12722290
A survey and measurement-based comparison of bandwidth management techniques
This article gives a brief tutorial for bandwidth management systems; a survey of the techniques used by eight real-world systems, such as class-based queuing (CBQ), per-flow queuing (PFQ), random early detection (RED), and TCP rate control (TCR); a compact testbed with a set of methodologies to differentiate the employed techniques; and a detailed black-box evaluation. The tutorial describes the needs for the three types of policy rules: class-based bandwidth limitation, session-bandwidth guarantee, and inter/intra-class bandwidth borrowing. The survey portion investigates how the eight chosen commercial/open-source real systems enforce the three policy types. To evaluate the techniques, the designed testbed emulates real-life Internet conditions, such as many simultaneous sessions from different IPs/ports, controllable wide area network (WAN) delay and packet loss rate for each session, and different TCP source implementations. The performance metrics include accuracy of bandwidth management, fairness among sessions, robustness under Internet packet losses and different operating systems, inter/intra-class bandwidth borrowing, and voice over IP (VoIP) quality. The black-box test results demonstrate that (1) only the combination of CBQ+PFQ+TCR can solve the most difficult scenario (multiple sessions competing for the narrow 20kb/s class); (2) the TCR approach may degrade the goodput, fairness, and compatibility even under slight packet loss rates (0.5 percent); (3) without PFQ, TCR and RED have limited ability to isolate the sessions (especially for RED); (4) the G.729 VoIP quality over a 125kb/s access link becomes good only after exercising MSS-clamping to shrink the packet size of the background traffic down to 256 byte.
26702573
Evolution and Evaluation of Internet Content Delivery
Discover the methods for content delivery and distribution of Web-based media in the Web 2.0 world. The concept of Web caches has existed as long as the Web and evolved from storage of frequently accessed files on an individual's personal computer or proxy server to Internet-based Web cache servers provided by companies as a paid subscription service for content providers. As multimedia has become more prevalent on the Web, content delivery networks (CDNs) have become a critical component of the Internet and an enabler of Web 2.0 applications like IPTV, mobile Web and TV devices, and content-rich Web databases such as Wikimedia.
13450793
On IEEE 802.14 medium access control protocol
In this article we present a comprehensive survey on the architecture, protocol issues, and standard of the hybrid fiber coaxial (HFC) networks which are evolving from the existing residential CATV networks. We first describe the HFC architecture and discuss the problems in providing two-way communication. Then, we identify three important medium access control (MAC) issues in designing the IEEE 802.14 standard; namely, synchronization, upstream channel access modes, and collision resolution. Resolutions adopted by the IEEE 802.14 Committee are illustrated after giving a protocol overview. Key resolutions include compensating round trip correction (RTC), interleaving minislots of data and request concurrently, and resolving collisions by multiple collision resolution engines, using the n-ary tree plus p-persistence algorithm with a first transmission rule. A comparative summary of some draft proposals that lead to the standard is given. Finally, we pinpoint two headend algorithms, minislot allocation and request scheduling, which are left open in the standard. They do not affect interoperability but may have a critical impact on performance.
2805042
A new random walk model for PCS networks
This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in personal communications services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n/sup 2/+3n-5) to n(n+1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n2-2n+1) to (n/sup 2/+2n+4)/4 if n is even and to (n/sup 2/+2n+5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%. Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks.
28041902
Guest Editorial: Special Section on Wireless Internet
WIRELESS communications have made spectacular progress in recent years. In particular, the merge of various wireless communication systems and the Internet has become more critical so that users can enjoy all kinds of services in the Internet while owning mobility. For example, modern wireless networks can support Internet applications for web accessing and multimedia services. Many issues need to be addressed for such combinations. Host mobility adds a new dimension to many research issues, such as network protocols, resource managements, Web access, and multimedia transmission. For different applications, diverse traffic types should be supported. Lightweight mobile computing devices, such as PDAs and Bluetooth, will be attached to the Internet. Various wireless communication devices, such as Bluetooth and wireless LANs, will be hooked up to the Internet. All these issues bring new challenges. This special section is targeted at the related issues in wireless Internet. More than 50 submissions were received, and 10 papers were accepted in this special issue. The first five papers cover the service issues in wireless Internet. The paper by B. Emako, R. Glitho, and S. Pierre discusses the design, implementation, and evaluation issues of wireless Internet telephony. Y. Lee and I.F. Akyildiz present a new scheme to reduce the link and signaling costs in Mobile IP. The paper by P. McKinley, U.I. Padmanabhan, N. Ancha, and S.M. Sadjadi describes a composable proxy infrastructure that enables mobile Internet users to collaborate via heterogeneous devices and network connections. V.A. Chitre and J.N. Daigle present an analytical model to assess GPRS’s capability of supporting IP-based Internet services. Performance optimization of VoIP calls over wireless links using H.323 protocol is proposed by S.K. Das, E. Lee, K. Basu, and S.K. Sen. Thenextsetof threepaperscovers issuesrelatedtowireless LANs and sensor networks. The important coverage issue concerning the deployment of sensors in a wireless ad hoc sensor network is addressed in the first paper by X.-Y. Li, P.-J. Wan, and O. Frieder. A polling mechanism to support QoS in IEEE 802.11 wireless LANs is proposed by S.-C. Lo, G. Lee, and W.-T. Chen. Formation of scatternets for Bluetooth-based wireless networks is discussed in the paper by C. Petrioli, S. Basagni, and I. Chlamtac. The last set of two papers covers management issues in mobile networks. An analysis for movement-based mobility management in mobile networks is discussed in the first paper by Y. Fang, who makes a thorough numerical analysis for finding the optimal mobility management under various network operation scenarios possible. Admission control for schedulingbursty traffic inCDMAsystems isdiscussed in the paper by Y.-K. Kwok and V.K.N. Lau, where six efficient rate allocation schemes are proposed. Finally, wewould like to take the opportunity to thank the contributingauthors, reviewers, theAreaEditor,Dr. S.L.Min, and the Editor-in-Chief, Professor J.-L. Gaudiot. Without their support, this special section would not be possible.
41129235
Determining the Global Progress of Parallel Simulation with FIFO Communication Property
Abstract In an optimistic parallel simulation, the global progress (i.e., the global virtual time or GVT) must be computed from time to time. We present a simple and efficient algorithm for computing the GVT in a distributed environment with FIFO communication delays. The accuracy and the complexity of the algorithm are discussed.
28386887
New Systolic Arrays for the Longest Common Subsequence Problem
Abstract New systolic arrays are presented to solve the longest common subsequence (LCS) problem. The first array is based on a previous work to compute the length of an LCS. The second array improves on the first one. The second array is about 1 4 faster than the first array, and each processing element (PE) of the second array requires one less port for both input and output to transfer one less value. Either of the two arrays can be equipped with a content-addressable memory in each PE to recover an LCS. The resulting array requires fewer steps than the previously proposed one.
6310496
Middleware based data replication providing snapshot isolation
Many cluster based replication solutions have been proposed providing scalability and fault-tolerance. Many of these solutions perform replica control in a middleware on top of the database replicas. In such a setting concurrency control is a challenge and is often performed on a table basis. Additionally, some systems put severe requirements on transaction programs (e.g., to declare all objects to be accessed in advance). This paper addresses these issues and presents a middleware-based replication scheme which provides the popular snapshot isolation level at the same tuple-level granularity as database systems like PostgreSQL and Oracle, without any need to declare transaction properties in advance. Both read-only and update transactions can be executed at any replica while providing data consistency at all times. Our approach provides what we call "1-copy-snapshot-isolation" as long as the underlying database replicas provide snapshot isolation. We have implemented our approach as a replicated middleware on top of PostgreSQL replicas. By providing a standard JDBC interface, the middleware is completely transparent to the client program. Fault-tolerance is provided by automatically reconnecting clients in case of crashes. Our middleware shows good performance in terms of response times and scalability.