### Methods of Connection  
Taking advantage of new continuous biometric sensors will create a technological structure in the patient that will generate a huge amount of data. Initially, it has to be ensured that the systems have enough compatibility between clinical devices, platform management, and computerized records in medical institutions in order to promote the sharing of data. This interoperability includes biosensors, which have to be ready to send collected data in an understandable way. In this sense, an accepted criterion is Health Level 7 (HL7) [26], which is the most important standard for the transfer of clinical and administrative data between software applications used by various healthcare providers. It defines a method of moving clinical data between independent medical applications in near real time.  
Initially, some approaches like Mobile Access to Health Information (MAHI) [27] introduced interaction between diabetic patients and medical staff through a phone connected by Bluetooth to a glucometer. Unfortunately, asynchronous communications meant that it was impossible to generate advice and warnings in real time.  
Managing data is a distinctive issue in Wireless Sensor Networks, where the main feature is the mobility of the source of the information [28]. Low-power body area networks can be a solution, because of their low power consumption and their mobility features. Today, these wireless communications can be hosted on smartphones, namely Bluetooth Low Energy (BLE), as well as Near Field Communication (NFC) or WiFi. An example can be health monitoring of patients in their bedrooms [29].  
As described above, several types of new sensors have burst onto the technological landscape, and this means there is a broad range of different communications requirements in the IoT environment. Therefore, the chosen method of transmitting data must allow for high continuous data transmission, low consumption, high payload size, and sufficient bandwidth. To achieve this, some approaches have been followed previously. The problem of energy saving in a heath monitoring system with smartphones is studied in [30]. Taking advantage of Zigbee and Bluetooth communications, low wastage of energy is achieved. However, such work is not focused on any disease in particular, and the study of forecasted situations is omitted. ZigBee and Bluetooth have been implemented successfully in low-power wireless body area networks with discrete sensors, such as blood pressure monitors and weighing scales [31]. Others with greater complexity like pulse oximeters or electrocardiograms have been simplified by reducing the sample frequency [32]. Recently, NFC has been proven as a proper choice to monitor glycemia in the successful device Abbot Freestyle Libre, a flash blood glucose monitoring system with a popularity constantly raising in the past two years [19].  
To provide inter-operability between devices, Continua Alliance (C.A.) has defined proper communications protocols, like the Bluetooth Health Device Profile (HDP), which ensures a reliable and secure way to transmit information. This ecosystem uses IEEE 1073 standards to define their protocols and create compatibility [33]. Although these standards have also been described by C.A. for ZigBee, some medical sensors are not still developed, such as electrocardiograms (ECG), due to their complexity. Notwithstanding, important researches have successfully taken place by using a 6 LoWPAN approach [34] as well as NFC [35]. In any case, these three methods (Bluetooth, ZigBee, NFC) provide a convenient IoT environment, which will be described later.