ITU-T Recommendations

The Continua Design Guidelines (CDG) define a framework of underlying standards and criteria that are required to ensure the interoperability of devices and data used for personal connected health. They also contain design guidelines (DGs) that further clarify the underlying standards or specifications by reducing options or by adding missing features to improve interoperability.
This specification defines the additional design guidelines for the Capability exchange-enabled AHD and WAN device certified device class (CDC). The purpose of the capability exchange is to reduce the amount of information that must be pre-configured on a device in order to obtain plug and play interoperability. Specifically, capability exchange enables application hosting devices (AHDs) to know what types of messages it can send to the WAN device, by identifying its Continua CDCs. Likewise, capability exchange provides a mechanism for the AHD to inform the WAN device of its capabilities, to enable the WAN device to tailor its communication with the AHD. Capability exchange is mandatory for all WAN devices while it is optional for AHDs.
It is assumed that the AHD is pre-provisioned with a URL, or a set of URLs, denoting the service endpoint of one or more WAN devices. The capability exchange process takes place when the AHD first contacts a WAN device. It may also take place intermittently, to update the information received in the first capability exchange. In most cases, the set of Continua CDCs implemented at a WAN device changes slowly, if at all. Therefore, it is expected that the AHD can store the information about WAN capabilities, and optionally, implement a policy for periodically updating that cache. An AHD might identify several WAN devices in this way, and communicate with one or more for different purposes.
The WAN device describes the information about its supported CDCs in a file called "root file". The root file is a special resource that describes the properties of CDCs and how AHD can start information exchange with these CDCs. The root file and other features of the exchange come from an HL7 standard called hData . It not only defines the root file format, but also defines the operations for exchanging root files, using HTTP using GET and POST operations, often referred to as "REST" (for representational state transfer).
Each Continua CDC (in addition to capability exchange) will use the root file to document information relevant to that capability, including the capability name, the information that can be exchanged under the capability and its format, and URLs for REST operations, if supported by that capability. Details are given in the documentation for the respective Continua CDCs.