Chapter 4. Distributed Sensor Networks
132
There are hybrid approaches in wireless networks. Though macro-scale
sensor networks profit from wireless technologies due to reduced installation
and deployment complexity, micro-scale network embedded in material
structure can profit from wired technologies, as these are in general more
energy efficient than their wireless counterparts (directed energy flow in the
former in contrast to non- or semi-directed energy flow in the latter).
One of the simplest and still widely used topologies are master-slave 1:N
star networks. These are mainly used in centralized processing architectures.
There is only one connection from each client to a server node (connectivity
degree 1, distance 1). The failure of the server is critical. A different situation is
shown in the bottom row (b) using a broadcast medium (bus, Ethernet) which
connects N individual nodes, with a connectivity degree (N-1) and a maximal
distance of 1. Here a failure of the broadcast medium (the interconnection) is
critical.
Two-dimensional mesh-like networks, either fully or partially connected
and using point-to-point links, are the preferred topologies for wired planar
material-integrated sensor networks having the lowest interconnect complex-
ity but still providing robustness in the presence of missing or defective links
due to path redundancy (there is more than one possible path from a source
to a destination node). They have a connectivity degree of 4 and a maximal
distance of log
2
N. Furthermore, the logical network topology corresponds to
the geometrical placement order of nodes.
In fully connected networks (a) each node is connected with each other
node, leading to a connectivity degree of N-1 and a distance of 1 with the high-
est degree of robustness and lowest message passing latency, but requiring
the highest resource demands. Cube networks (three-dimensional topology,
middle row, right side) provide a good compromise between the afore men-
tioned networks, having a connectivity degree of 6 and a distance of log
3
N
(resulting in a lower message passing latency compared with two-dimensional
networks). They are a special case of a generic hypercube networks (n-dimen-
sional), with very limited practical use in material-integrated sensor network
due to the complex interconnect structure.
In chain or ring networks (c) the connectivity is 2, the maximal distance N-1,
providing no (chain) or low (ring) robustness. Here, failure of a single node can
already be critical: The chain is only as strong as its weakest link.
Hierarchical networks (d) provide node partitioning in spatial bounded sub-
networks connected with each other by using dedicated routers (for example,
sub-star networks arranged in chain networks applied in [GHE10]).
A chain network has no redundancy, in contrast to two- and three-dimen-
sional mesh and cube networks (with four and six neighbour node
connections, respectively). They provide an increasing number of alternative
paths without introducing additional high connectivity complexity and costs
(number of connections are in the order of nodes).
S. Bosse, Unified Distributed Sensor and Environmental Information Processing with Multi-Agent Systems
epubli, ISBN 9783746752228 (2018)