I.1 Distributed Systems Prof. Dr. Alexander Schill Dresden Technical University Computer Networks Dept.

I.2 Motivation and development tendencies Desktop PC: multitasking networking direct manipulation, graphical interface high performance (CPU, transfer) large primary and secondary storage Areas of application: management / development (CASE – Computer Aided Software Engineering) team working (CSCW – Computer Supported Collaborative Work) group communication process control (CIM – Computer Integrated Manufacturing)

I.3 Sample topology networked workstations, also organizationally integrated super-proportionally increasing communication performance Distributed OS LAN (for instance high performance network) LAN L A N L A N WAN V.A.N. Value added network Distributed DB

I.4 Distributed System physical computer nodes (processor + storage) direct / indirect computer coupling –local networks (Ethernet (CSMA/CD), Token Ring, Token Bus) –high-performance networks (Gigabit Ethernet, ATM) –gateways / bridges –radio networks (GSM, UMTS) transport-oriented comm. protocols (TCP/IP, UDP/IP, IPng) communicating processes –complete logical connection –no complete physical connection (communication via inter-components) system oriented resources (file system, threads, system programs) distributed storage, decentralized, co-operative distributed applications (area specific) on top of distributed systems

I.5 Example: distributed application Distributed OS LAN for instance high performance network) LAN L A N L A N WAN V.A.N. Value added network Distributed DB Logical communication path Process

I.6 Distribution: Purposes data, function and load distribution decentralization and co-operation locality properties and efficiency integration of partial applications remote resource access fault tolerance: reliability and availability

I.7 Client (for instance Point of Sale) Client (for instance Automated Teller Machine) Server (for instance account server) Server (for instance database) Requirements: -decentralized system structure -Internet/Intranet-integration -scalability -security concepts -transaction processing -heterogeneity of systems Client (for instance Home Access) Application example

I.8 Network infrastructure: examples required bridging between heterogeneous networks, system platforms and applications Middleware Client (for instance Point of Sale) Client (for instance Automated Teller Machine) Server (for instance account server) Server (for instance database) Client (for instance Home Access) X.25 Modem / ISDN / ADSL Internet-access Fast Ethernet / Token Ring ATM ISDN / X.25 Fast Ethernet / Token Ring

I.9 N-tier-architectures Client (for instance Point of Sale) Client (for instance Automated Teller Machine) Server (for instance account server) Server (for instance database) 3-tier: three-level structure; preferable for complex applications 2-tier:two-level structure (user-interface Host); simpler, but less flexible Client (for instance Home Access) User interface, if necessary pre-processing (thin client vs. fat client) Application logic Data management

I.10 Middleware and Client/Server: coordination Client (for instance Point of Sale) Middleware (for instance Java RMI, CORBA,.NET, SOAP) Transport-oriented layers (for instance TCP/IP, SNA) Phys. network (for instance Fast Ethernet, Token Ring, ATM) Server (for instance account server) Middleware Transport-oriented layers Phys. network Application interaction Object interaction Def. of Middleware: “Infrastructure services for distributed applications for bridging of heterogeneity of different systems and networks”

I.11 Middleware: Basic technologies Java (Sun and others): - programming language, applets - Remote Method Invocation (RMI) - Enterprise JavaBeans (EJB): Components CORBA (Common Object Request Broker Architecture): - object-oriented, language independent; relatively low-level - standard of Object Management Group (OMG).NET / COM+ (Component Object Model): - object-oriented, COM+ relatively proprietary,.NET more open - development of Microsoft Further approaches: - MOM (Message Oriented Middleware) - SOAP (Simple Object Access Protocol), Web Services - transaction monitors, Application Servers

I.12 Middleware: general overview Integrity Flexibility Client/Server, Remote Procedure Call (RPC) (for instance DCE - Distributed Computing Environment) Transaction monitors Message Oriented Middleware CORBA-/ RMI-/.NET/SOAP- Object-oriented Basic comm. Object Transaction Monitor Component- Frameworks (CORBA, Enterprise JavaBeans,.NET, WebServices) Application Server / Enterprise Appli- cation Integration Usability by application developer

I.13 System models Client/Server (Remote Procedure Call): Client Call Result Server Offered procedures Control thread and data transfer Separate address spaces Object-oriented communication: Computer 1 Computer 3 Computer 2

I.14 Client A Copy Document 1 Client B Client C Copy Document 3 Document 1 Document 2 Document n Document Server... provide document (“Document 1”) generate index (“Document 1”) provide document (“Document 3”)

I.15 Client-Object A Client-Object B Client-Object C Document Server... D1 = Server.provideDocument (“Document 1”) D1.move (here) D1. D2 = Server... D2.generate Index () D3 = Server.provideDocument (“Document 3”) D3. Document 1 Document 2 Document n Document 1 Document 2 Document 3

I.16 Comparison of system models higher transparency grade and improved influence on distribution with object-oriented model