Networked sub-devices

1. Networked sub-devices MOTE Active Messages Communication Architectures for Networked Mini-Devices Phil Buonadonna, Jason HillCS-268, Spring 2000 The Study Active Messages • Paradigm for efficient overlap of computation and communication • Centered on lightweight RPC mechanism • 2-phase request-reply model • Credit based flow control • Implement and investigate an Active Messages based communication abstraction for a wireless network of “sub-devices”. • The Problem: • Limited computational ability & energy supply • Complex, dynamic network paths with potentially high fanout • Lossy wireless communications • What is a sub-device? • Small (I.e. 2”x2” and smaller) • Onboard processor and communication device (e.g IR, Radio) • Self-contained power source (e.g. Battery, Solar) • Mote (‘mOt) noun : a small particle • A sub-device with attached sensor(s). Autonomous Sensor Node. • Mote Active Messages • One endpoint per mote. One endpoint for host. • Binary credit scheme (single host request credit) • Ensures no overload of Mote resources • Allows trivial retransmission scheme (assuming idempotency) • We assume a collision resistant MAC layer • Message Handlers: • Mote handlers can initiate/propagate further requests depending on the applications needs. • Handler names are static and globally unique. Two special handlers: • Handler 0: A routing handler • Handler 255: Lists installed handlers • Mote handlers invoked through events, not polling • Dispatch routines generated at compile time • Active Messages defines the OS architecture for the Mote Active Message Model • We leverage aspects of the Active Messages model to address these problems • Good small message performance • Natural paradigm for requesting sensor data • Minimizes memory resources required • We demonstrate • A mote and host based library • A handler software design methodology based on events • A simple routing methodology • 78 msec RTT (mote-mote), ~800 B/sec throughput The weC Mote General Mote Architecture • The weC Mote • ATMEL 8535 Microcontroller (4Mhz, 512B SRAM, 8KB Flash) • Communication: RF (916.5 MHz), 10Kbps raw • Sensors: Light, Temperature • Features: Wireless reprogramming, 3 LEDs Using the AM model Analysis Sample Application & Future Work • Routing • First 9 bytes of message are used to implement a source based route path. • First 2 bytes are ALWAYS a Destination/Handler pair (R0/ H0) • Handler 0 forwards to the next hop. Will insert the destination handler (Hf) ID on the last hop (N = 1) • Routing information is preserved so that replies can be sent along the same path to the requestor (S) Round Trip Time • Route discovery application: • Nearest neighbor with a single, static root (the base station mote) • Each mote broadcasts a beacon every 1 second • Neighbor mote responds if it knows how to get to base station • Beacons propagate to base-station/host RTT breakdown RTT vs. # of Hops • Throughput • ~800 Bytes/sec (~6.5 Kbps) w/ 4b6 encoding • Software Footprint • Power consumption (sleep & idle states) • Event Model • Supports high conncurrency w/ minimal buffer requirements • Prevents multiple & deep stacks • Drawbacks • Its not IP! Screen Shot of Routing Application The AM Mote Message • Host Communication • PC Host has a reserved address (0x7e) • Can connect to any mote in the ‘school’ through an onboard connector. Mote connected to a host is the ‘base station’ mote. • Future Work • Layer AM over different MAC layers • Dynamic uploading of handler functions. • Comparison with other communication models • Examination of other routing schemes • Broadcast • Motes & Host can send broadcast messages through an endpoint using a reserved destination address (255) • Broadcast requests do not invoke credit scheme. • Permits a method of route discovery