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DISCRETE EVENT SIMULATION OF THE CSMA/CA PROTOCOL ASSUMING RTS/CTS |
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The simulator mimics the MAC level timing behaviour of communication between a number of clients and an Access Point. The two main components of the communication are the contention period, which depends on the collission history of all clients, and the transmission period, as soon as one client has occupied the medium. The first was explained in the introduction. The latter can follow two scenarios: with RTS/CTS, which gives more stability at the cost of a small overhead, or without. As this research focuses on the behaviour of the MAC layer under high loads, the RTS/CTS scheme is definitely the more relevant. All results quoted are obtained from simulations using RTS/CTS. Communication in this mode consists of the transmission of a Request To Send by the client. If this is received intact by the Access Point, it replies with a Clear To Send. This is the signal for the client to send a packet. The communication is terminated by the ACK from the Access Point. This schedule with the DCF and short InterFrame Spacings (DIFS and SIFS) is shown in the figure below. The times are simulated as transmission times (for the RTS/CTS/packet/ACK) and delays (for the InterFrame Spacings). |
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schematic communication between client and Access Point |
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