Ioannis Komnios

Cost-Effective Multi-Mode Offloading with peer-assisted communications

Data offloading through WiFi networks has been identified as a promising solution to cellular network congestion caused by the ongoing explosive growth in mobile data traffic. In this paper, we propose Cost-Effective Multi-Mode Offloading (CEMMO) that enhances offloading with multi-hop peer-assisted communications regardless of content and popularity. CEMMO enables three modes of communication: cellular delivery, delay-tolerant offloading, and peer-assisted offloading. Exploiting user knowledge on mobility and WiFi connectivity, CEMMO assists the cellular operator in selecting the best out of its three modes in order to reduce the overall cost in terms of financial settlement, energy consumption, and user satisfaction. Our simulations with a realistic mobility and connectivity prediction model based on a Markov process show that CEMMO offloads up to 59% of the mobile data traffic and reduces transfer cost per MB up to 16% over delay-tolerant offloading. This paper also discusses practical issues in CEMMO adoption.

SPICE Testbed: A DTN Testbed for Satellite and Space Communications

This paper presents SPICE testbed, a state-of-the-art Delay Tolerant Networking testbed for satellite and space communications deployed at the Space Internetworking Center, Greece. The core of the testbed relies on the Bundle Protocol and its architecture has been designed to support multiple DTN implementations and a variety of underlying and overlying protocols. SPICE testbed is equipped with specialised hardware components for the accurate emulation of space links and ground stations, such as Portable Satellite Simulator (PSS) and CORTEX CRT system, as well as protocols and mechanisms specifically designed for space DTNs. Performance and functionality evaluations on SPICE testbed show that it is an ideal platform to evaluate new mechanisms in a variety of space communication scenarios.

Evaluation of dynamic DTN routing protocols in space environment

As the number of space elements increases, routing becomes an issue of great interest. The majority of routing schemes that have been proposed till now, employ a fairly static design and, only recently, more sophisticated protocols have been introduced. In this study, we evaluate some of the most prominent routing protocols for Delay-Tolerant Networks, Epidemic, PRoPHET and Contact Graph Routing, in space environment. Using COMNET Labs DTN testbed, we show that for increasing delay, Contact Graph Routing significantly outperforms the other two routing schemes.

LEDBAT performance in sub-packet regimes

Wireless Community Networks in the developing world satisfy the basic needs of remote users to information access. However, community networks in developing regions usually rely on low-bandwidth backhaul links that are shared amongst a large user base, driving these links to sub-packet regimes where the per-flow throughput is less than one packet per RTT. TCP performance significantly degrades in such conditions, resulting in severe unfairness and high packet loss rates. In this paper, we investigate the performance of scavenger transport methods, namely LEDBAT and its fair modification fLEDBAT, in the sub-packet regime of shared backhaul links in developing regions. Our intention is to explore the feasibility of using such scavenger transport methods for uploading content over bandwidth constrained backhauls. Our findings show that LEDBAT achieves higher link efficiency and fairness compared to TCP in a variety of sub-packet regime scenarios. When TCP and LEDBAT flows share the same link in the sub-packet regime, LEDBAT flows are more aggressive, consuming more resources than TCP. Therefore, we conclude that a more conservative strategy after consecutive timeouts and shared bottleneck detection mechanisms need to be incorporated into the core LEDBAT algorithm, in order to correctly adjust its congestion window in the sub-packet regime.

CARPOOL: extending free internet access over DTN in urban environment

In order to address the challenge of digital exclusion, we introduce an access method based on message ferrying that enables free delay-tolerant Internet access to all. Targeting an urban scenario, where means of public transport, such as buses and trams, follow a predefined route and schedule, we utilise a priori knowledge about their current location to extend Internet access provided by hotspots to users and areas that are not typically covered. In this paper, we explore how the deployment of DTN-capable nodes can extend free Internet coverage in metropolitan areas, we depict the inefficiency of existing DTN routing protocols in highly-dense environments and we propose Connectivity plAn Routing PrOtOcOL (CARPOOL), a reference routing protocol to support our claims. CARPOOL exploits the connectivity plan of public transportation, achieving high delivery ratio with minimum overhead.

CARPOOL: Connectivity Plan Routing Protocol

Basic Internet access is considered a human right, however geographical, technological and socio-economic reasons set barriers to universal Internet access. To address this challenge, we have proposed an access method based on message ferrying that enables free delay-tolerant Internet access to all, and developed Connectivity plAn Routing PrOtOcOL (CARPOOL), a reference routing protocol for the proposed access method. In this paper, we describe CARPOOL in depth and evaluate its performance for increasing traffic load. Focusing on an urban scenario, where means of public transport, such as buses, follow predefined routes and schedules, CARPOOL utilises a priori knowledge about their current location to extend Internet access provided by hotspots to users and areas that are not typically covered. Our simulation results show that CARPOOL effectively exploits the existing connectivity plan of public transportation, achieving high delivery ratio with minimum overhead. This paper also discusses possible enhancements of the proposed routing protocol.

A DTN-based architecture for public transport networks

Delay/disruption-tolerant networking has been exploited in a variety of communication scenarios to provide basic delay-tolerant Internet services. In this paper, we propose a delay/disruption-tolerant networking (DTN)-based architecture for dense urban environments that exploits the existing infrastructure of public transport networks to provide Internet services through applications that can withstand certain delays without significantly affecting user experience. To achieve data delivery within the delay tolerance threshold that each user defines, we couple the proposed architecture with the enhanced connectivity plan routing protocol (CARPOOL+) that includes smart mechanisms for route calculation. In particular, the proposed architecture exploits both scheduled and opportunistic contact opportunities and mitigates the impact of typical delays caused by traffic, road accidents, etc. Our simulation results show that the proposed architecture achieves high delivery ratio with low latency, even when significant delays occur. We also compare CARPOOL+ with the most well-known DTN routing solutions and show that CARPOOL+ achieves the highest delivery ratio with the lowest overhead.