Analysis of QoS by Combining IEEE 802.11MAC Protocols with Selective Retransmission Mechanisms in MANETS

The individual layering techniques of wired networks are not suitable for Adhoc networks. So, combine the mechanisms of any two layers improve the QoS drastically. In Adhoc networks, certain QoS parameters like error rate, delay and packet loss are increased and certain parameters like throughput and delivery ratio are decreased in Transport layer is due to MAC problems and disconnection is also possible. This paper evaluates the performance evaluation by combining IEEE 802.11 MAC layer protocols with Selective retransmission mechanism of Transport layer congestion control mechanisms operating in a mobile adhoc network. We examine the effects of two different MAC protocols— IEEE 802.11and IEEE802.11e with Selective retransmission, Slow start, Arithmetic Increase and Multiplicative Decrease (AIMD) mechanism of TCP.IEEE802.11uses distributed coordination function (DCF) where IEEE802.11e uses enhanced distributed coordination function (EDCF). Specifically, we access the impact of multiple wireless hops and node mobility on the throughput performance of TCP on each MAC protocol with two routing algorithms. Results show that in all instances, the QoS parameters 15–20% improvement in throughput, 40–45% improvement in bandwidth-delay product, 10–15% improvement in delivery ratio, packet loss is reduced drastically to 40–50% in IEEE802.11e with AIMD mechanism in transport layer. Similarly Results shows, the QoS parameters 35–40% improvement in throughput, 25–30% improvement in bandwidth-delay product, 15–20% improvement in delivery ratio, packet loss is reduced drastically to 20–25% in IEEE802.11e with slow start mechanism in transport layer. But if Selective retransmission algorithm is used in the transport layer it enhances the QoS parameters very drastically in both MAC layer protocols. The results are 65–75% improvement in throughput, 60–70% improvement in bandwidth-delay product; 60–70% improvement in delivery ratio, packet loss is reduced drastically to 50–55% where IEEE802.11e with selective retransmission in transport layer.