Peer-to-Peer Streaming of Scalable Video in Future Internet Application Speaker : 吳靖緯 MA0G0101 Communications Magazine, IEEE, On page(s): , March 2011 Authors: Naeem Ramzan, Emanuele Quacchio, Toni Zgaljic, Stefano Asioli, Luca Celetto, Ebroul Izquierdo, Fabrizio Rovati

Outline Introduction Scalable video coding Streaming of scalable video over P2P networks The MMV platform The NextShare platform SEAcast platform Conclusion 2

Introduction In conventional streaming architectures the client-server model and the usage of content distribution networks (CDNs) along with IP multicast were the most desirable approaches for many years. However, severely limits the number of simultaneous users in video streaming. The reason is the bandwidth bottleneck at the server side, since usually many clients request the content from the server. 3

Introduction A CDN overcomes the same bottleneck problem by introducing dedicated servers at geographically different locations, resulting in expensive deployment and maintenance. Compared to conventional approaches, a major advantage of peer-to-peer (P2P) streaming protocols is that each peer involved in content delivery contributes its own resources to the streaming session. Administration, maintenance, and responsibility for operations are therefore distributed among the users instead of handled by a single entity. 4

Introduction The main advantage of P2P systems is bandwidth scalability, network path redundancy, and the ability to self organize. Nevertheless, several problems are still open and need to be addressed in order to achieve high quality of service and user experience. In particular, the bandwidth capacity of a P2P system is extremely varying, as it relies on heterogeneous peer connection speeds, and directly depends on the number of connected peers. 5

Introduction Moreover, displaying devices at the user side may range from small handsets (e.g., mobile phones) to large HD displays (e.g., LCD televisions). Therefore, video streams need to be transmitted at a suitable spatio-temporal (ST) resolution supported by the user’s display device. 6

Scalable video coding A scalable video sequence can be adapted in three dimensions: temporal spatial quality The complexity of adaptation is very low, in contrast to the adaptation complexity of non-scalable bitstreams. 7

Scalable video coding Figure 1 shows an example of video distribution through links supporting different transmission speeds and display devices. 8

Scalable video coding The SVC scheme gives flexibility and adaptability to video transmission over resource-constrained networks in such a way that. At each point where video quality/resolution needs to be adjusted, an adaptation is performed. Since the adaptation complexity is very low, the video can be efficiently streamed in such an environment. 9

Streaming of scalable video over P2P networks A generic P2P streaming architecture using SVC is depicted in Fig

Streaming of scalable video over P2P networks A chunk represents the smallest unit of data that will be transmitted over the P2P network. Sometimes, the term piece is used to denote a chunk. In BitTorrent, file chunks are downloaded in rarest-first fashion. 11

Streaming of scalable video over P2P networks In video streaming this can result in an interruption of the video playback since chunks are not received sequentially. Therefore, special care needs to be given to those chunks that are close to the playback position. An example of an algorithm that takes into account these considerations is Give-to-Get (G2G). 12

Streaming of scalable video over P2P networks In this algorithm chunks of compressed video are classified into three priority categories: high, medium, and low. This classification depends on the current playback position. Chunks close to the playback positions are marked as high- priority chunks. Medium- and low-priority chunks are downloaded according to the standard BitTorrent strategy: rarest-first. 13

The MMV platform A.Piece Picking Strategy At the beginning of the streaming session, information about GOPs(groups of pictures) and layers is extracted from the bitstream description file. A sliding window is defined, made of several GOPs (typically three to four). Chunks are picked only from those inside the window unless all of them have already been downloaded. 14

The MMV platform In the latter case, the piece picking policy will be rarest-first. Inside the window, chunks have different priorities, following the idea from the original G2G algorithm. First, a peer will try to download the base layer (BL), then the first enhancement layer (EL1). Figure 3 shows the behavior of the system with a window three GOPs wide. 15

The MMV platform An early stage of the prebuffering phase is shown in Fig. 3, first row. Second row, the first two layers have been downloaded, and chunks are being picked from EL2 according to the rarest-first policy. 16

The MMV platform Third row, the window has shifted. The system will pick chunks from GOP 3 until the quality of received layers is the same. Fourth row, all GOPs within the window have the same number of completed layers, and pieces are picked from EL3. 17

The MMV platform B.Peer Selection Strategy Good neighbors are those peers that own the piece with the highest download rates. Each time the window shifts, download rates of all the neighbors are evaluated, and the peers are sorted in descending order. Pieces are then requested from peers providing download rates above the threshold. 18

The MMV platform The performance of this framework is shown in Fig

The NextShare platform The procedure implemented in NextShare to download scalable data chunks is an extension of the G2G algorithm. Priorities are defined as in G2G and extended to the multiple files, as depicted in Fig

The NextShare platform In the high-priority set pieces are downloaded sequentially, while in the low-priority set pieces are downloaded in a rarest- first fashion. Each block in the figure represents a time slot. In Fig. 5 at time instance t (playback position), the algorithm has to decide which block to download for time point (t + x). 21

The NextShare platform The controller implemented in NextShare tries to switch to a higher quality as soon as there is enough saved buffer for the current quality. Therefore, a safe buffer of chunks downloaded and not yet delivered to the player is defined; the size of this buffer is a function of the parameter x depicted in Fig. 5. The minimum value for x corresponds to five time slots, and can vary depending on network performance. 22

SEAcast platform In SEACast data packets are simply forwarded from parent to children nodes. As shown in Fig. 6, the publisher is connected to the SEACast root node by means of a different Real-Time Transport Protocol (RTP) connection for each scalable layer. Each SEACast client keeps a buffer of a few seconds for each tree in which it participates. 23

SEAcast platform The structure of the P2P tree generated with the SEACast application is depicted in Fig

Conclusions In P2P networks video is streamed to the user in a fully distributed fashion. Network resources are distributed among users instead of handled by a single entity. However, due to the diversity of users’ displaying devices and available bandwidth levels in the Internet, the underlying coding and transmission technology needs to be highly flexible. 25

Conclusions In this article we have presented several advanced P2P systems supporting streaming of scalable video and designed to support future Internet applications. 26