Delay Tolerant Networks (DTNs) have evolved from Mobile Ad Hoc Networks (MANET). It is a network, where contemporaneous connectivity among all nodes doesn't exist. This leads to the problem of how to route a packet from one node to another, in such a network. This problem becomes more complex, when the node mobility also is considered. The researchers have attempted to address this issue for over a decade. They have found that communication is possible in such a challenged network. The design of routing protocol for such networks is an important issue. This work surveys the literature and classifies the various routing approaches.

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