A Semi-Markov Model of a Home Network Access Protocol

1 Abstract Home networks provide a means for interconnecting consumer products in home environments. In this paper the performance characteristics of the medium access protocol|a slotted persistent CSMA/CD protocol|of a twisted pair home network are investigated. Using a dedicated semi-Markov model throughput results are obtained by analyzing an overload situation. 2 Context and Introduction Nowadays we observe a still growing interest in having greater control of domestic appliances and of interconnecting several kinds of electronic devices in the home (and similar environments) so as to obtain additional features (IEEE Special Issue 1991). Typical applications are energy management, safety, security , home automation and entertainment. Thus the conventional trend of viewing consumer products in isolation is shifting towards a more system-oriented approach|The Home System. Several home systems are currently candidate for worldwide standardization: the Home Bus System (Japan), Consumer Electronic Bus (USA), Smart-House (USA), and Esprit Home Systems (Europe). The latter system (EHSA 1991) emerged from the cooperation of several European manufacturers and its architecture is based on the well-known OSI model (OSI 1984). The Home System has adopted four OSI layers: the Physical layer, the Data Link layer, the Network layer and the Application layer (Vlot and Katoen 1991). The Data Link layer has been subdivided into the Logical Link Control (LLC) sublayer and Medium Access Control (MAC) sublayer. The medium access protocol, that determines which station is allowed to use the medium when there is a competition for using it, is the major function of the MAC layer. A transmission medium ooers two communication services to products connected to it: a control channel provides a means for exchanging \commands" and (one or more) information channels ooer real-time connections of various capacities for transmitting e.g. speech, audio and video signals. Commands play an important role in the inter-operability of domestic appliances. Therefore, the performance characteristics of the control channel are of vital importance. It is well-known from the computer network eld that MAC protocols have a great impact on the performance of networks (Hammond and O'Reilly 1986) (Tobagi 1980). In this paper we investigate the throughput of the MAC protocol of a twisted pair home network by means of a semi-Markov model. The model considers the network under a high load situation. The protocol was originally described in (Tritton 1991). The paper is organized as follows. In Section 3 we describe the medium access protocol in detail. A motivation for …