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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: April 10, 2012                       China Mobile Communication
                                                             Corporation
                                                              V. Pascual
                                                             Acme Packet
                                                             C. Williams
                                                              Consultant
                                                                 L. Xiao
                                                  Nokia Siemens Networks
                                                        October 08, 2011


               P2P Streaming Protocol (PPSP) Requirements
                        draft-ietf-ppsp-reqs-05

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 April 10, 2012.

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



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   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 . . . . . . . . . . . .  8
     4.3.  PPSP Peer Protocol Requirements  . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13



































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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
   content from other peers.

   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, total amount of bytes uploaded/downloaded to neighbour
   peers, 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 tracker.  Some of this exchanged information may be explicitly
   marked as optional.  Exchanged information may include 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), streaming content, and QoS issues.

   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



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   swarm.

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

   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.ietf-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).

   PPSP.REQ-8: The tracker and peer protocol together MUST facilitate
   acceptable QoS (e.g. low startup delay, low channel/content switching
   time and minimal end-to-end delay) for both on-demand and live
   streaming, even for very popular content.  The tracker and peer
   protocol do not include the algorithm required for scalable
   streaming.  However, the tracker and peer protocol SHALL NOT restrict
   or place limits on any such algorithm.

   There are basic QoS requirements for streaming system.  Setup time to
   receive a new streaming channel or to switch between channels should
   be reasonable small.  End to end delay (time between content
   generation, e.g. camera and content consumption, e.g. user side
   monitor) will become critical in case of live streaming.  Especially
   in provisioning of sports events, end to end delay of 1 minute and



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   more are not acceptable.

   For instance, the tracker and peer protocols can support carrying QoS
   related parameters (e.g. video quality, delay requirements) together
   with the priorities of these parameters, and QoS situation (e.g.
   performance, available uplink bandwidth) of content providing peers.

   There are also some other possible mechanisms, e.g. addition of super
   peers, in-network storage, request of alternative peer addresses, and
   the usage of QoS information for an advanced peer selection.

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
   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 MUST have the ability to
   inform the tracker about the peer's activity in the swarm.

   PPSP.TP.REQ-7: The chunk availability information of the peer SHOULD



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   be reported to tracker when tracker needs such information to steer
   peer selection.  The chunk information MUST at least contain the
   chunk ID.

   PPSP.TP.REQ-8: The chunk availability information between peer and
   tracker MUST be as expressed as compactly as possible.

   The peers may report CHUNK AVAILABILTY DIGEST information (i.e.
   compact expression of chunk availability) to the tracker when
   possible to decrease the bandwidth consumption for messages in
   bandwidth constraint environment like mobile network.  For example,
   if a peer has a bitmap like 111111...1(100 continuous 1)xxx..., the
   100 continuous "1" can be expressed by one byte with seven bits
   representing 100 and one bit representing "1".  In this example, 100-
   8=92 bits are saved.  Considering the frequency of exchange of CHUNK
   AVAILBILITY and the fact that many bitmaps have quite a long length
   of continuous "1" or "0", such compression makes sense.

   PPSP.TP.REQ-9: The status of the peer SHOULD be reported to the
   tracker when tracker needs such information to steer peer selection.

   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.

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 first task for this WG will be to decide which signaling
   and media transfer protocols will be used.  The WG will consider
   existing protocols and, if needed, identify potential extensions to
   these protocols.

   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.  This chunk availability information MUST NOT be passed on
   to other peer, unless validated (e.g. prevent hearsay and DoS).

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



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   received from the tracker - with the same swarm ID.  The reply
   message MUST contain swarm-membership information of the peers that
   have explicitly indicated they are part of the swarm, verifiable by
   the receiver.  This additional list of peers MUST only contain peers
   which have been checked to be valid and online recently (e.g. prevent
   hearsay and DoS).

   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.  In the push based
   model, where peers advocate their own chunk availability proactively,
   the content availability request message described in PP.REQ-1 is not
   needed.  The peer protocol MUST implement either pull-based, push-
   based or both.

   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 chunk availability information between peers MUST
   be as expressed as compactly as possible.

   In PP.REQ-1/2/4, the peers may exchange CHUNK AVAILABILTY DIGEST
   information (i.e. compact expression of chunk availability) to with
   other peers when possible to decrease the bandwidth consumption for
   messages in bandwidth constraint environment like mobile network.

   PPSP.PP.REQ-6: 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.



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   With this information, a peer can select more appropriate peers for
   streaming.

   PPSP.PP.REQ-7: The peers MUST implement the peer protocol for chunk
   data (not availability information) 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.

   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



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   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.

   PPSP.SEC.REQ-9: Integrity of the streaming content in PPSP MUST be
   supported to provide a peer with the possibility to identify
   inauthentic media content (undesirable modified by other entities
   rather than its genuine source).  The corresponding checksum
   distribution and verification scheme SHOULD scale well in P2P
   streaming system and be robust against distrustful trackers/peers.


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, Lingli Deng from China
   Mobile, Johan Pouwelse, Arno Bakker and Wesley Eddy.


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".



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   [UUSee]    "www.uusee.com".

   [Pando]    "www.pando.com".

   [I-D.ietf-ppsp-survey]
              Gu, Y., Zong, N., Zhang, H., Zhang, Y., Lei, J.,
              Camarillo, G., Liu, Y., Montuno, D., and X. Lei, "Survey
              of P2P Streaming Applications", draft-ietf-ppsp-survey-02
              (work in progress), July 2011.

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-09 (work in progress), June 2011.

   [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-05 (work in progress),
              September 2011.


Authors' Addresses

   Ning Zong (editor)
   Huawei Technologies
   Huawei Base, No.101 Software Avenue, Nanjing, China

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


   Yunfei Zhang
   China Mobile Communication Corporation

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


   Victor Pascual
   Acme Packet
   Anabel Segura 10, Madrid 28108, Spain

   Email: VPascual@acmepacket.com








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   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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