01-12-2012, 12:25 PM
Wireless mesh networks
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INTRODUCTION
Wireless mesh networks can easily, effectively and wirelessly connect entire cities using inexpensive, existing technology. Traditional networks rely on a small number of wired access points or wireless hotspots to connect users. In a wireless mesh network, the network connection is spread out among dozens or even hundreds of wireless mesh nodes that "talk" to each other to share the network connection across a large area.
Mesh nodes are small radio transmitters that function in the same way as a wireless router. Nodes use the common WiFi standards known as 802.11a, b and g to communicate wirelessly with users, and, more importantly, with each other.
Nodes are programmed with software that tells them how to interact within the larger network. Information travels across the network from point A to point B by hopping wirelessly from one mesh node to the next. The nodes automatically choose the quickest and safest path in a process known as dynamic routing.
The biggest advantage of wireless mesh networks -- as opposed to wired or fixed wireless networks -- is that they are truly wireless. Most traditional "wireless" access points still need to be wired to the Internet to broadcast their signal. For large wireless networks, Ethernet cables need to be buried in ceilings and walls and throughout public areas.
In a wireless mesh network, only one node needs to be physically wired to a network connection like a DSL Internet modem. That one wired node then shares its Internet connection wirelessly with all other nodes in its vicinity. Those nodes then share the connection wirelessly with the nodes closest to them. The more nodes, the further the connection spreads, creating a wireless "cloud of connectivity" that can serve a small office or a city of millions.
Wireless mesh networks advantages include:
• Using fewer wires means it costs less to set up a network, particularly for large areas of coverage.
• The more nodes you install, the bigger and faster your wireless network becomes.
• They rely on the same WiFi standards (802.11a, b and g) already in place for most wireless networks.
• They are convenient where Ethernet wall connections are lacking -- for instance, in outdoor concert venues, warehouses or transportation settings.
• They are useful for Non-Line-of-Sight (NLoS) network configurations where wireless signals are intermittently blocked. For example, in an amusement park a Ferris wheel occasionally blocks the signal from a wireless access point. If there are dozens or hundreds of other nodes around, the mesh network will adjust to find a clear signal.
• Mesh networks are "self configuring;" the network automatically incorporates a new node into the existing structure without needing any adjustments by a network administrator.
• Mesh networks are "self healing," since the network automatically finds the fastest and most reliable paths to send data, even if nodes are blocked or lose their signal.
Applications for Wireless Mesh Networks
Cities and Municipalities
With wireless mesh networks, cities can connect citizens and public services over a widespread high-speed wireless connection.
A growing number of downtown areas are installing public WiFi hotspots. Mesh networks allow cities to inexpensively and simply link all those hotspots together to cover the entire municipality.
Some advantages of municipal mesh networks:
• Commuters can check their e-mail on the train, in the park, at a restaurant.
• Public works officials can monitor the diagnostics of the city's power and water supply by installing wireless nodes in water treatment facilities, sewers and generators. There's no need to dig trenches to run cables.
• Public safety and emergency workers can access secure virtual networks within the larger network to keep communication lines open, even when regular phone or cellular service is down. With mesh nodes mounted on streetlights and stop lights, police and firefighters can remain connected to the network, even while moving.
According to a report by MuniWireless.com in March 2007, 81 U.S. cities have already installed citywide or region-wide municipal wireless networks and 164 more are actively building such networks. The report also says that 38 U.S. cities already have municipal wireless networks for the exclusive use of public safety and city employees.
Not all existing municipal wireless networks are mesh networks, however. Some are powered by a technology called WiMAX which has the ability to broadcast signals over large distances using powerful microwave transmissions. Other municipal networks use a combination of mesh, WiMAX and others.