The main difference between the opportunistic routing and the traditional routing in MANET is that the former can employ several lossy broadcast links to support a reliable transmission.
The characteristics of MANET are dynamic topology, network partitions and constrained resources. Due to this, there are many issues while designing routing protocol for MANET. The issues such as error prone channel state, hidden and exposed terminal problem, bandwidth constrained, and variable capacity links and energy constrained operations are found. For efficient data transmission and to improvise throughput and avoid retransmissions in MANET, various opportunistic routing techniques are used.
Opportunistic routing is mainly used for delay tolerant networks or disruption tolerant networks. However, the routing protocol used for opportunistic networks are different from opportunistic forwarding used in MANET as the opportunistic routing in MANET is used to fully utilize the broadcast nature of wireless medium and to improve transmission reliability.