## 7 Routing Protocols proposed by Spanish Universities
### SHRP (Simple Hierarchical Routing Protocol)
Newer radios that are based on IEEE 802.15.4 standard such as CC2420 implement a parameter called link quality indicator (LQI) which is believed to be a better indicator than RSSI [20]. SHRP protocol uses the metric called \"AvgLQI\" that represents this parameter. Protocol designers looking for inexpensive and agile link estimators may choose RSSI over LQI [34], but RSSI at the edge of the threshold of -87 dBm does not have a good correlation with PRR, so SHRP uses both of the metrics, LQI and RSS, in choosing the best route. LQI and RSSI metrics are obtained from the link layer of the wireless network. In our experiments we used the CC2420 radio chip. Figure 2 shows the interaction of SHRP protocol with SP to get information about neighbor nodes and to decide about the best route into the sink node. The metrics shown in bold font are the new ones defined by SHRP protocol. In this manner, other protocol that makes use of any of these metrics will have them already available in SP module. The SHRP protocol defines three kinds of sensing data messages: (i) periodic; (ii) alert; (iii) alarm. The sink node sends the query message, that is explained later, with the information that the monitoring system is interested to collect periodically. Based on this message, the sensing nodes know what and when they have to sense. The alert message is sent when the sensed data value is above an average value, specified by the monitoring system. The alarm message is sent when the value of the data sensed is below a minimum or above a maximum threshold, also specified by the system. This message is sent with the Urgent and Reliability bits 'on', so they have priority over any other message and the sender waits for an ACK message, to confirm that the alarm message have arrived. To do some experimental tests was defined the 'convergence time' as a period that takes long for all NC nodes update its routing tables, so it includes all transmission and processing times. In a Wireless Sensor Network, the clocks that come with each more works independently, so in order to calculate the convergence time of SHRP protocol, was  
Figure 2: Interaction between SHRP protocol and SP. implemented a synchronization mechanism based on the TPSN scheme. The experimental tests were done in four different topologies (see Figure 3) to observe the worst case (maximum) of convergence time. Was repeated five times each experiment. Tests were done using TMote motes from the Moteiv Company with the TinyOS operating system and the CC2420 Radio Chip. In the star topology (see Figure 3.1) all NC nodes have a direct link with the sink node. The results of the convergence time of this topology can be seen on Figure 4. In the topology 3.2 the NC1 and NC2 nodes have a direct link with the sink node, but node NC3 just has a direct link with NC1 and NC2 nodes. With this topology NC3 has a redundant path until sink node and has two 'father' nodes (see Figure 5.). As we can notice in Figure 6, topology 3.3, NC2 and NC3 are two hops far from the sink node, having just one 'father' node (NC1). In the topology 3.4 (see Figure 7.) there are three hops until sink node with the following direct links: sink-NC1, NC1-NC2 and NC2-NC3, showing a tandem topology. Figure 3: Topologies of the Experiments. Figure 4: Convergence Time of Topology 1. Figure 5: Convergence Time of Topology 2. Figure 6: Convergence Time of Topology 3. Figure 2:0 Convergence Time of Topology 4. The consolidation of the data is shown in Figure 8 with the media of the results from each topology. As can be seen, topologies 2, 3 and 4 maintain the same convergence time behavior, increasing in a linear way regarding to the number of hops. This result was obtained due to each NC node has only one neighbor to learn route table. In the second topology, the convergence time had a different behavior when comparing it with the topology 3.