Opportunistic routing (OR) is promising routing technique, which takes advantage of broadcast nature of wireless communication. The key idea behind OR is to utilize overheard packets from a neighbouring node, which in traditional routing technology were dropped or ignored. By utilizing these packets, OR saves the cost of retransmission and achieves energy efficiency which is one of the most challenging problem in design of routing protocol in wireless sensor networks. This paper reviews existing opportunistic routing protocols in wireless sensor networks. It also gives details about basic concept and components of OR in WSNs.

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Mobile Ad-Hoc Network (MANET) is a dynamic, multi-hop and autonomous network composed of light wireless mobile nodes. Multicast has great importance in MANET due to their inherent broadcast capability. However, due to the dynamic topology of MANETs to build optimal multicast trees and maintaining group membership a lot many control messages required. These overhead consume the mobile node resources like power and network resources like wireless links bandwidth that creates hurdle in implementing energy assurance and reduced overhead multicast protocol for Mobile Ad hoc Networks (MANET). This paper presents an energy efficient multicast routing protocol for MANET with minimum control overhead. The protocol creates shared multicast tree using the physical location of the nodes for the multicast sessions. Protocol employs a distributed location service to obtain the physical location information of the nodes, which effectively reduces the overheads for route searching and shared multicast tree maintenance. The algorithm uses the concept of small overlapped zones around each node for proactive topology maintenance with in the zone. To search for an existing multicast tree outside the zone, constrained directional forwarding is used which guarantees a good reduction in overhead in comparison to network wide flooding for search process. In this paper local connectivity technique and preventive route reconfiguration on the basis of the current status of the nodes are being proposed that attempts to improve the performance and reliability in terms of reduced overhead, power and bandwidth requirement. These techniques also ensure good reduction in latency in case of link breakages and prevention of the network from splitting. General TermsTopological routing protocol, tree based multicast, mesh based multicast, shared-tree based multicast protocol, source-tree based multicast protocol.

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