1,720,995 research outputs found
Design and Features of Unibo-BP, the Unibo Implementation of the DTN Bundle Protocol
Full text linkChallenged networks, including space networks, require the Delay-/ Disruption-Tolerant Networking architecture (DTN), which is based on the introduction of a new layer and a new associate protocol, the Bundle Protocol (BP). The recent release of RFC 9171, which standardizes version 7 (BPv7), has led the University of Bologna to develop its own implementation, Unibo-BP. The aim of this paper is to provide the reader with a comprehensive description of its design principles and innovative features. Unibo-BP is written in C++, is fully compliant with RFC 9171, is research-driven, and space-oriented, thus matching the main research interests of the authors. Unibo-BP is not a stand-alone application, but the core of a wide ecosystem that includes DTNsuite applications, LTP and TCPCLv3 convergence layers, and CGR/SABR routing. Unibo-BP interfaces to these additional components are thoroughly analyzed in the paper, as they present a number of advanced features. Unibo-BP supports one or multiple nodes on the same machine and a few template scripts to facilitate the user are described here. The paper also provides a section devoted to interoperability tests and first research applications An appendix, with an overview of Unibo-BP commands, completes this work. Unibo-BP is released as Open Source Software under GPLv3 license
Delay-tolerant networks (DTNs) for satellite communications
No full textThis chapter discusses the advantages of delay/disruption-tolerant networking (DTN) when applied to satellite communications, considering geosynchronous (GEO) and low Earth orbit (LEO) constellations. The chapter analyses the challenges of GEO communications and shows how the DTN architecture can be interpreted as an elegant architectural extension of TCP-splitting PEPs, with the same excellent goodput performance but with better robustness and superior compatibility with security protocols. It examines LEO constellations and highlights the advantages offered by some bundle protocol features, such as scheduled links, and by contact graph routing (CGR), a DTN routing algorithm designed by NASA to cope with intermittent scheduled connectivity typical of both LEO satellite and deep-space communications. Results prove that the DTN architecture, although still experimental, is mature enough for real deployment
Multicolor Licklider Transmission Protocol: An LTP Version for Future Interplanetary Links
Full text linkThe Licklider Transport Protocol (LTP) is the "convergence layer" of choice in Interplanetary networks based on Delay-/Disruption-Tolerant architecture. It was designed for long-delay scheduled-intermittent links, offering either a reliable or an unreliable service, with "red" and "green" parts, respectively. The aim of this article is to present multicolor LTP, an LTP version consisting in a series of enhancements of which the most significant are the use of monochrome sessions, the introduction of an additional orange color offering a "notified" service, and the definition of default link colors. After a thorough examination of basic LTP mechanisms for all color variants, this article discusses two scenarios where orange seems particularly appealing: video streaming and optical interplanetary links. Numerical results offer further insight into the complex LTP mechanisms and also highlight the difference between LTP retransmissions and bundle protocol retransmissions, the latter benefitting from routing reprocessing. Multicolor LTP has already been implemented as an interplanetary overlay network (ION) plug-in and its enhancements have been proposed to Consultative Committee for Space Data Systems Space Internetworking Services Delay-/Disruption-Tolerant Networking working group for a possible inclusion in the next version of LTP specifications (LTPv2)
DTNbox: A DTN Application for Peer-to-Peer Directory Synchronization
No full textThis paper aims to present DTNbox, an application for peer-to-peer directory synchronization between DTN nodes, suitable for challenged networks. By contrast to similar applications, DTNbox neither relies on a server node on Internet, which would be impractical in challenged networks, nor is restricted to direct pairing of devices, as in Bluetooth. To cope with possible link disruptions and long delays typical of challenged networks, DTNbox uses the Bundle Protocol (BP), running on top of other ordinary Transport protocols, such as TCP. In order to be compatible with all three major BP implementations, ION, DTN2 and IBR-DTN, DTNbox is built on top of an interface, called Abstraction Layer, which decouples the application from the specific BP implementation in use. DTNbox rationale, design and potential uses are fully described in the paper
LTP Performance on Near Earth Optical Links
Full text linkThe Licklider Transport Protocol (LTP) has been designed to cope with long-delay and error-prone scheduled-intermittent links, and thus is envisaged as the Bundle Protocol (BP) “convergence layer” of choice in future Inter-planetary networks (IPN) based on the Delay-/Disruption-Tolerant architecture. Moreover, LTP's remarkable ability to cope with multiple losses when operating in “red” reliable mode also makes it potentially appealing when coupled with Near Earth optical links. The aim of this paper is to assess LTP performance in this scenario, so we have developed a test bed based on real machines, real implementations of BP and LTP, and a channel emulator; this is based on “erasure vectors”, i.e. time series describing the on/off state of the optical link, derived from real data measurements conducted by DLR. Our results show that, when properly configured, LTP is able to use all available bandwidth even under the most severe conditions, which makes it a perfect match to Near Earth Optical links
Evaluation of spectral efficiency of high capacity mobile radio systems for different scenarios
No full textThe authors discuss the problems related to a proper definition and evaluation of spectral efficiency in order to find out which aspects are relevant for comparison among different solutions, and which aspects determine only the final absolute value. In particular, it is shown that different coverage strategies and propagation conditions not only affect the absolute value of spectral efficiency but also the comparison among different systems. The concept of a 'scenario' for evaluation and comparison is introduced, and examples of computation of spectral efficiency are given in a deterministic and in a statistical scenario (in the presence of log-normal fading). A reference optimum system is introduced in order to be able to express system spectral efficiency in a relative way
HSLTP - An LTP Variant for High Speed Links and Memory Constrained Nodes
Full text linkDelay/disruption-tolerant networking architecture relies on the use of Licklider Transmission Protocol (LTP) on interplanetary links. LTP loss recovery is based on automatic repeat request retransmissions, which, when the propagation delay is very long, are costly. Alternatively, losses could be recovered by using Packet Layer Forward Error Correcting codes, as done by the authors in ECLSA (error Coding Link Service Adapter), recently presented in a companion paper, where LTP segment retransmissions are limited to the unlikely case of decoding failures. However, on high bandwidth-delay-product links, the very possibility of segment retransmission requires that a huge number of Rx buffers be available. To resolve this problem, high-speed LTP, presented here, has a more disruptive approach than ECLSA: it enforces almost one-to-one correspondence between LTP blocks and FEC codewords, and never requires LTP segment retransmissions. In the unlikely case of a FEC failure, the partially received block is discarded and its bundles are resent directly by the bundle protocol. The advantages and disadvantages of this approach are explored in the article. On nodes limited in memory, the results are significantly improved
General approach for the comparison of spectrum efficiency of digital mobile radio systems
No full textEvaluation of spectrum efficiency in mobile radio systems is often performed by different authors starting from different working assumptions; that yields results that are not easily comparable outside the `scenario' where they have been achieved. This paper attempts to settle this controversial matter providing some criteria for overcoming these difficulties. The results of this investigation allow to assess that relative capacity comparisons are fairly independent of some quality parameters, such as specified outage probability, or propagation parameters, such as the standard deviation of lognormal shadowing, so that these parameters need not complicate the comparison of competing approaches. As a consequence, a very simple scenario, providing an adequate basis for deriving constant efficiency curves, turns out to be of great relevance for comparisons. Associated with it, a graphic tool, allowing to perform quick relative comparisons among systems, is presented
Performance evaluation of a DS Spread Spectrum system over a 60 GHz multipath channel
No full textThis work aims at evaluating the performance of a Direct Sequence Spread-Spectrum (DS-SS) system over a 60 GHz real indoor channel characterized by the presence of severe multipath. The channel has been described by 1680 impulse response data calculated by means of a 3-D ray-tracing program. Both multipath components with delays shorter and longer than the chip time have been examined, and a special emphasis has been placed onto the study of the multipath effects on the DLL tracking circuit. The obtained results show the spatial distribution of the effective received energy per bit at the data demodulator input and provide some useful indications about the design criteria for an indoor wireless wideband local area network at EHF
Impact of fast fading compensations on mobile radio system performance
No full textThis paper explores what benefits can result from the compensation of both log-normal shadowing and Rayleigh/Rice-fading fluctuations in a mobile radio environment. The focus is on those power-control policies that exclusively make use of local power-level measurements in order to improve the performance, measured in terms of signal-to-cochannel interference ratio, of time-division multiple-access cellular radio systems; the aim is in fact to demonstrate under what circumstances the power compensation can be advantageously exploited. The corresponding analysis accounts for the errors due to the delay constraints that time-division and transmission techniques such as interleaving inevitably force onto the control loops. The numerical results quantitatively outline the maximum benefits on system performance that derive from the introduction of fast fading compensation for the class of power-control policies investigated in this paper. The remarkable influence of delay errors on the effectiveness of the fast fading control procedures are clearly revealed
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