Mobileman

Peer-to-peer and WiFiin Mobileman – Cambridge 3/7/03

Jon Crowcroft

The Computer Laboratory

University of Cambridge

jon.crowcroft@cl.cam.ac.uk

Mobileman

People and Projects in Cambridge

• Faculty: • Jon Crowcroft, Ian Pratt

• Research Staff: • Sven Ostring, +

• PhDs: • Rajiv Chakravorty & Meng How Lim• Daavid Spence, Andrew Twigg, Tim Moreton

• Projects: • COM(vodafone)• CMI• MobileMAN• Intel (marcello Pias_

Mobileman

Relevant p2p technologies

• Pastry/Scribe/Xenostore – • Storage, notification, searching• Consistent Hash + location• +++ Its Local +++

• Eternity, Freenet• Privacy, persistence,caching• Robustness• Rabin fingerprint, bloom filter

• Xen – OS which can run XP, Linux, BSD, Symbian, JVM…(c.f. vmware, denali)

• Seek Input from partner on Middleware

Mobileman

Location Services Experiment

• P2p makes use of techniques such as consistent hashing, rabin fingerprints, bloom filters and so on, for mapping key to location

• Perhaps a similar model could be used for addressing

• Would note that these often lead to very poor latency

• Techniques such as landmarks, shortcuts, lighthouse, chord etc are worth looking at

• Paper in to IPTPS on “lighthouses” – MSR now implementing in Pastry (to get proximity closer to “triangle” law…

Mobileman

Notification Services

• Could look at Scribe (P2P based Event service based on Pastry)

• Could look at event services as driving model – could be information or applications like games….

• enlist PhDs at cambridge!!!…• Depends on input from SUSPI on application of

intererest

Mobileman

Other Applications on the Move

• Notification (context – e.g. nearest gas station, nearest restaurant)

• Streaming (p2p – see later) audio (prob not video for cars content share, or server based slipstream is a Pastry service that does this

• Collaborative tools (field workers – engineer working on fixing problem with other engineers remotely helping)

• Other? (characteristics, security, cost etc etc) e.g. see Pastry (Xenostore and Xenostrust and Xenosearch)

• Seek input from partner on Applications!

Mobileman

3 layer architecture

• 3 Layer of System:• Ad hoc wireless

• P2p information layer

• Application layer

• Two problems to tackle• Align incentives across layers

• Deal with heterogeneity

Mobileman

Align Incentives

• Use WiOpt paper model for p2p layer as well as for ad hoc wireless

• Control law for earning and spending tokens• Control law for discounting tokens over time• Control law for minting of new tokens as

population grows• Tokens for sharing spectrum, storage, content etc

Mobileman

Heterogeneity

• Not all people have same resources

• Not all people are so honest

• How to create a system where equilibrium is close to trust and even share, but policy can be used to weight share?

• Relay on Wiopt algorithm property of approximate cconservation of token:• In any region, after any change of population, and after usage

has gone quiet, the system will reach equilibiu =>

• Can police propert

• Central agency (regulator)

• Distributed (witnesses)

Mobileman

Tolerating cheats, supporting the poor

• Strategy for treatment of cheats (deteected by regulator or witnresses consensus that more tokens in use than should be:• Ostravcisum (“tit-for-tat”) – one shot – not long term

• Strategy for supporting the poor:• Subsidy/Tax – weight tokens (change rate of accrueing

and discounting of tokens (similar to proposals for service differentiation using weighted ECN pricing in TCP!)

Mobileman

Heterogeneity in P2P

• It has been observed that “free riders” are not 100% idle in the community – they often just reduce what they offer to a lower %age than a team player would

• This may reflect poverty (dealt with before) or meanness (also dealt with)

• Main extension to WiOpt ideas are that we may have to factor in more than 2 parameters (capacity, battery, storage, etc)

Mobileman

Ongoing work with MSR and Intel

• See if can add token scheme to multihop version of MAC

• See if can add token scheme to pastry • Use in one application – one of

• Scribe (event architecture)

• Splitstream (media streaming with layered adatpive QoS)

• Again, need to consider User Community• Possible synergy with MMAPPS and Equator

Mobileman

Other Cambridge Efforts

• Hosting WiOpt ’04• Infocom ‘04 2 submissions on seamless handover

from gprs and 802.11• Several (4) posters and papers (5) in SIGCOMM