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Live Streaming over Subscription Overlay Networks CS587x Lecture Department of Computer Science Iowa State University. Outline. Subscription Overlay Network (SONet) Subscription and topology management Streaming over SONet Performance Study Concluding Remarks. - PowerPoint PPT Presentation
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Live Streaming over Subscription Overlay
Networks
CS587x LectureDepartment of Computer Science
Iowa State University
Outline
Subscription Overlay Network (SONet) Subscription and topology
management
Streaming over SONetPerformance StudyConcluding Remarks
Subscription Overlay Network
Two components One central server
Streaming source (eg., live TV broadcast, etc.) A number of subscribing nodes
Pay monthly fee in return of video services A node can be offline/online/idling/playing
One Service Streaming video data from source to all online nodes
Three goalsMinimize the server workloadMinimize network trafficMinimize data latency
S
1
2
3
65
4
rr
r
r
Solution I: Unicast
Dedicating one stream for each online node
AdvantagesSimple implementationGood data freshness (shortest distance)
DisadvantagesServer bottleneck: not scalable
Solution II: IP Multicast
One multicast stream can serve many clients simultaneously
AdvantagesSimple implementationAchieve all three goals
DisadvantagesIP Multicast is not widely deployed on the Internet (due to security issues, etc.)
Solution III: Application Layer Multicast
A node receiving data can forward its incoming stream to serve others
Existing ALM techniquesChaining/ESMNICE/ZIPZAG, etc.
s
c1
c3
c4c2
c5
c6
Solution III: Application Layer Multicast
A node receiving data can forward its incoming stream to serve others
Existing ALM techniquesChaining/ESMNICE/ZIPZAG, etc.
Advantageseach server stream can serve many clientsLeverage the entire network resource
s
c1
c3
c4c2
c5
c6
Solution III: Application Layer Multicast
A node receiving data can forward its incoming stream to serve others
Existing ALM techniquesChaining/ESMNICE/ZIPZAG, etc.
Advantageseach server stream can serve many clientsLeverage the entire network resource
DisadvantagesOnly the playing nodes can contributeDifficult to maintain topology, etc.
s
c1
c3
c4c2
c5
c6
Observation and Motivation
A SONet may consist of a large number of subscribers, but at any one time, only a small percentage of them are playing
American watch TV 4 hours/day in average
A majority of SONet not playing may be idling Unlike regular TV sets, a node not playing is likely to
be online
Recruiting appropriate idling nodes for data forwarding can effectively reduce network traffic
Motivation Examples
R1
R2
R3
R4 R5
R6 R7
S
A B
I
R1
R2
R3
R4 R5
R6 R7
S
A B
I
R1
R2
R3
R4 R5
R6 R7
S
A B
I
Server workload?Network traffic?Data freshness?
Subscription/Topology Management
Account database The server maintains all subscriber information, including IP,
password, the amount of data forwarded (for discount purpose), etc.
Topology graph When a new member M joins, the server S detects its path to
the members A path is denoted as PATH(S, M) = SR1R2M
When a member M1 is asked to forward data to another member M2, M1 reports the actual PATH(M1, M2) to the server
The connections among the members are detected and updated as needed
The topology graph becomes more and more accurate to the server
For each stream, the server records its actual streaming path Given a router, the server can find out the set of streams flowing
through it.
Notations/Definitions
Path(X, Y) The sequence of routers on the
shortest path from X to Y (as known to the server)
Ring(R, i) The set of routers that are i-hop
away from R
Capacity(N) The number of streams N can
forward
Local node and local router A node and a router is local to
each other if they connect directly
R1
R2
R3
R4 R5
R6 R7
S
A B
I
Changing of Node Status
incentive
idling
playing
onlineoffline
A node can make itself only offline, idling, or playing
Only the server can decide when a node can become an incentive node
A node becomes online
When an offline node becomes online, the server may bundle the streams flowing through N’s local router
X1=>Y1, X2=>Y2, X3=>Y3X1=>N, X2=>Y2, N=>Y3
R N
Y2
X1
X2
X3
Y3
Y1
R N
Y2
X1
X2
X3
Y3
Y1
Bundling Procedure
A node becomes playing
The node is in incentive Simply turn on its player
The node was in idling Find a parent (should be
as close as possible to N) Find the joint router Rj Search Ring(Rj, 0)
Prefer playing node If not, recruit an
incentive node, more than one candidates may be available (choosing criteria?)
Repeat on Ring(Rj, 1), …, until a parent is found
Rj
R6
R11
R9
R10
R5
R7 R8
Ry3
Ry1
Ry2
Rx3
X1
Y1
Y3
X3X2
Y2
R4
R3
R2
R1
N
S
P
Rx1
Find Parent Candidates
Choosing Incentive Node
Cost(XY, I, N) = Hop(X, I) + Hop(I, Y) + Hop(I, N) – Hop(X, Y)
Y1
N
X1
I
Y1
N
X1
I
If N’s capacity is not 0
It can help serve others The server finds the parent by
searching Ring(Rj, 0), …, but stops at Ring(Rj, d), where d is Hop(N, Rj)
Since N can serve at least one child, it can redirect its incoming stream to its parent’s current child
A node becomes offline or idling
Find a new parent for each child of this node The parent can be either an incentive
or playing node
Performance Study
Performance Metrics Mean Relative Delay (MRP)
The MRP of a node X is to defined to HOP(S, X)/StreamingPath(S, X)
Measure the data freshness Link Stress
The total amount of traffic flowing through each network links
Our study focus on Effect of subscription size Effect of topology size Effect of active rate
Effect of Subscription Size
Concluding Remarks
SONet: a framework for video streaming over the Internet
Similar to cable/satellite broadcast networks Allows effective incentive mechanisms Centralized subscription and topology maintenance
A new topology-oriented technique for building application layer multicast
Unique in its ability of incorporating idling nodes to assist in data forwarding
Simulation confirms its performance advantage
Future work???