Data Retrieval in Intermittedly Connected Networks

Transcription

1 Humboldt University Computer Science Department Data Retrieval in Intermittedly Connected Networks Dirk Neukirchen, Christian Beier ({neukirch, Interplanetary Internet Seminar, May 2006

2 Overview the scenario why traditional network technologies won't adapt well to it how new technologies try to solve the problem: a new approach to Distributed Information Retrieval a draft for the underlying DTN architecture

3 The scenario imagine a larger earthquake that destroys critical infrastructure, including: roads electricity phone networks Internet access rescue personnel carrying radios experience temporal disruptions of connectivity if there's limited connectivity, the most important information has to get through first!

4 Distributed IR for DTN Similar to P2P ideas Each peer caches: query + documents Exchange during transfer opportunities Buffer space constraints Buffer Management Routing Metric: Rank(D) ~ (1-α)Deliverable(D) + α Score(D) α=0 traditional

5 Distributed IR for DTN What about Score(D)? SNAQ Score Normalization Across Queries Use statistics about queries and documents Simulation Conclusion: Random Drop is bad More documents are delivered using document ranking

6 An architecture for the DTN... in the case of our scenario, the network looks like that: nodes may get disconnected or the network may get partitioned probably no direct end-to-end paths between nodes, BUT maybe periodical connectivity high probability of packet loss along the way high latency asymmetric data rates low bandwidth traditional protocols (like TCP/IP) assume quite contrary environments, so we need a new approach...

7 An architecture for the DTN: EDIFY enhance traditional protocols or start from scratch? enhancements to existing protocols are insufficient! why? because they inherently rely on the existence of an end-to-end path between nodes EDIFY: Enhanced Disruption and Fault Tolerant Bundle Delivery System: - can address nodes in partitioned networks via a flexible naming convention - means of DTN neighbor discovery, gateway selection, mobility management and route discovery

8 EDIFY: flexible naming convention. hierarchical naming scheme that supports multiple namespaces: every node has a unique identifier every node can get assigned temporal names like US.Army.Battalion42.soldier-007 Germany.Berlin.idle.soldier-007 allowing names based on administration, location, network structure... nodes can get Visitor ID's from groups other than their own

9 EDIFY: an example assume node 007 has ID Group1.soldier007 and GW's can communicate via some other instance node 007 gets seperated from its group, but gets connected to Group2 gets temporary additional ID Group2.visitor42 GW2 gets notified about the visitor GW2 can inform GW1 that it can reach Group1.soldier007 members of Group1 are still able to communicate with 007 via GW1 and GW2

10 More to come... the upcoming speech will cover: how does Document Scoring in Distributed IR work? how does EDIFY solve the problems that emerge in mobile ad-hoc nets? more examples more pictures thanks for listening!

11 References "Enhanced Disruption and Fault Tolerant Network Architecture for Bundle Delivery (EDIFY)", Mooi Choo Chuah, Liang Cheng, Brian D. Davison, Department of Computer Science and Engineering, Lehigh University "Distributed Information Retrieval For Disruption- Tolerant Mobile Networks" Yun Zhao, Brian Neil Levine, W. Bruce Croft Department of Computer Science, University of Massachusetts, Amherst