Today's universal communications increasingly involve mobile and battety-powered devices (e.g. hand-held, laptop) over wired and wireless networks. Energy eficiency, as well as throughput, are becoming service characteristics of dominant importance in communication protocols. Although standard TCP versions lack the finctionali5 to efficiently adjust their error-control strategies to distinct characteristics of network environments and to specific constraints of communicating devices, the wide range of TCP-based applications have rendered TCP the de facto standard for reliable end-to-end communications. In this work we propose "grafting" two components of strategic significance onto standard TCP: a Probing mechanism and an Immediate Recovery strategy. Our results show that these enhancements yield higher throughput while maintaining lower levels of energy expenditure, and thus have the potential of promoting TCP's congestion control to a universal error-control schema for heterogeneous wiredwireless channels. Furthermore, the enhancements do not damage the end-to-end characteristics of the TCP, nor do they require changes to its semantics: the mechanisms are implemented as option extensions to the TCP header. We compare "TCP-Probing " with Tahoe, Reno, and New Reno, and show that it can be a protocol of choice for heterogeneous wiredwireless communications with respect to energy and throughput performance.

We discuss the design principles of TCP within the context of heterogeneous wired/wireless networks and mobile networking. We identify three shortcomings in TCP's behavior: (i) the protocol's error detection mechanism, which does not distinguish different types of errors and thus does not suffice for heterogeneous wired/wireless environments, (ii) the error recovery, which is not responsive to the distinctive characteristics of wireless networks such as transient or burst errors due to handoffs and fading channels, and (iii) the protocol strategy, which does not control the tradeoff between performance measures such as goodput and energy consumption, and often entails a wasteful effort of retransmission and energy expenditure. We discuss a solution-framework based on selected research proposals and the associated evaluation criteria for the suggested modifications. We highlight an important angle that did not attract the required attention so far: the need for new performance metrics, appropriate for evaluating the impact of protocol strategies on battery-powered devices.

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AlthoughInterplanetary Telecommunications rely on preconfigured contact schedules to make routing decisions, there is a lack of appropriate mechanisms to notify the network about contact plan changes. In order to fill this gap, we propose and evaluate a framework for disseminating information about queueing delays and link disruptions. In this context, we present such a mechanism, focusing not only on its functional properties, but rather on its impact objectives: to improve accuracy and routing performance. Supportively, we couple this mechanism with a DTN-compatible protocol, namely Contact Plan Update Protocol (CPUP), which implements our dissemination policy. Through simulation of space scenarios we show that accuracy can be significantly improved in all cases while routing performance can achieve a wide range, from minor through to significant gains, conditionally.

SUMMARYIn this paper, we analyze the performance of two contact graph routing (CGR) enhancements, namely, CGR with earliest transmission opportunity (CGR-ETO) and overbooking management. CGR-ETO aims to improve the accuracy of predicted bundle delivery time by exploiting existing information on queueing delay, in routing decisions. Overbooking management aims to proactively handle contact oversubscription, which occurs when high-priority bundles are forwarded to a contact that is already fully subscribed by lower-priority bundles. These two enhancements have been recently included in the official CGR version as part of the Interplanetary Overlay Network delay-tolerant/disruption-tolerant networking implementation maintained by the National Aeronautics and Space Administration. In parallel to the comparative evaluation of the enhancements against the original CGR, we introduce an experimental version of CGR-ETO that exploits information on locally routed data to calculate queueing delays in all hops through the path to destination, rather than in the first hop only. We evaluate the aforementioned enhancements in a set of emulation experiments conducted on a GNU/Linux testbed and compare official and experimental versions of CGR. Results show that the two enhancements are complementary and can significantly improve routing decisions compared with older versions of CGR, particularly in the presence of parallel routes and traffic of different priorities. These advantages are further extended when the experimental version of ETO is considered.