Law & Disorder / Civilization & Discontents

Multi-hop matters: the state of wireless mesh networking

After many years of hype, multi-hop mesh networking has finally become an …

Multi-hop mesh networks, confined to university labs at the start of this decade, are now widely available from commercial vendors. These vendors tout a number of advantages for mesh technologies: lower costs of deployment, easier administration, better coverage, and lower power consumption. Mesh networking is now being used in an impressive range of applications, from large-scale institutional deployments to networks of tiny sensors.

Mesh networking is sometimes mentioned as a solution to the much-discussed "last mile" problem in US telecommunications policy. Unfortunately, the inherent capacity limits of the wireless medium means that mesh networks are unlikely to provide a serious alternative to fiber or coax broadband connections in this market. Mesh is a reasonable way to provide broadband to consumers in developing countries who might not otherwise be able to afford access at all. But in the developed world, mesh technologies are best viewed as a supplement to wired Internet connections and traditional single-hop access points.

To help us understand the state of technology, Ars talked to two experts on mesh networking: Sanjit Biswas, the CEO of mesh wireless startup Meraki Networks, and Jinyang Li, a computer science professor at NYU. Each did pioneering work on mesh networks at MIT earlier this decade, and both continue working on mesh networking technologies today.

Both identified the relative paucity of spectrum available for mesh networking applications as a major constraint on the technology's continued growth. Most mesh networks today operate on the same unlicensed bands used by WiFi and other consumer electronics devices. The amount of unlicensed spectrum available has increased with the deregulation of the 5GHz band, but the vast majority of the spectrum is locked up for other uses.

The evolution of mesh

Computer scientists have been studying mesh networks for a quarter century. In the 1980s, the military funded research into self-configuring multi-hop wireless networks suitable for use on the battlefield, but a lack of affordable hardware limited researchers' ability to build working systems. In the 1990s, researchers began building and testing mesh networks. In one influential test in 1998, a team at Carnegie Mellon mounted computers and networking gear into five cars and drove them around campus. The car-mounted nodes were able to automatically adapt to changes in network topology, maintaining reliable connectivity among themselves and providing continuous connectivity between two fixed nodes at opposite ends of campus.

By the turn of the century, wireless networking gear had become cheap and powerful enough to allow more ambitious tests. One of the most famous is Roofnet, an experimental mesh network built by MIT researchers earlier this decade, and Meraki, the commercial spin-off that counts Google among its investors. Sanjit Biswas co-led the Roofnet team and co-founded its commercial spin-off Meraki.

In 2001, Biswas was a grad student at MIT exploring ways to provide wireless broadband access to residents near the MIT campus in Cambridge. An initial plan for a single large antenna was scrapped when it became clear that it would not provide sufficient range or throughput. Biswas and his fellow grad student John Bicket switched to a multi-hop design, with multiple nodes cooperating to cover a large area.

When fully operational, Roofnet covered about 5 square miles of Cambridge, MA, between the MIT and Harvard campuses. At its peak, it had almost 100 nodes, and Biswas estimates the network served thousands of MIT and Harvard students over its lifetime. Each Roofnet node was an ordinary PC with a WiFi card and antenna. Because the project relied on volunteers to deploy Roofnet nodes in their homes, the Roofnet team had no real control over the topology of the network.

"We had to understand what it takes to build a network that can survive a lot of failures," Biswas said. "People would move from their apartments, or trees would go up in the springtime, blocking the signal." The network's routing protocols had to be robust enough to handle a network with constantly-changing topology and disappearing nodes.

The Roofnet team found that traditional routing protocols designed for wired networks didn't work well in the wireless setting. For example, Biswas told Ars that before Roofnet started its research, "It was widely believed that wireless links either worked or they didn't." In reality, there is "a continuous range of packet-delivery rates, all the way from 0 to 100 percent." This means that nodes cannot assume that any reachable node is a reliable node. Instead, mesh routing protocols need to constantly monitor link reliability and avoid routes with high rates of dropped packets.

Mesh routing protocols also have to worry about interference issues that don't crop up in wired networks. This can be a serious obstacle to high throughput for single-radio mesh nodes, because it prevents adjacent nodes in a route from broadcasting simultaneously. The Roofnet team found that in mesh networks with a single radio per node, this means that a two-hop route has less than half the throughput of a single-hop route. Some recent mesh products deal with this problem by having two or three radios in each node. This allows adjacent nodes on a route to transmit on different frequencies, dramatically improving throughput.


In 2006, with several years of experience running a full-scale mesh network under their belts, Biswas and Bicket founded Meraki to commercialize their technology. The firm attracted an early investment from Google, and closed a $20 million venture capital round in 2008.

The most lucrative segment of Meraki's mesh networking business is sales to large institutions. Leading hardware vendors such as Cisco have long sold gear designed to blanket a campus, apartment building, or office tower with WiFi coverage. But Biswas argues that the sophisticated meshing technology in its routers makes them easier to configure and manage than products offered by established vendors. Meraki's access points self-configure and then phone home to Meraki servers for further instructions; customers tweak their networks using a Web-based interface hosted on Meraki's servers.

At the low end of Meraki's product line are mesh nodes optimized for providing basic connectivity for areas that lack traditional wired connectivity. These products are popular internationally; Biswas touts customers in 143 countries worldwide. Mesh networks are especially appealing in nations that lack the resources to put extensive fiber or copper networks in the ground. In these areas, a mesh network can extend connectivity to homes and businesses that would not be able to access it in other ways. The XO laptop distributed by the One Laptop Per Child project uses mesh networking protocols for similar reasons.

For remote areas of developing nations, omnidirectional mesh networks must be paired with backhaul connections that use directional antennas for increased range. For example, Lakshminarayanan Subramanian, a computer science professor at NYU, has used WiFi and directional antennas to transmit 7-10 Mbps over a distance of 100 km. These links will never be as fast as a fiber connection, but for poor villages who otherwise wouldn't be able to afford an Internet connection, mesh networking is a boon.

Going the "last mile"

Mesh networks may provide a cheap way to get villages in the developing world online, but they do not seem likely to pose a serious threat to telecom incumbents in the developed world. One of Meraki's leading competitors, Tropos networks, focuses on public-sector clients such as police departments, public utilities, and municipalities wishing to build city-wide wireless networks. One case study on the Tropos website touts the experience of Chaska, MN, which hired Tropos in 2004 to build a municipal WiFi network for the city's 23,000 residents at a cost of $1.3 million.

Tropos says its 802.11 b/g-based network in Chaska offered "1+ Mbps" connectivity. Biswas says Meraki's newer 802.11n-based products boast typical speeds on the order of 10 Mbps. But with Verizon and Comcast already offering 50Mbps connections in some areas, mesh networking technology seems unlikely to be a serious threat to cable and telephone incumbents in the developed world.

Biswas told Ars that Meraki's low-end gear is primarily used in the United States to supplement traditional wired network connections. So, for example, a neighborhood association might deploy Meraki routers in parts of the neighborhood that are not one hop away from a wired access point, on the theory that relatively slow access is better than no access at all. But these small-scale applications are best thought of as a complement, rather than an alternative, to incumbent broadband providers.

Listing image by Wikimedia Commons

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16 Reader Comments

  1. mesh |me sh |

    Computing a computer network in which each computer or processor is connected to a number of others, esp. as an n-dimensional lattice.

    wire mesh: netting, net, network; web, webbing, lattice, latticework.
    1 one gear meshes with the other: engage, connect, lock, interlock.
    2 our ideas just do not mesh: harmonize, fit together, match, dovetail.


    Can someone please take the word «mesh» out back and put it out of its misery - forever.

    The word alone is the single biggest obstacle for this, otherwise I’m sure, interesting piece of technology to ever be successful.

    Simply because it obfuscates absolutely, explains nothing, and is a sure way to complicate even the most benign terminology. As an example, replace the word «mesh» in this article with a concise description of whatever it is trying to explain, and just like magic, it would be comprehensible.

    Of all the buzz words in technology, and no shortage of those, «mesh» has to be the least efficient. That is if failure is not the objective.

    To paraphrase one nasty piece of human scum (and fittingly, to do so is inappropriate just about anytime, anywhere):

    «whenever I hear the word mesh, I reach for my gun»
    95 posts | registered
  2. Thanks for an intesresting article.

    Same remark as always though: info on throughput is always nice, but what about latency ?
    1111 posts | registered
  3. I would like to see research on small wired mesh topologies. If I and my neighbors all have DSL and/or Cable or better FiOS, what should stop us from stringing together ethernet along our fence lines, and load-balancing across all our connections, to get up to 6x the bandwidth of what we get alone?

    Also, wouldn't these wireless meshes be much better with 4x4 MIMO configurations, with each node beamforming connections to each other? 2 radios don't seem like enough to cut it -- just 2 broadcasts stomping on each other rather than 1 broadcast timesharing. 4x4 with beamforming eliminates a lot of interference issues, and increases usable range even with NLOS interference. All this is a part of newer 802.11n router designs. MIMO and Cognitive Radio get around interference issues without any need for licensing schemes, which are just another way of saying local monopoly grants.
    26 posts | registered
  4. Maybe I skipped over a lot of this article, but why are the benefits of redundancy in mesh networks not mentioned? Are they inferred somewhere besides reconfigurability? This is the military's main interest in mesh tech.

    @FredMcTaker - While I agree MIMO would help alleviate inter-frequency interference, the point of Meraki is to be as cheap as possible. The main issues with any kind of "true" cognitive radio configuration are similar - expensive RF front-end, expensive band-discriminator, massive CPU time (each node is acting like a true router with a constantly changing routing table, in addition to continually probing for optimum and unused frequency). Also, cognitive radio is still a really undefined technology, unless you are talking 802.22 WRAN, which really isn't applicable here.

    I'm not trying to knock your ideas, because I think wireless networks are moving towards a more "aware" state, implying cognition. The big thing holding back such technology is the FCC's current policy of static spectrum allocation, as opposed to dynamic or sharing systems. Spectrum brokering is a step in the right direction, but I digress... The hidden node issue is also a problem. And cost, of course.
    124 posts | registered
  5. I think the true benefit to "mesh" networks is the possibilities that exist for mobile communications. It seems somewhat laughable to suggest it for "last-mile" solutions with all the unlicensed band p-to-p solutions on the market.

    Having experienced the spotty mobile data coverage offered by the national cell carriers in Chaska, MN first-hand I know that the city would've had a huge interest in "mesh" from a public safety/municipal perspective. Your options for mobile data are somewhat limited if you can't get a dependable 3G (or even 1x) signal on your aircards. All other options are quite expensive and can be pretty slow relative to 3G or even 802.11 style networks.

    Plus, once you've built it there's no monthly subscription costs if you're the service provider!
    25 posts | registered
  6. What interests me about networks such as this is their potential for secure, anonymous communication of the type thats been sadly lacking in the internet of the past few years.

    I suppose its too much to hope for that any protocols for this wouldn't have some skanky spyware slipped in somewhere.
    2417 posts | registered
  7. quote:
    Originally posted by FredMcTaker:

    They would be even better with 16x16 MIMO :-) The throughput (diversity, etc...) of a wireless network will increase if you add more antennas, but this does not solve the interference problem. Modern multi-hop networks are inherently not suited for the broadband scenarios that MIMO is most suited for.
    Contact the first author of if you'd like more info.
    35 posts | registered
  8. Anyone interested in open/free mesh networking should also check out R.O.B.I.N.

    Resonably priced pre-flashed nodes and accessories are available at Open-Mesh

    I've had these deployed at a camp with pretty good success. FYI - There is a new release (r2671) of firmware that is touted to resolve many issues (although I've not used it yet).
    1 post | registered

    Sounds a lot like Cisco's unified wireless network, though the centralized management you host yourself.
    20 posts | registered
  10. I'm surprised your history of wireless mesh networking didn't include the rise, fall, partial revival, and ultimate demise of Ricochet:

    Wireless mesh entrepreneurs ignore Ricochet's obvious, and not so obvious lessons at their peril.
    3 posts | registered
  11. For more open source mesh goodness check out the mesh routing daemon OLSR ( that runs nicely on OpenWRT Linux (, win32, Android, iPhone, and Nokia which is currently the base for the following networks worldwide (with many others not listed):

    Freifunk in Germany (
    Funkfeur in Vienna (
    CUWiN in the U.S. (
    AWMN in Greece (
    1 post | registered
  12. This article seems to be one of the many that push Big Telecom's ripoff product. It is utter bunk and does serious disservice to folks trying to put up a faster and cheap communication alternative.

    daleq mentions open mesh which does the same thing as meraki at a fraction of the price.

    In fact I wonder why ARS fronted the despised Meraki, who so thoroughly shafted the open mesh community in 2008, avoiding all mention of the equally effective and much less costly open-mesh alternative.

    The authors here fail to mention that wireless mesh is usually exactly as fast as the wired networks provide to the host router - in the US the average is around 1 mbs. Very few connections use more than one wireless hop to get to a wired link.

    As well in their support of Big Telecom, the authors refuse to point out that municipal wifi operations can put meshed routers on every block with far more spectrum available to smart phones and laptops, than their pet alternatives from Big Telecom and at a tiny fraction of the cost.

    Citizens can do it for themselves with the cheap open-mesh router for $25 which lets them share their internet and secure the home network at the same time. The more plugged in, the more they mesh up. No fuss no programming just plug em in. Open-mesh allows restricting the amount of bandwidth available to neighbors. Contributors can also require logins, resell it if desired, restrict on mac addresses, and boot heavy users.

    If people with enlightened social attitudes or a just a dislike of the phone company, switched to open-mesh WiFi routers from their junk easily compromised equipment Big Telecom sells, Big Telecom would be taking a serious beating and the world would be a better place.
    234 posts | registered
  13. Agreed that the author did us a disservice in not mentioning Meraki's price rises and restrictions while not mentioning at all it's obvious successor in the low-income connectivity space: and are now available on several hardware platforms so administrators are not locked into one hardware source such as is Meraki's condition.

    Also, the lower end open-mesh hardware is very affordable, which is something that low-income services need.
    4 posts | registered
  14. This sounds like this might make sense from the perspective of expanding a wireless network over a campus or neighborhood, but how well does it scale beyond that? Seems like latency would rise dramatically.

    Also, the cell phone example seems problematic. Cell phones already have noticeable latency. You're either gonna increase the latency with a lot of short hops (and there might not even be enough nodes to do so at any point in time), or you're gonna have to actually use more power. Cell communications rely on the tower transmitting a relatively powerful, focused signal, and having a lot of processing power to pick out the relatively weak handset signal. If the handsets have to talk directly to each other, they would have to have more signal processing, more powerful transmitters and/or be pretty close together. I guess you could develop a device/network that uses the mesh when the node density is high enough (i.e. handsets have a fairly limited peer-to-peer range) and the network defaults to direct tower communications when node density is low or if latency is too high (for a latency-critical operation, that is). But that just sounds like it's getting really complicated, and then you still have the battery problem and the disappearing node problem (what if you are out of range of a tower but in range of a peer-node, and that peer-node gets turned off).
    10026 posts | registered
  15. Here's my prediction for how Mesh-type self-forming decentralized networks will attain mainstream success in developed countries. Someone will come out with a WiFi router that functions in both long-range (range up to a mile or so, with a protocol for passing on encrypted data in order to prevent snooping by the super-node router operators) and short-range (i.e. standard WiFi router) modes, equipped with Mesh-like software to organize base nodes and super-nodes on-the-fly for an optimal performance in a Metropolitan Area Network (MAN) type setup. To keep things working smoothly, the amount of bandwidth you can access could be related to the amount of super-node routing data you distribute, in order to prevent leeching. People will buy these routers for the ability to share pirated content with people living nearby (think large MAN-scale filesharing networks), similar to the driving force behind the current ISP and backbone-routed internet's popularity back in the day.

    Since these networks will be completely decentralized, with private parties owning the key infrastructure, there will be no way to regulate the information they distribute, and this will prove very attractive as an alternative to the increasingly limited internet proper. This will be effectively like sneaker-netting, but on a metropolitan scale. As these MAN networks become more established, you'll find local businesses using them to reach customers (advertising), and even the connection of various MANs to eventually form a second decentralized internet parallel to the current internet. Information from the internet doesn't need to actually make it to these decentralized networks for them to be popular; instead, they'll build up their own content from scratch and supplement the internet rather than replace or co-opt it.
    1085 posts | registered
  16. Meraki is going to be a better option for a lot of organizations with limited budgets. Their solution has decent manageability, while being much cheaper than other wireless vendors (who all seem to have insanely high prices). At my school we have Cisco wireless, and most of the people agree that it's crap, although a big part of this has to do with Cisco's buggy signin system. But yeah, Meraki screwed over the open mesh folks.

    The most interesting solution I've seen is one that uses WiMax for backhauls. Having a lot of backhauls reduces the maximum number of hops, which can dramatically increase reliability. This makes it a lot more practical to do things like cover a city and offer live streaming of video from police cars.
    1350 posts | registered

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