A MAC protocol for HFC networks: Design issues and performance evaluation

  • Authors:

  • Nada Golmie;Sandrine Masson;Gerard Pieris;David H. Su

  • Affiliations:

  • National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;National Institute of Standards and Technology, Gaithersburg, MD 20899, USA

  • Venue:
  • Computer Communications
  • Year:
  • 1997

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Abstract

Medium Access Control (MAC) layer protocols are designed to control transmissions over shared mediums. Bi-directional Cable TV networks using Hybrid Fiber/Coazial (HFC) systems are good examples of broadcast environments where a MAC protocol is needed to allocate the multiaccess medium among the various nodes. 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 head-end 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 granting 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.