# A Network Architecture and Routing Protocol for the MEDIcal WARNING System
## 4 Research Challenges and Solutions
### Requirements  
The wireless network involved in the MEDIWARN system must satisfy several application requirements, which pose the following design challenges.  
**High data rate.** The monitors may need to transmit a significant amount of data within short intervals (e.g., waveforms). For this reason, a wireless technology that support high data rates is required.  
**Local communications.** The patients' data have to be transferred over a private network that is locally managed within the hospital. This design choice was driven by the explicit request of the medical staff involved in the MEDIWARN project to avoid transmitting sensitive data to remote servers. This choice is beneficial to privacy and it also makes the data availability independent of any network provider.  
**Reliability and fault-tolerance.** The MEDIWARN communication system needs to provide high reliability and availability, as the monitoring must work and the patient's vital parameters must be delivered to the MEDIWARN Virtual Biosensor even in the case of faults. Consequently, negative conditions, such as interference or faults in one or multiple nodes, shall not make the communication network fail. For these reasons, suitable mechanisms, such as retransmissions and node/path redundancy, are needed. In addition, the host running the MEDIWARN Virtual Biosensor must be fault tolerant, thus hardware and software redundancy have to be introduced.  
**Mobility.** The MEDIWARN system involves handheld devices, i.e., mobile nodes. As a consequence, mechanisms to support node mobility are required.  
**Multi-hop communication.** The target application may demand for large-scale communication network deployments, and therefore the monitors can be multiple hops away from the MEDIWARN Virtual Biosensor. This requires the adoption of a number of relay nodes, i.e., intermediate nodes that receive the messages intended for other nodes and forward them up to their final destination. The number and placement of such relay nodes must be accurately evaluated according to some metrics, such as the coverage range of each node and the number of senders in a specific area. Moreover, a trade-off between the number of relay nodes and the network reliability (node/path redundancy) has to be found. In fact, while a higher number of relay nodes provides multiple paths for each message transmission from a source to the intended destination, and therefore alternative ways to reach the destination even in case of faults (e.g., a node failure), it entails higher costs in terms of network devices and energy consumption.  
**Routing.** In the MEDIWARN network architecture, routing, i.e., the process of selecting one or multiple paths for message forwarding, is a critical issue. In fact, the routing protocol should not introduce a significant overhead, in terms of network workload, to not impair the communication network performance in terms of end-to-end delay. This turned out to be a research question, as explained in the following subsection. The solution here proposed is presented in Section 5.  
**Real-time.** The MEDIWARN system continuously collects and processes data in order to promptly alert the medical staff. Consequently, bounded delivery times must be guaranteed to the messages carrying such data. In particular, the Virtual Biosensor considers the monitor transmission period as a soft deadline on the message delivery time, which can be occasionally exceeded without compromising the proper system operation. However, any data delivered to the receiver with a delay longer than the transmission period are not useful for real-time monitoring, and therefore they are not forwarded to the virtual biosensor. This aspect, combined with the requirements on routing previously mentioned, also poses a research challenge. In the following, the design choices corresponding to the above-mentioned requirements are described in detail.