Roberto Roverso

NATCracker: NAT Combinations Matter

In this paper, we report our experience in working nwith Network Address Translators (NATs). Traditionally, there nwere only 4 types of NATs. For each type, the (im)possibility nof traversal is well-known. Recently, the NAT community has nprovided a deeper dissection of NAT behaviors resulting into at nleast 27 types and documented the (im)possibility of traversal nfor some types. There are, however, two fundamental issues that nwere not previously tackled by the community. First, given the nmore elaborate set of behaviors, it is incorrect to reason about ntraversing a single NAT, instead combinations must be considered nand we have not found any study that comprehensively states, nfor every possible combination, whether direct connectivity with nno relay is feasible. Such a statement is the first outcome of the npaper. Second, there is a serious need for some kind of formalism nto reason about NATs which is a second outcome of this paper. nThe results were obtained using our own scheme which is an naugmentation of currently-known traversal methods. The scheme nis validated by reasoning using our formalism, simulation and nimplementation in a real P2P network.

On the feasibility of centrally-coordinated Peer-to-Peer live streaming

In this paper we present an exploration of central coordination as a way of managing P2P live streaming overlays. The main point is to show the elements needed to construct a system with that approach. A key element in the feasibility of this approach is a near real-time optimization engine for peer selection. Peer organization in a way that enables high bandwidth utilization plus optimized peer selection based on multiple utility factors make it possible to achieve large source bandwidth savings and provide high quality of user experience. The benefits of our approach are also seen most when NAT constraints come into play.

Through the wormhole: Low cost, fresh peer sampling for the Internet

State of the art gossip protocols for the Internet are based on the assumption that connection establishment between peers comes at negligible cost. Our experience with commercially deployed P2P systems has shown that this cost is much higher than generally assumed. As such, peer sampling services often cannot provide fresh samples because the service would require too high a connection establishment rate. In this paper, we present the wormhole-based peer sampling service (WPSS). WPSS overcomes the limitations of existing protocols by executing short random walks over a stable topology and by using shortcuts (wormholes), thus limiting the rate of connection establishments and guaranteeing freshness of samples, respectively.We show that our approach can decrease the connection establishment rate by one order of magnitude compared to the state of the art while providing the same levels of freshness of samples. This, without sacrificing the desirable properties of a PSS for the Internet, such as robustness to churn and NAT-friendliness. We support our claims with a thorough measurement study in our deployed commercial system as well as in simulation.

SmoothCache: HTTP-Live streaming goes peer-to-peer

In this paper, we present SmoothCache, a peer-to-peer live video streaming (P2PLS) system. The novelty of SmoothCache is threefold: i ) It is the first P2PLS system that is built to support the relatively-new approach of using HTTP as the transport protocol for live content, ii ) The system supports both single and multi-bitrate streaming modes of operation, and iii ) In Smoothcache, we make use of recent advances in application-layer dynamic congestion control to manage priorities of transfers according to their urgency. We start by explaining why the HTTP live streaming semantics render many of the existing assumptions used in P2PLS protocols obsolete. Afterwards, we present our design starting with a baseline P2P caching model. We, then, show a number of optimizations related to aspects such as neighborhood management, uploader selection and proactive caching. Finally, we present our evaluation conducted on a real yet instrumented test network. Our results show that we can achieve substantial traffic savings on the source of the stream without major degradation in user experience.

Peer2View: A peer-to-peer HTTP-live streaming platform

Peer2View is a commercial peer-to-peer live video streaming (P2PLS) system. The novelty of Peer2View is threefold: i) It is the first P2PLS platform to support HTTP as transport protocol for live content, ii) The system supports both single and multi-bitrate streaming modes of operation, and iii) It makes use of an application-layer dynamic congestion control to manage priorities of transfers. Peer2View goals are to achieve substantial savings towards the source of the stream while providing the same quality of user experience of a CDN.

SmoothCache 2.0: CDN-quality adaptive HTTP live streaming on peer-to-peer overlays

In recent years, adaptive HTTP streaming protocols have become the de-facto standard in the industry for the distribution of live and video-on-demand content over the Internet. This paper presents SmoothCache 2.0, a distributed cache platform for adaptive HTTP live streaming content based on peer-to-peer (P2P) overlays. The contribution of this work is twofold. From a systems perspective, to the best of our knowledge, it is the only P2P platform which supports recent live streaming protocols based on HTTP as a transport and the concept of adaptive bitrate switching. From an algorithmic perspective, the system describes a novel set of overlay construction and prefetching techniques that realize: i) substantial savings in terms of the bandwidth load on the source of the stream, and ii) CDN-quality user experience in terms of playback latency and the watched bitrate. In order to support our claims, we conduct a methodical evaluation on thousands of real consumer machines.

MyP2PWorld: Highly Reproducible Application-Level Emulation of P2P Systems

In this paper, we describe an application-level emulator for P2P systems with a special focus on high reproducibility. We achieve reproducibility by taking control over the scheduling of concurrent events from the operating system. We accomplish that for inter- and intra- peer concurrency. The development of the system was driven by the need to enhance the testing process of an already-developed industrial product. Therefore, we were constrained by the architecture of the overlying application. However, we managed to provide highly transparent emulation by wrapping standard/widely-used networking and concurrency APIs. The resulting environment has proven to be useful in a production environment. At this stage, it started to be general enough to be used in the testing process of applications other than the one it was created to test.

Hive.js: Browser-Based Distributed Caching for Adaptive Video Streaming

Peer-to-peer (P2P) technology has long been considered a natural complement to standard CDN infrastructure for video distribution since it greatly reduces costs and improves quality of user experience. However, P2P solutions have traditionally required the installation of additional software or plugins to be deployed, which significantly hinders adoption. In this paper, we present Hive.js, a browser-based plugin-less distributed caching platform for video streaming. Hive.js is layered over WebRTC, a new set of HTML5 APIs for direct browser-to-browser communication, and it is designed to transport adaptive HTTP streaming protocols, specifically MPEG-DASH. Initial results obtained by evaluating Hive.js in a controlled test environment show that our approach significantly reduces the load on CDN infrastructure and does not sacrifice quality of user experience.

On HTTP live streaming in large enterprises

In this work, we present a distributed caching solution which addresses the problem of efficient delivery of HTTP live streams in large private networks. With our system, we have conducted tests on a number of pilot deployments. The largest of them, with 3000 concurrent viewers, consistently showed that our system saves more than 90% of traffic towards the source of the stream while providing the same quality of user experience of a CDN. Another result is that our solution was able to reduce the load on the bottlenecks in the network by an average of 91.6%.

DTL: dynamic transport library for peer-to-peer applications

This paper presents the design and implementation of the Dynamic Transport Library (DTL), a UDP-based reliable transport library, initially designed for - but not limited to - peer-to-peer applications. DTL combines many features not simultaneously offered by any other transport library including: i) Wide scope of congestion control levels starting from less-than-best-effort to high-priority, ii) Prioritization of traffic relative to other non-DTL traffic, iii) Prioritization of traffic between DTL connections, iv) NAT-friendliness, v) Portability, and vi) Application level implementation. Moreover, DTL has a novel feature, namely, the ability to change the level of aggressiveness of a certain connection at run-time. All the features of the DTL were validated using a controlled environment as well as the Planet Lab testbed.