MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Self-similar Least-Action Walk (SLAW) <s> Mobile Wireless Delay-Tolerant Networks (DTNs) are wireless networks that suffer from intermittent connectivity, but enjoy the benefit of mobile nodes that can store and forward packets or messages, and can act as relays, bringing packets and messages closer to their destination through a selective forwarding policy. Many DTN protocols compensate for the unpredictability of the network by distributing multiple message copies in the hopes that at least one will eventually be delivered. As the number of message carriers becomes large these schemes experience diminishing marginal benefits from the addition of more message carriers. We describe and analyze the Simple Counting Protocol, an extremely simple and robust method for limiting the fraction of nodes that carry a copy of a message. We examine the performance of this protocol in conjunction with several abstract mobility models and show that the protocol performs reasonably well in diverse circumstances. The Simple Counting Protocol does not assume much about node mobility, and therefore should be useful for applications where little is known about node encounter patterns. The simplicity of its implementation will hopefully make it a useful substitute for epidemic routing as a naive lower bound in protocol performance comparisons. We also show how the same simple techniques and principles can be applied in conjunction with more complex heuristic DTN protocols to reduce network resource usage, a scheme we call Intermediate Immunity. <s> BIB001 </s> MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Self-similar Least-Action Walk (SLAW) <s> Mobile wireless delay-tolerant networks (DTNs) are wireless networks that suffer from intermittent connectivity, but enjoy the benefit of mobile nodes that can store, carry, and forward packets or messages, bringing them closer to their destinations through a selective forwarding policy. The evaluation of DTN routing protocols has primarily relied on simulation because most theoretical mobility models are unable to represent the mobility patterns that such protocols seek to take advantage of. In this paper we present and analyze a mobility model that we call localized random walk. This model is simple enough that it can be incorporated into mathematical models, but is spatially localized, which unlike other common mobility models, will make it possible to showcase the properties of heuristic-based DTN routing protocols. We derive the stationary spatial distribution of the mobility model, approximate what we call its spatial cross section, approximate the properties of its interaction with nodes following other mobility models, and use it to model some relatively simple DTN scenarios. <s> BIB002
SLAW is one of the composite models that produce synthetic mobility traces which comprise all the five statistical features in various mobility settings. This also includes user-created virtual features, but no empirical information is available for these features. Virtual environments based on synthetic traces play important role for the performance evaluation of mobile networks as the networks are required to test in many diverse network settings when one design new network architecture. Performance evaluations of mobile routing protocols based on synthetic traces produced by SLAW demonstrate that SLAW gets the unique performance features of various routing protocols. Lee et al. BIB002 has developed SLAW depending on Global Positioning Systems traces of human walks that counted 226 daily traces collected from 101 volunteers in five different outdoor sites. Especially, many of these traces are derived considering people who have common interests such as students in the same university campuses and tourists in a theme park. By faithfully representing the properties present in these traces, SLAW can represent social contexts among walkers manifested by visits to common gathering places and walk patterns therein BIB001 .