1. DELAY TOLERANT NETWORK

2. Delay Tolerant Network
Delay tolerant networks are categories of sparse wireless networks. Sparse networks have no complete network from source to destination in intermediately connected mobile networks.
Examples; wildlife tracking sensor networks, military networks and interplanetary networks .

3. INTRODUCTION
DTNs use store-and-forward message switching to overcome the problems associated with intermittent connectivity, long or variable delay, asymmetric data rates and high error rates.
Messages are forwarded from a storage place on one node to a storage place on another node along a path that eventually reaches the destination.

4. INTRODUCTION Figure 1: store carry and forward mechanism

5. INTRODUCTION
The DTN architecture implements store-and-forward message switching by overlaying a new protocol layer called the bundle layer on top of heterogeneous region-specific lower layers.
The bundle layer ties together the region specific lower layers so that application programs can communicate across all regions that make up a DTN.

6. INTRODUCTION All regions that make up a DTN use a single bundle layer.
The layers below the bundle layer e.g transport layer are chosen for their appropriateness to the communication environment of each region.
In DTN, there is no preexisting complete path provided. To route a packet from source to destination Intermediate nodes take part in process. When the transmitting node comes into range of intermediate node, it simply forwards the message to that intermediate node and this way the message reaches to the destination.

7. INTRODUCTION SPRAY AND WAIT ROUTING SCHEME Contains two phases;
Spray phase: source node forwards the message or packet to intermediate node.
Wait phase: if destination is not found in spray phase, each node carry the message and whenever the destination is encountered, the node itself will forward the message to destination.

8. PROPERTIES OF DTN
Low date rate and high latency- due to frequent change of network topology and node’s mobility.
Disconnection- created from unexpected fault and network partition.
Long queuing delay-In DTN source node initiate the transmission that may be expensive because of the limited number of transmission opportunity. Combine this issue suggest that message need to be stored for long period of time in message buffer.

9. PROPERTIES OF DTN
Limited longevity-the end to end delay from the sensor node to the destination node is larger than the surviving time of the node which stores the data temporarily because of environmental dangers or hostile action
Limited resources- nodes are mobile and battery operated, limited memory space will restrict the data buffering.

10. ROUTING PROTOCOLS

11. ROUTING PROTOCOLS Categories of routing protocols:
Deterministic routing
Stochastic routing

12. ROUTING PROTOCOLS DETERMINISTIC ROUTING
Assumes knowledge of network topology and its characteristics for computing the optimal route from source to destination.
Classified into ;
Oracle based routing
Link state based routing
Space time based routing

13. ROUTING PROTOCOLS STOCHASTIC ROUTING
Network topology and its characteristics are not known.
classified into;
Active protocol routing
Passive protocol routing

14. ROUTING PROTOCOLS TYPES OF ACTIVE ROUTING PROTOCOLS
Meet and visit (MV)
Message Ferrying (MF)
TYPES OF PASSIVE ROUTING PROTOCOLS
Epidemic routing
Spray and wait

15. CONCLUSION
In DTN, a node is an entity with a bundle layer which is the heart of DTN, and it supports node to node retransmission by means of custody transfer.

16. REFERENCES
1] Delay tolerant networking research group.
[2] Disruption tolerant networking.
[3] S. Jain, K. Fall, and R. Patra. ―Routing in a delay tolerant network‖ In Proc. ACM/ Sigcomm, Aug
[4] D. B. Johnson, D. A. Maltz, and J. Broch. ―Ad hoc networking, chapter 5 - DSR: the dynamic source routing protocol for multihop wireless ad hoc networks. Addison-Wesley, 2001.
[5] W. Zhao, M. Ammar, and E. Zegura. ―A message ferrying approach for data delivery in sparse mobile ad hoc networks. In Proc. MobiHoc’04, 2004.
[6] T. Spyropoulos, K. Psounis, and C. S. Raghavendra. ―Spray and wait: Efficient routing in intermittently connected mobile networks.‖ In Proceedings of ACMSIGCOMM workshop on Delay Tolerant Networking (WDTN), 2005.
[7] Vahdat and D. Becker. ―Epidemic routing for partially connected ad hoc networks‖ Technical Report CS , Duke University, 2000.
[8] K. Fall, ―A delay–tolerant network architecture for challenged internets,‖ in Proceedings of ACM SIGCOMM, pp. 27–34, August 2003.
[9] Forrest warthman. ―Delay Tolerant Networks (DTNS):‖ a TUTORIAL V1.1, mar 2003.
[10] Jain Shen, Sangman Moh, Ilyong Chung ―routing protocols in Delay Tolerant Networks: A Comparative Survey‖ international technical conference on computers and communication-2008.