1. Cooperative Mobile Live Streaming Considering Neighbor Reception SPEAKER: BO-YU HUANG ADVISOR: DR. HO-TING WU 2015/10/15 1

2. Outline Introduction Related Work Problems CSANR Simulation Result Conclusion Reference 2

3. Introduction In live streaming service, two delivery systems are mainly used, Client-Server (C/S) and Peer-to- Peer (P2P) system. A video content data is sliced into a sequence of fragments, called chunk, and delivered to user watching the video. In C/S system, The cost for provider to delivers video contents increases, if there are too many users requesting it. In P2P system, a user is called a peer, and plays a roll of not only receiver but also sender. 3

4. Introduction(Cont.) With the spread of smartphones, a demand for mobile live streaming system is increasing. However, the existing live streaming services are not sufficient for mobile. Different from peer in wired-network, Mobile peers have some characteristics should be considered: mobility and erratic bandwidth. Therefore, this paper propose CSANR (Chunk Select method Adaptive to Neighbor Reception), a method that enables peers change usage of their own cellular links adaptively by considering the reception of their neighbor peers. 4

5. Related Work A. P2P Live Streaming in Mobile Environment B. Cellular-WiFi Hybrid Network 5

6. P2P Live Streaming in Mobile Environment Mobile peer have some characteristics that should be considered. Mobility: Different from wired-network, mobile peer can move anywhere while watching a video content. Due to peer mobility, the topology of P2P network including mobile peer changes dynamically. Erratic bandwidth: Mobile peers download chunks by using their own cellular links. However, cellular bandwidth is easy to be affected by their position and environment. Even if there is a good area for communication, cellular bandwidth often decreases by the interference of other electric waves called Multi-path fading. 6

7. Cellular-WiFi Hybrid Network Mobile peer can use two communications in parallel, its own cellular link and Wi-Fi communication with other mobile peers. 7

8. Problems Using Cellular-WiFi hybrid network, mobile peers can enjoy watching live video contents more comfortably because of their chunk exchanges using Wi-Fi communication. However, there are some problems should be solved to apply it to the real environment.  Static Scheduling  Stochastic Chunk Selection 8

9. Static Scheduling In real environment, the case that all peer watching the video content keep staying at the place is rare. And, because of peer’s mobility, cellular bandwidth of peers changes dynamically. Static scheduling method is effective when the users watching same video content together are already determined, but real-time scheduling are more effective in other case. 9

10. Stochastic Chunk Selection In live streaming, all peer’s video progress are same and each peer selects chunks near from its video progress. That’s why, by using stochastic chunk selection in live streaming, it happens frequently that peers select same chunk. 10

11. Problems(Cont.) Cellular bandwidth dynamically changes in real environment. By decrease of peer’s cellular bandwidth, timeout chunk occurs frequently. Existing method, probability of chunk selection based on only number of peers, not considering the neighbor peer’s cellular bandwidth. 11

12. CSANR We propose CSANR (Chunk Select method Adaptive to Neighbor Reception), a method that changes the usage of peer’s own cellular link adaptively by considering the reception of the neighbor peers. In our method, peers can use their own cellular links and Wi-Fi communication between peers in parallel. Peers use cellular network to access video server and download chunks to be selected, and peers communicate with each other and exchange their information using Wi-Fi communication. 12

13. Scheduling Based on Offer-Select Method CSANR use Offer-Select method to exchange peer information. Offer-Select method is for chunk scheduling in P2P live streaming system. 13

14. Exchanging Offer Message In the proposed method, peers send offer message to the neighbor peers. Exchanging this message each other periodically enables peers perform real-time scheduling. Offer message includes peer information: IP address of sender and receiver, chunk ID that the peer select to download using its own cellular link, and a random number to avoid collisions of chunk selection. 14

15. Chunk Scheduling After exchanging peer information by sending an offer message to the neighbors, each peer determines which chunk it receives from whom. Chunks can be obtained through Wi-Fi communications only if the chunks are offered by the neighbor peers. When any neighbor peer does not offer the chunk, the peer has to download the chunk using its own cellular link, regardless of previous decision. 15

16. Rescheduling Mechanism In the chunk scheduling based on Offer-Select method, there is the case frequently that peer selects the chunks that is selected by the neighbor peers. To avoid this collision, CSANR have Rescheduling mechanism. CSANR offer message has random number to avoid collision of chunk selection between peers. 16

17. Sending Select Message By exchanging peer information, each peer can decide which communication can be used to get the chunk ready to be delivered, cellular or Wi-Fi communication. To receive the chunks offered by the neighbor peers, the peer sends a request packet to the neighbor peer, select message. The requested peer sends its chunks in response to the select message. 17

18. Reception by Overhearing In wireless communication, each peer can receive the packets that are sent to other peer. This is called overhear. Using overhear, each peer receives the chunk they do not have whether the chunk are sent to them or not. In proposed method, peers memorize IDs of the chunks which they sent in the past. If they are requested the chunk already sent, they do not respond to the request. 18

19. Dynamic Stochastic Chunk Selection To reduce usage of cellular bandwidth, each peer stochastically selects some chunks to download using its own cellular link based on chunk selection probability, p. This chunk selection probability has a influence on cellular traffic usage. If this probability is too high, each peer downloads most of the chunks by self using its own cellular link. If this probability is too low, there will be the chunks that any peer does not select to download by itself. We named this isolated chunk, timeout chunk. 19

20. Dynamic Stochastic Chunk Selection(Cont.) Suppose n users participate same Wi-Fi network and watch the same live video content. In stochastic selection, if each peer selects chunk without considering the neighbor reception, the most suitable value of p can be calculated using n. However, eq. (1) does not consider the changes of the neighbor peers' cellular bandwidth. CSANR calculates p dynamically by considering the neighbor reception. 20

21. Dynamic Stochastic Chunk Selection(Cont.) When Video rate is v[Kbps] and chunk size is Lchunk[Kbit], the number of the chunks delivered in tw second, Nchunk is as follows. If n peers cooperate and schedule Nchunk(tw) chunks, the number of chunks expected to be offered by the neighbor peers in time t, Oexpected(t), can be calculated using n and Eq. (2). 21

22. Dynamic Stochastic Chunk Selection(Cont.) Due to the frequent changes of cellular bandwidth, there can be the case that peer can not offer enough number of chunks. In Offer-Select method, each peer offers the chunks which can be downloaded. If peer’s cellular bandwidth decreases and it can not download the chunk they selected, the peer revokes its selection and these chunks are not offered. Therefore, we can presume peer’s cellular bandwidth by using number of chunks offered by the neighbor peers. 22

23. Dynamic Stochastic Chunk Selection(Cont.) Suppose the number of chunks that a peer is offered by the neighbor peers in time t is noffered(t). When the interval of offer message exchanging is tw, the number of chunks that were offered by the neighbor peers in the interval tw second just before that, Ooffered(t) is as follows. By using Eqs. (3) and (4), We can calculate the ratio of Ooffered(t) and Oexpected(tw). 23

24. Dynamic Stochastic Chunk Selection(Cont.) nv represents the value of the neighbors which is calculated by considering the neighbor peer’s cellular bandwidth. According to nv, each peer can regard that it cooperates with nv peers. Therefore, we can calculate chunk selection probability p in time t, p(t) using Eq. (1). 24

25. Dynamic Stochastic Chunk Selection(Cont.) In CSANR, each peer always calculates p(t) when it performs chunk scheduling. 25

26. Simulation Result We assume a full mesh topology, which all peers can communicate with each other directly by Wi-Fi connection. This topology is already formed before watching a video content. Each chunk must be exchange within the limited time, called play-out delay, to prevent the delay of video progress. After this time limit, each chunk can not be requested. We compare our method to the Cellular-WiFi live streaming system using fixed p(t) for chunk selection, which is labeled existing method. 26

27. Simulation Result(Cont.) Simulation parameters are shown in Table I. 27

28. Reduction of Cellular Traffic Figure 9 shows that the ratio of occurrence of timeout chunk. 28

29. Reduction of Cellular Traffic(Cont.) As shown in Fig. 10, CSANR can reduce unnecessary cellular traffic to occur with timeout chunks about 50% compared with the existing method. 29

30. Influences of the Changes of Cellular Bandwidth In order to confirm that CSANR chunk scheduling is adaptive to the neighbor reception. We performed simulation with setting that there are two peers and only peer 1’s cellular bandwidth changes. 30

31. Influences of the Changes of Cellular Bandwidth(Cont.) Figure 11 shows that chunk availability for each peer, the video quality each peer actually watched. 31

32. Influences of the Changes of Cellular Bandwidth(Cont.) Cellular usage of each peer is shown in Fig. 12. Cellular bandwidth usage means the ratio of the cellular usage in the video rate. For example, a peer is downloading 0.5Mbps data and video rate is 1Mbps, this value is 50%. 32

33. Influences of Difference of Cellular Bandwidth Resources Figure 13 shows the average of chunk availability in each value of ρ. 33

34. Conclusion In this paper, we proposed CSANR, a method enables peers change usage of their own cellular links adaptively by considering the reception of the neighbor peers. If the bandwidth of the peers decreases suddenly, CSANR can keep their chunk scheduling efficient. We evaluated our proposal method through network simulation. The simulation results show that CSANR can reduce increase of traffic occur with timeout chunk, and if the cellular bandwidth of the neighbor peers decreased, peer can be aware it and adjust its usage of cellular link adaptively. 34

35. Reference HATAKEYAMA, Sho; SAKATA, Yuji; SHIGENO, Hiroshi. Cooperative Mobile Live Streaming Considering Neighbor Reception. In: Advanced Information Networking and Applications (AINA), 2014 IEEE 28th International Conference on. IEEE, 2014. p. 65-72. 35