The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things. The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation.
CoAP is an application layer protocol that is intended for use in resource-constrained internet devices, such as WSN nodes. CoAP is designed to easily translate to HTTP for simplified integration with the web, while also meeting specialized requirements such as multicast support, very low overhead, and simplicity.
Definition of CoAP
The Constrained Application Protocol (CoAP) is a software protocol intended to be used in very simple electronics devices that allows them to communicate interactively over the Internet. It is particularly targeted for small low power sensors, switches, valves and similar components that need to be controlled or supervised remotely, through standard Internet networks.
CoAP is an Internet Engineering Task Force (IETF) standard that allows devices to communicate over the Internet. It is designed for use between devices on the same constrained network (e.g., low-power, lossy networks), between devices and general nodes on the Internet, and between devices on different constrained networks both joined by an internet.
Technical Overview of CoAP
CoAP is a client/server protocol that, like HTTP, is request/response. Unlike HTTP, CoAP messages can be multicast. CoAP messages are encoded in a binary format. The header is minimal and fixed in size (4 bytes), to make the protocol suitable for constrained devices.
CoAP uses the User Datagram Protocol (UDP) instead of the Transmission Control Protocol (TCP). This makes CoAP a lighter weight protocol because UDP does not require the devices to maintain connections to each other. This is important for devices that are battery powered and need to sleep to conserve power.
CoAP and HTTP
CoAP is not a compressed version of HTTP or a way to tunnel HTTP through firewalls. CoAP messages are not HTTP messages, and they cannot be directly mapped to HTTP. However, CoAP was designed with a similar philosophy to HTTP: CoAP features a subset of HTTP methods and return codes, and it includes an option mechanism similar to HTTP headers.
CoAP can be translated to HTTP and vice versa using a simple HTTP-CoAP proxy. This means that CoAP can be integrated into the existing architecture of the World Wide Web. CoAP devices can communicate with HTTP servers, and HTTP clients can communicate with CoAP devices.
History of CoAP
The Constrained Application Protocol (CoAP) was developed by the Constrained RESTful Environments (CoRE) working group of the Internet Engineering Task Force (IETF). The CoRE group was chartered to standardize a framework for resource-oriented applications intended to run on constrained IP networks. A constrained IP network has limited packet sizes, may exhibit a high degree of packet loss, and may have a substantial number of devices that may turn on or off at any time.
The CoRE group began work on CoAP in 2010. The protocol was designed for machine-to-machine (M2M) applications such as smart energy and building automation. CoAP is an application layer protocol that is intended for use in resource-constrained internet devices, such as WSN nodes. CoAP is designed to easily translate to HTTP for simplified integration with the web, while also meeting specialized requirements such as multicast support, very low overhead, and simplicity.
CoAP and the Internet of Things
CoAP has been widely adopted for use in the Internet of Things (IoT). The protocol is ideal for IoT applications because of its low overhead and simplicity. CoAP is used in IoT devices to allow them to communicate over the Internet. It is particularly targeted for small low power sensors, switches, valves and similar components that need to be controlled or supervised remotely, through standard Internet networks.
The Internet of Things (IoT) is a network of physical objects—devices, vehicles, appliances—and other items embedded with electronics, software, sensors, and network connectivity, which enables these objects to collect and exchange data. CoAP is a protocol that can be used to facilitate this data exchange between IoT devices.
Use Cases of CoAP
CoAP is primarily used in constrained networks, which are typically characterized by high packet error rates, low data rates, and a high latency. These networks are often used in machine-to-machine (M2M) communication and the Internet of Things (IoT). Examples of constrained networks include wireless sensor networks, building automation, and smart grid networks.
One of the main use cases of CoAP is in building automation systems. In these systems, CoAP is used to communicate between devices such as sensors, actuators, and controllers. These devices often need to communicate over a constrained network, and CoAP provides a lightweight and efficient protocol for this communication.
CoAP in Smart Grid Networks
In smart grid networks, CoAP is used to communicate between devices such as smart meters and energy management systems. These devices need to communicate over a constrained network, and CoAP provides a lightweight and efficient protocol for this communication. CoAP allows these devices to communicate in a reliable and secure manner, despite the constraints of the network.
CoAP is also used in smart grid networks to facilitate demand response. Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. CoAP can be used to send demand response signals from the utility to the customer, allowing the customer to adjust their power consumption accordingly.
CoAP in Wireless Sensor Networks
In wireless sensor networks, CoAP is used to communicate between sensors and the network gateway. These sensors often need to communicate over a constrained network, and CoAP provides a lightweight and efficient protocol for this communication. CoAP allows these sensors to communicate in a reliable and secure manner, despite the constraints of the network.
CoAP is also used in wireless sensor networks to facilitate data collection. The sensors in these networks collect data about the environment, such as temperature, humidity, and light levels. CoAP can be used to send this data from the sensors to the network gateway, where it can be processed and analyzed.
Examples of CoAP
One specific example of CoAP in use is in the Philips Hue lighting system. The Philips Hue system uses CoAP to communicate between the lighting devices and the Hue Bridge, which is the device that connects the lights to the user's home network. The Hue Bridge uses CoAP to send commands to the lights, such as turning them on or off, changing their color, or adjusting their brightness.
Another specific example of CoAP in use is in the Nest thermostat. The Nest thermostat uses CoAP to communicate with the Nest Cloud, which is the service that allows users to control their thermostat remotely. The Nest Cloud uses CoAP to send commands to the thermostat, such as changing the temperature or adjusting the schedule.
CoAP in Philips Hue Lighting System
The Philips Hue lighting system is a smart lighting system that allows users to control their lights remotely using a smartphone app. The system uses CoAP to communicate between the lighting devices and the Hue Bridge. The Hue Bridge sends commands to the lights using CoAP, such as turning them on or off, changing their color, or adjusting their brightness.
The Hue Bridge also uses CoAP to receive status updates from the lights. The lights send status updates to the Hue Bridge using CoAP, such as their current state (on or off), their current color, and their current brightness. This allows the Hue Bridge to keep the smartphone app up to date with the current state of the lights.
CoAP in Nest Thermostat
The Nest thermostat is a smart thermostat that allows users to control their home's heating and cooling remotely using a smartphone app. The thermostat uses CoAP to communicate with the Nest Cloud. The Nest Cloud sends commands to the thermostat using CoAP, such as changing the temperature or adjusting the schedule.
The Nest thermostat also uses CoAP to send status updates to the Nest Cloud. The thermostat sends status updates to the Nest Cloud using CoAP, such as the current temperature, the current schedule, and the current energy usage. This allows the Nest Cloud to keep the smartphone app up to date with the current state of the thermostat.