peer-to-peer(p2p) zhenxiang chen network center of jinan university [email protected]
TRANSCRIPT
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Table of Contents
• Background• Definitions• P2P based applications• P2P structure• Challenges• Platform and tools• Conclusion• References and workgroup
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Background
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What is peer
Firewall
因特网洲际主干
洲际主干
ISP
消费者用户
第三方内容
Web 服务器
应用服务器
因特网主干
地区网络
企业网提供商
ISP
专业提供商
本地 ISP
T1
社团用户社团网络
数据库
消费者用户
Peer
Peer
Peer
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What is overlay network
• Overlay networks create a structured virtual topology above the basic transport protocol level that facilitates deterministic search and guarantees convergence.
IP
Overlay
IP
Overlay
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Application Layer Network
• Application Layer Network• Overlay Network• 网络:定义主机之间通信的寻址
方式、路由方式和服务模型• 在现有的 Internet 传输网络之
上构建一个完全位于应用层的网络系统• 拓扑发现,路由等功能完全由
应用层自己完成,不依赖网络层
• 基于 Internet 网络的大规模的分布式应用
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Futures of Application layer Network
• 优点:• 易于部署,不依赖于网络设备的升级• 可扩展性好
• 缺点:• 增加了复杂性和处理开销• 无法利用最佳路由,增加了延迟• 破坏了网络的分层结构模型
• 路由具有“自私”特性 (AS/bandwidth/get and offered)
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Other Overlay Networks
• Peer-to-Peer systems• Application layer multicast• VPN• Service Overlay Networks• 6bone• Content distribution networks
6/4
Internet v4
6/4 4
6
6
6
6/4NAT
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12
… …
n-1
A:Sarnoff A:Sarnoff ’’law :law : 规模是规模是 O(n)O(n)
B: Metcalfe B: Metcalfe ’’law :law : 规模是规模是 O(nO(n22))
CCnn33
CCnnn-1n-1
CCnn22
CCnn22
C: Reed C: Reed ’’lawlaw :规模是:规模是 O(2O(2nn))
Sarnoff Sarnoff ’’law(law( 萨萨罗夫定律罗夫定律 )) :效益规:效益规模是模是 O(n)O(n) :网络是:网络是广播媒介,任广播媒介,任 11 发送发送者(设备)和多个者(设备)和多个(n-1)(n-1) 接收者(设接收者(设备)。备)。
Metcalfe Metcalfe ’’lawlaw (( 梅特卡夫定律):效梅特卡夫定律):效益规模是益规模是 O(nO(n22)) 网络网络是全互连媒介,任何是全互连媒介,任何11 个设备可与其它个设备可与其它 n-n-11 个交互,同时存在个交互,同时存在n(n-1)=nn(n-1)=n22-n-n 个并个并发执行的事务发执行的事务
Reed Reed ’’lawlaw (瑞德(瑞德定律):效益规模是定律):效益规模是O(2O(2nn)) :网络是群组:网络是群组媒介。网络可建立媒介。网络可建立CnCn22+Cn+Cn33++……CnCnnn--1+Cn1+Cnnn = 2 = 2nn-n-1 -n-1 个个小组小组
Network service scale rules
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Problem
• Client-Server and Web architectures are inherently centralized.
• Some problems involve distributed control, distributed data, or a hierarchical organizational structure.
• Fitting a centralized solution to a decentralized problem makes a poor solution.
Thick Thick ClientClient
Thick Thick ClientClient
ServerServer
Thin ClientThin Client
Web ServerWeb Server
Database Database ServerServer
Middle TierMiddle Tier
BrowserBrowserBrowserBrowser
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P2P Architecture
• P2P means actors in the system talk directly with each other as equals.
• Can decentralize some or all of the solution.• Represents distributed or hierarchical information
models.• Moves data and control to where the action is.
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Definitions
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Definitions of P2P
• Intel 工作组:通过在系统之间直接交换来共享计算机资源和服务的一种应用模式
• R.l.Granham: 通过 3 个关键条件定义• 具有服务器质量的可运行计算机• 具有独立于 DNS 的寻址系统• 具有与可变连接合作的能力
• C.Shirky:• 利用因特网边界的存储 /CPU/ 内容 / 现场等资源的一种应用• 访问这些非集中资源意味着运行在不稳定连接和不可预知 IP 地址环境下, P2P
节点必须运行在 DNS 系统外边• 具备有效或全部的自治
• Milojicic et al. (HP) : P2P refers to a class of systems and applications that employ distributed resources to perform a critical function in a decentralized manner.
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Controversy
• Is p2p a new approach?
Problems is peer-to-peer systems are neither new nor unique; they make us look for solutions
to old problems that we all worked around or tried to ignore before.
Andy Oram (O'Reilly & associates)speech at Free and Open Source
Software Developers's MeetingBrussels, BE, Feb. 2002
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P2P based applications
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Examples of p2p usage
• File-sharing applications• Distributed databases• Distributed computing (grid?)• Collaboration• Distributed games• Instant messaging• Ad hoc networks• Application-level multicast• Etc.
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Peer-to-Peer Systems
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Interesting P2P Applications
• Gnutella for dictionaries (with supernode)• Worldwide Lexicon, http://picto.weblogger.com
• Infrastructure for interoperability• Edutella (RDF-based Metadata Infrastructure),
http://edutella.jxta.org/
• Global-scale storage• Oceanstore, http://oceanstore.cs.berkeley.edu/
• Payments (not involving a bank)• PayPal (more than 0.4 billion accounts, payment
volume 15B/year per year, profit 230M/year)• eCount.com (email payment)
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Interesting P2P Applications
• Instant Messaging• Jabber, http://www.jabber.org/• Skype, http://www.skype.com
• VoIP (good quality, latency and 256-bit encry, NAT/firewall traversal)• Skype , www.skype.com/
• Groupware• Groove, http://www.groove.net/
• FOAF (Friends-of-a-Friend)• FOAFNaut, http://www.foafnaut.org/ • Friends Reunited, http://www.friendsreunited.com/ • Orkut, http://www.orkut.com/ • Tribe.net, http://www.tribe.net/
• Application-layer multicast• PPlive,QQlive
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Interesting P2P Applications
• 虚拟超级计算机 peer-to-peer technology 产生空前大量的计算能力
• 使医疗研究者能加速治疗方法的改进和药物的设计
• 加快癌研究的新发现
http://www.stanford.edu/group/pandegroup/Cosm/
http://members.ud.com/vypc/cancer/
Folding@home/ 蛋白质折叠和药物设计
Site@home/ 寻找地外文明计划http://www.equn.com/seticn/
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P2P Structure
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P2P Overlay Network structure
• Unstructured• Without prior knowledge
of the topology• Flooding
• Freenet• Gnutella• FastTrack/KaZaA• BitTorrent• Overnet/eDonkey
• Structured• Topology is tightly
controlled• DHT (distributed hash
table)
• CAN• Chord• Tapestry• Pastry• Kademlia• Viceroy
hybrid
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Centralized model (Napster)
• File-sharing system• Almost distributed system
• The location of a document is centralized• The "transfer" is peer-to-peer
• Problems• Robustness• Scalability (?)
• Impacts• Lawsuits• Denial of service
INTERNET
locationserver
register
Document x?OK: Peer ZIP = a.b.c.d
Document x!
x
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Non-structured system (Gnutella-like)
• Two phases (like Napster)• Localization + exchange
• No server• Open source
• gnutella.wego.com
• Distributed search• The query is flooded• Loop avoidance• Limited TTL (not all nodes are visited)
1
1
2
34
1
5
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Freenet
• Anonymity• Replication, cache
• Routing• Local knowledge• cache• TTL limits search
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FastTrack/KaZaA
5
3
2
11
4
metadata
metadata
Supernodes still use a broadcast protocolforsearch.
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Related work: Skype From the KaZaA community
• Promote to super nodes• Peer cache of some super nodes• Based on availability, capacity
• Protocol among super nodes: ???• Other features
• Auto-detect NAT/firewall settings• Allows searching a user (e.g., kun*)• History of known buddies• All communication is encrypted• Conferencing
P
P
P
P
PP
PP
P
P P P
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BitTorrent
seed
url
The tracker keeps track of all the owners and lookup peers.
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Why structured?
• Query time, number of messages,network usage, per node state, etc.
Unstructured
P2P systems
Structured
Data availability• Decentralization• Scalability• Load balancing• Fault tolerance
Maintenance• Join/leave• Repair
Efficient searching• Proximity• Locality
• If present => find it• Flooding: not scalable• Blind search: inefficient
Core facility—DHT ( Distribute Hash Tables )
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General concepts of DHTs
• Every object has a (hash) key• An object is stored at the node responsible for its
key• Every node maintains a small routing (hash) table
consisting of its neighboring nodes• All DHTs provide one elementary function
• lookup(key) node
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The role of DHT in structured P2P
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Chord lookup
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Chord lookup w/ finger table
id-space = 2m
m = 6
size = m
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Challenges
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Technical Challenges of P2P
• Decentralization• Control• Security• Sustainability• Management
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Decentralization
• Fully decentralized means every peer is an equal participant and no peers have special or administrative abilities
• Fully decentralized is difficult and many P2P systems are hybrids
• Decentralization is a tool, not a goal• Centralize the parts that need to be fast and need
to scale• Decentralize the parts required by the problem
model
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Control
• Myth: P2P has no control over their systemsTruth: P2P has no central control, but each peer is constrained by its own rules
• Myth: P2P systems must rely on honor system and are prone to malicious usersTruth: P2P systems have a design tradeoff, openess vs. susceptibility
• Myth: There is no way to control the data in a P2P systemTruth: No one has super-user access to the data. But users control the data they create.
• Myth: P2P has anonymous users with no accountabilityTruth: Mechanisms like pseudonyms allow anonymity while enforcing accountability
• Myth: P2P systems can’t exclude known malicious usersTruth: Decentralized user access is possible but tricky
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Security
• P2P applications can be made secure much like the IP protocol
• Encryption can ensure that a file is unread and unmodified even if it passes through the control of malicious peers (eg. Freenet)
• Data’s origin can be ensured even though anyone can add data to the system (eg. Groove)
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Sustainability
• You need a cool idea and a critical mass• System must be easy to use• Normal use of the system needs to contribute to
the system • Imposition on users must be things they don’t mind
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Managemnet
• Selfishness• Equitableness• Impact to IP networks• Copyright and laws
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Platform and tools
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Jini – a service broker
• Jini is a Java-based service toolkit• Provides service broker called Jini Lookup Service• Provides discovery and notification API• Service stubs passed to requester
Jini Lookup Service
ServiceRequester
Jini ServiceProvider 1
Jini ServiceProvider 2
Jini ServiceProvider 3
Need service X with attribute A
Service XAttributes: B, D
Service YAttributes: C
Service XAttributes: A, D
ServiceProvider 3
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JXTA (Sun)
• Open platform for p2p cooperation
• Interoperability• Any system/peer/application
• Platform independency• Languages (C, Java, etc)• Systems platforms (Unix, Windows, etc)• Networking platforms (802.11, Bluetooth, TCP/IP, etc)
• Ubiquity• Sensors, PDAs, routers, desktops, laptops, storage
systems
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JXTA (Sun)
• Objectives• Find peers and resources• Share files with anyone across the network • Create a particular group of peers across different
networks • Communicate securely with peers across public networks
• Projects• Applications (24 projects)• Core (13 projects)• Demos (3 projects)• Forge (15 projects)• Other (12 projects)• Services (24 projects)
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JXTA (Sun) Protocols
• Peer discovery protocol• Peer resolver protocol• Peer information protocol• Pipe binding protocol• Endpoint routing protocol• ……
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JXTA (Sun)
Peer (Desktop, cell phone, PDA, etc.)
Security
Peer Groups Peer Pipes Peer Monitoring
JXTA Community ServicesSun JXTAServices
JXTAShell
PeerCommands
JXTA Community Applications
CORE
JXTA
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JXTA applications
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PlanetLab
• Testbed to experiment with your networked applications. • >400 nodes, >150 sites, • PlanteLab consortium: 80+ universities, Intel, HP
• View presented to users: a distributed set of VMs• Allocation unit: a slice = a set of virtual machines (VM),
one VM at each node.
452 nodes162 sites450 research projects
VMM VMM VMM VMM
S
lice
K
OS S
lice
K
OS S
lice
K
OS S
lice
K
OS
http://www.planet-lab.org/
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PlanetLab usage examples
• Stress-test your Grid services (Globus RLS)• GSLab: a playground to experiment with grid-services • ‘Better-than-Internet’ services:
• Resilient Overlays • Multipath TCP (mTCP)• Multicast Overlays
VMM VMM VMM VMM
OS
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Conclusions
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Reviews
• P2P solutions can fit the problem model better than client-server or web solutions
• P2P solutions can do some cool things• P2P solutions can be production quality, but have
different issues than client-server or web solutions• It is not hard to code a P2P solution• Interesting application • Big challenge
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Final remarks
• P2P implies a very large spectrum of areas• High interest in both academicals/industrials• Much has already been done, but no conclusions
are definitive• IPv6 and P2P
• NAT, firewalls, IPv6 as an overlay
• Many open issues• Trust, security, scalability, QoS, etc.
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P2P related research in future
安全和保护诚信匿名声誉
智能代理 /Web-based 服务
比赛安排服务描述
网络结构和设计Network Topology
RoutingOverlay Networks
分布式数据库查询分解查询分布
仲裁
P2P
社会人际小世界现象
Power-Law 网络
商业和法律问题商业模式知识产权
分布式数据结构分布式 Hash 表
可扩展分布式数据
网络结构和设计网络拓扑路由
重叠网络
可扩展路由和对象可扩展路由和对象定位定位
性能提高性能提高 语义重叠网络语义重叠网络 P2PP2P 算法算法 复制复制 基于基于 WebWeb 的信息的信息
搜索搜索 激励和公平激励和公平 隐私隐私 // 安全安全 // 诚信诚信
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What can we learn from P2P?
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P2P 系统实例研究摘要 ----- 系统特点
分类 可选解 平台 语言 / 工具 不同点 网络
Avaki 分布式计算
单装置 HPC超级计算
Linux, WinSolaris
OO,ParalFort.Ada,C
分布管理、异质、安全高并
因特内网
SETI@home 分布式对象 所有通用OS
Closed source 大规模 因特
Groove
协同
Web-Based协同
Windows JavaScript,VB,Perl,C++,XML 回放、自更新 因特内网
Magi 分布文件聊天 / 消息
WindowsMac
Java,XML,HTTP,WebDAV
基于 HTTP平台独立
因特Ad-hoc
Freenet内容共享
匿名可信单点
Any withJava
Java 实现和 APIs 匿名保存 因特
Gnutella 中心服务 WindowsLinux
Java,C 协议 因特
JXTA平台
C/S Solaris Linux, Win
Java,C,Perl 开发源码 因特
.NET/My Service
Web-Based Windows C#,VC++,JScripVBScrip,VB
基于 MS 应用 因特移动
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P2P系统
实例特点比较研究 -------- 系统特点
非集中化 可扩展性 匿名 自组织 权成本
Ad-hoc 性能 安全 透明性 容错 交互
Avaki 无中心 1000测 2-3千
N/A 失效重构 低 进出计算资源 加速 加密认证管理域
本地HW/SW异质
校验重启可靠报文
同 SUN网格
SETI@home
主从 百万 中 低 很低 进出计算资源 大加速 私有 高 定时校验 IP?
Groove 混合P2P
N/A 差 高 低 协同进出
中 共享空间 /认证授权
高 消息进队列
基于 IP
Magi 混合P2P
约 100 N/A N/A 低 伙伴进出
N/A 证书授权 离线伙伴通信
消息进队列
JXTA/WEebD
AV
Freenet 纯 P2P 理论LogN
高 高 低 Peers 的进出 中 匿名 / 防DOS
高 无单点故障
低
Gnutella 纯 P2P 千 低 高 低 Peers 的进出 低 不明 中 再用下载 IP?
JXTA 纯 P2P 嵌入式系统
N/A N/A 低 Peers 的进出 N/A 加密算法 / 分布
信任
低 低 低
.NET/My 混合 世界范围 N/A 中 低 Peers 的进出 高 基于护照 高 复制 SOAP/XML/UDDI/WSDL
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P2P系统
实例商业模式的比较研究 ----- 系统特点
收入模式 支持应用 知名用户 竞争者 基金 商业模式
Avaki 产品和开放源码 计算网格共享安全数据
无 /科学实验室评价
平台计算Globus
Startup N/A
SETI@home
学术研究 关闭 学术 cancer@home...
政府 售机加屏保
Groove 产品 进销存 N/A Magi IPO 选 Lotus协同工具
Magi 产品和开放源码 共享文件消息聊天 全球 e 技术媒体软
Groove Startup N/A
Freenet 开放源码 文件共享 公共 N/A Startup N/A
Gnutella 开放源码 文件共享 公共 N/A 公共领域 选 P2P 算法
JXTA 开放源码& 所有权扩展
文件共享事件通知 多 P2P端口到 NET/Myservice
Sun支持的公域
公用 P2P 平台
.NET/My 所有权 & 开放源码标准
微软办公其它 MS 大基数 AOL/J2EE/JXTA
MS 内部 普适平台
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系统和应用需求
解决方案比较 1---- 系统类型
Centralized C/S Peer to Peer
非集中化 低(无) 高 很高
Ad-hoc 行为 无 中 高
产权成本 很高 高 低
匿名 低(无) 中 很高
可扩展性 低 高 高
性能 单独高聚合低 中 单独低聚合高
容错 单独高聚合低 中 单独低聚合高
自组织 中 中 中
透明性 低 中 中
安全 很高 高 低
交互性 标准化 标准化 正在进行
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目标 标准 解决方案比较 2---- 系统类型Centralized C/S P2P
用户普适性 低 中 高技术水平 低 高 中
复杂性 高 低 中信誉声望 高 中 低
开发者复杂性 高 直接 典型- N0
支撑能力 低 高 中工具 中(私有) 高-标准 低(少)兼容性 中 高 低
IT记帐能力 高 中 低
在控 高(全) 中 低管理能力 中 高 低标准 中(私有) 高 低(无)
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Main references
• Eng Keong Lua et al. “A Survey and Comparison of Peer-to-A Survey and Comparison of Peer-to-Peer Overlay Network SchemesPeer Overlay Network Schemes,” IEEE Communications Surveys and Tutorials, Vol 7, No 2 (Second Quarter, 2005), pp. 72-93.
• Ion Stoica, Robert Morris, et al. “Chord: A Scalable Peer-to-Chord: A Scalable Peer-to-peer Lookup Service for Internet Applicationspeer Lookup Service for Internet Applications,” Proceedings of ACM SIGCOMM 2001, San Deigo, CA, August 2001, pp. 149-160.
• Diego Doval and Donal O’Mahony, “Overlay networks: a Overlay networks: a scalable alternative for P2Pscalable alternative for P2P,” IEEE Internet Computing, Vol 7, No 4 (July-August 2003), pp. 79-82.
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References
• Distributed Computing• Distributed (www.distributed.net)• SETI@home (www.seti.org)• Genome@home (gah.stanford.edu)• Folding@home
(www.stanford.edu/group/pandegroup/folding)• Global Grid Forum (www.globalgridforum.org)• Globus Project (www.globus.org)
• File sharing• Napster (www.napster.com)• Gnutella (gnutella.wego.com)• Kazaa (www.kazaa.com)
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References
• Distributed hash tables• CAN (www.acm.org/sigs/sigcomm/sigcomm2001/p13-
ratnasamy.pdf)• Pastry (research.microsoft.com/~antr/Pastry)• Chord (www.pdos.lcs.mit.edu/chord)• Tapestry (www.cs.berkeley.edu/~ravenben/tapestry)• Freenet (freenet.sourceforge.net)• Kademlia (kademlia.scs.cs.nyu.edu)
• Ad hoc networking• AODV (www.ietf.org/internet-drafts/draft-ietf-manet-
aodv-13.txt)• OLSR (www.ietf.org/internet-drafts/draft-ietf-manet-olsr-
10.txt)• Tribe (rp.lip6.fr/site_rp/_publications/350-79Viana.ps.gz)
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References
• Platforms • JXTA (www.jxta.org)• .NET (www.microsoft.com/net)
• Collaboration• Groove (www.groove.net)• Endeavors (www.endeavors.com)
• IPv6 as a p2p overlay• Working Groups
• p2p.internet2.edu• www.openp2p.com
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Slides borrowed
• Chord: A Scalable Peer-to-peer Lookup Service for Internet Applicationshttp://pdos.csail.mit.edu/~rtm/slides/sigcomm01.ppt
• P2P-SIP: Peer to peer Internet telephony using SIPhttp://www1.cs.columbia.edu/~kns10/research/p2p-sip/
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Working groups et al.
• A generic site on p2p from O'Reilly• www.openp2p.com
• P2P working group• www.peer-to-peerwg.org/
• Internet2 p2p working group• p2p.internet2.edu
• Peer-to-peer development (p2p-hackers)• zgp.org/mailman/listinfo/p2p-hackers
• Interesting meeting• www.codecon.org
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Reading
• CAN• Chord
• Tapestry• Pastry