# A Network Architecture and Routing Protocol for the MEDIcal WARNING System
## 4 Research Challenges and Solutions
### Design Solutions
Since MEDIWARN requires low latency communications, the above mentioned protocols are not suitable solutions, whereas proactive or hybrid routing protocols could be considered. However, both the Destination-Sequenced Distance-Vector Routing (DSDV) and the Temporally Ordered Routing Algorithm (TORA), as discussed in ref. [38], would significantly increase the network workload in the MEDIWARN system. Another option could be the hybrid routing protocol for wireless mesh routing that is defined in the IEEE amendment 802.11s [39, 40]. However, the IEEE 802.11s requires specific hardware/software features that may not be supported by a number of COTS devices. Due to the limitations in this respect of the state-of-the-art solutions previously mentioned, here, a custom routing protocol is proposed for the MEDIWARN system. The protocol, called the MultiPath Routing Protocol for MEDIWARN (MP-RPM), is described in Section 5 and aims to support reliable transmissions on a dynamic network, while limiting the network overhead due to the control messages. Being totally hardware independent, MP-RPM can be used on any COTS device without any hardware/software modifications (unlike the IEEE 802.11s standard). **Soft real-time communications support. ** Soft real-time messages have deadlines that are taken into account when routing and forwarding messages, but without strict guarantees, so an occasional deadline miss may happen and it is tolerated. However, the messages carrying, for example, a patient's physiological parameters, if not delivered on time, will not be used for real-time monitoring and will not be displayed on the screen that shows the patient's current conditions. To minimize the number of deadline misses, here, we propose an IEEE 802.11-based mesh network that includes on the relay nodes suitable mechanisms to improve the soft real-time performance of the MEDIWARN system. Each relay node implements a priority queue of outbound messages. When a node receives a message to forward, the message is inserted in the queue. Message priority is assigned according to a configurable criterion, for example, the hop count, i.e., the number of hops that the message has traversed so far. This way, the messages that traverse more links to reach the destination would be favored to compensate for the longest path. In addition, the custom routing protocol (i.e., the MP-RPM) here proposed allows choosing the best next hop for each message to be forwarded based on a route selection algorithm. In particular, every time a message needs to be forwarded by a relay node, the latter searches its routing table for all the possible routes to the destination. The routes are sorted from best to worst according to a configurable metrics, e.g., the hop distance, so the relay node selects the first path to forward the message. This way, each message follows the best path between the sender and the receiver based on a specific metrics. Note that, as discussed in Section 5.2, the MP-RPM implements multipath routing, and therefore each message can be sent over multiple paths to provide redundancy and increase the protocol reliability. Consequently, each relay node selects the first \(n\_path\) paths thanks to the route selection algorithm. Summarizing, the MEDIWARN system needs a simple, lightweight and configurable routing protocol able to both take the message priority into account to reduce the delay of soft real-time messages and provide path redundancy and mobility support without significantly increasing the network workload and latency. The solution here proposed is described in detail in the following Section.