# An Improved Hybrid Routing Protocol Combining MANET and DTN
## 2 Related Works  
In Reference [13], a hybrid social based routing algorithm (HSBR) was proposed, where a whole MANET network is fragmented into subnetworks or islands. In each island, a message is delivered from a source node to a last node which does not have connection with the next hop towards a destination node, and this node acts as a virtual source node and operates based on MANET firstly. Figure 1: A hybrid MANET (mobile ad hoc network) and DTN (delay tolerant network). Then it switches to DTN later if MANET does not work. In Reference [14], DTN/MANET routing study for energy critical infrastructure protection project (DMRS) was proposed, where MANET protocol was extended to integrate MANET and DTN by improving the route discover mechanism which includes information from DTN-capable nodes along the routing discover path and taking decisions based on the criticality of the sent messages. The topology of DMRS includes sensor nodes, cluster coordinator nodes, central office nodes, vehicular nodes, recovery/maintenance mobile nodes, and gateway nodes. For integration between MANET and DTN, DTN information is added during the route discovery and criticality based routing is achieved using MANET protocol extension. In Reference [15], hybrid DTN-MANET routing for dense and highly dynamic wireless networks (HYMAD) protocol was proposed, where network is split into disjoint groups of connected nodes and MANET is used for communication between nodes within the same group and DTN is used for communication between nodes belonging to different groups. Two control messages, i.e., enhanced distance vector and a list of messages held by nodes, are broadcast. An enhanced distance vector is used for intra-group distance vector routing and a list of the messages held by nodes are used for inter-group routing protocol. In addition, DTN protocol is used to transfer messages between nodes located in different groups. In Reference [16], a hybrid MANET and DTN protocol was proposed to cope with the limitation of infrastructure-based communication when a natural disaster, such as an earthquake and tsunami. Either MANET or DTN routing protocol is used to deliver messages depending on the number of neighboring mobile nodes, mobility and the remaining battery energy. If the number of neighboring mobile nodes is small, DTN mode is operated. If the mobility is high, DTN mode is selected to avoid link disruption problem of MANET. Since MANET exchanges more control messages, DTN is operated if the remaining battery power is substantially low. In Reference [17], a hybrid MANET-DTN routing scheme was proposed for emergency response scenarios, where a node operated based on MANET mode switches to DTN mode if a link is not active for a predefined time duration and falls back to MANET mode if a new routing path to a destination nodes is established or a broken link becomes active. In Reference [18], trust is calculated based on contact history and parameter values. Whenever a packet, such as route response (RREP), route request (RREQ), route acknowledgement (RACK), route error (RERR), and data, exists, the value of trust is calculated, which is divided into two parts: 1) trust calculation based on routing information and 2) trust calculation based on data packets. Then, the final value of trust is calculated. If a node which operates based on MANET faces a link failure, messages are delivered to a node with a higher trust and receiving node operates based on DTN. In Reference [19], a new hybrid protocol of MANET and DTN was proposed, where optimized link state routing (OLSR) protocol is assumed for MANET. If a routing path to the destination node for a packet exists, the packet is forwarded using MANET mode. On the other hand, if a routing path to the destination node is broken, the packet is stored in the queue and the node operates in DTN mode. In DTN mode, a packet is forwarded to neighboring nodes and if there is no end-to-end routing path to the destination node, they also store the packet in the queue and operate in DTN mode.