# Body Area Networks in Healthcare: A Brief State of the Art
## 5 Network Layer Components, Configuration and Middleware Layer  
As mentioned before, a BAN is a network of nodes with sensors and actuators that communicate with each other. These nodes are worn on the body and store environmental, activity and/or physiological information [15]. BAN nodes are commonly classified into two broad categories:  
* Peripheral nodes: Devices with a low processing platform. Peripheral nodes have sensors to monitor their environment and communication interfaces to transfer and receive information.
* Central nodes: Devices with enhanced processing and communication capabilities. Central nodes are in charge of gathering the information of the sensor nodes and make the data available (usually through the cloud).  
A good architecture is vital for developing wearable applications, especially for emergency and medical systems where a human life depends on a correct acquisition of information in some cases. Regarding the hardware of BAN nodes, there are multiple configurations. The IEEE 802.15 task group 6 (IEEE TG6) [51] suggests the following types of nodes:* A low-power microcontroller attached with multiple sensors that monitor the environment,
* Nodes for medical purposes,
* Devices that collect or aggregate information,
* Nodes that control the administration of medication like an infusion-pump controller,
* Devices acting like a gateway or access point.  
The selection of hardware for a BAN application depends on the requirements of the system to be developed. This is the reason why it is highly important to understand the problem at hand in order to choose the right components to build the whole system.  
As mentioned before, generally, a BAN is composed of two different nodes: (1) peripheral nodes with a low-power microcontroller, and (2) central nodes that manage the information generated by the peripheral nodes. The network topology means the arrangement of nodes in a BAN, describing the communication between nodes. There are several options to connect nodes in a BAN. The IEEE TG6 suggests three types of network topologies, as shown in Figure 2. In Figure 1(a), representing a star topology, each peripheral node has a direct connection to the central node. Another recommended topology is mesh topology, as depicted in Figure 1(b). In a mesh topology, not all peripheral nodes have a direct connection to the central node. Lastly, Figure 1(c) shows a combination of the previous topologies, which is a hybrid topology.  
In addition to the network layer configuration, the middleware layer is also relevant in order to provide an abstraction mechanism making the system able to interact with different components in an easy manner. There are some articles that tackle this issue, providing specific platforms to enable the use of diverse devices as coordinators of the body sensor network and body-side of the  
Figure 2: Body area network topologies: (**a**) star topology; (**b**) mesh topology; and (**c**) hybrid topology.  
cloud platform [52; 53], treating interoperability issues between different IoT platforms oriented to healthcare services, and performing a fusion of sensor data to the detection of emotions [54; 55]. Regarding this topic, data fusion in body sensor networks contributes with interesting articles [56]. The authors performed a survey about emotion recognition and general health articles. Finally, in another example of the use of body sensors in healthcare [57], an electrocardiogram analysis is performed to automatically detect the cardiac defence response to understand the patient's mental and health status.