# Energy-Efficient Check-and-Spray Geocast Routing Protocol for Opportunistic Networks
## 2 Related Work  
Very few works in the literature have investigated geocasting routing protocols for OppNets. In [5], [PERSON] et al. proposed a routing protocol called Geoppp for OppNets, which is used to transfer the messages from a node to a stationary destination based on selected encountered neighbors within its geographical location. In doing so, the selected relay nodes accept messages that are being routed by interchanging the visiting and meeting records with each other. For forwarding the message to a specified geocast region, a geographic greedy routing scheme is utilized in conjunction with a progress within radius metric (PWRM) that measures how much progress a node has achieved in carrying the message towards the destination cast. In this process, the Chebyshev's inequality is utilized to estimate the probabilities that a node visits a region and establishes some contact in that region. In this sense, the contact availability per visiting and inter-visiting time are the node's mobility patterns that are used to estimate the number of regular visits and contacts in that specific geocast region. In [6], [PERSON] et al. proposed a location-based geocasting routing protocol for OppNets (called Location-based routing for Opportunistic networks (LOOP)), which makes use of a greedy mechanism to transmit the messages towards the destination region. Their scheme exploits the regularity encountered in the human movement mobility as a pattern to estimate a node's future locations based on its mobility trace. In doing so, the movement pattern-mining of a node is formulated as a classification problem, based on which a Bayes' predictive model is constructed to estimate the node's versatility history, a parameter taken into consideration in the selection of the relay node to which to forward the message. In [7], [PERSON] et al. introduced a distributed content sharing scheme for OppNets, in which the geographical vicinity of the mobile nodes is utilized as a means for information dissemination, taking into account the spreading and lifetime of information. In their content distribution scheme, the content is exclusively created and distributed locally and cannot be explicitly deleted. An analysis of their proposed scheme in terms of assessing the operational range for floating content is performed, showing promising results. In [8], [PERSON] and [PERSON] proposed a geocasting routing protocol for delay tolerant networks (called Expected Visiting Rate (EVR)), which relies on the idea of forwarding the messages to the destination location rather than to all nodes in that cast based on the EVR information, itself derived based on the historical information on the visited areas in the network. In this routing process, for a particular source node, the node with the highest EVR, which is qualified as node with the expected visiting rate, is selected for carrying the message forward towards its destination. In [9], [PERSON] et al. proposed a geocasting routing protocol for OppNets (called Flexible Geocasting for Opportunistic Networks (GSAF)), where the casts are defined as polygons by the sender node and then carried in the routed message in such a way that potential relay nodes only need to check whether they reside, or not, within the defined cast, noting that a node can still send a message in a cast even if it is located outside it. In their scheme, most of the messages follow random walks en route to the destination cast and those messages that do not follow a path to the destination cast are subject to deletion when the node's buffer become full. Whenever a message has reached the destination cast, it gets disseminated via a controlled flooding mechanism and will no longer be rerouted when it exits the destination cast. In [10], [PERSON] et al. proposed a multi-copy based geocasting routing protocol for OppNets (called Centrality-Based Geocasting for Opportunistic networks (CGOPP)), which transmit the messages towards its destination cast by using an integrated uni-casting and flooding mechanism.