On-Demand Media Streaming Over the Internet Mohamed M. Hefeeda, Bharat K. Bhargava Presented by Sam Distributed Computing Systems, FTDCS Proceedings. The Ninth IEEE Workshop on Future Trends of, 2003

2 Agenda Introduction Peer-to-peer model Peer-to-peer streaming protocol Architecture  Index-search algorithm  Index-dispersion algorithm Simulations Evaluation Conclusion

3 Introduction Overall system capacity is the total number of concurrent clients (peers) the system can support Mainly Limited by out bound network bandwidth Others limitations  Processing power, memory size, I/O speed

4 Peer to Peer (p2p) Model Peer acts as min-server and client.  As a client, it requests media files from the system  Then the client stores segments of the media files that it is already consumed for a specific period of time  It can provide these segments to other requesting peers in the system

5 P2p Model P Denote P = {P 1, P 2, … P N } the set of all peers in the system For every P i, where 1 ≤ I ≤ N, R i (in Kb/s) : max. rate peer P i is willing the share with others G i (in bytes) : max. storage space the peer is willing to allocate to store segments of one or more media files C i : max. number of connections that can be opened to serve requesting peers

6 P2p Model Media files The set of movies currently available in the system Bit rate = R kb/s Each divided into N segments, a minimum unit which a peer can cache. Multiple peers can stream to the requesting peer, sending a rate less than R.

7 P2P Streaming Protocol The requesting peer checks for the availability of the desired media file in the system Stream segment by segment The peer cache the segments Three Phases

8 Phase I The requesting peer checks for the availability of the desired media file in the system Store other peers information about IP address Available streaming rate Some reliability information from the peer’s history k b/sLow

9 Phase I The requesting peer checks for the availability of the desired media file in the system Sort based on Proximity to client (i.e. hop count) Available streaming rate Average on-line time k b/sLow

10 Phase I The requesting peer checks for the availability of the desired media file in the system End with a verification step to make sure all segments are available. Otherwise, backoff and try later

11 Phase II Stream segment by segment For every segment s i, the protocol concurrently connects to all peers that are scheduled to provide pieces of that segment. Define P j as the set of peers supplying segment j (s j ). If a peer P x Є P j has a rate R x ≤ R, it provides |s j |(R x /R) bytes starting at wherever peer P x-1 ends Since every peer supplies a different piece of the segment and All pieces of the segment will be downloaded by the end of time of ς, which is the time to stream the whole segment

12 Phase III The peer cache the segments Runs the dispersion algorithm  Caching the right segments of the media files in right places  Discuss in later section

13 P2P Architecture Two approaches for the model  Index approach : a set of servers maintained information about the currently participating peers  Overlay approach : does not assign special roles to any peer. Index approach is presented.

14 Pros and Cons of Index Approach Pros Easier and faster to deploy The load (eg. CPU, bandwidth, storage) is load More appropriate to commercial media provider, for accounting and charging customers Cons Alleviates the scalability Single point of failure arises

15 Index searching To make the index server up-to-date  If a peer gracefully shuts down -> a daemon sending notification message to index server  Request client checks the list of candidate peers by pinging them. Client returns to index server the status in one message

16 Index Search Algorithm a. Get all peers within the same cluster b. Ask those peers to send each segment d. if those peers still can not provide the shortage, back off c. If peers within the cluster can not provide enough segments, ask the peers outside the cluster

17 Index Dispersion Objective : Store enough copies of the media files in each cluster to serve all expected client requests from that cluster. Client P y sends the request and also declare the willingness to cache up to N y segments serving others with rate R y in future The algorithm should make sure that on average, same number of copies of each segment is cached.

18 Index dispersion algorithm Consider 1 media file with N segments, rate R kb/s, and duration T hours. The index server maintains the followings For each peer P x N x : # of segment cached by P x R x : the streaming rate for N x U x : (0≤U x ≤1) fraction of time P x is online For each cluster c L c : next segment to cache q c : average request rate (per hour) within the cluster. a c : average # of copies of the movie cached by peers in cluster

19 Index Dispersion Algorithm Global A, the average # of copies of the movie cached by all peers in the system Q, average movie request rate in system Q : global required capacity (1/T)A: global available capacity

20 Index Dispersion Algorithm a. Identify which cluster the peer resides b. Compute a c, q c, A, Qc. If the demand is larger than available capacity within the cluster OR If the global available capacity is too low compared with the global request rate d. Allow the cache N y segments in a cluster-wide round-robin fashion. P y allows to cache N y segments with rate R

21 Simulation Parameters  13,000 nodes, hierarchical, Internet-like topology  A seeding peer with a limited capacity introduces a media file into the system.  Other peers joins the system and request the file  UDP and CBR  If the peer does not find all segments with full rate, it back off again after an exponentially increased waiting time. For a particular threshold, it is rejected.

22 Simulation results Average Service Rate

23 Simulation results Average Waiting time

24 Simulation results Load on the seeding peer

25 Evaluation Similar to our project The Index-based search, acting like directory server, is trivial Not deployed the index-based dispersion algorithm in simulations Low caching ratio seems useless in their system Multiple video files may need to delete the other file cache.

26 Conclusion Based on the P2P streaming protocol, two important of these steps are presented:  Index search algorithm locating peers with the required media files  Index dispersion algorithm disseminating media files into the system