Accurate estimation of capacities and cross-traffic of all links in a path using ICMP timestamps

The estimation of the link capacity and its available bandwidth in an end-to-end path is crucial for network management, admission control and flow control for adaptive applications. This paper introduces an estimation mechanism able to accurately estimate the available bandwidth of all links in an end-to-end path, through its capacity and cross-traffic estimation. The estimation procedures resort to the dispersions of packet pairs and trains using the concepts of ICMP Timestamp and Traceroute that, efficiently used together, enable the measurement of the dispersions in all links in the path. These mechanisms were evaluated through simulation experiments, where we analyzed the influence of the several network parameters on each estimation mechanism. The results show that these estimation methods are able to accurately estimate both the capacity and the cross-traffic of all links in a path with moderate length and with low overhead.     

时间戳顺序在分布式并发控制中的应用

分布式系统以其优越的性能正在逐步取代传统的客户/服务器结构,时间戳顺序由于其控制精确,不会中断处理事务的优点而在分布式事务管理系统中占有重要的地位.介绍了分布式并发控制的主要技术--时间戳顺序技术及其应用.     

无线Mesh网中的伪装节点检测研究

为了有效的检测无线Mesh网的骨干网络中的伪装节点,依据最新的IEEE 802.11s标准,对无线网状网中伪装节点攻击的原理、特点和危害进行了深入研究.针对802.11s协议下的无线网状网提出了两种伪装节点攻击模型,提出了基于移动终端代理,结合节点访问控制机制,利用序列号与时间戮间一对一递增关系来检测伪装节点的方法.实验结果表明,该方法可以及时有效的检测出无线网状网络中的伪装节点,且具有较低的误报率和较高的检测精度.     

Improving Predictability of Transaction Execution Times in Real-time Databases

We present a design for multi-versionconcurrency control and recovery in a main memory database, anddescribe logical and physical versioning schemes that allowread-only transactions to execute without obtaining data itemlocks or system latches. Our schemes enable a system to providethe guarantee that updaters will never interfere with read-onlytransactions, and read-only transactions will not be delayeddue to data contention. Consequently, transaction executionsbecome more predictable—this partially alleviates a majorproblem in real-time database system (RTDBS) scheduling, namely,significant unpredictability in transaction execution times.As a result, in addition to a transaction's deadline, a moreaccurate estimate of its execution time can also be taken intoaccount, thus facilitating better scheduling decisions. Our contributionsinclude several space saving techniques for the main-memory implementation,including improved methods for logical aging of data items andthe introduction of physical aging for low-level structures.Some of these schemes have been implemented on a widely-usedsoftware platform within Lucent, and the full scheme is implementedin the Dalí main-memory storage manager.     

Highly-fair bakery algorithm using symmetric tokens

This note proposes a new version of the bakery algorithm that: (i) assures fair tie-breaking when two or more processes choose same token number; and (ii) bounds the token numbers within the range [−n,n]. The algorithm is simple and uses one additional shared bit.     

Client-Server Caching with Expiration Timestamps

We study client-server caching of data with expiration timestamps. Although motivated by the potential for caching in telecommunication applications, our work extends to the general case of caching data that has known expiration times. Toward this end, we tailor caching algorithms to consider expiration timestamps. Next, we consider several different client-server paradigms that differ in whether and how the server updates client caches. Finally, we perform simulation studies to evaluate the empirical performance of a variety of strategies for managing a single cache independent of the server and for managing caches in a client-server setting.