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Definition: Wireless Mesh Networking

Wireless Mesh Networking is a method to route data, voice and instructions between wireless nodes or wireless Wi-Fi access points. It allows for continuous connections and reconfiguration around broken or blocked paths by "hopping" from node to node until the destination is reached. A mesh network whose nodes are all connected to each other is a fully connected network. Wireless mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile. Mesh networks can be seen as one type of ad hoc network.


Wireless Mesh Networks Contents

Wireless mesh networking is a wireless network that is implemented over a series of outdoor Wi-Fi access points that that all meshed together into a single, unified wireless network.

Whereas the Internet is mostly a wire-based, co-operative electronic communication infrastructure similar to the international postal agreement, in that messages are mutually delivered and relayed within their separate domains free of charge (i.e. if you relay my messages within your domain I'll relay yours within mine), Mesh is a wireless co-operative communication infrastructure between a massive amount of individual wireless transceivers (i.e. a wireless mesh) that have Ethernet type capabilities.

This type of infrastructure can be decentralized (with no central server) for less scalable applications or centrialized controlled for high scalable applications (with a central server), both are relatively inexpensive, and very reliable and resilient, as each node need only transmit as far as the next node. Nodes act as repeaters to transmit data from nearby nodes to peers that are too far away to reach, resulting in a network that can span large distances, especially over rough or difficult terrain.

Wireless mesh networks are also extremely reliable, as each node is connected to several other nodes. If one node drops out of the network, due to hardware failure or any other reason, its neighbours simply find another route. Extra capacity can be installed by simply adding more nodes. Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communications in difficult environments such as emergency situations, tunnels and oil rigs to battlefield surveillance and high speed mobile video applications on board public transport or real time racing car telemetry.

The principle is similar to the way packets travel around the wired Internet — data will hop from one device to another until it reaches a given destination. Dynamic routing capabilities included in each device allow this to happen. To implement such dynamic routing capabilities, each device needs to communicate its routing information to every device it connects with, "almost in real time". Each device then determines what to do with the data it receives — either pass it on to the next device or keep it. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

The choice of wireless router technology for wireless mesh networks is crucial. In a traditional wireless network where laptops connect to a single access point, each laptop has to share a fixed pool of bandwidth. With mesh technology and adaptive radio, devices in a mesh network will only connect with other devices that are in a set range. The advantage is that, like a natural load balancing system, the more devices the more bandwidth becomes available, provided that the number of hops in the average communications path is kept low.

There are three distinct generations of wireless mesh products today. In the first generation one radio provides both backhaul (packet relaying) and client services (access to a laptop). In the second generation, one radio relays packets over multiple hops while another provided client access. This significantly improved backhaul bandwidth and latency. Third generation wireless mesh products use two or more radios for the backhaul for higher bandwidth and low latency. Third generation mesh products are replacing previous generation products as more demanding applications like voice and video need to be relayed wirelessly over many hops of the mesh network.

First Generation of Wireless Mesh Networks

One-radio "Ad Hoc" Wireless Mesh. In first-generation mesh products, a single radio provides both service (connection to individual user devices) and backhaul (links across the mesh to the wired or fiber connection), so wireless congestion and contention takes place at every node. Users soon discovered that only one or two radio "hops" were possible between connections to the wired or fiber Ethernet. Support is also very poor for Video and Voice applications because of excessive and varying delay (latency) across the network.

Second Generation of Wireless Mesh Networks

Two-radio Wireless Mesh, shared backhaul. To solve these contention and congestion issues, second-generation mesh was developed by placing two radios in each node, combining an 802.11b/g service radio with an 802.11a backhaul radio.While this offered a performance improvement in terms of bandwidth over first-generation mesh, problems remain. With heavy user demand, there is still significant contention and congestion on the backhaul links. This limits the number of radio hops before another costly wired or fiber Ethernet connection is needed.

Third Generation of Wireless Mesh Networks

Three Radio with Multi-radio Wireless Backhaul. Third-generation mesh networking products add at least two physical radios for the backhaul. One backhaul radio is used to create a link to its upstream (nearer the wired source or "root") node. Another backhaul radio creates a link downstream to the next neighbor node. Unlike second-generation solution, these two radios may make use of different channels.

This increases the performance of the network in three ways:

  • Each node may be sending and receiving simultaneously to its upstream and downstream neighbors, unlike first-or second-generation nodes, which must continually "turn around" between sending and receiving upstream and downstream.
  • Because each link is managed independently, the available channels may be re-used across the network. This expands the available spectrum, increasing performance of the network 50 times or more compared to first- and second-generation solutions.
  • Radio is a shared medium. Nearby radios not part of the mesh network are constantly competing for air space. In first and second generation technologies, the backhaul channel is effectively "locked" once selected. They have only one backhaul radio on each node and if the channel has to be changed it affects all nodes.
    In contrast, third generation mesh nodes have two backhaul radios. Those

Mobile Ad-Hoc Networking(MANet)

Mobile ad-hoc networking(MANet), and mesh networking are therefore closely related, but mobile ad hoc networks also has to deal with the problems introduced by the mobility of the nodes.

Mesh networks are self-healing: the network can still operate even when a node breaks down or a connection goes bad. As a result, a very reliable network is formed. This concept is applicable to wireless networks, wired networks, and software interaction.

Understanding How Wireless Mesh Network Technology Works

802.11s Wireless Mesh Network Standard

Devices in an 802.11s wireless mesh network are labelled as Mesh Points (MP). They form mesh links with one another, over which mesh paths can be established using a routing protocol. 802.11s defines a default mandatory routing protocol (Hybrid Wireless Mesh Protocol, or HWMP), yet allows vendors to operate using alternate protocols, one of which is described in the draft (Radio Aware Optimized Link State Routing). HWMP is inspired by a combination of AODV (RFC 3561)and tree-based routing, while RA-OLSR is based on OLSR (RFC 3626).

MPs can be individual devices using mesh services to communicate with other devices in the network. They can also be 802.11 Wi-Fi Access Points (APs) and provide access to the mesh network to mobile clients, which have broad market availability. Also, MPs can take the role of a gateway and provide access to one or more 802.3 networks through a Mesh Portal. In both cases, 802.11s provides a proxy mechanism to provide addressing support for non-mesh 802 devices, allowing for end-points to be cognizant of external addresses.

802.11s also includes mechanisms to provide deterministic network access, congestion control and power save.

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Will Municipal Government Metro Wi-Fi Mesh Networks Ever Be Profitable?


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