# An Architecture for Reliable Transportation of Delicate Goods
## 4 The Main Scenario
### The Monitoring Device
* Type B--the advertise mode is activated by pressing a button and the device stays on that mode for a limited time. The devices can be placed differently when accompanying the merchandises, translating into different network topologies and operational modes. The choice of topology may be dictated by power limitations, like the autonomy of the devices, or operational constrains, as explained below. Figure 3 shows the common usage scenarios for each topology. On topology (a) there is a single device of type A, placed inside the packaging, working in a continuous advertise mode. This is suitable for the transport of individual goods, with a reduced or medium size volume, or of living animals, where it is not possible to reach the device to activate the advertise. For larger volumes, it is possible to increase the power of the transmission signal or use an external indication of the position of the device inside the packaging. The relationship between journey time, battery lifetime and power of the transmission signal might have to be considered. On topology (b) there is a single type B device placed within reach so that it is possible to press the button to activate the advertise. With this topology it should be possible to monitor the context variables from the place where the device is placed. It is also applicable for the transport of individual merchandises or non-dangerous living animals. On topology (c) there are several devices that work together on a star topology. The central node is a type B device that works as a router from the other devices to the mobile network. The devices that monitor the merchandise, that is, the terminal nodes of the star  
Figure 3: Device usage—topologies. (a) Type A device placed inside. (b) Type B device placed outside. (c) Star network with type B device operating as central (one of the Bluetooth Low Energy (BLE) roles) and placed outside the container and type A or B devices operating as peripherals (another BLE role) placed together with the goods. topology, can be of type A or B. The connection among the terminal nodes and the central node is established periodically, at each 15 min, giving the opportunity to the terminal nodes to report any non-compliance to the central node. To put the later in advertise mode, the push button must be pressed. Once connected with the mobile network, it can provide the latest information reported from the related terminal nodes. This topology is adequate whenever there are many goods, it is not feasible to use type A devices on continuous advertise, or the goods are inside a container. The terminal devices are placed with the goods and the central device is placed outside the container or on a place where is possible the manual activation of the advertise. The decision to use type A or B devices as terminals depends on how the tracking will be done before the aggregation and after the disaggregation of the container. The most common situation is that the transportation of a merchandise starts with topology (a) or (b), and, during the transport process be aggregated and disaggregated several times, switching to topology (c). In the final stage of the route, it is disaggregated, returning to topology (a) or (b). The device type is assigned at service initialization (Section 5.1). The aggregation/disaggregation procedures are explained in Section 5.3.