Title: PeertoPeer Live Video Streaming on the Internet Issues, Existing Approaches, and Challenges
1Peer-to-Peer Live Video Streaming on the Internet
Issues, Existing Approaches, and Challenges
2Introduction (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.
3Introduction (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.
4Introduction (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.
5Introduction (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
6Introduction (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.
7Multi-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 best-effort Internet.
8Fig.1
9Multi-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
10P2P 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.
11P2P 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.
12P2P 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.
13Application-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.
14Application-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 .
15Application-Layer Multicast (iii)
- In general, overlay multicast has not been
adopted in real commercial systems.
16Coolstreaming (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.
17Coolstreaming (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.
18Fig.2
19Coolstreaming (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.
20Coolstreaming (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).
21Coolstreaming (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
22- 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.
23Topology
- 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.
24Traffic 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.
25Content 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.
26Content 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.
27Conclusion
- In this article, we provided an overview of the
state-of-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.