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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: Feb 2011                                          July 12, 2010




             Problem Statement of P2P Streaming Protocol (PPSP)
                 draft-zhang-ppsp-problem-statement-06.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

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt





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   The list of Internet-Draft Shadow Directories can be accessed at
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   This Internet-Draft will expire on February 2,2011.

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   described in the Simplified BSD License.





























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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.......................................21
   9. Acknowledgments ..............................................22
   10. Informative References.......................................22













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1. Introduction

    1.1. Background

   Streaming traffic is among the fastest growing traffic on the
   Internet. In a recent white paper, Cisco predicts that by 2012, 90%
   of all Internet traffic will be video [Cisco].

   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. 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
   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 peak time in 2008. In the beginning of 2010,
   CNTV, China National Network Television for CCTV launched its
   software named CBox supporting P2P live and VoD programs. To date, it
   has a rapid user increase. With the opening of FIFA world cup, CBox
   has increased 5 times in user number with 3 million online users a
   day and altogether 350 million times view. It is reported that CNTV
   can support 10 million simultaneous user visit[CNTV]. Similarly there
   were also reports that major video distributors such as Youtube
   [youtube] and tudou [tudou] are conducting trials of using P2P
   streaming as a component of their delivery infrastructures.

   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. More importantly, we notice that more participants beyond
   P2P streaming vendors have involved in P2P streaming industry, like


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   infrastructure vendors Akamai[Akamai], ChinaCache and ISP like
   ComCast[ComCast]. That is, P2P streaming has become an open industry
   with different 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 shows that existing P2P streaming systems
   are largely converging, sharing similar architecture and signaling
   protocols [draft-zhang-ppsp-protocol-comparison-measurement-00].

   The aim of standardization in P2P streaming systems is to 1) decouple
   the information exchange with the following delivery so that the most
   common part in P2P streaming can use a generic and open protocol;

   2) standardize the information exchange message so that equipments
   from different providers can interact with each other for 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
   system [P2PStreamingSurvey]. We call those protocols P2P streaming
   protocols.

   The objective of the PPSP work is 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. Note that the complete set of standard P2P
   streaming protocols for a whole P2P streaming system could be
   developed following or parallel to the PPSP work.

   - PPSP will serve as an enabling technology, building on the
     development experiences of existing P2P streaming systems. Its


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     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/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 and therefore discuss 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, which is
   used by a peer for the purpose of storage, advertisement and exchange
   among peers [Sigcomm:P2P streaming].

   Content Distribution Network (CDN) node: A CDN node refers to a
   network entity that usually is deployed at the network edge 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. The lags between the play points
   of the clients and that of the streaming source are 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 multiple
   protocols such as streaming control, resource discovery, streaming
   data transport, etc. which are needed to build a P2P streaming system.





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   Peer/PPSP peer: A peer/PPSP peer refers to a participant in a P2P
   streaming system. The participant 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) sharing 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 lists 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 watch
   different parts of the media recorded and stored during past events.





























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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 in which swarm in some
      directory service, a.k.a. tracker.

   2) In each swarm, exchange information about content availability
      (e.g. which chunks stored by a peer) among peers, or between
      tracker and peer.

   3) In each swarm, exchange the actual 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 the peers on the
   obtained peer list.

   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 swarms 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                                  |
         |             +------------+                            |
         |             |   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 leads 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 in case
       of multiple parties involved in the delivery

   Let's first see a simplest case.In an open P2P streaming industrial
   environment, it's a common thing for different streaming vendors(esp.
   spread in different regions) cooperatively take the broadcasting.
   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's hard to realize efficient P2P delivery by
   PPLive network only. Borrowing peer resources from an ally like
   Pando may help the efficient distribution. However different messages
   and interactions in the two systems cause the difficulty in
   interoperability among PPLive peers and Pando peers.

   Consider a more complex case where P2P streaming vendors cooperate
   with CDN providers. People can refer to UUSee, RayV and Forthtech
   practice for this use case. In the context of P2P streaming,
   infrastructure devices such as edge caches and CDN nodes have been
   shown as promising means to both 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 mostly differing in 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.

   Things get worse 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 the private protocols, although there are quite much in
   common, application developers cannot reuse the common parts, wasting
   a lot of repeated work.

   This makes a terminal installing multiple different software for
   different purpose. For example a user installs CBox for CCTV program
   watching and PPLive for Japanese and Korean movies. This brings two
   problems:

   1) Terminal limitation may don't allow for many clients in one
   machine, esp. for mobile terminals. The limited CPU,storage and cache
   often limit the concurrent threads and processes.

   2) Because different software are independent, it may lead to vicious
   competitions. We even see the competitors to delete each other's
   software when automatically running the software. If there are
   standard protocols and some common part to co-use, such things are
   hard to occur.

    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
   the imagined PPSP task)and every application uses proprietary
   protocol for storage and bandwidth usage, then for a same content,
   many on-the-way data in different applications have to be
   cached/stored and transferred repeatedly, which 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
   the 2008 Beijing Olympic Games, more than one million users utilize
   China mobile's mobile TV service.


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   Considering 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 are much more
   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 mainly designed in fixed Internet environment and don't
   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 be small in low
   bandwidth mobile Internet. Also, information exchange in PPSP should
   support mobility, low battery 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 Components of P2P streaming system

   To organize our efforts, we show the components of a complete P2P
   streaming system in Figure 2.

   1) Transport Layer is responsible for data transmission between peers.
   UDP, TCP or other protocols can be used.

   2) Communication layer includes three components:

   2.1) Tracker communication is a component that enables each peer to
   get peer list from the tracker and/or provide content availability to
   the tracker.

   2.2) Peer communication is a component that enables each peer to
   exchange content availability and request other peers for content.

   2.3) Bootstrap is a component that enables newly joined nodes to
   obtain tracker information.

   3) Information layer is responsible for peer and content information
   collection and management.


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   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 regards.

   4) Play-out layer is responsible for controlling the action of media
   play (e.g. start, pause, resume, stop, fast-forward, and rewind).

   5) 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 are only a part of P2P streaming protocols. The complete
   set of standard P2P streaming protocols for a whole P2P streaming
   system could be developed following or parallel to the PPSP work.

   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.

   Therefore, PPSP include 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:


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   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 to each other, as well as the signaling
   for requesting the 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 the potential
   large number of peers, some lightweight (possibly binary) protocols
   could also be good candidates.

    6.2. Service types to be considered

   As stated in Section 1, PPSP will serve as enabling technology and
   tools for building various P2P streaming systems. We are not
   standardizing certain streaming services. The reason why we list
   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(including time-shift), 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


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   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 media
   recorded and stored 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
   fixed Internet, mobile Internet constitute the peer overlay for
   streaming content sharing. 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
   a 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

   The hierarchical P2P streaming distribution have many advantages over
   non-hierarchical conterparters such as better QoS(start-up latency
   and service interruption reduction[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 Gateway/GGSN acting as Super Nodes assisting
         P2P streaming delivery in Cellular mobile environment

   In 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. 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.
   It's more likely to select GGSN as the super nodes assisting the
   delivery. The interactions between serving gateway/GGSN and tracker, between
   different serving gateways/GGSNs and between serving gateway/GGSN and mobile
   terminal is explicated in Fig6.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 mode for streaming service simply taking
   serving gateway/GGSN a source.

   There are basically two scenarios in cellular networks:

   1) Self operational P2P streaming services for mobile operators: PPSP
   is the suitable protocol for tracker-serving gateway/GGSN and serving
   gateway/GGSN-mobile nodes interaction. The serving gateway/GGSN can be
   both a super node or a complete proxy for different mobile terminals with
   different capabilities.

   2) The 3rd party P2P streaming service with optimized localization by
   GGSN. When introducing a popular P2P streaming application like
   PPLive in the mobile network, serving gateway/GGSN can coordinate with the 3rd party
   trackers to cache the content without needing continuous update of
   the 3rd 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 GGSN assisting P2P streaming delivery

      8. Security Considerations

   PPSP has a similar assumption in peer privacy as P2PSIP[ID.ietf-
   p2psip-base], i.e., all participants in the system are issued unique
   identities and credentials through some mechanism not in the scope of
   PPSP, such as a centralized server. Hence PPSP will not attempt a
   solution to these issues for P2P streaming networks in general.
   However PPSP have some unique security issues:

   1) The content published by peers may not be checked by centralized
   certificating server. Therefore P2P streaming network may have the
   danger of malicious content distribution.

   2) Content pollution is another common problem faced by P2P streaming.

   3) Because there is a tracker who is critical to the P2P streaming
   systems. There is an increased probability that threats may involve
   launching attacks against the tracker.




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   PPSP may include some mechanisms to prevent malicious nodes from
   polluting the streaming content or launch attacks to the tracker. The
   protocol documents will contain a complete description of the
   security/privacy concerns of PPSP.

      9. Acknowledgments

   We would like to acknowledge the following who provided feedback or
   suggestions for this document: D. Bryan from Cogent Force; E. Marocco
   from Telecom Italia; V. Gurbani from AT&T; 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; X. 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] www.uusee.com

   [youtube] www.youtube.com

   [tudou] www.tudou.com

   [CNN] www.cnn.com

   [Octoshape] www.octoshape.com

   [ATT]http://mobile.sooyuu.com/Article/content/200905/2173150946
         29281_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,



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   [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

   [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.9ed3
         d9924aeb0dcd82ccc6716bbe36ec/index.jsp?&pName=dso_level1&path=d
         sonline/2006/10&file=o10003.xml&xsl=article.xsl&.





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   [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/c
         omcast_invests_in_p2p_streaming_startup

   [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.



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   zongning@huawei.com



   Gonzalo Camarillo

   Ericsson

   Gonzalo.Camarillo@ericsson.com



   James Seng

   PPLive

   james.seng@pplive.com



   Richard Yang

   Yale University

   yry@cs.yale.edu























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