The main deficiency of standard TCP and all existing variations in ad hoc mobile network arises in its inability to classify packet losses. Conventional TCP diagnoses all losses due to congestion since non-congestion losses are rare and ignorable in wired network. However, these losses are generated frequently in MANET due to signal attenuation, interference and node's mobility. In order to prevent TCP form invoking congestion control over non-congestion loss and vice versa, Packet loss classification with high accuracy is desirable. This paper proposes an end-to-end sender-side approach which aims to classify congestion loss, wireless channel loss and link failure loss using queue usage estimation. Relative One-way Trip Time is key factor in calculating queue usage. Packet losses with queue usage rate greater than predefined threshold is always interpreted as congestion loss no matter how loss recognized. However, queue usage less than threshold signify presence of non-congestion losses. Non-congestion loss which recognized by three duplicate ack labels loss due to wireless channel error since it is indication of route existence between communicating end point that duplicate ACKs moved along. However Non-congestion loss which recognized after retransmission timer expiration has been probably due to link failure. Different approaches efficiency are evaluated based on loss classification's accuracy under different conditions such as various flow numbers, various wireless loss rates and variable speed for nodes. Simulations illustrate that obtained accuracy of enhanced scheme is the highest among proposed methods.
展开▼
