Current Peer-to-Peer (P2P) file sharing systems make use of a considerable percentage of Internet Service Providers (ISPs) bandwidth. This paper presents the Collaborative Locality-aware Overlay SERvice (CLOSER), an architecture that aims at lessening the usage of expensive international links by exploiting traffic locality (i.e., a resource is downloaded from the inside of the ISP whenever possible). The paper proves the effectiveness of CLOSER by analysis and simulation, also comparing this architecture with existing solutions for traffic locality in P2P systems. While savings on international links can be attractive for ISPs, it is necessary to offer some features that can be of interest for users to favor a wide adoption of the application. For this reason, CLOSER also introduces a privacy module that may arouse the users' interest and encourage them to switch to the new architecture.

The wide diffusion of network address translators (NATs) (and, in some respect, firewalls) may prevent some applications that require direct end-to-end connectivity (e.g. real-time media) from being able to connect to the remote party. Although the solutions currently adopted rely on centralised nodes as third party relays, the distributed connectivity service (DISCOS) architecture has been recently proposed and aims at distributing such functionalities across a peer-to-peer (P2P) overlay. The original study presented some performance characteristics of the overlay, but the ability to resist to both failures and attacks was not taken into consideration. This study illustrates the robustness feature of the DISCOS overlay and suggests some minor modifications to the original mechanisms, in order to improve the overall robustness. The key component of DISCOS is its dynamic scale-free topology. Hence, the study also extends the existing literature concerning the robustness of scale-free networks, which considers only static graphs.

While peer-to-peer networks are mainly used to locate unique resources across the Internet, new interesting deployment scenarios are emerging. Particularly, some applications (e.g., VoIP) are proposing the creation of overlays for the localization of services based on equivalent servants (e.g., voice relays). This paper explores the possible overlay architectures that can be adopted to provide such services, showing how an unstructured solution based on a scale-free overlay topology is an effective option to deploy in this context. Consequently, we propose EQUATOR (EQUivalent servAnt locaTOR), an unstructured overlay implementing the above mentioned operating principles, based on an overlay construction algorithm that well approximates an ideal scale-free construction model. We present both analytical and simulation results which support our overlay topology selection and validate the proposed architecture.

Wireless IEEE 802.11 networks are typically deployed as a convenient and flexible way to access wired backbones. However, due to the inherently shared nature and physical properties of their communication medium, performance limits are easily reached. Some standard medium access control (MAC) solutions trade simplicity for performance yielding an overall throughput possibly much lower than the actual transmission rate. Moreover, given that many applications with real-time requirements, such as VoIP phones, IPTV, videoconferencing, distributed gaming, are getting increasingly deployed and important to users, it is mandatory for the wireless access to support them. However, the delay and jitter introduced by current IEEE 802.11 standard MAC solutions in some critical, although not uncommon, scenarios can be unacceptable for real-time applications. This work proposes a novel MAC solution for wireless networks that can offer deterministic quality of service for priority traffic while fully supporting statistical multiplexing and possibly increasing the aggregated network throughput. Being based on IEEE 802.11 physical layers and integrating some of the IEEE 802.11 MAC mechanisms, the implementation can leverage on existing components to take advantage of their economy of scale. The throughput and delay achieved with the proposed solution are compared with the ones of standard IEEE 802.11 protocols in various simulation scenarios.