bluuebunny/crossref_metadata_2025 huggingface dataset:
A classification of interdomain actions
Authors: Kühnhauser Winifried E.
Published: October 2004

This paper contributes to the recent discussion on unmet information security challenges for operating system designers. It focusses on the problem that in order to meet these challenges operating systems must be capable of supporting a multitude of information domains, each domain defined by its own and individual security policy. In such multi-domain systems, the interoperability between different information domains constitutes a major problem. While the security policies of the system control the interactions
within
their domains, it is an unsolved problem how interactions
between
different domains can be made secure.In order to provide a precise foundation for the discussion of secure interdomain actions as well as for the development of concepts for their implementation, the paper proposes a classification of interdomain actions that clearly identifies two major types of interdomain actions: interactions that cause conflicts between the involved security policies and interactions for which none of the involved policies can provide any security rule. The paper concludes that in order to support multiple information domains, operating systems must be capable of classifying interdomain actions, and they must support new types of interdomain security policies that mediate security conflicts in interdomain actions and complete the set of security rules for interdomain actions. The paper concludes with a discussion of the computational complexity of interdomain action classification.
SFT
Authors: Wei Xiaohui , Ju Jiubin
Published: October 2004

SFT algorithm, a consistent checkpointing algorithm with shorter freezing time, is presented in this paper. SFT is able to implement fault-tolerance in distributed systems. The features of the algorithm include shorter freezing time, lower overhead, and simple roll backing. To reduce checkpointing time, a special control message (Munblock) is used to ensure that at any given time a process can respond the checkpoint event quickly. Moreover, a main memory algorithm is used to improve concurrency of checkpointing. By using SFT algorithm, the freezing time resulted by checkpointing is less than 0.03s. The control message number of SFT is only O (n).
Survivability performance analysis of rerouting strategies in an ATM/VP DCS survivable mesh network
Authors: Kyandoghere Kyamakya
Published: October 2004

Several self-healing protocols utilizing virtual paths have been proposed in the relevant literature. Those which work in a mesh topology function according to three main rerouting strategies (though specific flooding administrations differ): local rerouting, source-destination rerouting, and local-destination rerouting. Most performance studies of self-healing protocols have considered restoration time as sole performance metric. This would have to be within the 2s threshold in order to guarantee service continuity. This one-sided metric needs to be completed. In this paper, I propose an extended performance(or goodness) metric framework in order to catch more performance aspects. In addition, this analysis uses survivability functions to measure the performance of rerouting strategies.
Consensual trends for optimizing the constitution of middleware
Authors: Spahni Stéphane , Scherrer Jean-Raoul , Sauquet Dominique , Sottile Pier-Angelo
Published: October 2004

Middleware is now a commonly used expression and anyone building distributed applications is referring to "middleware services". Nevertheless this notion lacks of sound theoretical foundation. This paper tries to clarify the relationship between the components of the distributed environment, and establishes some classification aiming at gaining a common understanding of the functionality and interdependency of the existing modules of distributed environments.
A new approach to the first theory course
Authors: Savage John E.
Published: October 2004

This article describes a novel first theory course, entitled "Models of Computation, " that I've been teaching at Brown University for the last three years with considerable success. In fact, many students tell me that they enjoy it very much, a somewhat unusual reaction for a required theory course. I believe its appeal is due to my efforts to make the material relevant to their experience and interests by introducing new topics, namely, circuits, computer organization, and programming, and covering the standard material in an unusual order. Highlights of the course are that students acquire a good understanding of NP-complete languages by midsemester, learn almost all of the material normally taught in a theory course on formal languages and automata and computability, and develop a very good appreciation for the importance of reductions in theoretical (and non-theoretical) computer science. More information on the course can be found at www.cs.brown.edu/courses/cs051.
Yet another reachability algorithm for Petri nets
Authors: Kostin Alexander E. , Tchoudaikina Svetlana A.
Published: October 2004

A new algorithm for the determination of reachability of a marking in generalized Petri nets is proposed. The algorithm is based on the matrix-equation approach. Given a Petri net, a so called complemented Petri net is created that consists of the given Petri net and a complementary transition with input and output places depending on the initial and target markings. Then the reachability task is reduced to the investigation of T-invariants of the complemented Petri net. Using a technique of search for T-invariants, the algorithm determines minimal-support T-invariants, that include the complementary transition, and then calculates the finite set of their linear combinations. For each T-invariant, the algorithm tries to create sequentially all reachability paths from the given initial marking to the target marking or determines that there are no such paths at all. During creation of the reachability paths, the algorithm needs memory only for storing the reachability path being created. If it is sufficient to determine only one firing sequence that transforms the initial marking into the target one, then the algorithm may be terminated after successful creation of the first reachability path.
Clarifying straight replays and forced delays
Authors: Kwon Taekyoung , Song Jooseok
Published: October 2004

This paper clarifies straight replays which are one of replay attacks but have been somewhat misunderstood. There are various kinds of replay attacks on authentication protocols but most of the formal methods are not capable of detecting them because a replayed message may have appropriate data and structure for the protocols. [1] classified them and proposed their taxonomy that is useful for readily determining the effectiveness of some replay countermeasures and the appropriateness of analysis techniques for replays. [1] urges that any kinds of replay attacks are classified in the taxonomy. Among those classified attacks, however, straight replay attacks are ambiguous to be distinguished from forced delays which are really not regarded as replays.
Quasi-asynchronous migration
Authors: Dan Pei , Dongsheng Wang , Youhui Zhang , Meiming Shen
Published: October 2004

Process migration is a desirable and useful facility for the Network of Workstations (NOW). This paper presents a novel migration protocol called quasi-asynchronous migration for PVM tasks, which allows non-migrating tasks to execute during most of the time of migration. Message flushing and message delaying are the key mechanisms used in quasi-asynchronous migration. Because the protocol is implemented on top of PVM and at user-level, it is both transparent to users and portable. Both the analysis of the migration protocol and the experimental results show that quasi-asynchronous migration has lower overhead than other migration protocols.
WASS
Authors: Patiyoot Danai , Shepherd S. J.
Published: October 2004

Recent years have witnessed the rapid growth in demanding for the use of wireless networks especially the one with can transmit all the service. Wireless ATM is the one that fulfil those requirements. Various architectures have been proposed depending on the intended application domain. One of the key components is the security protocol. This paper tries to propose security service into the wireless ATM network.
Cryptographic security Techniques for wireless networks
Authors: Patiyoot Danai , Shepherd S. J.
Published: October 2004

This paper deals with security techniques for wireless Networks. The work presented is based on a review of literature regarding current and future wireless security networks systems. The aspects discussed in this paper included the choices of cryptographic algorithms such as protocols for key management and authentication. Various conclusions are drawn from existing security networks and proposed in new wireless ATM network security. Also a proposal for future research into security techniques for wireless ATM networks included.
A real-time, path guidance cue
Authors: Newport John R.
Published: October 2004

This paper describes an implementation of some simple control laws for following a predefined path. The application might be generation of an aircrew cue or an autopilot capability. Even in the simplest physical representation, there are two complicating factors. These are:• Lead time to avoid overshooting the centerline of the next path, and• Spiral path due to wind drift.This paper describes the algorithms involved and some lessons learned from the implementation. (Among those lessons are the appropriateness of Ada for complex applications.)
Using ASIS for data base insulation
Authors: Drury Pace
Published: October 2004

The SIDPERS-3 project uses ASIS (Ada Semantic Interface Specification) to create Ada code that insulates the typical developer from the intimate details of, and any variations in, COTS (Commercial Off The Shelf) generated Ada code for data base interaction.
A collaborative fuzzy expert system for the Web
Authors: Sedbrook Tod A.
Published: October 2004

A convergence of Internet and fuzzy logic technologies provides an opportunity for experts and end users to collaborate in developing, refining, and testing knowledge-based systems. Internet technology removes geographical and time-based restraints, and fuzzy rule bases are easier to understand and maintain. This paper describes an architecture and a prototype for developing, delivering, and maintaining expert systems on the World Wide Web.The system's collaboration components allowed experts to monitor user consultations remotely, view summaries of responses, and trace-rule inference chains. Experts and users participated in real-time chat sessions or posted questions on extended discussion lists. The system allowed experts and users to experiment with real-time enhancements of knowledge bases. Fuzzy rules resulted in semantically richer knowledge bases that flexibly handled complex and uncertain knowledge. A fuzzy inference engine supported hedges and partial matching to assist users in applying knowledge and exploring Web-based data.
A model, analysis, and protocol framework for soft state-based communication
Authors: Raman Suchitra , McCanne Steven
Published: October 2004

"Soft state" is an often cited yet vague concept in network protocol design in which two or more network entities intercommunicate in a loosely coupled, often anonymous fashion. Researchers often define this concept operationally (if at all) rather than analytically: a source of
soft state
transmits periodic "refresh messages" over a (lossy) communication channel to one or more receivers that maintain a copy of that state, which in turn "expires" if the periodic updates cease. Though a number of crucial Internet protocol building blocks are rooted in soft state-based designs --- e.g., RSVP refresh messages, PIM membership updates, various routing protocol updates, RTCP control messages, directory services like SAP, and so forth --- controversy is building as to whether the performance overhead of soft state refresh messages justify their qualitative benefit of enhanced system "robustness". We believe that this controversy has risen not from fundamental performance tradeoffs but rather from our lack of a comprehensive understanding of soft state. To better understand these tradeoffs, we propose herein a formal model for soft state communication based on a probabilistic delivery model with relaxed reliability. Using this model, we conduct queueing analysis and simulation to characterize the data consistency and performance tradeoffs under a range of workloads and network loss rates. We then extend our model with feedback and show, through simulation, that adding feedback dramatically improves data consistency (by up to 55%) without increasing network resource consumption. Our model not only provides a foundation for understanding soft state, but also induces a new fundamental transport protocol based on probabilistic delivery. Toward this end, we sketch our design of the "Soft State Transport Protocol" (SSTP), which enjoys the robustness of soft state while retaining the performance benefit of hard state protocols like TCP through its judicious use of feedback.
IP multicast channels
Authors: Holbrook Hugh W. , Cheriton David R.
Published: October 2004

In the IP multicast model, a set of hosts can be aggregated into a group of hosts with one address, to which any host can send. However, Internet TV, distance learning, file distribution and other emerging large-scale multicast applications strain the current realization of this model, which lacks a basis for charging, lacks access control, and is difficult to scale.This paper proposes an extension to IP multicast to support the
channel
model of multicast and describes a specific realization called
EXPlicitly REquested Single-Source (EXPRESS)
multicast. In this model, a multicast
channel
has exactly one explicitly designated source, and zero or more channel
subscribers
. A single protocol supports both channel subscription and efficient collection of channel information such as subscriber count. We argue that EXPRESS addresses the aforementioned problems, justifying this multicast service model in the Internet.
Proportional differentiated services
Authors: Dovrolis Constantinos , Stiliadis Dimitrios , Ramanathan Parameswaran
Published: October 2004

Internet applications and users have very diverse service expectations, making the current
same-service-to-all
model inadequate and limiting. In the
relative differentiated services
approach, the network traffic is grouped in a small number of
service classes which are ordered based on their packet forwarding quality
, in terms of per-hop metrics for the queueing delays and packet losses. The users and applications, in this context, can
adaptively
choose the class that best meets their quality and pricing constraints, based on the assurance that
higher classes will be better, or at least no worse, than lower classes
. In this work, we propose the
proportional differentiation model
as a way to refine and quantify this basic premise of relative differentiated services. The proportional differentiation model aims to provide the network operator with the '
tuning knobs
' for adjusting the quality spacing between classes,
independent of the class loads
; this cannot be achieved with other relative differentiation models, such as strict prioritization or capacity differentiation. We apply the proportional model on queueing-delay differentiation only, leaving the problem of coupled delay and loss differentiation for future work. We discuss the
dynamics
of the proportional delay differentiation model and state the conditions under which it is
feasible
. Then, we identify and evaluate (using simulations) two
packet schedulers
that approximate the proportional differentiation model in heavy-load conditions, even in short timescales. Finally, we demonstrate that such per-hop and class-based mechanisms can provide consistent end-to-end differentiation to
individual flows
from different classes, independently of the network path and flow characteristics.
Packet classification on multiple fields
Authors: Gupta Pankaj , McKeown Nick
Published: October 2004

Routers classify packets to determine which flow they belong to, and to decide what service they should receive. Classification may, in general, be based on an arbitrary number of fields in the packet header. Performing classification quickly on an arbitrary number of fields is known to be difficult, and has poor worst-case performance. In this paper, we consider a number of classifiers taken from real networks. We find that the classifiers contain considerable structure and redundancy that can be exploited by the classification algorithm. In particular, we find that a simple multi-stage classification algorithm, called RFC (recursive flow classification), can classify 30 million packets per second in pipelined hardware, or one million packets per second in software.
A scalable Web cache consistency architecture
Authors: Yu Haobo , Breslau Lee , Shenker Scott
Published: October 2004

The rapid increase in web usage has led to dramatically increased loads on the network infrastructure and on individual web servers. To ameliorate these mounting burdens, there has been much recent interest in web caching architectures and algorithms. Web caching reduces network load, server load, and the latency of responses. However, web caching has the disadvantage that the pages returned to clients by caches may be
stale
, in that they may not be consistent with the version currently on the server. In this paper we describe a scalable web cache consistency architecture that provides fairly tight bounds on the staleness of pages. Our architecture borrows heavily from the literature, and can best be described as an
invalidation
approach made scalable by using a caching hierarchy and application-level multicast routing to convey the invalidations. We evaluate this design with calculations and simulations, and compare it to several other approaches.
An integrated congestion management architecture for Internet hosts
Authors: Balakrishnan Hari , Rahul Hariharan S. , Seshan Srinivasan
Published: October 2004

This paper presents a novel framework for managing network congestion from an end-to-end perspective. Our work is motivated by trends in traffic patterns that threaten the long-term stability of the Internet. These trends include the use of multiple independent concurrent flows by Web applications and the increasing use of transport protocols and applications that do not adapt to congestion. We present an end-system architecture centered around a Congestion Manager (CM) that ensures proper congestion behavior and allows applications to easily adapt to network congestion. Our framework integrates congestion management across all applications and transport protocols. The CM maintains congestion parameters and exposes an API to enable applications to learn about network characteristics, pass information to the CM, and schedule data transmissions. Internally, it uses a window-based control algorithm, a scheduler to regulate transmissions, and a lightweight protocol to elicit feedback from receivers.We describe how TCP and an adaptive real-time streaming audio application can be implemented using the CM. Our simulation results show that an ensemble of concurrent TCP connections can effectively share bandwidth and obtain consistent performance, without adversely affecting other network flows. Our results also show that the CM enables audio applications to adapt to congestion conditions without having to perform congestion control or bandwidth probing on their own. We conclude that the CM provides a useful and pragmatic framework for building adaptive Internet applications.
Routing with a clue
Authors: Bremler-Barr Anat , Afek Yehuda , Har-Peled Sariel
Published: October 2004

We suggest a new simple forwarding technique to speed-up IP destination address lookup. The technique is a natural extension of IP, requires 5 bits in the IP header (IPv4, 7 in IPv6) and performs IP lookup nearly as fast as IP/Tag-switching but with a smaller memory requirement and a much simpler protocol. The basic idea is that each router adds a "clue" to each packet, telling its downstream router where it ended the IP lookup. Since the forwarding tables of neighboring routers are similar, the clue either directly determines the best prefix match for the downstream router, or provides the downstream router with a good point to start its IP lookup. The new scheme thus prevents repeated computations and distributes the lookup process across the routers along the packet path. Each router starts the lookup computation at the point its up-stream neighbor has finished. Furthermore, the new scheme is easily assimilated into heterogeneous IP networks, does not require routers coordination, and requires no setup time. Even a flow of one packet enjoys the benefits of the scheme without any additional overhead. The speedup we achieve is about 10 times faster than current standard techniques. In a sense this paper shows that the current routers employed in the Internet are clue-less; Namely, it is possible to speedup the IP-lookup by an order of magnitude without any major changes to the existing protocols.
Using pathchar to estimate Internet link characteristics
Authors: Downey Allen B.
Published: October 2004

We evaluate
pathchar
, a tool that infers the characteristics of links along an Internet path (latency, bandwidth, queue delays). Looking at two example paths, we identify circumstances where
pathchar
is likely to succeed, and develop techniques to improve the accuracy of
pathchar
's estimates and reduce the time it takes to generate them. The most successful of these techniques is a form of adaptive data collection that reduces the number of measurements
pathchar
needs by more than 90% for some links.
On estimating end-to-end network path properties
Authors: Allman Mark , Paxson Vern
Published: October 2004

The more information about current network conditions available to a transport protocol, the more efficiently it can use the network to transfer its data. In networks such as the Internet, the transport protocol must often form its own estimates of network properties based on measurements performed by the connection endpoints. We consider two basic transport estimation problems: determining the setting of the retransmission timer (RTO) for a reliable protocol, and estimating the bandwidth available to a connection as it begins. We look at both of these problems in the context of TCP, using a large TCP measurement set [Pax97b] for trace-driven simulations. For RTO estimation, we evaluate a number of different algorithms, finding that the performance of the estimators is dominated by their minimum values, and to a lesser extent, the timer granularity, while being virtually unaffected by how often round-trip time measurements are made or the settings of the parameters in the exponentially-weighted moving average estimators commonly used. For bandwidth estimation, we explore techniques previously sketched in the literature [Hoe96, AD98] and find that in practice they perform less well than anticipated. We then develop a receiver-side algorithm that performs significantly better.
Performance improvements for ISO transport
Authors: Colella Richard , Aronoff Robert , Mills Kevin
Published: October 2004

The NBS Protocol Performance Laboratory is developing enhanced protocol mechanisms for OSI class 4 transport that will improve the throughput efficiency achieved on a satellite channel. A selective acknowledgement mechanism has been shown to improve throughput efficiency by as much as 34%. Several alternative expedited data mechanisms have demonstrated throughput efficiency improvements as great as 38%. Most of the protocol mechanism enhancements considered require only minor changes to the international standard OSI transport protocol.
Protocols for large data transfers over local networks
Authors: Zwaenepoel Willy
Published: October 2004

In this paper we analyze protocols for transmitting large amounts of data over a local area network. The data transfers analyzed in this paper are different from most other forms of large-scale data transfer protocols for three reasons: (1) The definition of the protocol requires the recipient to have sufficient buffers available to receive the data before the transfer takes place; (2) We assume that the source and the destination machine are more or less matched in speed; (3) The protocol is implemented at the network interrupt level and therefore not slowed down by process scheduling delays.

We consider three classes of protocols:
stop-and-wait, sliding window
and
blast
protocols. We show that the expected time of blast and sliding window protocols is significantly lower than the expected time for the stop-and-wait protocol, with blast outperforming sliding window by some small amount. Although the network error rate is sufficiently low for blast with full retransmission on error to be acceptable, the frequency of errors in the network interfaces makes it desirable to use a more sophisticated retransmission protocol. A go-back-n strategy is shown to be only marginally inferior to selective retransmission and is, given its simplicity, the retransmission strategy of choice.

Our results are based on measurements collected on SUN workstations connected to a 10 megabit Ethernet network using 3-Com interfaces. The derivation of the elapsed time in terms of the network packet error rate is based on the assumption of statistically independent errors.
A grammar-based methodology for protocol specification and implementation
Authors: Anderson David P. , Landweber Lawrence H.
Published: October 2004

A new methodology for specifying and implementing communication protocols is presented. This methodology is based on a formalism called “Real-Time Asynchronous Grammars” (RTAG), which uses a syntax similar to that of attribute grammars to specify allowable message sequences. In addition RTAG provides mechanisms for specifying data-dependent protocol activities, real-time constraints, and concurrent activities within a protocol entity. RTAG encourages a top-down approach to protocol design that can be of significant benefit in expressing and reasoning about highly complex protocols. As an example, an RTAG specification is given for part of the Class 4 ISO Transport Protocol (TP-4).

Because RTAG allows protocols to be specified at a highly detailed level, major parts of an implementation can be automatically generated from a specification. An
RTAG parser
can be written which, when combined with an RTAG specification of a protocol and a set of interface and utility routines, constitutes an implementation of the protocol. To demonstrate the viability of RTAG for implementation generation, an RTAG parser has been integrated into the kernel of the 4.2 BSD UNIX operating system, and has been used in conjunction with the RTAG TP-4 specification to obtain an RTAG-based TP-4 implementation in the DoD Internet domain.
Line operations network growth issues (panel session, abstract only)
Authors: White G. D.
Published: October 2004

The task of keeping customer impact to a minimum while attempting to grow, modernize and improve the network in todays packet switching environment is becoming increasingly more difficult. As the network evolves and the customer demand for higher network availability increases, the need for line operations personnel to reduce customer impact has presented a unique challenge for innovative ideas to accomplish this objective.

Although the equipment supplier may provide excellent technical documentation for the provisioning, testing and maintenance of their products, they cannot provide the means to administer, manage and control a large network. This is the sole area where the network provider is responsible for deciding how his network will impact the customer.

This presentation will deal with some of the operational problems encountered in growing a network from 5 nodes to 55 nodes over a period of 9 years. Some of the subject areas that will be covered are: the maintenance window - is it required?; administrative documentation; utilization of network statistics; hardware retrofits; and software updates - major and minor. These are but a few of the problem areas challenging packet switching network providers today. Their resolution are limited only by the imagination of the personnel charged with the responsibility of resolving them.
Operations considerations in a large privated packet switching network
Authors: Stubbs R. D. , Swymer L. Dee , Quinn T. L.
Published: October 2004

In early 1977, Southern Bell began to study ways to reduce terminal and leased line costs associated with internal computer communications. Because a large volume of these communications were of an asynchronous, character-mode nature, packet switching emerged as the most attractive solution to reducing these costs. In May, 1979, the first application went on-line with one switch, one host concentrator and three terminal concentrators. Operation of this network was simple, with operations and planning residing in the same work group.

Today, the network consists of twenty tandem switches, 185 local switches and 85 packet assembler/disassemblers, interconnected by 15,928 miles of trunk facilities. The network architecture has evolved to geographically distributed “principle switching points” interconnected through a single major switching center in Atlanta, Georgia. Each “principle switching point” serves an area of company interest by supporting a number of local switches and concentrators.

As the complexity of the network has increased, so has the complexity of network operation. Operations have been both functionally and geographically differentiated to keep up with the evolution of the network, and to stay consistent with changing packet switch architecture. This talk will cover the network operations and maintenance considerations associated with the operation of today's very large network.
Solving growth problems in a rapidly expanding PDN (panel session, abstract only)
Authors: Poppe Stephen C.
Published: October 2004

Tymnet's public data network has been expanding in size and revenues at about a 35% per year rate since its inception. Maintaining this growth has put strain more on the organization than the technology. I will discuss several dimensions of the problem of managing prolonged rapid growth, including capacity management (bandwidth, switching, interfaces, and floor-space), topological complexity, job specialization, order processing, forecasting, and deploying new versions of code. The topic selection will favor issues that are likely to be common to other operations and the discussion will be biased toward solutions and pro-active management.
A new method for topological design in large, traffic laden packet switched networks
Authors: Chen Kim-Joan , Stach Jerrold F. , Wu Tsong-Ho
Published: October 2004

The AN/1 network architecture employs compact LANs as integrated switching nodes. The multibussed nodal architecture imposes a natural hierarchy to the network interconnection problem. A nodal interconnection method is introduced as a generalization of hierarchical topology design techniques. Based on traffic and distance, a flat nodal topology is decomposed into several level, overlapped subnetworks. Each subordinate subnetwork communicates with its ordinate subnetwork via two formal gates. The traffic matrix for each subnetwork can be obtained. Linear programming techniques are used to determine bandwidth requirements. Perturbation procedures are applied to determine the appropriate groupings of LANs into subnetworks and the appropriate hierarchy. A flat topology may be returned if it is optimal.
Mixing traffic in a buffered banyan network
Authors: Wu L. T.
Published: October 2004

A model of Banyan networks is developed to account for their operational as well as topological characteristics. The model incorporates a description of the states of individual switching nodes and explicitly captures the interconnection patterns between stages. Accordingly, the performance of a network can be evaluated via an iterative procedure. Using the model, we analyzed one class of nonuniform traffic pattern referred to as “point-to-point” traffic that has particular significance to mixed voice, data, and video applications. The results obtained indicate that even a single dedicated channel (with point-to-point traffic) can significantly limit the throughput of the background uniform traffic. The paper concludes with several switch design strategies for switching point-to-point traffic using a self-routing switching network.
A resilient communication structure for local area networks
Authors: El Abbadi Amr , Rauchle Thomas
Published: October 2004

Reliable communication is crucial to the correct functioning of distributed systems. We propose a multi-ring communication structure and a reconfiguration algorithm that tolerate multiple link failures before the network divides into more than one partition. In case of partitioning, each partition is reconfigured to allow communication among the sites within the partition. The algorithm handles recovery of links and merges partitions once links become operational again. The algorithm itself is fault-tolerant, and it is fully distributed and does not require global knowledge about the status of the network at any one site.
Issues in using DARPA domain names for computer mail
Authors: Comer Douglas E. , Peterson Larry L.
Published: October 2004

Although the principle goal of the
DARPA
Domain Name project is to provide a distributed name resolution mechanism for host names in the
DARPA
Internet, it is envisioned that the domain naming scheme will also support names for mailboxes in a
global
mail system that extends to mail networks beyond the
DARPA
Internet. In addition to overviewing the fundamental ideas behind the domain name scheme and outlining a proposal for using domain names as an umbrella naming system for computer mail, we discuss the administrative and technical problems involved in using domain names in the global mail system.
An approach for interconnecting SNA and XNS Networks
Authors: Zoline Kenneth O. , Lidinsky William P.
Published: October 2004

Interest in computer internetworking has resulted from the proliferation of wide area and local area networks. The CCITT, DARPA/DoD, and ISO/ECMA internetworking models, which have become widely accepted for doing this, do not address the pragmatic problem of interconnecting computer networks that are based upon closed-system, vendor-proprietary network architectures. This paper presents an approach for interconnecting private data networks that are based upon IBM's System Network Architecture (SNA) and Xerox's Network System (XNS). Paramount to the solution of the SNA/XNS network interconnection problem is the identification and definition of a number of gateway-provided data transport and application protocol support services, which can be incorporated into a multi-function, multi-level, protocol translation gateway.
CNMGRAF—graphic presentation services for network management
Authors: Gilbert Richard S. , Kleinöoder Wolfgang B.
Published: October 2004

Two key problems in the design of systems and network management applications are: how to efficiently manage large quantities of related data, and how to allow the application user to view this data at a user-defined level of detail. This paper describes an architecture for network management facilities that may help solve these problems. It also describes CNMgraf (Communications Network Management Graphics Facility), which was developed to test the presentation service model defined by this architecture.
What future for the distributed systems annex?
Authors: Pautet Laurent , Tardieu Samuel
Published: October 2004

In this paper, we report our experience as implementors and users of the Ada 95 Distributed Systems Annex (annex E of the Ada reference manual). We identify the principal strengths and weaknesses of the annex, and make some proposals to improve it either immediately or for the next revision of the language (Ada0X). Our goal is to get an annex that is more open and compatible with other distributed systems such as CORBA, without loosing the capability of developing pure Ada rock solid distributed systems.We assume that the reader is familiar with Ada. Knowledge of the Distributed Systems Annex is useful but not required to understand the main ideas exposed in this article.
Reducing maintenance costs through the application of modern software architecture principles
Authors: Hulse Christine , Edgerton Scott , Ubnoske Michael , Vazquez Louis
Published: October 2004

Large software programs are usually long lived and continually evolve. Substantial maintenance effort is often extended by engineers trying to understand the software prior to making changes. To successfully evolve the software, a thorough understanding of the architect's intentions about software organization is required. Software maintenance costs can be reduced significantly if the software architecture is well defined, clearly documented, and creates an environment that promotes design consistency through the use of guidelines and design patterns. Building a maintainable system depends upon the consistent application of these architectural practices. This paper describes the application of modern software architecture methods to achieve a maintainable implementation of a large, distributed, real-time, embedded software system.
Experiences using Ada in a real-time and distributed laboratory
Authors: Ballbastre P. , Terrasa S. , Vila J. , Crespo A.
Published: October 2004

This paper reviews our experience in the laboratory of two courses in the Control Engineering Curriculum at the Politechnical University of Valencia: Real-time Systems and Distributed Control Systems. These courses, in a Control Engineering curriculum, require the development of industrial prototypes to validate different aspects of the system development: control algorithms, real-time software design, external devices integration, distributed control, etc. To meet all these goals a robot guidance experience has been selected. In this paper, we describe the experience in the design and implementation of a virtual and real environment developed in Ada to complete the student laboratory activities. The system is complex enough to allow the students to analyze, design and implement a complete prototype
Ada+SQL—an overview
Authors: Lopes Arthur V.
Published: October 2004

Ada+SQL is a programming environment for Ada 95 extended with basic SQL single user capabilities. It incorporates a very fast compiler and interpreter, with debugging options, library generator and browser, syntax template editors, programmer wizard, two-dimensional graphics, SQL interactive interface and hypertext documentation on the environment, Ada 95 and SQL. Several implementation aspects are discussed.
Optimizing Ada on the fly
Authors: Bernstein Sheri J. , Duff Robert S.
Published: October 2004

One of the features that makes Ada such a reliable programming language is its use of run-time constraint checks. However, such checks slow program execution and increase program size.The AdaMagic™ compiler uses one-pass, on-the-fly flow analysis during intermediate-language generation specifically to eliminate unnecessary constraint checks and to warn about potential error situations such as the use of uninitialized variables.The one-pass nature of our method allows for faster compile times than more elaborate multi-pass flow analysis. Thus, we are able to generate efficient code without the impact on compile-time, and without the added implementation complexity, associated with a traditional separate optimization phase.
Towards a distributed object-oriented propagation model using Ada95
Authors: Needham Donald M. , Demurjian Steven A. , Peters Thomas J.
Published: October 2004

Representing interdependencies between the objects of an object-oriented software application requires design-time mechanisms for specifying object interrelationships, as well as software constructs for the runtime maintenance of these relationships. We present a portion of our software engineering research environment ADAM, (short for Active Design and Analyses Modeling), which incorporates a technique for design-time modeling of
propagations
(our term for the relationships between interdependent objects). We examine the ADAM environment's support for the automated generation of Ada95 software constructs that maintain object interdependency at runtime. We focus on our propagation model's use of Ada95 tasking constructs and protected objects, with an emphasis on the source level mechanisms through which our model utilizes concurrency.
Formal modeling of synchronization methods for concurrent objects in Ada 95
Authors: Gedela Ravi K. , Shatz Sol M. , Xu Haiping
Published: October 2004

One important role for Ada programming is to aid engineering of concurrent and distributed software. In a concurrent and distributed environment, objects may execute concurrently and need to be synchronized to serve a common goal. Three basic methods by which objects in a concurrent environment can be constructed and synchronized have been identified [1]. To formalize the semantics of these methods and to provide a formal model of their core behavior, we provide some graphic models based on the Petri net formalism. The purpose of this formal modeling is to illustrate the possibility of automatic program analysis for object-oriented features in Ada-95. Models for the three distributed- object synchronization methods are discussed, and a potential deadlock situation for one of the methods/models is illustrated. We conclude with some comparison of the three methods in terms of the model abstractions.
Pinching pennies while losing dollars
Authors: Lowe Tony
Published: October 2004

All real-time embedded software projects eventually hit the wall when they trade elegance for efficiency. The major recipient of the blame is often 'that darn tasking' or 'those silly OO concepts'. The actual culprit, unknowingly, is the front line software engineer. This paper is a group of test cases that can be applied to compiler to give direction to the developers as to the performance of the compiler.
Active network vision and reality
Authors: Wetherall David
Published: October 2004

Although active networks have generated much debate in the research community, on the whole there has been little hard evidence to inform this debate. This paper aims to redress the situation by reporting what we have learned by designing, implementing and using the ANTS active network toolkit over the past two years. At this early stage, active networks remain an open research area. However, we believe that we have made substantial progress towards providing a more flexible network layer while at the same time addressing the performance and security concerns raised by the presence of mobile code in the network. In this paper, we argue our progress towards the original vision and the difficulties that we have not yet resolved in three areas that characterize a "pure" active network: the capsule model of programmability; the accessibility of that model to all users; and the applications that can be constructed in practice.
Integrating segmentation and paging protection for safe, efficient and transparent software extensions
Authors: Chiueh Tzi-cker , Venkitachalam Ganesh , Pradhan Prashant
Published: October 2004

The trend towards extensible software architectures and component-based software development demands safe, efficient, and easy-to-use extension mechanisms to enforce protection boundaries among software modules residing in the same address space. This paper describes the design, implementation, and evaluation of a novel intra-address space protection mechanism called
Palladium,
which exploits the segmentation and paging hardware in the Intel X86 architecture and efficiently supports safe kernel-level and user-level extensions in a way that is largely transparent to programmers and existing programming tools. Based on the considerations on ease of extension programming and systems implementation complexity,
Palladium
uses different approaches to support user-level and kernel-level extension mechanisms. To demonstrate the effectiveness of the
Palladium
architecture, we built a Web server that exploits the user-level extension mechanism to invoke CGI scripts as local function calls in a safe way, and we constructed a compiled network packet filter that exploits the kernel-level extension mechanism to run packet-filtering binaries safely inside the kernel at native speed. The current
Palladium
prototype implementation demonstrates that a protected procedure call and return costs 142 CPU cycles on a Pentium 200MHz machine running Linux.
The Click modular router
Authors: Morris Robert , Kohler Eddie , Jannotti John , Kaashoek M. Frans
Published: October 2004

Click is a new software architecture for building flexible and configurable routers. A Click router is assembled from packet processing modules called
elements.
Individual elements implement simple router functions like packet classification, queueing, scheduling, and interfacing with network devices. Complete configurations are built by connecting elements into a graph; packets flow along the graph's edges. Several features make individual elements more powerful and complex configurations easier to write, including
pull processing,
which models packet flow driven by transmitting interfaces, and
flow-based router context,
which helps an element locate other interesting elements.We demonstrate several working configurations, including an IP router and an Ethernet bridge. These configurations are modular---the IP router has 16 elements on the forwarding path---and easy to extend by adding additional elements, which we demonstrate with augmented configurations. On commodity PC hardware running Linux, the Click IP router can forward 64-byte packets at 73,000 packets per second, just 10% slower than Linux alone.
Soft timers
Authors: Aron Mohit , Druschel Peter
Published: October 2004

This paper proposes and evaluates soft timers, a new operating system facility that allows the efficient scheduling of software events at a granularity down to tens of microseconds. Soft timers can be used to avoid interrupts and reduce context switches associated with network processing without sacrificing low communication delays.More specifically, soft timers enable transport protocols like TCP to efficiently perform rate-based clocking of packet transmissions. Experiments show that rate-based clocking can improve HTTP response time over connections with high bandwidth-delay products by up to 89% and that soft timers allow a server to employ rate-based clocking with little CPU overhead (2-6%) at high aggregate bandwidths.Soft timers can also be used to perform network polling, which eliminates network interrupts and increases the memory access locality of the network subsystem without sacrificing delay. Experiments show that this technique can improve the throughput of a Web server by up to 25%.