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OverviewThis 10-minute video movie illustrates the principle of delay-tolerant communication in a mobile ad hoc network. It was primarily designed for non-specialists. It is meant to illustrate how communication can be achieved in a disconnected mobile ad hoc network (or MANET), using the combined principles of opportunistic networking and of delay-tolerant networking.The movie shows a typical scenario, where a number of users carrying laptop computers move in and between the buildings of a small university campus. The laptops are assumed to be equipped with Wi-Fi interfaces running in ad hoc mode (that is, without any infrastructure network).The movie is quite self-explanatory, with popup windows explaining what is being shown. Yet further comments are available below for interested viewers. You can download this video: Synopsis of the movieThe first part of the movie (up to timecode 03:30) presents the main characteristics of the simulation scenario, such as the limitation in radio coverage, the fact that laptops are assumed to be in suspend mode while their owners are moving, etc. It is most important to understand that the mobile ad hoc network that is composed by these 20 laptops is a disconnected one. In other words there is never any temporaneous end-to-end connectivity between all devices in this network. At any time each laptop can only interact with at most a couple of other laptops, and sometimes, with none at all.The second part of the movie (after timecode 03:30) shows how communication can be achieved in such an environment, in spite of the abovementioned constraints. As a general rule, the approach consists in exploiting transient contacts between laptops in order to have them exchange pieces of information. Since these contacts are neither planned in advance, nor easily predictable, they must be exploited in a purely opportunistic manner (hence the notion of “opportunistic networking”).In this particular case we illustrate how a message sent by a user to another user can propagate in the network thanks to the cooperation of all mobile laptops. Basically each laptop is expected to help disseminate a copy of the message by storing, carrying, and ultimately forwarding this copy when circumstances permit. This is actually a typical application of the so-called “epidemic model”, whereby each message is perceived as a benign virus that disseminates in the network until each mobile device has been “infected” by this message. The video shows that, with this approach and with the mobility scenario considered, the message reaches its destination after about 23 minutes. It also shows that once the message reaches its destination, it is advisable for the receiver to send another message back in the network, in order to acknowledge the former message while cancelling its epidemic propagation. |
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