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P2P On-DemandVideo Streaming and Caching

丁建文

高雄應用科大資管系

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OutlineOutline

Motivation IntroductionOn-Demand Streaming and CachingConclusions

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Motivation (1) Motivation (1)

Different approaches for video streaming Client/Server architecture

• IP-Unicast solution– Non scalable

• IP-Multicast solution– Most ISPs do not support

CDN architecture• Replicate servers + multiple proxies

– Too expensive P2P architecture

• AP-level multicast– Scalable and cheap– Unstable

Hybrid architecture• CDN+P2P

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Client-Server Streaming ArchitectureClient-Server Streaming Architecture

Yiu, W.-Pk.; Xing Jin; Chan, S.-H.G., "Challenges and Approaches in Large-Scale P2P Media Streaming," Multimedia, IEEE , vol.14, no.2, pp.50-59, April-June 2007

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CDN-Based Streaming ArchitectureCDN-Based Streaming Architecture


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P2P Streaming ArchitectureP2P Streaming Architecture


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Motivation (2)Motivation (2)

Advantages of P2P streaming Huge storage

• Each user contribute some storage space• # of users may be 1000, 10,000, 100,000, …

Huge bandwidth• Each user contribute some forwarding bandwidth• # of users may be 1000, 10,000, 100,000, …

Very light load on server Distributed load on network

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OutlineOutline


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IntroductionIntroduction

P2P streaming is very popular nowFamous examples:

PPLive• http://www.pplive.com/

PPStream• http://www.ppstream.com/

http://www.pplive.com/

http://www.ppstream.com/

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IntroductionIntroduction

Types of P2P streaming Live P2P streaming

• Example: traditional TV channel, live sport event• Many users share a stream• Less challenge

On-demand P2P streaming• Example: Movie-on-demand• Each user is allocated a stream• More challenge

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Two Main Design Issues Two Main Design Issues

How to locate peers?How to deliver data to peers?

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How to locate peers?How to locate peers?

Centralized search Hierarchical search Flooding-based searchDHT-based search

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Centralized Approach


Examples:

PPStream, PPLive

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Hierarchical Search Zigzag, Nice, P2Cast, P2VoD

Tran, D.A.; Hua, K.A.; Do, T.T., "A peer-to-peer architecture for media streaming," Selected Areas in Communications, IEEE Journal on , vol.22, no.1, pp. 121-133, Jan. 2004

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Hierarchical Search – Zigzag Zigzag organizes receivers into a hierarchy of

clusters A cluster has a head and an associate head

• Head is responsible for monitoring the memberships of the cluster

• Associate-head is responsible for transmitting the content to cluster members.

• The failure of the head does not affect the service continuity of other members

• Or in case the associate-head departs, the head is still working and can designate a new associate-head quickly

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Hierarchical Search – Zigzag A peer X do the following when receiving a joining request from

a new client

D(Y): delay between server and Yd(Y,P): delay between Y and P

Tran, D.A.; Hua, K.A.; Do, T.T., "A peer-to-peer architecture for media streaming," Selected Areas in Communications, IEEE Journal on , vol.22, no.1, pp. 121-133, Jan. 2004

By doing so, nearby peers are grouped together, making the data transmission based on that structure efficient!

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Flooding-Based Approach (1)Example:

• GnuStream

Gnutella Protocol: 1. Query message

sent over existing TCP connections

2. Peers forwardquery message

3. The query message is associated with a time-to-live (TTL) value.

4. QueryHit sent over reverse path Computer Networking: A Top Down Approach, 4th edition.

Jim Kurose, Keith Ross, Addison-Wesley, July 2007.

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Flooding-Based Approach (2)

Problems with GnuStream:• Depending on the degree

of connectivity among peers, the flooding of queries can generate a lot of network traffic.

• Objects located out of the search scope (which the TTL determines) wouldn’t be found in the system.

Computer Networking: A Top Down Approach, 4th edition. Jim Kurose, Keith Ross, Addison-Wesley, July 2007.

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DHT-Based Approach Each peer is assigned a peer ID by hashing

its own IP address using a common known hash function such as SHA-1,17

Each object is assigned a object ID in the same space of peer IDs by hashing the object itself.

The peer with an ID equal to the hashed object ID is responsible for storing the object’s location (or the actual object)

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DHT API: Get(), Remove(), Put()DHT API: Get(), Remove(), Put()

Eng Keong Lua et al., "A survey and comparison of peer-to-peer overlay network schemes," Communications Surveys & Tutorials, IEEE , vol.7, no.2, pp. 72-93, 2005.

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P2P-ChordP2P-Chord


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Comment on DHT-based search Pros:

• Use well-developed DHT protocols, which are scalable and offer good load balancing.

• Famous protocols: Chord, Pastry, CAN

Cons:• DHT search do not consider the physical location

or bandwidth of target peers

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How to Construct Delivery Paths?How to Construct Delivery Paths?

Design Issues: Real-time delivery

• P2P relay incurs long delay

Sufficient-bandwidth delivery• Asymmetric upload/download bandwidth

Failure recovery of peers • Frequent peer join/leave

Load imposed on network• P2P relay incurs more traffic

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How to Construct Delivery Paths?How to Construct Delivery Paths?

IP routing use physical network Physical topology Neighbors are connected by

routers/switches/hubs P2P routing use overlay network

Logical topology is built on physical topology Neighbors are connected by TCP/UDP

connections

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Overlay Network is Not EfficientOverlay Network is Not Efficient

PLS (Physical Link Stress) # of identical packets sent over a physical link

RDP (Relative Delay Penalty) For two hosts, RDP = overlay delay/unicast

delayDifferent P2P schemes have different

PLS and RDP

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PLS Example (1/3)PLS Example (1/3)

Avg. PLS of IP Multicast

= PLS(A-R1)+

PLS(R1-B)+

PLS(R1-R2)+

PLS(R2-C)+

PLS(R2-D)

= (1+1+1+1+1)/5

= 1

Yang-hua Chu; Rao, S.G.; Seshan, S.; Hui Zhang, "A case for end system multicast," Selected Areas in Communications, IEEE Journal on , vol.20, no.8, pp. 1456-1471, Oct 2002

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Avg. PLS of IP Unicast

= PLS(A-R1)+

PLS(R1-B)+

PLS(R1-R2)+

PLS(R2-C)+

PLS(R2-D)

= (3+1+2+1+1)/5

= 1.6 (60% higher stress)


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Avg. PLS of P2P Overlay

= PLS(A-R1)+

PLS(R1-B)+

PLS(R1-R2)+

PLS(R2-C)+

PLS(R2-D)

= (2+1+1+2+1)/5

= 1.4 (40% higher)


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RDP Example RDP Example

RDP of P2P Overlay

RDP(A-B) = 27/27 = 1

RDP(A-C) = 3/3 = 1

RDP(A-D) = 29/27 = 1.074


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Topology of Overlay NetworkTopology of Overlay Network

Single multicast treeMultiple multicast treeMesh Yiu, W.-Pk.; Xing Jin; Chan, S.-H.G., “Challenges and Approaches in Large-

Scale P2P Media Streaming”, IEEE Multimedia, Vol. 14, No.2, 2007.

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Overlay Topology (1/3)Overlay Topology (1/3)

Single Tree Topology Appraoch

• Each peer has fixed single parent Advantage

• Easy to optimize a single tree– Example: delay + bandwidth

• Easy to implement Disadvantage

• Unbalanced load– Few heavy-loaded interior nodes vs. many light-loaded leaf

nodes • Not robust

– Each peer connects to its only parent node via a single link Example

• NICE, Zigzag, Overcast, …

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Multiple Tree Topology Appraoch

• Each peer has fixed multiple parents Advantage

• More balanced load & more robust– Multiple paths + layered video– Multiple paths + MDC-based video– Interior-node-disjoint trees: a node can be an interior node in at

most one tree Disadvantage

• Difficult to optimize multiple trees at the same time• Difficult to implement

– Synchronization between multiple parents Example

• SplitStream, CoopNet, …

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Mesh Topology Appraoch

• Each peer has dynamic multiple parents due to (1) Unpredictable online/offline of peers(2) Time-variable bandwidth and packet-loss rate of the Internet

Advantage• Most balanced load• Most robust

Disadvantage • Difficult to manage

– Synchronization between peers– Real-time Internet behavior measurement

Example• GnuStream, CoolStreaming, …

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OutlineOutline


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Prominent P2P On-Demand Streaming ProtocolProminent P2P On-Demand Streaming Protocol

P2Cast 2003, University of Massachusetts, USA

P2VoD 2004, University of Central Florida, USA

DCS 2005, Huazhong University of Science and

Technology, ChinaVMesh

2007, Hong Kong University of Science and Technology, China

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P2P VoD: P2CastP2P VoD: P2Cast

Session Base tree Base stream Patch stream

Y. Guo, K. Suh, J. Kurose, D. Towsley, “P2Cast: P2P Patching Schemefor VoD Service,” in WWW 2003.

Snapshot at time 40

T=10

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P2Cast - New Client (X) AdmissionP2Cast - New Client (X) Admission

If new client X belongs to an already existing session (S) (1) X tries to join S’s base tree (2) X tries select a patch server in S or the

server If (1) & (2) is successful, X is admitted

• Else, X will be rejected

Else, X starts a new session The server streams the entire video to X

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P2Cast - Base Tree Construction (1/2)P2Cast - Base Tree Construction (1/2)

Design principles Bandwidth first principle Local information only principle

• Information about this node itself, its parent node, and its child nodes

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P2Cast - Base Tree Construction (2/2)P2Cast - Base Tree Construction (2/2)

1. New client X contacts a candidate parent P Default parent = server

2. P estimates bandwidth B(P, X) 3. All children Ci of P estimate bandwidth B(Ci, X)

4. P identifies Cmax with largest B(Ci,X)

If B(P, N) > B(Cmax, N) then• P provides base/patch stream or one of them (patch stream

has higher priority)

• If P cannot fully fulfill, then redirect X to Cmax, starting from step 1.

If B(P, N) <= B(Cmax, N) then• X is re-directed to Cmax, starting from step 1

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P2Cast - Patch Server SelectionP2Cast - Patch Server Selection

The patch server selection process for a client X is identical to X’s base tree joining process

Y. Guo, K. Suh, J. Kurose, D. Towsley, “P2Cast: P2P Patching Schemefor VoD Service,” in WWW 2003.

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P2Cast - Failure Recovery (1/2)P2Cast - Failure Recovery (1/2)

Network Problem: If incoming traffic is low (base or patch stream)

• Client A sends TEST_ERROR message to parent P

then P responds A• (1) No response

– A contacts the server and initiates the failure recovery process

• (2) Poor traffic condition– A contacts the server and initiates the failure recovery process

• (3) WAIT– P is still in its own recovery process

– A sets up a timer

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P2Cast - Failure Recovery (2/2)P2Cast - Failure Recovery (2/2)

Client Departure Problem Early leaving parent B sends

DEPART_RECOVER message to all clients Ci, i=1, 2, …

Ci initiate the recovery process

Failure recovery process Base stream recovery

• Identical to a new client joining the base tree

Patch stream recovery• Identical to path server selection process

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P2P VoD – P2VoDP2P VoD – P2VoD

Do, T.T.; Hua, K.A.; Tantaoui, M.A., "P2VoD: providing fault tolerant video-on-demand streaming in peer-to-peer environment," Communications, 2004 IEEE International Conference on , vol.3, no., pp. 1467-1472 Vol.3, 20-24 June 2004

A video session

(snapshot at time 36)

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P2VoD vs. P2CastP2VoD vs. P2Cast

Streaming and caching (CBR) P2VoD

• Cache the most recent content• A peer X can serve clients whose joining time is in the range of [tjX, tjX +abX]• tjX: joining time of X• abX: actual buffer size (display time) of X• Use one relay stream

P2Cast• Cache the initial part• Use two streams: base/patch streams

Failure Recovery P2VoD

• Handled locally, most of the times without involvement of the source P2Cast

• Get the source involved• Vulnerable to disruption due to server bottleneck• Resulting in long blocking time

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P2VoD - Joining Algorithm (1/2)P2VoD - Joining Algorithm (1/2)

If all of the existing video sessions are closed A new video session is created, and new client X is

the first member of G1 of that video session

Else, X will try to join existing video session 1. X contacts a random member of the youngest

generation Gy, and acquires the list of peers at Gy-1

2. If the first block expiring time tGy-1exp > joining time

of X, go to step 3; else go to step 4. 3. X becomes a member of Gy

4. X is the first member of Gy+1 of that video session

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P2VoD - Joining Algorithm (2/2)P2VoD - Joining Algorithm (2/2)

Introducing system parameter K To limit the maximum number of clients

allowed in G1 of each video session

Parent selection: heuristic solutions Round Robin: the shortest serving time Smallest Delay: bandwidth-enough, discover-

first

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P2VoD – DCS (Distributed Cache Service)P2VoD – DCS (Distributed Cache Service)

DSC is a DHT-Based P2P On-Demand Streaming Protocol

Zuoning Yin; Hai Jin, "DHT Based Collaborative Multimedia Streaming and Caching Service," TENCON 2005 2005 IEEE Region 10 , vol., no., pp.1-6, Nov. 2005

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DCS - The Roles of PeersDCS - The Roles of Peers

Rendezvous Peer (RP) Its id is closest to the hash result of the video’s name

and the Unit’s location in the video Preserving the location information of all the

segments of its corresponding Unit Root

Id is closest to the hash result of the movie name preserving the global information of the movie

Ordinary Peers are peers neither RP nor Root

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DHT Example: Pastry Routing TableDHT Example: Pastry Routing Table


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Pastry Routing Table - Leaf SetPastry Routing Table - Leaf Set


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Pastry Routing Table – Neighborhood SetPastry Routing Table – Neighborhood Set


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Pastry - RoutingPastry - Routing


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ConclusionConclusion

Future Research Issues for P2P Streaming Location-Aware DHT-Based Searching

Algorithm Wired/Wireless Hybrid P2P Streaming Scalable Video Coding Based P2P Streaming

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Thank You!

Q & A

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