1. 2010 IEEE Global Telecommunications Conference, GLOBECOM 2010 Zheng Guo; Bing Wang; Jun-Hong Cui Prediction Assisted Single-copy Routing in Underwater Delay Tolerant Networks Advisor: Prof. Han-Chieh Chao Student: Yu-Shan Li Date: 2011/10/11 1

2. Outline Abstract Introduction Network Model Aggressive Chronological Projected Graph Prediction Assisted Single-Copy Routing Related Work Conclusions and Future Work 2

3. Abstract DTN as the lack of contemporaneous end-to-end paths makes conventional routing schemes inapplicable. Many existing DTN routing protocols adopt multi-copy replication and are incognizant of mobility models. This paper,authors propose a generic prediction assisted single-copy routing (PASR) scheme. PASR employs an effective greedy algorithm. PASR provides guidance on how to use historical information. 3

4. Introduction Many routing protocols have been proposed to deal with the lack of contemporaneous end-to-end paths in DTN. Many protocols are designed for specific mobility models. (1) propose a small-scale trace-based greedy algorithm, named aggressive chronological projected graph (ACPG). (2) design a heuristic prediction assisted single-copy routing protocol based on the guidance from ACPG 4

5. Network Model 5

6. 6 All sensors use store-and-forward mechanism. Each sensor broadcasts a short hello message to its neighbors. Each sensor is equipped with a buffer that can accommodate W packets and a battery that can transmit P packets. Sensors work in a half-duplex mode. Network Model(cont.)

7. Aggressive Chronological Projected Graph A. Construction of G(V,E) Authors assume the network contains M layers and N nodes in each layer. V s : super source V d : super sink v ij ∈ V (i = 1,..., M, j = 1,..., N) (v ij, v kl ) ∈ E To differentiate edges in different time slots, they use (u, v, t, C) to represent an edge in G, Each node v also maintains the following information: Uv 、 Iv(i) 、 Cv(i) 、 Pv 7

8. B. Operations of ACPG Edge projection :during which connections in a time slot are projected to G as edges. Only the one with the lowest time slot value is available on graph G and can be used for route discovery until it is replaced by the next earliest edge. Routes reservation and graph update :during which routes are discovered and G is updated. There must exist at least one flow from the super source vs, whose route can be traced back along the upstream nodes from vd. It is the minimum node capacity or edge capacity along the route. After reservation, nodes whose batteries are exhausted and edges whose capacities are reached become dead, and hence are removed from G. 8 Aggressive Chronological Projected Graph(cont.)

9. The first route Find the another route 9 Aggressive Chronological Projected Graph(cont.)

10. C. Performance of ACPG 10 Aggressive Chronological Projected Graph(cont.) Each layer covers600m×600m The distance between two adjacent layer 90m Buffer size30 packet Transmission range100m The simulation length3000s The slot interval10s

11. Compare the delivery ratio of ILP and ACPG 11 Aggressive Chronological Projected Graph(cont.)

12. 12 Compare the average delay of ILP and ACPG Aggressive Chronological Projected Graph(cont.)

13. Prediction Assisted Single-Copy Routing A. How PASR Works? 1) Historical information: If the mobility pattern is stable for a long time, the history can tell the future. Recent trajectory Average contact duration Average inter-contact duration Last contact time Contact frequency (or contact probability) 13

14. 2) Guidance from ACPG: The following properties of routes and node contacts, which are closely related to the underlying mobility pattern, can be captured by ACPG: Geographic preference Contact periodicity Inter-contact time distribution Contact probability 14 Prediction Assisted Single-Copy Routing(cont.)

15. 15 3) Predict the future: After ACPG characterizes the mobility pattern, it suggests what historical information can be used for prediction. The guidance exhibits geographic preference Mobility shows contact periodicity The inter-contact time follows some well-known distribution A node contacts another node or landmark with a certain probability Prediction Assisted Single-Copy Routing(cont.)

16. 16 B. Instantiating PASR UWSN in Regular Currents 1)Guidance from ACPG: geographic preference :an upper layer node is more preferred than other layer nodes. contact periodicity :nodes have varying periodic contacts 2) Protocol following ACPG Based on the above guidance, authors propose a specific PASR for this network, energy efficient history prediction assisted routing (EEHPA). EEHPA have two essential operations: prediction update and per-contact forwarding decision. Prediction Assisted Single-Copy Routing(cont.)

17. 17 For the prediction, each node u maintains its own prediction vector (PV), which is a vector of tuples (i,v,Dv) PV is recursively updated through the neighbors PVs and the predicted future contacts with these neighbors. Forwarding decisions are made based on the PV and the guidance from ACPG every time a node encounters neighbors. UWSN in Currents with Randomness PASR can tolerant these errors to some extent since ACPG just captures the general properties of the majority of nodes UWSN in Irregular Currents (1) a node in the same layer is preferred. (2) only predict for nodes in the same layer. Prediction Assisted Single-Copy Routing(cont.)

18. 18 C. Performance Evaluation Prediction Assisted Single-Copy Routing(cont.) Each layer covers800m×800m The distance between two adjacent layer 40m Buffer size100 packet Transmission range 5 0m The simulation length3000s The slot interval10s

19. 19 ACPG: serves as the lower-bound. EEPA: energy efficient prediction assisted routing. First Contact (FC): The single-copy routing by forwarding packets to the first node encountered without any prediction Epidemic: a flooding based scheme Prediction Assisted Single-Copy Routing(cont.)

20. 20 Fig. 4. Performance comparison of various routing schemes in UWSN with regular currents. Prediction Assisted Single-Copy Routing(cont.)

21. 21 Prediction Assisted Single-Copy Routing(cont.)

22. 22 Prediction Assisted Single-Copy Routing(cont.)

23. Related Work 23 Space-time graph to select routing paths using dynamic programming and shortest path algorithm. Epidemic is a representative multi-copy routing scheme by replicating a packet to any node in the network Spray and wait, in which a certain number of copies of a packet are replicated. PROPHET to limit the number of copies

24. Conclusions and Future Work 24 Authors present a generic scheme prediction, assisted single-copy routing (PASR). And propose ACPG, which is a greedy algorithm that provides results close to optimal and characterizes the properties of the underlying mobility pattern. Authors design online heuristic protocols by choosing appropriate historical information and forwarding criteria based on the guidance from ACPG. The instantiated PASR schemes outperform others.

25. 25 (1) compare this schemes with other multi-copy schemes and study the tradeoffs between using single copy and multiple copies, (2) explore more mobility prediction technologies suitable for underwater sensor networks (3) examine PASR under different mobility models. Conclusions and Future Work(cont.)