Flyspec – a network for silicon fly sensors

1. Flyspec – a network for silicon fly sensors David L. Mills University of Delaware http://www.eecis.udel.edu/~mills mailto:mills@udel.edu

2. Assumptions • Designed for ultra-simple ad-hoc sensor nets with short range burst radios • Simple undisciplined ALOHA medium access without carrier sense or backoff. • Transmissions consist of omnidirectional bursts with limited range. • Entities are of two types • End nodes (sources and sinks) • Intermediate nodes (repeaters) • All nodes must be able to transmit, some sources might not be able to receive. • There is no routing table, no routing algorithm and no congestion control. • Routing principles are based on dynamic reverse-path forwarding.

3. Routing principles • Basic routing principle is to determine when a burst for a designated sink is received, should it be repeated or not. • Sources and sinks are assigned distinct IDs; repeaters have no IDs. • Every burst sent carries the source ID, sink ID, sequence number, which increments for each burst, and hop count, which is initialized at zero and increments at each repeater. • When a burst is received, buffer it and initialize a counter, which then decrements at a fixed rate. • If the counter value falls below a specified threshold, increment the hop count and repeat the burst. • If a burst is received with the same source ID, sink ID, sequence number and • greater than the hop count, purge the buffer. • equal or less than the hop count, ignore the burst.

4. Minding the thresholds • The basic idea is to delay an appropriate time to allow some other node closer to the destination to repeat a burst without wasting bandwidth for multiple transmissions. • Each repeater has a list of recently heard burst source and sink IDs, together with hop count and threshold. Initially, the threshold is set depending on the hop count from the source. • The threshold degrades slowly so to allow reconfiguration should a repeater be lost. • If a packet is received with destination ID not on the list, the threshold is set relatively low. • The repeater will hold on to the burst waiting a relatively long time to give other repeaters with knowledge time to transmit first. • A nearby repeater with knowledge will repeat it at greater hop count, which will kill the buffer.

5. Questions • We must assume bursts flow both ways between source and sink in order to learn the reverse path. So, sinks might run a low-level whisper campaign to the sources. • When the network launches, repeaters don’t know anything, so bursts will random-walk until finding sinks, all the time leaving a trails behind where they have been. • Is this thing stable? Dies it eventually converge to shortest paths? • What are the failure/recovery dynamics? Does it scale?