Storage Routing based Congestion control in Delay Tolerant Network (DTN)

1. Storage Routing based Congestion control in Delay Tolerant Network (DTN) Presenter: Anika Aziz National Institute of Informatics (NII), The Graduate University for Advanced Studies, Tokyo, Japan

2. Objective • In a Delay Tolerant Network (DTN), a custodian node which is storage constrained, can mitigate the congestion by reserving buffer space and applying queuing algorithm as a function of priority classes that is Class Of Services(COS). • These COS can be mapped to a shared Priority Queuing (PQ) approach or to the separate PQs with different thresholds of the buffer.

3. Outline • The DTN architecture, the Bundle protocol • Custody transfer in DTN • Congestion in DTN • The Storage Routing (SR) • Proposed algorithms • Analysis & comparison of the algorithms • Conclusion • Q & A

4. The DTN Architecture: Internetwork of challenged internets, the Bundle protocol

5. Custody transfer • An acknowledged transfer of data to persistent, reliable storage A msg B ack (store the msg) (delete the msg) custody transfer complete (assumes custody transfer complete) • To use hop-by-hop reliability to improve end-to-end reliability • To free retransmission buffers at a sender as soon as possible • When faced with persistent demand…….congestion occurs

6. DTN congestion • Rate based or window based congestion control techniques-nearly ineffective • A region under the administrative control of a single entity can apply some form of admission control as a proactive means • If its insufficient or unavailable, reactivemeans ( involving direct flow control) must be used • Different solutions…cease accepting bundles with custody transfer & move bundles somewhere else

7. The Storage-based Congestion Control • Networks containing traffic sources which continuously generate application data (e.g. sensor networks) can not be flow controlled instead Storage routing int -Message selection -Node selection push -Retrieval selection pull alternate custody transfer source custody transfer int dest -No custody refusal - Messages are dropped under the worst case situation

8. Selecting the message to push to the alternate destination is crucial • Apply some standard queue management or scheduling algorithm • Priority classes that is Classes Of Service (COS), “bulk”,” normal” and “expediated” priorities, • Applications specify the COS & data lifetime (TTL) for each message they send, based upon its desire to affect the delivery urgency for messages • Push Lowest Priority mechanism as the push policy • Expanding Ring Search (ERS) method

9. Message ׀m׀ arrives at node n ׀m׀>Fn(t) ? N Y Priority0 ? ? Compare with others in the queue N Is it the lowest one? Y Y Find alternative custodian x such that ax(t)>׀m׀ N Push the lowest one in the queue Is x Found? (ERS) N Y If all are of equal priority, push the message with the highest TTL Drop ׀m׀ Push ׀m׀ to x Y Does ׀m׀ has the highest TTL? Fn(t) is increased Y N Enqueue ׀m׀ at n Is still |m| > Fn(t)? N Figure 4. The SR algorithm: COS mapped to the shared PQ

10. Message ׀m׀ arrives at node n N ׀m׀> Fn(t)? Enqueue ׀m׀ At node n Y Priority0 ? Priority1 ? N Y Y N ABM1 Compute avg queue lengthof Fn(t) Priority 2 ABM2 avg<minth0 ? Y Active Buffer Management (ABM0) technique ׀m׀ is selected for push policy N N avg>max0 ? Look into residual TTL value Y High residual TTL? N Drop Y Figure 5. SR algorithm: COS mapped to PQ and thresholds of Active Buffer Management

11. Analysis & Comparison of the Algorithms: Qualitative Analysis • Both the algorithm ensures to push the lowest priority message • Messages are dropped in the worst case situation • the 2nd approach works more dynamically and precisely • No Priority Inversion & Head-Of-Line blocking

12. Analysis & Comparison of the Algorithms: Quantitative Analysis

13. Conclusion • The value of Custody Transfer and DTN congestion remains to be fully understood… until the DTN architecture is widely deployed and carries significant traffic loads • Similar story as TCP protocol specification included no management of congestion… more than 10 years after the 1st experiments with Internet technology were performed.

14. Q & A ?