Assuring quality and reliability of complex electronic systems:hardware and software

Some of the most recent trends in expanding the scope of traditional quality-assurance techniques to include all phases of design, development, manufacture, and deployment, considering both hardware and software, are discussed. Emerging views on quality management are discussed. The life cycle of a product, beginning with the setting of requirements, and including assuring parts reliability, evaluating a fault-tolerant architecture, avoiding physical design hazards, enforcing software development methodology, measuring conformance to requirements in manufacture, and tracking performance in the field is considered. The author's goal is to review in a general way, what can be accomplished through use of the various assurance techniques with references given to examples from the literature, which gives historical background as well as teaches the technical methods in detail     

Buffer Management in a Packet Switch

Consider a single packet switch with a finite number of packet buffers shared between several output queues. An arriving packet is lost if no free buffer is available, as in the CIGALE network. It has been observed by simulation that if load increases too much, congestion may occur, i.e., throughput declines; it appears that the busiest link's queue tends to hog the buffers. Therefore, we will limit the queue length and when the queue is full the packet will be dropped. We expect that this restricted buffer sharing policy will avoid congestion under conditions of heavy load. A queueing model of a packet switch is defined and solved by local balance. Loss probability is evaluated, and values of queue limit to minimize loss are found; they depend on load. A Square-Root rule is introduced to make the choice of queue limit independent of load. For a sample switch, with three output links, a comparison is made between performance under different buffer sharing policies; it is shown that restricted sharing prevents congestion by making throughput an increasing function of load.     

Ice storms and forest impacts

Ice storms, or icing events, are important meteorological disturbances affecting forests over a surprisingly large portion of the USA. A broad belt extending from east Texas to New England experiences major ice storms at least once a decade; and truly major events occur in the heart of this belt once or twice a century. In the areas most affected, icing events are a factor that shapes stand composition, structure, and condition over wide areas. Impacts of individual storms are highly patchy and variable, and depend on the nature of the storm. Impacts also depend on how (or if) forest managers conduct subsequent salvage cuttings. Important research needs remain to be considered by the forest ecology and meteorology communities. At present, how ice storm frequency and severity may change with future climate change is unknown.