1. Unlocking the demo…. Jason Hill

2. Data Aggregation  Reduce network bandwidth requirements by aggregating data close to the source.  Two types aggregation: –Strongest magnetometer data –Shortest time-of-flight distance measurements  High value data transported to base station

3. Aggregation Protocol  All nodes announce to their neighbors strong sensor readings  All nodes collect local readings  “Leader” is chosen as the node with the highest quality data  “Leader” is responsible for sending a collection of the best readings to base stations

4. Data Transport  Aggregation results in high value data –Packet loss becomes significant  Aggregated data must be send over a reliable transport mechanism  Added: –Per link acknowledgements –REL_DEL geographic based reliable delivery mechanism

5. Reliable Transport  X, Y grid of nodes  Up to 6 retransmissions  First try last parent 3 times  Then try other neighbors  Base station at (0,0)

6. Per-link Acknowledgements  Packets sent to TOS_BCAST or TOS_LOCAL_ADDRSS automatically acknowledged  TOS_MsgPtr->ack set to 1 when returned in MSG_SEND_DONE event  Acknowledgement signals packet received and passed CRC by at least 1 node.

7. Acknowledgement Costs  Acknowledgement immediately follows signal strength pulse. Start Symbol Preamble 4-byte Header Length Field Data Payload CRC Strength Pulse Phase Shift ACK

8. Breakdown of Time  30-byte packet (1/40 th of a second)

9. System Buffering  Reliable delivery required in-network buffering  REL_DEL networking layer provides multi- hop reliability  Up to 16 local messages and 16 transient messages can be stored –Local node can have 16 “sends” pending  Local messages serviced first (use MSG_REL_SEND_MSG)

10. Other networking pieces…  All packets acknowledged upon reception  Variable length packets added to improve bandwidth utilization  CRC calculation performed in parallel with transmission and data encoding –CRC calculation must be completed in time for acknowledgement  Signal strength detection added to high-speed stack  All packets have CRC field (1 == passed CRC check, 0 == failed)