Abstract. From mid-94 to end-95 the "Pelfonnance Working Group (PWG)" of the ATM PILOT has carried out a lot of measurements (in relationship to functions available on test equipments). The results obtained were mainly related to ATM layer performance measurements (availability and non time-related performance parameters) and to traffic characterization. Performance measurements aimed at checking the validity of the set of proposed or standardized ATM layer performance parameters, at studying the sensitivity of the parameters definitions and at obtaining early results in order to propose performance objectives for the relevant recommendations. These results have shown that the ATM layer performance is very much dependent of the observation period of time and of the physical path of the connection under test. Furthermore it has been observed that the ATM layer performance is not so sensitive to the parameter definitions and the associated thresholds. Traffic characterisation is necessary to identify what is going on in the network (will the cells be equally spaced or will they come in bursts ?). The PWG had taken the opportunity to do field trials with real traffic coming from Pilot and has carried out a range of tests on both CBR sources (carrying voice or video applications) and VBR sources (multimedia application or LAN to LAN interconnection). Two main traffic types have been observed during the tests: -CBR sources carrying voice or video applications.-VBR sources with multimedia applications or LAN to LAN interconnection using the SMDS/-CBDS service.
Specific queueing models are derived in order to size the buffers of ATM switching elements in the cases of ATM or STM multiplexed traffic. Buffering is performed either at the outputs or in a central memory for ATM multiplexed traffic; for STM multiplexed traffic, buffers can also be provided at the inputs. The buffer size is chosen in order to ensure a loss probability in the switch smaller than 10-10.It is shown that the buffer size per output in the case of central queueing is smaller than the buffer size in case of output queueing for both ATM and STM multiplexed traffics. Moreover, for STM multiplexed traffic, buffer sizes are identical for input and output queueing. Lastly, it is pointed out that buffers used for STM multiplexed traffic should be 4 to 20 times larger than the corresponding buffers for ATM multiplexed traffic.
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