Peer-to-peer is emerging as a potentially disruptive technology for content distribution in the mobile Internet. In addition to the already well-known peer-to-peer file sharing, real-time peer-to-peer streaming is gaining popularity. This paper presents an effective real-time peer-to-peer streaming system for the mobile environment. The basis for the system is a scalable overlay network which groups peer into clusters according to their proximity using RTT values between peers as a criteria for the cluster selection. The actual media delivery in the system is implemented using the partial RTP stream concept: the original RTP sessions related to a media delivery are split into a number of so-called partial streams according to a predefined set of parameters in such a way that it allows low-complexity reassembly of the original media session in real-time at the receiving end. Partial streams also help in utilizing the upload capacity with finer granularity than just per one original stream. This is beneficial in mobile environments where bandwidth can be scarce. 1. Introduction Peer-to-Peer (P2P) streaming applications are gaining more and more users around the world. These applications allow end-users to broadcast content throughout the Internet in real-time without the need for any special infrastructure, since the user's device, together with all other peers, collectively forms the infrastructure. Furthermore, dedicated servers are no longer required since every peer can serve data to other peers. This is in contrast to a service like YouTube [1] which still requires content to be uploaded to a central server first. Some of the currently existing P2P streaming applications, such as Octoshape [2] and SopCast [3], are suitable to be used in a mobile environment but still there are many issues to be solved before an optimized solution for mobile devices can be realized [4]. With real-time P2P streaming there is no need to download the entire media file before playback can be started. Decoding can be started as soon as enough data is buffered in the peer. This avoids long startup times, and eliminates the need to store the entire content on the mobile device which still has a relatively small amount of internal memory compared to the increasing size of the actual media. In live streaming, video of an ongoing event, like a football match, is delivered as a stream in real-time. After an initial buffering period, the user starts to watch the stream from a certain location and all peers consume data in the same time window. With a Video-on-Demand (VoD)
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