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Versions: (draft-zhang-ppsp-problem-statement) 00 01 02 03 04 05 06 07 08 09 10 11 13 14 15 12 RFC 6972

PPSP                                                           Y. Zhang
Internet Draft                                             China Mobile
                                                                N. Zong
                                                                 Huawei

Intended status: Informational                         January 31, 2013
Expires: July 2013



        Problem Statement and Requirements of Peer-to-Peer Streaming
                              Protocol (PPSP)
                 draft-ietf-ppsp-problem-statement-12.txt


Abstract

   Peer-to-Peer(P2P for short) streaming systems show more and more
   popularity in current Internet with proprietary protocols. This
   document identifies problems of the proprietary protocols, proposes
   the development of Peer to Peer Streaming Protocol(PPSP) including
   the Tracker and Peer protocol, and discusses the scope, requirements
   and use cases of PPSP.





























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Internet-Draft  Problem Statement and Requirements of PPSP      January 2013

Status of this Memo

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   This Internet-Draft will expire on July 31, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal Provisions
   Relating to IETF Documents (http://trustee.ietf.org/license-info)
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   and are provided without warranty as described in the Simplified
   BSD License.












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Internet-Draft  Problem Statement and Requirements of PPSP      January 2013

Table of Contents

   1. Introduction  ................................................ 4
      1.1. Background  ............................................. 4
      1.2. Requirements Language ................................... 4
   2. Terminology and concepts ..................................... 5
   3. Problem statement  ........................................... 7
      3.1. Heterogeneous P2P traffic and P2P cache deployment ...... 7
      3.2. QoS issue and CDN deployment ............................ 7
      3.3. Extended applicability in mobile and wireless environment 7
   4. Tasks of PPSP: Standard peer to peer streaming protocols...... 9
      4.1. Tasks and design issues of Tracker protocol ............ 10
      4.2. Tasks and design issues of Peer protocol ............... 11
   5. Use cases of PPSP  .......................................... 12
      5.1. Worldwide provision of live/VoD streaming .............. 12
      5.2. Enabling CDN for P2P VoD streaming ..................... 12
      5.3. Cross-screen streaming ................................. 14
      5.4. Cache service supporting P2P streaming ................. 15
      5.5. Proxy service supporting P2P streaming ................. 16
         5.5.1. Home networking scenario .......................... 16
         5.5.2. Browser-based HTTP streaming ...................... 17
   6. Requirements of PPSP ........................................ 17
      6.1. Basic Requirements ..................................... 17
      6.2. Operation & Management Requirements .................... 18
      6.3. PPSP Tracker Protocol Requirements ..................... 19
      6.4. PPSP Peer Protocol Requirements ........................ 20
   7. Security Considerations ..................................... 21
   8. IANA Considerations  ........................................ 22
   9. Acknowledgments  ............................................ 22
   10. References  ................................................ 23
      10.1. Normative References .................................. 23
      10.2. Informative References ................................ 24

















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1. Introduction

  1.1. Background

   Streaming traffic is among the largest and fastest growing traffic
   on the Internet [Cisco], where peer-to-peer (P2P) streaming
   contributes substantially. With the advantage of high scalability
   and fault tolerance against single point of failure, P2P streaming
   applications are able to distribute large-scale, live and video on
   demand (VoD) streaming programs to a large audience with only a
   handful of servers. What's more, along with the players like CDN
   providers joining in the effort of using P2P technologies in
   distributing their serving streaming content, there are more and
   more various players in P2P streaming ecosystem.

   Given the increasing integration of P2P streaming into the global
   content delivery infrastructure, the lack of an open, standard P2P
   streaming signaling protocol suite becomes a major missing component.
   Almost all of existing systems use their proprietary protocols.
   Multiple, similar but proprietary protocols result in repetitious
   development efforts for new systems, and the lock-in effects lead to
   substantial difficulties in their integration with other players
   like CDN. For example, in the enhancement of existing caches and CDN
   systems to support P2P streaming, proprietary protocols may increase
   the complexity of the interaction with different P2P streaming
   applications.

   In this document we propose the development of an open P2P Streaming
   Protocol, which is abbreviated as PPSP, to standardize signaling
   operations in P2P streaming systems to solve the above problems.

  1.2. Requirements Language

   The key words "MUST" and "MUST NOT" in this document are to be
   interpreted as described in RFC 2119 [RFC2119] and indicate
   requirement levels for compliant implementations.













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2. Terminology and concepts

   CHUNK: A CHUNK is a basic unit of data organized in P2P streaming
   for storage, scheduling, advertisement and exchange among peers
   [VoD]. A CHUNK size varies from several KBs to several MBs in
   different systems. In case of MBs size CHUNK scenario, a sub-CHUNK
   structure named piece is often defined to fit in a single
   transmitted packet. A streaming system may use different
   granularities for different usage, e.g., using CHUNKs during data
   exchange, and using a larger unit such as a set of CHUNKs during
   advertisement.

   CHUNK ID: The identifier of a CHUNK in a content stream.

   CLIENT: A CLIENT refers to a participant in a P2P streaming system
   that only receives streaming content. In some cases, a node not
   having enough computing and storage capabilities will act as a
   CLIENT. Such node can be viewed as a specific type of PEER.

   CONTENT DISTRIBUTION NETWORK (CDN): A CDN is a collection of nodes
   that are deployed, in general, at the network edge like Points of
   Presence (POP) or Data Centers (DC) and that store content provided
   by the original content servers. Typically, CDN nodes serve content
   to the users located nearby topologically.

   LIVE STREAMING: It refers to a scenario where all the audiences
   receive streaming content for the same ongoing event. It is desired
   that the lags between the play points of the audiences and 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,
   streams content to other PEERs.

   PEER: A PEER refers to a participant in a P2P streaming system that
   not only receives streaming content, but also caches and streams
   streaming content to other participants.

   PEER LIST: A list of PEERs which are in a same SWARM maintained by
   the TRACKER.  A PEER can fetch the PEER LIST of a SWARM from the
   TRACKER or from other PEERs in order to know which PEERs have the
   required streaming content.

   PEER ID: The identifier of a PEER such that other PEERs, or the
   TRACKER, can refer to the PEER by using its ID.





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   PPSP: The abbreviation of Peer-to-Peer Streaming Protocols. PPSP
   refer to the primary signaling protocols among various P2P streaming
   system components, including the TRACKER and the PEER.

   TRACKER: A TRACKER refers to a directory service that maintains a
   list of PEERs participating in a specific audio/video channel or in
   the distribution of a streaming file. Also, the TRACKER answers PEER
   LIST queries received from PEERs. The TRACKER is a logical component
   which can be centralized or distributed.

   VIDEO-ON-DEMAND (VoD): It refers to a scenario where different
   audiences may watch different parts of the same recorded streaming
   with downloaded content.

   SWARM: A SWARM refers to a group of PEERs who exchange data to
   distribute CHUNKs of the same content (e.g. video/audio program,
   digital file, etc) at a given time.

   SWARM ID: The identifier of a SWARM containing a group of PEERs
   sharing a common streaming content.

   SUPER-NODE: A SUPER-NODE is a special kind of PEER deployed by ISPs.
   This kind of PEER is more stable with higher computing, storage and
   bandwidth capabilities than normal PEERs.

























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3. Problem statement

   The problems caused by proprietary protocols for P2P streaming
   applications are listed as follows.

  3.1. Heterogeneous P2P traffic and P2P cache deployment


   ISPs are faced with different P2P streaming application introducing
   substantial traffic into their infrastructure, including their
   backbone and their exchange/interconnection points. P2P caches are
   used by ISPs in order to locally store content and hence reduce the
   P2P traffic. P2P caches usually operate at the chunk or file
   granularity.

   However, unlike web traffic that is represented by HTTP requests and
   responses and therefore allows any caching device to be served (as
   long as it supports HTTP), P2P traffic is originated by multiple P2P
   applications which require the ISPs to deploy different type of
   caches for the different types of P2P streams.

   This increases both engineering and operational costs dramatically.

  3.2. QoS issue and CDN deployment

   P2P streaming is often criticized due to its worse QoS performance
   compared to client/server streaming (e.g., longer startup delay,
   longer seek delay and channel switch delay). Hybrid CDN/P2P is a
   good approach in order to address this problem [Hybrid CDN P2P].

   In order to form the hybrid P2P/CDN architecture, the CDN must be
   aware of the specific P2P streaming protocol in the collaboration.
   Similarly to what is described in section 3.1, proprietary P2P
   protocols introduce complexity and deployment cost of CDN.

  3.3. Extended applicability in mobile and wireless environment

   Mobility and wireless are becoming increasingly important in today's
   Internet, where streaming service is a major usage. It's reported
   that the average volume of video traffic on mobile networks has
   risen up to 50% in the early of 2012 [ByteMobile]. There are
   multiple prior studies exploring P2P streaming in mobile and
   wireless networks [Mobile Streaming1] [Mobile Streaming2].


   However it's difficult to directly apply current P2P streaming
   protocols (even assuming we can re-use some of the proprietary ones)
   in mobile and wireless networks.


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   Following are some illustrative problems:
   First, P2P streaming assumes a stable Internet connection in
   downlink and uplink direction, with decent capacity and peers that
   can run for hours. This isn't the typical setting for mobile
   terminals. Usually the connections are unstable and expensive in
   terms of energy consumption and transmission (especially in uplink
   direction). To enable mobile/wireless P2P streaming feasible,
   trackers may need more information on peers like packet loss rate,
   peer battery status and processing capability during peer selection
   compared to fixed peers. Unfortunately current protocols don't
   convey this kind of information.

   Second, current practices often use a "bitmap" message in order to
   exchange chunk availability. The message is of kilobytes in size and
   exchanged frequently, e.g., an interval of several seconds or less.
   In a mobile environment with scarce bandwidth, the message size may
   need to be shortened or it may require more efficient methods for
   expressing and distributing chunk availability information, which is
   different from wire-line P2P streaming.

   Third, for a resource constraint peer like mobile handsets or set-
   top boxes (STB), there are severe contentions on limited resource
   when using proprietary protocols. The terminal has to install
   different streaming client software for different usages, e.g., some
   for movies and others for sports. Each of these applications will
   compete for the same set of resources even when it is sometimes
   running in background mode. PPSP can alleviate this problem with the
   basic idea that the "one common client software with PPSP and
   different scheduling plug-ins" is better than "different client
   software running at the same time" in memory and disk consumption.



















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4. Tasks of PPSP: Standard peer to peer streaming protocols

   PPSP is targeted to standardize signaling protocols to solve the
   above problems that support either live or VoD streaming.
   PPSP supports both centralized tracker and distributed trackers. In
   distributed trackers, the tracker functionality is distributed in
   decentralized peers. In the following part of this section, the
   tracker is a logic conception, which can be implemented in a
   dedicated tracker server or in peers.

   The PPSP design includes a signaling protocol between trackers and
   peers (the PPSP "Tracker protocol") and a signaling protocol among
   the peers (the PPSP "Peer protocol") as shown in Figure 1. The two
   protocols enable peers to receive streaming content within the time
   constraints.

   PPSP design in general needs to solve the following challenges,
   e.g.,:

   1) When joining a swarm, how does a peer know which peers it should
   contact for content?

   2) After knowing a set of peers, how does a peer contact with these
   peers? in which manner?

   3) How to choose peers with better service capabilities, and how to
   collect such information from peers?

   4) How to improve the efficiency of the communication, e.g. compact
   on-the-wire message format and suitable underlying transport
   mechanism (UDP or TCP)?

   5) How to improve the robustness of the system using PPSP, e.g. when
   the tracker fails? How to make the tracker protocol and the peer
   protocol loose coupled?














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             +------------------------------------------------+
             |                                                |
             |     +--------------------------------+         |
             |     |            Tracker             |         |
             |     +--------------------------------+         |
             |        |     ^                   ^             |
             |Tracker |     | Tracker           |Tracker      |
             |Protocol|     | Protocol          |Protocol     |
             |        |     |                   |             |
             |        V     |                   |             |
             |     +---------+    Peer     +---------+        |
             |     |   Peer  |<----------->|   Peer  |        |
             |     +---------+   Protocol  +---------+        |
             |       | ^                                      |
             |       | |Peer                                  |
             |       | |Protocol                              |
             |       V |                                      |
             |     +---------------+                          |
             |     |      Peer     |                          |
             |     +---------------+                          |
             |                                                |
             |                                                |
             +------------------------------------------------+
                     Figure 1 PPSP System Architecture

  4.1. Tasks and design issues of Tracker protocol

   The tracker protocol handles the initial and periodic exchange of
   meta-information between trackers and peers, such as peer list and
   content information.

   Therefore tracker protocol is best modeled as a request/response
   protocol between peers and trackers, and will carry information
   needed for the selection of peers suitable for real-time/VoD
   streaming.

   Special tasks for the design of the tracker protocol are listed as
   follows. This is a high-level task-list. The detailed requirements
   on the design of the tracker protocol are explicated in section 6.

   1) How should a peer be globally identified? This is related to the
   peer ID definition, but irrelevant to how the peer ID is generated.

   2) How to identify different peers, e.g. peers with public or
   private IP address, peers behind or not behind NAT, peers with IPV4
   or IPV6 addresses, peers with different property?




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   3) The tracker protocol must be light-weight, since a tracker may
   need to server large amount of peers. This is related to the
   encoding issue(e.g., Binary based or Text based) and keep-alive
   mechanism.

   4) How can the tracker be able to report optimized peer list to
   serve a particular content? This is related to status statistic,
   with which the tracker can be aware of peer status and content
   status.

   PPSP tracker protocol will consider all these issues in the design
   according to the requirements from both peer and tracker perspective
   and also taking into consideration deployment and operation
   perspectives.

  4.2. Tasks and design issues of Peer protocol

   The peer protocol controls the advertising and exchange of content
   between the peers.

   Therefore peer protocol is modeled as a gossip-like protocol with
   periodic exchanges of neighbor and chunk availability information.

   Special tasks for the design of the peer protocol are listed as
   follows. This is a high-level task-list. The detailed requirements
   on the design of the peer protocol are explicated in section 6.

   1) How does the certain content be globally identified and verified?
   Since the content can be retrieved from everywhere, how to ensure
   the exchanged content between the peers is authentic?

   2) How to identify the chunk availability in the certain content?
   This is related to the chunk addressing and chunk state maintenance.
   Considering the large amount of chunks in the certain content,
   light-weight expression is necessary.

   3) How to ensure the peer protocol efficiency? As we mentioned in
   section 3, the chunk availability information exchange is quite
   frequent. How to balance the information exchange size and amount is
   a big challenge. What kind of encoding and underlying transport
   mechanism (UDP or TCP) is used in the messages?

   PPSP peer protocol will consider all the above issues in the design
   according to the requirements from the peer perspective.






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5. Use cases of PPSP

   This section is not the to-do list for the WG, but for the
   explanatory effect to show how PPSP could be used in practice.

  5.1. Worldwide provision of live/VoD streaming

   The content provider can increase live streaming coverage by
   introducing PPSP in between different providers. This is quite
   similar to the case described in CDNI [RFC6707][RFC6770].

   We suppose a scenario that there is only provider A (e.g,, in China)
   providing the live streaming service in provider B (e.g., in USA) and
   C(e.g., in Europe)'s coverage. Without PPSP, when a user (e.g., a
   Chinese American) in USA requests the program to the tracker (which
   is located in A's coverage), the tracker may generally return to the
   user with a peer list including most of peers in China, because
   generally most users are in China and there are only few users in
   USA. This may affect the user experience.

   But if we can use the PPSP tracker protocol to involve B and C in
   the cooperative provision, as shown in Figure 2, even when the
   streaming is not hot to attract many users in USA and Europe to view,
   the tracker in A can optimally return the user with a peer list
   including B's Super-nodes (SN for short) and C's SN to provide a
   better user performance.

   Furthermore User@B and User@C can exchange data (availability) with
   these local SNs using the peer protocol.

  5.2. Enabling CDN for P2P VoD streaming

   Figure 3 shows the case of enabling CDN to support P2P VoD streaming
   from different content providers by introducing PPSP inside CDN
   overlays. It is similar to Figure 2 except that the intermediate SNs
   are replaced by 3rd party CDN surrogates. The CDN nodes talk with
   the different streaming systems (including trackers and peers)with
   the same PPSP protocols.

   Furthermore the interaction between the CDN nodes can be executed by
   either existing (maybe proprietary) protocols or the PPSP Peer
   protocol. The Peer protocol is useful for building new CDN systems
   (e.g., operator CDN) supporting streaming in a low cost.

   Note that for compatibility reason both HTTP streaming and P2P
   streaming can be supported by CDN from the users' perspective.




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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   |
   | Protocol|                |              |               |protocol|
   |         |                |              |                |       |
   |         |                |              |                |       |
   |         |                |              |                |       |
   |         v                v              v                v       |
   |      +------+ Peer    +------+    +---------+  Peer   +---------+|
   |      | A's  |<------> | B's  |    |A's      |<------> |C's      ||
   |      | User1|Protocol | User2|    | User1   |Protocol | User2   ||
   |      +------+         +------+    +---------+         +---------+|
   |                                                                  |
   +------------------------------------------------------------------+
                 Figure 2 Cooperative Vendors Interaction


















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   +------------------------------------------------------------------+
   |                                                                  |
   |                   +-------------+    +--------------+            |
   |            +----->| A's Tracker |    |  B's Tracker |<---+       |
   |            |      +-------------+    +--------------+    |       |
   |     Tracker|              ^  ^        ^    ^             |       |
   |    Protocol|       Tracker|  |Tracker |    |Tracker      |Tracker|
   |            |      Protocol|  |Protocol|    |Protocol    |Protocol|
   |            |              |  |        |    |             |       |
   |            |              |  |        |    |             |       |
   |            v              v  |        |    v             v       |
   |      +------+ Peer   +------+|        |  +------+Internal+------+|
   |      | CDN  |<------>| CDN  ||        |  | CDN  |<-----> | CDN  ||
   |      | Node1|Protocol| Node2||        |  | Node3|Protocol| Node4||
   |      +------+        +------+|        |  +------+        +------+|
   |         ^  ^                 |        |        ^         ^       |
   |         |  |                 |        |        |         |       |
   |         |  | Peer Protocol   |        |   HTTP |         |       |
   | Peer    |  +-------------+   |        | +------+         | Peer  |
   | Procotol|                |   |        | | Protocol      |protocol|
   |         |                | +-+        | |                |       |
   |         |                | |          | |                |       |
   |         |                | |          | |                |       |
   |         v                v v          v v                v       |
   |      +------+ Peer    +------+    +---------+  Peer   +---------+|
   |      | A's  |<------> | A's  |    |B's      |<------> |B's      ||
   |      | User1|Protocol | User2|    | User3   |Protocol | User4   ||
   |      +------+         +------+    +---------+         +---------+|
   |                                                                  |
   +------------------------------------------------------------------+
                   Figure 3 CDN Supporting P2P Streaming



  5.3. Cross-screen streaming

   In this scenario PC, STB/TV and mobile terminals from both fixed
   network and mobile/wireless network share the streaming content.
   With PPSP, peers can identify the types of access networks, average
   load, peer abilities and get to know what content other peers have
   even in different networks( potentially with the conversion of the
   content availability expression in different networks) as shown in
   Figure 4.

   Such information will play an important role on selecting suitable
   peers, e.g., a PC or STB is more likely to provide stable content
   and a mobile peer within a high-load cell is unlikely to be selected,
   which may otherwise lead to higher load on the base station.


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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 with PPSP

  5.4. Cache service supporting P2P streaming

   In Figure 5, when peers request the P2P streaming data, the cache
   nodes intercept the requests and ask for the frequently visited
   content (or part of) on behalf of the peers. To do this, it asks the
   tracker for the peer list and the tracker replies with external
   peers in the peer list. After the cache nodes exchange data with
   these peers, it can also act as a peer and report what it caches to
   the tracker and serve inside requesting peers afterward. This
   operation greatly decreases the inter-network traffic in many
   conditions and increases user experience.

   The cache nodes do not need to update their library when new
   applications supporting PPSP are introduced, which reduces the cost.












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   +----------------------------------------------------------------+
   |                                                                |
   |    Tracker Protocol +---------+                                |
   |  +----------------> | Tracker |                                |
   |  |                  +---------+                                |
   |  |                       ^                                     |
   |  |                       |                                     |
   |  |                       | Tracker Protocol                    |
   |  |                       |                                     |
   |  |                       |                                     |
   |  |             +---------|-------------------------------------|
   |  |             |         V                                     |
   |  |             |     +---------+                               |
   |  |  +----------|---> | Cache   |<-------------------+          |
   |  |  |          |     +---------+        Tracker/Peer|          |
   |  |  | Peer     |                          Protocol  |          |
   |  |  | Protocol |                                    |          |
   |  |  |          |                                    |          |
   |  |  |          |                                    |          |
   |  V  V          |                                    V          |
   |  +-----------+ |        ISP Domain             +------------+  |
   |  |  External | |                               |   Inside   |  |
   |  |  Peer     | |                               |   Peer     |  |
   |  +-----------+ |                               +------------+  |
   +----------------------------------------------------------------+
           Figure 5 Cache Service Supporting Streaming with PPSP

  5.5. Proxy service supporting P2P streaming

5.5.1. Home networking scenario

   For applications where the peer is not co-located with the Media
   Player in the same device (e.g. the peer is located in a Home Media
   Gateway), we can use a PPSP Proxy, as shown in figure 6.

   As shown in figure 6, the PPSP Proxy terminates both the tracker and
   peer protocol allowing the legacy presentation devices to access P2P
   streaming content. In figure 6 the DLNA protocol [DLNA] is used in
   order to communicate with the presentation devices thanks to its
   wide deployment. Obviously, other protocols can also be used.









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      +---------------------------------------------------------------+
      |                                                               |
      |    Tracker Protocol +--------+                                |
      |  +----------------> | Tracker|                                |
      |  |                  +--------+                                |
      |  |                       ^                                    |
      |  |                       |                                    |
      |  |                       | Tracker Protocol                   |
      |  |                       |                                    |
      |  |             +---------|------------------------------------|
      |  |             |         V                                    |
      |  |             |     +---------+                              |
      |  |  +----------|---> |  PPSP   |<-------------------+         |
      |  |  |          |     |  Proxy  |       DLNA         |         |
      |  |  | Peer     |     +---------+      Protocol      |         |
      |  |  | Protocol|                                     |         |
      |  |  |          |                                    |         |
      |  V  V          |                                    V         |
      |  +-----------+ |        Home Domain            +-----------+  |
      |  |  External | |                               |DLNA  Pres.|  |
      |  |  Peer     | |                               |Devices    |  |
      |  +-----------+ |                               +-----------+  |
      +---------------------------------------------------------------+
              Figure 6 Proxy service Supporting P2P Streaming

5.5.2. Browser-based HTTP streaming

   P2P Plug-ins are often used in browser-based environment in order to
   stream content. With P2P plug-ins, HTTP streaming can be turned into
   a de facto P2P streaming. From the browser (and hence the user)
   perspective, it's just HTTP based streaming but the PPSP capable
   plug-in can actually accelerate the process by leveraging streams
   from multiple sources/peers [P2PYoutube]. In this case the plug-ins
   behave just like the proxy.

6. Requirements of PPSP

   This section enumerates the requirements that should be considered
   when designing PPSP.

  6.1. Basic Requirements

   PPSP.REQ-1: Each peer MUST have a unique ID (i.e., peer ID).

     It's a basic requirement for a peer to be uniquely identified
     in a P2P streaming system so that other peers or tracker can refer to
     the peer by ID.



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     Note that a peer can join multiple swarms with a unique ID, or
     change swarm without changing its ID.

   PPSP.REQ-2: The streaming content MUST be uniquely identified by a
   swarm ID.

     A swarm refers to a group of peers sharing the same streaming
     content. A swarm ID uniquely identifies a swarm. The swarm ID can
     be used in two cases: 1) a peer requests the tracker for the peer
     list indexed by a swarm ID; 2) a peer tells the tracker about the
     swarms it belongs to.

   PPSP.REQ-3: The streaming content MUST be partitioned into chunks.

   PPSP.REQ-4: Each chunk MUST have a unique ID (i.e., chunk ID) in the
   swarm.

     Each chunk must have a unique ID in the swarm so that the peer can
     understand which chunks are stored in which peers and which chunks
     are requested by other peers.

  6.2. Operation & Management Requirements

   PPSP.OAM.REQ-1: PPSP protocols MUST provide adequate mechanisms for
   operation & management, as outlined in RFC5706 [RFC5706].

   PPSP.OAM.REQ-2: PPSP protocols MUST be sufficiently configurable.

     For example, a set of configuration parameters with default values
     should be defined to allow for operator specification.

   PPSP.OAM.REQ-3: PPSP protocols MUST support diagnostic operations.

     Protocol designers need to consider how to verify the effect of the
     protocol including the impact on the network, device status, and
     other management information.

   PPSP.OAM.REQ-4: PPSP protocols MUST facilitate achieving QoS
   acceptable to both live and VoD streaming application.

     There are basic QoS requirements for streaming systems. Setup time
     to receive a new streaming channel or to switch between channels
     should be reasonably small. End to end delay, which consists of the
     time between content generation (e.g., a camera) and content
     consumption (e.g., a monitor), will become critical in case of live
     streaming especially in provisioning of sport events where end to
     end delay of one minute and more are not acceptable.



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     For instance, the tracker and peer protocol can carry QoS related
     parameters (e.g. video quality and delay requirements) together
     with the priorities of these parameters in addition to the measured
     QoS situation (e.g., performance, available uplink bandwidth) of
     content providing peers.

   PPSP.OAM.REQ-5: PPSP protocols MUST be extensible to support
   algorithms required for scalable streaming.

   PPSP.OAM.REQ-6: PPSP MUST support operation mode where peer is in
   streaming consumer or third-party entity like proxy.

   PPSP.OAM.REQ-7: PPSP MUST support version numbering or similar
   mechanism for compatibility.

   PPSP.OAM.REQ-8: PPSP MUST support peers behind NATs with other peers
   on good connectivity.

  6.3. PPSP Tracker Protocol Requirements

   PPSP.TP.REQ-1: The tracker protocol MUST allow the peer to solicit
   a peer list in a swarm generated and possibly tailored by the
   tracker in a query and response manner.

     The tracker request message may include the requesting peer's
     preference parameter (e.g. preferred number of peers in the peer
     list) or preferred downloading bandwidth. The tracker will then be
     able to select an appropriate set of peers for the requesting peer
     according to the preference.

     The tracker may also generate the peer list with the help of
     traffic optimization services, e.g. ALTO [I-D.ietf-alto-protocol].

   PPSP.TP.REQ-2: The tracker protocol MUST report the peer's activity
   in the swarm to the tracker.

   PPSP.TP.REQ-3: The tracker protocol MUST take the frequency of
   messages and efficient use of bandwidth into consideration, when
   communicating chunk availability information.

     For example, the chunk availability information between peer and
     tracker can be presented in a compact method, e.g., to express a
     sequence of continuous "1" more efficiently.

   PPSP.TP.REQ-4: The tracker protocol MUST have a provision for
   tracker to authenticate the peer.




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     This ensures that only the authenticated users can access the
     original content in the P2P streaming system.

   PPSP.TP.REQ-5: PPSP tracker MUST be robust.

     When centralized tracker fails, the P2P streaming system should
     still work by supporting distributed trackers.

  6.4. PPSP Peer Protocol Requirements

   PPSP.PP.REQ-1: The peer protocol MUST allow the peer to solicit the
   chunk information from other peers in a query and response manner.

   PPSP.PP.REQ-2: The chunk information exchanged between a pair of
   peers MUST NOT be passed to other peers, unless the chunk
   information is validated (e.g. preventing hearsay and DoS attack).

   PPSP.PP.REQ-3: The peer protocol MUST allow the peer to solicit an
   additional list of peers to that received from the tracker.

     It is possible that a peer may need additional peers for certain
     streaming content. Therefore, it is allowed that the peer
     communicates with other peers in the current peer list to obtain an
     additional list of peers in the same swarm.

   PPSP.PP.REQ-4: When used for soliciting additional list of peers,
   the peer protocol MUST contain swarm-membership information of the
   peers that have explicitly indicated they are part of the swarm,
   verifiable by the receiver.

   PPSP.PP.REQ-5: The additional list of peers MUST only contain peers
   which have been checked to be valid and online recently (e.g.,
   preventing hearsay and DoS attack).

   PPSP.PP.REQ-6: The peer protocol MUST report the peer's chunk
   availability update.

     Due to the dynamic change of the buffered streaming content in each
     peer and the frequent join/leave of peers in the swarm, the
     streaming content availability among a peer's neighbors (i.e., the
     peers known to a peer by getting the peer list from either tracker
     or peers) always changes and thus requires being updated on time.
     This update should be done at least on demand. For example, when a
     peer requires finding more peers with certain chunks, it sends a
     message to some other peers in the swarm for streaming content
     availability update. Alternatively, each peer in the swarm can
     advertise its streaming content availability to some other peers
     periodically. However, the detailed mechanisms for this update such


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     as how far to spread the update message, how often to send this
     update message, etc. should leave to the algorithms, rather than
     protocol concerns.

   PPSP.PP.REQ-7: The peer protocol MUST take the frequency of messages
   and efficient use of bandwidth into consideration, when
   communicating chunk information.

     For example, the chunk availability information between peers can
     be presented in a compact method.

   PPSP.PP.REQ-8: The peer protocol MUST exchange additional
   information, e.g., status about the peers.

     This information can be, for instance, information about the access
     link or information about whether a peer is running on battery or
     is connected to a power supply. With such information, a peer can
     select more appropriate peers for streaming.

7. Security Considerations

   This document discusses the problem statement and requirements
   around P2P streaming protocols without specifying the protocols.
   However we believe it is important for the reader to understand
   areas of security introduced by the P2P nature of the proposed
   solution. The main issue is the usage of un-trusted entities (peers)
   for service provisioning. For example, malicious peers/trackers may:

     - Originate denial of service (DOS) attacks to the trackers by
       sending large amount of requests with the tracker protocol;

     - Originate fake information on behalf of other peers;

     - Originate fake information about chunk availability;

     - Originate reply instead of the regular tracker (man in the middle
       attack);

     - leak private information about other peers or trackers.

   We list some important security requirements for PPSP protocols as
   below:

   PPSP.SEC.REQ-1: PPSP MUST support closed swarms, where the peers are
   authenticated or in a private network.

     This ensures that only the trusted peers can access the original
     content in the P2P streaming system. This can be achieved by


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     security mechanisms such as peer authentication and/or key
     management scheme.

     Another aspect is that confidentiality of the streaming content in
     PPSP need to be supported. In order to achieve this, PPSP should
     provide mechanisms to encrypt the data exchange among the peers.

   PPSP.SEC.REQ-2: Integrity of the streaming content in PPSP MUST be
   supported to provide a peer with the possibility to identify
   unauthentic content (undesirable modified by other entities rather
   than its genuine source).

     In a P2P live streaming system a polluter can introduce corrupted
     chunks. Each receiver integrates into its playback stream the
     polluted chunks it receives from its neighbors. Since the peers
     forwards chunks to other peers, the polluted content can
     potentially spread through the P2P streaming network.

     The PPSP protocol specifications will document the expected
     threats(and how they will be mitigated by each protocol) and also
     considerations on threats and mitigations when combining both
     protocols in an application. This will include privacy of the users
     and protection of the content distribution.

   PPSP.SEC.REQ-3: The security mechanisms in PPSP, such as key
   management and checksum distribution MUST scale well in P2P
   streaming systems.

8. IANA Considerations

   This document has no actions for IANA.

9. Acknowledgments

   Thank you to J.Seng, G. Camarillo, R. Yang,C. Schmidt, R. Cruz, Y.
   Gu, A.Bakker and S. Previdi for contribution to many sections of this
   draft. Thank you to C. Williams,V. Pascual and L. Xiao for
   contributions to PPSP requirements section.

   We would like to acknowledge the following people who provided
   review, feedback and suggestions to this document: M. Stiemerling, D.
   Bryan, E. Marocco, V. Gurbani, R. Even, H. Zhang, D. Zhang, J.
   Lei, H.Song, X.Jiang, J.Seedorf, D.Saumitra, A.Rahman, J.Pouwelse,
   W.Eddy, B. Claise, D. Harrington, J. Arkko and all the AD reviewers.

   This document was prepared using 2-Word-v2.0.template.dot.




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10. References

  10.1. Normative References

   [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6707]B. Niven-Jenkins, "Content Distribution Network
   Interconnection (CDNI) Problem Statement", RFC 6707, Sep 2012.

   [RFC6770] G. Bertrand, "Use Cases for Content Delivery Network
   Interconnection", RFC6770, Nov 2012.

   [RFC5706] D. Harrington, "Guidelines for Considering Operations
   and Management of New Protocols and Protocol Extensions", RFC5706,
   Nov 2009.
































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  10.2. Informative References

   [Cisco] Cisco Visual Networking Index: Forecast and Methodology,
   2009-2014,
   http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns
   705/ns827/white_paper_c11-
   481360_ns827_Networking_Solutions_White_Paper.html

   [VoD] Y. Huang et al,Challenges,"Design and Analysis of a Large-
   scale P2P-VoD System", Sigcomm08.

   [ByteMobile]http://www.bytemobile.com/news-
   events/2012/archive_230212.html

   [Mobile Streaming1] Streaming to Mobile Users in a Peer-to-Peer
   Network,J. Noh etal,MOBIMEDIA '09.

   [Mobile Streaming2] J.Peltotaloetal.,"A real-time Peer-to-Peer
   streaming system for mobile networking environment",in Proceedings
   of the INFOCOM and Workshop on Mobile Video Delivery (MoVID '09).

   [Hybrid CDN P2P]D. Xu et al, "Analysis of a CDN-P2Phybrid
   architecture for cost-effective streaming mediadistribution,"
   SpringerMultimediaSystems, vol.11, no.4, pp.383-399, 2006.

   [PPTV] http://www.pptv.com

   [PPStream] http://www.ppstream.com

   [DLNA] http://www.dlna.org

   [P2PYoutube] https://addons.opera.com/en/extensions/details/p2p-
   youtube/
















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Authors' Addresses

   Yunfei Zhang
   China Mobile Communication Corporation
   zhangyunfei@chinamobile.com

   Ning Zong
   Huawei
   zongning@huawei.com








































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