Overview#Constrained Networks is defined in RFC 7228 as a network where some of the characteristics pretty much taken for granted with link layers in common use in the Internet at the time of writing are not attainable.
Constraints may include:
- low achievable bitrate/throughput (including limits on duty cycle),
- high packet loss and high variability of packet loss (delivery rate),
- highly asymmetric link characteristics,
- severe penalties for using larger packets (e.g., high packet loss due to link-layer fragmentation),
- limits on reachability over time (a substantial number of devices may power off at any point in time but periodically "wake up" and can communicate for brief periods of time), and
- lack of (or severe constraints on) advanced services such as IP multicast.
More generally, we speak of constrained networks whenever at least some of the nodes involved in the network exhibit these characteristics.
Again, there may be several reasons for this:
- cost constraints on the network,
- constraints posed by the nodes (for Constrained-Node Networks),
- physical constraints (e.g., power constraints, environmental constraints, media constraints such as underwater operation, limited spectrum for very high density, electromagnetic compatibility),
- Regulatory compliance constraints, such as very limited spectrum availability (including limits on effective radiated power and duty cycle) or explosion safety
- technology constraints, such as older and lower-speed technologies that are still operational and may need to stay in use for some more time.