Design of D istributed S ystems Programming of Interactive System s Lecture 3

1. Design of Distributed Systems Programming of Interactive Systems Lecture 3 Fredrik Kilander Wei Li

2. Agenda • RMI • Jini (Dynamic Service Discovery) • Overlay Networks • Web naming scheme • Data Representation (XML) • Web Service • System Architecture • Perspectives on interactive systems Distributed System Support for Ubiquitous computing

3. Binding a Client to a Server 2-15 Endpoint= IP+Port (server, endpoint) pairs Client-to-server binding in DCE (distributed computing environment 1990-) Distributed System Support for Ubiquitous computing

4. RMI Registry stub Service stub Java RMI • Clientsget the service location directly from the registry • RMI Registry is known to both RMI Client and RMI Server http://download.oracle.com/javase/tutorial/rmi/TOC.html Lookup Register(Service Binding) 2 3 1 Client 5 stub 4 Distributed System Support for Ubiquitous computing

5. Machine C MP3Selector Skeleton MediaPlayerController proxy1 proxy2 “http://myhost/a.mp3” “http://myhost/a.mp3” Passing Object by Value or Reference (RMI) • The object to send to another machine has to be Serializable. • The object to send has to have the class definition in the classpath of the receiving side • Setup security policy file Interface Method: void Play();void Play (String filename);void Play (MP3Selector mps); Machine A Machine B proxy2 Interface Method: void Play ();void Play (String filename);void Play (MP3Selector mps); Media Player Skeleton Three cases:1) Play () without parameters. // only method name will be sent 2) Play (“http://myhost/a.mp3”) // send filename as a copied object (value/copy) 3) Play (mps) { // send the copy of proxy2 play(mps.getLatestMP3()) // (reference to MP3Selector) } http://java.sun.com/developer/onlineTraining/rmi/RMI.html Distributed System Support for Ubiquitous computing

6. Java Jini • Jini is a technology for building service- oriented architectures. • Jini defines a programming model which exploits and extends Java technology. • Jini is a generally stable, fault-tolerant, scalable, dynamic, and flexible solution. Distributed System Support for Ubiquitous computing

7. Java Jini • Services discover lookup servers and register with multiple properties • Clients discover lookup servers and query them for services • Discovery with multicast (LAN) or unicast (WAN) Distributed System Support for Ubiquitous computing

8. Java Jini • RMI: registry is co-located with the service • Jini: lookup services can be anywhere • RMI: client must know the registry host • Jini: clients discover lookup services • RMI: service found by name • Jini: service found by name, attributes and interfaces Distributed System Support for Ubiquitous computing

9. Jini • Two ways to connect to a Lookup Service: • Multicast to discover local lookup services automatically (i.e. previously unknown) • Unicast to connect to a lookup service on a known host (e.g., remote subnet) Distributed System Support for Ubiquitous computing

10. Jini • Two ways to connect to a Lookup Service: • Multicast (1-M) to discover local lookup services automatically (i.e. unknown) • Unicast (1-1) to connect to a lookup service on a known host (e.g. on a remote subnet) Multicast Client Unicast Local Area Network Lookup service Firewall Internet Lookup service Distributed System Support for Ubiquitous computing

11. Jini (Registering a Service) (1) Multicast/Unicast to discover the LUS (2) Retrieve a registrar object from the LUS (3) Use registrar to send a service object to the LUS Distributed System Support for Ubiquitous computing

12. Jini (Discover a service) (1) Multicast/Unicast to connect to LUS (2) Retrieve a registrar object from LUS (3) Search service using registrar (4) Retrieve a service object (proxy) Distributed System Support for Ubiquitous computing

13. JINI • 2) Dynamic Service Discovery: • Multicast to discover local lookup service automatically • Unicast is used for a service to register from a remote subnet • 1) Simplified Running Environment: • Only one Jini lookup service is necessary in a local Jini network (local subnet). RMI and RMIRegistry is optional. (LookupService) (2) (4) (1) (3) (5) http://jan.netcomp.monash.edu.au/java/jini/tutorial/Jini.html http://www.jini.org Distributed System Support for Ubiquitous computing

14. Jini distributed garbage collection • Leases (time-delimited promises) • Example: • A service registers a service object on the lookup server in return for a lease • The service must renew the lease every five minutes (”I am still here”) • When the lease expires the LUS deletes the service object from its database Distributed System Support for Ubiquitous computing

15. Jini – dead service Lookup service Service Client Service registers a service object Client queries LuS LuS returns a lease LuS return service object Service renews lease Service crashes Client tries to call service Client gets RemoteException Lease expires LuS discards the service object Client discards the service object Distributed System Support for Ubiquitous computing

16. Middleware and Openness In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. Early Binding: Language, Interface. Distributed System Support for Ubiquitous computing

17. Overlay Network Based on MOC & Socket • Sockets gives a simple abstraction for message transfer over network • With sockets one can construct a new abstract network over the underlying IP network • Prerequisites: • New address schema (Naming) and its • Name resolution mechanism (routing) Distributed System Support for Ubiquitous computing

18. Web naming scheme • Uniform Resource Identifiers (URI) come in two forms: • URL: Uniform Resource Locator • URN: Uniform Resource Name Distributed System Support for Ubiquitous computing

19. Uniform Resource Locators Often-used structures for URLs. • Using only a DNS name. • Combining a DNS name with a port number. • combining an IP address with a port number. Common schemes Distributed System Support for Ubiquitous computing

20. Uniform Resource Names • Three parts:Scheme :Name space identifier : Name of resource • The name space identifier determines the syntactic rules for the third part. The third part may have different structure depending on the name space identifier. So URNs are not publicly resolveable. • In contrast to URLs, URNs are location-independent which means URNs usually are not related to any specific entity (only used as a name space). urn : isbn : 0-13-349945-6 Distributed System Support for Ubiquitous computing

21. Locating URL (Name Resolving) • Domain Name System (HostName -> IP) • Each computer has to be assigned an IP address and DNS server IP address manually or through DHCP server. • DNS Request (nslookup) sends the hostname to the specified DNS server. • The DNS server returns the IP if it knows it, otherwise, the request is forwarded to upper-layer DNS server. Record of E’s IP User host Distributed System Support for Ubiquitous computing

22. Data Representation / XML (1) • Extensible Markup Language (XML) is a standard format for interchanging structured documents. • XML is designed to describe data • HTML was designed to present data. • Anyone can use XML to define data in any tree-based structure. • To be able to distinguish different structures, XML Name Spaces are used to enable different structures of data to co-exist in one document. <?xml version="1.0" ?> <note xmlns:note=“http://tv.com/note.xml”> <note:to>Tove</note:to> <note:from>Jani</note:from> <note:heading>Reminder</note:heading> <note:body>Don't forget me this weekend!</note:body> </note> Distributed System Support for Ubiquitous computing

23. Data Representation /XML (2) • It is the reader application’s responsibility to understand (parse) the elements in the XML document. • Extensible Stylesheet Language Transformations (XSLT) is a language for converting XML document from one structure to another. • XSLT is one way to help the interoperation between distributed systems using different standards. Output text Input XML XSLT processor XSL transformation rules Distributed System Support for Ubiquitous computing

24. Data Representation /XML (3) • XML is self-describing • XML treats all data as text • Significant memory overhead • Examples: • XML-RPC • JXTA messages • Web Service, SOAP Distributed System Support for Ubiquitous computing

25. Overlay Networks • Examples: • P2P networks (Content-oriented network/P2P file sharing, SIP) • Naming: auto-generate UUID and register • Routing: JXTA Rendezvous etc Distributed System Support for Ubiquitous computing

26. Web Services XML Web services are the fundamental building blocks in the move to distributed computing on the Internet, it takes the ideas and principles of the Web and apply them to enable computer-computer interactions (B-to-B transactions): • SOAP (Simple Object Access Protocol): provides a simple and lightweight mechanism for exchanging structured and typed information using XML: • WSDL (Web Services Description Language): describing service information including message contents, service location, communications protocol (IDL). • UDDI (Universal Discovery Description and Integration): for registering Web services so that potential users can find them easily (service yellow pages/directory service). • programming-language neutral SOAP Distributed System Support for Ubiquitous computing

27. Clients/Servers Architecture • General interaction between a client and a server. 1.25 Distributed System Support for Ubiquitous computing

28. Three-tiered C/S model • The general organization of an Internet search engine into three different layers 1-28 Distributed System Support for Ubiquitous computing

29. Multitiered Architectures • Alternative client-server organizations (a) – (e). 1-29 Distributed System Support for Ubiquitous computing

30. Conclusion • Distributed System technologies: • Procedure- and object-based communication • MOM and socket • Naming and resolution • Overlay networks • XML, Software architecture • Today • Service-Oriented Architecture (cloud computing) • Dynamic service access (late binding) • Open standards • Still ’standards wars’: e.g. HTML5 video, Android versions Distributed System Support for Ubiquitous computing

31. Perspectives on interactive systems

32. Contents • Interactive systems from a user perspective • Interactive systems from a systems perspective • Desirable properties of tools • Analysis of Java, Python, C# • Other considerations Distributed System Support for Ubiquitous computing

33. Interactive systems from a user perspective • Supports cooperation between, and in, groups of users • CSCW, Wiki, Facebook, Twitter, Second Life, Blue Mars • Interactive spaces • Supports shifting modalities and forms of interaction • WWW • Cell phones, PDA • Voice, gesture and tactile interfaces (wii, iPhone)

34. Interactive systems from a user perspective • Supports mobility and distance • Users moving in the real world • Users moving between different systems • Supports interaction with resources in the environment • File sharing (transparent document management) • Useful devices, sensors

35. Interactive systems from a systems perspective • Distributed systems • Hierarchy: Client-Server, Peer-to-peer, open/closed • Computer communication issues • Transport, interaction protocols, security • Heterogenous systems and general interoperability • Hardware • Operating systems • Programmering languages • Software versions

36. Interactive systems from a systems perspective • Exotic hardware • Cell phones, sensors, RFID, micronets • Dynamics • The availability of resources; users, clients, services • Establishing and maintaining interaction sessions

37. To build interactive systems tools are needed • Communication methods and protocols • Programming languages • Runtime environments Distributed System Support for Ubiquitous computing

38. Desirable properties of tools • Hardware independence • Cell phones • PDA:s • Wearable computers (laptops) • Server computers • OS independence • Linux/Unix/OS X • Symbian/Android • Windows family • Computer communication • Remote Procedure Call (RPC) • TCP/IP, Serial ports, USB, FW

39. Desirable properties of tools • Hardware independence • Cell phones • PDA:s • Wearable computers (laptops) • Server computers • OS independence • Linux/Unix/OS X • Symbian/Android • Windows family • Computer communication • Remote Procedure Call (RPC) • TCP/IP, Serial ports, USB, FW Virtualization

40. Desirable properties of tools • Hardware independence • Cell phones • PDA:s • Wearable computers (laptops) • Server computers • OS independence • Linux/Unix/OS X • Symbian/Android • Windows family • Computer communication • Remote Procedure Call (RPC) • TCP/IP, Serial ports, USB, FW Virtualization Host system: vmWare, C++.. Language system: Java, Python, elisp

41. Analysis of Java, Python, C# Java Python C# yes yes yes Hardware independence OS independence Computer communication Security yes yes no* yes yes* yes yes yes* no

42. Analysis of Java, Python, C# Java Python C# yes yes yes Hardware independence OS independence Computer communication Security yes yes no* yes yes* yes yes yes* no

43. To reflect upon … • interaction implies communication • choose tools that enable and simplify communication (e.g. C# i Windows) • make abstract communication (t ex XML-RPC, SIP, SOAP) Distributed System Support for Ubiquitous computing

44. Other considerations: • asyncronous communication • object-oriented programming • mobile code • the agent metaphor • launch and maintenance • code distribution • version management Distributed System Support for Ubiquitous computing

45. End Distributed System Support for Ubiquitous computing