PPSP N. Zong, Ed. Internet-Draft Huawei Technologies Intended status: Standards Track Y. Zhang Expires: April 25, 2010 China Mobile Communication Corporation V. Pascual Tekelec C. Williams Consultant October 22, 2009 P2P Streaming Protocol (PPSP) Requirements draft-zong-ppsp-reqs-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 25, 2010. Zong, et al. Expires April 25, 2010 [Page 1] Internet-Draft PPSP Requirements October 2009 Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. 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. Zong, et al. Expires April 25, 2010 [Page 2] Internet-Draft PPSP Requirements October 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of PPSP . . . . . . . . . . . . . . . . . . . . . . . 5 4. PPSP Requirements . . . . . . . . . . . . . . . . . . . . . . 6 4.1. PPSP Tracker Protocol Requirements . . . . . . . . . . . . 6 4.2. PPSP Peer Protocol Requirements . . . . . . . . . . . . . 7 4.3. PPSP Error Handling and Overload Protection Requirements . . . . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Zong, et al. Expires April 25, 2010 [Page 3] Internet-Draft PPSP Requirements October 2009 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 [WWW.PPLive], PPStream [WWW.PPStream], UUSee [WWW.UUSee], Pando [WWW.Pando] etc. Take PPLive for example, it has over 5 million online users at the same time for real-time streaming. Also some web2.0 streaming applications such as Youtube [WWW.YouTube], Tudou [WWW.Tudou] are reported to use or are preparing to use P2P engine to accelerate its downloading rate and cut down the transmission cost. 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.[PPSPPS] 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.[PPSPPS] 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.[PPSPPS] 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 Zong, et al. Expires April 25, 2010 [Page 4] Internet-Draft PPSP Requirements October 2009 indicate requirement levels for compliant implementations. This document uses the terms defined in [PPSPPS], including: Chunk: A chunk is a basic unit of partitioned streaming, which is used by a peer for the purpose of storage, advertisement and exchange among peers. Live streaming: The scenario where all clients receive streaming content for the same ongoing event. The lags between the play points of the clients and that of the streaming source are small. Peer/PPSP peer: A peer/PPSP peer refers to a participant in a P2P streaming system. The participant not only receives streaming content, but also stores and uploads streaming content to other participants. PPSP: PPSP refer to the key signaling protocols among various P2P streaming system components including the tracker and peer. PPSP are a part of P2P streaming protocols. Swarm: A swarm refers to a group of clients (i.e. peers) sharing the same content (e.g. video/audio program, digital file, etc) at a given time. Tracker/PPSP tracker: A tracker/PPSP tracker refers to a directory service which maintains lists of peers/PPSP peers storing chunks for a specific channel or streaming file and answers queries from peers/ PPSP peers for peer lists. Video-on-demand (VoD): The scenario where different clients watch different parts of the media recorded and stored during past events. 3. Overview of PPSP As described in [PPSPPS], 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 Zong, et al. Expires April 25, 2010 [Page 5] Internet-Draft PPSP Requirements October 2009 streaming status to the tracker. The information may include peer inbound/outbound traffic, 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: 1) Standard format/encoding of information between PPSP peers and PPSP trackers, such as peer list, 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) General functionalities of PPSP tracker protocol and basic types of information communicated by PPSP tracker protocol. 2) General functionalities of PPSP peer protocol and basic types of information communicated by PPSP peer protocol. 3) Error handling and overload protection requirements. 4) Security requirements. 4. PPSP Requirements 4.1. PPSP Tracker Protocol Requirements PPSP.TP.REQ-1: PPSP tracker protocol MUST be able to carry peer list information, such that each peer can get the list of peers which Zong, et al. Expires April 25, 2010 [Page 6] Internet-Draft PPSP Requirements October 2009 could provide the content. PPSP.TP.REQ-2: PPSP tracker protocol MUST be able to carry swarm ID (e.g. channel ID, streaming file ID). 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.TP.REQ-3: PPSP tracker protocol MAY carry content availability of the peers. In some cases tracker may maintain the information of which pieces of content reside in which peers, such that the tracker can assign the appropriate peers for the requesting peer. For example, a common expression of content availability is called buffer map, indicating which chunks a peer currently has buffered and can share with other peers. The buffer map can include the offset (the ID of the first chunk stored by the peer), the length of the buffer map, and a string of zeroes and ones indicating which chunks are available (starting with the chunk designated by the offset). <------- Buffer Map Length -------------> +---+---+---+---+---+---+---+---+---+---+ <---------->| 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | offset +---+---+---+---+---+---+---+---+---+---+ |--------------------------------------------------------------------> Content Length Figure 1: Buffer Map PPSP.TP.REQ-4: PPSP tracker protocol MAY carry streaming status of the peers. Streaming status of the peer include online time, link status, peer capability and other streaming parameters of the peer. Therefore, the tracker is able to select better candidate peers for streaming based on the streaming status of the peers. PPSP.TP.REQ-5: PPSP tracker protocol MAY be able to carry the service status of the tracker, e.g. work load, capacity, etc. 4.2. PPSP Peer Protocol Requirements PPSP.PP.REQ-1: PPSP peer protocol MUST be able to carry content availability of the peers. In order to share content among peers, peers must be able to tell each other which pieces of content reside in which peers. After a Zong, et al. Expires April 25, 2010 [Page 7] Internet-Draft PPSP Requirements October 2009 peer receives content availability from other peers, the peer can request content with other peers. PPSP.PP.REQ-2: PPSP peer protocol May exchange additional peer list in the communication after the first hand-shake between peers. Note that tracker may only return an initial list of peers to the requesting peer. A peer may need additional peers to connect with and share content. Therefore, it is allowed that the peer communicates with the peers in the current peer list to obtain additional peer lists with which it aggregates the current peer list. PPSP.PP.REQ-3: PPSP peer protocol May carry streaming status of the peers. Streaming status information should be related to the content delivery, including online time, link status, peer capability and other streaming parameters of the peer. With this information, a peer can select more appropriate peers for content sharing based on some content sharing strategies and/or application requirements. 4.3. PPSP Error Handling and Overload Protection Requirements PPSP.ERR.REQ-1: A peer MUST be able to respond with error information to the peers sending PPSP messages, when some information (e.g. peer list, chunk expression) cannot be understood in the message. Local Peer Peers/Tracker | | | PPSP Message | |<-----------------------------------------------| | | | Error Information | |----------------------------------------------->| | | | | Figure 2: Error Handling PPSP.ERR.REQ-2: A tracker, when is operating close to its capacity limit, MUST be able to inform the peers about its overload status, and reject the following PPSP messages from the peers or redirect the following PPSP message to other trackers. 5. IANA Considerations This document presently raises no IANA considerations. Zong, et al. Expires April 25, 2010 [Page 8] Internet-Draft PPSP Requirements October 2009 6. Security Considerations The scope of this section is to analyze the security threats and provide the requirements for PPSP. While P2P streaming system prevails in recent years, an important but less studied problem is security. PPSP.SEC.REQ-1: PPSP must ensure that only authorized users can access the original media in the P2P streaming system. This can be achieved by defining or adopting such mechanisms as user authentication and/or key management scheme. PPSP.SEC.REQ-2: Confidentiality of the streaming data should be supported and the corresponding key management scheme must scale well without degrading the system performance. PPSP.SEC.REQ-3: PPSP must provide an option to encrypt data exchange among PPSP entities. PPSP.SEC.REQ-4: PPSP must prevent stream pollution attacks. In the stream pollution attack, the attacker mixes into the stream bogus chunks, or declare the chunks it doesn't have. 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 must have mechanisms to limit potential damage caused by malfunctioning and badly behaving peers in the P2P streaming system. In addition there must be a way to identify badly behaving peers, and exclude or reject them from the P2P streaming system. PPSP.SEC.REQ-6: PPSP must prevent peers from exhausting the P2P streaming system's available resource, e.g. processing capacity, bandwidth, etc. 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 minimize the dependency on reachability of centralized servers. Zong, et al. Expires April 25, 2010 [Page 9] Internet-Draft PPSP Requirements October 2009 PPSP.SEC.REQ-8: PPSP Peers must be able to participate in the streaming network in private manner without any aspect of the peers privacy violated. PPSP.SEC.REQ-9: Existing security mechanisms should be re-used as much as possible in PPSP, to avoid developing new security mechanisms. PPSP.SEC.REQ-10: Security mechanisms of PPSP should not limit the scalability, performance and reliability of the P2P streaming system. 7. Acknowledgements The authors would like to thank many people for discussing P2P streaming. We would particularly like to thank: Haibin Song, Xingfeng Jiang from Huawei Technologies, Hui Zhang from NEC Labs, Jun Lei from University of Goettingen, James Seng from PPLive, Das Saumitra from Qualcomm, Lin Xiao and Christian Schmidt. 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 [WWW.PPLive] "www.pplive.com". [WWW.PPStream] "www.ppstream.com". [WWW.UUSee] "www.uusee.com". [WWW.Pando] "www.pando.com". [WWW.YouTube] "www.youtube.com". [WWW.Tudou] "www.tudou.com". Zong, et al. Expires April 25, 2010 [Page 10] Internet-Draft PPSP Requirements October 2009 [Survey] Zong, N. and X. Jiang, "Survey of P2P Streaming", IETF PPSP BoF, November 2008. [ProbSta] Zhang, Y., "Problem Statement of P2P Streaming Protocol (PPSP)", IETF PPSP BoF, November 2008. [P2PLive] Guo, Y., Liang, C., and Y. Liu, "Adaptive Queue-based Chunk Scheduling for P2P Live Streaming", IFIP Networking Proceedings, May 2008. [LiveStream] Pascual, V., "Live Streaming over P2PSIP", International SIP Conference 10th Edition, January 2009. [I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base Protocol", draft-ietf-p2psip-base-01 (work in progress), December 2008. [PPSPPS] Zhang, Y., Zong, N., Camarillo, G., Seng, J., and R. Yang, "PPSP Problem Statement", draft-zhang-ppsp-problem-statement-05 (work in progress). Authors' Addresses Ning Zong (editor) Huawei Technologies Phone: +86 25 84565866 Email: zongning@huawei.com Yunfei Zhang China Mobile Communication Corporation Phone: +86 13601032119 Email: zhangyunfei@chinamobile.com Victor Pascual Tekelec Email: victor@iptel.org Zong, et al. Expires April 25, 2010 [Page 11] Internet-Draft PPSP Requirements October 2009 Carl Williams Consultant Palo Alto, California 94306 Email: carlw@mcsr-labs.org Zong, et al. Expires April 25, 2010 [Page 12]