| Summary: | 碩士 === 義守大學 === 電機工程學系 === 87 === The ABR service defined by ATM forum is to increase the utilization of bandwidth on the ATM network. However, the introduced ABR service on the TCP over ATM network might bring up the problem of network congestion. As a result, it will cause cell lose and the degradation of quality of service. Therefore, it''s essential to provide congestion control mechanism within the ATM layer.
In this study, two congestion control algorithms, EPRCA (Enhanced Proportional Rate Control Algorithm) and NIST ER (National Institute of Standards and Technology Explicit Rate), are investigated. Both algorithms use the information in the RM cell and variable parameters in the ATM switch to compute the optimal transmission rate, then pass the information to the source host to adjust its transmission rate.
Simulations were performed to evaluate the performance of the two algorithms in terms of throughput and retransmission rate. Results are also compared with the performance of a switch without any congestion control. Simulation results show that increasing the buffer size in ATM switches will increase the throughput and decrease the retransmission rate. However, if the buffer size were raised to more than 5K cells, the throughput will be saturated. This result may be used to determine the optimal buffer size within an ATM switch.
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