What are peer to peer networks?
The short answer to this question is simple, depending on your politics.One group sees peer to peer (P2P) networks as evil file sharing tools allowingmillions of otherwise law abiding citizens to inflict mortal damage to themusic, film and book publishing industries, mainly by downloading free ofcharge someone else’s “intellectual property”. Another side seesP2P as the dominant technology which empowers individuals to publishand consume media free of stricture or control.
If I ever get around to it, I’ll write a short article on the politicsof file-sharing. This article contains only technical information.
Technical discussion
The long answer to the question is not quite as simple. Technically, peer-to-peer (P2P) computing is a networking paradigm in which distributed, homogenous peered devices can notionally consume and provide resources (processing capability, network bandwidth, data storage capacity, content, etc.). P2P networks are classified either as pure: each peer has equal status and is non-essentialto the network’s integrity; or hybrid: a coordination authority (nodeserver) is central to the network’sfunctioning Schollmeier. Further classificationof P2P systems Kant has been undertaken to accommodate such networks as multiuser games and media streaming, amongst others.
Advantages of P2P networks
One advantage of P2P over client-server (C/S) is its robustness Parameswaran andthe dependability Walkerdine associatedwith the increased robustness. If the server in a C/S network becomes unavailablethen the entire network is nonfunctional, whereas pure P2P networks are virtuallyas resilient as the underlying network topology. (This is not, however, truefor hybrid P2P networks). Another advantage is the dynamic load balancingnature of P2P networks. As new services or content become available, andthe demand for them increases, the P2P network is quickly able to disseminatesuch content thereby structurally adapting to change.
Disadvantages of P2P networks
One disadvantage of P2P networks over CS networks is the controldeficit Marti they offer. It is not possible to guarantee that a particularnode will have access to a particular resource at a particular time,due to the fluid arrangement of network membership in P2P nets; peers generallymake no contracts as to their continued association or their trustworthiness Wang.Another disadvantage of P2P over CS networks is that their inefficient directory lookup Mizrak (search)algorithms cause scalability problems compared to centralized networks.P2P networks must query much of the network to ascertain a peer’smembership or the location of a service, CS systems generally constantlyand consistently provide a centralized repository (the server).
P2P networks can be used for a variety of applications:
- File Sharing (including music and video)
- Groupware, including project management
- News dissemination (RSS Feeds, NNTP)
- Distributed computing, distributed computations
P2P in vivo
P2P has become synonymous with file sharing, a contentious issue withinthe current legal framework of copyright and intellectual property law. Thisis, however, not what P2P is, just how P2P has been used.An analogy can be found in the early days of the printing press: when itwas first invented Gutenberg’s press was primarily used as a way to providesubversive views and political ideas to the populace, leading to the riseof Lutherism in Europe. Gutenberg’s press was not the subversive elementof the time, it was merely the disruptive technology enabling Lutherism.P2P networks and distributed computing have in large part been funded bygovernmental grants.
There are a large number of popular peer to peer networks. I have listedsome of them here and categorized them as either pure or hybrid accordingto the definition I gave earlier. It should be noted that each network isdefined by a common protocol, with potentially several different and competingimplementations running on each protocol.
| Implementation | Protocol | Type | Major Use | Licensing Model | Revenue Model | Tech Details | URL |
|---|---|---|---|---|---|---|---|
| BCDC++ | Direct Connect | Hybrid, hubs and supernodes | File Sharing | ?? | ?? | C++ |
 |
| BearShare | Gnutella | Hybrid, hubs | File Sharing | Closed Source | Advertising | Windows Only |
|
| BitTorrent | BItTorrent | Decentral-ized, mixed roles | File Sharing, RSS Feed sharing | Open Source, MIT License |
Voluntary – donations, some advertising ? | Python with xWindos client. |
|
| DC++ | Direct Connect | Hybrid, hubs and supernodes | File Sharing | Open Source, GNU GPL |
Voluntary | C++, Client only |
|
| eDonkey | eDonkey | Decentral-ized | File Sharing | Closed Source | Voluntary, not for profit ?? |
|
|
| eMule | eDonkey | Decentralized | File Sharing | Closed Source | Voluntary, not for profit | Windows only |
|
| Freenet | Freenet | Hybrid, nodes | Information dispersal, Anonymous | Open Source, GNU GPL |
Voluntary | Java |
|
| GnouGat | JXTA | Decentralized | FileSharing | Open Source,SunProject JXTA Software License |
Voluntary | Java only (JINI) |
|
| GnuNet-GTK | GnuNet | Decentralized, anonymous | File Sharing | Open Source, GNU GPL |
Voluntary | Source only, UNIX GTK,HTTP, SMTP, UDP over TCP-IP |
|
| Grokster | FastTrack | Hybrid | File Sharing | Closed Source | Advertising, Content distribution fee | Windows Only |
|
| Groove | Groove | Decentralized | Groupware | Closed Source | Fee Based | Windows Only |
|
| iMesh | FastTrack | Decentral-ized | File Sharing | Closed Source , freeware | Advertising | Windows Client |
|
| KaZaa | FastTrack | Hybrid | File Sharing | Closed source | Advertising, Spyware, Malware |
|
|
| Morpheus | FastTrack, Gnutela2, Direct Connect | Hybrid | File Sharing | Closed Source | Advertising | Windows only |
|
| Napster | Napster | Napster is now defunct as a P2P network. |
|
||||
| NeoModus | Direct Connect | Hybrid, hubs and supernodes | File Sharing | Closed Source | Advertising | C++, C# |
|
| OverNet | Overnet,eDonkey | Decentral-ized | File Sharing (large files) | Closed Source | Voluntary, some advertising ?? | Windows client only |
|
| Piolet / Blubster | Manolito, MP2P | Decentral-ized | File Sharing, MP3 only | Closed Source | ?? | Windows Only |
|
| Rebol | Rebol IOS | Decentralized | Internet Operating System | Closed Source | Commercial | Over 40 OSs |
|
| ShareAza | BitTorrent,eDonkey,
Gnutella,Gnutella2 |
Hybrid | File Sharing | Closed Source, freeware | Advertising | Windows Client |
|
| Soulseek | Soulseek | Centralized | MP3 File Sharing | Closed Source | Contribution based |
|
|
| WinMX | OpenNap,WPNP | Hybrid | File Sharing | ? | ? | Windows Client |
|
P2P Network Topologies
Most of the examples given here are based on the works of TanenbaumTanenbaum andNelson Minar. P2P networks implement a particular topology. In orderto qualify as P2P, as stated earlier, they may implement any topology except the centralized one,shown here.
The simplest avoidance of this reliance on the central server is a ringtopology. This kind of reminds of IBM’s token ring network. The problem hereis, that some nodes will most likely see data not destined for them, routingis very inefficient.
A popular P2P network topology is the hierarchical one. Famously, this systemwas in use by Napster, which made it very easy to shut down the entirenetwork. This system is also in force in the Domain Name System (DNS),which is by coincidence possibly the world’s most important P2P network.
The previous systems all had some degree of centralization, common amongthem was their fallibility, their reliance on a particular node for coordinationservices. The following topology does not have that problem. It is adecentralized, random, chaotic and entropic network. Communication canoccur between any two nodes, with each node holding routing informationfor others. Gnutella uses this network. Decentralized networks, withno coordinating authorities, rely on broadcast flooding. Flooding ishardly efficient and entails some bandwidth overhead for the network.
Hybrid topologies are formed from a combination of the preceding three basictopologies. There is the ring/centralized topology, a common favouriteof web server farms. The ring represents the farm of web / streaming/ database servers which are redundant and provide fail over safety. Thering itself is centralized, processing request from many clients. Thisis an improvement over the C/S topology, but it is still centralized.
The centralized – centralized topology is more complex. These can arise whenthe central server acts as a gateway server between two different networksusing two separate protocols.
There is also the centralized – decentralized topology currently in use onnetworks such as FastTrack. One of the internet’s core protocols, SMTP,also relies heavily on this topology for routing email between mail exchanges.
P2P research & development
Many of the worlds largest governmental and privately owned organizationsare conducting or funding research into all aspects of P2P networks. Hereis a short sample:
- Microsoft,CoopNet
- Microsoft, FarSite
- Microsoft, Pastry
- To find out exactly what microsoft are doing in this field, try thisGoogle search.
- Sun, JXTA
- Intel® Philanthropic Peer-to-Peer
- IBMHyperdatabase Research
- DARPA Oasis
Correspondingly, academic research efforts in the area of P2P computingis growing at an alarming rate, there is too much to do justice to here.
One very interesting area of research is in the field of broadcast optimization.When a P2P node issues a search query, this is typically broadcast toevery other node on the network, within the query’s time to live (TTL),the same as in any other TCP broadcast network. The introduction of “RumorMongering”Portmann, based on gossip message broadcast seems very promisingNovaes.
An old idea which doesn’t seem to have come far due to hash based distributiontables was IP multicasting.Vahamaki Thisis an interesting and efficient possibility, being revived in the contextof P2P multimedia streaming.
Any distributed, collaborative application must deal with connectivityissues. Typically, most computers are on private networks which are inaccessiblefrom the internet, hidden behind NAT boxes, routers and firewalls. SOAPand Web Services, based around the WDSL and UDDI protocols offer promisingalternatives to the current practice of punching holes in firewalls Rein.The ability to tunnel through the HTTP protocol will come as a boom tomany users, leaving network admins free to use stateful packet inspectionfor their security needs.
With the huge success of the rating systems implemented for books and goodsat Amazon, and for people and services at Ebay Mui,the utility of trust and reputation (T&R) systems has attracted hugeacademic attention. The degree of attention is unsurprising, since itseats neatly between computer technology and human sociology Barkai.This kind of thing has always attracted seriously large amounts of funding,since it is superficially able to answer the questions “What good isit to me,how can it beused” .Trust and reputation based P2P applications are likely to soon beginappearing on the scene, along with T&R web searches and more. T&Rbased systems are subject to abuse Damiani,of course, the challenge for academics is to integrate abuse resistance Surridge into theirT&R models.Unsurprisingly, research has already been published on how to misuseP2P systems in order to trick users in to downloading fake (misleading)mp3 music files Kwong.
References
- R. Schollmeier, “Adefinition of peer-to-peer networking for the classification of peer-to-peerarchitectures and applications,” presented at Peer-to-Peer Computing,2001. Proceedings. First International Conference on, 2001.
- K. Kant, R. Iyer, and V. Tewari, “Aframework for classifying peer-to-peer technologies,” presented at ClusterComputing and the Grid 2nd IEEE/ACM International Symposium CCGRID2002, 2002.
- M. Parameswaran,A. Susarla, and A. B. Whinston, “P2P networking: an information sharingalternative,” Computer, vol. 34, pp. 31-38, 2001.
- J. Walkerdine,L. Melville, and I. Sommerville, “Dependability properties of P2P architectures,” presentedat Peer-to-Peer Computing, 2002. (P2P 2002). Proceedings. Second InternationalConference on, 2002.
- S. Marti and H. Garcia-Molina, “Identitycrisis: anonymity vs reputation in P2P systems,” presented at Peer-to-PeerComputing, 2003. (P2P 2003). Proceedings. Third International Conferenceon, 2003.
- Y. Wang and J. Vassileva, “Trustand reputation model in peer-to-peer networks,” presented at Peer-to-PeerComputing, 2003. (P2P 2003). Proceedings. Third International Conferenceon, 2003.
- A. T. Mizrak, Y. Cheng,V. Kumar, and S. Savage, “Structured superpeers: leveraging heterogeneityto provide constant-time lookup,” presented at Internet Applications.WIAPP 2003. Proceedings. The Third IEEE Workshop on, 2003.
- A. S. Tanenbaum,Distributed Systems: Principles and Paradigms: Prentice Hall, 2001.
- M. Portmann andA. Seneviratne, “The cost of application-level broadcast in a fullydecentralized peer-to-peer network,” presented at Computers and Communications,2002. Proceedings. ISCC 2002. Seventh International Symposium on, 2002.
- O. J. Vahamaki,A. J. Allen, and J. T. Gaff, “High speed peer-to-peer communicationsystem for integrated protection and control in distribution networks,” presentedat Developments in Power System Protection, Sixth International Conferenceon (Conf. Publ. No. 434), 1997.
- M. Novaes and C. Codella, “Peerto peer multicast: an infrastructure for dynamically trading network resources,” presentedat Universal Multiservice Networks, 2002. ECUMN 2002. 2nd European Conferenceon, 2002.
- L. Rein, “Peer-to-peerXML,” Internet Computing, IEEE, vol. 6, pp. 100, 2002.
- D. Barkai, “Technologiesfor sharing and collaborating on the Net,” presented at Peer-to-PeerComputing, 2001. Proceedings. First International Conference on, 2001.
- L. Mui, M. Mohtashemi, and A.Halberstadt, “A computational model of trust and reputation,” presentedat System Sciences, 2002. HICSS. Proceedings of the 35th Annual HawaiiInternational Conference on, 2002.
- M. Surridge and C. Upstill, “Grid security: lessons for peer-to-peersystems,” presented at Peer-to-Peer Computing, 2003. (P2P 2003).Proceedings. Third International Conference on, 2003.
- T. C. H. Kwong and M. K. O. Lee, “Behavioral intention model forthe exchange mode Internet music piracy,” presented at System Sciences,2002. HICSS. Proceedings of the 35th Annual Hawaii International Conferenceon, 2002.
- E. Damiani, S. De Capitani Di Vimercati, S. Paraboschi, and P. Samarati, “Managingand sharing servants’ reputations in P2P systems,” Knowledge andData Engineering, IEEE Transactions on, vol. 15, pp. 840-854, 2003.
This reference list is available as an XML document.
Page created by Richard Quinn on March 19th 2004.
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