Do mesh networks scale? Gosh darn it, 802 Planet did something that DailyWireless probably should have done first — ask!
Tropos Networks is one of several firms working to deploy Wi-Fi on a city-wide scale in several areas. As usual, the devil is in the details. Let’s suppose large scale Wi-Fi mesh networks really are due to replace the hotspot model. What technology hurdles are there to this idea, and how will the economics work out? We asked the company’s marketing vice president, Bert Williams, to lay out the scenario.
Q: Some have said that large-scale outdoor Wi-Fi networks will run into quality-of-service trouble as connectivity breaks down over multiple hops within a mesh. How are you getting around that problem?
A: We say the idea that throughput in a mesh networks [degrades] with the number of hops is just incorrect. It does roll off, but not with the kind of exponential decay that some folks are claiming. In any case, we look at it in a very different way. Our idea is to have a routing algorithm which, rather than trying to minimize the number of hops, is instead aimed at maximizing end-to-end throughput.
Q: So, rather than minimizing hops and risking hitting a bad link, your algorithm may take the long way around, but it will only move through good links?
A: Exactly. It makes sense to minimize hops in a wired network, where you are not likely to lose a packet at the link, but it is a very different thing in the wireless world.
Q: Even so, there have been claims that big outdoor networks will be fundamentally flawed since they invite too many users to share too little bandwidth.
A: It can be true, but the way you eliminate it is by having an architecture that allows you to add more aggregate capacity as you add more backhaul points. You’ve got the mesh network and then you have one or more connections from the mesh network to the wired Internet.
The way our architecture works is that one connection to the Internet gives you an aggregate of 11 megabits of throughout. Now if you add a second connection to the Internet, some cells cluster around the first connection, while others cluster around the second connection. Now we have gone from an aggregate of 11 megabits of bandwidth to an aggregate of 22 megabits. So the mesh networks can be made to be very scalable if you have the ability to add more capacity to the network as you add more Internet connections.
Q: If you think these likely problems can be solved, what other technical hurdles remain for big outdoor mesh networks?
A: The challenges we have run into are, number one, finding enough suitable locations to bring backhaul to the network.
Q: For example.?
A: Let’s say I have a network that covers 10 square miles and has 100 nodes in it. Say I need to bring a wired Internet connection to one out of every 10 of those nodes. That means I need to find 10 places within those 10 square miles where I can drop a backhaul connection into that system.
Q: Why is that hard?
A: City fiber rings tend to go where they go, and if you want them to go somewhere else there is trenching and things like that involve. Putting out T1s can be expensive both on a provisioning and a monthly basis.
Q: How have you addressed this?
A: We have ended up using a lot of point to multi-point solutions, which have in a lot of cases has ended up being the least costly way to do it. But it is really something you have to take care of in the planning stage. When you are designing these large networks you have to really think hard about the backhaul availability that you have and how you going to get that distributed around that network.
Q: Given all these factors, what does it cost to deploy a big outdoor mesh?
A: A comprehensive deployment over 10 square miles will cost about $300,000 with operating expenses that can be less than $10 per month per subscriber.
Q: Can a service provider turn a profit here? What economics do you envision driving Wi-Fi mesh deployments in the future?
A: In Chaska, Minn. they have done the entire 16 square miles of their town, and the city will do better than break even selling broadband residential service at $16 a month. We have seen similar experiences around the country. The hotspot model is like the old payphone model: You have to go to the place where the service is available, rather than having than having that service available wherever you go. People want just as much mobility with their data as they get with their voice. So we believe this is going to be a profitable venture for service providers, given the demand we see among consumers and among governments, coupled with the low cost of deployment and ongoing operation.
BTW, Tropos and Airpath have combined forces bringing WiBOSS operational software to metro-scale mesh with roaming and management using one login ID. The partnership already has deployments underway in Nantucket, MA, and other cities to be announced in the near future. Tropos and Pronto have a similar agreement.
Nantucket’s 9,000 full-time residents will use a Tropos mesh which requires installing nine to 15 transmitter boxes per square mile at a cost of $20,000 to $30,000.
And there’s nothing wrong with free.
Hermosa Beach City Councilman Michael Keegan championed the vision to provide the FREEway to the Internet, as “a public amenity and convenience”. The California beach town of 21,000 will offer free broadband wireless service (802.11 a/g) to all city residents and businesses. Fancy WiFi-Plus, multi-polarity antennas will be used with mesh networking provided by Calabasas-based Strix Systems (right).
The system, designed and installed by LA Unplugged, a Hermosa Beach Systems Integrator, will deploy “the most advance municipal WiFi system in the country”. Each communication node consists of multiple radios, advanced mesh networking software, AES encrypted wireless backhaul links, and multi-polarized (MP) antennas.
The city-funded “cloud” will cost the city between $75,000 and $85,000 for installation to provide free access to every one of the city’s 18,000+ residents, with annual operating costs totalling around $18,000 per year.
Encinitas, California, about 25 miles north of San Diego, has 250 businesses, 150 offices and 1,500 residents downtown. Their WiFi network consists of eight BelAir200 nodes, deployed by CWTI, from the tops of buildings covering 18 blocks. Residential customers pay $30/month, business users $40/month. The BelAir200 uses the 2.4GHz band to support Wi-Fi client access, while separate backhaul radio modules use 5GHz for the point to point links.
Examples of commercial mesh networking gear include BelAir Networks, Firetide, Mesh Networks, RoamAD, SkyPilot, Strix and Tropos.
PacketHop, (above), is based on the TBRPF protocol, one of two mobile ad hoc networking (Manet) protocols specified by the Internet Engineering Task Force. AODV is the other.
Companies like PacketHop, a spinoff of SRI, and MeshNetworks (Maitland, Fla.), have dominated mobile ad hoc networking by using specialized (non 802.11) multi-hopping clients. MeshNetworks Adaptive Transmission Protocol tightly binds to the underlying radio platform. One problem with mesh, whether it’s used just for the backbone or whether data traffic gets routed through multiple end users, like in PacketHop & MeshNetworks, is there’s no standard (yet). That means you’ll have to stick with one mesh vendor.
Viasys is implementing MeshNetwork’s system in Medford, Oregon. Officials said the initial deployment will cost about $700,000, much of it covered by a $500,000 grant from the Federal Emergency Management Agency. The city is phasing out its cellular-based CDPD network and has coverage limitations with GPRS.
Motorola will integrate components of MeshNetworks, including the MeshNetworks Positioning System and MeshConnex software suites, into future data products such as those in the recently allocated 4.9GHz FCC licensed band allocated to the public safety infrastructure. Currently, the Motorola-Mesh Networks products utilize the 2.4GHz band.
Autocell says their automatic load balancing system will work with commodity 802.11a/b/g hardware. Their software in clients and APs, automatically enables the client to choose the best available channel and access point. I’m not sure if you should call it “mesh”, though.
Wireless sensor networks are a different problem. They aren’t city-scale. Sensor networks relay temperature, vibration and pressure over small areas using protcols like Zigbee, which has an embedded mesh protocol. Crossbow, Ember, MillennialNet, and Sensicast work in that space.
MobileMesh is an ad-hoc routing protocol from Mitre for community networks. PersonalTelco says it’s pretty easy to get running. Download the Linux or Windows software, for free.
Microsoft’s Mesh Networking Summit in Snoqualmie, Washington, June 23-24, 2004, had a ton of interesting papers.
MIT’s Roofnet is an experimental multi-hop 802.11b mesh network. Roofnet consists of about 50 nodes in apartments in Cambridge, MA. Each node is in radio range of a subset of the other nodes, and can communicate with the rest of the nodes via multi-hop forwarding. A few of the nodes act as gateways to the wired Internet. The Click Modular Router Project with an Optimized Link State Routing protocol may do the trick.
Roofnet can now be powered by a pared down Pebble Linux, a click modular router, stripped madwifi and an image for the Metrix Kit or a LiveCD for standard PCs. Locustworld, also has a MeshAP hardware solution.
From August 20-22, 2004, the Champaign-Urbana Community Wireless Network, Free Press, and Prairienet Community Network will host the 2004 National Summit for Community Wireless Networks. The Summit is expected to be the largest community wireless networking event to date.
“More than 150 participants (including Matt Westervelt, Seattle Wireless) from 30 countries will discuss on how to overcome the digital divide building wireless community networks. The freifunk.net summer convention 2004 takes place from 3rd to 10th September in Djursland, Denmark.
The convention’s location is well chosen — DjurslandS.net (in Danish) itself is probably the most ambitious wireless community network of the world. About 200 volunteers installed more than 100 masts on the remote area’s 32 000 sq mi. Using the wireless standards 802.11a/b/g about 1’500 households enjoy a symmetric 1-2 MBit internet connection via WI-FI (the WI-FI network has 8 direct uplinks to the danish backbone and several DSL fallbacks).
The wireless4development track organized by wire.less.dk will show other projects how to follow the DjurslandS.net example. The convention starts off with a 3 day program including VoIP, development for the meshcube and antenna building and finishes off with a 5 day hands-on workshop“.
O’Reilly has more on mesh. DailyWireless related mesh articles include Mesh Projects & Gear, MetroFi Goes Long, Mesh: Baton Rouge Et Al Citywide Mesh, Mesh Goes Downtown, Aiirnet & Telerama, Strix and Air Magnet, San Jose Free Cloud, Meshing at Intel, Meshed Roofnets, Mesh ISP, and City Mesh.
