[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

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

PPSP                                                            Y. Zhang
Internet-Draft                                              Unaffiliated
Intended status: Informational                                   N. Zong
Expires: November 15, 2013                           Huawei Technologies
                                                            May 14, 2013


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

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.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 15, 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) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



Zhang & Zong           Expires November 15, 2013                [Page 1]

Internet-Draft           PPSP Problem Statement                 May 2013


   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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

1.  Introduction









Zhang & Zong           Expires November 15, 2013                [Page 2]

Internet-Draft           PPSP Problem Statement                 May 2013


1.1.  Backgrounds

   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.

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.




Zhang & Zong           Expires November 15, 2013                [Page 3]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

   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.






Zhang & Zong           Expires November 15, 2013                [Page 4]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

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





Zhang & Zong           Expires November 15, 2013                [Page 5]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

   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.

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



Zhang & Zong           Expires November 15, 2013                [Page 6]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

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


   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?



Zhang & Zong           Expires November 15, 2013                [Page 7]

Internet-Draft           PPSP Problem Statement                 May 2013


      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?

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?

      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




Zhang & Zong           Expires November 15, 2013                [Page 8]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

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



Zhang & Zong           Expires November 15, 2013                [Page 9]

Internet-Draft           PPSP Problem Statement                 May 2013


   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.

   +-------------------------------------------------------------------+
   |                                                                   |
   |                          +------------------+                     |
   |            +------------>| 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


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.



Zhang & Zong           Expires November 15, 2013               [Page 10]

Internet-Draft           PPSP Problem Statement                 May 2013


   +-------------------------------------------------------------------+
   |                                                                   |
   |                   +-------------+    +--------------+             |
   |            +----->| 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


   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.

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



Zhang & Zong           Expires November 15, 2013               [Page 11]

Internet-Draft           PPSP Problem Statement                 May 2013


   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 Heterogeneous P2P Streaming with PPSP


   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.

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.

   +----------------------------------------------------------------+
   |                                                                |
   |    Tracker Protocol +---------+                                |
   |  +----------------> | Tracker |                                |



Zhang & Zong           Expires November 15, 2013               [Page 12]

Internet-Draft           PPSP Problem Statement                 May 2013


   |  |                  +---------+                                |
   |  |                       ^                                     |
   |  |                       |                                     |
   |  |                       | 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


   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 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.

      +---------------------------------------------------------------+
      |                                                               |
      |    Tracker Protocol +--------+                                |
      |  +----------------> | Tracker|                                |
      |  |                  +--------+                                |
      |  |                       ^                                    |
      |  |                       |                                    |
      |  |                       | Tracker Protocol                   |
      |  |                       |                                    |
      |  |             +---------|------------------------------------|
      |  |             |         V                                    |
      |  |             |     +--------+                               |
      |  |  +----------|---> |  PPSP   |<------------------+          |



Zhang & Zong           Expires November 15, 2013               [Page 13]

Internet-Draft           PPSP Problem Statement                 May 2013


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


   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.

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.

      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.




Zhang & Zong           Expires November 15, 2013               [Page 14]

Internet-Draft           PPSP Problem Statement                 May 2013


      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 and Management Requirements

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

6.2.1.  Operation Considerations

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

      According to basic requirements, when setting up PPSP, content
      provider should generate chunk IDs and swarm ID for each streaming
      content.  Original content server and tracker are configured and
      setup.  Content provider then should publish this 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
      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
      time to receive a new streaming channel or to switch between



Zhang & Zong           Expires November 15, 2013               [Page 15]

Internet-Draft           PPSP Problem Statement                 May 2013


      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 1 minute and more are not acceptable.

      For instance, the tracker and peer protocol can carry quality
      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 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 to be supported in
   implementation, PPSP MUST support remote management using standard
   interface, as well as a basic set of management information.

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

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

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

      Peer and server health will at least include node activity and
      connectivity especially for peers behind NAT.  As mentioned in
      OAM.REQ-4, streaming behavior of peer can be learnt 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
      PPSP setup stage can be defined by content providers via a
      management interface to content servers.





Zhang & Zong           Expires November 15, 2013               [Page 16]

Internet-Draft           PPSP Problem Statement                 May 2013


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

   PPSP.OAM.REQ-9: PPSP MUST support security management.  See section
   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.  preferred number of peers in the
      peerlist) 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.

      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.  preventing hearsay and DoS attack).



Zhang & Zong           Expires November 15, 2013               [Page 17]

Internet-Draft           PPSP Problem Statement                 May 2013


   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 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.







Zhang & Zong           Expires November 15, 2013               [Page 18]

Internet-Draft           PPSP Problem Statement                 May 2013


      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
      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



Zhang & Zong           Expires November 15, 2013               [Page 19]

Internet-Draft           PPSP Problem Statement                 May 2013


      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.  Acknowledgements

   Thanks 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.

10.  References

10.1.  Normative References

   [RFC2119] Bradner, S., "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.



Zhang & Zong           Expires November 15, 2013               [Page 20]

Internet-Draft           PPSP Problem Statement                 May 2013


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/ns705/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/

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

11.  References

Authors' Addresses

   Yunfei Zhang
   Unaffiliated

   Email: hishigh@gmail.com







Zhang & Zong           Expires November 15, 2013               [Page 21]

Internet-Draft           PPSP Problem Statement                 May 2013


   Ning Zong
   Huawei Technologies

   Email: zongning@huawei.com














































Zhang & Zong           Expires November 15, 2013               [Page 22]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/