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Abstract-Network Address Translators (NAT) are ubiquitous on the Internet and any peer-to-peer (p2p) game will almost certainly need to perform NAT traversal through such devices. Our experiments suggest that while NAT hole punching techniques are relatively mature, they succeed only about 90% of the time and thus p2p games will inevitably need to employ NAT proxies to establish the remaining connections. We demonstrate with an implementation and a measurement study that using peers as NAT proxies is feasible for both UDP and TCP connections. We found that it is relatively easy to find peers capable of acting as proxies and that the performance achieved is comparable to that of server-based NAT proxies.

Abstract-The capacity of access links has increased dramatically in recent times, and bottlenecks are moving deeper into the Internet core. When bottlenecks occur in a core (or AS-AS peering) link, it is possible to use additional detour paths to improve the end-to-end throughput between a pair of source and destination nodes. We propose and evaluate a new massively-multipath (mPath) source routing algorithm to improve end-to-end throughput for high-volume data transfers. We demonstrate that our algorithm is practical by implementing a system that employs a set of proxies to establish one-hop detour paths between the source and destination nodes. Our algorithm can fully utilize the available access link bandwidth when good proxied paths are available, without sacrificing TCPfriendliness, and achieves throughput comparable to TCP when such paths cannot be found. For 40% of our test cases on PlanetLab, mPath achieved significant improvements in throughput. Among these, 50% achieved a throughput of more than twice that of TCP.

This paper presents Kahawai 1 , a system that provides high-quality gaming on mobile devices, such as tablets and smartphones, by offloading a portion of the GPU computation to server-side infrastructure. In contrast with previous thin-client approaches that require a server-side GPU to render the entire content, Kahawai uses collaborative rendering to combine the output of a mobile GPU and a server-side GPU into the displayed output. Compared to a thin client, collaborative rendering requires significantly less network bandwidth between the mobile device and the server to achieve the same visual quality and, unlike a thin client, collaborative rendering supports disconnected operation, allowing a user to play offline -albeit with reduced visual quality.Kahawai implements two separate techniques for collaborative rendering: (1) a mobile device can render each frame with reduced detail while a server sends a stream of per-frame differences to transform each frame into a high detail version, or (2) a mobile device can render a subset of the frames while a server provides the missing frames. Both techniques are compatible with the hardwareaccelerated H.264 video decoders found on most modern mobile devices. We implemented a Kahawai prototype and integrated it with the idTech 4 open-source game engine, an advanced engine used by many commercial games. In our evaluation, we show that Kahawai can deliver gameplay at an acceptable frame rate, and achieve high visual quality using as little as one-sixth of the bandwidth of the conventional thin-client approach. Furthermore, a 50-person user study with our prototype shows that Kahawai can deliver the same gaming experience as a thin client under excellent network conditions.