Abstract

The requirement of reliable communication protocols is that all the intended receivers of a message receive it unimpaired and complete. Automatic Repeat Request (ARQ) techniques are used in unicast protocols. The main advantage of this scheme is bandwidth conservation because no redundant packets are transmitted. ARQ based protocols do not scale well to multicast protocols with large groups of receivers. Effectiveness of retransmissions is reduced since losses tend to become independent and the advantage of conserving bandwidth does not hold. Forward Error Correction (FEC) is another method for loss recovery. Redundant packets are sent together with regular data packets from the sender to the receiver. In this thesis we have implemented a code that integrates FEC with ARQ-based technique. We have performed the test of our proposed QOS scheme in the laboratory. The communication between two PCs was tested using this hybrid FEC/ARQ technique while network impairments such as packet drops were applied by a network impairment emulator. The performance of the system was studied. We have also simulated a multicast environment where our QOS techniques were used. The scheme was applied to a network consisting of different multicast flows. Various cases such as independent and shared losses for homogeneous receivers and also heterogeneous receivers were considered. Effect of using NAK implosion avoidance mechanism was also studied. Then behavior of the network considering queuing delays and losses due to buffer overflow was observed. In the end, the results were compared to ARQ based technique and improvements obtained by our proposed scheme were determined.

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