Findings in Reliable Bulk Data Transfer Experiments

GGB projectSukun Kim, David Culler,

James Demmel, Gregory Fenves,Steve Glaser, Shamim Pakzad

NEST MeetingMar 9, 2005

Table of Content

1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1. Larger Packet Size2. Compression

4. Conclusion

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

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

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

Table of Content

1.Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1.Larger Packet Size2.Compression

4.Conclusion

Routing

75%

80%

85%

90%

95%

100%

28 29 30 31 32Interval (ms)

Succ

ess

Rate

Mica2, 36bytes/pkt

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)

Mica2, 36bytes/pkt

Packets per second (Out of 50pkts/s)

14%

24%

0%

3%

59%

UARTRadioRoutingReliableCapacity

Mica2, 36bytes/pkt

Effect of header is considered here

Bandwidth (Out of 14400bps)

31%

19%12%

5%

33%UARTRadioRoutingReliableCapacity

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

Table of Content

1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1. Larger Packet Size2. Compression

4. Conclusion

Options for Increasing Bandwidth

• Multiple Base Station

• 802.15.4 radio

• Larger Packet Size

• Compression

Table of Content

1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1. Larger Packet Size2. Compression

4. Conclusion

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)

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

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

Sharing packet buffer

GenericComm

Routing Forward

QueuedSend

Drip

RBR Component 2

Component 1

Forward ForwardComponent 3

Actual packet buffer

BcastForward

Table of Content

1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1. Larger Packet Size2. Compression

4. Conclusion

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

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

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

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

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

Table of Content

1. Reliable Bulk Transfer2. Where Packet Time Goes?3. Increasing Bandwidth

1. Larger Packet Size2. Compression

4. Conclusion

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

Questions

For Mica2, packet size = 36 bytes

Top, Left: Packet SizeBottom, Right: pkts/sec

0 10 20 30 40

CapacityReliableRoutingGenericComm

0 20 40 60

CapacityReliableRoutingRadioUART

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