Design and evaluation of mac protocols for hybrid fiber/coaxial systems

The Community Antenna Television (Cable TV) networks are currently being upgraded to support two-way communication. The resulting system, refered to as the Hybrid Fiber/Coaxial (HFC) system, is potentially capable of supporting high transmission rates. HFC systems seem to be in a leading position to first deliver two-way high speed communication to the home. To make the communication possible several challenges, in both the physical and medium access control (MAC) layers, need to be first solved. The Cable TV network was especially designed to broadcast TV signals and thus optimized to broadcast high quality signals in only one direction (from the central office or head-end to the homes). The best operational frequency range is reserved for this communication, defining a high-quality high-bandwidth downstream channel. The communication from the station to the head-end was introduced very recently. It has to operate in the remaining frequency range which is small and noisy. Moreover it is shared between all the users in the system. This imposes very challenging constraints to the design of digital systems to efficiently exploit the upstream channel. This work focuses on how best to share the upstream channel between all the users (stations). Long round-trip delay, contention, synchronization, downstream overhead are some of the technical issues that need to be considered in engineering the access mechanism. Of equal importance is the economic factor. To deploy a system that potentially reaches every single home involves an enormous investment. The investment is mitigated if the cable modem at the home, required in millions of units, is relatively inexpensive. The head-end cost is not so critical since it is amortized over all the homes in the neighborhood. Therefore, we put special emphasis in designing a simple station protocol. We define a centralized reservation-based MAC protocol, called Centralized Priority Reservation (CPR), that yields a very simple implementation of the station. Stations send requests at the head-end and the head-end grants access to the channel. The protocol supports priorities and stream traffic without imposing a frame structure at the station. An adaptive control mechanism is designed to adjust the system configuration to workload changes. The control operates mini-slot by mini-slot maintaining the frameless nature of the protocol. A contention slot allocator (CSA) is used to distribute the channel capacity between the contention channel to send requests and the data channel to send useful data. There is an optimal distribution. The CSA reacts to system changes in an optimal manner through a self-regulating mechanism. This simple scheme works extremely well in short round-trip delay systems. For long round-trip delays, a CSA that predicts the need for contention capacity works better. The variable slot structure specified by the CSA defines a contention channel with variable capacity. The contention resolution algorithm (CRA) specifies the rules to follow when a collision occurs. We study the implementation of several CRAs that range from simple to efficient in this variable capacity channel with long feedback delay. The overall architecture proposed in this dissertation is simple, efficient and flexible. (Abstract shortened by UMI.)