ATM traffic control in hybrid fiber–coax networks – problems and solutions

The IEEE 802.14 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 802.14 will be its ability to support higher layer traffic services, namely, ATM Constant Bit Rate (CBR), Variable Bit Rate (VBR) and Available Bit Rate (ABR) traffic classes. In this study, we investigate the inter-operation of the MAC protocol, defined by 802.14, with ABR transmissions. An important finding 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 traffic control. This interference 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 traffic management specifications. Numerous simulation scenarios are presented to illustrate our findings. Parts of the results have been presented to the IEEE 802.14 standardization committee.