Internet DRAFT - draft-ietf-ppsp-problem-statement
draft-ietf-ppsp-problem-statement
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.
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This Internet-Draft will expire on November 15, 2013.
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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
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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.
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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.
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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
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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
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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?
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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
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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
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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.
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+-------------------------------------------------------------------+
| |
| +-------------+ +--------------+ |
| +----->| 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
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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 | |
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| | +---------+ |
| | ^ |
| | | |
| | | 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 |<------------------+ |
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| | | | | 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.
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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
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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.
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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).
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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.
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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
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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.
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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
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Ning Zong
Huawei Technologies
Email: zongning@huawei.com
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