Guidelines Evolution and Reference Architecture.

By exploiting existing industry standards to have interoperable building blocks, Continua is providing guidelines and certifications that will allow multiple vendors to reduce differentiation and cut market costs. The publication of the Continua Health Alliance Version 1.0 Design Guidelines was announced in 2007, and was modeled primarily on connectivity standards. After the announcement, it took almost two years and the collaboration of more than 175 member companies to release the official Version 1 Design Guidelines in February 2009. The First Version Guideline was a major milestone since it was based on the specifications and standards that Continua selected following on their interoperability vision. In order to achieve the required interoperability, also further requirements and constraints were specified in this version, making possible the reduction of the available choices in the underlying standard: this was done by adding some specifications not mentioned previously. The function of these guidelines is primarily to give a design specification tool for companies than intend to certify their devices with the Continua logo. The Version 1.0 Design Guidelines deals with the interfaces necessary for realizing the entire eHealth process, starting from collecting health data to the accumulation of information on the databases of healthcare structures. Since Continua only focuses on interoperability and does not suggest any specification, the interest for Continua’s guidelines is based on the definition of the interfaces essential for connecting between different components of a personal eHealth system, thus, LAN, PAN, WAN, and the electronic or personal health record network xHRN.
These Interfaces are the principal elements to be considered for interoperability goals, and form the basis of Continua Certification process.
The interfaces considered for the Version 1.0 were the PAN Interface (Personal Area Network) between PAN devices and AHD (Application Hosting Devices), and the xHRN Interface (Health Record Network) between WAN (Wide Area Network) devices and health record devices to export medical personal data. The Continua Reference Architecture including the connections and interfaces to be tested in Version 1.0 are shown in the following figure:

Continua Reference Architecture and V1 interfaces to be tested

The Continua End-to-End (E2E) Architecture gives a clear overview of the general distributed-systems structure, highlighting possible topology constraints. The structure is based on five device classes and four network interfaces that are the the principal elements to investigate for interoperability. The network interfaces are subject of certification and testing processes and are responsible of connecting the devices to a reference topology. In order to have a better understanding of  the possible selected standards and interfaces, it is necessary to analyze first the Continua Reference Architecture.
The Peripheral Area Network Interface (PAN) describes the connection between PAN devices such as sensors (for example a heart-rate monitor) or actuators( for example an output text) and an application hosting device (AHD) , such as a mobile phones, tablets , PC. Continua has developed standards for the two layers of the PAN interface; for the lower layers or transport level component comprising the open-systems interconnection layers 1-4, Continua has selected the Bluetooth Health Device Profile for a Wireless communication and USB for wired communications. In the above level is the data level or upper-layer component comprising the classic OSI layers 5-7, for which Continua has selected to use the ISO/IEEE 11073-20601 Optimized Exchange Protocol to enable data exchange and interoperability.
The Local Area Network (LAN) is the Interface between a LAN device and an application hosting device. This device has a proxy function, thus collects and shares the PAN devices information. If we consider a Lan device it is important to underline that it can be seen both as a sensor or as and actuator; this has the direct consequence that the LAN interface upper layers and the PAN interface upper layers can maintain the same data model, the ISO/IEEE 11073-20601 model. The fact to have the same data model in the upper layers of the both PAN and Lan Interfaces is very important for assuring the required interoperability feature.
The Wide Area Networ (WAN) is the Interface between a variety of WAN devices and an application-hosting device. The function of a WAN device is to collect the information, thus acting as a managed-network-based service. The upper layers have a device data model compatible with the LAN Interface data model, thus to make sure an interoperable and exchangeable data model.
Untill this point we have analyzed Interfaces where the data exchange is made possible between an application hosting device and a Continua’s device. The Electronic and Personal Health Records Network (xHRN) is the connection between WAN devices and electronic or personal health records. Typically a xHRN interface is necessary for creating the connection between different companies offering a sevice such as weight loss or chronic disease management for example, and the electronic health records which traditionally come from the healthcare provider domain, such as a hospital where the doctor has all the available electronic data for keeping track of their patients. The Personal Health Records platforms (PHR) such as Google Health and Microsoft HealthValut, allow a patient to access and store their own health data and have control of their data. The merit of the xHRN Interface is to allow data exchange between electronic health records and personal health records promoting in this way data sharing between different parts of the process. For making possible a communication between WAN devices and xHR systems Continua selected the Integrating the Healthcare (IHE) and Cross-Enterprise Document Reliable Interchange (XDR) profile. For having a reliable data encoding the Health Level 7 (HL7) and the Personal Monitoring (PHM) document formats were adopted.

In its Version1.0 Guidelines, Continua selected to focus in two specific interfaces, namely the Personal Area Network (PAN) interface and Electronic or Personal Health Record Network (xHRN) interface. The decision to focus on the PAN and xHRN interfaces was taken by Continua, considering which were the highest priority interfaces to work on, and also considering the necessity to show visible results in a limited amount of time. Based on the interoperability goal, for its Version 1.0 several standards in the PAN interface have been selected and then constrained to meet Continua Guidelines for certification. In addition, the PAN interface for devices was focused on wireless protocols that need to be energy or battery efficient. In the seek of interoperability in the Version 1.0 several standards in the PAN and device data exchange have been developed. In this version of particular note is the expansion of IEEE 11073 which is supposed to have a prescriptive approach which ensures that devices from different manufacturers can be used by the same application. Precisely Continua prescribes in the Version1 eight PAN devices  as it is shown in the following figure:

Overview of Continua Interface Standards
Source: Continua Health Alliance

In addition to the currently released Design Guidelines are even more oriented towards interoperability and data sharing since they also incorporate Wide Area Network (WAN) interface to link a hub device or health appliance with servers. Continua selected ZigBee and Bluetooth Low Energy (BLE) for the updated Design Guidelines. The choice to select ZigBee wireless technology as a Continua’s low power local area network (LAN) standard was due to the fact that this wireless protocol works efficiently for multiple sensing and controlling in a variety of settings both professional and familiar offering secure wireless connectivity and it coexists with other wireless technologies.
The recent Version 2011 of Design Guidelines “Adrenaline” were made freely available to the public just recently during April 2012, in order to promote creativity and integration among systems developers. In the 2010 and 2011 Design Guidelines, the standards used for transporting data were Zigbee, Bluetooth, Bluetooth Low Energy and USB : let’s see now the reasons that led to the selection of some standards and if in the newest Version the standardization process has evolved by selecting new technology.