Analytic Approach of Voice / Data Integration on Token Passing Lan ' S Based on Ieee 802 . 5

The increasing range 01 applications 01 local area networks (LAN) reflects their importance in todays inhouse communication. The requirements in office scenarios to support both, voice and data connections, locus the point 01 view to LAN systems, which are capable 01 integrating these different traffic streams. Recently, various LAN access schemes including voice communications have been developed [1} [S}. In this paper we derive an analytic approach lor token passing LAN's with a priority strategy according to IEEE 802.5. The model is based on a nonezhaustive polling system with finite buffer capacity and non-zero switchover times. The system is described 'by two station types, voice stations and data stations, polled in an arbitrary manner. The service discipline is characterized by timer-controlled voice scanning cycles imbedded ,in the normal data polling cycles. The results are obtained by an approximate analysis and can be used to estimate the quality 01 this voice integration strategy in terms 01 loss probabilities and mean waiting times lor voice and data traffic. Detailed computer simulations have been performed to validate the results given by this analytic approach. 1 INTEGRATION OF VOICE AND DATA Voice and data integration on LAN's has received a lot of interest. This seems to be the first step towards a completely supported office scenario for integrated voice and data facilities. Supporting voice communication in LAN's by using synchronous or quasi-synchronous transmission schemes, the main objectives are to minimize the end-to-end voice transmission delay and to guarantee the required bandwidth for the voice connections. Token passing LAN's can provide these requirements, since their media access control part offers the capability to select several priority classes. These priority classes can be used to provide concurrently packet-oriented and synchronous traffic. The media access control part of token ring LAN's is basically an asynchronous access , scheme, where data packets with variable length can be transmitted over a ring-structured media. The prioritization and reservation mechanism, recommended in IEEE 802.5, can be adapted to support synchronous voice transmission, too. The ring priority is switched periodically to a higher level by a special station called Synchro'nous Bandwidth Manager (SBM). This higher priority level, indicate~ by a high-priority token issued by the SBM,