1. The Wireless mesh network
When you travel from one city to another,
chances are that you end up using the highway
network which interconnects the two cities.
Similar to the highway network, a wireless mesh
network is a high speed interconnection
between different kind of networks, for example
wireless LANs, sensor networks or a backbone
connected to the internet as shown in
illustration 1. The mesh consists of devices,
called mesh nodes, having multiple radio's or
interfaces. Similar to tuning in on a radio
station's frequency, a mesh node can listen and
broadcast on a certain frequency or channel with
a single interface. Having multiple interfaces
allows a node to listen and broadcast on a set of
frequencies at the same time. This greatly
increases the amount of data that can be
processed by the wireless mesh network.
Illustration 1: Network layout The nodes can communicate when they are
within each others communication range and
have an interface tuned on the same frequency, much like people need to be close enough to each
other and speak the same language to communicate. Similar to people having a conversation, we
say that nodes share a link.
The mesh network is formed by placing the mesh nodes in such a way that each node can
communicate with at least one other node. Some nodes are also connected to the different networks
that the mesh network interconnects. The nodes will then transport the data from one network to
the other by passing it to other nodes via the links in the mesh network until it reaches its
destination. But it does more than just that. The wireless mesh network is self-configuring, self-
optimizing, self-recovering, self-healing and provides different levels of quality of service (QoS).
The self-configuring property translates into the mesh nodes setting up a network on their own,
without the need for any configuration. From an installer point of view it is sufficient to just power
on the nodes. Nodes connected to the backbone are called root nodes and can configure themselves,
other nodes start the initialization phase when turned on. The initialization starts with listening, or
scanning, on every channel , gathering information about the neighbouring nodes. The scanning is
repeated until the new node has at least one neighbour which is part of the network. The new node
contacts that neighbour to join the network. The surrounding nodes start the binding phase where
they construct links with the new node, configuring the new node in the network. The new node is
now configured and can be used to further extend the network.
To increase the quality of the links and communication, the mesh network is self-optimizing. Links
close to each other interfere when they transmit at the same time on the same channel. Each node
independently optimizes the allocation or selection of channels for their links reducing interference
and increasing the quality and throughput of the links. Also the power on which a node sends
information is optimized. Reducing power, decreases the communication range of a node but also
decreases the interference range of that node. A node minimizes the power level so that all the
neighbours sharing a link can still hear the node.
Whenever a link reduces in quality, the self-healing property of the wireless mesh network takes
over. The node detecting the reduction in quality improves the link by running the power adjustment
and channel change algorithm to improve the quality. If a wireless link fails, the node detecting the

2. failure will immediately reroute traffic and tries to replace the broken link, providing the self-
recovering property of the wireless mesh.
QoS is provided by reserving paths through the network. The quality analysis of the links done in the
different nodes is sent to a central unit where it is processed and mapped onto a graph. A
reservation path is then calculated on the central unit with the gathered information. The actual
reservation is done by sending control messages to the nodes forming the reserved path. The
reservation ability is the only property which needs a central processing unit. The network routes
data on a best effort level and thus preserves connectivity when the central processing unit should
fail.
The wireless mesh network is fully autonomous with respect to configuration, optimization, healing
and recovering, routing and is therefore very easy to set up and maintain.