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Peer-to-Peer Multicast Video

clients nodes distribution tree

Definition: Peer-to-peer multicast video refers to the concept of peer-to-peer communication, where nodes are both clients and’ servers.

In the tradition video distribution scheme, a client contacts a server and establishes a unicast session before starting to receive the required content. Although this configuration is enough in many simple scenarios, it presents a number of problems. Indeed, the source’s maximum output bandwidth limits the number of parallel clients. Moreover, since this approach follows a centralized configuration, it is vulnerable to attacks. A number of alternative solutions have appeared to overcome these limitations. They generally propose the use of replicated servers to increase both the robustness and the capacity of the system to serve more clients. A more recent approach relies upon the concept of peer-to-peer (p2p) communication, where nodes are both clients and servers. Virtual links associating two IP addresses are established forming an overlay network.

In addition to being more resistant to attacks, the inherent distributed nature of p2p is asolution for the problem of multiple clients bottlenecking the source. Peer-to-peer Page 686  overlays have been rapidly adopted as a promising substrate for video distribution, for both video sharing (in the same way people share general data files) and streaming. In the latter case, a distribution tree is established between the source and the receivers. The particularity here is that intermediate nodes are also end-systems (and in general also a client). In this way, the source sends the video to a number of clients that, in turn, send to other clients, and so on until all clients receive the video. We refer to this approach as application- ayer multicast (since it forms an overlay distribution tree). Figure 1 shows an example of a video multicast tree using p2p concepts.

Although very attractive, video transmission over p2p networks presents a number of technical challenges. First, the distribution tree cannot grow indefinitely, since nodes closer to the leaves may experience high delays. While in a video on demand service this may not be a real issue, for other applications, such as interactive video communication, delays beyond a certain threshold are unacceptable. Another challenge is inherently related to the dynamic nature of peer-to-peer communications: nodes in an overlay may join/leave whenever they want, without any notice. A third problem concerns the complexity of establishing the distribution tree. Indeed, nodes are extremely heterogeneous in terms of receiving, transmitting, and storage capacities. For a small network, managing such a structure is feasible, but for larger dynamic topologies (even millions of receivers) it is likely that the overlay always operates in a sub-optimum configuration. Different solutions have been (and are being) proposed to overcome such limitations, which include, for instance, advanced algorithms for correctly placing nodes on the overlay. Recent results show that p2p video distribution is a promising solution to contour the limitations of the current Internet architecture.

Peer-to-Peer Streaming - Streaming P2P Architectures, Streaming Process, Peer-to-Peer System Operation [next] [back] Peele, George (c. 1556–c. 1596) - BIOGRAPHY, CRITICAL RECEPTION

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