The ranging algorithm allows active stations to measure their distances to the headend for synchronization purpose in Hybrid Fiber Coax (HFC) networks. A practicable mechanism to resolve contention among numerous stations is to randomly delay the transmission of their control messages. Since shorter contention cycle time increases slot throughput, this study develops three mechanisms, fixed random delay, variable random delay, and optimal random delay, to minimize the contention cycle time. Simulation demonstrates that the optimal random delay effectively minimizes the contention cycle time and approaches the theoretical optimum throughput of 0.18 from pure ALOHA. Furthermore, over-estimation reduces the impact on contention cycle time more than under-estimation through sensitivity analysis, and both phenomenon damage slot throughput. Two estimation schemes, maximum likelihood and average likelihood, are thereby presented to estimate the number of active stations for each contention resolution round. Simulation proofs that the proposed estimation schemes are effective even when the estimated number of active stations in initial contention round is inaccurate.

Data-Over-Cable Service Interface Specifications v1.1 (DOCSIS v1.1), developed for data transmissions over Hybrid Fiber Coaxial (HFC) networks, defines five upstream services for supporting per-flow Quality of Services (QoS). The cable modem termination system (CMTS) must periodically grant upstream transmission opportunities to the QoS flows based on their QoS parameters. However, packets may violate QoS requirements when several flows demand the same interval for transmission. This study proposes a two-phase, i.e., the scheduling sequence determination phase and the minislot assignment phase, minislot scheduling algorithm to reduce the QoS violation rate. In the scheduling sequence determination phase, the flow whose packets are most unlikely to violate QoS is scheduled first. Then, in the minislot assignment phase, the scheduler allocates to a flow the available interval where the likelihood of packet violation is minimum. Simulation results demonstrate that our scheduling algorithm can reduce the QoS violation rate by 80-35% over that of the first-come-first-serve-random-selection algorithm. It increases the utilization by 25% as well. The two-phase minislot scheduling algorithm can work within the DOCSIS v1.1 framework.