Networkcentric approach for tiny devices

1
Network-centric approach for tiny devices

• Distributed
• Dynamic
• Adaptive
• Critically resource constrained
• Communication centric for providing concurrency

2
Characteristics of these tiny devices

• Restoration of energy reserves by tapping into
  local energy resources
• Photovoltaic cells
• Telephone lines
• Perform multihop routing network
• Huge application space
• Disaster management
• Ubiquitous computing environments

3
Developments which it led to

• RF wireless sensor devices
• Tiny Operating System
• The hardware developed out of Macromote

4
Tiny OS

• It is component based.
• To maintain concurrency in a storage and energy
  limited context.
• Robustness is essential.
• Lean communication stack
• Non-blocking discipline

5
Challenges in TinyOS

• Highly constrined resources
• Application specific
• Uncertainty over the abstraction of layers

6
Tiny OS Applications

• It consists of a scheduler and a graph of
  components.
• Component described by
• Interface
• Internal implementation
• Interface has
• synchronous commands
• asynchronous events
• .

7
Tiny OS Applications

• Each component has
• lower interface
• upper interface.
• The storage in a component is done by a frame and
  the concurrency is done by tasks.
• Concurrency model is a two-level scheduling
  hierarchy.
• Events pre-empt tasks
• Tasks do not pre-empt other tasks

8
Application level communication challenges

• Tiny Active Messages
• Managing Packet Buffers
• Network Discovery and ad hoc Routing

9
Tiny Active Messages

• Paradigm of message based communication
• Used in parallel and distributed computing
• Limited buffer space which leads to the refusal
  of many message requests.

10
Managing Packet Buffers

• There are three issues
• 1. Encapsulating useful data with trailers and
  headers
• 2. Determining when output message data storage
  can be reused.
• 3. Providing an input buffer for incoming
  messages.

11
Functioning of packet buffers

• Only the reference to the message buffer is
  provided by the Active message component.
• Send command
• Transmit buffer
• Considered owned by the network
• Released when the transmission is complete

12
More functions

• The receiving end
• It gets a pointer to the system owned buffer
• Processes the information
• Returns the buffer.

13
Network Discovery and ad hoc Routing

• It is used in supporting dynamic network and
  multihop ad hoc routing
• Forms a breadth first spanning tree.
• Routing is done in the tree by forwarding the
  packets to the nodes parent using a buffer swap.
• The discovery algorithm is non-optimal
• Could be eliminated using piggybacking.

14
Lower level communication challenges

• Crossing layers without buffering
• Listening at low power
• Physical layer interface
• Media access and transmission rate control

15
Crossing layers without buffering

• It is done using cross layer data pump
• Data is partitioned into sub units
• Packet layer pumps it byte-by-byte into the byte
  layer
• Byte layer pumps the data bit-by-bit into the
  radio.

16
Listening at low power

• Active transmission is the most power intensive
• Substantial energy is wasted when the radio is on
  and is doing nothing.
• Ways to save energy loss
• Periodic listening
• Low power listening

17
Periodic listening

• It gives the time slots for listening 10 sec out
  of 100 sec window.
• Reduces the network bandwidth by the same amount
• Eg-90

18
Low power listening

• In this method the time scale is reduced to 30us
  out of 300us window.
• Doesnt decrease the channel capacity
• One precautionary measure
• To spend extra energy to see that the receiver
  has its radio on.

19
Physical layer interface

• Component stack that maintains bit timing
• Bit-by-bit transfer from a byte level component
  to the physical layer.
• Transmission requires two commands
• To tell RFM that it is in the transmit mode
• To transfer a single bit down to RFM components

20
More issues

• Complex encoding must be done on each byte
• Data is encoded one byte in advance of
  transmission
• For this we use buffering

21
Media access and transmission rate control

• It has a shared channel
• Added with MAC protocol
• Uses CSMA technique
• Also uses Adaptive transmission control scheme