Generalized stochastic Petri nets (GSPNs) are often used to specify flexible manufacturing systems (FMSs) and their control systems. While GSPNs are a powerful tool for system modeling, their ...complexity can become unmanageable for all but the simplest `toy' systems. Thus, manual construction of GSPNs can quickly become unacceptably slow and error-prone. In this paper, a formal method is developed to automatically construct a GSPN model for a given FMS. An FMS description language (FMSDL) is presented as the language for the input file of a GSPN construction program named FMSPet. FMSPet translates FMSDL input files into a GSPN system model, maps the specified process plans onto the given physical system, and attaches control stubs to resolve conflicts. The output GSPN is formatted as an input file for the stochastic Petri net package (SPNP) to support the analysis and evaluation of the structural and temporal properties of the net.
An unavailability analysis of firewall sandwich configurations Goddard, S.; Kieckhafer, R.; Yuping Zhang
Proceedings Sixth IEEE International Symposium on High Assurance Systems Engineering. Special Topic: Impact of Networking,
2001
Conference Proceeding
Odprti dostop
Firewalls form the first line of defense in securing internal networks from the Internet. A Firewall only provides security if all traffic into and out of an internal network passes through the ...firewall. However, a single firewall through which all network traffic must flow represents a single point of failure. If the firewall is down, all access is lost. A common solution to this problem is to use firewall sandwiches, comprising multiple firewall processors running in parallel. A firewall sandwich system needs load-balancing processes executing on separate processors to manage the flow of packets through the firewall processors. The number of redundant load balancing processors and their redundancy management policies have a major impact on system unavailability. We present a model to analyze the steady-state unavailability of firewall sandwiches and compare the unavailability of various load-balancing configurations. The results show that, using representative non-proprietary values for system parameters, redundancy management policies are at least as important as the number of redundant processing nodes.
DIMPLE: DynamIc Membership ProtocoL for epidemic protocols Jin Sun; Weber, Paul J.; Choi, Byung K. ...
2007 Fourth International Conference on Broadband Communications, Networks and Systems (BROADNETS '07),
2007-Sep.
Conference Proceeding
Epidemic protocols assume that information of a random set of nodes is provided at each protocol round. By definition, the random set needs to be chosen uniformly and randomly from the entire set to ...gossip with. Consequently, a node observes a different set of randomly chosen nodes at each different protocol round. Several proposals have addressed the issue of providing a different random set of nodes at each different round. In general, for large systems, this is done by creating a partial view of the entire membership at each node and exchanging part of the partial view among nodes. While many interesting properties of this approach have been found, investigation is needed to study the performance of this approach with practically high network churn. Without an action specifically designed for churn, shuffling would produce many dangling pointers in the partial view which point to an already left node. This in turn would significantly degrade the quality of epidemic protocols. The reason for the poor quality of the partial view is that the procedures of leave and join can take too long time to handle churn efficiently. To address this issue, an additional action of reinforcement and a new join procedure are proposed and evaluated in this paper. The reinforcement detects and removes dangling pointers at each shuffle more effectively, and the new join procedure accommodates a newly joining node remarkably fast. The subsequent simulations show that these ideas enhance the shuffling mechanism such that the system processes network churn much faster and the quality of the node degrees is significantly enhanced.
The voltage-gated potassium (Kv) channel Kv1.5 mediates the IKur repolarizing current in human atrial myocytes and regulates vascular tone in multiple peripheral vascular beds. Understanding the ...complex regulation of Kv1.5 function is of substantial interest because it represents a promising pharmacological target for the treatment of atrial fibrillation and hypoxic pulmonary hypertension. Herein we demonstrate that posttranslational modification of Kv1.5 by small ubiquitin-like modifier (SUMO) proteins modulates Kv1.5 function. We have identified two membrane-proximal and highly conserved cytoplasmic sequences in Kv1.5 that conform to established SUMO modification sites in transcription factors. We find that Kv1.5 interacts specifically with the SUMO-conjugating enzyme Ubc9 and is a target for modification by SUMO-1, -2, and -3 in vivo. In addition, purified recombinant Kv1.5 serves as a substrate in a minimal in vitro reconstituted SUMOylation reaction. The SUMO-specific proteases SENP2 and Ulp1 efficiently deconjugate SUMO from Kv1.5 in vivo and in vitro, and disruption of the two identified target motifs results in a loss of the major SUMO-conjugated forms of Kv1.5. In whole-cell patch-clamp electrophysiological studies, loss of Kv1.5 SUMOylation, by either disruption of the conjugation sites or expression of the SUMO protease SENP2, leads to a selective almost equal to15-mV hyperpolarizing shift in the voltage dependence of steady-state inactivation. Reversible control of voltage-sensitive channels through SUMOylation constitutes a unique and likely widespread mechanism for adaptive tuning of the electrical excitability of cells.
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