## 4 Discussion  
In the field of WHMS the design of the communications infrastructure is a critical point. An extensive study on such systems has been done for the preparation of this paper in which different communications architectural solutions and communications technologies have been analyzed. As a result some basic WHMS design guidelines can be drawn. Figure 13: Real-time ECG. Regarding the communications architecture, as it has been previously shown it can be divided into different network segments, namely BAN, PAN/AN and WAN/Backhaul (Figure 1). Despite every system implements its own solution in this sense, they all have in common the presence of at least a BAN segment. According to this and depending on the concrete \"Ubiquity level\", advices on the additional necessary network segments can be given:  
* \"Self-Monitoring\" systems may probably require a PAN network segment to provide connectivity with a data processing device that is not part of the BAN, as in LifeGuard [22]. Despite this such segment might not be necessary, like in HealthGear [28]. * \"Controlled Area\" type systems communications architecture may also need the addition of a PAN network segment to the BAN segment in order to expand the coverage area. An example of this is MASN [38]. Again this segment might not be necessary, as in [PERSON] _et al._[50]. * \"Wide Area\" systems compulsory require a WAN/Backhaul network segment to allow for the remote monitoring. All the analyzed systems belonging to this category implement it. From the communications architecture point of view, systems which ubiquity level corresponds to both the \"Wide Area\" and the \"Self Monitoring\" are equivalent to \"Wide Area\" systems. Additional network segments can be necessary in any of the \"Ubiquity level\" types of system depending on the specific functionalities of the concrete application. An example of this is the study case of the present paper. In the LOBIN [44] system a WAN/Backhaul segment is added in order to allow for remote access to the data base through the Internet. A study on the communications technologies that can be used in each type of network segment has also been performed. The following discussion analyzes how traffic density and delivery frequency system properties make some technologies more appropriate than others. * Projects which sources generate little traffic, like [PERSON] _et al._[50] and [PERSON] _et al._[49] or low delivery frequencies (order of seconds or minutes), can afford the use of technologies providing lower bandwidth that allow for lesser energy consumption in the BAN and PAN network segments, without incurring in packet losses. Such technologies are MICS, ANT, IEEE 802.15.4/Zigbee and some proprietary communication technologies in the ISM band. Despite this, some other projects with low traffic pattern use more popular technologies that involve higher power consumptions, such as Wi-Fi (IEEE 802.11) and Bluetooth, for monetary or technology compatibility reasons. * Projects with information sources generating a higher amount of traffic, such as AUBADE [31] or LifeGuard [22], or with higher delivery frequencies, like Mithril LiveNet [17,18] (order of miliseconds) require communication technologies with a higher bandwidth and therefore higher energy consumption in the BAN or PAN/AN network segments. The communication technologies most commonly used in such systems are Bluetooth, Wi-Fi (IEEE 802.11) and wired technologies. * There are also systems, like LOBIN [44], CodeBlue [25] and MASN [38] that, despite handling a high level of traffic, rely in IEEE 802.15.4/Zigbee in order to optimize energy consumption and decrease the size of the batteries and therefore the size of the wearable devices. These projects assume the loss of a small percentage of packets and compensate the bandwidth restrictions of the IEEE 802.15.4 technology with a careful design of several communication protocols.