How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1,...
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Transcript of How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1,...
![Page 1: How to Evaluate Exotic Wireless Routing Protocols? 1 Dimitrios Koutsonikolas 1, Y. Charlie Hu 1, Konstantina Papagiannaki 2 1 Purdue University, 2 Intel.](https://reader036.fdocuments.us/reader036/viewer/2022062417/551506505503465e608b4710/html5/thumbnails/1.jpg)
How to Evaluate Exotic Wireless Routing Protocols?
1
Dimitrios Koutsonikolas1, Y. Charlie Hu1, Konstantina Papagiannaki2
1Purdue University , 2Intel Research, Pittsburgh
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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
1994 1996 1997 1998 2000 2003 2004 2005 2006 2007
DSDV
DSR
AODVTORA
Performance comparisons
ETX ETT
ExORROMER SOAR
COPE
MOREMC2
noCoCo
Ad Hoc Networking Era Mesh Networking Era
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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
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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
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Mesh Networking Era• Static routers
– Mobility not a concern
• Commercial applications– Compete with other internet
technologies
• New research focus– High Throughput
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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
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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
S B DC S DA
A
B
C
50%
50%
50%
0%
0%
0%
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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
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!
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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
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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
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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 layers10
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Evolution of Protocol Stack
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Physical Layer Physical Layer
MAC LayerMAC Layer
Network Layer
Network Sublayer 1
Transport LayerNetwork 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
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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
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Evaluation of Unreliable Protocols
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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
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ProblemRemoves spatial reuse from traditional routing
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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)
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ProblemPDR drops quickly as network capacity is
exceeded
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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
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ProblemNot clear what fraction of gain comes from
opportunistic routing and what from rate control
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Evaluation of Reliable Protocols
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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
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Problem•Srcr suffers losses due to congestion•Same amount of data sent by src, different amount delivered to dst
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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
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ProblemTCP performs poorly in multihop wireless networks Solution – Practice 7
Modify COPE to use noCoCo’s congestion control/reliability
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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 “fair”comparison
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ProblemMethodology can be unfair to traditional routing
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Recommendations for more consistent and meaningful
evaluation
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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
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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
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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 routing24
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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
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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?
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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
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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
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Thank You!
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