## 3 Proposed Method  
Ring Routing is a hierarchical routing protocol based on a virtual ring structure which is designed to be easily accessible and easily reconfigurable. Ring Routing [31] is a secure and energy efficient routing protocol providing quick data delivery. Wide simulation was done for evaluating the performance of Ring Routing, and it indicated that it performs better than the existing mobile sink routing protocol, whether LBDD [29] and Railroad [30] based on energy consumption, lifespan and measures for delay in reporting the routing data. The ring performs almost better than its competitors in all states. According to what mentioned above, and for the better performance of Ring Routing, the initial selection of the ring is conducted by using a gravitational search algorithm causing increased lifespan of the network. The ring protocol imposes three roles to sensor nodes: ring node; normal node, and; anchor node. Ring nodes form a circular structure that is a closed ring of the width of the node (Figure 10). The basis for Ring Routing involves (a) noticing the sink position to the ring, (b) normal nodes obtaining the information about sink position from the ring at any time required and (c) nodes disseminating their data by anchor nodes performing as factors for connecting the sink to the grid. These three roles of sensor are not static; it means that the role of sensor nodes might be changed during operation from wireless receiver network. The network center is marked with an \"X\" in various example ring structures shown in Figure 10.  
Figure 10: Structure of a ring. Figure 9: Ring Routing architecture. After the establishment of a wireless sensor network, a ring is initially made by following mechanism, namely, a radius of the initial ring must be determined. Nodes closer to the ring that has been defined by this radius and the center of grid are determined by a specific threshold to act as a nomination for converting to the ring node. By beginning from a specific node (for example, closest node to the left side of the point in the ring), by geological transmission in a given direction (in clockwise/counterclockwise direction), ring nodes are selected by using gravitational search random optimization algorithm to attain the beginning node and complete the closed ring as indicted in Figure 11. More, we explain gravitational search algorithm (GSA) detailed as below. In this section, gravitational search optimization algorithm is introduced based on gravitational law. The gravitational search algorithm (GSA) is a nature-inspired algorithm, which is based on [PERSON]'s law of gravity and the law of motion [35]. In the proposed algorithm [36; 37; 38], some factors are considered as objects and their performance is measured as their mass. The algorithm is comprised of collection of searcher agents that interact with each other through the gravity force [35]. All such objects attract themselves by gravity and this force may cause the movement of all objects towards heavier masses. Therefore, masses those are together, having direct connection by gravity. Heavier masses, according to equation, move slower than lighter objects; this ensures the step for exploiting the algorithm. In GSA, any mass (factor) has four characteristics including place, inertial mass, gravitational active mass and gravitational passive mass. The place of the mass is according to the solution of the problem and gravitational and inertial masses are determined by using the fitness function. On the other hand, any mass provides a solution, and an algorithm is developed by properly setting the inertial and gravitational mass. Over time, objects are expected to be attracted towards heavier objects. This provides an optimal solution for search space. Different steps for gravitational search algorithm detailed as below:  
1. Identifying the exploration space;
2.