Maximizing User Gain in Multi-flow Multicast Streaming on Overlay Networks

1. Maximizing User Gain in Multi-flow Multicast Streaming on Overlay Networks Y.Nakamura, H.Yamaguchi and T.Higashino Graduate School of Information Science and Technology, Osaka University

2. Research 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 FMUIT'06

3. 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 ALM A A B S B S C C D D FMUIT'06

4. Related works • Overcast，CAN，RMX • aiming at an efficient delivery of video stream in a large-scale group • HBM • aiming at overlay network construction for the mobile terminal • Narada，ALMI，Yoid • aiming at delivery of single video stream in small-scale group • also target the conference application Few research to deliver the two or more streams simultaneously and continuously for the video conferencing FMUIT'06

5. Issues to be considered • 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 video Internet FMUIT'06

6. Internet Overlay Network Emma/QoS • New ALM protocol for multi-party communication systems • Users construct overlay network • Each user sends its own video continuously and receives some of other user hosts’ video streams on overlay networks • Each user filters and adjusts the quality of streams and make the space for a new requested stream Red Red FMUIT'06

7. Overlay Network A C E B D Overlay network construction • New user joins the session by constructing the overlay link • Measuring the delay with another user, and constructing the overlay link with the number of appropriate users • When the link is constructed, the link capacity (number of streams that can be delivered) is negotiated and decided • The participating users enhance the delivery routing tree • The routing tree of the source user is constructed with the shortest path tree by flooding Underlying Network FMUIT'06

8. Leaving failure management • Many users frequently leave on the overlay network • Descendant node cannot receive the stream • We need guarantee the continuance delivery of the stream • Need to make the streamhad delivered through the leftnode can immediately delivered from another node again • Each node knows the nodes can deliver the stream by periodical message • If neighbor node leaves, the node is immediately reconnected to one of them FMUIT'06

9. Loss/Gain-based rate adaptation • Problem • Because of the restriction and a decrease of the link capacity, all requests of stream cannot be accepted • Solutions • Simple way • When the stream cannot be delivered, all requests of the stream are not accepted • Narada • When it is impossible to deliver the stream in the received rate in each user, user reduces the rate of the stream so that it can be delivered • Emma/QoS • Each user decides that it increases / reduces the rate of the stream according to the value of the gain obtained by receiving the requested stream and cutting the rate of the delivering stream • Requests are accepted as many as possible FMUIT'06

10. User gain function • Every user defines for each stream • User gain is added when a unit of bandwidth is added to current receiving stream • We use utility function • This function shows the priority of the user for each unit of bandwidth e.g. In the typical streaming, utility tends to increase suddenly by the rate of a at least necessary quality, and to increase gradually in a rate increase after that • User gain is calculated by the difference of the following two values • Value on utility function of k-1 units • Value on utility function of added k-th unit Linear approximation ｝User gain Utility function k-1 k k denotes certain amount of bandwidth on the overlay links FMUIT'06

11. Protocol operations • Every node periodically sends messages about user gain (negative gain) for each stream • Negative gain : Value of user gain lost in descendant nodes when a unit is deprived from delivering stream • Request message is transmitted calculating the optimal allocation of each unit • from user gain and a negative gain that increases by the request acceptance when requesting it • As a result, each user can know and decide which stream should be reduced B # of units of links is 3 ： Streams FMUIT'06

12. Performance evaluations • We have • implemented a simulator of Emma/QoS • simulated in a typical video conferencing scenario • compared with Narada (one of the most popular ALMs) • We examined the following items • Link stress : the number of copies of a single packet delivered on a physical link • Path stretch : the ratio of the sum of unicast hops of the overlay links between two nodes to that on the shortest path on the underlying physical network • User satisfaction ratio : the ratio of the sum of user gain obtained by each node to that of user gains requested by the node • Variation of user gain FMUIT'06

13. Unicast Emma/QoS Narada 1000 50 Emma/QoS Narada # of physical links # of users 0 100 10 1 0 1 4 8 Link stress and path stretch • Compare with the performance of Narada • Narada assumes the delay between hosts to be optimizing metric and constructs mesh-like overlay network • On this overlay network Narada constructs shortest path tree • Emma/QoS has better values than unicast • Maximum link stress is about 10th of the unicast • The performance of Narada is not so quite different from that of Emma/QoS Link Stress Path Stretch FMUIT'06

14. Distribution of users’ satisfaction • The ratio of the total gain of accepted requests to that of all requests • Requests not accepted at all is much smaller than Narada and FCFS (First Come First Serve method) • The admission control mechanism of Emma/QoS is useful to video-conference systems FMUIT'06

15. # of users Emma/QoS Narada 800 45 gain (avg.) # of users 0 0 31 1 15 time Variation of user gain • Emma/QoS achieves higher user gain than Narada • when users join/leave during the session • when users’ preferences to stream s are changed during the session FMUIT'06

16. Conclusion • We have proposed new ALM protocol called Emma/QoS • To avoid resource competition, we use utility-based admission control in decentralized way • 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 FMUIT'06