1. ON DESIGING END-USER MULTICAST FOR MULTIPLE VIDEO SOURCES Y.Nakamura, H.Yamaguchi, A.Hiromori, K.Yasumoto †, T.Higashino and K.Taniguchi Osaka University † Nara Institute of Science and Technology

2. ICME2003 2 July/9/2003 Goal Realizing Multi-party video conferencing systems  Many-to-many multicast application which consists of hundreds of users  User hosts exchange multiple video streams in real-time Efficient use of bandwidth is required Internet

3. ICME2003 3 July/9/2003 Application Layer Multicast (ALM) ALM is multicast on overlay networks  End users act as multicast routers  Does not require special hardware such as IP multicast enable routers  Application-specific routing protocols can be designed  More efficient than Unicast because a sender does not need to send data to all receivers Unicast A B C S D A B C S D ALM

4. ICME2003 4 July/9/2003 Design Issues Each video uses some amount of bandwidth on overlay networks →In delivering multiple video streams, they compete for bandwidth on overlay links Users may have priority requirements to video streams e.g. users may prefer the speaker’s video than audience’s Internet

5. ICME2003 5 July/9/2003 Internet Overlay Network End-user Multicast for Multi-party Application (Emma) New ALM protocol for multi-party communication systems  Users construct overlay networks  Each user host sends its own video continuously and receives some of other user hosts’ video streams on overlay networks  The sending and receiving video streams are controlled based on users’ priority requirement given to the video streams Red

6. ICME2003 6 July/9/2003 Users’ Join When a new user wants to join a session, the user gets the current users’ addresses from a central server The user measures delay with these users and establish overlay links with the closest two or three users to construct mesh-like overlay networks Existing routing trees are expanded so that they do not overlap each other as long as they can ECA BD Routing tree can be expanded with small delay from each source less duplication Address Management Server A:133.1.xx.xx B:129.3.yy.yy C: …

7. ICME2003 7 July/9/2003 Priority-based Video Delivery Each user specifies a priority requirement as a priority value to each video stream. A request message with a priority value is forwarded to the video source user But there is no enough bandwidth on the path CA B D B: 5 A: 8 C: 6 D:15

8. ICME2003 8 July/9/2003 Priority-based Video Delivery In forwarding the message, the followings are calculated step by step  how to stop existing video streams  how to minimize the loss of priority values If the loss of priority value < the gain of priority value by accepting the request  The existing streams are stopped and the new stream is delivered CA B D B: 5 A: 8 C: 6 D:15 The sum of the satisfied priority values becomes larger than before

9. ICME2003 9 July/9/2003 Users’ Leave and Failure Even if an user host leaves, trees can be recovered  When a user leaves, the simplest way to recover tree is to let child nodes connect with the parent of the leaving user  However, this may cause the concentration of overlay links to the parent user  To prevent this, each user periodically collects the information of # of overlay links of its descendant users  When a user leaves, its parent can immediately suggest the children of the leaving user where to connect again C A B G HFD E User E leaves D,F,GC,D Recovery can be done quickly without causing unbalanced trees

10. ICME2003 10 July/9/2003 Performance Evaluation We have developed a simulator for evaluating performance of Emma  Written in an object oriented scripting language Ruby Network model  Hierarchical topology model based on tiers  146 nodes, 66 users  Users give priority values to video by Zipf’s law

11. ICME2003 11 July/9/2003 Users’ Satisfaction The variation of average of satisfied priority value per user  Compared with First-Come-First-Serve (FCFS) method which accepts user requests in a greedy manner  Simulation Scenario Until 5 units of time, 66 users joined After 21 units of time, 1 user joins or leaves at one time

12. ICME2003 12 July/9/2003 Users’ Satisfaction Emma achieves 1.5 times higher values than FCFS Under the presence of users’ leave and join, priority values are kept high

13. ICME2003 13 July/9/2003 Routing Tree Duplication on Overlay Link # of routing trees on an overlay link  Less duplication is desirable Simple estimation of average duplication in the ideal case  # of users × (# of users -1) / # of total overlay links = about 20 →Measure the # of routing trees on each overlay link

14. ICME2003 14 July/9/2003 Routing Tree Duplication on Overlay Link 80% of overlay links have at most 10 routing trees

15. ICME2003 15 July/9/2003 Conclusion We have proposed new ALM protocol called Emma  Avoiding resource competition From the experimental results  Higher satisfaction of users than a simple method  Even though some users leave from or join to a session, users’ satisfaction is kept high We have designed and implemented Java middleware based on Emma ( http://www-tani.ist.osaka-u.ac.jp/software/s2.html )

16. ICME2003 16 July/9/2003