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Abstract: We present Delay-Tolerant Transport Protocol (DTTP) which enables fast and reliable communications in deep space. The proposed protocol regularly measures its performance through available paths towards destination, and develops its routing strategy accordingly. We evaluate DTTP performance across a wide range of network scenarios that pertain to Mars-to-Earth distances. Based on simulation results, we show that: (i) Delay-Tolerant Networking does not necessarily imply belated communications; (ii) DTTP can efficiently support reliable data transfers in challenged networks; and (iii) dynamic routing is feasible in space. [ABSTRACT FROM AUTHOR]

We discuss a new packet service paradigm, called "Less Impact Better Service" (LIBS), which is realized through a novel queuing discipline, called "Noncongestive Queuing" (NCQ). NCQ prioritizes small packets when conditions permit and utilizes service thresholds to confine the delay impact of prioritization on congestive applications. We show that LIBS and NCQ satisfy more users with diverse demands on delay and throughput. We obtained both analytical and simulation results, which are very promising. Diversity is simulated by using FTP, sensor, and VoIP traffic. [ABSTRACT FROM AUTHOR]

We investigate the energy-saving potential of transport protocols. We seek an answer to strategic issues of maximising energy and bandwidth exploitation, without damaging the dynamics of multiple-flow equilibrium. We claim that (i) an energy-saving strategy of the transport level needs to be associated with some energy potential index which, unlike energy expenditure, is not device-specific and (ii) system-wise an energy-efficient system of flows is not always a better choice: we show that a less energy-efficient system may be more reliable in terms of packet multiplexing and, in turn, may reduce the probability that some flows may expend their energy with zero gain. We perform experiments using a real testbed and ns-2 based simulations. [ABSTRACT FROM AUTHOR]

We investigate whether the current best-effort technology of Internet stands up to the high quality standards of real-time voice communication. More precisely, we assess VoIP quality within the context of transport protocol support and efficiency. Initially, we focus on TCP and UDP supportive role from the perspective of VoIP performance. Applying our metric for real-time performance, we reach the outcome that UDP is always not the protocol of choice for VoIP, since it occasionally exhibits inadequate performance. Beyond that, we evaluate a solution-framework based on TCP protocols, which favour real-time traffic. Based on our measurements, we assess the efficiency of the associated congestion control and congestion avoidance mechanisms in terms of VoIP performance. We also study the effect of packet size on protocol behaviour and VoIP quality. Furthermore, we investigate VoIP traffic friendliness, as well as potential tradeoffs between protocol performance and fairness. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work we first describe an asynchronous-feedback model which corresponds to the diverse roundtrip times (RTTs) of competing flows within the same communication channel. We show that even when the feedback of the receivers/network is asynchronous, the duration of a congestion epoch represents ‘common knowledge’ for the competing flows. Based on this property, we propose a diverse linear increase scheme in proportion to the RTT of each flow and we adjust periodically the windows of the competing flows accordingly, in order to enhance fairness of asynchronous-feedback environments. We name this scheme τ-AIMD and show that fairness of flows in asynchronous systems is improved since the increase-rate diversity of long and short RTT flows is largely canceled. We use the max–min notion of fairness to show that τ-AIMD can constitute the foundation for other window-based, end-to-end algorithms that target a good balance between efficiency and fairness. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We study opportunistic forwarding in a community-based networking paradigm where mobile users and shared access points (SAPs) collectively provide Internet access to users (mobile or not), including those in areas where other connectivity options are not available. Our approach is based on an efficient interoperation of two challenging network types: the opportunistic and the user-provided networks (UPNs). This requires a re-evaluation of the existing assumptions regarding inter-contact patterns and their alignment to this hybrid environment. We confirm our arguments with numerical results from a stochastic model as well as experimental scenarios with realistic parameters using the ONE simulator. Our experiments are based on a reference routing algorithm we designed and implemented that extends the spray ’n focus protocol and exhibits the following characteristics: (i) is oriented to this integrated environment; (ii) employs delay-tolerant networking (DTN) technologies along with contact prediction; and (iii) is independent of the deployed UPN approach. According our results, the proposed methodological approach achieves lower communication overhead, latency and storage requirements compared to representative opportunistic routing algorithms. [ABSTRACT FROM AUTHOR]

We present a method for predicting delivery time of bundles in space internetworks. The bundle delivery time estimation (BDTE) tool exploits contact graph routing (CGR), predicts bundle route, and calculates plausible arrival times along with the corresponding probabilities. Latency forecasts are performed in an administrative node with access to an instrumentation database (DB) appropriate for statistical processing. Through both analysis and experimentation, we demonstrate that estimates of bundle earliest plausible delivery time and destination arrival probabilities can be provided. [ABSTRACT FROM AUTHOR]

While there exist extensive research works on congestion control and active queue management, or the joint dynamics of a congestion control strategy with the random early detection (RED) algorithm, little has been done on the interactions between different window adjustment strategies and different queue management schemes such as DropTail and RED. In this paper, we consider a spectrum of TCP-friendly additive increase and multiplicative decrease (AIMD) parameters. At the one end of this spectrum, smooth-TCP enhances smoothness for multimedia applications by reducing the window decrease ratio upon congestion, at the cost of the additive increase speed and the responsiveness to available bandwidth. At the other end, responsive-TCP enhances the responsiveness by increasing the additive increase speed, at the cost of smoothness. We investigate the network dynamics with various combinations of AIMD parameters and queue management schemes, under different metrics. The investigation is conducted from the deployment (especially incremental deployment) point of view. We discussed the impact of the interactions on the goodput, fairness, end-to-end delay, and its implications to energy consumption on mobile hosts. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Internet is a heterogeneous environment comprising wired and wireless components, and transport protocols with different error recovery strategies. We use simulations to study the behaviour of random early detection (RED) gateways in such heterogeneous environments. We investigate two issues: (i) the performance trade-offs of the dropping policy of RED over Drop-Tail's, and (ii) the impact of RED's active queue management on more sophisticated protocols such as TCP-SACK. Some of our results indicate that RED does not deal adequately with heterogeneity. In particular, it may happen that RED applies congestion avoidance techniques even when wireless errors force some senders to back off prior to actual congestion. Our scenarios involve a non-monotonic transmission behaviour of transport protocols within one and the same congestion epoch; RED may escalate further bandwidth under-utilization by applying false congestion avoidance tactics. Furthermore, our results indicate that RED's dropping policy of ‘proportional’ fairness, which is realized through a Send-more/Drop-more scheme, can also penalize sophisticated protocols like TCP-SACK, which attempt to recover more aggressively from wireless losses. In summary, our results call for further investigation of RED's efficiency in heterogeneous networks and naturally raise the concern of RED's compliance with the end-to-end argument. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Internet has crossed new frontiers with access to it getting faster and cheaper. Considering that the architectural foundations of today's Internet were laid more than three decades ago, the Internet has done remarkably well until today coping with the growing demand. However, the future Internet architecture is expected to support not only the ever growing number of users and devices, but also a diverse set of new applications and services. Departing from the traditional host-centric access paradigm, where access to a desired content is mapped to its location, an information-centric model enables the association of access to a desired content with the content itself, irrespective of the location where it is being held. UMOBILE tailors the information-centric communication model to meet the requirements of opportunistic communications, integrating those connectivity approaches into a single architecture. By pushing services near the edge of the network, such an architecture can pervasively operate in any networking environment and allows for the development of innovative applications, providing access to data independent of the level of end-to-end connectivity availability. [ABSTRACT FROM AUTHOR]

Recent trends in scientific low Earth orbit satellite missions involve small, low-cost satellites communicating with multiple low-cost ground stations. We propose a peer-to-peer multicast ground distribution scheme accompanied by a best-effort broadcasting mechanism with randomized retransmissions that is tailored for such satellite missions. Through our simulation tools, we assess the performance of the new, low-cost model; evaluate the benefits of decentralized ground distribution; and quantify the trade-off between data reliability and data return volume. [ABSTRACT FROM PUBLISHER]