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This paper concentrates on the provision of isochronous services to users via the existing IEEE 802.6 framework using Q.931 as the signalling protocol for providing call control functions. We present possible scenarios of isochronous service provisioning via the IEEE 802.6 network. Real time performance for call setup procedures is simulated and analyzed with different priority schemes for transferring signalling messages. The results show that using a prioritized Queue Arbitrated (QA) bandwidth to send signalling messages greatly reduces call setup delay. Call setup delays are determined using both Poisson-type and bursty type data traffic models. The positioning of the Bandwidth Manager, the Virtual Channel Identifier (VCI) server and the Q.931 Signalling Termination is shown to influence call setup performance.

The performance of the FDDI token ring and IEEE 802.6 DQDB protocols are compared using discrete event simulation models. A Metropolitan Area Network (MAN) of 100 km and with 50 stations was modeled. A 100 Mbps channel is used for both networks, with a traffic model with large (1 kbyte) low priority packets and smaller (100 byte) high priority packets. The delay and fairness characteristics of both networks are analyzed. The simulations show that FDDI has advantages in fairness and maximum capacity, while DQDB offers lower delay at all except very heavy loads and has a stronger priority mechanism.

A new solid unit cell model is developed based on the microstructure analysis of three-dimensional (3D) six-directional braided composite (6DBC) produced by four-step 1 × 1 procedures in this research. First, the volume control method is applied to analyze the spatial movement traces of yarns. Then the microstructure configuration and squeezing condition of yarns is analyzed in detail by the mathematical modeling. The relationships between the microstructure parameters of unit cell and the braiding process parameters are derived. The parametrical solid unit cell model for modeling the microstructure of 6DBC is established. Finally, the main microstructure parameters of specimens are calculated to validate the effectiveness of the model. The predicted results agree well with the available experimental data. In addition, the squeezing conditions of the braiding yarns and the axial yarns are analyzed in detail, respectively. The variations of the key microstructure parameters with the braiding angle are discussed. Results indicate that the parametrical unit cell model has provided a better understanding of the relationship between the microstructure and the braiding process parameters for 3D 6DBC. [ABSTRACT FROM AUTHOR]

In this study, a new multiunit cell model is proposed based on the microstructure analysis of three-dimensionally full five-directional braided composites produced by four-step 1 × 1 procedures. The new multiunit cell model consists of five kinds of unit cells, namely interior, exterior surface, interior surface, exterior corner, and interior corner unit cells, which are developed by control volume method to characterize the unique microstructure features for different regions of three-dimensionally full five-directional braided composites. The relationships between the microstructure parameters of unit cells and the braiding process parameters are analyzed in detail and the structural parameters of the preform are derived. Especially, the squeezing condition of the yarns in the interior region is studied. Finally, the main microstructure parameters of braided specimens are calculated to validate the effectiveness of the multiunit cell model. Good agreement has been obtained between the predicted values and the available experimental data. In addition, the variation of the volume proportion of five kinds of unit cells to the overall specimen with the number of yarn carriers is discussed, respectively. The effect of braiding angle on the squeezing factor of braiding yarn is analyzed. Results indicate that the presented multiunit cell model can be adopted to effectively predict the microstructure and structural parameters of three-dimensionally full five-directional braided composites. [ABSTRACT FROM AUTHOR]