Dynamical quality of service (QoS) support for DOCSIS HFC networks

The Data Over Cable Service Interface Specifications (DOCSIS) of the Multimedia Cable Network. System (MCNS) organization intends to support IP traffics over HFC (hybrid fiber/coax) networks with significantly higher data rates than analog modems and Integrated Service Digital Network (ISDN) links. The availability of high speed-access enables the delivery of high quality audio, video and interactive services. To support quality-of-service (QoS) for such applications, it is important for HFC networks to provide effective medium access and traffic scheduling mechanisms. In this world, we consider an HFC network that has a shared upstream channel for transmissions from stations assigned with different service priorities to the headend. We first present a multilevel priority collision resolution scheme with adaptive contention window adjustment. The proposed collision resolution scheme separates and resolves collisions for different classes of critically delay-sensitive and best effort traffics, thereby, achieving the capability for preemptive priorities. To enhance the performance of the proposed scheme, we adopt a novel methodology in which the headend dynamically selects the optimal backoff window size according to the estimate of the number of contending stations for each priority class. A traffic scheduling policy with multiple priority queues is also employed in the headend to schedule data transmissions. This scheduling strategy is used to satisfy bandwidth requirements for higher priority traffics. Simulations are conducted by using OPNET. We present a set of simulation scenarios to demonstrate the performance efficiency of the proposed scheme.