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Higashino Lab.Higashino Lab.Higashino Lab.Higashino Lab.
Maximizing User Gain Maximizing User Gain in Multi-flow Multicast in Multi-flow Multicast Streaming on Overlay Streaming on Overlay NetworksNetworks
Y.Nakamura, H.Yamaguchi and T.Higashino
Graduate School of Information Science and Technology,
Osaka University
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Research GoalResearch 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
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Higashino Lab.Higashino Lab.Higashino Lab.Higashino Lab.Application Layer Multicast Application Layer Multicast (ALM)(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
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Related worksRelated 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
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Issues to be consideredIssues 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 streamse.g. users may prefer the speaker’s video than audience’s
video
Internet
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Emma/QoSEmma/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
InternetOverlay Network
Red
Red
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Overlay Network
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
Overlay network Overlay network constructionconstruction
Underlying Network
D
A
B
E
C
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Leaving failure managementLeaving failure management Many users frequently leave on
the overlay network Descendant node cannot recei
ve the stream We need guarantee the continu
ance delivery of the stream Need to make the stream ha
d delivered through the left node 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
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Higashino Lab.Higashino Lab.Higashino Lab.Higashino Lab.Loss/Gain-based rate Loss/Gain-based rate adaptationadaptation 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
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User gain functionUser 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 us
er for each unit of bandwidthe.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 uni
t k denotes certain amount of bandwidthon the overlay links
Utility function
k-1 k
} User gain
Linear approximation
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Protocol operationsProtocol 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
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Performance evaluationsPerformance 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
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50
1 84
# of
use
rs
0
Emma/QoSNarada
1000
01 10 100
Emma/QoSNarada
Unicast
# of
phy
sica
l lin
ks
Link stress and path stretchLink 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 Emm
a/QoS
Link Stress Path Stretch
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0
50
100
150
200
250
0 0.2 0.45 0.6 0.8 0.88 0.89 0.9 1
satisfaction ratio
# of
req
uest
s
Emma/ QoSNaradaFCFS
Distribution of users’ Distribution of users’ satisfactionsatisfaction 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
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45
01 31
0
800Emma/QoSNarada
# of users
gain
(av
g.)
15
# of
use
rs
time
Variation of user gainVariation 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
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ConclusionConclusion 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
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