bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infection of Specific Dendritic Cells by CCR5-Tropic Human Immunodeficiency Virus Type 1 Promotes Cell-Mediated Transmission of Virus Resistant to Broadly Neutralizing Antibodies
Authors: Ganesh Lakshmanan , Leung Kwanyee , Loré Karin , Levin Reuven , Panet Amos , Schwartz Owen , Koup Richard A. , Nabel Gary J. 
Published: October 2004

ABSTRACT
The tropism of human immunodeficiency virus type 1 for chemokine receptors plays an important role in the transmission of AIDS. Although CXCR4-tropic virus is more cytopathic for T cells, CCR5-tropic strains are transmitted more frequently in humans for reasons that are not understood. Phenotypically immature myeloid dendritic cells (mDCs) are preferentially infected by CCR5-tropic virus, in contrast to mature mDCs, which are not susceptible to infection but instead internalize virus into a protected intracellular compartment and enhance the infection of T cells. Here, we define a mechanism to explain preferential transmission of CCR5-tropic viruses based on their interaction with mDCs and sensitivity to neutralizing antibodies. Infected immature mDCs differentiated normally and were found to enhance CCR5-tropic but not CXCR4-tropic virus infection of T cells even in the continuous presence of neutralizing antibodies. Infectious synapses also formed normally in the presence of such antibodies. Infection of immature mDCs by CCR5-tropic virus can therefore establish a pool of infected cells that can efficiently transfer virus at the same time that they protect virus from antibody neutralization. This property of DCs may enhance infection, contribute to immune evasion, and could provide a selective advantage for CCR5-tropic virus transmission.
Amino Acid Insertions near Gag Cleavage Sites Restore the Otherwise Compromised Replication of Human Immunodeficiency Virus Type 1 Variants Resistant to Protease Inhibitors
Authors: Tamiya Sadahiro , Mardy Sek , Kavlick Mark F. , Yoshimura Kazuhisa , Mistuya Hiroaki 
Published: October 2004

ABSTRACT
A variety of amino acid substitutions in the protease and Gag proteins have been reported to contribute to the development of human immunodeficiency virus type 1 (HIV-1) resistance to protease inhibitors. In the present study, full-length molecular infectious HIV-1 clones were generated by using HIV-1 variants isolated from heavily drug-experienced and therapy-failed AIDS patients. Of six full-length infectious clones generated, four were found to have unique insertions (TGNS, SQVN, AQQA, SRPE, APP, and/or PTAPPA) near the p17/p24 and p1/p6 Gag cleavage sites, in addition to the known resistance-related multiple amino acid substitutions within the protease. The addition of such Gag inserts mostly compromised the replication of wild-type HIV-1, whereas the primary multidrug-resistant HIV infectious clones containing inserts replicated significantly better than those modified to lack the inserts. Western blot analyses revealed that the processing of Gag proteins by wild-type protease was impaired by the presence of the inserts, whereas that by mutant protease was substantially improved. The present study represents the first report clearly demonstrating that the inserts seen in the proximity of the Gag cleavage sites in highly multi-PI resistant HIV-1 variants restore the otherwise compromised enzymatic activity of mutant protease, enabling the multi-PI-resistant HIV-1 variants to remain replication competent.
The Ability of Chloroquine To Prevent Tat-Induced Cytokine Secretion by Monocytes Is Implicated in Its In Vivo Anti-Human Immunodeficiency Virus Type 1 Activity
Authors: Rayne Fabienne , Vendeville Agnès , Bonhoure Anne , Beaumelle Bruno 
Published: October 2004

ABSTRACT
Hydroxychloroquine at 1 μM reduces the load of human immunodeficiency virus type 1 (HIV-1) in patients, whereas chloroquine (CQ) concentrations above 3 μM are required for inhibition of HIV-1 replication in peripheral blood mononuclear cells. Exogenous HIV-1 Tat reaches the cytosol of T cells by using low endosomal pH, and endosome neutralization by CQ prevents Tat from entering and affecting T cells. We show here that 0.6 μM CQ inhibits cytokine secretion induced by Tat in monocytes without affecting lipopolysaccharide-triggered cytokine release. This finding suggests that the in vivo anti-HIV-1 effect of CQ results not from a direct effect on the infected cell but rather from the capacity of CQ to prevent Tat from perturbing the cytokine balance.
Selection for Loss of Ref1 Activity in Human Cells Releases Human Immunodeficiency Virus Type 1 from Cyclophilin A Dependence during Infection
Authors: Sayah David M. , Luban Jeremy 
Published: October 2004

ABSTRACT

Capsid (CA)-specific restrictions are determinants of retroviral tropism in mammalian cells. One such restriction, human Ref1, targets strains of murine leukemia virus bearing an arginine at CA residue 110 (N-MLV), resulting in decreased accumulation of viral cDNA. The cellular factors accounting for Ref1 activity are unknown. As
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increases N-MLV titer in Ref1-positive cells, possibly by counteracting Ref1. Restriction factor saturation experiments suggest that Ref1 may also target human immunodeficiency virus type 1 (HIV-1), but only if its CA is not bound to the cellular protein cyclophilin A (CypA). As a step towards understanding the genetic determinants of Ref1, we subjected Ref1-positive TE671 cells to three sequential rounds of selection with N-MLV reporter viruses. We isolated a subclone, 17H1, that was permissive for N-MLV infection and therefore deficient in Ref1 activity. Stimulation of N-MLV replication by As
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was attenuated in 17H1, confirming that the drug acts by overcoming Ref1 activity. HIV-1 infection of 17H1 cells was resistant to disruption of the CA-CypA interaction, demonstrating that Ref1 restricts CypA-free HIV-1. Our results suggest that interaction with CypA evolved to protect HIV-1 from this human antiviral activity.
Protocol conversion—correctness problems
Authors: Lam Simon S 
Published: October 2004

Consider the problem of providing a logical channel for message exchange between two user processes in a network environment. When is protocol conversion needed? To answer this question, we first define a model of layered architectures. Specifically, three stepwise refinement rules are given. Any architecture that can be obtained by a sequence of applications of the stepwise refinement rules is said to be well-structured. We show that this class of well-structured architectures has several correctness properties. It is also very general and includes many well-known networking and internetworking architectures in the literature. Logical connectivity in such an architecture is defined recursively. As a result, to determine if a logical channel can be provided between two user processes, it is sufficient to examine peer protocols specified for each level of the architecture's hierarchy of processes one at a time. Thus the original problem reduces to the problem of determining if a set of processes will interoperate.
When protocol conversion is needed to achieve interoperability between processes that implement different protocols, how should it be done? How does one prove that a conversion is correct? What is meant by a correct conversion? We propose the use of projections and image protocols (previously developed by Lam and Shankar for protocol verification [10]) for specifying conversions and for reasoning about the correctness of conversions. Given two processes implementing different protocols P and Q, our objective is to find the largest protocol that is an image protocol of P as well as Q. The correctness of the conversion is a consequence of the correctness properties of image protocols.
There are several open problems. Most importantly, heuristics are used for finding the necessary image protocol for conversion. Although, an image protocol common to both P and Q can always be found, it may not be easy to find one with useful functionality. There are also some implementation and design issues to be addressed, such as: the construction of converters that are transparent and converters that add functionality to an image protocol common to P and Q.
Voice and data performance measurements in L-express net
Authors: Borgonovo F , Cadorin E , Fratta L , Pezze M 
Published: October 2004

L-Express is a protocol for Local Area Networks based on a single bus topology. It utilizes a simple and efficient virtual token access scheme which provides ordered and collision-free transmission.
This paper presents results of measurements performed to investigate in details the behavior of the L-Express protocol under different network speeds, configurations and traffic environments. The measurements are obtained using a mix of simulation and field tests on a network prototype. Voice and integration of voice and data are also taken into account.
The results indicate a good behavior (compared with Ethernet) for small size networks (500 m) and Low data rates (10 Mb/s) as well as for Large size networks (5000 m) and high data rates (100 Mb/s).
Flow control for real-time communication
Authors: Cohen Danny 
Published: October 2004

Flow Control is a problem of resource allocation in communication systems; typically the critical resources are the bandwidth of the medium, memory space and processing capabilities.
Traditionally, protecting the resources of the communicating processes is called Flow Control, and the protecting the communication system is called Congestion Control. Hence, the flow control is the protection of one process from the other(s), and the congestion control is protection of the communication-system from the processes.
This note argues that real-time communication requires different flow control and congestion control schemes than the familiar ones used for non-real-time communication.
Security problems in computer communication systems
Authors: Turn Rein 
Published: October 2004

At the present time there is a rapid growth in computer communications associated with terminal-based, multi-user computer systems, and in networks of computers [1,2,3]. Nearly all such systems communicate, process, or store information which is considered private or proprietary by their owners and users, or which must be safeguarded from unauthorized access as required by law. Furthermore, associated terminals, telecommunication systems, communication processors, and computers must be protected from intruders that may seek to alter programs or data in the system, or to disrupt the services provided. These threats are real, since it is not difficult to intercept transmissions in telecommunication networks [4,5], and it is possible to connect illicit terminals (or even computers) into the system for the purposes of "managing" the normal terminal-computer communications, masquerading as a legitimate user, or simply making the system unavailable to others [6,7].
The protection of a computer communication system against the various threats involves: (1) identification, and authentication of the identity, (2) controlled access to computers and their data bases, and (3) protection of the data in transit in the telecommunication system. Associated with each are a number of problems -- conceptual, as well as technical -- and a variety of solutions. In this brief survey, the emphasis is on the problems.
A formalised technique for expressing message generators
Authors: Payne A. J. 
Published: October 2004

The testing of real time systems for overload conditions is often performed by systems exercisers and message generators. Messages are usually expressed informally for their content, whilst languages use much formality in their definition. This paper gives a formalised description of messages and their contents so that they may be generated in defined proportions for testing real time systems.
The first part of the paper surveys the previous work that has been done in the field. In the second section we develop a theoretical model of the problem. Part three describes a method for collecting information which can be used to drive the theoretical model. The fourth portion gives the algorithms for generating the test data. In the fifth part examples demonstrate how effective the system is.
Graph theory applied to optimal connectivity in computer networks
Authors: McQuillan J. M. 
Published: October 2004

This is a report on some of the research that has been carried out in applying graph theoretical results to communications networks. The networks that we wish to investigate here consist of computers at various sites which are linked together by telecommunications circuits.
Many of the results of graph theory may be applied to such networks; we will restrict ourselves to the consideration of connectivity. In designing a computer communications network, it is desirable to provide good connectivity among all sites at reasonable cost. For this reason, extremes like the fully-connected network (too expensive) and the star network (only as reliable as its center) are usually not considered. The connectivity constraints or reliability measures can be stated in different ways, and analytic techniques have been developed for some of these measures. Further, procedures for the synthesis of well-connected networks have also been invented.
The reliability of communications networks is an important issue in their design and operation. Telecommunications circuits become noisy and unusable, and the communications computers may also fail. This report is a survey of that part of applied graph theory which is useful in the study of the connectivity of communications networks.
SDLC and BSC on satellite links
Authors: Traynham K. C. , Steen R. F. 
Published: October 2004

The emergence of satellite communication links offers the data communication designer increased throughput, but at the same time forces him to deal with greatly increased signal transmit time which may eliminate all potential throughput increases. Using a mathematical model, this paper compares batch throughput efficiency of two IBM line control methods, Binary Synchronous Communications (BSC) and Synchronous Data Link Control (SDLC), along with some hypothetical extensions to SDLC. Although the model treats links of any description, the focus here is on links with long signal transit time and low bit error rate, such as satellite links. Classic analog terrestrial links are included for comparison.
The model consists of an information source with an infinite supply of data transmitting to an information sink which transmsits no data but does acknowledge received frames as defined in the various protocols. Throughput efficiency is defined as the ratio of the time spent by the data source transmitting original information bytes (i.e., bytes in the SDLC or BSC Information Field, excluding those bytes retransmitted due to errors) to the time spent transmitting all bytes (i.e., information, control, and error recovery) plus time taken by any gaps in continuous transmission.
The comparison applies to steady-state batch transmission, so the link is assumed to be point-to-point. Both full duplex and half duplex protocols are considered in SDLC, but only half duplex protocols are contained in BSC. A hypothetical extension to SDLC, Asynchronous Response Mode (ARM), and SDLC Normal Response Mode (NRM) are included in full duplex. The model shows no difference in throughput efficiency between half duplex NRM and ARM, so only one result is presented for half duplex SDLC. Both SDLC and BSC are data link control architectures; for details concerning a particular implementation, the reader should consult the product description. More detail on SDLC and BSC is available in References 1-4.
Two transmission links are considered. The terrestrial analog link consists of traditional analog facilities, while the satellite link consists of only a satellite connection between the end points (i.e., the end points are very close to the satellite earth stations, such that negligible transit time and link errors are introduced in the terminal-to-earth station links). Each link is characterized by its bit error rate (BER) and round trip delay (RTD). Bit error rate is the long-term average of bit errors per bit transmitted, while round trip delay is defined as the amount of time between the last bit of a given SDLC frame or BSC block being transmitted and the first bit of its response being received at the source. RTD includes the time (in seconds) necessary to generate and transmit a line-control response at the receiving end, as well as any delay in equipment between the end points. Results are obtained using a simple bit-independent error model.
The next section describes the applicable equations, while the following section discusses results.
Notes on the X.25 procedures for virtual call establishment and clearing
Authors: Bochmann Gregor V. 
Published: October 2004

The packet level of the CCITT Recommendation X.25 describes how the virtual circuit communication service of public packet-switched data networks can be used. The recommendation contains in particular a specification of how to establish and clear virtual circuits through a given DTE-DCE interface. We comment in this paper on the following three aspects of these procedures for call establishment and clearing:
(a) The recommendation contains state diagrams to clarify the operation of the DTE-DCE interface. The reader may assume that the diagrams show, at each instant in time, the unambiguous state of the interface. This is, however, not always true since the DTE and the DCE may be in different states.
(b) We have analysed the operation of the interface using a finite state validation method, and have found that in some rare cases a conflicting situation (i.e. when the DTE and the DCE are in different states) may sustain through the repetitions of some cyclic behavior.
(c) The procedures of X.25 are very symmetrical. However, the packet level call establishment procedure contains a non-symmetrical element for the handling of call collisions. We consider as alternatives some symmetrical procedures for this purpose.
For each of these aspects we try to explain the problem and give some suggestions for its solution.
The ISO connectionless transport standards
Authors: Stein Scott A. 
Published: October 2004

The term Open Systems Interconnection (OSI) has increased in familiarity to those involved in distributed processing and data communications to such an extent that an understanding of the architecture it describes and the principles behind its development have quite nearly become commonplace. OSI consists of two closely related pieces: the OSI Basic Reference Model, ISO 7498, which provides a coordinated framework for the development of protocols to support distributed processing environments; and the set of related protocols which achieve that objective. The Reference Model describes an architecture wherein functions which provide communications are separated into a hierarchy of seven layers. Each layer provides services to the next higher layer, utilizing the services provided by subordinate layers in order to achieve that end. At each layer, protocols are employed to convey information between peer layer entities in communicating systems. When in compliance with the suite of standard protocols prescribed for OSI, systems are considered to be "open".
Initially, ISO 7498 defined only the requirements of connection mode services within the Reference Model. However, in recognition of the importance which connectionless-mode applications play in the data communications environment, an addendum to ISO 7498 was produced which defines the requirements for connectionless-mode services in the Reference Model. The purpose of this paper is to present an overview of the development of connectionless-mode service and protocol within the Transport Layer of the OSI Reference Model.
Dynamic Time Windows
Authors: Faber Theodore , Landweber Lawrence H. , Mukherjee Amarnath 
Published: October 2004

We present a feedback congestion control method, Dynamic Time Windows, for use in high speed wide area networks based on controlling source variance. It is part of the two-level integrated congestion control system introduced in our earlier work[1].
The method consists of a packet admission control system and a feedback system to dynamically control source burstiness. Source throughput is not modulated as with traditional packet windows, allowing system throughput to remain high while avoiding congestion. Furthermore, the admission control bounds congestion times in the network, allowing feedback to be effective in the face of large bandwidth delay products.
The basic control mechanisms are analogs to traditional packet windows applied to controlling time windows - a new mechanism which allows switches to modulate source variances. The proposed system is simulated, and the results reported and analyzed. Enhancements to the basic system are also proposed and analyzed.
We wish to stress that the system described here is the second level of a two-level congestion control. Previous work[1] concentrated on the switch queueing mechanism, Pulse, while this work is a detailed examination of the feedback system used to adjust time windows to changing network load.
User-space protocols deliver high performance to applications on a low-cost Gb/s LAN
Authors: Edwards Aled , Watson Greg , Lumley John , Banks David , Calamvokis Costas , Dalton C. 
Published: October 2004

Two important questions in high-speed networking are firstly, how to provide Gbit/s networking at low cost and secondly, how to provide a flexible low-level network interface so that applications can control their data from the instant it arrives.
We describe some work that addresses both of these questions. The Jetstream Gbit/s LAN is an experimental, low-cost network interface that provides the services required by delay-sensitive traffic as well as meeting the performance needs of current applications. Jetstream is a combination of traditional shared-medium LAN technology and more recent ATM cell- and switch-based technology.
Jetstream frames contain a channel identifier so that the network driver can immediately associate an incoming frame with its application. We have developed such a driver that enables applications to control how their data should be managed without the need to first move the data into the application's address space. Consequently, applications can elect to read just a part of a frame and then instruct the driver to move the remainder directly to its destination. Individual channels can elect to receive frames that have failed their CRC, while applications can specify frame-drop policies on a per-channel basis.
Measured results show that both kernel- and user-space protocols can achieve very good throughput: applications using both TCP and our own reliable byte-stream protocol have demonstrated throughputs in excess of 200 Mbit/s. The benefits of running protocols in user-space are well known- the drawback has often been a severe penalty in the performance achieved. In this paper we show that it is possible to have the best of both worlds.