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  1. Peering Peer-to-Peer Providers Hari Balakrishnan Scott Shenker Michael Walfish MIT CSAIL UC Berkeley / ICSI IRIS Project 24 February 2005

  2. Academic P2P: An Abridged History • Early days: B.Y.O.I. (Bring Your Own Infrastructure) <k1,v1> <0x2da7, > <k2,v2> DHT • Recently: proposals to use P2P technology (DHTs resolve flat names) for core network services • Examples: CoDoNs, HIP, P6P, DOA <0x2da7, 8.2.9.2> DNS client CoDoNS node CoDoNS node DNS client DHT

  3. Academic P2P: An Abridged History, Cont. CoDoNS node CoDoNS node DHT • The DHT still has to run somewhere • But core network services cannot (or should not) depend on teenagers with cable modems … • Solution?

  4. A New School of DHT Research Open DHT [IPTPS04]: • DHT nodes should be managed • Run DHT as shared service • Running one is complex • Reuse minimal put-get iface • From B.Y.O.I. to Frat Party • Open DHT is a communal keg Sean Rhea

  5. So What’s the Problem? Sean has made Open DHT a stable, available, high-performance infrastructure … … but can’t afford to run it by himself, forever Shared infrastructure should be supported by a market, not by a benevolent donor

  6. Shared, Commercial DHT Service? • Must present users with a uniform “DHT dialtone” … • … in a competitive market for DHT service • Can multiple, competing providers coordinate? • Analogy: competing ISPs peer to give IP “dialtone” • Imagine: DSPs (DHT Service Providers) do likewise • For now, assume market demand exists • Investigate: federated P4 Infrastructure (Peering Peer-to-Peer Providers) of DSPs

  7. Requirements for a Global DHT Dialtone get (k) put(k,v) DSP DSP v Customer Customer P4 Infrastructure Customer pays its DSP for this service: • Puts of <k,v> accessible to all other P4 customers • Gets on keys will be fulfilled, no matter which provider serviced the put of <k,v> • Best effort service model

  8. Outline • P4 Design Spectrum • Challenges • Conclusion

  9. Scenario P4 Proxy <k4,v4> P4 Proxy <k1,v1> <k5,v5> DSP DSP v1 = get(k1) put(k1,v1) <k2,v2> <k3,v3> DSP Home User Company • Each DSP owns hosts, stores subset of {<k,v>} • Customer/provider interface: P4 Proxy (like DNS) • Assume for now DSPs all talk to each other • We now discuss possible relationships …

  10. Possible DSP Relationships (First Two) • All one DHT • Existing DHT mechanisms work • No incentive for DSP to contribute resources • Administrative separation (separate DHTs) • DSP coded into key  right incentives • DSPs store <k,v> only for customers • Switching DSPs means switching keys DSP ID Rest of the key

  11. Possible DSP Relationships (Third) • Now assume: • Every DSP runs own lookup infrastructure • Keys don’t encode DSP • Therefore: • DSPs must exchange customers’ <k,v> pairs • We believe this 3rd relationship is the tenable one • But how will it work? (For now, assume small set of top-level DSPs)

  12. Different Exchange Regimes • Get-broadcasting; local puts (can cache <k,v>) put (k, v) get (k) <k,v> • Put-broadcasting of <k,v>; local gets <k,v> put (k, v) get (k) <k,v> <k,v> • Put-broadcasting of keys only; forwarded gets provider’s id <k,*> put (k, v) <k,v> get (k) <k,*>

  13. More on the Regimes • They split put and get bandwidth differently • Can and should coexist; putter chooses regime • Different pricing schemes?

  14. Outline • P4 Design Spectrum • Challenges • Conclusion

  15. DSPs’ Incentives • Incentive to be honest? • Commercial relationships; market discipline • No different from DNS or IP service today • Incentive to peer? Settlements (i.e., payments between two peers): • Needed if two DSPs gain unequally from peering • Preclude caching and put-broadcast • Introduce complexity • Paper argues DSPs gain equally from peering w/out settlements?

  16. Coherence and Correctness • <k,v> inserted by a customer must be visible to customers of other providers • Discussed earlier • Customers must not be able to own the same key or overwrite each other’s <k,v> pairs • Inherit from existing DHTs, especially Open DHT • k=hash(v), k=(salt, pubkey),e.g. • Cryptography unaffected by # of providers

  17. Market Structure and Scale Top-level DSPs Child DSPs Forest structure (ISP analogy again) • Top-level DSPs do put- and get-broadcasting • Children of top-level DSPs either: • Redirect customer put/get requests to top-level • Maintain a local lookup service

  18. Outline • P4 Design Spectrum • Challenges • Conclusion

  19. Conclusion • P2P: technical revolution, yes. Economic novelty? • A social theory of DHTs (compare with Marx): Anarchism (B.Y.O.I.) Communism (benevolent entity) Capitalism (P4 a form of privatization) • Our goals: DHT dialtone for customers, proper incentives for providers • Peering arrangements necessary but not sufficient • Market requires demand, too

  20. Appendix Slides

  21. DSPs Gain Roughly Equally From Peering • Assume DSP’s benefit proportional to: • Its customers’ benefit from reads in other DSPs • Its customers’ benefit from having their data read • Case I: avg. benefit to a customer from a “get” is equal to avg. benefit from having its “put” read • Case II: avg. benefits not equal. Under certain assumptions, # of “gets” in each direction equal. # from B to A (larger fraction of smaller #) # from A to B (smaller fraction of larger #) # “gets” from DSP B # “gets” from DSP A

  22. Latency • Puts: customer talks to P4 Proxy. Low latency. • For gets, separate by exchange regime: • Get-broadcast: • Latency can be high • But opportunistic caching can mitigate • Put-broadcast of key; forwarded get: (same.) • Put-broadcast of <k,v>; local get: • All DSPs have copies of <k,v>; low latency • Adaptive algorithm to decide which propagation regime is optimal for a key?

  23. Can’t Google Do This? • Sure. • Will they charge for the service? • If not, great! • If so … • This talk: whether P4 infrastructure could emerge • Not whether P4 infrastructure will emerge • (We assumed market demand exists.)