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Fig 1:Self-Healing Mesh
Fig 2:Three generations of Mesh
Fig 3: Single Radio Mesh Cycle
Fig 4:Third Generation Cycle

The core advantage of wireless mesh networks is their inherent ability to form a network on power up. Watch what happens in Fig 1, when the mesh nodes power up (green LED on box turns on). The nodes hear each other's broadcast and a network is self-formed. Also watch what happens when a node fails and how the nodes re-discover an alternate routing path. Network connectivity is thus preserved automatically.

Over the years, wireless mesh networking has seen three unique deployments based on radio technology, each incorporating iterative improvements allowing for greater scalability and higher network performance - both throughput and latency. This early stage of pre IEEE standard technological development is known a first Generation of Wireless Mesh. The following deployments are briefly described of various configuration of first generation Wireless Mesh Networking:

Contents

First Configuration: 1-Radio Mesh

As shown in Fig 2, this configuration uses one radio channel both to service clients and to provide the mesh backhaul (routing path back to a wired or satellite link). The single mesh radio, provides both services - client access and backhaul. Comparative performance analysis indicates this architecture provides the worst services of all the options , as expected- both backhaul and service compete for bandwidth. Also all single radio mesh architectures suffer from the send-receive-wait cycle shown in Fig 3. Since there is only radio, the mesh node has to listen, then send, then listen again. This intermittent stop-and-go behavior adversely affects network performance especially if the destination is far away and the traffic has to be re-transmitted ("hop") across many intermediate nodes first.

Second Configuration: Dual-Radio with 1-Radio backhaul mesh

This configuration can also be referred to as a "1+1" network, since each node contains two radios, one to provide service to the clients, and one to create the mesh network for backhaul. The "1+1" appellation indicates that these radios are separate from each other - the radio providing service does not participate in the backhaul, and the radio participating in the backhaul does not provide service to the clients. These two radios can operate in different bands. For example, a 2.4 GHz 802.11 b/g radio can be used for service and an 802.11a (5 GHz) radio can be used exclusively for backhaul.

Most mesh products available today fall into this category. Separating the service from the backhaul improves performance when compared with conventional ad hoc mesh networks. But since a single radio mesh is still servicing the backhaul, packets traveling toward the Internet share bandwidth at each hop along the backhaul path with other interfering mesh backhaul nodes - all-operating on the same channel. This leads to throughput degradations as shown in Fig 3, which are not as severe as for the single radio mesh, but which are sizeable nevertheless. Second generation mesh products are best employed in 1 or 2 hop configurations.

Third Configuration: 2 radio backhauls

The last architecture shown (far right in Fig 2) is one that provides separate backhaul and service functionality and dynamically manages channels of all of the radios so that all radios are on non-interfering channels. Performance analysis indicates that this provides the best performance of any of the methods considered here. Note that the two backhaul radios for the 3-radio configuration shown in Fig 2 right are of the same type - not to be confused with 1+1 so-called dual radio meshes where one radio is typically of type 802.11 a (backhaul) and the other of type 802.11 b/g (service). In the 3-radio configuration, 2 radios provide up link and down link backhaul functionality, and the other radio provides service to clients. Fig 4 shows how the two radios of the backhaul transmit traffic, with both radios operating independently and on separate channels.

Examples

The Naval Postgraduate School, Monterey CA, demonstrated a third configuration multi-radio wireless mesh network for border security.[1] In a 2007 pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a mesh network.

A MIT Media Lab project has developed the XO-1 single radio laptop or "OLPC" for under-privileged schools in developing nations and uses mesh networking (based on the IEEE 802.11s standard) to create a robust and inexpensive infrastructure.[2] The instantaneous connections made by the laptops are claimed by the project to reduce the need for an external infrastructure such as the internet to reach all areas, because a connected node could share the connection with nodes nearby. A similar concept has also been implemented by Greenpacket with its application called SONbuddy.[3]

SMesh is an 802.11 multi-hop single radio wireless mesh network developed by the Distributed System and Networks Lab at Johns Hopkins University.[4] A fast handoff scheme allows mobile clients to roam in the network without interruption in connectivity, a feature suitable for real-time applications, such as VoIP.

Many mesh networks operate across multiple radio bands. For example Firetide and Wave Relay second configuration dual radio mesh networks have the option to communicate node to node on 5.2 GHz or 5.8 GHz, but communicate node to client on 2.4 GHz (802.11). This is accomplished using SDR (Software Defined Radio.)

See also

External links

References

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