CM0256 Pervasive Computing

Transcription

1 CM0256 Pervasive Computing Guest lecture A World of Dots and SOAs Ian Taylor Ian.J.Taylor@cs.cardiff.ac.uk

2 Lecture Outline In this lecture we look at: Distributed computing techniques/middleware from 50,000 feet P2P Examples Gnutella Video Hype, round 1 cooltown Grid Computing Background, tools Video Hype, round 2 IBM Web Services Background benefits of service SOAs Convergence of all Technologies? Video Hype, round 3 JISC

3 Back to the Dawn of P2P Peer to Peer (P2P) - originally used to describe the communication of two peers. The internet started as peer to peer system e.g. ARPANET goal - to share computing resources around the USA using different networks UCLA, SRI, Utah and Santa Barabara all had equal status P2P From late 1960 s until 1994, machines were assumed to be switch on, connected and had an IP address assigned Then, invention of Mosaic and WWW led to a different type of user. The 1990's Client-Server Internet dial-up modems IP addresses changing unpredictable Late 1990 s Naptser, then Gnutella 2000 the new P2P started

4 The Brains Behind Gnutella We are Geeky and Rich! And now I am writing songs and eating toxic waste QuickTime and a TIFF (Uncompressed) decom are needed to see this

5 What is Gnutella???? Gnutella is a protocol for distributed search peer-to-peer comms decentralized model No third party lookup

6 Searching a Gnutella Network: Broadcasting 3-D Cayley Tree Searching in Gnutella involves broadcasting a Query message to all connected peers. Each connected peer will send it to their connected peers (say 3) and so on. Typically, this search will run 7 hops. If the number of connected peers, c=3 and the hops i.e. TTL=7 then the total number of peers searched (in a fully connected network) will be: S = c + c2 +c3 +.. ch = = 3279 Nodes

7 Searching a Gnutella Network: All nodes

8 Scaling Gnutella - Social Networks Stanley Milgram (Harvard professor) 1967 social networking experiment How many social hops would it take for messages to traverse through the US population (200 million) Posted 160 letters randomly chosen people in Omaha, Nebraska Boston Asked them to try to pass these letters to a stockbroker working in Boston, Massachusetts Omaha Rules: use intermediacies whom they know on a first name basis chosen intelligently make a note at each hop 42 letters made it!! Average of 5.5 hops Demonstrated the small world effect Proved that the social network of the United States is indeed connected with a pathlength (number of hops) of around 6 The 6 degrees of separation! Does this mean that it takes 6 hops to traverse 200 million people??

9 Lessons Learned from Milgrim s Experiment Social circles are highly clustered A few members have wide-ranging connections these form a bridge between far-flung social clusters this bridging plays a critical role in bringing the network closer together For example A quarter of all letters passed through a local storekeeper A half were mediated by just 3 people Lessons Learned These people acted as gateways or hubs between the source and the wider world A small number of bridges dramatically reduces the number of hops

10 Centralized + Decentralized New Wave of P2P Clip2 Gnutella Reflector (next) FastTrack KaZaA Morpheus Skype Jxta Like Social Networks perhaps?

11 The Gnutella Network Today The figure below is a view of the topology of a Gnutella network as shown on the LimeWire web site, the popular Gnutella file-sharing client. Notice how the power-law or centralized-decentralized structure is demonstrated.

12 So, What is New? Direct communication between two nodes on the Internet acting as both client and server is not novel. P2P addresses issues that have arisen through the nature and rapid growth of the Internet. Nodes that were not part of the fabric of an Internet application, now can constitute the majority. It is this ability to reach the edges is what is new about P2P.

13 Modern Peer to Peer What is an P2P application? P2P is a class of applications that takes advantage of resources e.g. storage, cycles, content, human presence, available at the edges of the Internet Clay Shirky Computers/devices at the edges of the internet are those: Operating within transient environments - computers come and go frequently They can be behind a firewall or NAT systems Have to operate outside of DNS Often have to deal with differing transport protocols, devices and operating systems

14 Maybe P2P is not a definition Oram writes: In fact, definitional inadequacies aside, peer topeer isn t really a set of technologies as much as it is a set of problems.

15 Cooltown:the future?? QuickTime and a YUV420 codec decompressor are needed to see this picture.

16 Grid Computing

17 Grid Computing Grid takes its name from analogy with electrical power Grid: electricity on demand via wall socket source unknown but reliable transparency and resilience are keys to its success The Grid dream is to allow users to tap into resources off the internet as easily as electrical power can be drawn from a wall socket - imagine

18 Get To Know Your Grid QuickTime and a TIFF (Uncompressed) d are needed to see th QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Foster I, Kesselman C and Tuecke S, (2001) The Anatomy of the Grid: Enabling Scalable Virtual Organizations The Grid is flexible, secure, coordinated resource sharing among dynamic collections of individuals, institutions, and resources The concept of Virtual Organisations

19 Globus Tools GT2 Recap: consists of four elements: Resource Management: to allocate resources provided by a Grid - GRAM Data Management: involves accessing and managing data GridFTP, GASS Information Services: to provide information about Grid services - MDS And of course: Security: to provide authentication, delegation and authorization

20 Grid computing by IBM Macintosh HD:Users:scmijt:Documents:WorkDoc:ComScJob:DistributedSystems:Lectures:PervasiveLecture:gridintroToOGSA.mov

21 Services A common Language? Web Services, P2P services, SOA and WS RF

22 What is a Service? A network-enabled entity that provides some capability (Foster/Kesselman) A service is a view of some resource, usually a software asset. Implementation detail is hidden behind the service interface. Some commentators also stress that this interface should be programming language independent. P2P applications normally work at the service level - adverts & queries - file sharing service, phone service, Jxta, etc. Web Services are seen as the standardized answer.

23 A Simple Web Service A minimal web service has three components: The Service: a software component which is capable of processing an XML document. Transport, programming language etc is not important The Document: the XML document that contains all of the application-specific information. The Address: describes the protocol binding (e.g. TCP or HTTP) & network address that can be used to access the service. also called an endpoint or port-reference In practice, also need an envelope (e.g. SOAP) adds things like security/routing info without altering the content of the message

24 XML Soap Client XML Envelope (SOAP) XML Web Server - Tomcat/Axis Or P2P? Why not XML XML Java Java Soap Client XML Java Envelope (SOAP) XML XML Web Service Interface (WSDL) SOAP Server Example when Client and Service implementations are Java

25 Service Oriented Architecture

26 The Service Oriented Architecture (SOA) The dynamic discovery and binding of services is often described in terms of the publish, find, bind triad of operations software components should be dynamically discoverable clear separation of the capabilities and implementation possible to quickly assemble impromptu computing communities with minimal coordinated planning efforts, installation technicalities or human intervention. Web Services are seen as the current optimum SOA - combination of SOA qualities plus XML message passing and stateless This model has been adopted by Grid computing

27 Globus V.4 Users/Clients Internet Routing VO VO GSI X. 509 Web Services VO (OGSA) VO GRAM Single Sign-on GridFTP VO MDS MDS Resources MDS Mutual Authentication Middleware (Globus)

28 QuickTime and a Sorenson Video 3 decompressor are needed to see this picture.

29 Summary Grid Computing P2P Standardized approach Strong trusted toolbase/ security Scalability Decentralized (fault tolerance, searching) Useful File Algorithms: Bittorrent, file swarming Web Services SOAs Standardised interface level tools Loosely Coupled XML + language of your choice Easy Development The Glue ties things together Grid computing tools exposed as services P2P Algorithms work at the services level

30 End of Lecture