How to Evaluate Exotic Wireless Routing Protocols.ppt

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How to Evaluate Exotic Wireless Routing Protocols.ppt

  1. 1. How to Evaluate Exotic Wireless Routing Protocols? Dimitrios Koutsonikolas 1 , Y. Charlie Hu 1 , Konstantina Papagiannaki 2 1 Purdue University , 2 Intel Research, Pittsburgh
  2. 2. Evolution of Wireless Routing Protocols <ul><li>From the Ad Hoc Era to the Mesh Era </li></ul><ul><ul><li>New design goals </li></ul></ul><ul><ul><ul><li>High throughput vs. connectivity </li></ul></ul></ul><ul><ul><li>New “exotic” optimization techniques </li></ul></ul><ul><ul><li>Cross – layer design </li></ul></ul>1994 1996 1997 1998 2000 2003 2004 2005 2006 2007 DSDV DSR AODV TORA Performance comparisons ETX ETT ExOR ROMER SOAR COPE MORE MC 2 noCoCo Ad Hoc Networking Era Mesh Networking Era
  3. 3. In This Talk… <ul><li>Review the evolution of wireless protocol design </li></ul><ul><ul><li>Reveal challenges to evaluation methodology of new routing protocols </li></ul></ul><ul><li>Discuss current practices </li></ul><ul><ul><li>Weaknesses </li></ul></ul><ul><li>Suggest guidelines for fair and meaningful evaluation </li></ul>
  4. 4. Ad Hoc Networking Era <ul><li>Primary challenge </li></ul><ul><ul><li>Deal with route breaks due to host mobility </li></ul></ul><ul><li>Layering principle </li></ul><ul><ul><li>Routing protocol discovers route </li></ul></ul><ul><ul><li>802.11 unicast transmits packets to next hop </li></ul></ul><ul><ul><ul><li>ACK/RETX, exponential backoff </li></ul></ul></ul><ul><li>Evaluation </li></ul><ul><ul><li>PDR, control overhead, tradeoffs </li></ul></ul><ul><ul><li>Low constant offered load </li></ul></ul>
  5. 5. Mesh Networking Era <ul><li>Static routers </li></ul><ul><ul><li>Mobility not a concern </li></ul></ul><ul><li>Commercial applications </li></ul><ul><ul><li>Compete with other internet technologies </li></ul></ul><ul><li>New research focus </li></ul><ul><ul><li>High Throughput </li></ul></ul>
  6. 6. Towards High Throughput <ul><li>Link-quality routing metrics </li></ul><ul><ul><li>Examples: ETX, ETT </li></ul></ul><ul><ul><li>Still follow layering principle </li></ul></ul><ul><li>“ Exotic” optimization techniques </li></ul><ul><ul><li>Examples: Opportunistic Routing, Network Coding </li></ul></ul><ul><ul><li>Abandon layering principle </li></ul></ul>
  7. 7. Opportunistic Routing <ul><li>First demonstrated in ExOR [SIGCOMM ‘05] </li></ul><ul><li>Packet broadcast at each hop, all neighbors can receive it </li></ul><ul><li>Neighbor closest to destination rebroadcasts </li></ul><ul><ul><li>Coordination required </li></ul></ul>S B D C S D A A B C 50% 50% 50% 0% 0% 0%
  8. 8. Intra-Flow Network Coding <ul><li>First demonstrated in MORE [SIGCOMM ‘07] </li></ul><ul><li>Routers randomly mix packets </li></ul><ul><li>Benefits </li></ul><ul><ul><li>Remove need for coordination </li></ul></ul><ul><ul><li>FEC-style reliability, no ACK/RETX </li></ul></ul>S D A B p1, p2 p1, p2 p1, p2 S D A B p1, p2 γ* p1 + δ* p2 α* p1 + β* p2 Who forwards? Both forward Coordination Required! No Coordination!
  9. 9. Inter-Flow Network Coding <ul><li>First demonstrated in COPE [SIGCOMM ‘06] </li></ul><ul><li>Routers mix packets from different flows </li></ul><ul><li>Increase network capacity! </li></ul><ul><li>Implied evaluation methodology </li></ul><ul><ul><li>Subject network to congestion </li></ul></ul><ul><ul><li>Use network coding to eliminate congestion </li></ul></ul>Alice Router Bob 1: p1 2: p2 4: p2 3: p1 Traditional Routing: 4 TX Alice Router Bob 1: p1 2: p2 3: p1 + p2 Network Coding: 3 TX 3: p1 + p2
  10. 10. Implications of 802.11 Broadcast <ul><li>802.11 broadcast has no ACK/RETX, no exponential backoff </li></ul><ul><ul><li>No reliability </li></ul></ul><ul><ul><li>Nodes can send faster than in unicast </li></ul></ul><ul><li>Exotic techniques do not work well with TCP </li></ul><ul><ul><li>Batching </li></ul></ul><ul><li>Consequence </li></ul><ul><ul><li>Reliability and rate control are brought to routing layer from lower or upper layers </li></ul></ul>
  11. 11. Evolution of Protocol Stack Physical Layer Physical Layer MAC Layer MAC Layer Network Layer Network Sublayer 1 Transport Layer Network Sublayer 2 Network Sublayer 3 Application Layer Application Layer Medium Access Hop-by-hop Reliability Packet Forwarding End-to-end Rate Control End-to-end Reliability Medium Access Hop-by-hop Reliability Hop-by-hop Rate Control Network Coding Packet Forwarding End-to-end Reliability End-to-end Rate Control Traditional Network Stack New Network Stack
  12. 12. Implications on Protocol Evaluation <ul><li>Evaluation becomes a much subtler task </li></ul><ul><ul><li>Possible conflicts between new and old mechanisms </li></ul></ul><ul><ul><ul><li>Inter-flow network coding vs. rate control </li></ul></ul></ul><ul><li>Current state </li></ul><ul><ul><li>Diverse set of evaluation methodologies </li></ul></ul><ul><ul><li>Lack of clear guidelines </li></ul></ul>
  13. 13. Evaluation of Unreliable Protocols
  14. 14. Practice 1: Making Both Protocols Reliable <ul><li>Evaluation of ExOR, comparison with Srcr </li></ul><ul><ul><li>ExOR guarantees delivery of 90% of the file </li></ul></ul><ul><ul><li>Srcr offers no guarantee </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>Download a 1MB file </li></ul></ul><ul><ul><li>Send 1.1MB with ExOR to compensate for loss </li></ul></ul><ul><ul><li>Carry the whole file hop-by-hop with Srcr to avoid collisions </li></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>Removes spatial reuse from traditional routing </li></ul></ul>
  15. 15. Practice 2: No Rate Control – Varying the Sending Rate <ul><li>Evaluation of COPE, comparison with Srcr </li></ul><ul><ul><li>COPE increases network capacity </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>UDP traffic </li></ul></ul><ul><ul><li>Vary offered load </li></ul></ul><ul><ul><li>Exceed nominal </li></ul></ul><ul><ul><li>capacity (6Mbps) </li></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>PDR drops quickly as network capacity is exceeded </li></ul></ul>
  16. 16. Practice 3: A Protocol With Rate Control Against a Protocol Without Rate Control <ul><li>Evaluation of SOAR, comparison with Shortest Path (SP) </li></ul><ul><ul><li>SOAR applies rate control </li></ul></ul><ul><ul><li>SP has no rate control </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>Saturate the network </li></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>Not clear what fraction of gain comes from opportunistic routing and what from rate control </li></ul></ul>
  17. 17. Evaluation of Reliable Protocols
  18. 18. Practice 5: A Reliable Against an Unreliable Protocol <ul><li>Evaluation of MORE, comparison with Srcr </li></ul><ul><ul><li>MORE offers FEC-style e2e reliability </li></ul></ul><ul><ul><li>Srcr offers no reliability </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>UDP sent at maximum possible rate </li></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>Srcr suffers losses due to congestion </li></ul></ul><ul><ul><li>Same amount of data sent by src, different amount delivered to dst </li></ul></ul>
  19. 19. Practice 6: Running an Unreliable Protocol Under TCP <ul><li>Evaluation of noCoCo, comparison with COPE </li></ul><ul><ul><li>noCoCo applies backpressure-based congestion control/reliability </li></ul></ul><ul><ul><li>COPE has no congestion control, weak reliability </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>Run COPE under TCP </li></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>TCP performs poorly in multihop wireless networks </li></ul></ul><ul><ul><li>Solution – Practice 7 </li></ul></ul><ul><ul><li>Modify COPE to use noCoCo’s congestion control/reliability </li></ul></ul>
  20. 20. Use (or No Use) of Autorate Adaptation <ul><li>Traditional routing uses 802.11 unicast </li></ul><ul><ul><li>Exploits autorate adaptation </li></ul></ul><ul><li>Exotic optimization techniques rely on 802.11 broadcast </li></ul><ul><ul><li>Operates on single rate </li></ul></ul><ul><li>Methodology </li></ul><ul><ul><li>Evaluation of most exotic protocols disables autorate adaptation for traditional routing </li></ul></ul><ul><ul><ul><li>For “fair”comparison </li></ul></ul></ul><ul><ul><li>Problem </li></ul></ul><ul><ul><li>Methodology can be unfair to traditional routing </li></ul></ul>
  21. 21. Recommendations for more consistent and meaningful evaluation
  22. 22. The Importance of Rate Control I Unreliable Protocols <ul><li>Traditional routing under UDP has no rate control </li></ul><ul><ul><li>Packets dropped beyond capacity </li></ul></ul><ul><ul><li>Throughput reduction </li></ul></ul><ul><li>Exotic protocols w/o rate control </li></ul><ul><ul><li>Increase throughput, may increase capacity </li></ul></ul><ul><ul><li>Packets still dropped beyond (new) capacity </li></ul></ul><ul><li>Exotic protocols w/ rate control </li></ul><ul><ul><li>Constant throughput beyond capacity </li></ul></ul><ul><ul><li>No need to increase offered load beyond capacity </li></ul></ul>
  23. 23. The Importance of Rate Control II Reliable Protocols <ul><li>FEC-style reliability provides no rate control </li></ul><ul><li>PDR remains 100%, rate control still needed </li></ul><ul><li>Exceeding capacity may lead to </li></ul><ul><ul><li>Increased delays </li></ul></ul><ul><ul><li>Unfairness among flows </li></ul></ul><ul><li>Related recommendation </li></ul><ul><ul><li>Evaluate with multiple flows </li></ul></ul>
  24. 24. Isolating the Benefit from Exotic Technique <ul><li>Evaluation should quantify the gain from new exotic optimization technique </li></ul><ul><li>Tricky part </li></ul><ul><ul><li>Adding an exotic technique may require old techniques to move to the routing layer </li></ul></ul><ul><li>Recommendation </li></ul><ul><ul><li>Old techniques should also be incorporated into traditional routing </li></ul></ul>
  25. 25. Separating Rate Control from End-to-end Reliability <ul><li>Running traditional routing under TCP </li></ul><ul><ul><li>+ No modification to the protocol itself </li></ul></ul><ul><ul><li>TCP performs poorly in multihop wireless networks </li></ul></ul><ul><ul><li>TCP provides both rate control and reliability </li></ul></ul><ul><ul><ul><li>If new protocol has only one mechanism, overkill to run old protocol under TCP </li></ul></ul></ul><ul><li>Recommendation </li></ul><ul><ul><li>Incorporate reliability/rate control mechanism of new protocol to old protocol </li></ul></ul>
  26. 26. How to Incorporate Reliability To Traditional Routing <ul><li>Case 1: reliability component disjoint to exotic technique </li></ul><ul><ul><li>Example: ARQ component in noCoCo </li></ul></ul><ul><ul><li>Method: add same component to traditional routing </li></ul></ul><ul><li>Case 2: reliability component merged with exotic technique </li></ul><ul><ul><li>Example: intra-flow NC in MORE </li></ul></ul><ul><ul><li>Method: add FEC to traditional routing? </li></ul></ul>
  27. 27. MAC Autorate Adaptation <ul><li>Exotic protocols should try to incorporate autorate adaptation </li></ul><ul><ul><li>Not always feasible </li></ul></ul><ul><li>Recommendation </li></ul><ul><ul><li>Enable autorate adaptation for traditional routing </li></ul></ul><ul><ul><li>Show exotic protocol outperforms traditional routing both with and without autorate adaptation </li></ul></ul>
  28. 28. Conclusions <ul><li>Inconsistencies in evaluating wireless mesh routing protocols </li></ul><ul><li>Fundamental reason </li></ul><ul><ul><li>No unified framework for understanding interactions among </li></ul></ul><ul><ul><ul><li>MAC </li></ul></ul></ul><ul><ul><ul><li>Congestion </li></ul></ul></ul><ul><ul><ul><li>Reliability </li></ul></ul></ul><ul><ul><ul><li>Interference </li></ul></ul></ul><ul><ul><ul><li>Network coding </li></ul></ul></ul><ul><li>Real problem goes beyond how to evaluate exotic protocols </li></ul>
  29. 29. Thank You!

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