1. Ad-hoc Storage Overlay System (ASOS): A Delay-Tolerant Approach in MANETs Guang Yang1, Ling-Jyh Chen2, Tony Sun1, Biao Zhou1, Mario Gerla1 1 University of California, Los Angeles 2 Academia Sinica, Taiwan

2. Motivation • MANETs often deployed in adverse environment that are less reliable. • Nodes in MANETs can crash, lose power, be blocked, or move out of communication range. • Difficult to guarantee continuous end-to-end connectivity in MANETs. MASS 2006

3. Background: What is DTN? • A new network architecture for challenged scenarios of intermittent connectivity: • Space communications, • Messages to remote villages, • Wildlife monitoring, • etc. • DTN highlights: • Mimics the post office model, • Data are aggregated into bundles, • Bundles are sent hop-by-hop to the destination (compared to end-to-end in the Internet). MASS 2006

4. Why DTN is needed in MANETs • In MANETs, connectivity is highly susceptible to mobility, interference, failures, etc. • As a result, e2e connections break frequently. • Many solutions aim to add new nodes to bridge the gaps. • We introduce the DTN concept into MANETs. • ASOS: Ad-hoc Storage Overlay System: • Deploy on existing MANET nodes • Data is stored in a distributed and redundant way among participating ASOS peers. • Opportunistic data delivery relies on node mobility. • Follows DTN semantics and complements end-to-end transport. MASS 2006

5. ASOS storage node Regular node ASOS Example D 4: ASOS data delivery 2: Network partitioning ASOS overlay 3: Data temporarily stored in nearby ASOS peers 1: Conventional end-to-end transport S MASS 2006

6. Basic Architecture When the destination node is at location 1 and disconnected from the source node, undeliverable data is submitted to ASOS for storage (1’). Stored data is delivered to the destination node (2’) after it is reconnected to the network at location 2. MASS 2006

7. Interaction with Routing Two methods to activate ASOS. The first is initiated by the source node after receiving a route error message. The second is initiated by an intermediate ASOS peer node. MASS 2006

8. Distributed Storage Distributed storage of a file in ASOS. The first 200 data units of File 1 have been delivered end-to-end to the destination. The next 150 units have been submitted for storage at an earlier ASOS agent A. The current ASOS agent is B with 50 units already submitted. MASS 2006

9. Data Replication Probabilistic replication of data. Node B has a lower but non-zero probability of holding a copy. Nodes C and D have comparable probabilities; though neither of them deterministically hold a copy. MASS 2006

10. Evaluation – Mobility Model Key concepts: Switch stations Tracks Mobile/static nodes Groups Split/merge The Virtual Track mobility model. One group is split into three subgroups at the center switch station, while two groups merge at the bottom-right switch station. MASS 2006

11. Evaluation – Scenario MASS 2006

12. Evaluation – Instantaneous Throughput ASOS instantaneous throughput may temporarily go above the input rate. Reason: stored + fresh data. MASS 2006

13. Evaluation – Delivery Ratio Cumulative amount of data delivered to the destination. ASOS delivers both fresh and stored data; overall delivery ratio is higher. MASS 2006

14. Summary • DTN concept is very useful in MANETs where continuous connectivity cannot be guaranteed, • ASOS is designed for native DTN support in MANETs. • Available immediately after network is deployed, • ASOS stores data safely during connectivity disruptions. • Opportunistic data delivery in ASOS eventually increases the delivery ratio compared to pure end-to-end transport. MASS 2006

15. Q & As Thank you! MASS 2006