1. Ad-hoc Storage Overlay System (ASOS): A Delay-Tolerant Approach in MANETs Guang Yang, Ling-Jyh Chen, Tony Sun, Biao Zhou and Mario Gerla The 3 rd IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS) 2006 Integrating DTN and MANET Routing Jörg Ott, Dirk Kutscher and Christoph Dwertmann ACM SIGCOMM Workshop on Challenged Networks (CHANTS) 2006 Jun 01, 2007 Nakjung Choi

2. -2/23- Contents Motivation Background DTN interworking over MANETs – Ad hoc Storage Overlay System – Integration of ADOV and DTN Summary

3. -3/23- 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 For throughput enhancement ?

4. -4/23- Background: What is DTN? A new network architecture for challenged scenarios of intermittent connectivity – Space communications – Messages to remote villages – Wildlife monitoring – etc. DTN (Delay and Disruption Tolerant Network) 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)

5. -5/23- 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 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 Why DTN is needed in MANETs

6. -6/23- S D 2: Network partitioning 1: Conventional end-to-end transport 3: Data temporarily stored in nearby ASOS peers 4: ASOS data delivery ASOS overlay ASOS storage node Regular node ASOS Scenario

7. -7/23- 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

8. -8/23- Initialization & Maintenance of ASOS Assumptions – All ASOS peers form a multicast group, of which the address is known a priori by all peers Periodic HELLO messages for overlay Periodic ADVERITSE messages for regular nodes – Only contain file IDs

9. -9/23- 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.

10. -10/23- 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. push pull

11. -11/23- 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. 1.A peer closer to the destination node should have a higher probability to be selected 2.A peer further away from other ASOS peers that have been selected as storage locations should have a higher probability to be selected 3.A peer less heavily loaded should have a higher probability to be selected

12. -12/23- Evaluation – Mobility Model 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. Key concepts: Switch stations Tracks Mobile/static nodes Groups Split/merge

13. -13/23- Evaluation – Scenario

14. -14/23- Evaluation – Instantaneous Throughput ASOS instantaneous throughput may temporarily go above the input rate. Reason: stored + fresh data.

15. -15/23- Evaluation – Delivery Ratio Cumulative amount of data delivered to the destination. ASOS delivers both fresh and stored data; overall delivery ratio is higher.

16. -16/23- AODV+DTN based Routing (1/5) Conceptual overview – AODV route discovery becomes an implicit service discovery mechanism for DTN routers Reporting DTN routing metrics for the target (and originator) node in the AODV route discovery – The originator then decides whether to use e2e IP communication, to go for hop-by-hop DTN messaging, or to declare failure for this point in time (retrying later)

17. -17/23- AODV+DTN based Routing (2/5) AODV extension – The proposed extension headers for AODV to carry DTN- specific information DTN router info header extensions –Appended to both RREQ & RREP DTN EID extension –Used by the originating endpoint to specify the DTN layer source and target EIDs AODV Packet Extensions

18. -18/23- AODV+DTN based Routing (3/5) – RREQ Generation & Processing Originating node –Include DTN Router Info extension with its own contact information & T bit set to 0 An AODV node –Simply forward the RREQ packet after local processing of the fields it understands A DTN-capable AODV node –Add another DTN Router Info extension including its contact information & its hop count to the originator (up to MTU size) –T bit is set to 1 unless another DTN Router Info has it already set – RREP Generation & Processing Target node –If DTN-capable, copy the DTN Router Info fields from the RREQ into the RREP packet, and add its own contact information –Otherwise, simply generate a plain RREP without the extension headers

19. -19/23- AODV+DTN based Routing (4/5) –DTN-capable nodes additionally extract DTN router information for their DTN routing tables, and if the target is not AODV-DTN- capable, recreate RREP with the previously included DTN Router Info fields A node N having a route to the target –If AODV node »The only part of the path may be searched for DTN routers »E2E route is most likely to exist that can be used for E2E or DTN- based forwarding and thus likely outweighs this “deficiency” –If DTN-capable »Immediately generate an RREP or forward the RREP after local processing along the existing route towards the target – Route Discovery Failure For a given iteration of the expanding ring search –If the target node is not found by AODV, DTN-capable nodes follow a slightly modified procedure for RREQ packets that contain DTN Routing Info extensions

20. -20/23- AODV+DTN based Routing (5/5) For each round of the expanding ring search –One DTN-capable router along each broadcast search path »Watch over the route discovery process (use the T bit) »Start a timer when the RREQ packet passes »Generate a DTN-only RREP which indicates a lifetime of zero for the indicated AODV route but includes the DTN Router Info and EID fields from its local state (if no RREP) – Route Collection at the Sender RREP packets returned –One or more routes to the target node and their respective path lengths –A collection of zero or more reachable DTN-capable routers »Along the path to the destination »Within its environment (depending on # of iterations & lifetimes of the expanding ring search) No RREP packet –The originator’s attempt has failed

21. -21/23- Measurement Implementation Multi-hop Wireless Measurements IEEE 802.11b/g 1460 byte TCP segment # of hopsThroughput 17.4 Mbit/s 23.4 Mbit/s 32.9 Mbit/s 42.0 Mbit/s 51.3 Mbit/s 61.4 Mbit/s Up to 30% variation

22. -22/23- DTN-AODV Emulation NSEMULATION – TCPx client sends a single message of 29200 bytes every 150s – DTN bundle lifetime is 5min – Each emulation lasted for 30min → Improve the total delivery ratio (by 1-5 messages), sometimes achieving 100%

23. -23/23- Summary ASOS – 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 Integration of ADOV and DTN – DTN-based hop-by-hop communication can improve throughput compared to e2e TCP so that the choosing DTN does only affect semantics but not the net throughput of an application

24. -24/23- Q & A