Abstract
Delay Tolerant Networks are characterized by (i) intermittent connectivity that is there is no reliable end-to-end path,(ii) long delay in delivery of packets from source to destination and (iii) the nodes are sparse and mobile. Traditional protocols do not work for such an environment. DTN is deployed in interplanetary networks, wild life tracking, disaster management, underwater networks. Routing in DTN is by store-carry-forward technique, where the source or the intermediate node stores the packet until it meets the node for forwarding. The major constraints or challenges are energy level constraint, mobility patterns, selection of intermediate nodes, effective usage of the limited network resources like buffer space etc. This paper provides the study of various DTN routing algorithms and their categories are summarized.