PPSP
Internet Engineering Task Force (IETF)                          Y. Zhang
Internet-Draft                                              Unaffiliated
Intended status:
Request for Comments: 6972                                       Coolpad
Category: Informational                                          N. Zong
Expires: November 15, 2013
ISSN: 2070-1721                                      Huawei Technologies
                                                            May 14,
                                                               June 2013

    Problem Statement and Requirements of the Peer-to-Peer Streaming
                            Protocol (PPSP)
                  draft-ietf-ppsp-problem-statement-15

Abstract

   Peer-to-Peer(P2P for short)

   Peer-to-Peer (P2P) streaming systems show becoming more and more
   popularity in current Internet with popular
   on on the Internet, and most of them are using proprietary protocols.
   This document identifies problems of the associated with proprietary protocols,
   protocols; proposes the development of Peer to Peer the Peer-to-Peer Streaming Protocol(PPSP) including
   Protocol (PPSP), which includes the tracker and peer protocol, protocols; and
   discusses the scope, requirements requirements, and use cases of PPSP.

Status of This Memo

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   This Internet-Draft will expire on November 15, 2013.
   http://www.rfc-editor.org/info/rfc6972.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2 .  3
     1.1.  Backgrounds  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Terminology and concepts Concepts . . . . . . . . . . . . . . . . . . .  3
   3.  Problem statement Statement  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Heterogeneous P2P traffic Traffic and P2P cache deployment Cache Deployment . . . .  5
     3.2.  QoS issue Issue and CDN deployment Deployment . . . . . . . . . . . . . . .  5
     3.3.  Extended applicability Applicability in mobile Mobile and wireless environment   5 Wireless
           Environments . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Tasks of PPSP: Standard peer to peer streaming protocols Peer-to-Peer Streaming Protocols . .   6 .  7
     4.1.  Tasks and design issues Design Issues of the Tracker protocol . . Protocol  . . . . .  8
     4.2.  Tasks and design issues Design Issues of the Peer protocol  . Protocol . . . . . . .   8  9
   5.  Use cases Cases of PPSP  . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Worldwide provision Provision of live/VoD streaming Live/VoD Streaming  . . . . . . . .  9
     5.2.  Enabling CDN for P2P VoD streaming Streaming . . . . . . . . . . . . 10
     5.3.  Cross-screen streaming  Cross-Screen Streaming . . . . . . . . . . . . . . . . . . 11
     5.4.  Cache service supporting Service Supporting P2P streaming Streaming . . . . . . . . . . 12
     5.5.  Proxy service supporting Service Supporting P2P streaming Streaming . . . . . . . . . . 13
       5.5.1.  Home Networking Scenario . . . . . . . . . . . . . . . 13
       5.5.2.  Browser-based  Browser-Based HTTP Streaming . . . . . . . . . . . . . 14
   6.  Requirements of PPSP . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Basic Requirements . . . . . . . . . . . . . . . . . . .  14 . 15
     6.2.  Operation  Operational and Management Requirements  . . . . . . . . . . 15
       6.2.1.  Operation  Operational Considerations . . . . . . . . . . . . . . 15
       6.2.2.  Management Considerations  . . . . . . . . . . . . . . 16
     6.3.  PPSP Tracker Protocol Requirements . . . . . . . . . . . . 17
     6.4.  PPSP Peer Protocol Requirements  . . . . . . . . . . . . .  17 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   10.
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     10.1.
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     10.2.
     9.2.  Informative References . . . . . . . . . . . . . . . . .  21
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 21

1.  Introduction

1.1.  Backgrounds

   Streaming traffic is among the largest and fastest growing traffic on
   the Internet [Cisco], where peer-to-peer [Cisco].  Peer-to-Peer (P2P) streaming contributes
   substantially.
   substantially to this growth.  With the advantage of high scalability
   and fault tolerance against a single point of failure, P2P streaming
   applications are able to distribute large-scale, live live, and video on 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  More and more providers are joining in the effort of P2P
   streaming ecosystem, e.g., Content Distribution Networks (CDN)
   providers started using P2P technologies in distributing to distribute their
   serving
   streaming content, there are more and more various players in
   P2P streaming ecosystem. content.

   Given the increasing integration of P2P streaming into in the global
   content delivery infrastructure, the lack of there is a need for an open, open and
   standard P2P streaming signaling protocol suite becomes a major missing component. suite.  Almost all of existing
   systems use their proprietary protocols.
   Multiple, similar but  Having multiple proprietary
   protocols result that perform similar functions results in repetitious
   development efforts for new systems, and the lock-in effects lead to
   substantial difficulties in their integration difficulties with other players like
   CDN. (e.g., 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 interactions with different P2P streaming applications.

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

2.  Terminology and concepts Concepts

   CHUNK: A CHUNK is a basic unit of data organized in P2P streaming for
   storage, scheduling, advertisement advertisement, and exchange among peers [VoD].
   A CHUNK size varies from several KBs to several MBs in different
   systems.  In the case of MBs the MB 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, 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 a 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 edge, like Points of
   Presence (POP) or Data Centers (DC) (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 LIVE STREAMING 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 that are in a the 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.

   PPSP: The abbreviation of Peer-to-Peer Streaming Protocols.  PPSP

   PEER-TO-PEER STREAMING PROTOCOL (PPSP): PPSPs 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
   that can be centralized or distributed.

   VIDEO-ON-DEMAND

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

   SWARM: A SWARM refers to a group of PEERs who that exchange data to
   distribute CHUNKs of the same content (e.g. (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 storage, and
   bandwidth capabilities than normal PEERs.

3.  Problem statement Statement

   The problems caused by proprietary protocols for P2P streaming
   applications are listed as follows. described in this section.

3.1.  Heterogeneous P2P traffic Traffic and P2P cache deployment Cache Deployment

   ISPs are faced with different P2P streaming application applications 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 that 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 Issue and CDN deployment Deployment

   When compared to client/server streaming, P2P streaming is often
   criticized due to its worse poorer QoS performance
   compared to client/server streaming (e.g., longer startup
   delay, longer seek delay delay, and channel switch delay).  Hybrid CDN/P2P
   is a good approach in order to address this problem [Hybrid CDN P2P]. [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
   Similar to what is described in section Section 3.1, proprietary P2P
   protocols introduce complexity and the deployment cost of CDN.

3.3.  Extended applicability Applicability in mobile Mobile and wireless environment
   Mobility Wireless Environments

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

   However [Mobile-Streaming1]
   [Mobile-Streaming2].

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

   Following are some illustrative problems:

      First, P2P streaming assumes a stable Internet connection in
      downlink and uplink direction, directions, with decent capacity and peers
      that can run for hours.  This isn't the typical setting for mobile
      terminals.  Usually  Usually, the connections are unstable and expensive in
      terms of energy consumption and transmission (especially in uplink
      direction).  To enable make mobile/wireless P2P streaming feasible,
      trackers may need more information on peers like packet loss rate,
      peer battery status status, and processing capability during peer
      selection as compared to fixed peers.  Unfortunately  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 size is of kilobytes in size kilobytes and
      is 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 shortened, or it may require more efficient
      methods for expressing and distributing chunk availability chunk-availability
      information, which is different from wire-line wireline P2P streaming.

      Third, for a resource constraint peer resource-constrained peers, like mobile handsets or set-
      top
      set-top boxes (STB), there are severe contentions on multiple systems competing for
      severely limited resource resources 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
      resources, even when it one of the applications 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.

4.  Tasks of PPSP: Standard peer to peer streaming protocols Peer-to-Peer Streaming Protocols

   PPSP is targeted to standardize signaling protocols aims to solve the
   above problems mentioned above by standardizing
   signaling protocols that support either live or VoD streaming.  PPSP fPPSP
   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 conception that 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.
                +------------------------------------------------+
                |                                                |
                |     +--------------------------------+         |
                |     |            Tracker             |         |
                |     +--------------------------------+         |
                |        |     ^                   ^             |
                |Tracker |     | Tracker           |Tracker      |
                |Protocol|     | Protocol          |Protocol     |
                |        |     |                   |             |
                |        V     |                   |             |
                |     +---------+    Peer     +---------+        |
                |     |   Peer  |<----------->|   Peer  |        |
                |     +---------+   Protocol  +---------+        |
                |       | ^                                      |
                |       | |Peer                                  |
                |       | |Protocol                              |
                |       V |                                      |
                |     +---------------+                          |
                |     |      Peer     |                          |
                |     +---------------+                          |
                |                                                |
                |                                                |
                +------------------------------------------------+

                    Figure 1 1: PPSP System Architecture

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

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

      2) After knowing determining a set of peers, how does a peer make contact
      with these peers?  In which manner?
      3) How to choose peers with better service capabilities, capabilities and how to
      collect such information from peers?

      4) How to improve the efficiency of the communication, e.g. e.g., which
      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. e.g.,
      when the tracker fails?  How to make the tracker protocol and the
      peer protocol loose loosely coupled?

4.1.  Tasks and design issues Design Issues of the Tracker protocol Protocol

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

   Therefore

   Therefore, the 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.
   below.  This is a high-level task-list. task list.  The detailed requirements on
   the design of the tracker protocol are explicated in section Section 6.

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

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

      3) The tracker protocol must be light-weight, light weight, since a tracker may
      need to server serve a large amount number 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 an optimized peer list to serve a
      particular content. content?  This is related to the status statistic, with
      which the tracker can be aware of the peer status and content
      status.

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

4.2.  Tasks and design issues Design Issues of the Peer protocol Protocol

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

   Therefore

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

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

      1) How does the is 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 chunk-addressing and chunk state 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
      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?

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

5.  Use cases Cases of PPSP

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

5.1.  Worldwide provision Provision of live/VoD streaming 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 [RFC6707] [RFC6770].

   Let us assume a scenario that in which there is only provider A (e.g., in
   China) providing the live streaming service in provider B B's (e.g., in the
   USA) and
   C C's (e.g., in Europe)'s Europe) coverage.  Without PPSP, when a user(e.g. user
   (e.g., a Chinese American) in the 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 to the user including most of the peers in China,
   because generally most users are in China and there are only few
   users in the USA.  This may affect the user experience.  But  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
   does no attract many users in the USA and Europe to view, Europe, the tracker in A
   can optimally return the user with a peer list to the user including B's Super-nodes and C's
   Super-Nodes (SN for short) and C's SN to provide a better user performance.
   Furthermore User@B
   Furthermore, B's User2 and User@C C's User3 can exchange data (availability)
   with these local SNs using the peer protocol.
   +-------------------------------------------------------------------+
   |                                                                   |
   |                          +------------------+                     |
   |            +------------>| 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|                |Protocol|
   |         |                |              |                |        |
   |         |                |              |                |        |
   |         |                |              |                |        |
   |         v                v              v                v        |
   |      +------+ Peer    +------+    +---------+  Peer   +---------+ |
   |      | A's  |<------> | B's  |    |A's      |<------> |C's      | |
   |      | User1|Protocol | User2|    | User1   |Protocol | User2 User3   | |
   |      +------+         +------+    +---------+         +---------+ |
   |                                                                   |
   +-------------------------------------------------------------------+

                 Figure 2 2: Cooperative Vendors Interaction

5.2.  Enabling CDN for P2P VoD streaming Streaming

   Figure 3 shows the case an example of enabling CDN to support P2P VoD
   streaming from different content providers by introducing PPSP inside
   CDN overlays.  It is similar to Figure 2 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 using the same PPSP protocols.
   +-------------------------------------------------------------------+
   |                                                                   |
   |                   +-------------+    +--------------+             |
   |            +----->| 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       |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 3: CDN Supporting P2P Streaming

   Furthermore

   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 that support streaming in at a low cost.

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

5.3.  Cross-screen streaming  Cross-Screen Streaming

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

              Figure 4 4: Heterogeneous P2P Streaming with PPSP

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

5.4.  Cache service supporting Service Supporting P2P streaming 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
   enhances the user experience.

      +----------------------------------------------------------------+
      |                                                                |
      |    Tracker Protocol +---------+                                |
      |  +----------------> | Tracker |                                |
      |  |                  +---------+                                |
      |  |                       ^                                     |
      |  |                       |                                     |
      |  |                       | Tracker Protocol                    |
      |  |                       |                                     |
      |  |                       |                                     |
      |  |             +---------|-------------------------------------|
      |  |             |         V                                     |
      |  |             |     +---------+                               |
      |  |  +----------|---> | Cache   |<-------------------+          |
      |  |  |          |     +---------+        Tracker/Peer|          |
      |  |  | Peer     |                          Protocol  |          |
      |  |  | Protocol |                                    |          |
      |  |  |          |                                    |          |
      |  |  |          |                                    |          |
      |  V  V          |                                    V          |
      |  +-----------+ |        ISP Domain             +------------+  |
      |  |  External | |                               |   Inside   |  |
      |  |  Peer     | |                               |   Peer     |  |
      |  +-----------+ |                               +------------+  |
      +----------------------------------------------------------------+

          Figure 5 5: Cache Service Supporting Streaming with PPSP

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

5.5.  Proxy service supporting Service Supporting P2P streaming Streaming

5.5.1.  Home Networking Scenario

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

       +---------------------------------------------------------------+
       |                                                               |
       |    Tracker Protocol +--------+                                |
       |  +----------------> | Tracker|                                |
       |  |                  +--------+                                |
       |  |                       ^                                    |
       |  |                       |                                    |
       |  |                       | Tracker Protocol                   |
       |  |                       |                                    |
       |  |             +---------|------------------------------------|
       |  |             |         V                                    |
       |  |             |     +--------+                               |
       |  |  +----------|---> |  PPSP   |<------------------+          |
       |  |  |          |     |  Proxy  |       DLNA         |         |
       |  |  | Peer     |     +--------+       Protocol     |          |
       |  |  | Protocol|                                    |          |
       |  |  |          |                                    |         |
       |  V  V          |                                    V         |
       |  +-----------+ |        Home Domain            +-----------+  |
       |  |  External | |                               |DLNA  Pres.|  |
       |  |  Peer     | |                               |Devices    |  |
       |  +-----------+ |                               +-----------+  |
       +---------------------------------------------------------------+

             Figure 6 6: Proxy service Service Supporting P2P Streaming

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

5.5.2.  Browser-based  Browser-Based HTTP Streaming

   P2P Plug-ins are often used in browser-based environment in order browser-based environments 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 HTTP-based streaming, but the PPSP capable PPSP-capable plug-in can actually
   accelerate the process by leveraging streams from multiple sources/peers sources/
   peers [P2PYoutube].  In this case 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 trackers can refer to
      the peer by ID.

      Note that a peer can join multiple swarms with a unique ID, 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. (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  Operational and Management Requirements

   This section lists some operation operational and management requirements
   following based
   on the checklist presented by in Appendix A in of [RFC5706].

6.2.1.  Operation  Operational Considerations

   PPSP.OAM.REQ-1: PPSP MUST be sufficiently configurable.

      According to basic requirements, when setting up PPSP, a content
      provider should generate chunk IDs and a swarm ID for each streaming stream
      of content.  Original  An original content server and tracker are configured
      and
      setup.  Content set up.  The content provider then should then publish this information
      information, typically by creating web links.

      The configuration should allow the proxy-based and end-client
      scenarios.

   PPSP.OAM.REQ-2: PPSP MUST implement a set of configuration parameters
   with default values.

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

      Mechanisms must be supported by PPSP to verify correct operation.
      The PPSP tracker should collect the status of the peers including
      the peer's activity, whether it obtained chunks in time, etc.
      Such information can be used to monitor the streaming behavior of
      PPSP.

   PPSP.OAM.REQ-4: PPSP MUST facilitate achieving quality acceptable to
   the streaming application.

      There are basic quality requirements for streaming systems.  Setup  The
      setup time to receive a new streaming channel or to switch between
      channels should be reasonably small.  End to end  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 streaming, especially in provisioning of sport sporting
      events where end to end an end-to-end delay of 1 minute and or more are not
      acceptable.

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

      PPSP implementations may use techniques such as scalable streaming
      to handle bandwidth shortages without disrupting playback.

6.2.2.  Management Considerations

   PPSP.OAM.REQ-5: When management purpose needs objectives need to be supported in
   implementation,
   implementations, PPSP MUST support remote management using a standard
   interface, as well as a basic set of management information.

      Due to large-scale peer network, networks, PPSP tracker service or seeders
      should remotely collect information from peers and expose the
      information via a standard interface for management purpose. purposes.
      Peer information can be collected via a PPSP tracker protocol or
      peer protocol.

      The minimum set of management objects should include swarm
      information such as content characteristics, characteristics and rate limits, limits;
      tracking information such as swarm list, list and log events, events; and peer
      information such as peer activity, chunk statistics, and log
      event.

   PPSP.OAM.REQ-6: PPSP MUST support fault monitoring including peer and
   server health, as well as the streaming behavior of peers.

      Peer and server health will at least include node activity and
      connectivity
      connectivity, especially for peers behind NAT.  As mentioned in
      OAM.REQ-4,
      PPSP.OAM.REQ-4, streaming behavior of the peer can be learnt learned from
      chunk distribution information.

   PPSP.OAM.REQ-7: PPSP MUST support configuration management to define
   the configuration parameters.

      A set of configurable parameters related to chunk generation in
      the PPSP setup stage can be defined by content providers via a
      management interface to content servers.

   PPSP.OAM.REQ-8: PPSP MUST support performance management with respect
   to streaming performance based on chunk distribution statistics,
   network load, and tracker and peer monitoring.

   PPSP.OAM.REQ-9: PPSP MUST support security management.  See section Section 7
   of "Security Considerations" in this document.

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. (e.g., preferred number of peers in the
      peerlist) 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]. e.g., Application-Layer Traffic
      Optimization [ALTO].

   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
   message exchange and efficient use of bandwidth use into consideration, 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 the
   tracker to authenticate the peer.

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

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. (e.g., preventing hearsay and DoS attack). attacks).

   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 is allowed to communicate
      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 an 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,
   which is verifiable by the receiver.

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

   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. (i.e., the
      peers known to a peer by getting the peer list from either the
      tracker or peers) always changes 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 a
      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 update, such as how far to spread the update message, how
      often to send this update message, etc. etc., should leave be left to the
      algorithms, rather than protocol concerns.

   PPSP.PP.REQ-7: The peer protocol MUST take the frequency of messages message
   exchange and efficient use of bandwidth use into consideration, 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  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 untrusted entities (peers) for service
   provisioning.  For example, malicious peers/trackers may:

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

   o  Originate fake information on behalf of other peers;

   o  Originate fake information about chunk availability;

   o  Originate fake reply instead messages on behalf of the regular tracker (man in the middle
      attack);

      leak tracker;

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

      Another aspect is that confidentiality of the streaming content in
      PPSP need needs 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 of identifying
   unauthentic content (undesirable modified modifications by other entities
   rather than its genuine source).

      In a P2P live streaming system 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
      forward 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 distribution, MUST scale well in P2P
   streaming systems.

8.  IANA Considerations

   This document has no actions for IANA.

9.  Acknowledgements

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

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

10.

9.  References

10.1.

9.1.  Normative References

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

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, November 2009.

   [RFC6707] B.  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, Sep September 2012.

   [RFC6770] G.  Bertrand, G., Stephan, E., Burbridge, T., Eardley, P., Ma,
              K., and G. Watson, "Use Cases for Content Delivery Network
              Interconnection", RFC6770, Nov RFC 6770, November 2012.

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

10.2.

9.2.  Informative References

   [ALTO]     Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol", Work
              in Progress, December 2009.

   [ByteMobile]
              Bytemobile, "Mobile Video Traffic Hits Nearly 70% on
              Certain Networks", February 2012, <http://
              www.bytemobile.com/news-events/2012/archive_230212.html>.

   [CDN-P2P]  Xu, D., Kulkarni, S., Rosenberg, C., and H-K. Chai,
              "Analysis of a CDN-P2P Hybrid Architecture for
              Cost-Effective Streaming Media Distribution", Multimedia
              Systems , vol. 11, no. 4, pp. 383-399, 2006.

   [Cisco] Cisco    Cisco, "Cisco Visual Networking Index: Forecast and
              Methodology,
   2009-2014, http://www.cisco.com/en/US/solutions/collateral/ns341/ 2012 - 2017", Visual Networking Index (VNI) ,
              <http://www.cisco.com/en/US/solutions/collateral/ns341/
              ns525/ns537/ns705/ns827/
   white_paper_c11-481360_ns827_Networking_Solutions_White_Paper.html

   [VoD] Y.  Huang et al,Challenges,"Design
              white_paper_c11-
              481360_ns827_Networking_Solutions_White_Paper.html>.

   [DLNA]     "DLNA", <http://www.dlna.org>.

   [Mobile-Streaming1]
              Noh, J., Makar, M., 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 B. Girod, "Streaming To Mobile
              Users in a In A Peer-to-Peer
   Network,J.  Noh etal,MOBIMEDIA '09.

   [Mobile Streaming2] J.Peltotaloetal.,"A real-time Network", MOBIMEDIA , 2009.

   [Mobile-Streaming2]
              Peltotalo, J., Harju, J., Saukkoh, M., Vaatamoinen, L.,
              Bouazizi, I., Curcio, I., and J. van Gassel, "A Real-Time
              Peer-to-Peer
   streaming system Streaming System for mobile networking environment",in Mobile Networking
              Environment", Proceedings of the INFOCOM and Workshop on
              Mobile Video Delivery (MoVID '09).

   [Hybrid CDN P2P]D.  Xu et al, "Analysis '09) , 2009.

   [P2PYoutube]
              "Youtube Extension-Opera Add-Ons", Opera Software, <https:

              //addons.opera.com/en/extensions/details/p2p-youtube/>.

   [VoD]      Huang, Y., Fu, T., Chiu, D-M.,  Lui, J., and C. Huang,
              "Challenges, Design and 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/

   [I-D.ietf-alto-protocol] R.Alimi et al, "ALTO Protocol", draft-ietf-
   alto-protocol-13 (work in progress), Sep.  2012.

11.  References Large-Scale P2P-VoD
              System", SIGCOMM , 2008.

Authors' Addresses

   Yunfei Zhang
   Unaffiliated

   Email:
   Coolpad

   EMail: hishigh@gmail.com

   Ning Zong
   Huawei Technologies

   Email:

   EMail: zongning@huawei.com