Findings in Reliable Bulk Data Transfer Experiments
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Findings in Reliable Bulk Data Transfer Experiments
GGB projectSukun Kim, David Culler,
James Demmel, Gregory Fenves,Steve Glaser, Shamim Pakzad
NEST MeetingMar 9, 2005
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Table of Content
1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1. Larger Packet Size2. Compression
4. Conclusion
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State Diagram of Sender
More
Start
Request / Set Timer
Yes / Read
Timer Fired /Send
No / Stop Timer
• Simple (intelligence in receiver)
• Interface is simple– read(start, size, *buffer)
• Send everything once, and fill holes
• Read depth in routing tree, and adjust shooting speed, RTT estimate, etc
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State Diagram of Receiver
Start
More
Send Network-Info Request
Receive / Send Transfer Request, Set Timer
Receive & Last || Timeout / count = 0
Timeout / FAIL
Receive & not Last / Set Timer
Yes / Send ReadRequest, Set Timer
Receive / count = 0
More in Round
count < threshold
Yes
No
Yes /++count
No /FAIL
No / SUCCESS
Timeout
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Test Result
95.6%560B/s96.6%
576B/s
91.4%296B/s
91.8%304B/s
93.2%299B/s
* End-to-end Raw Reliability Effective Bandwidth (Byte/s)
• 10KB of data– 500 packets
• Mica2dot, 36 bytes/pkt
• Max in theory– 630B/s for 1 hop
• Up to 91.4% efficiency
– 352B/s for 2 hops• Up to 86.4% efficiency
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Table of Content
1.Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1.Larger Packet Size2.Compression
4.Conclusion
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Routing
75%
80%
85%
90%
95%
100%
28 29 30 31 32Interval (ms)
Succ
ess
Rate
Mica2, 36bytes/pkt
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For Mica2, packet size = 36 bytes
• Channel capacity– UART: 57.6Kbps = 200pkts/s– Radio: 19.2Kbps = 66.7pkts/s– 1 hop: 50pkts/s
• Usable capacity– UART: 120pkts/s– Radio: 42pkts/s– Routing: 31pkts/s (1 hop)– Reliable: 29.4pkts/s (1 hop)
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Mica2, 36bytes/pkt
Packets per second (Out of 50pkts/s)
14%
24%
0%
3%
59%
UARTRadioRoutingReliableCapacity
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Mica2, 36bytes/pkt
Effect of header is considered here
Bandwidth (Out of 14400bps)
31%
19%12%
5%
33%UARTRadioRoutingReliableCapacity
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Mica2, 36bytes/pkt
Packet Time (for 1bit)
8%
25%
5%
14%13%
0%
21%
5%9% UART Channel
Radio ChannelUART OverheadRadio OverheadGenericComm HeaderRouting OverheadRouting HeaderReliable OverheadReliable Header
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Table of Content
1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1. Larger Packet Size2. Compression
4. Conclusion
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Options for Increasing Bandwidth
• Multiple Base Station
• 802.15.4 radio
• Larger Packet Size
• Compression
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Table of Content
1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1. Larger Packet Size2. Compression
4. Conclusion
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Effect on Bandwidth
• Doubled packet size: 36B 72B
• Payload: 20B 56B (2.8 times)
• Packets/sec: 29.4 20.9 (71%)
• Bandwidth doubled: 588B/s 1172B/s (1.99 times)
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RAM space
• From 3437 to 4733– 36Bytes RAM increase per 1Byte increase in packet
size• Reason – Packet buffer space
– 4 below GenericComm– 3 in TimeSync– 16 in Routing– 4 in Bcast– 2 + 5 in Reliable– 2 in application
• Basic services (Comm + TimeSync + Routing + Bcast + Reliable) can go beyond 4KB RAM with packet size = 72Bytes
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Why so much RAM(packet buffer)?
GenericComm
Routing Forward
QueuedSend
Drip
RBR Component 2
Component 1
Forward Forward
*There is mismatch between incoming speed and outgoing speed of packetsNot to drop packet, forward buffer is needed for each componentEach end component using network has at least 1 buffer – 2 or more if we don’t want to wait
Component 3
Queue of pointers
BcastForward
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Sharing packet buffer
GenericComm
Routing Forward
QueuedSend
Drip
RBR Component 2
Component 1
Forward ForwardComponent 3
Actual packet buffer
BcastForward
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Table of Content
1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1. Larger Packet Size2. Compression
4. Conclusion
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Run Length Encoding (RLE)
• 94720, 94704, 94715, 94708 becomes 947 + 20, 04, 15, 08
• Exception– 94720, 94704, 92345, 94708 becomes– 947 + 20, 04, \92345, 08
• Run simulation on footbridge vibration data
Fragment Size: 4
Threshold: 2
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
5
40
3200
20
40
60
80
100
120
140
160
Threshold
Fragment Size
Compression Ratio
High ResolutionFootbridge data
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
5
40
3200
20
40
60
80
100
120
140
Threshold
Fragment Size
Compression Ratio
Low ResolutionFootbridge data
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Analysis
High Resolution Low Resolution
RLE 66% 45%
gzip * 68% 49%
Theory 56.25%
(9 random bits)
37.5%(6 random bits)
• Basic algorithm of gzip utilizes repetition of same pattern
• Algorithm of RLE fits better to sensor data
* Windows zip showed 0.64% increase
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Analysis (continued)
• There exists room for lossless or lossy compression
• Compression ratio is sensitive to parameters (even go above 100%)
• Selecting RLE parameter (either statically or dynamically) is critical
33789679201Similar
CompressRandom garbage Drop
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Table of Content
1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth
1. Larger Packet Size2. Compression
4. Conclusion
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Conclusion
• Reliable Bulk Transfer– 5.2% decrease in packet throughput– 13.8% decrease in bandwidth
• Packet is small compared to the size of header, so doubling packet size doubles bandwidth– RAM limit due to many packet buffers
• RLE decreases the size of vibration data by 45%, and will be applicable to other sensor data
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Questions
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For Mica2, packet size = 36 bytes
Top, Left: Packet SizeBottom, Right: pkts/sec
0 10 20 30 40
CapacityReliableRoutingGenericComm
0 20 40 60
CapacityReliableRoutingRadioUART
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Test Result
99.0%80.699.0%
73.2
96.6%40.0
97.7%41.5
96.3%35.0
98.5%49.0
* End-to-end Connection Quality Effective Bandwidth (Byte/s)
• 2KB of data– 143 packets
• Mica2dot