Peer-to-Peer Streaming of Scalable Video in Future Internet Application

2012.04.24

Speaker : 吳靖緯 MA0G0101

Communications Magazine, IEEE, On page(s): 128 - 135, 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

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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.

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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.

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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.

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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.

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Scalable video coding

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

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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.

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

Fig. 2.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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The MMV platform

• The performance of this framework is shown in Fig. 4.

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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. 5.

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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).

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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.

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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.

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SEAcast platform

• The structure of the P2P tree generated with the SEACast application is depicted in Fig. 6.

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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.

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