Vasco N. G. J. Soares

From Delay-Tolerant Networks to Vehicular Delay-Tolerant Networks

This paper provides an introductory overview of Vehicular Delay-Tolerant Networks. First, an introduction to Delay-Tolerant Networks and Vehicular Delay-Tolerant Networks is given. Delay-Tolerant schemes and protocols can help in situations where network connectivity is sparse or with large variations in density, or even when there is no end-to-end connectivity by providing a communications solution for non real-time applications. Some special issues like routing are addressed in the paper and an introductory description of applications and the most important projects is given. Finally, some research challenges are discussed and conclusions are detailed.

GeoSpray: A geographic routing protocol for vehicular delay-tolerant networks

Vehicular networks are characterized by a highly dynamic network topology, and disruptive and intermittent connectivity. In such network environments, a complete path from source to destination does not exist on the most part of the time. Vehicular delay-tolerant network (VDTN) architecture was introduced to deal with these connectivity constraints. VDTN assumes asynchronous, bundle-oriented communication, and a store-carry-and-forward routing paradigm. A routing protocol for VDTNs should make the best use of the tight resources available in network nodes to create a multi-hop path that exists over time. This paper proposes a VDTN routing protocol, called GeoSpray, which takes routing decisions based on geographical location data, and combines a hybrid approach between multiple-copy and single-copy schemes. First, it starts with a multiple-copy scheme, spreading a limited number of bundle copies, in order to exploit alternative paths. Then, it switches to a forwarding scheme, which takes advantage of additional contact opportunities. In order to improve resources utilization, it clears delivered bundles across the network nodes. It is shown that GeoSpray improves significantly the delivery probability and reduces the delivery delay, compared to traditional location and non location-based single-copy and multiple-copy routing protocols.

A layered architecture for Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Network (VDTN) is a new network architecture based on the concept of Delay Tolerant Networks (DTN). It aims to be an architecture that handles non-real time applications at low cost, under unreliable conditions, enabling connectivity in diverse scenarios, using vehicles to carry data between terminal nodes. For example, it can be applied in rural and remote areas, or in emergency scenarios. This paper proposes a layered architecture for VDTNs, using out-of-band signaling, based on the separation of the control plane and data plane. It presents the layers interactions and the envisioned protocols required at each layer. The paper provides a deep understanding of the characteristics of VDTN and reveal some design issues in its modeling, leading to insights for future theoretic study and protocol design.

Improving Vehicular Delay-Tolerant Network Performance with Relay Nodes

Vehicular Delay-Tolerant Networking (VDTN) is an extension of the Delay-Tolerant Network (DTN) architecture concept to transit networks. VDTN architecture handles non-real time applications, exploiting vehicles to enable connectivity under unreliable scenarios with unstable links and where an end-to-end path may not exist. Intuitively, the use of stationary store-and-forward devices (relay nodes) located at crossroads where vehicles meet them and should improve the message delivery probability. In this paper, we analyze the influence of the number of relay nodes, in urban scenarios with different numbers of vehicles. It was shown that relay nodes significantly improve the message delivery probability on studied DTN routing protocols.

Improvement of Messages Delivery Time on Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks (VDTNs) are an application of the Delay-Tolerant Network (DTN) concept, where the movement of vehicles and their message relaying service is used to enable network connectivity under unreliable conditions. To address the problem of intermittent connectivity, long-term message storage is combined with routing schemes that replicate messages at transfer opportunities. However, these strategies can be inefficient in terms of network resource usage. Therefore, efficient scheduling and dropping policies are necessary to improve the overall network performance. This work presents a performance analysis, based on simulation, of the impact of different scheduling and dropping policies enforced on Epidemic and Spray and Wait routing schemes. This paper evaluates these policies from the perspective of their efficiency in reducing the message’s end-to-end delay. In our scenario, it is shown that when these policies are based on the message’s lifetime criteria, the message average delay decreases significantly and the overall message delivery probability also increases for both routing protocols. Further simulations show that these results outperform the MaxProp and PRoPHET routing protocols that have their own scheduling and dropping mechanisms.

Performance assessment of a geographic routing protocol for vehicular delay-tolerant networks

This paper analyses the performance of a new routing protocol for vehicular delay-tolerant networks, called GeoSpray. This geographic routing protocol performs a store-carry-and-forward, combining replication and forwarding/ routing decisions based on location information, with explicit delivery acknowledgments to improve network resources utilization. The performance of the proposed routing protocol is evaluated through simulation. The results have shown that GeoSpray achieves higher delivery ratios and lower delivery delays with a considerably low communication overhead, compared to six well-known routing protocols for delay-tolerant networks.

VDTNsim: A simulation tool for vehicular delay-tolerant networks

Developing an adequate network architecture for supporting data communications in vehicular networks is critical to overcome the challenges caused by highly dynamic network topology, connectivity disruption, and intermittent connectivity issues. Among several approaches available in the related literature to address these problems, vehicular delay-tolerant networks (VDTNs) appear as a recent and innovative solution that integrates the concepts of end-to-end, asynchronous, and variable-length bundle oriented communication; Internet protocol over VDTN; and out-of-band signaling. VDTN architecture, protocols and services are in a fairly early stage of development. Therefore, simulation appears as an important tool providing a highly flexible, low-cost, and fast answer for research questions, and furnishes important inputs for exploring through prototyping. This paper presents and describes the proposal and construction of a simulation tool for VDTN networks, called VDTNsim.

Evaluating the Impact of Storage Capacity Constraints on Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Network (VDTN) was proposed as a particular application of a mobile Delay-Tolerant Network (DTN), where vehicles act as the communication infrastructure for the network, relaying messages between the network nodes. In this paper, we consider the use of a VDTN to provide low-cost asynchronous communication between sparse populations spread over a remote vast region. We analyze the influence of the VDTN network node’s storage capacity (buffer size), on the efficiency of four DTN routing protocols, in terms of message delivery probability. Our scenarios show that the routing protocols message replication strategies react differently to the increase of buffer size in specific network nodes. Epidemic and MaxProp protocols benefit from the increase of the storage capacity on all network nodes. Spray and Wait protocol only takes advantage on the increase of the vehicles buffer capacity. We expect that this paper will provide a deep understanding of the implications of storage constraints over the performance of a VDTN, leading to insights for future routing algorithm and buffer management theoretic studies and protocol design.

Vehicular Wireless Burst Switching Network: Enhancing Rural Connectivity

This paper introduces a network architecture called vehicular wireless burst switching (VWBS). The main objective of this architecture is to provide low-cost connectivity solution for isolated and dispersed regions with no networks infrastructure. The proposed architecture is based on the concept of delay tolerant networks (DTN) and can be applied to various scenarios, including rapid deployment of emergency communication systems when all communication links have failed. In this paper, we present an overview of VWBS networks and show how their performance, in terms of average packet delays, can be improved using store-and-forward devices called relay nodes. Furthermore, we introduce several heuristic algorithms, which can be used to place minimum number of relay nodes. Through computer simulations, we compare the performance of the algorithms and their tradeoffs. We conclude our work by examining possible open research issues in VWBS.

Past, Present and Future of IP Telephony

Since the late 90s IP telephony, commonly referred to as Voice over IP (VoIP), has been presented as a revolution on communications enabling the possibility to converge historically separated voice and data networks, reducing costs, and integrating voice, data and video on applications. This paper presents a study over the standard VoIP protocols H.323, session initiation protocol (SIP), media gateway control protocol (MGCP), and H.248/Megaco. Given the fact that H.323 and SIP are more widespread than the others, we focus our study on them. For each of these protocols we describe and discuss its main capabilities, architecture, stack protocol, and characteristics. We also briefly point their technical limitations. Furthermore, we present the advanced multimedia system (AMS) project, a new system that aims to operate on Next Generation Networks (NGN) taking the advantage of its features, and it is viewed as the successor to H.323 and SIP.