Preemptive and delay-based mechanisms to provide preference to emergency traffic

Preemptive and delay-based policies are derived here to provide preferential treatment to emergency users as motivated by the need to respond to natural or man-made disasters. These are applied in circuit switched networks or IP-based networks in conjunction with reservation mechanisms at single links or routers where congestion occurs. A unique optimization formulation is provided where policies are constrained by blocking requirements for emergency traffic, then optimized to provide lowest preemption probabilities. An iterative optimization approach is derived for a multi-dimensional Markov chain to provide an approximate solution for a non-linear integer program. Markov state space concerns are mitigated by introducing and analyzing algorithmic simplifications. Polices are found for hard preemption where sessions are interrupted or soft preemption where session quality is reduced. In addition, delay-based approaches are also examined where emergency users are allowed to wait for network resources if they are first blocked. All of the above approaches are compared with each other and with traditional approaches that hold back resources for emergency traffic. The results demonstrate that in general no approach is superior based on network performance characteristics alone. Qualitative factors must also be considered, most notably the nuisance to non-emergency users from preemption.     

均匀同轴电缆的瞬态响应的研究

一、前言均匀同轴电缆因其优良性能在现代测量技术中获得了广泛的应用。早期是研究正弦电信号的传输,寻求电缆传输特性的稳态解。近来,需测诸如亚微秒宽度、纳秒变化沿的单次脉冲,则要研究其瞬态解,目前已有若干研究结果。巴纳研究理想同轴电缆端接失配电阻的传输特性,得阶跃响应的解析解。Zaengle则研究端接混合元件的情况,给出了阶跃响应的计算机解,而非解析解。Wigington研究了低损电缆匹配端接时的传输特性的解析解。     

Connections in cold-formed steel

A survey has been given of the fastening possibilities in cold-formed steel, being mechanical fasteners, welding and adhesive bonding. The selection of a fastening type should not be based only on structural requirements but also on non-structural requirements. For the mechanical properties of the connections has been referred to Eurocode 3 part 1.3. Furthermore, background studies has been presented for the rules for the mechanical fasteners. These studies are based on statistical evaluations and have led to improved versions of existing design rules and a uniform partial safety factor for resistance.     

A distributed laxity-based priority scheduling scheme for time-sensitive traffic in mobile ad hoc networks

Characteristics of Mobile Ad hoc Networks such as shared broadcast channel, bandwidth and battery power limitations, highly dynamic topology, and location dependent errors, make provisioning of quality of service (QoS) in such networks very difficult. The Medium Access Control (MAC) layer plays a very important role as far as QoS is concerned. The MAC layer is responsible for selecting the next packet to be transmitted and the timing of its transmission. We have proposed a new MAC layer protocol that includes a laxity-based priority scheduling scheme and an associated back-off scheme, for supporting time-sensitive traffic. In the proposed scheduling scheme, we select the next packet to be transmitted, based on its priority value which takes into consideration the uniform laxity budget of the packet, the current packet delivery ratio of the flow to which the packet belongs, and the packet delivery ratio desired by the user. The back-off mechanism devised by us grants a node access to the channel, based on the rank of its highest priority packet in comparison to other such packets queued at nodes in the neighborhood of the current node. We have studied the performance of our protocol that combines a packet scheduling scheme and a channel access scheme through simulation experiments, and the simulation results show that our protocol exhibits a significant improvement in packet delivery ratio under bounded end-to-end delay requirements, compared to the existing 802.11 DCF and the Distributed Priority Scheduling scheme proposed recently in [ACM Wireless Networks Journal 8 (5) (2002) 455–466; Proceedings of ACM MOBICOM '01, July 2001, pp. 200–209].     

某研究院高层住宅节能设计

通过工程实例，详细探讨了高层住宅采用围护结构节能措施后，不仅经济上是可行的，还提高了住宅的舒适性及其品味，并对以后的设计提出了建议。     

Online pricing for bandwidth provisioning in multi-class networks

We consider the problem of pricing for bandwidth provisioning over a single link, where users arrive according to a known stochastic traffic model. The network administrator controls the resource allocation by setting a price at every epoch, and each user’s response to the price is governed by a demand function. We formulate this problem as a partially observable Markov decision process (POMDP), and explore two novel pricing schemes––reactive pricing and spot pricing––and compare their performance to appropriately tuned flat pricing. We use a gradient-ascent approach in all the three pricing schemes. We provide methods for computing unbiased estimates of the gradient in an online (incremental) fashion. Our simulation results show that our novel schemes take advantage of the known underlying traffic model and significantly outperform the model-free pricing scheme of flat pricing.