Findings in Reliable Bulk Data Transfer Experiments GGB project Sukun Kim, David Culler, James Demmel, Gregory Fenves, Steve Glaser, Shamim Pakzad NEST Meeting Mar 9, 2005

Table of Content 1.Reliable Bulk Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.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 Read Request, Set Timer Receive / count = 0 More in Round count < threshold Yes No Yes / ++count No / FAIL No / SUCCESS Timeout

Test Result 95.6% 560B/s 96.6% 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 Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.Compression 4.Conclusion

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

Effect of header is considered here

Mica2, 36bytes/pkt

Table of Content 1.Reliable Bulk Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.Compression 4.Conclusion

Options for Increasing Bandwidth Multiple Base Station radio Larger Packet Size Compression

Table of Content 1.Reliable Bulk Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.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 RBRComponent 2 Component 1 Forward *There is mismatch between incoming speed and outgoing speed of packets Not to drop packet, forward buffer is needed for each component Each end component using network has at least 1 buffer – 2 or more if we don’t want to wait Component 3 Queue of pointers Bcast Forward

Sharing packet buffer GenericComm Routing Forward QueuedSend Drip RBRComponent 2 Component 1 Forward Component 3 Actual packet buffer Bcast Forward

Table of Content 1.Reliable Bulk Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.Compression 4.Conclusion

Run Length Encoding (RLE) 94720, 94704, 94715, becomes , 04, 15, 08 Exception –94720, 94704, 92345, becomes – , 04, \92345, 08 Run simulation on footbridge vibration data Fragment Size: 4 Threshold: 2

High Resolution Footbridge data

Low Resolution Footbridge data

Analysis High ResolutionLow Resolution RLE66%45% gzip *68%49% Theory56.25% (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 Similar  Compress Random garbage  Drop

Table of Content 1.Reliable Bulk Transfer 2.Where Packet Time Goes? 3.Increasing Bandwidth 1.Larger Packet Size 2.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 Size Bottom, Right: pkts/sec

Test Result 99.0% % % % % % 49.0 * End-to-end Connection Quality Effective Bandwidth (Byte/s) 2KB of data –143 packets Mica2dot