Networked sub-devices

1
Networked sub-devices
MOTE Active Messages
Communication Architectures for Networked
Mini-Devices
Phil Buonadonna, Jason HillCS-268, Spring 2000
Active Messages
The Study

• 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. 2x2 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

• 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

• 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)

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