bluuebunny/crossref_metadata_2025 huggingface dataset:
Scalable TCP
Authors: Kelly Tom
Published: October 2004

TCP congestion control can perform badly in highspeed wide area networks because of its slow response with large congestion windows. The challenge for any alternative protocol is to better utilize networks with high bandwidth-delay products in a simple and robust manner without interacting badly with existing traffic. Scalable TCP is a simple sender-side alteration to the TCP congestion window update algorithm. It offers a robust mechanism to improve performance in highspeed wide area networks using traditional TCP receivers. Scalable TCP is designed to be incrementally deployable and behaves identically to traditional TCP stacks when small windows are sufficient. The performance of the scheme is evaluated through experimental results gathered using a Scalable TCP implementation for the Linux operating system and a gigabit transatlantic network. The preliminary results gathered suggest that the deployment of Scalable TCP would have negligible impact on existing network traffic at the same time as improving bulk transfer performance in highspeed wide area networks.
An empirical analysis of the IEEE 802.11 MAC layer handoff process
Authors: Mishra Arunesh , Shin Minho , Arbaugh William
Published: October 2004

IEEE 802.11 based wireless networks have seen rapid growth and deployment in the recent years. Critical to the 802.11 MAC operation, is the
handoff
function which occurs when a mobile node moves its
association
from one
access point
to another. In this paper, we present an empirical study of this handoff process at the link layer, with a detailed breakup of the latency into various components. In particular, we show that a MAC layer function -
probe
is the primary contributor to the overall handoff latency. In our study, we observe that the latency is significant enough to affect the quality of service for many applications (or network connections). Further we find variations in the latency from one hand-off to another as well as with APs and STAs used from different vendors. Finally, we discuss optimizations on the probe phase which can potentially reduce the probe latency by as much as 98% (and a minimum of 12% in our experiments). Based on the study, we draw some guidelines for future handoff schemes.
Tradeoffs in certificate revocation schemes
Authors: Zheng Peifang
Published: October 2004

Cryptographic
certificates
are a powerful tool for security concerned applications where the participants must be authenticated in order to access some resources or commit a transaction. However, due to various reasons, the validity of such certificates can change over time, introducing the risk of an invalid certificate being used to authenticate an entity. Various methods of mitigating this risk have been devised, known broadly as "certificate revocation" schemes. In this paper, we categorize and analyze them based on our identified characteristics. We further discuss tradeoffs among them and suggest how system designers might apply the analyses.
PlanetLab
Authors: Chun Brent , Culler David , Roscoe Timothy , Bavier Andy , Peterson Larry , Wawrzoniak Mike , Bowman Mic
Published: October 2004

PlanetLab is a global overlay network for developing and accessing broad-coverage network services. Our goal is to grow to 1000 geographically distributed nodes, connected by a disverse collection of links. PlanetLab allows multiple service to run concurrently and continuously, each in its own slice of PlanetLab. This paper discribes our initial implementation of PlanetLab, including the mechanisms used to impelment virtualization, and the collection of core services used to manage PlanetLab.
Bench-style network research in an Internet Instance Laboratory
Authors: Barford Paul , Landweber Larry
Published: October 2004

Network researchers employ a variety of experimental methods and tools including analytic modeling techniques, simulators, and widely depolyed measurement infrastructures. It is natural to assume that the overall scope of network research may be limited by the type and capability of the tools and test systems that are available. In this paper we describe a new, bench-style approach for conducting network research that we argue is essential for effectively investigating different classes of important problems. We describe the architecture for the workbench environment that enables this approach-what we call the Internet Instance Laboratory (IIL). The conceptual model for an IIL is a highly configurable laboratory environment containing commercial networking equipment typical of any end-to-end path in the Internet. An IIL would also have the capability to create accurately a broad range of conditions across all networking layers. The two most important advantages of an IIL are the ability to instrument entire end-to-end paths and the ability to install new equipment or protocols in any location in the environment. Clearly, neither of these opporutnities is available in the live Internet. while an IIL offers significant challenges. We describe these challenges and approaches for addressing them. Finnlay, we discuss different classes of research questions that would become tractable if an IIL were available.
An Internet scale simulation setup for BGP
Authors: Hao Fang , Koppol Pramod
Published: October 2004

BGP convergence issues in the Internet have been extensively studied in recent years. It has been shown through formal analysis that BGP convergence is not always guaranteed. When it does converge, active measurement based techniques have determined that the convergence process may take upto 15 minutes while also causing intermittent packet loss/latency. As BGP enhancements are explored to address this convergence problem, controlled simulation experiments offer the most convenient and feasible mechanism to compare the efficacy of enhanced BGP procedures with respect to the current protocol mechanisms. Since the convergence behavior can be significantly influenced by network topology, it is desirable to use large Internet like topologies in such controlled simulations.In this paper, we present first steps towards realizing a large scale BGP simulation environment for reasoning about current BGP procedures and also for evaluating the efficacy of BGP protocol enhancements.
NIST Net
Authors: Carson Mark , Santay Darrin
Published: October 2004

Testing of network protocols and distributed applications has become increasingly complex, as the diversity of networks and underlying technologies increase, and the adaptive behavior of applications becomes more sophisticated. In this paper, we present
NIST Net
, a tool to facilitate testing and experimentation with network code through emulation. NIST Net enables experimenters to model and effect arbitrary performance dynamics (packet delay, jitter, bandwidth limitations, congestion, packet loss and duplication) on live IP packets passing through a commodity Linux-based PC router. We describe the emulation capabilities of NIST Net; examine its architecture; and discuss some of the implementation challenges encountered in building such a tool to operate at very high network data rates while imposing minimal processing overhead. Calibration results are provided to quantify the fidelity and performance of NIST Net over a wide range of offered loads (up to 1 Gbps), and a diverse set of emulated performance dynamics.
Maximising student exposure to networking using FreeBSD virtual hosts
Authors: Armitage Grenville
Published: October 2004

A Remote Unix Lab Environment (RULE) is being developed that allows student access to networked hosts for their coursework and research projects. This paper describes our first generation solution using FreeBSD's "jail" functionality to emulate many FreeBSD hosts on a small handful of physical machines. Our primary constraint is to minimise the incremental infastructure cost to the Univeristy. Students access the RULE hosts through pre-existing PC labs scattered around campus and 802.11-equipped laptops. The FreeBSD hosts themselves are rackmounted in a small back room, minimising their impact on scarce University lab space. This paper describes our requirements, trade-offs, available tools, and how specific FreeBSD features are being utilized to create multiple virtual hosts for teaching purposes.
Resource management portal for laboratories using real devices on the Internet
Authors: Zimmerli Stefan , Steinemann Marc-Alain , Braun Torsten
Published: October 2004

Internet-based distance learning is slowly gaining new territories and substituting current teaching methodologies. However, distance learning not only consists of transferring documents to web pages, but also of developing new concepts, methods, and implementation architectures. This article presents concepts and implementation issues for an example remote hands-on networking laboratory. The described course gives access to real network hardware via the Internet. In particular, authentication, authorization, scheduling, and error recovery issues had to be solved.
Online system performance measurements with software and hybrid monitors
Authors: Svobodova Liba
Published: October 2004

Two monitors were implemented to collect information about the behavior of the online system developed and run at Stanford. The response of this online system was slow and main memory was a critical resource. The goal was to extract desired information by a method that requires only a negligible amount of monitored system resources. Results presented in this paper indicate that this effort has been successful. A software monitor that requires less than 700 bytes of main memory collects statistics about utilization of special online system resources and about the scheduler mechanism, detects system deadlocks, and measures online executive overhead. This software monitor helped to discover various facts about the system behavior; however, to understand the reasons behind certain situations, it was necessary to learn more about properties of individual terminal tasks. Since a software monitor would cause an intolerable system degradation and hardware monitoring is not directly applicable for such measurements, a hardware/software monitor interface was implemented which enables recording of software events by a hardware monitor. The monitoring artifact is thus kept close to zero. This technique has been applied to measure time a task spends in various states and it has many other uses.
Optimal folding of a paging drum in a three level memory system
Authors: Scheffier Lee J.
Published: October 2004

This paper describes a drum space allocation and accessing strategy called “folding”, whereby effective drum storage capacity can be traded off for reduced drum page fetch time. A model for the “folded drum” is developed and an expression is derived for the mean page fetch time of the drum as a function of the degree of folding. In a hypothetical three-level memory system of primary (directly addressable), drum, and tertiary (usually disk) memories, the tradeoffs among drum storage capacity, drum page fetch time, and page fetch traffic to tertiary memory are explored. An expression is derived for the mean page fetch time of the combined drum-tertiary memory system as a function of the degree of folding. Measurements of the MULTICS three-level memory system are presented as examples of improving multi-level memory performance through drum folding. A methodology is suggested for choosing the degree of folding most appropriate to a particular memory configuration.
On the probability of deadlock in computer systems
Authors: Ellis Clarence A.
Published: October 2004

As the number of processes and resources increases within a computer system, does the probability of that system's being in deadlock increase or decrease? This paper introduces Probabilistic Automata as a model of computer systems. This allows investigation of the above question for various scheduling algorithms. A theorem is proven which indicates that, within the types of systems considered, the probability of deadlock increases.
Scheduling independent tasks to reduce mean finishing-time (extended abstract)
Authors: Eruno J. , Coffman E. G. , Sethi R.
Published: October 2004

In this paper we study the problem of scheduling a set of independent tasks on m ≥ 1 processors to minimize the mean finishing-time (mean time in system). The importance of the mean finishing-time criterion is that its minimization tends to reduce the mean number of unfinished tasks in the system. In the paper we give a reduction of our scheduling problem to a transportation problem and thereby extend the class of known non enumerative scheduling algorithms [1]. Next we show that the inclusion of weights (weighted mean finishing-time) complicates the problem and speculate that there may be no non enumerative algorithm for this case. For the special case of identical processors we study the maximum finishing-time properties of schedules which are optimal with respect to mean finishing-time. Finally we give a scheduling algorithm having desirable properties with respect to both maximum finishing-time and mean finishing-time.
Protection and control of information sharing in multics
Authors: Saltzer Jerome H.
Published: October 2004

This paper describes the design of mechanisms to control sharing of information in the Multics system. Seven design principles help provide insight into the tradeoffs among different possible designs. The key mechanisms described include access control lists, hierarchical control of access specifications, identification and authentication of users, and primary memory protection. The paper ends with a discussion of several known weaknesses in the current protection mechanism design.
From the chair
Authors: Sipior Janice C. , Schatzberg Laurie , Leidner Dorothy , Niederman Fred , Lending Diane
Published: October 2004

A warm invitation is extended to you and your invited guests to attend "The Third Annual ACM-SIGMIS Reception," to be held as an ACM-SIGMIS event prior to the International Conference on Information Systems (ICIS2002) in Seattle, WA USA, December 14-17, 2003. Light refreshments will be served.

What:
Third Annual ACM-SIGMIS Reception

Where:
International Conference on Information Systems (ICIS2003) Sheraton Seattle Hotel & Towers, Room 418/420, Seattle, WA, USA

When:
5:30 to 7:00 pm Saturday, December 13, 2002

Who:
All ACM-SIGMIS members and their invited guests are welcome

I would like to take this opportunity to thank Sajda Qureshi, University of Nebraska at Omaha, for her outstanding service as Program Chair of the Knowledge Management Track for the International Conference on Information and Knowledge Management (CIKM) held November 3-8, 2003 in New Orleans, LA, USA. After graciously serving in this role for both CIKM'02 and CIKM'03, Sajda has decided not to continue. I would like to ask for volunteers to serve as Chair or Co-Chair of the Knowledge Management Track. For additional information on the role of Track Chair, please contact me at janice.sipior@villanova.edu or Sajda at squreshi@ist.unomaha.edu. CIKM is co-sponsored by SIGMIS and ACM-SIGIR (Special Interest Group on Information Retrieval). For more information on CIKM, please visit http://www.csee.umbc.edu/cikm.We would like to thank you for your continued support of SIGMIS. We encourage your comments and suggestions. Please feel free to contact any one of us.We look forward to seeing you at ICIS'03!
The evolution of the corporate IT function and the role of the CIO at Texaco
Authors: Hirschheim Rudy , Porra Jaana , Parks Michael S.
Published: October 2004

While senior management's confidence in the IT function and the CIO appears to be at an all time low, the field's understanding of why this condition exists is still confused. This paper suggests that the problem lies in how perceptions about IT are formed. To this end, the paper briefly looks at the growth and evolution of the corporate IT department at the oil giant Texaco, Inc. The analysis paints a somewhat disturbing picture of a top performing IT organization, intimately responsible for the success of the corporation, yet being perceived by much of senior management as an overhead that was costly and ineffective. The paper suggests some reasons as to why such perceptions might have come about, and what lessons the field can learn from what happened at Texaco. It is our belief that through such historical analyses, like the one performed at Texaco, a richer and broader understanding of the nature of organizational IT units is possible. These analyses shed light on the root causes for why IT is often perceived negatively. We suggest that IT organizations might change these perceptions by partnering with business units to share the credit for successful implementations and managing the perceptions about IT's contribution.
Two simple attacks on Lin-Shen-Hwang's strong-password authentication protocol
Authors: Ku Wei-Chi , Tsai Hao-Chuan , Chen Shuai-Min
Published: October 2004

In 2001, Lin, Sun, and Hwang proposed a strong-password authentication protocol, OSPA, which was later found to be vulnerable to a stolen-verifier attack and a man-in-the-middle attack. Recently, Lin, Shen, and Hwang [10] proposed an improved protocol of OSPA and showed that the improved protocol can resist the guessing attack, the replay attack, the impersonation attack, and the stolen-verifier attack. Herein, we show that their protocol is still vulnerable to a replay attack and a denial-of-service attack.
ULT
Authors: Pinilla Ruben , Gil Marisa
Published: October 2004

Java is known to be a valuable technology for building platform independent applications, based on an independent execution environment provided by a virtual machine (JVM, Java Virtual Machine) and an API formed by a set of classes. The Java platform was conceived as a solution for application transportation between heterogeneous platforms without the need of adapting and recompiling the source code. Some previous analyses of Sun JVM implementation (Java 2 SDK 1.2.2-006) establish that the HPI (Host Porting Interface) layer does not abstract enough the concurrency offered by the underlying platform.Consequently, the execution of the same Java application over distinct HPI platform implementations offers different behavior, being a possible cause of incorrect program execution. We consider that it's necessary a new HPI layer that can really abstract the concurrency supplied by the platform, giving a set of operations whose semantic does not vary between diverse platform implementations. With the new HPI, the JVM will be capable to perform a uniform behavior independently of the operating system. The new JVM with ULT offers an acceptable performance on multiprocessor architectures increasing the throughput and it implements a synchronization mechanism that achieves better results than the original JVM on SMP architectures.
Towards peer-to-peer content indexing
Authors: Baquero Carlos , Lopes Nuno
Published: October 2004

Distributed Hash Tables are the core technology on a significant share of system designs for Peer-to-Peer information sharing. Typically, a location mechanism is provided and object identifiers act as keys in the index of object locations. When introducing a search mechanism, where single words are used as keys, the key image cardinality will be driven by the word popularity and most of the present designs will be unable to load balance the index among the nodes. We present two contributions: A design that allows participating nodes to load balance the indexing of popular keys and avoid content hot-spots on single nodes; A distributed mechanism for probabilistic filtering of popular keys (with low search relevance) that paves the way for scalable full content indexing.
Session summary
Authors: Tokar Joyce L. , Dobbing Brian
Published: October 2004

The first session in the 12th International Real-Time Ada Workshop was a summary of the new core language features that are proposed for the Amendment to Ada that is scheduled for 2005.
Is Java augmented with the RTSJ a better real-time systems implementation technology than Ada 95?
Authors: Wellings Andy
Published: October 2004

This paper argues that Java (augmented by version 1.1 of the Real-Time Specification) will become superior to Ada 95 as a real-time systems implementation technology-once efficient and full implementations of version 1.1 become available. This is because the RTSJ will have an integrated set of mechanisms for representing the characteristics of real-time activities and a framework from within which those activities can be scheduled. Ada 95, in contrast, has a set of orthogonal low-level mechanisms which are invisible to the scheduler. Ada must, therefore, rise to the challenge and enhance its real-time support.
Task attribute-based scheduling
Authors: Burns A. , Wellings A. J.
Published: October 2004

Scheduling policies are of crucial importance to realtime systems. Ada currently gives full support to the most popular policy, fixed priority dispatching. In this paper we argue that the language should be extended to support new paradigms such as Earliest Deadline First (EDF), and combined paradigms. Possible extensions to the language in the form of new pragmas are described.
Verifying, validating and monitoring the open Ravenscar real time kernel
Authors: Maia R. , Moreira F. , Barbosa R. , Costa D. , Hjortaes Kjeld , Rodriguez Patricia , Pinho Luis Miguel
Published: October 2004

Business and mission critical real-time systems need to be fully predictable, in order that their behavior is known before deployment, even in the presence of faults. The Open Ravenscar Real Time Kernel (ORK) is a small size with reduced complexity kernel designed to be used in this type of applications. This kernel was implemented to be fully compliant with the Ravenscar profile, which defines a subset of the tasking features of Ada which can be used to implement a small and reliable kernel. Critical Software has recently conducted an evaluation on this kernel as well as started a new project to provide a monitoring tool for ORK, thus further enhancing the already existing range of hard real-time verification and validation tools. This paper summarizes the objectives and results of the ORK evaluation and presents the main goals and functionalities of the monitoring tool.
4+4
Authors: Turányi Zoltán , Valkó András , Campbell Andrew T.
Published: October 2004

We propose 4+4, a simple address extension architecture for Internet that provides an evolutionary approach to extending the existing IPv4 address space in comparison to more complex and disruptive approaches best exemplified by IPv6 deployment. The 4+4 architecture leverages the existence of Network Address Translators (NATs) and private address realms, and importantly, enables the return to end-to-end address transparency as the incremental deployment of 4+4 progresses. During the transition to 4+4, only NATs and end-hosts need to be updated and not the network routers. The 4+4 architecture retains the existing semantics of Internet names and addresses, and only proposes simple changes to the network layer that focus entirely on address extension. Encapsulation is used as the main tool to maintain backward compatibility. We present the design, implementation, and evaluation of the 4+4 architecture and discuss our implementation experiences and results from local and wide-area Internet experimentation. The 4+4 source code is freely available from the Web (comet.columbia.edu/ipv44) for experimentation.
NETKIT
Authors: Coulson Geoff , Blair Gordon , Hutchison David , Joolia Ackbar , Lee Kevin , Ueyama Jo , Gomes Antonio , Ye Yimin
Published: October 2004

While there has already been significant research in support of openness and programmability in networks, this paper argues that there remains a need for generic support for the integrated development, deployment and management of programmable networking software. We further argue that this support should explicitly address the management of run-time reconfiguration of systems, and should be independent of any particular programming paradigm (e.g. active networking or open signaling), programming language, or hardware/ operating system platform. In line with these aims, we outline an approach to the structuring of programmable networking software in terms of a ubiquitously applied software component model that can accommodate all levels of a programmable networking system from low-level system support, to in-band packet handling, to active networking execution environments to signaling and coordination.
Workshop on network-I/O convergence
Authors: Aggarwal Vinay , Maennel Olaf , Mogul Jeffrey , Romanow Allyn
Published: October 2004

This is a summary of the NICELI workshop, based on scribe reports written by Olaf Maennel and Vinay Aggarwal, and edited by Jeffrey Mogul and Allyn Romanow with help from the NICELI attendees. The workshop was held in conjunction with SIGCOMM 2003 on 27 August 2003 in Karlsruhe, Germany.Papers and presentations from the workshop are available on the Web at http://www.acm.org/sigs/sigcomm/sigcomm2003/workshop/niceli/Note-taking during an active discussion is a fallible process, so these notes may contain errors. We have encouraged participants to help us find these errors. Corrections made after this article goes to press may be found at the NICELI Web site.
Internetting between VAX and Apollo ring network
Authors: Chu N. N. Y.
Published: October 2004

Specifications for a network design to connect the Apollo DOMAIN network with the VAX system are discussed in this paper. Three networking approaches were considered which represent three distinct chronological stages in the evolution of computer communications. Based on a comparison of data transfer rate and the installation cost among these three alternatives, the LAN, represented by the Ethernet, was recommended as the connecting hardware.

The OSI Reference Model was used as a starting basis to discuss protocol issues to be built for the chosen LAN. Of particular interest are the transport, presentation, and application layers. The transport layer was designed to perform functions of the network and session layers in the OSI model. The presentation layer incorporated a text mapping algorithm to convert incompatible characters in filenames created on the VAX versus those on the Apollo. The application layer was designed with the capability to send and receive files between these two systems.
Office information and telecommunications
Authors: Shurig Russ
Published: October 2004

In order to understand the relationship of office information to office products and to telecommunications, the category of information media must be introduced. Voice, image, text and data information media can be related to one another, to computer and telecommunications technologies and to the needs of different types of workers.

The purpose of business offices, however, is not usually primarily information, computing or telecommunications, but rather knowledge, products and useful work. The information categories including media, transfer, products and work can be related to one another for a better understanding of office information products and telecommunications and in order to predict their future.
Exception handling in communication protocols
Authors: Atkins M. Stella
Published: October 2004

This paper describes structures used for exception handling in multi-process implementations of the X.25 and X.29 protocols. Each protocol layer is implemented as a collection of cooperating processes. These are structured in one of two alternative ways, reflecting differences in the type of exceptional situations that may occur.

Within each of the
lower
protocol layers, one process takes the form of a Finite State Machine. In these lower level protocols, where it is difficult to identify “normal” transitions, there are no special exception cases; we treat all transitions as being equally likely to occur.

For
higher
level protocols such as the X.29 protocol, exceptions occur less frequently. Here, transmitting and receiving are performed by two independent processes, and exception handling is performed by an auxiliary process which is invoked as needed. This multi-process structure matches the functionality of the protocol, and results in software which is easy to program and easy to understand.
Incorporation of multiaccess links into a routing protocol
Authors: Perlman Radia
Published: October 2004

Conventional routing protocols and algorithms work most efficiently on sparsely connected networks. Network topologies today include multiaccess links which include hundreds of nodes, all of which are capable of direct communication with each other. Some of these multiaccess links have broadcasting ability. This paper presents protocols and algorithms for efficiently dealing with the characteristics of various types of multiaccess links, when they are included as links in a general topology net.
A message handling system for public networks
Authors: Nakayama Toshihiko , Shimazu Yoshihiro , Haruta Katsuhiko
Published: October 2004

As a message handling system installed in the public communication networks, SSC (Store and Processing Service Control Facility) provides convenient communication processing services using storage and conversion technologies. The SSC conversion facilities, including media conversion from teletex codes to facsimile image, increase the communicable terminal range. Mailbox services, using four different kinds of personal Message Boxes in the SSC, bring about much benefit to personal communications. The SSC service requesting procedures facilitate multi-address delivery, timed delivery and automatic conversions. The SSC is a prototype which realizes the Message Handling Systems being studied in CCITT. The system is under developmental research in the NTT Laboratory.

This paper describes the basic SSC development concept, the relationship to the CCITT standard, the SSC service outline and the field trial system configuration.
Novanet communications network for a control system
Authors: Hill J. R. , Severyn J. R. , VanArsdall P. J.
Published: October 2004

Novanet is a control system oriented fiber optic local area network that was designed to meet the unique and often conflicting requirements of the Nova laser control system which will begin operation in 1984. The computers and data acquisition devices that form the distributed control system for a large laser fusion research facility need reliable, high speed communications. Both control/status messages and experimental data must be handled. A subset of NOVANET is currently operating on the two beam Novette laser system.
Network security considerations in BLN
Authors: Yao J.
Published: October 2004

In a heterogeneous computer network, resources on each node are protected by the local security mechanism. Network services allow local resources to be accessed remotely from other nodes. Without appropriate network security measures, each node is vulnerable to attack from the network. This paper analyzes the heterogeneous Bell Labs Network (BLN) environment and lists the potential network security risks. By assessing the risks, counter-measures are proposed for minimizing potential exposure. These counter-measures are part of a global network security mechanism being implemented for BLN.
Establishment communication systems
Authors: Kümmerle K.
Published: October 2004

In the sixties and early seventies, major activities in networking were focused on private and public data networks using either circuit and packet-switching technology or integrating both switching methods into a single network. In this time frame, manufacturers of main frames defined and implemented network architectures, ISO started work on the reference model of the Open-System Interconnect Architecture, and CCITT recommended the X-series of interfaces.

Local-area communication networks (LAN's) represent a comparatively new field of activity which can be viewed as an extension to data networks for making high-speed packet-switching services available to the in-house domain. Currently, much research and development work is being pursued in this field, both at universities and in industry. The term local refers to communication on the users' premises, i.e., within a building or among a cluster of buildings.

Local data and voice communication are not new. A typical example of a system widely used today for local data communication between hosts and display terminals is a star configuration where the terminals are attached to control units tightly coupled to a processor via I/O channels. The necessary terminal control functions are provided in the control unit and shared among a set of terminals. The most widely used local communication system is the Private Automatic Branch Exchange (PABX). Most PABX's installed today are optimised for real-time voice, and use analog technology.
Prioritizing packet transmission in local multiaccess networks
Authors: Ni Lionel M. , Li Xianji
Published: October 2004

Carrier sense multiple access with collision detection (CSMA/CD) protocols have been extensively studied and developed for local area networks. In CSMA/CD protocols, all messages are treated equally in competing for the communication channel. Thus, important or time-critical messages may be severely delayed. In this paper, a new CSMA/CD protocol with message-based priority functions is proposed. A priority code comparison period is needed to determine the highest priority class that can compete for the comunication channel. A contention period based on CSMA/CD scheme is then followed. Both nonpreemptive discipline and preemptive discipline are discussed. In each discipline, both the single mode and the batch mode are considered and compared. The overhead in implementing the proposed protocol, either for a few or for a large number of priority classes, is shown to be minimal. In general, a preemptive single mode scheme provides a better performance. The requirements of hierarchical independence of performance and fairness are satisfied.
Performance potential of communications interface processors
Authors: Woodside C. M.
Published: October 2004

Interface processors are being developed in hardware and firmware for communications protocols at higher and higher levels (HDLC, X.25, Ethernet ...), for smaller and smaller host systems. How far this process will go depends on the driving factors of increased performance and simpler implementation of the systems which use the protocols. A simplified performance model with parameters, which encompasses a large part of all systems using communications, is used to find those parameter combinations offering various degrees of performance improvement. The results can be used to approximately distinguish those cases which will provide the market for performance improvement via higher-level interface processors.
Optical storage of page images and pictorial data - opportunities and needed advances in information retrieval
Authors: Nugent William R. , Harding Jessica R.
Published: October 2004

We describe two current development projects at the Library of Congress using high-density optical storage, both of which require more advanced and improved computer-based information retrieval methodologies than existing bibliographic retrieval systems. A much greater emphasis will be placed on the information content of the articles rather than on the broad subject categories in general use for computer retrieval citations to book materials. Needed approaches include the linking of selected external reference sources and the extraction of character-encoded index information from the page images by OCR techniques. Our position is that extremely high density storage of articles in a single subject area requires a finer resolution in the retrieval system accessing the material. A single side of a 12-inch digital optical disk, for example, can hold 15 years of the
Journal of the ACM.
On the effectiveness of route-based packet filtering for distributed DoS attack prevention in power-law internets
Authors: Park Kihong , Lee Heejo
Published: October 2004

Denial of service (DoS) attack on the Internet has become a pressing problem. In this paper, we describe and evaluate route-based distributed packet filtering (DPF), a novel approach to distributed DoS (DDoS) attack prevention. We show that DPF achieves proactiveness and scalability, and we show that there is an intimate relationship between the effectiveness of DPF at mitigating DDoS attack and power-law network topology.The salient features of this work are two-fold. First, we show that DPF is able to proactively filter out a significant fraction of spoofed packet flows and prevent attack packets from reaching their targets in the first place. The IP flows that cannot be proactively curtailed are extremely sparse so that their origin can be localized---i.e., IP traceback---to within a small, constant number of candidate sites. We show that the two proactive and reactive performance effects can be achieved by implementing route-based filtering on less than 20% of Internet autonomous system (AS) sites. Second, we show that the two complementary performance measures are dependent on the properties of the underlying AS graph. In particular, we show that the power-law structure of Internet AS topology leads to connectivity properties which are crucial in facilitating the observed performance effects.
On the impact of policing and rate guarantees in DiffServ networks
Authors: Ashmawi Wael , Guerin Roch , Wolf Stephen , Pinson Margaret
Published: October 2004

Over the past few years, there have been a number of proposals aimed at introducing different levels of service in the Internet. One of the more recent proposals is the Differentiated Services (Diff-Serv) architecture, and in this paper we explore how the policing actions and associated rate guarantees provided by the Expedited Forwarding (EF) translate into perceived benefits for applications that are the presumed users of such enhancements. Specifically, we focus on video streaming applications that arguably have relatively strong service quality requirements, and which should, therefore, stand to benefit from the availability of some form of enhanced service. Our goal is to gain a better understanding of the relation that exists between application level quality measures and the selection of the network level parameters that govern the delivery of the guarantees that an EF based service would provide. Our investigation, which is experimental in nature, relies on a number of standard streaming video servers and clients that have been modified and instrumented to allow quantification of the perceived quality of the received video stream. Quality assessments are performed using a Video Quality Measurement tool based on the ANSI objective quality standard. Measurements were made over both a local Diff-Serv testbed and across the QBone, a QoS enabled segment of the Internet2 infrastructure. The paper reports and analyzes the results of those measurements.
Statistical bandwidth sharing
Authors: Fred S. Ben , Bonald T. , Proutiere A. , Régnié G. , Roberts J. W.
Published: October 2004

In this paper we study the statistics of the realized throughput of elastic document transfers, accounting for the way network bandwidth is shared dynamically between the randomly varying number of concurrent flows. We first discuss the way TCP realizes statistical bandwidth sharing, illustrating essential properties by means of packet level simulations. Mathematical flow level models based on the theory of stochastic networks are then proposed to explain the observed behavior. A notable result is that first order performance (e.g., mean throughput) is insensitive with respect both to the flow size distribution and the flow arrival process, as long as "sessions" arrive according to a Poisson process. Perceived performance is shown to depend most significantly on whether demand at flow level is less than or greater than available capacity. The models provide a key to understanding the effectiveness of techniques for congestion management and service differentiation.
Chord
Authors: Stoica Ion , Morris Robert , Karger David , Kaashoek M. Frans , Balakrishnan Hari
Published: October 2004

A fundamental problem that confronts peer-to-peer applications is to efficiently locate the node that stores a particular data item. This paper presents
Chord
, a distributed lookup protocol that addresses this problem. Chord provides support for just one operation: given a key, it maps the key onto a node. Data location can be easily implemented on top of Chord by associating a key with each data item, and storing the key/data item pair at the node to which the key maps. Chord adapts efficiently as nodes join and leave the system, and can answer queries even if the system is continuously changing. Results from theoretical analysis, simulations, and experiments show that Chord is scalable, with communication cost and the state maintained by each node scaling logarithmically with the number of Chord nodes.
A scalable content-addressable network
Authors: Ratnasamy Sylvia , Francis Paul , Handley Mark , Karp Richard , Shenker Scott
Published: October 2004

Hash tables - which map "keys" onto "values" - are an essential building block in modern software systems. We believe a similar functionality would be equally valuable to large distributed systems. In this paper, we introduce the concept of a Content-Addressable Network (CAN) as a distributed infrastructure that provides hash table-like functionality on Internet-like scales. The CAN is scalable, fault-tolerant and completely self-organizing, and we demonstrate its scalability, robustness and low-latency properties through simulation.
SRR: An O(1) time complexity packet scheduler for flows in multi-service packet networks
Authors: Chuanxiong Guo
Published: October 2004

In this paper, we present a novel fair queueing scheme, which we call Smoothed Round Robin (SRR). Ordinary round robin schedulers are well known for their burstiness in the scheduling output. In order to overcome this problem, SRR codes the weights of the flows into binary vectors to form a Weight Matrix, then uses a Weight Spread Sequence (WSS), which is specially designed to distribute the output more evenly, to schedule packets by scanning the Weight Matrix. By using the WSS and the Weight Matrix, SRR can emulate the Generalized Processor Sharing (GPS) well. It possesses better short-term fairness and schedule delay properties in comparison with various round robin schedulers. At the same time, it preserves
O
(1) time complexity by avoiding the time-stamp maintenance employed in various Fair Queueing schedulers. Simulation and implementation experiments show that SRR can provide good average end-to-end delay for soft real-time services. SRR can also be implemented in high-speed networks to provide QoS for its simplicity and low time complexity.
Stability issues in OSPF routing
Authors: Basu Anindya , Riecke Jon
Published: October 2004

We study the stability of the OSPF protocol under steady state and perturbed conditions. We look at three indicators of stability, namely, (a) network convergence times, (b) routing load on processors, and (c) the number of route flaps. We study these statistics under three different scenarios: (a) on networks that deploy OSPF with TE extensions, (b) on networks that use subsecond HELLO timers, and (c) on networks that use alternative strategies for refreshing link-state information. Our results are based on a very detailed simulation of a real ISP network with 292 nodes and 765 links.
On inferring TCP behavior
Authors: Pahdye Jitendra , Floyd Sally
Published: October 2004

Most of the traffic in today's Internet is controlled by the Transmission Control Protocol (TCP). Hence, the performance of TCP has a significant impact on the performance of the overall Internet. TCP is a complex protocol with many user-configurable parameters and a range of different implementations. In addition, research continues to produce new developments in congestion control mechanisms and TCP options, and it is useful to trace the deployment of these new mechanisms in the Internet. As a final concern, the stability and fairness of the current Internet relies on the voluntary use of congestion control mechanisms by end hosts. Therefore it is important to test TCP implementations for conformant end-to-end congestion control. Since web traffic forms the majority of the TCP traffic, TCP implementations in today's web servers are of particular interest. We have developed a tool called TCP Behavior Inference Tool (TBIT) to characterize the TCP behavior of a remote web server. In this paper, we describe TBIT, and present results about the TCP behaviors of major web servers, obtained using this tool. We also describe the use of TBIT to detect bugs and non-compliance in TCP implementations deployed in public web servers.
On the correctness of IBGP configuration
Authors: Griffin Timothy G. , Wilfong Gordon
Published: October 2004

The Border Gateway Protocol (BGP) has two distinct modes of operation. External BGP (EBGP) exchanges reachability information between autonomous systems, while Internal BGP (IBGP) exchanges external reachability information within an autonomous system. We study several routing anomalies that are unique to IBGP because, unlike EBGP, forwarding paths and signaling paths are not always symmetric. In particular, we focus on anomalies that can cause the protocol to diverge, and those that can cause a router's chosen forwarding path to an egress point to be deflected by another router on that path. Deflections can greatly complicate the debugging of routing problems, and in the worst case multiple deflections can combine to form persistent forwarding loops. We define a correct IBGP configuration to be one that is anomaly free for every possible set of routes sent by neighboring autonomous systems. We show that determination of IBGP configuration correctness is NP-hard. However, we give simple sufficient conditions on network configurations that guarantee correctness.
On the long-run behavior of equation-based rate control
Authors: VojnoviΕ Milan , Le Boudec Jean-Yves
Published: October 2004

We consider unicast equation-based rate control, where a source estimates the loss event ratio $p$, and, primarily at loss events, adjusts its send rate to $f(p)$. Function $f$ is assumed to represent the loss-throughput relation that TCP would experience. When no loss occurs, the rate may also be increased according to some additional mechanism. We assume that the loss event interval estimator is non-biased. If the loss process is deterministic, the control is TCP-friendly in the long-run, i.e, the average throughput does not exceed that of TCP. If, in contrast, losses are random, it is a priori not clear whether this holds, due to the non-linearity of $f$, and a phenomenon similar to Feller's paradox. Our goal is to identify the key factors that drive whether, and how far, the control is TCP friendly (in the long run). As TCP and our source may experience different loss event intervals, we distinguish between TCP-friendliness and conservativeness (throughput does not exceed $f(p)$). We give a representation of the long term throughput, and derive that conservativeness is primarily influenced by various convexity properties of $f$, the variability of loss events, and the correlation structure of the loss process. In many cases, these factors lead to conservativeness, but we show reasonable experiments where the control is clearly non-conservative. However, our analysis also suggests that our source should experience a higher loss event ratio than TCP, which would make non-TCP friendliness less likely. Our findings provide guidelines that help understand when an equation base control is indeed TCP-friendly in the long-run, and in some cases, excessively so. The effects of round trip time and its variations are not included in this study.