Chapter 1
Introduction
Today many personal mobile devices include capabilities to communicate
with infrastructure networks but also with each other. The latter can be
used to form ad-hoc networks where common infrastructure is no longer
needed for communication among hosts participating in the network. Ad-
hoc networks can also help mobile nodes to reach infrastructure if some node
in the network is able and willing to act as a gateway and possibly other
nodes as relays for the traffic. Networks can be formed this way as long as the
node density is large enough so that there exists possible end-to-end paths
between all nodes wanting to communicate. However, if the node density
decreases or the connectivity breaks for some other reason (e.g., the radios
are switched off occasionally), traditional network communication protocols
are no longer able to provide means for multi-hop communication.
Delay Tolerant Networking (DTN) [10, 4] is a communication networking
paradigm that enables communication in environments where there may be
no end-to-end paths, communication opportunities come and go and their
interval can be very long and not even known beforehand. Routing messages
in this kind of environments can be quite different compared to traditional
networks. This has created a need to find new routing protocols that take
efficiently into account the distinct nature of these networks. Different ap-
proaches can be tested and evaluated by simulation, but the simulation
results are really useful only if they are a result of somewhat credible simu-
lation scenarios.
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