# Cooperative Buffering Schemes for Time-Shifted Live Streaming of Distributed Appliances
## 2 Related Work  
In addition to recent advances in information technologies, the proliferation in smart devices such as PVRs equipped with built-in storage devices have enabled people to watch video in a convenient way [1; 2; 3]. However, unless the PVRs are connected to broadband, they can support only limited time-shifting hours due to the shortage of their local storage space. To overcome this problem, networked PVRs with broadband connections have been developed so that they can receive data from a network.  
On the other hand, video data traffic on the Internet have been growing rapidly and are predicted to be 82% of all Internet traffic in 2022 [17]. The increasing demands for VOD services, over-the-top (OTT) services such as Netflix, and time-shifted TV services are expected to continue driving this trend. To meet the demands of the tremendous amount of network traffic, CDNs have been employed by providing highly managed and globally distributed infrastructure as reliable backbones for video delivery. From a cost perspective, however, it is necessary to alleviate the burdens caused by the increasing video traffic on CDNs since CDNs require significant investments for expanding their services. To address the scalability issue in terms of cost, P2P technology has been employed as an alternative approach to CDNs [8; 9; 10]. Note that available resource capacity in P2P systems increases with the number of peers without additional investment.  
Increasing buffering efficiency has been one of the most important research topics in P2P streaming systems because peers can play videos back without delays by exchanging the data each of them is currently buffering. To improve the system performance, it is therefore critical to make each peer keep buffering the data needed by others. Thus, many buffering schemes have been proposed in P2P VOD and live streaming systems [18; 19; 20; 21; 22]. However, they have different environments from time-shifted streaming systems. That is, peers store the entire part of each video on their storage devices in P2P VOD systems, while they receive live broadcast data generated on the fly in the time-shifted streaming systems. Smaller buffers in a main memory are used to buffer a shorter time period around live broadcast, and video data are received only from servers or other peers in P2P live streaming systems, while the reserved local storage space is used to time-shift live broadcast programs, and video data can be also received directly through broadcast channels in the time-shifted streaming systems. Therefore, the existing buffering schemes for P2P VOD and live streaming cannot be applied directly to the time-shifted streaming, and relatively fewer studies have been thus conducted on buffering techniques for time-shifted live streaming. They have tried to increase the availability of data required by PVRs based on different methods. In P2 TSS [12], the authors proposed a buffering scheme to reduce the amount of data received from servers by increasing the hit ratio even though peers locally decide which blocks to cache for sharing with others through distributed cache algorithms. In [13], authors proposed a buffering scheme to adjust the ratio of caching and prefetching areas in a buffer of each peer according to its relative playback position in each playback group.  
Unlike these existing studies, in this paper, we propose cooperative buffering schemes to exploit the characteristics of P2P time-shifted streaming that are different from existing P2P VOD and live streaming. Our contributions are twofold: first, we extend the time-shifting hours significantly and improve the performance by utilizing the idle resources of PVRs playing at the live broadcast time that are otherwise unused. Second, we present how to reduce the computational complexity by adaptively adjusting evaluation loads depending on request arrival rates and computation capacity of tracker servers.