manager for state and local governments at chip-maker Intel Corp.
Intel's WiFi chips are in more and more mobile devices, and interoperable standards mean government agencies can choose from several mesh WiFi proposals when shopping for the best, most affordable deployments. But there are choices other than traditional mesh WiFi to consider.
'People think it's the safe choice, but it's not necessarily the smart choice,' said Carl J. Weisman, vice president of engineering for 5G Wireless Solutions Inc. of Marina del Rey, Calif.
Not even the folks at Tropos Networks Inc. of Sunnyvale, Calif., which sells mesh WiFi, claim the technology is the be-all and end-all of wireless networking.
'I don't want to say the technology is perfect,' said vice president of marketing Ellen Kirk. 'This is radio, people, and radio has a mind of its own. You put up an RF network and you're going to be tuning it forever.'
Large-scale WiFi networks draw concerns over range, bandwidth, scalability, mobility and complexity, and there is not yet enough real-world experience to adequately address those concerns. The alternatives emerging to challenge or complement mesh WiFi include WiMax, cellular architectures and multiradio access points. Each has its own strengths and weaknesses.The growth of mesh WiFi
WiFi is a broad term, covering the spectrum of 802.11 standards from the Institute of Electrical and Electronics Engineers. It was designed primarily for short-range, indoor wireless connections between nonmobile clients and a wired LAN. As bandwidth and range have improved, its scope has expanded to include public hotspots for Internet access, as well as campus and municipal deployments.
Mesh WiFi is a method for extending wireless networks by routing connections through multiple access points that communicate wirelessly with each other. Traditionally, each AP would be wired back to the main network and would communicate with it directly. Mesh WiFi is theoretically affordable and easy to deploy, with access points typically installed in public places such as on utility poles.
'It's pretty easy to put the devices up,' said Intel's Butcher. 'Once you get it configured on the ground, you get the guy in the bucket truck to install it. It's straightforward.'
But the bandwidth consumed by multiple hops back to a network can impair a mesh network's scalability. WiFi also is a line-of-sight technology, so radio interference and physical objects can significantly reduce theoretical ranges and throughput. And although WiFi allows remote access, it is not really built for roaming'that is, moving seamlessly from one AP to another. It might work fine while from a park bench or in an airport lounge, but not when you're driving down the street, although a new standard expected next year might help (see timeline, this page).
Implementing WiFi in a cellular model could overcome some of these limitations, according to 5G Wireless. That company's scheme involves mounting access points in high locations such as towers or buildings to get the maximum coverage area in a standard range of 400 to 800 meters.
'If you're going to put it up on a light pole, you're not going to get that range,' Weisman said. 'But it can be done with standard WiFi if you are judicious about picking the right location, and the hardware and software.'
5G's solution also requires using the maximum power for each access point, and because the points do not communicate with each other, each must have its own backhaul connection to the LAN. This ends up being both simpler and more complicated than a standard municipal mesh network. 'It takes fewer deployment points, but each point is more of a headache,' Weisman said.
Weisman said such a scheme probably is not suitable for a large-scale deployment such as Philadelphia's. But he maintains that the mesh network being pursued there is equally unsuitable because of the cost and complexity of deploying and managing a large number of access points.
'Philadelphia scares the heck out of me,' he said. 'I would not want to try to cover the city of Philadelphia with anything.' [For more about the Philadelphia WiFi project, visit GCN.com and type 543 in the GCN.com/box.]
The sweet spots for cellular-style WiFi networks are campuses and communities that can be covered by two or three access point cells, Weisman said.
'We're running as fast as we can from the 200 biggest cities,' he said. But there are 50,000 smaller communities that he wants to target. Currently, 5G's technology is being deployed in Rockford, Ill., New Smyrna Beach, Fla., Westminster, Calif., and on several college campuses.The end of municipal WiFi?
If you don't want to use WiFi at all, the most visible alternative is WiMax.
'Mesh networking is big now, but I see WiMax taking over from mesh pretty soon,' said Amith Krishnan, enterprise wireless product manager for 3Com Corp. of Santa Clara, Calif.
WiMax is based on the emerging IEEE 802.16 family of standards for delivering high-bandwidth data transmission over long distances. It is seen initially as a wide-area complement to the WiFi services and a competitor for such last-mile technologies as digital subscriber line and cable modems.
The 802.16 Air Interface Standard focuses on fixed broadband wireless access operating between 10 GHz and 66 GHz or from 2 GHz to 11 GHz. The first iteration, 802.16a, addressed the lower end of the spectrum. Another standard, 802.16e, ratified late last year, addresses roaming for mobile applications.
The lower-frequency spectrums in the 3.5-GHz band now being used in WiMax products primarily are for outdoor installations because they do not have the penetration needed for interior deployment. But they can provide non-line-of-sight connections, which can make setting up base stations easier.
Early WiMax implementations primarily are fixed-access points providing last-mile alternatives to DSL and cable modem connections. The range for each access point typically is three to 10 kilometers, with a capacity of up to 20 Mbps per channel for fixed-access applications.
This bandwidth and range could be used to provide backhaul from WiFi access points, but also could eliminate some of the problems of mesh WiFi when used for primary access, Krishnan said.
'The object is to cover a huge area,' he said. WiMax could eliminate many of the hops in a mesh network, improving bandwidth and decreasing latency. [For more information about WiMax, visit GCN.com and type 544 in the GCN.com/box.]
WiMax also can provide quality of service and is optimized for outdoor use, said Intel's Butcher. 'It's a very compelling outdoor solution.'
But it probably will be several years before client-side devices are small enough, efficient enough and cheap enough to provide an effective alternative to WiFi.
Until then, Motorola Inc. is offering the Motomesh multiradio system, which adds its proprietary Mesh Enabled Architecture equipment to standard WiFi.
Each Motomesh access point contains four radios'one WiFi and one MEA operating in each of two bands, the unlicensed 2.4-GHz WiFi band and the new 4.9-GHz band restricted to public safety organizations. The separate bands and radios let cities separate public safety and less critical public service networks, said Rick Rotondo, director of marketing for Motorola's mesh networks products group.
'What Motomesh is targeted at is the municipality deploying a broadband network for e-government and for public safety,' he said. 'WiFi is not mission-critical-grade stuff.'
Public Internet access is secondary but can be provided on the same infrastructure without compromising critical missions.
MEA is a proprietary wireless networking technology developed by Motorola for battlefield communications systems. It can maintain broadband links at speeds of up to 250 miles per hour, Rotondo said. It can handle bursts of up to 6 Mbps, with sustained full-duplex links of 1.5 Mbps. MEA also supports client meshing for ad-hoc networks that rely on client devices as nodes when outside the range of fixed access points.
Customers pay only for the radios they use in each access point. A typical implementation would put public safety operations, such as fire, police and emergency medical, on the 4.9-GHz band using MEA radios, with WiFi radios on the same band providing additional connectivity. The 2.4-GHz band with MEA radios could support a network used by city employees, while the WiFi radio provides public Internet access.To build or sit still
With wireless technologies evolving so quickly, the question becomes whether you should wait for the next big thing or invest in a technology based on current standards.
'The problem with waiting is that you defer the benefits,' said Tropos' Kirk. 'What you are getting by waiting are things that will benefit networks that are already grown. So you might as well start growing now.'
It depends on what value you expect to gain from your wireless network, Butcher said. If you can justify a WiFi implementation with efficiencies gained through re-engineering your processes now, then you're golden (see story, this page).
'The real question is, 'Should I wait for WiMax?' ' he said. 'The tech industry is very resistant to removing technology from their platforms.' Which is to say that WiFi will not go away any time soon.
'A community investing in WiFi mesh should be comfortable that the network is going to be useable for the foreseeable future,' Butcher said.