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How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1, Konstantina Papagiannaki 2 1 Purdue University, 2 Intel.

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Presentation on theme: "How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1, Konstantina Papagiannaki 2 1 Purdue University, 2 Intel."— Presentation transcript:

1 How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1, Konstantina Papagiannaki 2 1 Purdue University, 2 Intel Research, Pittsburgh

2 Evolution of Wireless Routing Protocols From the Ad Hoc Era to the Mesh Era – New design goals High throughput vs. connectivity – New exotic optimization techniques – Cross – layer design 2 1994199619971998200020032004200520062007 DSDV DSR AODV TORA Performance comparisons ETXETT ExOR ROMER SOAR COPE MORE MC 2 noCoCo Ad Hoc Networking EraMesh Networking Era

3 In This Talk… Review the evolution of wireless protocol design – Reveal challenges to evaluation methodology of new routing protocols Discuss current practices – Weaknesses Suggest guidelines for fair and meaningful evaluation 3

4 Ad Hoc Networking Era Primary challenge – Deal with route breaks due to host mobility Layering principle – Routing protocol discovers route – 802.11 unicast transmits packets to next hop ACK/RETX, exponential backoff Evaluation – PDR, control overhead, tradeoffs – Low constant offered load 4

5 Mesh Networking Era Static routers – Mobility not a concern Commercial applications – Compete with other internet technologies New research focus – High Throughput 5

6 Towards High Throughput Link-quality routing metrics – Examples: ETX, ETT – Still follow layering principle Exotic optimization techniques – Examples: Opportunistic Routing, Network Coding – Abandon layering principle 6

7 Opportunistic Routing First demonstrated in ExOR [SIGCOMM 05] Packet broadcast at each hop, all neighbors can receive it Neighbor closest to destination rebroadcasts – Coordination required SBDCSDA A B C 50% 0%

8 Intra-Flow Network Coding First demonstrated in MORE [SIGCOMM 07] Routers randomly mix packets Benefits – Remove need for coordination – FEC-style reliability, no ACK/RETX SD A B p1, p2 SD A B γ*p1+ δ*p2 α*p1+ β*p2 Who forwards? Both forward Coordination Required!No Coordination!

9 Inter-Flow Network Coding First demonstrated in COPE [SIGCOMM 06] Routers mix packets from different flows Increase network capacity! Implied evaluation methodology – Subject network to congestion – Use network coding to eliminate congestion 9 AliceRouterBob 1:p12:p2 4:p23:p1 Traditional Routing: 4 TX AliceRouterBob 1:p12:p2 3:p1+p2 Network Coding: 3 TX 3:p1+p2

10 Implications of 802.11 Broadcast 802.11 broadcast has no ACK/RETX, no exponential backoff – No reliability – Nodes can send faster than in unicast Exotic techniques do not work well with TCP – Batching Consequence – Reliability and rate control are brought to routing layer from lower or upper layers 10

11 Evolution of Protocol Stack 11 Physical Layer MAC Layer Network Layer Network Sublayer 1 Transport Layer Network Sublayer 2 Network Sublayer 3 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 Implications on Protocol Evaluation Evaluation becomes a much subtler task – Possible conflicts between new and old mechanisms Inter-flow network coding vs. rate control Current state – Diverse set of evaluation methodologies – Lack of clear guidelines 12

13 Evaluation of Unreliable Protocols 13

14 Practice 1: Making Both Protocols Reliable Evaluation of ExOR, comparison with Srcr – ExOR guarantees delivery of 90% of the file – Srcr offers no guarantee Methodology – Download a 1MB file – Send 1.1MB with ExOR to compensate for loss – Carry the whole file hop-by-hop with Srcr to avoid collisions 14 Problem Removes spatial reuse from traditional routing

15 Practice 2: No Rate Control – Varying the Sending Rate Evaluation of COPE, comparison with Srcr – COPE increases network capacity Methodology – UDP traffic – Vary offered load – Exceed nominal capacity (6Mbps) 15 Problem PDR drops quickly as network capacity is exceeded

16 Practice 3: A Protocol With Rate Control Against a Protocol Without Rate Control Evaluation of SOAR, comparison with Shortest Path (SP) – SOAR applies rate control – SP has no rate control Methodology – Saturate the network 16 Problem Not clear what fraction of gain comes from opportunistic routing and what from rate control

17 Evaluation of Reliable Protocols 17

18 Practice 5: A Reliable Against an Unreliable Protocol Evaluation of MORE, comparison with Srcr – MORE offers FEC-style e2e reliability – Srcr offers no reliability Methodology – UDP sent at maximum possible rate 18 Problem Srcr suffers losses due to congestion Same amount of data sent by src, different amount delivered to dst

19 Practice 6: Running an Unreliable Protocol Under TCP Evaluation of noCoCo, comparison with COPE – noCoCo applies backpressure-based congestion control/reliability – COPE has no congestion control, weak reliability Methodology – Run COPE under TCP 19 Problem TCP performs poorly in multihop wireless networks Solution – Practice 7 Modify COPE to use noCoCos congestion control/reliability

20 Use (or No Use) of Autorate Adaptation Traditional routing uses 802.11 unicast – Exploits autorate adaptation Exotic optimization techniques rely on 802.11 broadcast – Operates on single rate Methodology – Evaluation of most exotic protocols disables autorate adaptation for traditional routing For faircomparison 20 Problem Methodology can be unfair to traditional routing

21 Recommendations for more consistent and meaningful evaluation 21

22 The Importance of Rate Control I Unreliable Protocols Traditional routing under UDP has no rate control – Packets dropped beyond capacity – Throughput reduction Exotic protocols w/o rate control – Increase throughput, may increase capacity – Packets still dropped beyond (new) capacity Exotic protocols w/ rate control – Constant throughput beyond capacity – No need to increase offered load beyond capacity 22

23 The Importance of Rate Control II Reliable Protocols FEC-style reliability provides no rate control PDR remains 100%, rate control still needed Exceeding capacity may lead to – Increased delays – Unfairness among flows Related recommendation – Evaluate with multiple flows 23

24 Isolating the Benefit from Exotic Technique Evaluation should quantify the gain from new exotic optimization technique Tricky part – Adding an exotic technique may require old techniques to move to the routing layer Recommendation – Old techniques should also be incorporated into traditional routing 24

25 Separating Rate Control from End-to-end Reliability Running traditional routing under TCP + No modification to the protocol itself – TCP performs poorly in multihop wireless networks – TCP provides both rate control and reliability If new protocol has only one mechanism, overkill to run old protocol under TCP Recommendation – Incorporate reliability/rate control mechanism of new protocol to old protocol 25

26 How to Incorporate Reliability To Traditional Routing Case 1: reliability component disjoint to exotic technique – Example: ARQ component in noCoCo – Method: add same component to traditional routing Case 2: reliability component merged with exotic technique – Example: intra-flow NC in MORE – Method: add FEC to traditional routing? 26

27 MAC Autorate Adaptation Exotic protocols should try to incorporate autorate adaptation – Not always feasible Recommendation – Enable autorate adaptation for traditional routing – Show exotic protocol outperforms traditional routing both with and without autorate adaptation 27

28 Conclusions Inconsistencies in evaluating wireless mesh routing protocols Fundamental reason – No unified framework for understanding interactions among MAC Congestion Reliability Interference Network coding Real problem goes beyond how to evaluate exotic protocols 28

29 Thank You! 29

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