MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Community-based Mobility Model (CMM) <s> The conventional analysis of Delay-Tolerant Network (DTN) routing assumes that the terrain over which nodes move is closed implying that when the nodes hit a boundary, they either wrap around or get reflected. In this work, we study the effect of relaxing this closed terrain assumption on the routing performance, where a continuous stream of nodes enter the terrain and get absorbed upon hitting the boundary. ::: ::: We introduce a realistic framework that models the open terrain as a queue and compares performance with the closed terrain for a variety of routing protocols. With three different mobility scenarios and four different routing protocols, our simulation shows that the routing delays in an open terrain are statistically equivalent to those in closed terrains for all routing protocols. However, in terms of cost some protocols differ widely in two cases while some continue to demonstrate the statistical equivalence. We believe that this could be a new way to classify routing protocols based on the difference in their behavior under churn. <s> BIB001 </s> MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Community-based Mobility Model (CMM) <s> Abstract Opportunistic networks (OppNets) are modern types of intermittently connected networks in which mobile users communicate with each other via their short-range devices to share data among interested observers. In this setting, humans are the main carriers of mobile devices. As such, this mobility can be exploited by retrieving inherent user habits, interests, and social features for the simulation and evaluation of various scenarios. Several research challenges concerning human mobility in OppNets have been explored in the literature recently. In this paper, we present a thorough survey of human mobility issues in three main groups (1) mobility characteristics, (2) mobility models and traces, and (3) mobility prediction techniques. Firstly, spatial, temporal, and connectivity properties of human motion are explored. Secondly, real mobility traces which have been captured using Bluetooth/Wi-Fi technologies or location-based social networks are summarized. Furthermore, simulation-based mobility models are categorized and state-of-the art articles in each category are highlighted. Thirdly, new human mobility prediction techniques which aim to forecast the three aspects of human mobility, i.e.; users׳ next walks, stay duration and contact opportunities are studied comparatively. To conclude, some major open issues are outlined. <s> BIB002
The CMM is the first and flexible model which is directly drawn from a social network. In CMM, nodes are grouped as friends who belong to the same community and non-friends who are with different community. At the beginning, the movement area is divided into some regions as a grid and each community is assigned into a cell of the grid. A link is established between all the friend and non-friend nodes in the network which will be used later to drive node movements. In this model, nodes move between the communities based on node attraction feature BIB002 . The drawback of this model is gregarious behaviour of nodes. In this case, when a node has decided to exit the community, all other nodes of the community follow this node. The variant that resolve this issue by considering both node and location attraction is home-cell community-based mobility model (HCMM). HCMM introduces the idea of foreign community to mention that some nodes have also social links with communities other than the home. In this model, each node is initially is assigned to a specific community as well as each node has social links with all the other members of its home community. Some special nodes also have social links with foreign communities other than the home community  . The probability of moving a node from its home community towards a given community is proportional to the number of ties with nodes of the destination community BIB001 .