<title>Performance evaluation of MAC protocol components for HFC networks</title>

Abstract

The IEEE 802.14 standard group is aimed at defining the physical and medium access control (MAC) layer protocols of a bi-directional cable TV network using hybrid fiber/coaxial (HFC) cables. Several MAC protocol proposals have been submitted to the 802.14 working group that has started the evaluation process in order to conceive a single MAC protocol satisfying all the HFC requirements. One can think of a MAC protocol as a collection of components each performing a certain number of functions. An HFC MAC protocol can be broken into the following set of components: ranging or acquisition process, frame format, support for higher layer traffic classes, bandwidth allocation, bandwidth request, contention resolution mechanism. Ranging is the phase during which the round trip delay time to the headend is calculated and the station synchronization to the downstream timing is performed. The frame format element of the MAC defines the upstream and downstream frames and describes their contents. If the MAC needs to provide support for ATM, it also needs to differentiate between different classes of traffic supported by ATM, such as constant bit rate (CBR), variable bit rate (VBR), and available bit rate (ABR). Bandwidth allocation represents an essential part of the MAC and controls the grating of requests at the headend. Finally, the contention resolution mechanism which is maybe the most important aspect of the MAC consists of a backoff phase and a retransmission phase. This paper examines two of the MAC elements mentioned above, namely the contention resolution and the bandwidth allocation mechanisms. Different solutions for each component are considered and evaluated. Performance is measured in terms of request delay, mean access delay and access delay probability distribution. Simulation results for configurations and scenarios of interest are also presented.