PPSP Y. Zhang
Internet Draft China Mobile
Intended status: Standard track N.Zong
HuaweiTech
G.Camarillo
Ericsson
J.seng
PPlive
R.Yang
Yale University
Expires: April 18, 2011 October 18, 2010
Problem Statement of P2P Streaming Protocol (PPSP)
draft-ietf-ppsp-problem-statement-00.txt
Abstract
We propose to standardize the key signaling protocols among various
P2P streaming system components including the tracker and the peers.
These protocols, called PPSP, are a part of P2P streaming protocols.
This document describes the terminologies, concepts, incentives, and
scope of developing PPSP, as well as the use cases of PPSP.
Status of this Memo
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This Internet-Draft will expire on April 18, 2011.
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Table of Contents
1. Introduction ................................................ 4
1.1. Background ............................................. 4
1.2. Research or Engineering ................................ 5
1.3. Objective and outline................................... 5
2. Terminology and concepts .................................... 6
3. Introduction of P2P streaming system ........................ 8
4. Problem of proprietary protocols and incentives for developing
standard PPSP .................................................. 9
4.1. Proprietary signaling leads to difficult interactions in case
of multiple parties involved in the delivery ................ 10
4.2. Proprietary signaling leads to multiple client software in a
terminal .................................................... 11
4.3. Proprietary signaling leads to low network resource
utilization ................................................. 11
4.4. Proprietary signaling doesn't handle well with mobile and
wireless environment......................................... 11
5. Components of P2P streaming system........................... 13
6. Scope of PPSP ............................................... 14
6.1. Protocols to be standardized............................ 14
6.2. Service types to be considered ..........................15
7. Use cases of PPSP ........................................... 16
7.1. Worldwide Provision by cooperative P2P Streaming vendors with
PPSP......................................................... 16
7.2. Three Screen P2P streaming in heterogeneous environment using
PPSP ....................................................... 17
7.3. CDN supporting streaming ............................... 18
7.4. Hierarchical P2P Streaming Distribution with PPSP ...... 19
7.5. Serving Gatwway/GGSN acting as Super Nodes assisting P2P
streaming delivery in Cellular mobile environment ........... 20
8. Security Considerations ..................................... 22
9. Acknowledgments ............................................. 22
10. Informative References...................................... 23
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1. Introduction
1.1. Background
Streaming traffic is among the fastest growing traffic on the
Internet. As Cisco Visual Network Traffic index measured, video
streaming already generates the largest volume of Internet traffic in
2010, and the percentage is expected to rise to as high as 91% of the
total Internet traffic in 2014.
There are two basic architectures for delivering streaming traffic on
the global Internet: the client-server paradigm and the peer to peer
(P2P) paradigm [P2PStreamingSurvey]. A particular advantage of the
P2P paradigm over the client-server paradigm is its scalability and
its fault tolerance against failures of centralized infrastructures.
As an example, PPLive [PPLive], one of the largest P2P streaming
vendors, is able to distribute large-scale, live streaming programs
such as the CCTV Spring Festival Gala to more than 2 million users
with only a handful of servers. CNN [CNN] reported that P2P streaming
by Octoshape played a major role in its distribution of the
historical inauguration address of President Obama. It is well
demonstrated in practice that P2P streaming can deliver videos
encoded at a rate of at least about 400 Kbps, in the presence of
rapid user joins/leaves, with positive user experiences.
With the preceding technical advantages, P2P streaming is seeing
rapid deployment. Large P2P streaming applications such as PPLive
[PPLive], PPstream [PPstream] and UUSee [UUSee] each has a user base
exceeding 100 millions. P2P streaming traffic is becoming a major
type of Internet traffic in some Internet networks. For example,
according to the statistics of a major Chinese ISP, the traffic
generated by P2P streaming applications exceeded 50% of the total
backbone traffic during the peak time in 2008. In early 2010, CNTV,
China National Network Television for CCTV, launched its software
named CBox, which supports P2P-based live and VoD programs. The user
base of CBox has increased rapidly. During the opening of 2010 FIFA
World Cup, the user base of CBox increased 5 times, reaching 3
million online users a day and altogether 350 million times view. It
is reported that CNTV can support 10 million simultaneous user visits
[CNTV]. The latest release of Adobe Flash, a major platform of
streaming distribution in the Internet, has introduced Stratus, a
client-to-client data exchange mode. There were reports that other
major video distributors such as Youtube [youtube] and tudou [tudou]
are also conducting trials of using P2P streaming as a component of
their delivery infrastructures.
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Given the increasing integration of P2P streaming into the global
content delivery infrastructure, the lacking of an open, standard P2P
streaming protocol becomes a major missing component in the Internet
protocol stack. Multiple, similar but proprietary P2P streaming
protocols result in repetitious development efforts and lock-in
effects. On the other hand, we observe a recent trend that more
participants beyond traditional P2P streaming vendors are joining the
efforts in the development of P2P streaming. Some of these additional
participants include infrastructure vendors as Akamai [Akamai],
ChinaCache, and ISPs like ComCast [ComCast]. That is, the P2P
streaming ecosystem is becoming an increasingly diverse industry with
participants from the source, infrastructure (in P2P mode although
all the peers are super nodes), delivery and local P2P distribution
to the terminals.
We argue that proprietary P2P streaming protocols lead to substantial
difficulties when integrating P2P streaming as an integral component
of a global content delivery infrastructure. For example, proprietary
P2P streaming protocols do not integrate well with existing cache and
other edge infrastructures.
1.2. Research or Engineering
As [P2PStreamSurvey] identifies, there exist multiple proprietary P2P
streaming systems including PPLive, PPstream, UUsee, Pando, abacast,
and Coolstreaming. A natural question to ask is whether the
development of P2P streaming is mature and ready for standardization.
We admit that P2P streaming will continue to improve and evolve.
However, our investigation also shows that existing P2P streaming
systems are largely converging, sharing similar architecture and
signaling protocols [draft-zhang-ppsp-protocol-comparison-
measurement-00].
The role of standardization in P2P streaming systems is to 1)
decouple the information exchange with the data delivery so that some
most common functions of P2P streaming can use a generic and open
protocol;
2) standardize the information exchange message so that network and
service equipments from different providers can interact with each
other to produce a complete P2P streaming system.
1.3. Objective and outline
Multiple protocols such as streaming control, resource discovery,
streaming data transport, etc. are needed to build a P2P streaming
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system [P2PStreamingSurvey]. We call those protocols P2P streaming
protocols.
The objective of PPSP(Peer to Peer Streaming Protocol) is to
standardize the key signaling protocols among various P2P streaming
system components, including the tracker and the peers. Note that the
complete set of standard P2P streaming protocols for a complete P2P
streaming system could be developed following or in parallel to the
development of PPSP.
PPSP will serve as an enabling technology, building on the
development experiences of existing P2P streaming systems. Its design
will allow it to integrate with IETF protocols on distributed
resource location, traffic localization, and streaming control and
data transfer mechanisms. Regarding to the components it involves,
PPSP allows effective integration between the peer index server named
tracker and different kinds of peers including edge infrastructure
nodes such as cache, gateway and CDN nodes who can act as super peers
and ordinary peers.
This document describes the terminologies, concepts and common
architecture for P2P streaming systems, problems without standardized
PPSP (i.e., incentives to standardize PPSP), scope of PPSP as well as
its use cases.
The rest of this document is organized as follows. In Section 2, we
introduce some common terminologies and concepts. In Section 3, we
introduce P2P streaming system architecture. In Section 4, we
identify the problems without standardized protocols and incentives
for developing PPSP protocols. In Section 5 and 6, we describe the
software architecture and functional components of P2P streaming
systems in order to present the position and scope of PPSP. In
Section 7, we list some PPSP use cases.
2. Terminology and concepts
Chunk: A chunk is a basic unit of partitioned streaming. Peers may
use a chunk as a unit of storage, advertisement and exchange among
peers [Sigcomm:P2P streaming]. Note that a streaming system may use
different units for advertisement and data exchange, using chunks
during data exchange, and a larger unit such as a set of chunks
during advertisement.
Content Distribution Network (CDN) node: A CDN node refers to a
network entity that is deployed in the network (e.g., at the network
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edge or data centers) to store content provided by the original
servers, and serves content to the clients located nearby
topologically.
Live streaming: The scenario where all clients receive streaming
content for the same ongoing event. It is desired that the lags
between the play points of the clients and that of the streaming
source be small.
P2P cache: A P2P cache refers to a network entity that caches P2P
traffic in the network, and either transparently or explicitly as a
peer distributes content to other peers.
P2P streaming protocols: P2P streaming protocols refer to protocols
such as streaming control, resource discovery, streaming data
transport, etc. P2P streaming protocols are needed to build a
complete P2P streaming system.
Peer/PPSP peer: A peer/PPSP peer refers to a participant in a P2P
streaming system that not only receives streaming content, but also
stores and uploads streaming content to other participants.
PPSP: PPSP refer to the key signaling protocols among various P2P
streaming system components, including the tracker and peer. PPSP are
a part of P2P streaming protocols.
Swarm: A swarm refers to a group of clients (i.e., peers) exchange
data to distribute the same content (e.g. video/audio program,
digital file, etc) at a given time.
Tracker/PPSP tracker: A tracker/PPSP tracker refers to a directory
service which maintains a list of peers/PPSP peers storing chunks for
a specific channel or streaming file, and answers queries from
peers/PPSP peers for peer lists.
Video-on-demand (VoD): The scenario where different clients may watch
different parts of the same recorded media content during a past
event.
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3. Introduction of P2P streaming system
There are multiple available P2P streaming solutions. Some are
deployed solutions, while others are still under active study. A
survey of existing solutions can be found in [Survey].
In P2P streaming system, there are various swarms with each swarm
containing a group of clients sharing same streaming content (e.g.
channel, streaming file, etc) at a given time. These clients are
called peers, as each client not only receives streaming content, but
also stores and uploads streaming content to other clients. In a
broad sense of global content delivery infrastructure, peers can
include multiple types of entities such as end user applications,
caches, CDN nodes, and/or other edge devices. Therefore, the basic
functions of a P2P streaming system involve:
1) Maintaining information about which peers are in which swarms
using some directory service, a.k.a. tracker.
2) In each swarm, exchanging information about content availability
(e.g. which chunks stored by a peer) among peers, or between
tracker and peers.
3) In each swarm, exchange of the actual data content among peers.
As shown in Figure 1, common information flows in a P2P streaming
system include:
1) When a peer wants to receive streaming content:
1.1) Peer acquires a list of peers in the swarm from the tracker. A
swarm can be indexed by a channel ID, streaming file ID, etc.
1.2) Peer exchanges its content availability with other peers that
are its neighbors.
1.3) Peer identifies the peers with desired content and requests for
the content from the identified peers.
2) When a peer wants to share streaming content with others:
2.1) Peer sends information to the tracker about the swarm it belongs
to, plus streaming status and/or content availability.
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+-------------------------------------------------------+
| +-------------------+ |
| | Tracker | |
| +-------------------+ |
| ^ | ^ |
| | | |swarms, |
| query | | peer list |streaming status |
| | | |and/or content |
| | | |availability |
| | V | |
| +-------------+ +------------+ |
| | Peer1 |<------->| Peer 2 | |
| +-------------+ content +------------+ |
| ^ ^ availability |
| * | content |
| content * |availability |
| V V |
| +------------+ |
| | Peer 3 | |
| +------------+ |
+-------------------------------------------------------+
Figure 1 Common information flows in P2P streaming system
4. Problem of proprietary protocols and incentives for developing
standard PPSP
We start by considering the success of the Web. It is the standard
HTTP protocol that makes it possible to deploy the global content
distribution eco-system that consists of not only end devices such as
Web servers and Web clients, but also infrastructure devices such as
Web caches and CDN nodes. All of these devices communicate through
standard protocols and provide substantial benefits to the consumers,
the content publishers, and the network infrastructure.
As we discussed in Section 1, given the increasing integration of P2P
streaming into the global content delivery infrastructure,
proprietary P2P streaming protocols not only result in repetitious
development efforts and lock-in effect, but also lead to substantial
difficulties when integrating P2P streaming as an integral component
of a global content delivery infrastructure. The explicit incentives
to get rid of the proprietary protocols can be seen from the talks of
Johan Pouwelse, scientific director of P2P Next: "?broadcasters from
the BBC to Germany's ARD just seem to love the idea of ditching their
proprietary platforms [Johan Pouwelse]."
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Let's take a look of several cases for further problem identification.
4.1. Proprietary signaling leads to difficult interactions when
multiple parties are involved in the delivery
Consider a simplest case. In an open P2P streaming industrial
environment, it is possible for different streaming vendors (esp.
spread in different regions) to cooperatively deliver a broadcasting
event. Suppose PPLive broadcasts live Chinese spring festival gala
for American Chinese by Pando networks. At a first sight, this seems
reasonable because there are relatively few American Chinese PPLive
users. Therefore it can be challenging to achieve efficient P2P
delivery by PPLive alone. Utilizing peer resources from a partner
such as Pando may achieve higher efficiency. However, different
messages and interaction semantics between the two existing systems
can lead to challenges in achieving interoperability among PPLive
peers and Pando peers.
Consider a more complex case where P2P streaming vendors cooperate
with CDN providers. Such integration is already practiced by systems
such as UUSee, RayV and Forthtech. For P2P streaming, it has been
shown that infrastructure devices such as edge caches and CDN nodes
can improve the performance of P2P streaming (e.g., lower latency) by
providing more stable "super peers" and reduce traffic in ISP network
[CDN+P2P] [RFC 5693].
However, there can be substantial obstacles in deploying
infrastructure edge devices supporting proprietary P2P streaming
protocols [HTPT]. Unlike the Web with the standard HTTP protocol, the
current P2P streaming landscape consists of multiple, proprietary P2P
streaming protocols differing in their signaling transactions.
Consequently, in order to support P2P streaming, the infrastructure
devices need to understand and keep updated with various proprietary
P2P streaming protocols. This introduces complexity and deployment
cost of infrastructure devices.
The setting can become more challenging if there are M P2P streaming
vendors and N CDN providers for possible cooperative combination. How
does a specific CDN node identify different private systems and
report to different trackers with proprietary protocols? It seems
there are no good ways to address this. The CDN node has to update
its protocol through case-by-case negotiations.
With standard PPSP, edge caches and CDN nodes can be designed to
inter-operate with only the standard protocols, reducing the
complexity and cost to support streaming involving P2P.
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4.2. Proprietary signaling leads to multiple client software in a
terminal
Because of private protocols, although there can be much commonality
among many applications, application developers cannot share common
development efforts, leading to repeated efforts and thus wasting
work.
This may require that a terminal install multiple different software
systems for different purposes. For example a user installs CBox for
CCTV programming, and PPLive for Japanese and Korean movies. This
brings two problems:
1) Due to terminal limitations, it may not be possible to install
many clients in one machine, esp. for mobile terminals. The limited
CPU, storage and cache often limit the concurrent threads and
processes.
2) Different, independent software system may conduct vicious
competitions. In the past, we have even seen that competitors delete
each other's software when automatically running a software program.
Standard protocols and common components can lead to better co-use.
4.3. Proprietary signaling leads to low network resource utilization
From the network resource utilization perspective, if we have no
standard protocols in designating the resource availability (which is
a PPSP task) and every application uses its proprietary protocol for
storage and bandwidth usage, then for the same content, many on-the-
way data in different applications have to be cached/stored and
transferred repeatedly. This wastes storage and causes possible
congestion in the network.
4.4. Proprietary signaling doesn't handle well with mobile and
wireless environment
Mobility and wireless are becoming increasingly important features to
support in future Internet deployments [GENI], [FIND]. Currently
there are more and more mobile and wireless Internet users. By the
end of 2009, there are 233 million mobile users in China [CNNIC].
Along with the introduction of mobile and wireless capabilities into
the Internet, mobile streaming is becoming a key offered service
[MobileTV]. In Korea the number of mobile TV subscriber has reached
seventeen millions, accounting for one third of the mobile
subscribers. In Italy, there are one million mobile TV users. During
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the 2008 Beijing Olympic Games, more than one million users utilized
China mobile's mobile TV service.
Considering that the mobile and wireless nodes have better CPU,
memory and storage and the mobile network has better network
bandwidth (esp. there are more uplink bandwidth which is wasted for
transferring little data in current practice) than before, there is a
possibility for the mobile and wireless node to be peers supporting
P2P streaming.
However, mobile peers may face bigger challenges for supporting P2P
streaming with unsteady network connections, less steady power and
different media coding for mobile devices. Current proprietary
protocols are designed mainly for the fixed Internet and do not
address these challenges. We may therefore raise such a question:
Shall we let these private protocols to fit in mobile environment
system-by-system independently or solve these problems in the design
of an open PPSP protocol suite?
The answer is obviously clear. It is worth mentioning that the
development of PPSP should consider the specific requirements of
mobile Internet. For example, the overhead of PPSP should be small in
low bandwidth mobile Internet. Also, information exchange in PPSP
should support mobility, low battery usage and heterogeneous
capabilities of mobile terminals. Systematic requirements on the
development of PPSP will be addressed in the requirements documents.
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5. Components of P2P streaming system
+---------------------------------------------------+
| Application Layer |
|---------------------------------------------------|
| Play-out Layer |
| +----------+ +------------+ +-----------+ |
| |start/stop| |pause/resume| | FF/rewind | |
| +----------+ +------------+ +-----------+ |
|-------------------------------------------------- |
| Information Layer |
| +------------+ +------+ +-----------+ |
| |registration| |report| | statistics| |
| +------------+ +------+ +-----------+ |
|---------------------------------------------------|
| Communication Layer |
| +---------------------+ +------------------+ |
| |tracker communication| |peer communication| |
| +---------------------+ +------------------+ |
| +-------------+ |
| | bootstrap | |
| +-------------+ |
|---------------------------------------------------|
| Transport Layer |
+---------------------------------------------------+
Figure 2. Major components of a P2P streaming system.
To organize our efforts, we show the components of a complete P2P
streaming system in Figure 2.
1) The Transport Layer is responsible for data transmission among
peers. UDP, TCP or other protocols can be used.
2) The Communication Layer includes three components:
2.1) Tracker communication is a component that enables each peer to
get peer list from the tracker. It may also allow a peer to report
content availability to the tracker.
2.2) Peer communication is a component that enables each peer to
exchange content availability and neighbor peer information as well
as send requests other peers for content.
2.3) Bootstrap is a component that enables newly joined nodes to
obtain tracker information.
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3) The Information Layer is responsible for peer and content
information collection and management.
3.1) Registration is a component that enables nodes to register to
the system, and publish the content information. The information may
include but is not limited to: content description, content type,
creation time, node information such as physical location, IP address.
3.2) Report is a component that enables peers to report streaming
status to the tracker. The information may include peer
inbound/outbound traffic, amount of neighbor peers, peer health
degree and other streaming parameters.
3.3) Statistics is a component that enables trackers to manage the
aggregated system information for global control in upload bandwidth
consumption, overhead consumption and other tasks.
4) The Play-out Layer is responsible for controlling the action of
media play (e.g., start, pause, resume, stop, fast-forward, and
rewind).
5) The Application Layer is the top layer for streaming applications.
6. Scope of PPSP
6.1. Protocols to be standardized
We propose to standardize protocols in PPSP which enable the tracker
communication and the peer communication components in the
communication layer, as well as the report component in the
information layer. These protocols, called PPSP, are key mechanisms
involving two important roles - tracker and peer in P2P streaming
processes, as addressed in Section 3. These signaling protocols, in
essence, aim at standardizing the content information exchange
mechanisms among different devices in P2P streaming systems. Note
that PPSP is only a part of P2P streaming protocols. The complete set
of standard P2P streaming protocols for a complete P2P streaming
system could be developed following or in parallel to the PPSP
development.
Because bootstrap, registration and statistics components are out-of-
band mechanisms for streaming processes, they are not in current
scope of PPSP. Both transport, play-out and application layers in P2P
streaming system are also beyond the current scope of PPSP.
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Therefore, PPSP includes the PPSP tracker protocol - a signaling
protocol between PPSP trackers and PPSP peers, and the PPSP peer
protocol - a signaling protocol among PPSP peers.
1) PPSP tracker protocol
This protocol will define:
1.1) Standard format/encoding of information between PPSP peers and
PPSP trackers, such as peer list, content availability, streaming
status including online time, link status, node capability and other
streaming parameters.
1.2) Standard messages between PPSP peers and PPSP trackers defining
how PPSP peers report streaming status and request to PPSP trackers,
as well as how PPSP trackers reply to the requests.
Note that existing protocols should be investigated and evaluated for
being reused or extended as the messages between tracker and peer.
Possible candidates include the use of the HTTP, where the GET method
could be used to obtain peer lists, the POST method used for
streaming status reports, etc.
2) PPSP peer protocol
This protocol will define:
2.1) Standard format/encoding of information among PPSP peers, such
as chunk description.
2.2) Standard messages among PPSP peers defining how PPSP peers
advertise chunk availability and their neighbor peers information to
each other, as well as the signaling for requesting chunks among PPSP
peers.
Again, existing protocols should be investigated and evaluated for
being reused or extended as the messages among peers. Possible
candidates include the use of the HTTP, where the GET method could be
used to obtain chunk availability, etc. Considering that there can be
a large number of peers, the protocol should consider some
lightweight (possibly binary) protocols.
6.2. Service types to be considered
As stated in Section 1, PPSP will serve as an enabling technology and
provide tools for building multiple P2P streaming systems. We are not
standardizing certain streaming services. The reason that we list
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service types here is to show we would consider the properties of
these services as the requirements for PPSP design.
Common service types supported by current P2P streaming systems
include live streaming and video-on-demand (VoD).
In live streaming, all PPSP peers are interested in the media coming
from an ongoing event, which means that all PPSP peers share nearly
the same streaming content at a given point of time. In live
streaming, some PPSP peers may store the live media for further
distribution, which is known as TSTV (time-shift TV), where the
stored media are separated into chunks and distributed in a VoD-like
manner.
In VoD, different PPSP peers watch different parts of the recorded
media content during a past event. In this case, each PPSP peer keeps
asking other PPSP peers which media chunks are stored in which PPSP
peers, and then pulls the required media from some selected PPSP
peers.
7. Use cases of PPSP
7.1. Worldwide Provision by cooperative P2P Streaming vendors with
PPSP
As stated in section 4.1, the cooperation of P2P Streaming vendors
can easily expand the broadcasting scale with standard PPSP. The
interactions between cooperative P2P streaming provider A's tracker
server and P2P streaming provider B and C's SuperNodes is shown in
Figure 3.
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+-------------------------------------------------------------------+
| |
| +------------------+ |
| +------------>| A's Tracker |<----------+ |
| | +------------------+ | |
| Tracker| ^ ^ | |
| Protocol| Tracker| |Tracker |Tracker |
| | Protocol| |Protocol |Protocol |
| | | | | |
| | | | | |
| v v v v |
| +------+ Peer +------+ +------+ +------+ |
| | B's |<------->| B's | | C's | | C's | |
| | SN1 |Protocol | SN2 | | SN1 | | SN2 | |
| +------+ +------+ +------+ +------+ |
| ^ ^ ^ ^ |
| | | | | |
| | | Peer Protocol Peer Protocol| | |
| Peer | +-------------+ +--------------+ |Peer |
| Procotol| | | |protocol|
| | | | | |
| | | | | |
| | | | | |
| v v v v |
| +------+ Peer +------+ +---------+ Peer +---------+ |
| | A's |<------> | B's | |A's |<------> |C's | |
| | User1|Protocol | User2| | User1 |Protocol | User2 | |
| +------+ +------+ +---------+ +---------+ |
| |
+-------------------------------------------------------------------+
Figure 3 Cooperative Vendors Interactions
7.2. Three Screen P2P streaming in heterogeneous environment using
PPSP
This is a use case where PC, Setbox/TV and mobile terminals from both
fixed Internet and mobile Internet to construct a peer overlay for
streaming content distribution. Using PPSP protocols, peers from
different kinds of networks can share and download what they have
from each other to form a 3-screen streaming system.
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+-------------------------------------------------------------------+
| |
| Tracker Protocol +---------+ Tracker Protocol |
| +-------------> | Tracker |<------------------+ |
| | +---------+ | |
| | ^ | |
| | | | |
| | | | |
| V | V |
| +------+ | +------------+ |
| | STB | Tracker Protocol |Mobile Phone| |
| +------+ | +------------+ |
| ^ | ^ |
| | | | |
| | | | |
| | V | |
| |Peer Protocol +---------+ Peer Protocol | |
| +-------------> | PC |<------------------+ |
| +---------+ |
| |
+-------------------------------------------------------------------+
Figure 4 Heterogeneous P2P Streaming Interactions with PPSP
7.3. CDN supporting streaming
This scenario is similar to use case 1 except that this is more like
an M to N mapping while use case 1 is more often to be a case by case
mapping. This reduces the case by case negotiation between the
original provider and multiple CDN providers if otherwise proprietary
protocols are used makes it easier for both sides to interoperate.
The interactions between the P2P streaming provider's tracker server
and CDN surrogates as well as interactions between CDN surrogates are
the same as a normal peer as shown in Figure 4.
PPSP can be used in:
1) Interface between CDN nodes and tracker. This is very useful for a
small streaming provider who has no its own CDN surrogates and much
money to distribute its stream worldwide.
2) New construction of CDN systems by PPSP. This can often occur for
an operator or CDN vendor to build a P2P CDN system supporting
streaming or file sharing applications with low cost.
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+-------------------------------------------------------------------+
| |
| +------------------+ |
| +------------>| Original Tracker |<----------+ |
| | +------------------+ | |
| Tracker| ^ ^ | |
| Protocol| Tracker| |Tracker |Tracker |
| | Protocol| |Protocol |Protocol |
| | | | | |
| | | | | |
| v v v v |
| +------+ Peer +------+ +------+ +------+ |
| | CDN1 |<------->| CDN1 | | CDN2 | | CND2 | |
| | POP2 |Protocol | POP1 | | POP1 | | POP2 | |
| +------+ +------+ +------+ +------+ |
| ^ ^ ^ ^ |
| | | | | |
| | | Peer Protocol Peer Protocol| | |
| Peer | +-------------+ +--------------+ |Peer |
| Procotol| | | |protocol|
| | | | | |
| | | | | |
| | | | | |
| v v v v |
| +------+ Peer +------+ +---------+ Peer +---------+ |
| | USA |<------> | USA | |Caribbean|<------> |Caribbean| |
| | User1|Protocol | User2| | User1 |Protocol | User2 | |
| +------+ +------+ +---------+ +---------+ |
| |
+-------------------------------------------------------------------+
Figure 5 CDN Supporting P2P Streaming with PPSP
7.4. Hierarchical P2P Streaming Distribution with PPSP
Hierarchical P2P streaming has many advantages over non-hierarchical
streaming such as providing better QoS, e.g., lower start-up latency
and service interruption [P2broadcast], higher throughput and lower
packets drop ratio [Hybrid], topology-mismatch reduction and better
management [AHLSS].
PPSP is useful for clustering the peers because there are abundant
node information and content information exchange fetched in the
message.
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7.5. Serving Gatwway/GGSN acting as Super Nodes assisting P2P
streaming delivery in Cellular mobile environment
In a cellular mobile environment, with the increase in bandwidth and
mobile terminal capabilities, P2P streaming is better to be realized
than before. Note that we don't have compulsory mobile peers. The
network peers and WIFI peers are easier selected. Serving
gateway/GGSN, as the gateway for the cellular network to Internet, is
more and more viewed as a promising place to add the cache
functionality assisting P2P streaming services. Because it's deployed
by the operators, the stability and storage size are better
guaranteed than ordinary PC. Thus, it is desirable to to select
serving gateway/GGSN as the super nodes assisting delivery. The
interactions between serving gateway/GGSN and tracker, among serving
gateways/GGSNs, and between serving gateway/GGSN and mobile terminal
are shown in Figure 6. We name these kinds of serving gateway/GGSN as
Mobile Supporting Super Nodes (MSSN). Note that if mobile terminals
are not eligible to be a peer, it can use client/server streaming, by
simply taking GGSN as a source.
There are two basic scenarios in cellular networks:
1) Self operational P2P streaming services for mobile operators: PPSP
is a suitable protocol for tracker-GGSN and GGSN-mobile nodes
interaction. GGSN can be both a super node and a proxy for different
mobile terminals with different capabilities.
2) Third-party P2P streaming services with optimized localization by
GGSN. When introducing a popular P2P streaming application like PPLive in a mobile network, GGSN can coordinate with the third part trackers to cache the content without needing continuous update of the third party protocols.
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+-------------------------------------------------------------------+
| |
| Peer Protocol |
| +-------------------+ |
| | | |
| ,--?. | ,--?. | ,--?. |
| .' '. | .' '. | .' '. |
| / \ V / \ V / \ |
| ' Cellular +------+ Internet +------+ Cellular | |
| | Access | MSSN | | MSSN | Access / |
| \ Network +------+ +------+ Networks / |
| ' /^ ^ \ / \ .' |
| '. / | | ' / ' .' |
| '. .' | | '.+-------+' '. .' |
| '------' | | |Tracker| '-----' |
| Peer Protocol/| | +-------+ |
| +------+ HTTP | | Tracker ^Protocol |
| |Mobile|<------------+ +---------+ |
| |Phone |<-------------------------+ |
| +------+ (Tracker Protocol) |
+-------------------------------------------------------------------+
Figure 6 Serving Gateway/GGSN assisting P2P streaming delivery
7.6. Cache Service Supporting Streaming
Deploying cache nodes in the network edges can greatly decrease the
inter-network traffic and increase user experience in streaming
service. However, the cache nodes deployed by operators have to
execute DPI(deep packet inspection) and update their matching library
constantly to support more and more proprietary P2P streaming
protocols along with the increase of such applications. It increases
the operator's cost dramatically.
If PPSP were used in the cache nodes as well as the applications,
cache nodes can spend less cost to support more applications.
After the cache gets the content, it can reports to the P2P streaming
provider's tracker server just like as a normal peer and serves other
peers as shown in Figure 7.
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+-------------------------------------------------------------------+
| |
| Tracker Protocol +---------+ Tracker Protocol |
| +-------------> | Tracker |<--------------------+ |
| | +---------+ | |
| | | |
| | | |
| | | |
| V V |
| +-----------+ Peer Protocol +------------+ |
| | Cache |<---------------------------->| Peer | |
| +-----------+ +------------+ |
+-------------------------------------------------------------------+
Figure 7 Cache Service Supporting Streaming
8. Security Considerations
PPSP has similar assumptions regarding peer privacy as P2PSIP
[ID.ietf-p2psip-base];that is, all participants in the system are
issued unique identities and credentials through some mechanism not
in the scope of PPSP. One possibility is a centralized server. Hence
PPSP will not attempt a solution to these issues for P2P streaming in
general. However PPSP has some unique security issues:
1) The content published by peers may not be checked by a centralized
certificating server. Consequently, P2P streaming may conduct
malicious content distribution.
2) Content pollution is another common problem faced by P2P streaming.
3) Because we focus on P2P streaming with a tracker who is critical
to the P2P streaming system, there may be a higher probability that
attacks are launched against the tracker.
PPSP may include some mechanisms to prevent malicious nodes from
polluting the streaming content or launching attacks on the tracker.
The protocol documents will contain a complete description on the
security/privacy concerns of PPSP.
9. Acknowledgments
We would like to acknowledge the following people who provided
feedback and suggestions to this document: D. Bryan from Cogent Force;
E. Marocco from Telecom Italia; V. Gurbani from Bell Labs/ /Alcatel-
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Lucent; R. Even from Huawei; H. Zhang from NEC Labs, USA; C. Schmidt
and L. Xiao from NSN; C. Williams from ZTE; V. Pasual from Tekelec; D.
Zhang from PPlive; H. Deng from China Mobile; and J. Lei from Univ.
of Goettingen.
10. Informative References
[Cisco] Approaching the Zettabyte Era by Cisco.
[PPLive] www.pplive.com
[PPStream] www.ppstream.com
[UUSee] http://newteevee.com/2008/09/14/p2p-is-coming-to-youtube/
[youtube] www.youtube.com
[tudou] www.tudou.com
[CNN] www.cnn.com
[Octoshape] www.octoshape.com
[ATT]http://mobile.sooyuu.com/Article/content/200905/217315094629281_
1.shtml
[Sigcomm:P2P streaming]Challenges, Design and Analysis of a Large-
scale P2P-VoD System,Yan Huang et al, Sigcomm08.
[RFC 5693], Application-Layer Traffic Optimization (ALTO) Problem
Statement, E. Marocco et al, draft-ietf-alto-problem-statement-04
[Pando]www.pando.com
[CoolStreaming] CoolStreaming/DONet: A Data-Driven Overlay Network
for Efficient Live Media Streaming, Xinyan Zhang et al,
[HPTP] HPTP: Relieving the Tension between ISPs and P2P, Guobin Shen
et al,
[draft-zhang-ppsp-protocol-comparison-measurement-
00]www.ietf.org/internet-drafts/draft-zhang-ppsp-protocol-comparison-
measurement-00.txt
[GENI] www.geni.net
[FIND]www.nets-find.net
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[draft-zhang-ppsp-dsn-introduction-00]www.ietf.org/internet-
draft/draft-zhang-ppsp-dsn-introduction-00.txt
[MobileTV] MobileTV,Turning in or switching off, Arthur D. Little
[Computer Networks: Traffic] Traffic analysis of peer-to-peer IPTV
communities, Thomas Silverston et al, Computer Networks, 53 (2009)
470-484
[Survey]A survey on peer-to-peer video streaming systems Yong Liu et
al, Peer-to-Peer Netw Appl (2008) 1:18-28,Springer.
[draft-zhang-alto-traceroute-00] www.ietf.org/internet-draft/draft-
zhang-alto-traceroute-00.txt
[P2PStreamingSurvey] Zong, N. and X. Jiang, "Survey of P2P Streaming",
IETF PPSP BoF, November 2008.
[Challenge] Peer-to-Peer Live Video Streaming on the Internet: Issues,
Existing Approaches, and Challenges, Bo Li et al, IEEE Communications
Magazine, June 2007(94-99).
[CDN+P2P]Efficient Large-scale Content Distribution with Combination
of CDN and P2P Networks,Hai Jiang et al,International Journal of
Hybrid Information Technology, Vol.2, No.2, April, 2009.
[Peering CDN] A Case for Peering of Content Delivery Networks,
Rajkumar Buyya1 et al,
http://dsonline.computer.org/portal/site/dsonline/menuitem.9ed3d9924a
eb0dcd82ccc6716bbe36ec/index.jsp?&pName=dso_level1&path=dsonline/2006
/10&file=o10003.xml&xsl=article.xsl&.
[P2broadcast] P2broadcast: a hierarchical clustering live video
streaming system for P2P networks, De-kai Liu et al,International
Journal of Communication Systems,Volume 19,Issue 6.
[Hybrid]Hybrid Overlay Networks Management for Real-Time Multimedia
Streaming over P2P Networks, Mubashar Mushtaq et al, Lecture Notes in
Computer Science, Volume 4787/2007.
[AHLSS]AHLSS: A Hierarchical, Adaptive, Extendable P2P Live Streaming
System, Runzhi Li et al, International Journal of Distributed Sensor
Networks, Volume 5, Issue 1 January 2009.
[ComCast]http://www.afterdawn.com/news/article.cfm/2008/05/20/comcast
_invests_in_p2p_streaming_startup
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[Johan Pouwelse]http://newteevee.com/2008/07/24/open-source-p2p-
streaming-getting-ready-to-disrupt-cdn-business-models/
[CNTV] news.xinhuanet.com/2010-06/30/c_12281703.htm
[CNNIC] http://it.sohu.com/s2010/cnnic25/
[ID.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E., Baset,
S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)Base
Protocol", draft-ietf-p2psip-base-08.
[Akamai] Cheng Huang , Angela Wang , Jin Li , Keith W. Ross,
Understanding hybrid CDN-P2P: why limelight needs its own Red Swoosh,
Proceedings of the 18th International Workshop on Network and
Operating Systems Support for Digital Audio and Video, May 28-30,
2008, Braunschweig, Germany .
Author's Addresses
Yunfei Zhang
China Mobile Communication Corporation
zhangyunfei@chinamobile.com
Ning Zong
Huawei Technologies Co., Ltd.
zongning@huawei.com
Gonzalo Camarillo
Ericsson
Gonzalo.Camarillo@ericsson.com
James Seng
PPLive
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james.seng@pplive.com
Richard Yang
Yale University
yry@cs.yale.edu
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