Improving the E ectiveness of ATM Tra c Control over Hybrid Fiber Coax Networks

The IEEE working group is currently standardizing a new media access control MAC protocol for the emerging Hybrid Fiber Coax HFC networks Crucial for the success of will be its ability to support higher layer tra c services namely ATM Constant Bit Rate CBR Variable Bit Rate VBR and Available Bit Rate ABR tra c classes In this study we investigate the interoperation of the MAC protocol de ned by with ABR transmissions An important nding of our study is that the bandwidth contention on the upstream channel in the HFC network may interfere with the feedback congestion control mechanisms of ABR tra c control This inter ference can result in unfairness between ABR sources and decreased utilization of the upstream HFC channel As a solution to the problem we propose a scheme whereby the headend station of the HFC network returns congestion information contained in resource management RM cells to the ABR sources The proposed mechanism can be incorporated into the ABR rate control scheme without modifying the current tra c management speci cations Numerous simulation scenarios are presented to illustrate our ndings Parts of the results have been presented to the IEEE standardization committee