ON DESIGING END-USERMULTICASTFOR MULTIPLE VIDEOSOURCES
Y.Nakamura, H.Yamaguchi, A.Hiromori,K.Yasumoto†, T.Higashino and K.Taniguchi
Osaka University
†Nara Institute of Science and Technology
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Goal
Realizing Multi-party video conferencing systems
Many-to-many multicast application which consists ofhundreds of users
User hosts exchange multiple video streams in real-time
Efficient use of bandwidth is required
Internet
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Application Layer Multicast (ALM)
ALM is multicast on overlay networks
End users act as multicast routers
Does not require special hardware such as IP multicastenable routers
Application-specific routing protocols can be designed
More efficient than Unicast because a sender does notneed to send data to all receivers
Unicast
A
B
C
S
D
A
B
C
S
D
ALM
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Design Issues
Each video uses some amount of bandwidth on overlaynetworks
→In delivering multiple video streams, they compete forbandwidth on overlay links
Users may have priority requirements to video streams
e.g. users may prefer the speaker’s video than audience’s
Internet
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Internet
Overlay Network
End-user Multicast for Multi-partyApplication (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 otheruser 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
Red
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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 linkswith the closest two or three users to construct mesh-like overlaynetworks
Existing routing trees are expanded so that they do not overlap eachother as long as they can
E
C
A
B
D
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: …
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Priority-based Video Delivery
Each user specifies a priority requirement as a priority valueto each video stream.
A request message with a priority value is forwarded to thevideo source user
But there is no enough bandwidth on the path
C
A
B
D
B: 5
A: 8
C: 6
D:15
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Priority-based Video Delivery
In forwarding the message, the followings are calculated stepby 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 byaccepting the request
The existing streams are stopped and the new stream is delivered
C
A
B
D
B: 5
A: 8
C: 6
D:15
The sum of the satisfied priority values
becomes larger than before
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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 withthe 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 itsdescendant users
When a user leaves, its parent can immediately suggest the children of the leavinguser where to connect again
C
A
B
G
H
F
D
E
User E leaves
D,F,G
C,D
Recovery can be done quickly without causing
unbalanced trees
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Performance Evaluation
We have developed a simulator for evaluatingperformance of Emma
Written in an object oriented scripting languageRuby
Network model
Hierarchical topology model based on tiers
146 nodes, 66 users
Users give priority values to video by Zipf’s law
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Users’ Satisfaction
The variation of average of satisfied priorityvalue per user
Compared with First-Come-First-Serve (FCFS)method which accepts user requests in a greedymanner
Simulation Scenario
Until 5 units of time, 66 users joined
After 21 units of time, 1 user joins or leaves at one time
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Users’ Satisfaction
Emma achieves 1.5 times higher values than FCFS
Under the presence of users’ leave and join, priority valuesare kept high
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Routing Tree Duplication onOverlay Link
# of routing trees on an overlay link
Less duplication is desirable
Simple estimation of average duplication in the idealcase
# of users × (# of users -1) / # of total overlay links
= about 20
→Measure the # of routing trees on each overlaylink
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Routing Tree Duplication onOverlay Link
80% of overlay links have at most 10 routingtrees
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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 Javamiddleware based on Emma
(http://www-tani.ist.osaka-u.ac.jp/software/s2.html)
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