Streaming over Subscription Overlay

Networks

Department of Computer ScienceIowa State University

OutlineSubscription Overlay Network (SONet) Subscription and topology

managementStreaming 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

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Solution I: UnicastDedicating one stream for each online node

AdvantagesSimple implementationGood data freshness (shortest distance)

DisadvantagesServer bottleneck: not scalable

Solution II: IP MulticastOne 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.

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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

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c3

c4c2

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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.

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Observation and MotivationA 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 averageA 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

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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/DefinitionsPath(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 RCapacity(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

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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 onlineWhen 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

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Bundling Procedure

A node becomes playingThe node is in incentive

Simply turn on its playerThe 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

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Find Parent Candidates

Choosing Incentive Node

Cost(XY, I, N) = Hop(X, I) + Hop(I, Y) + Hop(I, N) – Hop(X, Y)

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If N’s capacity is not 0It 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 StudyPerformance 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 RemarksSONet: 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 advantageFuture work???