PPSP Yunfei.Zhang
Internet Draft
Intended status: Informational China Mobile
Expires: September 2009 March 3, 2009
Protocol Analysis and Comparison of PPlive and PPstream by Internet
Measurement
draft-zhang-ppsp-protocol-comparison-measurement-00.txt
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Internet-Draft Protocol Analysis and Comparison of PPlive and
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Abstract
In this draft we introduce an Internet measurement work for both
pplive and ppstream. First, we give a brief introduction about our
motivation and target of this measurement. We then introduce the
methodology, platform, data and modeling of our measurement. Finally
we outline the p2p media streaming protocols by the measurement.
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Table of Contents
1. Introduction................................................4
2. Motivation and Target of the Measurement.....................5
3. Methodology of Our Measurement...............................6
4. Measurement Platforms........................................8
5. Data Analysis and Modeling..................................10
6. Study of P2P Media Streaming Protocols by the Measurement....10
6.1. PPLive Live Streaming:.................................10
6.2. PPLive VoD............................................11
6.3. PPStream Live (early version, TCP).....................12
6.4. Conclusion............................................12
7. Security Considerations.....................................14
8. References.................................................15
8.1. Normative References...................................15
8.2. Informative References.................................15
Intellectual Property Statement....................
Disclaimer of Validity............................
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1. Introduction
P2p media streaming is one of the most popular p2p system and is a
new developing trend for modern video system. More and more users,
vendors as well as researchers have been attracted to it. Currently,
there are many such systems on Internet, such as PPLive, PPStream,
UUSee, etc. Usually all of them can provide Live and VoD programs to
users. They have a similar system structures according to our
measurement. In good network conditions, all of them can bring good
experiences to users; once the stable condition is broken, the p2p
applications will present different performance.
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2. Motivation and Target of the Measurement
Naturally, we care about how to evaluate system performance, what the
performance limitations are under current system models, how to
decrease the pressure on the network. In order to answer these
questions, we study the following aspects of p2p streaming systems:
1.To extract the general p2p media streaming system structure;
2.To analyze and evaluate the signaling (protocol) messages ( types,
format, function, exchange sequence)
3. To study and model the core mechanism such as initial buffer lag
policy, buffer cache schedule policy, data fetching policy, etc;
4.To optimize the system performance and improve network robustness;
5.To study its effect on physical layer network, transport lay
protocol ( TCP and UDP );
6.To study new p2p suitable transport protocol instead of application
lay p2p transportation;
7.To study the availability of current p2p streaming systems on
mobile ip;
8.To present related standard suggests.
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3. Methodology of Our Measurement
Real network based measurement is important in studying p2p media
streaming systems. However all current commercial p2p media streaming
systems are propriety protocol systems without any public document
about system' working mechanism available. Although some researchers
report some useful finds, most of our concerns are not resolved yet.
We have to firstly deeply understand how the system works. Usually we
use certain reverse-engineering method to analyze its working
principle. In the protocol cracking, we mainly focus on the top 2 of
very popular p2p streaming systems - PPLive and PPStream. Beside
their popular degree, several other reasons make them as the starting:
Both of them use plain text in their protocol exchanging; both udp
and tcp are adopted; both of them are the new generation data driven
p2p streaming systems.
Our reverse engineering are conducted in following 3 stages:
Firstly, by tracing a standard client, we capture interactive packets
between the local peer and others with ethereal/windump tool. Based
on our experience on the p2p streaming system, some basic protocol
types must be included such as buffer map, chunk request/response,
shake hand packet, etc. For each udp packet, it is reasonable to
assume that each packet is a completed protocol message, while for
tcp packets we must extract messages from all application data stream.
Usually we can get the rough protocol format by matching traced
packets to the known basic protocol types. But there are still many
unknown details left.
Secondly, the traced data is fed into our dumping tool, which can
filter data into a text file with composed conditions, such as source
ip/port, destination ip/port, VoD/Live protocol type. Through
inspecting the text file of different channels, we find many regular
changes that help us in parsing the protocol format in details. Of
course, there is still one-third irregular data. In this case, we
guess and try it based on our experiences in next step. At last, we
parse about nearly 90% of PPLive and PPStream protocols. In PPLive
system, there are about 15 message types, all of that haven't any
clearly protocol marks in order to escape from restrictions ISPs may
imposed on (we think). Among these types, buffermap and peerlist
messages are the most useful messages for us to measure and analyze
the system.
At the third stage, we analyze the time sequences of the protocol
messages. Some communication time sequence is obvious, such as chunk
request/response, while others are not. In later case, we guess and
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try differently composed events until a sequence makes right sound.
Ultimately, all time sequences in communications are resulted
successfully.
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4. Measurement Platforms
For different analysis, we take different measurement methods. In
general, our environment consists of 4 dell pc servers in a private
ip space (LAN) behind a 6mbps ADSL NAT router. each of which has
2.8Hz Pentium CPU, 1MB memory, 80GB hard disk, 10/100Mbps Ethernet,
windows OS, mysql database.
+------------------------------------------------+
| crawler tracker server peer |
| | | | |
| | Shake hand | | |
| |------------------>| | |
| | Peerlist request | | |
| |------------------>| | |
| | Peerlist response| | |
| |<------------------| | |
| | | | |
| |Notification for connecting a peer X | |
| |------------------>| | |
| | Shake hand to peer x | |
| |-------------------|---------------->| |
| | Buffermap of peer x | |
| |<------------------|-----------------| |
| | | | |
| |Notification for connecting a peer y | |
| |------------------>| | |
| | Shake hand to peer y | |
| |-------------------|---------------->| |
| | Buffermap of peer x | |
| |<------------------|-----------------| |
| | | | |
+------------------------------------------------+
Figure 1 Protocol sequence for crawling
1. Official client trace: use tcpdump/windump/wireshark to capture
exchanging packets between local peer and other peers.
2. System topology crawler: based on p2p streaming protocol, design
legal measurement tool to detect the whole network in short time. We
usually take some measures improve the probing efficiency such as
multi threads, fast data searching in memory, multi-tables in
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databases, master-slave distribution deployment, concurrent tcp
session limitation enlargement.
3. Long term multi online peers probe: different from topology
crawler, it will probe a certain online peers in a long term in order
to collect the detail information of these peers. Usually more
complete protocol set should be realized in it.
4. P2p streaming client measurement in mobile ip: A fix position PC
is used as the mobile device, where three types of software have been
installed: p2p streaming client software; packet capture software;
our mobile ip simulation software.
5. Special client accessing to official network in order to evaluate
the system robusticity and optimize the protocol: based on
protocols,we build the legal p2p client to join in the official p2p
network. By this client, we can test and evaluate new protocol design
and new core system models.
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5. Data Analysis and Modeling
As for data analysis and modeling, we have made some progress and
published some papers [1]~[6]. Interested readers can refer to them
for more details.
6. Study of P2P Media Streaming Protocols by the Measurement
We have measurement PPLive and PPstream and guessed the protocols
both for live streaming and VoD streaming respectively. However due
to some encryption(It's said to be Scrambling), VoD streaming data
from PPStream hasn't been analyzed yet. We list the signaling
transaction of pplive live streaming and VoD and ppstream live
streaming as follows:
6.1. PPLive Live Streaming:
Messages with Tracker
0101 (peer registration)
0100 (tracker response)
0201 (peerlist request)
0200 (peerlist response)
0301 (tracker offset request)
0300 (tracker offset response)
Messages with Peer
0x4101 (peerlist request)
0x 4201 (peerlist response)
0x 5400 (peerlist response)
0x 4400 (Buffermap response)
0x 5200 (chunk request)
0x 5300 (chunk response)
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0x 4601 (chunk response)
0x 6101 (chunk request)
0x6201 (chunk response)
0x 4000 (disconnect)
0x4500 (chunk request)
0x4901 (udp handshake)
0x4400: update/5s
6.2. PPLive VoD
0x04 (peers_data_request)
0x05 (peers_data_response_1)
0x06 (peers_data_response_2)
0x11 (peers_peerlist_request)
0x12 (peers_peerlist_response)
0x13 (peers_shakehand)
0x14 (peers_bitfield)
0x16 (trk shakehand)
0x17 (trk notification of a peer)
0x18 (peers_keepalive)
0x43 (host_ip)
0x44 (public_ip)
0x51 (host_ip_format2)
0x52 (public_ip_format2)
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6.3. PPStream Live (early version, TCP)
0x02 (buffermap)
0x22 (buffermap)
0x03 (chunk request)
0x04 (chunk response)
0x05 (nochunk response)
0x08 (peerlist request)
0x09 (peerlist response)
0x40 (media information)
0x1d (client version)
0x10 (protocol error information)
0x1b (remote live time)
0x1 (peer id)
0x19 (remote refuse)
0xA0 (vod bitmap)
6.4. Conclusion
Both PPLive and PPStream support Live and VoD programs, and have
similar system structures. As for the signaling protocol, both
systems have similar process. We have depicted the interactions
between peers and peers as well as trackers in the problem statement
draft. Interested readers can refer to draft-zhang-ppsp-problem-
statement for details.
However, there are still some difference between pplive and ppstream
which belongs to their high secrets. For example, in the buffer
aspect, pplive is a large buffer system, which can smooth time delay
jitters but contributes to relative large startup delay. The chunk
fetch policy is seqential fetcing and rarest first at same time. The
schema of the buffer is a variable length in chunks but fixed length
in playback time. The buffer map schedule is simple based on chunks
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id. On the other hand, PPStream is a small buffer system (early
version), which has small startup delay but leads to video freeze
with large jitters. The chunk fetch is randomly in each buffer window.
The schema of the buffer is of multi playable media blocks with fixed
playback time (mulit buffers) for each of them. Hence its buffer
schedule is based on multi buffer windows, where each chunk is
uniquely marks indicated by the buffer window offset and the internal
chunk id. According to our understanding, the mechanism of PPStream
is a litter complex.
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7. Security Considerations
We don't involve security measurement till now.
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8. References
8.1. Normative References
[1] Y. Chen, C. Chen and C. Li, "A Measurement Study of Cache
Rejection in P2P Live Streaming System", Workshop on Multimedia
Network Systems and Applications in conjunction with ICDCS-2008,
June, 2008, Beijing, China
[2] Y. Chen, C. Chen and C. Li, "Measure and Model P2P Streaming
System by Buffer Bitmap", HPCC '08, Sept. 2008, Dalian, China
[3] Cx.Li,Cj.Chen ''Fetching Strategy in the Startup Stage of p2p
Live Streaming'', http://arxiv.org/abs/0810.2134
[4] Cx.Li,Cj.Chen ''Initial Offset Placement in p2p Live Streaming
Systems'' http://arxiv.org/abs/0810.2063
[5] Cx.Li,Cj.Chen ''Inferring Playback Rate and Rate Resets of p2p
Video Streaming Transmissions by Piecewise Line Envelope
Approximation'' The Journal of China Universities of Posts and
Telecommunications March.2009
[6] Cx.Li,Cj.Chen ''Real P2P System Measurement under Mobile IP
Environment'' accepted by icnds2009
8.2. Informative References
Author's Addresses
Yunfei Zhang
China Mobile
Phone: 86 13601032119
Email: zhangyunfei@chinamobile.com
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