## 7 Routing Protocols proposed by Spanish Universities
### SHRP (Simple Hierarchical Routing Protocol)  
In a research project supported by Petr deos de Venezuela, S.A (PDVSA), the state-owned corporation of the Bolivarian Republic of Venezuela responsible for the efficient, profitable, and dependable exploration, production, refining, transport and commerce of hydrocarbons, our group wasinterested in considering a routing protocol that could deal with three different aspects: battery availability, number of hops and link quality to guarantee the arrival of messages in the sink node in a energy saving way. We could not find any WSN routing protocol that used these three parameters together and at the same time was concerned about energy saving and reliability features. For this reason a new routing protocol called SHRP was proposed [32]. The SHRP protocol is concerned with topology maintenance that is directed related to the reliability of data delivery. To arrange this it makes use of metrics like local battery availability and link quality between neighbor nodes in choosing the best route into the sink node. It is also concerned with energy saving as not all periodic data are sent to the sink, as there is a concern that transmission is the task that more wastes energy in wireless sensor networks [33]. The SHRP protocol just sends data that have not changed from the last sensing data. The coordinators nodes can aggregate various data messages and send just one message. In this manner SHRP protocol has also an energy saving behavior. SHRP provides a load balance scheme during the creation of best routes groups, so not always will the same best route be chosen. To be flexible and to contribute with new metrics for others routing protocols, the SHRP architecture uses SP [33], a specific unifying protocol of TinyOS operating system. SP allows network protocols to choose neighbors wisely, taking into account information available at the link layer, providing a great modularity. The SHRP protocol periodically monitors the battery lifetime and link quality, cutting off from the routing table nodes that can not contribute in maintaining a well connected topology. The proposed protocol takes care of link quality, cutting off neighbor nodes from the routing table nodes that have the average link quality indicator below a minimum threshold. This threshold is related to the IEEE LQI indicator [34]. The SHRP protocol also cuts off from the routing table neighbor nodes that have the RSSI (Received Signal Strength Indicator) values below a minimum threshold [35]. Also, the SHRP protocol cuts off nodes that do not have battery availability, at least to execute what we call \"_Minimum Task Cycle_\" (MTC) [36] (see Equation 1). \[\mathrm{MTC}=\mathrm{CCA}+\mathit{Sensing\ Task}+\mathit{Transmission\ Task}+ \mathit{Reception\ Task}+\mathit{Idle\ Period\ Task} \tag{1}\]  
All the tasks of cutting off neighbor nodes, shown before, represent that if a node does not have sufficient battery power or has a bad link quality, caused by interference, multipath or path loss it will not participate as a route node in the choosing of the best route. To provide the topology maintenance SHRP protocol defines new metrics that SP does not provide. To be aware about the state of the energy of the nodes, SHRP defines a metric called \"minbattrem\" that keeps information about the energy available in each node along each route until the sink node. SHRP protocol tries to choose the route that gives more reliability, this mean, the route that give the mayor energy available along all the possible routes until the sink node. Another metric defined by SHRP protocol is called \"n hops\". With this metric SHRP can choose a route that takes into account the number of hops to the sink node. As the transmission is the task that uses more energy, SHRP tries to choose the route that pass through the minor number of hops, saving more energy.