Delay Tolerant Network(DTN)s are basically the networks which suffer frequent and long duration partitions.Due to intermittent connectivity in the existing networks,Multicasting in DTN is very challenging.Multicasting means distribution of data to a group of users,which are needed for many potential DTN applications ie.Crisis environments,Deep space communications,Battle Fields,Remote areas etc.It is a new concept brought into picture especially for the hazardous ,unfavourable environments where our infrastructured networks ,Wifi etc fail as they are supposed 2 have end to end connection.DTN doesnt require end to end connection,rather bring forth the stored and forward paradigm.In present scenario,we do hav DAKNET available which are quite similar to DTN,still alot of features absent.Talking about multicasting over DTN....
Multicast supports the distribution of data to a group of users, a service needed for many potential DTN applications. While multicasting in the Internet and mobile ad hoc networks has been studied extensively, due to the unique characteristic of frequent partitioning in DTNs, multicasting in DTNs is a considerably different and challenging problem. It not only requires new definitions of multicast routing algorithms but also brings new issues to the design of routing protocols.
Many potential DTN applications operate in a group-based manner and require efficient network support for group communication. For example, in a disaster recovery scene, it is vital to disseminate information about victims and potential hazards among rescue workers. In a battlefield, soldiers in a squad need to inform each other about their surrounding environment. Although group communication can be implemented by sending a separate unicast packet to each user, this approach suffers from poor performance. The situation is especially acute in DTNs where resources such as connectivity among nodes, available bandwidth and storage are generally severely limited. Thus efficient multicast services are necessary for supporting these applications.
Due to large transfer delays in DTNs, group membership may change during a message transfer, introducing ambiguity in multicast semantics. Under these situations, it is necessary to make a distinction between group members and the intended receivers of a message, i.e., endpoints to which the message should be delivered. Group members may change with time as endpoints join and leave the group. The intended receivers, on the other hand, should be fixed for a message, even though they are defined based on group membership.
