1 / 22

PRoPHET Update

DTN Research Group @ IETF 78 27 March 2010 Elwyn Davies elwynd@folly.org.uk Avri Doria Samo Grasič Anders Lindgren avri@psg.com samo@grasic.net dugdale@gmail.com. PRoPHET Update. Progress with PRoPHET New Version http://tools.ietf.org/html/draft-irtf-dtnrg-prophet-06.

guang
Download Presentation

PRoPHET Update

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. DTN Research Group @ IETF 78 27 March 2010 Elwyn Davies elwynd@folly.org.uk Avri Doria Samo Grasič Anders Lindgren avri@psg.comsamo@grasic.netdugdale@gmail.com PRoPHET Update

  2. PRoPHET Update - IRTF 78 Progress with PRoPHETNew Versionhttp://tools.ietf.org/html/draft-irtf-dtnrg-prophet-06 • PRoPHET in use in N4C testbeds • Slovenia (continuous use for almost 2 years) • Arctic Sweden (Summer testing) • Simulation work by Samo and Elwyn • Draft update includes • Addressimg IRSG review comments • Improvements resulting from recent experiments • Additional capabilities to fix long standing issue

  3. PRoPHET Update - IRTF 78 Experiments in Progress - 1 • Slovenia • Gradually extending network of unattended environmental sensors (meteo and radiation) • Data mules • Active nodes in cars • Symbiotic (Parasitic) nodes – just a USB memory stick • Using PRoPHET routing • Analysis of results has found problem with transitive update algorithm

  4. PRoPHET Update - IRTF 78 Experiments in Progress - 2 • Arctic Sweden • See reports – previous DTNRG slides! • GSM to edge of area, Helicopter mules • Two systems running in parallel • 'Village Router' hot spot system - static routing/DTN2See http://village.n4c.eu - need to set HTTP proxy for best effect! Email and web caching proxy system • PRoPHET routing nomadic systemSee http://dtn.n4c.eu for more info, NSIM, web cam, logs, etc • Two months testing during reindeer marking/ hiking season in Padjelanta

  5. PRoPHET Update - IRTF 78 Refresher: Key Equations • Notation: P(A,B): Delivery Predictability in Node A for delivering a bundle to Node B. • Eqn 1: On A encountering B • P_(A,B) = P_(A,B)_old + ( 1 - P_(A,B)_old ) * P_encounter • Eqn 2: If A hasn't encountered D for a while: • P_(A,D) = P_(A,D)_old * gamma^K • Eqn 3: Does A meeting B mean that A is a better bet for delivering to C? Transitivity... • P_(A,C) = P_(A,C)_old + ( 1 - P_(A,C)_old ) * P_(A,B) * P_(B,C) * beta

  6. PRoPHET Update - IRTF 78 Simulation Work - 1 • Samo working to reproduce and validate results from RAPID paper comparison • PRoPHET came out very poorly in this work • Slow progress due to various problems • Competing demands of test bed deployment • Acquisition of simulation code used by RAPID team • Found RAPID PRoPHET implementation didn't match specification • Recently got comparative results using ONE sim • #1 conclusion: match proto to scenario • Otherwise random routing will work better!

  7. PRoPHET Update - IRTF 78 Simulation Work 2 • Elwyn has been working on visualizing the evolution of delivery predictability • Simple Excel Spreadsheet simulator • Python program + Excel display using mobility files generated by Anders original prpogram. • Using these to check how DPs evolve and ensure that they reflect the expected future encounters. • Evaluated proposed alternative evolution equations • Selected replacements now in field trials

  8. PRoPHET Update - IRTF 78 Main Problems Identified • Inappropriate evolution of delivery predictabilities (DPs) • Repeated encounters of '3rd party' nodes leads to jammed bundles . • Parking Lot Problem – When is an encounter not a (new) encounter? • Totally random encounters => noise in DPs • Deriving a relationship between the various PRoPHET parameters • Need guidelines for setting parameters appropriately

  9. PRoPHET Update - IRTF 78 Bundles Jammed in 3rd Parties • Scenario (at least 4 nodes: A - D): • Node B meets Node A & (separately) C occasionally. • Nodes C and D meet each other repeatedly between meetings of Nodes B.and C • DP for Node A increases steadily in Nodes C & D until bigger than DP for Node A in Node B • Result: Bundles for A not transferred from C/D to B; hence jam in C and are never delivered. • Identified in long term Slovenian experiment • Fix: Improved transitivity update algorithm

  10. PRoPHET Update - IRTF 78 Parking Lot Problem • Scenario: • Multiple Wi-FI nodes milling around in a small area • Multiple 'encounters' e.g. due to Wi-Fi reconnections. • Can result in • DP update 'loops' – changes propagated round loop • One actual encounter being treated as several • Identified from theoretical considerations • Fix: Allow nodes to suppress DP updates

  11. PRoPHET Update - IRTF 78 Noise in DPs from Random Encounters • Scenarios in which a node encounters lots of nodes that it will never meet again • Typical of some simulation scenarios • Can lead to random routing outperforming PRoPHET (and other algorithms) if there is little pattern to encounters • Make sure you are using PRoPHET in an appropriate scenario! • Fix: Set P_(A,B) to a lower value on 1st meeting • Could avoid applying transitivity on first encounter

  12. PRoPHET Update - IRTF 78 Too Many Degrees of Freedom? • PRoPHET has a lot of (apparently) independent parameters. • There wasn't a good story on how to choose a consistent set of parameters. • Fix: Describe how they each relate to the 'characteristic time period' of the PRoPHET zone. • and this also relates to the approptiate bundle lifetime and custody timer settings

  13. PRoPHET Update - IRTF 78 Improvements: Equation 1 • Reduce the effect of random, one-off encounters • On first encounter set DP to a lower value • Suggest 0.25 rather than the 0.75 in old version • Do the same if the DP has decayed below a threshold because last encounter was a long time ago. • Use existing equation 1 on subsequent encounters when P_(A,B) not below threshold

  14. PRoPHET Update - IRTF 78 Improvements: Equation 1 • Avoid DP actually reaching 1 ('Almost Sure') on repeated encounters • New equation: • P_(A,B) = P_(A,B)_old + ( 1 - delta - P_(A,B)_old ) * P_encounter • Delta is a small value that stops the value getting right to 1.0

  15. PRoPHET Update - IRTF 78 Improvements: Equation 3 • Avoid DP increasing inappropriately due to repeated encounters between 3rd parties that haven't actually met suitable intermediaries. • The improved equation is intended to converge the DPs for C in A and B after repeated encounters BUT only to the highest value that either of them started with • P_(A,C) = MAX( P_(A,C)_old, P_(A,B) * P_(A,C) * beta ) • Beta is a 'slowing factor' – reduces convergence rate

  16. PRoPHET Update - IRTF 78 Characteristic Time Period • Concept: A ProPHET zone has a characteristic time period (CTP) that is determined by the expected time intervals between encounters • Bundle expiry times should be set so that bundles will be around sufficiently long to be delievered but not hang around for too long • DP decay should reduce a DP to essentially zero after 3 to 5 multiples of CTP • An encounter should at least undo the expected decay between encounters • Treat closely spaced encounters as one

  17. PRoPHET Update - IRTF 78 Improvements: Suppress DP Recalc • Added a flag into the Hello TLV that requests suppression of DP recalculation phase. • Has to be agreed by both parties in an encounter • Otherwise recalculation is done on both sides • Nodes can choose to suppress recalculation if they have met very recently and they don't have new information to convey • Very recently means (say) 5% of CTP

  18. PRoPHET Update - IRTF 78 Progress towards RFC • RG Last Call completed • Various clarifications (especially thanks to Kevin) • Currently in IRSG Review process • Somer additional clarifications added in latest version (-06) • Some significant improvements since review • May need to repeat last call/review

  19. PRoPHET Update - IRTF 78 New Protocol Version • The protocol has been taken to version 2 as the changes to the equations and Hello TLV are not fully interoperable.

  20. PRoPHET Update - IRTF 78 Next Steps • Pass the improvements to IRSG reviewer • Check performance of improvements in the field • Do we need another Last Call? • There have been significant updates

  21. PRoPHET Update - IRTF 78 Thank You

  22. PRoPHET Update - IRTF 78 DTN2 Functional Spec • Product of N4C work – Elwyn and Avri Doria • Nearly 200 pages!! • Currently accessible athttp://www.n4c.eu/Download/n4c-wp2-023-dtn-infrastructure-fs-12.pdf • Contains: • Spec of API • A complete specification of the TCL command interface • Detailed operation of the core specification • Missing – Sessions and External Router/CL

More Related