bluuebunny/crossref_metadata_2025 huggingface dataset:
Congestion control for high bandwidth-delay product networks
Authors: Katabi Dina , Handley Mark , Rohrs Charlie
Published: October 2004

Theory and experiments show that as the per-flow product of bandwidth and latency increases, TCP becomes inefficient and prone to instability, regardless of the queuing scheme. This failing becomes increasingly important as the Internet evolves to incorporate very high-bandwidth optical links and more large-delay satellite links.To address this problem, we develop a novel approach to Internet congestion control that outperforms TCP in conventional environments, and remains efficient, fair, scalable, and stable as the bandwidth-delay product increases. This new eXplicit Control Protocol, XCP, generalizes the Explicit Congestion Notification proposal (ECN). In addition, XCP introduces the new concept of decoupling utilization control from fairness control. This allows a more flexible and analytically tractable protocol design and opens new avenues for service differentiation.Using a control theory framework, we model XCP and demonstrate it is stable and efficient regardless of the link capacity, the round trip delay, and the number of sources. Extensive packet-level simulations show that XCP outperforms TCP in both conventional and high bandwidth-delay environments. Further, XCP achieves fair bandwidth allocation, high utilization, small standing queue size, and near-zero packet drops, with both steady and highly varying traffic. Additionally, the new protocol does not maintain any per-flow state in routers and requires few CPU cycles per packet, which makes it implementable in high-speed routers.
Replication strategies in unstructured peer-to-peer networks
Authors: Cohen Edith , Shenker Scott
Published: October 2004

The Peer-to-Peer (P2P) architectures that are most prevalent in today's Internet are decentralized and unstructured. Search is blind in that it is independent of the query and is thus not more effective than probing randomly chosen peers. One technique to improve the effectiveness of blind search is to proactively replicate data. We evaluate and compare different replication strategies and reveal interesting structure: Two very common but very different replication strategies - uniform and proportional - yield the same average performance on successful queries, and are in fact worse than any replication strategy which lies between them. The optimal strategy lies between the two and can be achieved by simple distributed algorithms. These fundamental results o.er a new understanding of replication and show that currently deployed replication strategies are far from optimal and that optimal replication is attainable by protocols that resemble existing ones in simplicity and operation.
Routers with a single stage of buffering
Authors: Iyer Sundar , Zhang Rui , McKeown Nick
Published: October 2004

Most high performance routers today use combined input and output queueing (CIOQ). The CIOQ router is also frequently used as an abstract model for routers: at one extreme is input queueing, at the other extreme is output queueing, and in-between there is a continuum of performance as the speedup is increased from 1 toN(whereNis the number of linecards). The model includes architectures in which a switch fabric is sandwiched between two stages of buffering. There is a rich and growing theory for CIOQ routers, including algorithms, throughput results and conditions under which delays can be guaranteed. But there is a broad class of architectures that are not captured by the CIOQ model, including routers with centralized shared memory, and load-balanced routers. In this paper we propose an abstract model called Single-Buffered (SB) routers that includes these architectures. We describe a method called Constraint Sets to analyze a number of SB router architectures. The model helped identify previously unstudied architectures, in particular the Distributed Shared Memory router. Although commercially deployed, its performance is not widely known. We find conditions under which it can emulate an ideal shared memory router, and believe it to be a promising architecture. Questions remain about its complexity, but we find that the memory bandwidth, and potentially the power consumption of the router is lower than for a CIOQ router.
Tussle in cyberspace
Authors: Clark David D. , Wroclawski John , Sollins Karen R. , Braden Robert
Published: October 2004

The architecture of the Internet is based on a number of principles, including the self-describing datagram packet, the end to end arguments, diversity in technology and global addressing. As the Internet has moved from a research curiosity to a recognized component of mainstream society, new requirements have emerged that suggest new design principles, and perhaps suggest that we revisit some old ones. This paper explores one important reality that surrounds the Internet today: different stakeholders that are part of the Internet milieu have interests that may be adverse to each other, and these parties each vie to favor their particular interests. We call this process "the tussle". Our position is that accommodating this tussle is crucial to the evolution of the network's technical architecture. We discuss some examples of tussle, and offer some technical design principles that take it into account.
The experienced "sense" of a virtual community
Authors: Blanchard Anita L. , Markus M. Lynne
Published: October 2004

E-commerce strategists advise companies to create virtual communities for their customers. But what does this involve? Research on face-to-face communities identifies the concept of "sense of community:" a characteristic of successful communities distinguished by members' helping behaviors and members' emotional attachment to the community and other members. Does a sense of virtual community exist in online settings, and what does it consist of? Answering these questions is key, if we are to provide guidance to businesses attempting to create virtual communities.The paper explores the concept of sense of virtual community in a newsgroup we call Multiple Sports Newsgroup (MSN). We first demonstrate that MSN does indeed have a sense of virtual community, but that the dimensions of the sense of community in MSN differ somewhat from those reported for physical communities. The nature of these differences is plausibly related to the differences between electronic and face-to-face communication. We next describe the behavioral processes that contribute to the sense of virtual community at MSN-exchanging support, creating identities and making identifications, and the production of trust. Again, these processes are similar to those found in non-virtual communities, but they are related to the challenges of electronic communication. Lastly, we consider the question of how sense of community may come about and discuss the implications for electronic business.
Language, mathematics and other dangerous things
Authors: Fass Leona F.
Published: October 2004

We describe our original automata-theoretic, highly mathematical perspective on language representation and learning, and compare with some current research advances and some that are proposed. We find benefits of a mathematical approach to "real life" language learning by humans and today's machines, and review work of researchers who adapt such computational techniques to complex system development and language-related machine processes. Examples include design of communicating agents and proposed development of the Semantic Web. While emphasizing the success of a mathematical perspective on language representation and learning, we also note the danger of assuming that "perfect" results will always be produced by a mathematical approach.
Sophia
Authors: Wawrzoniak Mike , Peterson Larry , Roscoe Timothy
Published: October 2004

This paper motivates and describes an example network Information Plane, called Sophia, currently deployed on PlanetLab. Sophia is a distributed system that collects, stores, propagates, aggregates, and reacts to observations about the network's current conditions. Sophia's approach is novel: it can be viewed as a multi-user distributed expression evaluator in which sensors and actuators form the ground terms, and statements take on the complete expressiveness of a logic language like Prolog. This paper argues that this approach has several advantages in managing and controlling a complex, federated, and evolving network: (1) a declarative logic language provides a natural way to express the kinds of statements that are common to this application domain, through temporal and positional logic rules, facts and expressions; and (2) distributed evaluation of such logic expressions provides many opportunities for performance optimization yielding an efficient system.
Enabling large-scale wireless broadband
Authors: Karrer R. , Sabharwal A. , Knightly E.
Published: October 2004

The vision is tantalizing: a high-performance, scalable, and widely deployed wireless Internet that facilitates services ranging from radically new and unforeseen applications to true wireless "broadband" to residences and public spaces at rates of 10s of Mb/sec. However, while high-speed wireless access is easy to achieve in an enterprise network via low-cost IEEE 802.11 (WiFi) access points, wireless technology in public spaces is in its infancy. "Hot spots" provide high-speed wireless access, but do so in very few isolated "islands" at immense costs. Likewise, while fixed wireless (e.g. LMDS) and 3G can provide ubiquitous coverage and 3G can support mobility, throughputs can often be two orders of magnitude slower than WiFi.In this paper, we formulate the challenges of building a high-performance, scalable and widely deployed wireless Internet along 10 premises. We make the case for the requirement of a fundamental new architecture based on beamforming antennas deployed on fixed, wire-powered
Transit Access Points (TAPs)
that form a multi-hopping wireless backbone with a limited number of
wired
ingress/egress points. To address scalability, deployability, and performance challenges we present distributed, opportunistic and coordinated resource management problems and a novel "network is the channel" framework that searches for fundamental information-theoretic tradeoffs between protocol overhead and capacity.
Honeycomb
Authors: Kreibich Christian , Crowcroft Jon
Published: October 2004

This paper describes a system for automated generation of attack signatures for network intrusion detection systems. Our system applies pattern-matching techniques and protocol conformance checks on multiple levels in the protocol hierarchy to network traffic captured a honeypot system. We present results of running the system on an unprotected cable modem connection for 24 hours. The system successfully created precise traffic signatures that otherwise would have required the skills and time of a security officer to inspect the traffic manually.
Repeatable and realistic wireless experimentation through physical emulation
Authors: Judd Glenn , Steenkiste Peter
Published: October 2004

In wireless networking research, there has long existed a fundamental tension between experimental realism on one hand, and control and repeatability on the other hand. Hardware-based experimentation provides realism, but is tightly coupled to the physical environment and circumstances under which experiments are carried out. To overcome this, researchers have understandably embraced simulation as a means of evaluation. Unfortunately, wireless simulation is plagued with inherent inaccuracies. To overcome the stark tradeoff between the realism of hardware-based experimentation and the repeatability of simulation-based experimentation, we are developing a wireless emulator that enables both realistic and repeatable experimentation. Unlike previous emulators, our approach simultaneously achieves both a high degree of realism and fine-grained repeatability by leveraging physical layer emulation.
MAC-layer anycasting in ad hoc networks
Authors: Choudhury Romit Roy , Vaidya Nitin H.
Published: October 2004

A wireless ad hoc network is formed by a group of wireless hosts, without the use of any infrastructure. To enable communication, hosts cooperate among themselves to forward packets on behalf of each other. A key challenge in ad hoc networks lies in designing efficient routing strategies. While several routing protocols have been proposed, most of them aim to select one optimal route between the source and destination. The MAC layer at each intermediate node is then required to forward packets to the next downstream node on that route. We argue that choosing a single optimal route at the network layer may not be sufficient. Knowledge of short-term channel conditions at the MAC layer can play an important role in improving end-to-end performance. Instantaneous interference, channel contention, power constraints and other considerations may be taken into account along with the network layer's long-term view. This paper proposesMAC layer anycasting- a forwarding strategy that combines the guidelines from the network layer, with MAC layer knowledge of the local channel. We describe some applications ofMAC-layer anycasting, and discuss the performance related tradeoffs.
Practical verification techniques for wide-area routing
Authors: Feamster Nick
Published: October 2004

Protocol and system designers use verification techniques to analyze a system's correctness properties. Network operators need verification techniques to ensure the "correct" operation of BGP. BGP's distributed dependencies cause small configuration mistakes or oversights to spur complex errors, which sometimes have devastating effects on global connectivity. These errors are often difficult to debug because they are sometimes only exposed by a specific message arrival pattern or failure scenario.This paper presents an approach to BGP verification that is primarily based on static analysis of router configuration. We argue that: (1) because BGP's a configuration affects its fundamental behavior, verification is a
program analysis
problem, (2) BGP's complex, dynamic interactions are difficult to abstract and impossible to enumerate, which precludes existing verification techniques, (3) because of BGP's flexible, policy-based configuration, some aspects of BGP configuration must be checked against a higher-level specification of
intended
policy, and (4) although static analysis can catch many configuration errors, simulation and emulation are also necessary to determine the precise scenarios that could expose errors at runtime. Based on these observations, we propose the design of a BGP verification tool, discuss how it could be applied in practice, and describe future research challenges.
Practical, distributed network coordinates
Authors: Cox Russ , Dabek Frank , Kaashoek Frans , Li Jinyang , Morris Robert
Published: October 2004

Vivaldi is a distributed algorithm that assigns synthetic coordinates to internet hosts, so that the Euclidean distance between two hosts' coordinates predicts the network latency between them. Each node in Vivaldi computes its coordinates by simulating its position in a network of physical springs. Vivaldi is both distributed and efficient: no fixed infrastructure need be deployed and a new host can compute useful coordinates after collecting latency information from only a few other hosts. Vivaldi can rely on piggy-backing latency information on application traffic instead of generating extra traffic by sending its own probe packets.This paper evaluates Vivaldi through simulations of 750 hosts, with a matrix of inter-host latencies derived from measurements between 750 real Internet hosts. Vivaldi finds synthetic coordinates that predict the measured latencies with a median relative error of 14 percent. The simulations show that a new host joining an existing Vivaldi system requires fewer than 10 probes to achieve this accuracy. Vivaldi is currently used by the Chord distributed hash table to perform proximity routing, replica selection, and retransmission timer estimation.
Should we build Gnutella on a structured overlay?
Authors: Castro Miguel , Costa Manuel , Rowstron Antony
Published: October 2004

There has been much interest in both unstructured and structured overlays recently. Unstructured overlays, like Gnutella, build a random graph and use flooding or random walks on the graph to discover data stored by overlay nodes. Structured overlays assign keys to data items and build a graph that maps each key to a specific node. The structure of the graph enables efficient discovery of data items given their keys but it does not support complex queries.Should we build Gnutella on a structured overlay? We believe the answer is yes. We replaced the random graph in Gnutella by a structured overlay while retaining the content placement and discovery mechanisms of unstructured overlays to support complex queries. Our preliminary results indicate that we can use structure to improve the performance of floods and rondom walks. They also indicate that structure can be used to reduce maintenance overhead, which is surprising because it is commonly believed that unstructured overlays have lower maintenance overhead than structured overlays.
Root Kits
Authors: Kühnhauser Winfried E.
Published: October 2004

Root Kits are tool boxes containing a collection of highly skilled tools for attacking computer systems. Their algorithms and databases contain professional knowledge about methods and mechanisms for completely automated attacks both over a network as well as from within a system. Root kits attack by maneuvering a system into executing a script with supervisor privileges. Once having gained full control, such scripts begin to install several software packages, including backdoors for easy future access, deception packages and modified versions of administration utilities that conceal system modifications and refuse to counterattack any future infiltration.The security threat imposed by root kits is quite serious. A root kit attack is swift, fully automatic, and has long-lasting effects. An attack has a high success probability, and it requires only a very small amount of knowledge. Last not least, root kits axe easily available in the Internet.This paper is a survey of the works of root kits from an operating systems point of view. Keywords: error exploitation, error proliferation, privilege proliferation, kernel abstractions, trusted computing base, reference monitor, security domains, mandatory and discretionary access control, secure booting, secure program execution
On designing direct dependency
Authors: Gupta B. , Liu Z. , Liang Z.
Published: October 2004

In this paper, we have proposed two recovery algorithms for distributed systems. Both algorithms follow a revolving centralized scheme. The direct dependency tracking of an integer representing the number of messages sent by each process has been shown to be sufficient to determine the maximum consistent state. The main feature of the recovery algorithms is that they are executed simultaneously by all the participating processes while determining the maximum consistent state. It thus ensures fast execution. The time overheads of the recovery algorithms are reduced further because both algorithms avoid some unnecessary comparisons while determining a consistent global checkpoint. The second algorithm has been shown to be faster than the first one, because it avoids, in general, much larger number of unnecessary comparisons compared to the first one; however the trade off is the increased amount of control information to be stored at each checkpoint in the second algorithm.
Object-oriented design
Authors: Booch Grady
Published: October 2004

The current software depression is characterized by software that is late, erroneous, and costly. Experience indicates that the application of appropriate design methodolgies, embodied in a high-order language, is appropriate in combatting this depression. In particular, this paper describes an object-oriented design methodology, using Ada as the implementation language.
Ada training considerations
Authors: Braun Christine L.
Published: October 2004

The government has instituted the Ada program with the objective of reducing its rapidly-increasing software development costs. Ada will do this by providing programmers with modern capabilities that have been demonstrated to promote more cost-effective software development. Clearly, the government's objective can be met only if programmers actually learn to use these capbilities effectively. This requires significant change from the way they are used to working, and poses a massive retraining requirement. SofTech has been working with the U .S. Army to assess the training needs of various segments of the industry and government work forces, to identify training issues and effective techniques for addressing them, and to recommend a training approach . This effort has resulted in development of a complete recommended Ada curriculum. The curriculum provides training in the Ada language, the environment, and modern development methodologies. It consists of a set of modular building blocks that can be configured to meet varying individual or organizational needs, adapted to different organizations' practices, and packaged to meet scheduling needs . This approach answers many of the difficult questions that have been asked about Ada training, and presents a realistic roadmap to widespread industry competence in Ada.
Experiences with matrix multiplication using Ada tasks
Authors: Fernandez John D. , Carlisle Homer , Sheppard Sallie
Published: October 2004

This paper relates our experiences in learning Ada using Ada/Ed and presents a problem in its various stages of development and solution. The major focus of our efforts centered on the use of Ada tasking facilities and the conversion of the final solution into a generic package. Multiplication of square matrices was selected as the basis for our study, since the calculation of inner products (row X column) provided an excellent opportunity for using tasks.
The role of Ada in real time embedded applications
Authors: Phillips Stephen P. , Stevenson Peter R.
Published: October 2004

This paper discusses executive software requirements peculiar to real time embedded systems, such as spacecraft, missile and avionics, and the role of Ada in meeting those requirements. In these applications, the cyclical executive has traditionally played a large role because of its ability to work efficiently with resource and frequency constraints. The Ada pragma provides a way to implement this type of executive in a way that can be efficient and easy to use. Progmas of this type could become a standard for the avionics community.
Implementation implications of Ada generics
Authors: Bray Gary
Published: October 2004

Generic program units as defined in Ada pose several important design issues for compilers, both in semantic analysis and in runtime implementation. Chief among these issues are separate compilation of generic bodies and the sharing of code among several instantiations of a generic. An implementation is described that allows separate compilation of generic bodies with full semantic checking and that automatically shares instance bodies based on the characteristics of the actual parameters. A single instance body is generated for each "Instance class". Instance classes are formed by actual parameters with the same representation attributes.
Planning an AdaTEC/AdaJUG meeting
Authors: Moore Melody , Foreman John , Daily Paulan
Published: October 2004

During and after the October 1983 AdaJug/AdaTEC meetings, the Texas Instruments conference team received numerous inquiries for additional information concerning the techniques used in organizing and preparing for the conference. This article is a synopsis of a paper that chronicles the effort that went into those meetings, and shares the benefit of our experience with future meeting hosts. Our conference was an unexpectedly large one, and our conference team was considerably challenged. While the techniques and procedures identified in this paper proved very successful, we would urge any potential future host to contact the leadership of either AdaTEC or AdaJUG for further guidance and policies.
A simple approach to a relaxed syntax for an Ada PDL
Authors: Yavne Nancy Linden
Published: October 2004

Mayda Software Engineering is developing an Ada based design language, ADA/SDP. This effort is influenced by Mayda's experience in using and teaching SDP, the program design language developed and marketed by Mayda. Many organizations are planning to use Ada as a design language, sometimes with special features added. This paper presents a different approach for a PDL based on Ada. This approach uses a simplified Ada syntax with features that facilitate a more natural and readable design description. ADA/SDP provides nearly all the support the Ada compiler gives to the design process, but its relaxed syntax reflects human factors considerations unique to the design process, as opposed to coding. The argument is given that compared to using Ada as a design language, this approach is more appropriate for the design process and will be more acceptable to a large part of the software development community. It will also be a useful vehicle with which one can introduce Ada concepts.
First use of XAda methodology
Authors: Burkhardt Bonnie
Published: October 2004

This paper describes how the XAda[1] methodology was applied to project development in the software high-level design phase. It describes a project that translated an existing high-level design to Ada, compiled it, and executed it. The existing high-level design was written in the GTE methodology of expressing a design in English. The paper demonstrates how XAda provides a more accurate software design expression by writing the design in Ada and executing it. It also discusses how executing the design allows designers to test their design to detect flaws earlier, and it allows customers to approve of some of the man-machine interface. Included are descriptions of resource-consuming stubs, file descriptions, service routines, comments, documents produced from the comments, and execution of the high-level design. Sample stubs, file descriptions, documents, and graphs displaying various statistics about the test of XAda are also included. This paper concludes with two sections discussing problems with both the English high-level design and the XAda high-level design.
On the complexity of permutation network design
Authors: Afshar Siroos K.
Published: October 2004

The problem addressed is: Given a set of permutations of n objects, design a network consisting of 2-state switches which realizes the given permutations, and in which the number of switches is minimal. A general standard form for feedback-free permutation networks is proposed and used to formulate the problem mathematically. The complexity of an algorithm to solve the problem is studied, and it is shown that there is evidence to suspect that the problem is in the class NP
NP
.
Tests for primality under the Riemann hypothesis
Authors: Vélu Jacques
Published: October 2004

Assuming the extended Riemann hypothesis (ERH), G. Miller produced in a very interesting paper [1], an algorithm which tests primality and runs in O((log n)
4+ε
) steps. We provide a short proof of this result.
Improved authentication key exchange protocol without using one-way hash function
Authors: Lee Narn-Yih , Wu Chien-Nan
Published: October 2004

Recently, Hwang, Shiau and Lai proposed an efficient authentication key exchange protocol to decrease the computation cost of the Harn-Lin improved protocol. However, the Hawang-Shiau-Lai protocol cannot withstand the modification attack. Therefore, this paper will propose an improved protocol to enhance the security of the Hwang-Shiau-Lai protocol. The improved protocol is able to defeat the modification attack and is as efficient as the Hwang-Shiau-Lai protocol. Moreover, the improved protocol also provides the perfect forward secrecy.
Verifying linear time temporal logic properties of concurrent Ada programs with quasar
Authors: Evangelista S. , Kaiser C. , Pradat-Peyre J. F. , Rousseau P.
Published: October 2004

In this paper we present an original and useful way for specifying and verifying temporal properties of concurrent programs with our tool named Quasar. Quasar is based on ASIS and uses formal methods (model checking). Properties that can be checked are either general, like deadlock or fairness, or more context specific, referring to tasks states or to value of variables; properties are then expressed in temporal logic. In order to simplify the expression of these properties, we define some templates that can be instantiated with specific items of the programs. We demonstrate the usefulness of these templates by verifying subtle variations of the Peterson algorithm. Thus, although Quasar uses up-to-date formal methods it remains accessible to a large class of practitioners.
A DSA model for data access in self-organizing systems
Authors: Gantsou Dhavy
Published: October 2004

Data availability is an important issue for self-organizing systems, which include both Peer-to-Peer (P2P) systems and mobile ad hoc networks (MANETs). In P2P systems, the problem of data availability is solved by replicating data across the network. However, this approach wastes resources, and so is not appropriate for MANETs where resource frugality is essential. Unlike P2P systems, MANETs routing protocols require real-time features to cope with a highly dynamic environment, and efficient synchronization mechanisms to guarantee consistent updates of routing information. Unfortunately, due to the semantics of the languages that are most used in network programming, such mechanisms are extremely hard or even impossible to implement in efficient way. To build an application capable of meeting almost all of these requirements, while providing a framework capable of evolving over time, we propose an approach that is based on DSA.
European air traffic flow management
Authors: Allaert Gaetan , Craeynest Dirk , Waroquiers Philippe
Published: October 2004

Computer hardware evolves very quickly. To benefit from cheaper and more powerful systems, big applications have to be ported to new environments. The Ada language has been designed for portability, making such migrations easier. However, today's applications often complement their main implementation language by various extra technologies: shell scripts, direct usage of OS primitives, different programming languages to access some libraries e.g. for graphical user interfaces, etc. These technologies are not always standardized or as portable as Ada so it is important to have indications about the portability of the various languages, libraries and tools.ETFMS, the Enhanced Tactical Flow Management System, is a large Eurocontrol/CFMU application written mainly in Ada. This paper reports the findings of an exploratory port of ETFMS from HP-UX PA-RISC to GNU/Linux Intel. The performance figures obtained on both platforms are compared and several conclusions about portability are given.
A practical comparison between Java and Ada in implementing a real-time embedded system
Authors: Potratz Eric
Published: October 2004

This paper presents a student's observations from an undergraduate research project that explored using Java to implement the software for a real-time embedded system that was originally implemented in a university-level real-time systems course using Ada 95. It briefly gives an overview of the project, the decision made concerning which Java virtual machine to use, and how that virtual machine performed in the real-time environment. It then goes into detail about the merits and drawbacks of using Java to implement real-time and embedded systems such as this one and how using Java to implement them compares with using Ada.
Uniform access to Internet directory services
Authors: Comer D. , Droms R. E.
Published: October 2004

As networks and internetworks of computers expand in size and scope, discovery and location of resources becomes a primary function of the networked computing environment. Static tables describing network resources have been replaced by dynamic directory services, such as X.500 and the Internet Domain Name System. These dynamic directory services provide more timely and accurate information about network resources than static tables.

A wide variety of services address various components of the resource discovery and location problem. These services can be loosely classified as either low-level protocols or high-level services. Low-level protocols, such as RARP and ICMP, are simple delivery protocols and provide limited information; high-level services, such as the Internet Domain Name System and X.500, use complex delivery protocols to answer complex queries. Neither class of directory service is appropriate in all situations. Low-level services are too restrictive in the type of queries and information they support, while high-level services may be too expensive for some low-function networks.
A simple multiple access protocol for metropolitan area networks
Authors: Limb J. O.
Published: October 2004

As LANs/MANs operate at higher speeds (100 Mb/s-Gb/s) and over longer distances (10's - 100's km) the access mechanism has to be chosen carefully so as to provide high utilization. Protocols are available that operate efficiently at high speeds and long distances. We describe here a particularly simple access mechanism referred to as Simple (S). Performance is simulated under a range of traffic, physical lengths, number of stations and overload conditions. S is compared with both Fasnet and the Distributed Queue Dual Bus (DQDB) schemes. It is almost as efficient as more complex protocols and its overload performance is well behaved.
A theoretical analysis of feedback flow control
Authors: Shenker S.
Published: October 2004

Congestion is a longstanding problem in datagram networks. One congestion avoidance technique is feedback flow control, in which sources adjust their transmission rate in response to congestion signals sent (implicitly or explicitly) by network gateways. The goal is to design flow control algorithms which provide time-scale invariant, fair, stable, and robust performance. In this paper we introduce a simple model of feedback flow control, in which sources make synchronous rate adjustments based on the congestion signals and other local information, and apply it to a network of Poisson sources and exponential servers. We investigate two different styles of feedback, aggregate and individual, and two different gateway service disciplines, FIFO and Fair Share. The purpose of this paper is to identify, in the context of our simple model, which flow control design choices allow us to achieve our performance goals
.

Aggregate feedback flow control, in which congestion signals reflect only the aggregate congestion at the gateways, can provide time-scale invariant and stable performance, but not fair or robust performance. The properties of individual feedback flow control, in which the congestion signals reflect the congestion caused by the individual source, depend on the service discipline used in the gateways. Individual feedback with FIFO gateways can provide time-scale invariant, fair, and stable performance, but not robust performance. Individual feedback with Fair Share gateways can achieve all four performance goals. Furthermore, its stability properties are superior to those of the other two design choices. By making robust and more stable performance possible, gateway service disciplines play a crucial role in realizing effective flow control
.
Transport protocol processing at GBPS rates
Authors: Jain N. , Schawrtz M. , Bashkow T.
Published: October 2004

This paper proposes an architecture for accomplishing transport protocol processing at Gbps rates. The limitations of currently used transport protocols have been analyzed extensively in recent literature. Several benchmark studies have established the achievable throughput of ISO TP4 and TCP to be in the low Mbps range; several new protocols and implementation techniques have been proposed to achieve 100 Mbps and higher throughput rates. We briefly review some of these protocols and establish the need for a radically different approach to meet our objective. An estimate of the aggregate processing power required for Gbps throughput is developed. It is proposed that a cost effective and practical solution to the processing requirements could be based on a multi-processor system. The opportunities for parallel processing in a typical transport protocol are examined. Several alternate parallel processing approaches are examined and arguments are advanced for selecting a favored approach. A corresponding parallel processing architecture is described. Data structures used to preserve packet ordering and techniques for reducing contention in a multi-processing environment are discussed. An implementation methodology for conventional transport protocols (e.g. TP4) is outlined. Some suggestions are made for improving efficiency by making modifications to the protocol that do not compromise functionality. The performance achievable with this modified architecture is analyzed and some suggestions for further work are presented.
Multiplexing issues in communication system design
Authors: Feldmeier C. C.
Published: October 2004

This paper considers some of the multiplexing issues in communication system design by examining overall system issues. In particular, we distinguish physical multiplexing of resources from logical multiplexing of streams. Both physical-resource multiplexing and logical multiplexing determine the service that can be provided by a communication system. We also discuss two issues affected by logical multiplexing - flow control and the relationship between control and data streams of a connection.

We conclude that the granularity of physical resource sharing must be fine enough to meet the jitter and latency constraints of demanding applications. Also, high speed communication systems should restrict their logical multiplexing to layer 3.
Avoiding name resolution loops and duplications in group communications
Authors: Liang L. , Neufeld G. W. , Chanson S. T.
Published: October 2004

This paper generalizes group communications into nested groups for the internet environment. By using a name graph model, two problems in nested group name resolution are identified — resolution loops and resolution duplications. Existing approaches of solving these problems are surveyed and their shortcomings analyzed. The research contribution of this paper is the design and analysis of an algorithm which uses statically saved topology information of the name graph to detect and handle resolution and duplication loops at the time when group membership and/or group structure change. While preserving some necessary properties of loops, the algorithm transforms the name graph into one which avoids resolution loops and controls duplications. The communication complexity of the algorithm has an upper bound of Ο(|
A
|) in the worst case, where |
A
| is the number of arcs in the name graph.
Reliable broadband communication using a burst erasure correcting code
Authors: McAuley A. J.
Published: October 2004

Traditionally, a transport protocol corrects errors in a computer communication network using a simple ARQ protocol. With the arrival of broadband networks, forward error correction is desirable as a complement to ARQ. This paper describes a simplified Reed-Solomon erasure correction coder architecture, adapted for congestion loss in a broadband network. Simulations predict it can both encode and decode at rates up to 1 gigabit per second in a custom 1 micron CMOS VLSI chip.
Ada-Europe guidelines for Ada compiler specification and selection
Authors: Nissen J. C. D. , Wichmann B. A.
Published: October 2004

The Ada language reference manual defines the language rather than indicating a list of the desirable properties of an implementation of the language. The purpose of this report is to list the characteristics of an implementation that should be taken into account in the specification or selection of an Ada compiler.This report was produced by members of Ada-Europe, those contributing being Ted Dowling, Stephen Goldsack, Hans Jeanrond, Alan Montgomery, John Nissen, Ron Pierce, Mario Refice, Nguyen the Thanh, Sven Tafvelin, Peter Wallis who also acted as secretary, Tim White and Brian Wichmann who also dealt with the word processing (with mechanical and Secretarial assistance from the National Physical Laboratory). Helpful comments on drafts of this document have been received from other members of Ada-Europe.
A simple Ada compiler invalidation test
Authors: Ardö Anders , Philipson Lars
Published: October 2004

This small program tests some of the not-so-easily implemented features of Ada. Among the things tested are separate compilation, overloading, generics, aggregates, tasking and various real time facilities. The program can be used to get a quick assessment of the completeness of a non validated Ada compiler.
Heat shock regulates the respiration of cardiac H9c2 cells through upregulation of nitric oxide synthase
Authors: Ilangovan Govindasamy , Osinbowale Sola , Bratasz Anna , Bonar Mary , Cardounel Arturo J. , Zweier Jay L. , Kuppusamy Periannan
Published: October 2004

Mild and nonlethal heat shock (i.e., hyperthermia) is known to protect the myocardium and cardiomyocytes against ischemic injury. In the present study, we have shown that heat shock regulates the respiration of cultured neonatal cardiomyocytes (cardiac H9c2 cells) through activation of nitric oxide synthase (NOS). The respiration of cultured cardiac H9c2 cells subjected to mild heat shock at 42°C for 1 h was decreased compared with that of control. The O2 concentration at which the rate of O2 consumption is reduced to 50% was increased in heat-shocked cells, indicating a lowering of O2 affinity in the mitochondria. Western blot analyses showed a fourfold increase in the expression of heat shock protein (HSP) 90 and a twofold increase in endothelial NOS (eNOS) expression in the heat-shocked cells. Immunoblots of eNOS, inducible NOS (iNOS), and neuronal NOS (nNOS) in the immunoprecipitate of HSP90 of heat-shocked cells showed that there was a sevenfold increase in eNOS and no changes in iNOS and nNOS. Confocal microscopic analysis of cells stained with the NO-specific fluorescent dye 4,5-diaminofluorescein diacetate showed higher levels of NO production in the heat-shocked cells than in control cells. The results indicate that heat shock-induced HSP90 forms a complex with eNOS and activates it to increase NO concentration in the cardiac H9c2 cells. The generated NO competitively binds to the complexes of the respiratory chain of the mitochondria to downregulate O2 consumption in heat-shocked cells. On the basis of these results, we conclude that myocardial protection by hyperthermia occurs at least partly by the pathway of HSP90-mediated NO production, leading to subsequent attenuation of cellular respiration.
Gq/G13 signaling by ET-1 in smooth muscle: MYPT1 phosphorylation via ETA and CPI-17 dephosphorylation via ETB
Authors: Hersch Eric , Huang Jiean , Grider John R. , Murthy Karnam S.
Published: October 2004

We analyzed the signaling pathways initiated by endothelin receptors ETA and ETB in intestinal circular and longitudinal smooth muscle cells. The response to endothelin-1 (ET-1) consisted of two phases in both cell types. The initial, transient phase of contraction and phosphorylation of 20-kDa myosin light chain (MLC20) was mediated additively by ETA and ETB receptors and initiated by Gαq-, Ca2+/calmodulin-dependent activation of MLC kinase. In contrast, the sustained phase was mediated selectively by ETA receptors via a pathway involving sequential activation of Gα13, RhoA, and Rho kinase, resulting in phosphorylation of MYPT1 at Thr696 and phosphorylation of MLC20. Although PKC was activated, CPI-17 was not phosphorylated and hence did not contribute to inhibition of MLC phosphatase. The absence of CPI-17 phosphorylation by PKC reflected active dephosphorylation of CPI-17 by protein phosphatase 2A (PP2A). PP2A was activated via a pathway involving ETB-dependent stimulation of p38 MAPK activity. CPI-17 phosphorylation was unmasked in the presence of the ETB antagonist BQ-788, but not the ETA antagonist BQ-123, and in the presence of a low concentration of okadaic acid, which selectively inactivates PP2A. The resultant phosphorylation of CPI-17 was blocked by bisindolylmaleimide, providing direct confirmation that it was PKC dependent. We conclude that the two phases of the intestinal smooth muscle response to ET-1 involve distinct receptors, G proteins, and signaling pathways. The sustained response is mediated via selective ETA-dependent phosphorylation of MYPT1. In contrast, ETB initiates an inhibitory pathway involving p38 MAPK-dependent activation of PP2A that causes dephosphorylation of CPI-17.
Connexins are mechanosensitive
Authors: Bao Li , Sachs Frederick , Dahl Gerhard
Published: October 2004

Connexins form gap junction channels that provide a hydrophilic path between cell interiors. Some connexins, particularly the lens connexins, Cx46 and Cx50 and their orthologs, can form functional hemichannels in nonjunctional membranes. These hemichannels are a nonselective conduit to the extracellular medium and may jeopardize cell survival. The physiological function of hemichannels has remained elusive, but it has been postulated that hemichannels are involved in ATP-release caused by mechanical stimulation. Here we show with single-channel and whole cell electrophysiological studies that Cx46 hemichannels are mechanosensitive, like other families of ion channels and membrane-bound enzymes. The hemichannel response to mechanical stress is bipolar. At negative potentials stress opens the channel, and at positive potentials stress closes it. Physiologically, Cx46 hemichannels may assist accommodation of the ocular lens by providing a transient path for volume flow as the lens changes shape.
New insights into the molecular and cellular workings of the cardiac Na+/Ca2+ exchanger
Authors: Hilgemann Donald W.
Published: October 2004

The cardiac Na+/Ca2+ exchanger (NCX1) is almost certainly the major Ca2+ extrusion mechanism in cardiac myocytes, although the driving force for Ca2+ extrusion is quite small. To explain multiple recent results, it is useful to think of the exchanger as a slow Ca2+ buffer that can reverse its function multiple times during the excitation-contraction cycle (ECC). An article by the group of John Reeves brings new insights to this function by analyzing the role of regulatory domains of NCX1 that mediate its activation by a rise of cytoplasmic Ca2+. It was demonstrated that the gating reactions are operative just in the physiological range of Ca2+ changes, a few fold above resting Ca2+ level, and that they prevent the exchanger from damping out the influence of mechanisms that transiently increase Ca2+ levels. Furthermore, exchangers with deleted regulatory domains are shown to reduce resting Ca2+ to lower levels than achieved by wild-type exchangers. A study by the group of Kenneth Philipson demonstrated that the NCX1 regulatory domain can bind and respond to Ca2+ changes on the time scale of the ECC in rat myocytes. At the same time, studies of transgenic mice and NCX1 knockout mice generated by the Philipson group revealed that large changes of NCX1 activity have rather modest effects on ECC. Simple simulations predict these results very well: murine cardiac ECC is very sensitive to small changes of the Na+ gradient, very sensitive to changes of the sarcoplasmic reticulum Ca2+ pump activity, and very insensitive to changes of NCX1 activity. It is speculated that the NCX1 gating reactions not only regulate coupled 3Na+:1Ca2+ exchange but also control the exchanger’s Na+ leak function that generates background Na+ influx and depolarizing current in cardiac myocytes.