- Large number of heterogeneous devices
- Spread physically
- Ability to join and leave
- Process data in-network or send directly

# Challenges
- Fault tolerance
	- Nodes can
		- Get damaged
		- Run out of power
		- Lose comms
	- Redundant deployment
- Lifetime
	- Limited energy supply
	- Replacing sometimes not practical
		- Underwater
		- Large/remote field deployments
	- Energy efficient a necessity
- Scalability
	- WSM can have lots of nodes
	- Architectures and protocols need to scale
- Densities
	- Density of network can vary
		- Granularity
		- Coverage
	- Different applications warrant different numbers
		- Range of nodes
		- Space and time requirement
	- Not necessarily homogenous density throughout
		- Need to handle this
- Programmability
	- Flexible nodes with changing tasks
	- Changeable programs during operation
- Maintainability
	- WSN and environment can change
	- Adaptable system
	- Changing operational parameters
		- To increase energy efficiency for example

# Node Types
- Sensor
	- Low power
	- Sensing, memory, processor, radio
	- Resource-constrained
- Sink
	- Another sensor node
		- Or different wireless node
	- Normally more powerful/better resources
- Gateway
	- Bridge IoT and internet networks
	- More powerful
	- Can have
		- Service representation
		- Cache/storage
		- Discovery

# Application Types
- Event detection
	- Reporting event occurrences
	- Reporting abnormalities
	- May need collaboration with other nodes
	- Defining events and classification difficult
- Periodic measurements
	- Sense something and report
	- Period is application-dependent
- Approximation and pattern detection
	- Sense messages in space and time
	- E.g. combine wind, light, heat to detect forest fires
- Tracking
	- Source of event is mobile
	- Event updates with location information