Wireless Mesh Networks
Generally, wireless networks are built by placing a large number of access points at the places where the wireless access is required and controlling all those access points via a centralized controller. Though the clients (users) get wireless access to their laptops, the access points are always connected to the LAN network through a normal network cable. So, the back end of a wireless network is actually a wired network.
Mesh networks are those which give wireless back-end connectivity to such access points to connect to each other and the network, instead of the cables. Normally, a dual radio access point is used where, the 5 Ghz radio connects to another 5 Ghz radio of the neighbouring access point and the 2.4Ghz radio gives client access in both of them. (The reverse is also possible, but this is the common case). Some vendors allow normal dual radio access points to be upgraded to support mesh networks. They can form point to point mesh or point to multi-point mesh networks.
Applications of mesh networks and why they are exciting:
¤ Mesh networks extend the wireless connectivity to places where wires cannot be taken (Like historic sites, some factories etc.) and also to places where it is not feasible/ economical to take cables. If two buildings are more than 100 meters apart, then a OFC fiber cable needs to be laid in between them in order to connect. But mesh networks give the back-haul connectivity over wireless.
¤ Mesh networks can save time and money if they are properly planned.
¤ Mesh networks can support voice, video and data over wireless.
¤ They also support some applications like campus wide surveillance – which can be done simply and economically by the use of wireless mesh and wireless IP Cameras.
¤ Mesh networks support indoor and outdoor applications.
How are mesh networks formed?
Small mesh networks are formed by having an mesh enabled access point in the vicinity of another dual radio mesh enabled access point and having one of their radios connect to each other. This technique is used to just extend the wireless network (in a wired back-end enabled wireless network, for a few places).
Larger mesh networks are formed by a concept called mesh clustering. The mesh enabled access points are placed in a certain pre-planned arrangement where each access point is in the range of at least two more access points. Such clusters are generally closed – they might terminate in a circular shape. This is more feasible for the larger mesh networks because:
¤ They can determine the optimum route for the data packets to travel through the mesh cluster network based on load and interference (Meaning, multiple routes are always available to transmit data).
¤ Failures can be restricted to individual clusters (for covering a large area, multiple clusters may be required) rather than exposing the whole network.
¤ If a single Access point fails, the mesh automatically assigns an alternate route for the data packets to traverse. So, both load balancing and redundancy are available.
Management of mesh networks:
Mesh networks are managed centrally by the wireless controllers (with some wireless vendors). This makes life simpler as administrators need not go to individual mesh access points to manage/ trouble shoot them.
Certain vendors support centralized encryption with mesh networks. However this is possible with a wireless controller – so all the wireless data is encrypted across the network. And this also enables the storage of encryption keys in the controllers in order to prevent their exposure if the access points are stolen.
Certain vendors have a visualization heat map to actually visualize the signal strength across the mesh network. The users need to upload their floor plans or campus maps in to the controller and once the network is set-up, they can monitor how much signal strength is available in which part of the network. This greatly simplifies trouble shooting and monitoring of wireless networks. This is extended to mesh networks also, normally.
Dis-advantages of mesh networks:
When access points are connected by a cable in the back-end, they get 54 Mbps (Might be lesser in practical situations – For 802.11g and a radios) which can be shared with the users. But when a mesh topology is used, every wireless hop or every wireless back haul connection approximately reduces the available bandwidth by half. There is no fixed calculation for this, but with every hop, the bandwidth does decrease. So, if you have any bandwidth intensive applications – you need to take this in to consideration. If your user at the end of the mesh network is just going to browse the net, the performance may still be fine.
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