should be required to disclose such practices, and if they should be allowed at all to discriminate among different traffic types is the subject of an ongoing debate.

Independent of the outcome of this debate, the tension will have to be resolved in a way that allows P2P applications to thrive while ensuring the profitability of ISPs. A promising technical approach is to bias the peer selection in P2P applications toward nodes connected to the same ISP or to ISPs that peer with each other. 20 Another solution is for ISPs to change their pricing model.

A more fundamental tension is that some ISPs view many of the currently deployed P2P applications as competing with their own value-added services. For instance, ISPs that offer conventional telephone service may view P2P VoIP applications as competition, and cable ISP may view P2P IPTV applications as competing with their own IPTV services. In either case, such ISP’s market share in the more profitable value-added services is potentially diminished in favor of carrying more plain bits.

In the long term, however, ISPs will likely benefit, directly and indirectly, from the innovation and emergence of new services that P2P systems enable. Moreover, ISPs may find new revenue sources by offering infrastructure support for successful services that initially developed as P2P applications.

conclusion

In this article, we have sketched the promise, technology, and challenges of P2P systems. As a disruptive technology, P2P creates significant opportunities and challenges for the Internet, industry, and society. Arguably the most significant promise of P2P technology lies in its ability to significantly lower the barrier for innovation. But the great strength of P2P, its independence of dedicated infrastructure and centralized control, may also be its weakness, as it creates new challenges that must be dealt with through technical, commercial, and legal means.

One possible outcome is that P2P
will turn out to be especially valuable
as a proving ground for new ideas and
services, in addition to keeping its role
as a platform for grassroots services
that enable free speech and the unreg-
ulated exchange of information. Ser-
vices that turn out to be popular, legal,
and commercially viable may then be
transformed into more infrastructure-
based, commercial services. Here,
ideas from P2P systems may be com-
bined with traditional, centralized ap-
proaches to build highly scalable and
dependable systems.

References

1. about skype: 100 billion skype-to-skype Minutes served; http://about.skype.com/2008/02/100_ billion_skypetoskype_minut.html.

2. adar, e. and huberman, b.a. Free riding on gnutella. First Monday 5, 10 (oct. 2000).

3. anderson, d.P. boinc: a system for public-resource computing and storage. in Proceedings of the 5th IEEE/ACM International workshop on Grid Computing (2004), 4–10.

4. bbc news. one million viewers use iPlayer. http: // news.bbc.co.uk/2/hi/technology/7187967.stm.

5. bittorrent (protocol). wikipedia; http://en.wikipedia. org/wiki/bittorrent_(protocol)#adoption.

6. blake, c. and rodrigues, r. high availability, scalable storage, dynamic peer networks: Pick two. in

Proceedings of the 9th workshop on Hot Topics in Operating Systems (May 2003).

7. castro, M., druschel, P., ganesh, a., rowstron, a. and wallach, d.s. security for structured peer-to-peer overlay networks. in Proceedings of the 5th Symposium on Operating Systems Design and Implementation (dec. 2002).

8. christin, n., weigend, a.s. and chuang, J. content availability, pollution and poisoning in file sharing peer-to-peer networks. in Proceedings of the 6th ACM Conference on Electronic Commerce (June 2005).

9. clarke, i., sandberg, o., wiley, b. and hong, t.w. Freenet: a distributed anonymous information storage and retrieval system. in Proceedings of the Designing Privacy Enhancing Technologies— International workshop on Design Issues in Anonymity and unobservability (July 2000).

10. cohen, b. incentives build robustness in bittorrent. in Proceedings of the 1st International workshop on Economics of P2P Systems (June 2003).

11. cox, L.P. Murray, c.d. and noble, b.d. Pastiche: Making backup cheap and easy. in Proceedings of the 5th Symposium on Operating Systems Design and Implementation (dec. 2002).

12. cox, L.P. and noble, b.d. samsara: honor among thieves in peer-to-peer storage. in Proceedings of the 19th ACM Symposium on Operating Systems Principles (oct. 2003).

13. decandia, g., hastorun, d., Jampani, M., Kakulapati, g., Lakshman, a., Pilchin, a., sivasubramanian, s., Vosshall, P. and Vogels, w. dynamo: amazon’s highly available key-value store. in Proceedings of the 21st ACM Symposium on Operating Systems Principles (oct. 2007).

14. dischinger, M., Mislove, a. haeberlen, a. and gummadi, K.P. detecting bittorrent blocking. in Proceedings of the 8th Internet Measurement Conference (oct. 2008).

15. douceur, J. the sybil attack. in Proceedings of the First International workshop on Peer-to-Peer Systems (Mar. 2002).

16. Freedman, M.J., Freudenthal, e. and Mazières, d. democratizing content publication with coral. in Proceedings of the 1st uSENIX Symposium on Networked Systems Design and Implementation (Mar. 2004).

17. hei, X., Liang, c., Liang, J., Liu, y. and ross, K.w. insights into PPLive: a measurement study of a large-scale P2P iPtV system. in Proceedings of the 15th International world wide web Conference, IPTV workshop (May 2006).

18. hildrum, K., Kubiatowicz, J.d., rao, s. and Zhao, b.y. distributed object location in a dynamic network. in Proceedings of the 14th Annual ACM Symposium on Parallel Algorithms and Architectures (2002), 41–52.

19. huebsch, r., hellerstein, J.M., Lanham, n., Loo, b.t,
shenker, s. and stoica, i. Querying the internet
with Pier. in Proceedings of the 29th International
Conference on Very Large Data Bases (sept. 2003).

 

Rodrigo Rodrigues ( [e-mail]) is a tenure-track faculty member at the Max Planck institute for software systems (MPi-sws), where he heads the dependable systems group.

Peter Druschel ( [e-mail]) is the founding director of the Max Planck institute for software systems (MPi-sws), where he heads the distributed systems group.