| 14 | 14 | CoAP communicates based on Representational State Transfer (REST) architecture and supports four modes of REST which are PUT, GET, POST, and DELETE. A client sends a request with any one of the four modes and the server will respond with a reply in accordance with the request. The CoAP supports two modes: reliable and non-reliable. For instance, we use the reliable mode for activating the robot and non-reliable mode for sending force data. Reliability in CoAP is handled by using Confirmable (CON) messages. For every CON message send to the server, this will be replied by Acknowledge (ACK) packages to the client. In essence, CoAP's job is to define the URI structure (a hierarchy of objects accessible by GET/POST); handle GET/POST requests; handle the ACKs for confirmable transmissions; deal with dropped, reordered, or duplicate packets. MessagePack's job is to encode/decode structured data without resorting to encoding numbers as text. |
