PPSP N. Zong, Ed.
Internet-Draft Huawei Technologies
Intended status: Informational Y. Zhang
Expires: January 7, 2012 China Mobile Communication
Corporation
V. Pascual
C. Williams
Consultant
L. Xiao
Nokia Siemens Networks
July 6, 2011
P2P Streaming Protocol (PPSP) Requirements
draft-ietf-ppsp-reqs-03
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
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This Internet-Draft will expire on January 7, 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
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 . . . . . . . . . . . . . . . . . . . 10
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 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), 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
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.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 protocols MUST 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.
The quality for P2P live streaming system could be very bad.
Dependent from the number of peers in the chains between content
provider and displaying peer, the network conditions (quality and
load) and the performance of the involved entities, especially end-
to-end delay could be horrible. Actually, 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 more are not
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acceptable.
There are several solutions possible, e.g. addition of super peers,
in-network storage, and the usage of QoS information for an advanced
peer selection. This could be for example, the max length of a chunk
between source and peer or some information about the performance
capacity of the last peer. This information would have to be
transported via Tracker/Peer Protocol. The tracker protocol must
provide the possibility for the request of alternative peer
addresses, if the quality is not sufficient for the user.
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 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.
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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-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.
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
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
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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.
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-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.
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.
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.
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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.
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) and report this towards the tracker
to exclude the related source from the P2P streaming system. The
corresponding checksum distribution and verification scheme SHOULD
scale well in P2P streaming system and be robust against distrustful
trackers/peers.
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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, Lingli Deng from China
Mobile.
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.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-also-protocol-06 (work in progress),
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)",
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draft-ietf-ppsp-problem-statement-02 (work in progress),
July 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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