This brief presents emerging and promising communication methods for
network reliability via delay tolerant networks (DTNs). Different from
traditional networks, DTNs possess unique features, such as long latency
and unstable network topology. As a result, DTNs can be widely applied
to critical applications, such as space communications, disaster rescue,
and battlefield communications. The brief provides a complete
investigation of DTNs and their current applications, from an overview
to the latest development in the area. The core issue of data forward in
DTNs is tackled, including the importance of social characteristics,
which is an essential feature if the mobile devices are used for human
communication. Security and privacy issues in DTNs are discussed, and
future work is also discussed.