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Versions: (draft-zong-ppsp-reqs) 00 01 02 03 04 05

PPSP                                                        N. Zong, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                  Y. Zhang
Expires: August 27, 2011                      China Mobile Communication
                                                             Corporation
                                                              V. Pascual
                                                             C. Williams
                                                              Consultant
                                                                 L. Xiao
                                                  Nokia Siemens Networks
                                                       February 23, 2011


               P2P Streaming Protocol (PPSP) Requirements
                        draft-ietf-ppsp-reqs-02

Abstract

   The objective of the PPSP work is to standardize the key signaling
   protocols that apply to tracker and peers in a Peer-to-Peer (P2P)
   streaming system.  These protocols are called PPSP.  This document
   enumerates the requirements for the PPSP, which should be considered
   when designing 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 August 27, 2011.

Copyright Notice

   Copyright (c) 2011 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



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview of PPSP . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  PPSP Requirements  . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Basic Requirements . . . . . . . . . . . . . . . . . . . .  6
     4.2.  PPSP Tracker Protocol Requirements . . . . . . . . . . . .  7
     4.3.  PPSP Peer Protocol Requirements  . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12



































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1.  Introduction

   Peer to Peer (P2P) computing has been successfully used in many
   fields, from one to one communication like Voice over IP (VoIP) and
   Instance Messaging (IM), to one to many communication like streaming,
   file sharing and gaming.  In the streaming area, the popularity of
   P2P real-time and video on demand (VoD) streaming technology has been
   demonstrated by PPLive [PPLive], PPStream [PPStream], UUSee [UUSee],
   Pando [Pando] etc.  Take PPLive for example, it has over 5 million
   online users at the same time for real-time streaming.  P2P streaming
   applications account for more and more Internet traffic.  According
   to statistics in a major Chinese Internet Service Provider (ISP), the
   traffic generated by P2P streaming applications exceeded 50% of the
   total backbone traffic during peak time in 2008
   [I-D.ietf-ppsp-problem-statement].

   Given the increasing integration of P2P streaming into the global
   content delivery infrastructure, the lack of an open, standard P2P
   streaming protocol has become a major missing component in the
   Internet protocol stack.  Multiple similar but proprietary P2P
   streaming protocols result in repetitious development efforts and
   lock-in effects.  More importantly, it leads to substantial
   difficulties when integrating P2P streaming as a component of a
   global content delivery infrastructure.  For example, proprietary P2P
   streaming protocols do not integrate well with infrastructure devices
   such as caches and other edge devices
   [I-D.ietf-ppsp-problem-statement].

   The objective of the PPSP work is to standardize the key signaling
   protocols that apply to tracker and peers in a P2P streaming system.
   These protocols are called PPSP.  PPSP will serve as an enabling
   technology, building on the development experiences of existing P2P
   streaming systems.  Its design will allow it to integrate with IETF
   efforts on distributed resource location, traffic localization, and
   streaming control mechanisms.  It allows effective integration with
   edge infrastructures such as cache and mobile edge equipment
   [I-D.ietf-ppsp-problem-statement].

   This document enumerates the requirements for the PPSP, which should
   be considered when designing PPSP.


2.  Terminology

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



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   This document uses the following PPSP-related terms, which are
   defined in [I-D.ietf-ppsp-problem-statement], including:

   Chunk, Live streaming, Peer/PPSP peer, PPSP, Swarm, Tracker/PPSP
   tracker, Video-on-demand (VoD).

   Furthermore, the following additional terms will be used:

   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 either
   tracker or other peers to know which peers have the required
   streaming content.

   Peer ID: An identifier of a peer such that other peers or tracker can
   refer the ID for the peer.

   Swarm ID: An identifier of a swarm containing a group of peers
   sharing a same streaming content.

   Chunk ID: An identifier of a chunk in a streaming content.


3.  Overview of PPSP

   As described in [I-D.ietf-ppsp-problem-statement], the following
   components are considered in the scope of PPSP:

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

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

   3) Report.  Report is a component that enables peers to report
   streaming status to the tracker.  The information may include swarm
   IDs to show swarms that the peer is taking active part in, chunk list
   for each swarm to show the current content availability in the peer,
   inbound/outbound traffic capacity, amount of neighbor peers, peer
   health degree and other streaming parameters.

   Therefore, PPSP includes the PPSP tracker protocol - a signaling
   protocol between PPSP trackers and PPSP peers, and the PPSP peer
   protocol - a signaling protocol among PPSP peers.

   PPSP tracker protocol will define:




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   1) Standard format/encoding of information between PPSP peers and
   PPSP trackers, such as peer list, swarm ID, chunk information,
   content availability, streaming status including online time, link
   status, node capability and other streaming parameters.

   2) Standard messages between PPSP peers and PPSP trackers defining
   how PPSP peers report streaming status and request to PPSP trackers,
   as well as how PPSP trackers reply to the requests.

   PPSP peer protocol will define:

   1) Standard format/encoding of information among PPSP peers, such as
   chunk description.

   2) Standard messages among PPSP peers defining how PPSP peers
   advertise chunk availability to each other, as well as the signaling
   for requesting the chunks among PPSP peers.

   This document itemizes requirements for the following aspects of
   PPSP:

   1) Basic requirements to PPSP protocols (peer and tracker protocols),
   entities (peer and tracker), and the streaming content.

   2) General requirements to the tracker protocol.

   3) General requirements to the peer protocol.

   4) Security requirements.


4.  PPSP Requirements

4.1.  Basic Requirements

   PPSP.REQ-1: The tracker and the peer protocols SHOULD be as similar
   as possible, in terms of design, message formats and flows.

   It is desirable that the peer protocol would be an extension to the
   tracker protocol by adding a few message types, or vice versa.

   PPSP.REQ-2: The tracker protocol and the peer protocol SHOULD enable
   peers to receive streaming content within the required time
   constraints, i.e., fulfill streaming feature.

   PPSP.REQ-3: Each peer MUST have a unique ID (i.e. peer ID) in a
   swarm.




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   It's a basic requirement for a peer to be uniquely identified in a
   swarm that other peers or tracker can refer the ID for the peer.

   PPSP.REQ-4: 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-5: The streaming content MUST allow to be partitioned into
   chunks.

   A key characteristic of P2P streaming system is allowing the data
   fetching from different peers concurrently.  Therefore, the whole
   streaming content must allow to be partitioned into small pieces or
   chunks for transmission between peers.

   PPSP.REQ-6: Each chunk MUST have an unique ID (i.e. chunk ID) in the
   swarm.

   Each chunk must have an unique ID in the swarm such as the peer can
   understand which chunks are stored in which peers and which chunks
   are requested by other peers.  An example for generating the chunk ID
   is the buffer map approach [I-D.gu-ppsp-survey].

   PPSP.REQ-7: The tracker protocol and peer protocol are Recommended to
   be carried over TCP (or UDP, when delivery requirements cannot be met
   by TCP).

4.2.  PPSP Tracker Protocol Requirements

   The tracker protocol defines how the peers report and request
   information to/from the tracker and how the tracker replies to the
   requests.  The tracker discovery and the possible communication
   between trackers are out of the scope of tracker protocol.

   PPSP.TP.REQ-1: The tracker MUST implement the tracker protocol for
   receiving queries and periodical peer status reports/updates from the
   peers and for sending the corresponding replies.

   PPSP.TP.REQ-2: The peer MUST implement the tracker protocol for
   sending queries and periodical peer status reports/updates to the
   tracker and receiving the corresponding replies.

   PPSP.TP.REQ-3: The tracker request message MUST allow the requesting



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   peer to solicit the peer list from the tracker with respect to a
   specific swarm ID.

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

   PPSP.TP.REQ-4: The tracker reply message MUST allow the tracker to
   offer the peer list to the requesting peer with respect of a specific
   swarm ID.

   PPSP.TP.REQ-5: The tracker SHOULD support generating the peer list
   with the help of traffic optimization services, e.g.  ALTO
   [I-D.ietf-alto-protocol].

   PPSP.TP.REQ-6: The peer status report/update message MUST have the
   ability to inform the tracker about the peer's activity in the swarm
   and chunk information of the peer.  The chunk information MUST at
   least contain the chunk ID.

   PPSP.TP.REQ-7: The peer status report/update message SHOULD reflect
   the status of the peer.

   Peer status change should be reported to the tracker via the peer
   status report/update message.  For example, peer status can be online
   time, physical link status including DSL/WIFI/etc, battery status,
   processing capability, and other capabilities of the peer.
   Therefore, the tracker is able to select better candidate peers for
   streaming.  In some mobile scenario, peer status can include IP
   address change . [I-D.lu-ppsp-mobile]

4.3.  PPSP Peer Protocol Requirements

   The peer protocol defines how the peers advertise streaming content
   availability and exchange status with each other.  The peer protocol
   also defines the requests and responses of the chunks among the
   peers.  The data transport mechanism and transmission control are out
   of the scope.

   PPSP.PP.REQ-1: The streaming content availability request message
   MUST allow the peer to solicit the chunk information from other peers
   in the peer list.  The chunk information MUST at least contain the
   chunk ID.

   PPSP.PP.REQ-2: The streaming content availability reply message MUST
   allow the peer to offer the information of the chunks in its content



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   buffer.  The chunk information MUST at least contain the chunk ID.

   PPSP.PP.REQ-3: The streaming content availability request message
   SHOULD allow the peer to solicit an additional list of peers to that
   received from the tracker - with the same swarm ID.

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

   PPSP.PP.REQ-4: Streaming content availability update message among
   the peers MUST be supported by peer protocol.

   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 neighbours (i.e. the peers known
   to a peer by getting the peer lists 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 such
   update message, how often to send this update message, etc should
   leave to peer algorithms, rather than protocol concerns.

   PPSP.PP.REQ-5: The peer status report/update SHOULD be advertised
   among the peers to reflect the status of the peer.

   Peer status information should be advertised among the peers via the
   peer status report/update message.  For example, peer status can be
   online time, physical link status including DSL/WIFI/etc, battery
   status, processing capability, and other capabilities of the peer.
   With this information, a peer can select more appropriate peers for
   streaming.  In some mobile scenario, peer status can include IP
   address change [I-D.lu-ppsp-mobile].

   PPSP.PP.REQ-6: The peers MUST implement the peer protocol for chunk
   requests and responses among the peers before the streaming content
   is transmitted.


5.  Security Considerations

   The scope of this section is to analyze the security threats and
   provide the requirements for PPSP.



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   PPSP.SEC.REQ-1: PPSP MUST support closed swarms, where the peers are
   authenticated.

   This ensures that only the authenticated users can access the
   original media in the P2P streaming system.  This can be achieved by
   security mechanisms such as user authentication and/or key management
   scheme.

   PPSP.SEC.REQ-2: Confidentiality of the streaming content in PPSP
   SHOULD be supported and the corresponding key management scheme
   SHOULD scale well in P2P streaming system.

   PPSP.SEC.REQ-3: PPSP MUST provide an option to encrypt the data
   exchange among the PPSP entities.

   PPSP.SEC.REQ-4: PPSP MUST have mechanisms to limit potential damage
   caused by malfunctioning and badly behaving peers in the P2P
   streaming system.

   Such an attack will degrade the quality of the rendered media at the
   receiver.  For example, in a P2P live video streaming system a
   polluter can introduce corrupted chunks.  Each receiver integrates
   into its playback stream the polluted chunks it receives from its
   other neighbors.  Since the peers forwards chunks to other peers, the
   polluted content can potentially spread through much of the P2P
   streaming network.

   PPSP.SEC.REQ-5: PPSP SHOULD support identifying badly behaving peers,
   and exclude or reject them from the P2P streaming system.

   PPSP.SEC.REQ-6: PPSP MUST prevent peers from DoS attacks which will
   exhaust the P2P streaming system's available resource.

   Given the prevalence of DoS attacks in the Internet, it is important
   to realize that a similar threat could exist in a large-scale
   streaming system where attackers are capable of consuming a lot of
   resources with just a small amount of effort.

   PPSP.SEC.REQ-7: PPSP SHOULD be robust, i.e., when centralized tracker
   fails the P2P streaming system SHOULD still work by supporting
   distributed trackers.

   PPSP.SEC.REQ-8: Existing P2P security mechanisms SHOULD be re-used as
   much as possible in PPSP, to avoid developing new security
   mechanisms.






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6.  IANA Considerations

   This document presently raises no IANA considerations.


7.  Acknowledgements

   The authors would like to thank many people for discussing P2P
   streaming.  We would particularly like to thank: Yingjie Gu, Haibin
   Song, Xingfeng Jiang from Huawei, Hui Zhang, Jan Seedorf, Martin
   Stiemerling from NEC Labs, Jun Lei from University of Goettingen,
   James Seng from PPLive, Das Saumitra from Qualcomm, Christian Schmidt
   from NSN, Akbar Rahman from Interdigital.


8.  References

8.1.  Normative References

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

8.2.  Informative References

   [PPLive]   "www.pplive.com".

   [PPStream]
              "www.ppstream.com".

   [UUSee]    "www.uusee.com".

   [Pando]    "www.pando.com".

   [I-D.gu-ppsp-survey]
              Gu, Y., Zong, N., Zhang, H., Zhang, Y., Lei, J.,
              Camarillo, G., and Y. Liu, "Survey of P2P Streaming
              Applications", draft-gu-ppsp-survey-02 (work in progress),
              October 2010.

   [I-D.lu-ppsp-mobile]
              Lu, G., Zuniga, JC., and A. Rahman, "P2P Streaming for
              Mobile Nodes: Scenarios and Related Issues",
              draft-lu-ppsp-mobile-04 (work in progress),
              September 2010.

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-also-protocol-06 (work in progress),



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              October 2010.

   [I-D.ietf-ppsp-problem-statement]
              Zhang, Y., Zong, N., Camarillo, G., Seng, J., and R. Yang,
              "Problem Statement of P2P Streaming Protocol (PPSP)",
              draft-ietf-ppsp-problem-statement-01 (work in progress),
              January 2011.


Authors' Addresses

   Ning Zong (editor)
   Huawei Technologies

   Phone: +86 25 56624760
   Email: zongning@huawei.com


   Yunfei Zhang
   China Mobile Communication Corporation

   Phone: +86 13601032119
   Email: zhangyunfei@chinamobile.com


   Victor Pascual
   Consultant

   Email: victor.pascual.avila@gmail.com


   Carl Williams
   Consultant
   Palo Alto, California 94306

   Email: carlw@mcsr-labs.org


   Lin Xiao
   Nokia Siemens Networks

   Phone: +86 10 84358977
   Email: lin.xiao@nsn.com








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