Peer-to-Peer Live Video Streaming on the
Internet Issues, Existing Approaches, and
Challenges
指導教授：許子衡 教授
學生：王志嘉
Introduction (i)
 Live video streaming is still a controversial issue,
because it can play a best-effort and the ultimate
realization of Internet service quality and customer
satisfaction expectations.
 Many challenges were identified and pursued in the
design of video streaming systems, such packet loss,
network congestion, stream synchronization, and
lack of service guarantee.
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Introduction (ii)
 From the encoding perspective there were also
many proposals on error-resilient codec in attempts
to deal with packet loss using error concealment
techniques.
 There are two categories of proposals, one offering
multicast at the native IP layer.
 The other, called end system multicast, pushing
multicast functionality to the edge of the network,
that is, at the application level.
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Introduction (iii)
 Content distribution network (CDN) providers that
strategically place a large number of video servers
around the Internet.
 End users to obtain streaming video from one of the
nearby servers, thus reducing the end-to-end delay
and overall network congestion.
 Our study also revealed that multi-segment and
multi-path routing can help to reduce the connection
time while exhibiting little impact on video
playback quality.
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Introduction (iv)
 One of the key features in a P2P system is that each
node contributes resources including bandwidth,
storage space , and the total system capacity can
actually increase as more nodes join a system.
 It overcame some of the fundamental limitations in
classical IP multicast protocols
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Introduction (v)
 It demonstrated that an overlay architecture can be
effectively constructed in the dynamic and
heterogeneous Internet environment.
 In this article, we examine the P2P streaming
technology to determine what shapes the current
system design and what are the limitations and
challenges in the current systems.
 Coolstreaming system, we provide observations on
possible future development.
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Multi-Rate Multicast (i)
 The earlier Internet video streaming system was
largely built on the IP multicast model.
 The key innovation is to ensure simultaneous
dissemination of packets to a set of destinations
traversing each link only once without duplication.
 There are primarily two issues within the IP
multicast framework (Fig.1):
 Heterogeneity in that each receiver differs in its
computing capability and access bandwidth.
 Dynamic in that video playback quality varies in the besteffort Internet.
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Fig.1
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Multi-Rate Multicast (ii)
 IP multicast encountered the following problems in
the deployment:
 Scalability in that there are potentially a large number of
multi-cast groups that must be managed in a large
network.
 A requirement for coordination of dynamic spanning
tree(s) construction at routers across different autonomous
subnets.
 Routers must maintain the state, which violates the
principles and creates difficulty in the design of high-level
functions
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P2P File Distribution Protocols (i)
 P2P applications describe a class of applications
that take advantage of often untapped resources —
storage, cycles, and content such as file, audio, and
video.
 We examine the basic architecture in one of the
most popular P2P file distribution protocols,
BitTorrent or BT.
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P2P File Distribution Protocols (ii)
 BitTorrent consists of two major components, one is
the creation of torrent files and the other is the
mechanism associated with downloading files.
 The torrent contains metadata about a file that must
be shared and the host information.
 BitTorrent protocol is used for actual file
transmission. The group of peers sharing a
particular torrent is usually referred to as a swarm.
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P2P File Distribution Protocols (iii)
 There are two issues associated with this; the first is
the order in which a client should request the
chunks from a file.
 The second issue is with whom a peer should send
and receive the data.
 There could be many incentive-based schemes with
the objective of optimizing download and upload
performance.
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Application-Layer Multicast (i)
 There have been many proposals in the framework
of so called application-layer multicast or overlay
multicast.
 The construction of a multicast tree was performed
using an overlay network, that is, a virtual topology
over the unicast Internet.
 This demonstrated the feasibility of implementing
multicast functions at the end system while keeping
the core functionality of the Internet intact.
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Application-Layer Multicast (ii)
 In Sripanidkulchai used a large set of traces to
validate the following important requirements:
 Sufficient resources for an overlay network construction
 Inherent stability
 Can an potentially support large scale.
 Rao et al. evaluated a multi-tree framework and
proposed a contribution awareness index as the
incentive to enable better contribution from peer
nodes .
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Application-Layer Multicast (iii)
 In general, overlay multicast has not been adopted
in real commercial systems.
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Coolstreaming (i)
 Coolstreaming is based on a data-centric design, in
which the key novelty is that every peer node
periodically exchanges its data availability
information with a set of partners.
 The fundamental advantage of such a data-centric
approach is that it eliminates the requirement for
constructing and maintaining any specific overlay
network.
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Coolstreaming (ii)
 This also offers the following unique advantages:
 Easy to deploy
 Efficient
 Robust and resilient
 Figure 2 depicts the system diagram. There are three
basic modules in the CoolStreaming system:
 Membership manager, which helps peers to maintain a
partial view of other overlay nodes.
 Partnership manager, which establishes and maintain
partnership with other peer nodes.
 Scheduler, which is responsible for the transmission
schedule of the video segment.
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Fig.2
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Coolstreaming (iii)
 Membership Manager: each node has a unique
identifier, such as its IP address and maintains a
membership cache (mCache)
 In a basic node joining algorithm, a newly joined
node first contacts the origin node.
 It randomly selects a deputy node from its mCache
and redirects the new node to the deputy.
 The new node can obtain a list of partner candidates
from the deputy and contacts these candidates to
establish its partners in the overlay.
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Coolstreaming (iv)
 Partnership Management: a video stream is
divided into segments of a uniform length, and the
availability of the segments in the buffer of a node
can be represented by a buffer map (BM).
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Coolstreaming (v)
 Scheduler: Given the BM of a node and its partners,
a schedule is to be generated for fetching the
expected segments from the partners.
 The scheduling algorithm must meet two constraints:
the playback deadline for each segment and the
heterogeneous streaming bandwidth required from
the partners
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 There have been many studies on the overlay
topology.
 There are two primary measurements of interest;
one is the overlay efficiency, and the other is the
stability.
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Topology
 From our experience with Coolstreaming, we
present the following observations:
 On a small timescale, the data-centric approach does not
seem to lead to any specific topology given the random
assignment of peer partnership
 On a large timescale, there is strong evidence that the
overlay architecture converges to a tree-like topology,
especially for each sub-stream.
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Traffic Engineering And Scalablity (i)
 P2P streaming applications gain popularity largely
due to their cost-effectiveness and easy deployment.
 Longer start-up time or channel-switching time. In a
client and server system, the availability of servers
ensures that a client can easily locate the service.
 The P2P approach, however, relies on availability of
peers and content; given the dynamics of the system,
it usually takes a longer time to locate the service in
a P2P system.
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Content Distribution Networks
 Content distribution networks (CDN) strategically
place a large number of servers around the Internet.
 These collaboratively deliver content to end users
transparently.
 The existence of CDN might well complement P2P
streaming in two ways:
 One major problem of current P2P streaming
systems is that the content is retrieved from a
random set of peer nodes in the network.
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Content Distribution Networks
 It is difficult for a P2P network to provide the same
level of service guarantee comparable with that of
an infrastructure-based network.
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Conclusion
 In this article, we provided an overview of the stateof-the-art P2P streaming technologies.
 We summarized the main innovations in the
Coolstreaming system and described the main
challenges.
 Our intuition is that for a large system, the
combination of P2P and CDN might well be the
solution.
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