Wireless is a new technology that allows users to access information and services regardless of the geographic position. People can utilize and surf the Internet with computers (e.g., laptop, palmtop, smart phone and PDA) whenever and wherever possible. In general, wireless network can be classified into two types: infrastructure network and ad hoc network. Mobile ad hoc network (MANET) is an autonomous group of mobile users who communicate through relatively bandwidth constrained wireless links. Since the hosts are mobile, the network topology may change rapidly and unpredictably over time .
Congestion in a network may occur if the load on the network (the numbers of packets send to the network) is greater than the capacity of the network (the number of packets a network can handle). Thus network congestion can severely increase delay and packet loss and reduced network throughput. Congestion control refers to techniques and mechanisms that can either prevent congestion before it happens, or remove congestion after it happened.
The main objective of congestion control is to limit the delay and buffer overflow caused by network congestion and provide better performance of the network . In wire line networks, congestion control is implemented at the transport layer and is often designed separately from functions of other layers . However, these congestion control techniques do not apply directly to adhoc networks because the ad hoc network is challenged by limited wireless bandwidth, power constraints, route failures due to node mobility and limited buffer size. The final result is high packet-loss rate, re-routing instability, loss of energy, bandwidth and retransmission of lost packets, which means that even more packets are sent into the network. These delays and packet losses which are not caused by network congestion but this can lead to misinterpreted as congestion losses.
To answer those challenges, many routing algorithms in
MANETs were proposed. In adhoc networks, the routing protocols for MANETs fall into three categories based on the routing information update mechanism [3, 5, 11] proactive, reactive (or on- demand) and hybrid. The Examples of proactive routing protocols are DSDV and OLSR [1, 3, 11]. In the on-demand routing protocol examples are AODV  and DSR [10, 11]. The hybrid routing protocol [3, 5, 11] combines the features of both proactive and on-demand protocols.
There is another dimension for categorizing routing protocols: congestion-adaptive routing versus congestion-un-adaptive routing. We note that the existing routing protocols are congestion-un-adaptive [12, 15, 16]. When establishing a new route, it remains the same until mobility or failure results in disconnection. During packet transfer between source and destination congestion may happen, this is not handled by existing routing protocol. The above problems become more visible in large-scale transmission of traffic intensive data...