Chapter5 : Client Server Computing

Transcription

1 Chapter5 : Client Server Computing Lecture 10 TIM 50 Autumn 2012 Thursday October 30, 2012 Book By Musacchio

2 Announcement As TIM50Class ecommons now works, Students should submit business proposal and DB assignment 1 on ecommons. For details refer do class webpage. 3. The Mid-Term on November 1, Thursday 4. The grades for every assignment will be given in ecommons. 5. It's important to check webpage to get the latest information and assignments changes. 6. Business paper group released. Submit your business proposal through e-common Check class webpage Frequently!.

3 Review Information Technology ALU Memory RAM, ROM Mag/Flash/USB I/O Data Bus Clock Pulse, Speed Business Information Systems Computer System Architecture, Functions H/W S/W Binary System Data Formats Boolean Logic, Gate Machine Language Hi-level Language Operating System Window, Mac, Linux Data representation Data Copy Data Transfer Data communications Protocols Network Computing Architectures Data Processing through Network Systems Peer to peer Same Potential/Fn Client Server Functional Asymmetry ATM, Internet terminal M-phone Client, Server, Data Server Middle Ware

4 Contents are re-edited using materials from Internet Sites

5 Basic Computer System diagram Von Neumann and Harvard Architectures

6 Data Bus is Information Highway

7 Data Using in the Computer Systems

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10 Jpg, mpeg, gif file systems

11 PIXEL Pixel is a smallest component of digital image Pixel is a color point of digital image An image should be comprised of many Pixels.

12 PIXEL

13 RESOLUTION How quality of image With the same size of picture If high resolution, high memory is required to store data If low resolution, less memory is required to store data Its unit is call point per inch

14 RESOLUTION by pixel

15 Basic Computer Systems 1 byte = 8 bit 1 word = 4 byte = 32 bit Machine 8 byte = 64 bit Machine

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17 Digital VS. Analog

18 Connection Device Signals Types of signals Analog Digital CE06_PP09-18 Page 244

19 Analog Signals Analog signals directly measurable quantities in terms of some other quantity Examples: Thermometer mercury height rises as temperature rises Car Speedometer Needle moves farther right as you accelerate Stereo Volume increases as you turn the knob.

20 Digital Signals Digital Signals have only two states. For digital computers, we refer to binary states, 0 and 1. 1 can be on, 0 can be off. Examples: Light switch can be either on or off Door to a room is either open or closed

21 21 Analog and Digital Signals

22 Sampling Rate Sampling ADC: Analog to Digital Converter Frequency at which ADC evaluates analog signal. As we see in the second picture, evaluating the signal more often more accurately depicts the ADC signal.

23 How Computer systems are Working?

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25 Digital Value of Operations

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28 Systematic Operational Diagram

29 Levels of Computer Functions Abstraction Application Programming System Programming H/W Computer Design Processor Graphical Interface Application Libraries Operating System Programming Language Assembler Language Instruction Set Architecture - Machine Language Fabrication Firmware Datapath and Control Logic Design Circuit Design Semiconductors Materials IO System Microprogramming Digital Design S/W Circuits and devices

30 Computer system Operations Computer S/W Machine Language Assembler Compiler Language High Level Language Computer System H/W Digital Logic Outputs

31 Levels of Representation High Level Language P rogram Compiler Assembly Language Pr ogram Assembler Machine Language Pro gram temp = v[k]; v[k] = v[k+1]; v[k+1] = temp; lw $15, 0($2) lw $16, 4($2) sw $16, 0($2) sw $15, 4($2) Machine Interpretation Control Signal Spec ALUOP[0:3] <= InstReg[9:11] & MASK

32 Operating Systems(OS) the Operating System (OS) is a collection of programs that controls how the CPU, memory, and I/O devices work together kernel: manages the CPU's operations, controls how data and instructions are loaded and executed by the CPU, coordinates other hardware components file system: organizes and manages files and directories graphical user interface (GUI): provides intuitive, visual elements for interacting with the computer GUI's utilize windows, icons, menus, and pointers 32

33 Definition of a System revisited A systems is a collection of compone nts linked together and organized in s uch a way as to be recognizable as a s ingle unit. Linked components of a system also define the boundary for the system The environment is anything outside of the system Copyright 2010 John Wiley & Sons, Inc. 2-33

34 Information Systems An information system(is) is typically considered to be a set of interrelated el ements or components that collect(input), manipulate(processes), and disse minate (output) data and information and provide a feedback mechanism to meet an objective. Open System Close System

35 System Decomposition Components Irreducible or Subsystems Decomposition The division of a system into its components and linkages Hierarchical Copyright 2010 John Wiley & Sons, Inc. 2-35

36 General Representation of a System Copyright 2010 John Wiley & Sons, Inc. 2-36

37 System Architecture The fundamental properties, the patterns of relationships, connections, among the components and between the system environment are known collectively as the architecture of the system Copyright 2010 John Wiley & Sons, Inc. 2-37

38 What is Software Architecture? The architecture of a system consists of: the structure(s) of its parts including design-time, test-time, and runtime hardware and software parts the externally visible properties of those parts modules with interfaces, hardware units, objects the relationships and constraints between them Oscar Nierstrasz ESE Software Architecture ESE 10.38

39 Sub-systems, Modules and Components A sub-system is a system in its own right whose operation is independent of the services provided by other sub-systems. A module is a system component that provides services to other components but would not normally be considered as a separate system. A component is an independently deliverable unit of software that encapsulates its design and implementation and offers interfaces to the outside, by which it may be composed with other components to form a larger whole. Oscar Nierstrasz ESE Software Architecture ESE 10.39

40 How Architecture Drives Implementation Use a 3-tier client-server architecture: - all business logic must be in the middle tier, presentation and dialogue on the client, and data services on the server Scale the application server processing independently of persistent store. Oscar Nierstrasz ESE Software Architecture ESE 10.40

41 Coupling Coupling is a measure of the strength of the interconnections between system components. Coupling is tight between components if they depend heavily on one another, (e.g., there is a lot of communication between them). Coupling is loose if there are few dependencies between components. Loose coupling promotes maintainability and adaptability since changes in one component are less likely to affect others. Oscar Nierstrasz ESE Software Architecture ESE 10.41

42 Tight Coupling Module A Module B Module C Module D Shared data area Oscar Nierstrasz ESE Software Architecture ESE Ian Sommerville 2000

43 Loose Coupling Module A A s data Module B B s data Module C C s data Module D D s data Oscar Nierstrasz ESE Software Architecture ESE Ian Sommerville 2000

44 Architectural Parallels Architects are the technical interface between the customer and the contractor building the system A bad architectural design for a building cannot be rescued by good construction the same is true for software There are specialized types of building and software architects There are schools or styles of building and software architecture Oscar Nierstrasz ESE Software Architecture ESE 10.44

45 Architectural Styles An architectural style defines a family of systems in terms of a pattern of structural organization. More specifically, an architectural style defines a vocabulary of components, connector types, and a set of constraints on how they can be combined. Shaw and Garlan Oscar Nierstrasz ESE Software Architecture ESE 10.45

46 Layered Architectures A layered architecture organises a system into a set of layers each of which provide a set of services to the layer above. Normally layers are constrained so elements only see other elements in the same layer, or elements of the layer below Callbacks may be used to communicate to higher layers Supports the incremental development of subsystems in different layers. When a layer interface changes, only the adjacent layer is affected Oscar Nierstrasz ESE Software Architecture ESE 10.46

47 Definitions Software Architectures describe the organization and interaction of software components; focuses on logical organization of software (component interaction, etc.) System Architectures - describe the placement of software components on physical machines The realization of an architecture may be centralized (most components located on a single machine), decentralized (most machines have approximately the same functionality), or hybrid (some combination).

48 Architectural Styles The (a) layered architectural style (b) The object-based architectural style.

49 Architectural Styles Communication via event propagation, in dist. systems seen often in Publish/ Subscribe; e.g., register interest in market info; get updates Decouples sender & receiver; asynchronous communication Event-based arch. supports several communication styles: Publish-subscribe Broadcast Point-to-point (a) The event-based architectural style

50 Architectural Styles (5) Data Centric Architecture; e.g., shared distributed file systems or Web-based distributed systems Combination of data-centered and event based architectures Processes communicate asynchronously The shared data-space architectural style.

51 General Building Blok of Data Processing Equipment, H/W Software Building Block Administrative an Operational Supports What is Object of Project? What are Major Information? How can We Process the Information? Network H/W S/W

52 Business Organization Chart Copyright 2010 John Wiley & Sons, Inc. 2-52

53 Evolution of Information Technology Infrastructure Web Services Ability to fill information needs Mainframe PC/LAN Client/Server Distributed db db db db db db db db S1

54 Communication Components Communication channel (provide connections) Wire cable Fiber optic Telephone line Wireless technologies Hardware modem network interface card (NIC) Software (establishes connections, controls the flow of data, directs data to the proper applications) Protocols/Standards 54

55 Communication Concepts Any transmission May be: analog or digital Serial or parallel Graham Betts

56 Communication Systems Four basic elements Sending and receiving devices Communication channel Connection devices Data transmission specifications Page 241 CE06_PP09-56

57 What is a network A network as a "group of computers and associated devices that are connected by communications facilities." A network provides two principle benefits: the ability to communicate and the ability to share. A network can consist of two computers connected together on a desk or It can consist of many Local Area Networks (LANs) connected together to form a Wide Area Network (WAN) across a continent.

58 Network Classifications Scope Local area network (LAN) Metropolitan area (MAN) Wide area network (WAN) Ownership Closed versus open Topology (configuration) Bus (Ethernet) Star (Wireless networks with central Access Point) Ring

59 Network Topologies A topology refers to the manner in which the cable is run to individual workstations on the network. the configurations formed by the connections between devices on a local area network (LAN) or between two or more LANs There are three basic network topologies (not counting variations thereon): the bus, the star, and the ring. It is important to make a distinction between a topology and an architecture.

60 NETWORK TOPOLOGIES (categorizing by shape) Graham Betts

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62 Information Transfer Methods Ethernet Developed at Xerox in First protocol approved as an industry standard protocol 1983 LAN protocol used on bus and star Most popular LAN protocol Inexpensive Graham Betts

63 Peer-to-Peer Nodes act as both client and server; interaction is symmetric Each node acts as a server for part of the total system data Overlay networks connect nodes in the P2P system Nodes in the overlay use their own addressing system for storing and retrieving data in the system Nodes can route requests to locations that may not be known by the requester.

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65 Peer-to-Peer Computing Computers on a network are treated as equals Each computer can share resources with the other computers on the network Disadvantages Difficult to establish centralized control of services Difficult to locate services Difficult to synchronize versions of files or software Difficult to secure network from unauthorized access and from viruses Advantages Sharing files between personal computers Internet file sharing Copyright 2010 John Wiley & Sons, Inc. 2-65

66 Client/Server Computing In client/server computing, computer processing is split between client machines and server machines linked by a network. Users interface with the client machines. Functional Asymmetry

67 A Multitiered Client/Server Network (N-Tier).

68 Encoding First step is to understand how to connect them so that bits can be transmitted. Next encode binary data that the source want to send into signals that the links can carry Then decode the data back into the corresponding data at the receiving end. 68

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71 Originally Created by Bob Baker Modified 2006 Graham Betts Encapsulation Device 1 Device 2 Application Presentation Session Transport Network Data Link Physical H6 H5 H4 data data data data T6 T5 T4 H3 data T3 (packet) Network H2 data T2 H1 data T1 Application Presentation Session (Packet) Transport Data Link Physical carrier FRAME FRAME FRAME FRAME A typical frame Preamble Destination Address Graham Betts Source Address Data Padding CRC

72 Serial Transmission Data is transmitted, on a single channel, one bit at a time one after another - Much faster than parallel because of way bits processed (e.g. USB and SATA drives) Sender transmitted 0 1 Receiver received Graham Betts

73 Parallel Transmission -each bit has it s own piece of wire along which it travels - often used to send data to a printer Sender transmitted Receiver received All bits are sent simultaneously Graham Betts

74 Why Not use Parallel Instead of serial? Due to inconsistencies on channels data arrives at different times Because of the way it is transmitted packet switching cannot be used The above two points makes parallel slower than serial and requires higher bandwidth. Parallel transmissions are rarely used anymore Graham Betts

75 TCP/IP(Protocol) Developed in 1973 for use on the ARPANET which was a defense force research network. -Adopted in 1983 as the Internet standard. all hosts on the Internet are required to use TCP/IP. - Allows transfer of data using packet switching Graham Betts

76 Elements of a Network communication links: point-point (e.g., A-to-B) broadcast (e.g.,: Ethernet LAN) host: computer running applications which use network (e.g.: H1 router: computer (often w/o applications-level programs) rout ing packets from input line to output line. (e.g., A->C) gateway: router directly connected to 2+ networks (e.g. A) network: set of node (hosts/routers/gateways) within single a dministrative domain internet: collection of interconnected networks

77 Transmission Media Speed Bandwidth:The amount of data which can be transmitted on a medium over a fixed amount of time (second). It is measured on Bits per Second or Baud Bits per Second (bps): A measure of transmission speed. The number of bits (0 0r 1) which can be transmitted in a second (more) Baud Rate: Is a measure of how fast a change of state occurs (i.e. a change from 0 to 1) (more) Graham Betts

78 System Architectures for Distributed Systems Centralized: traditional client-server structure Vertical (or hierarchichal) organization of communication and control paths (as in layered software architectures) Logical separation of functions into client (requesting process) and server (responder) Decentralized: peer-to-peer Horizontal rather than hierarchical comm. and control Communication paths are less structured; symmetric functionality Hybrid: combine elements of C/S and P2P Edge-server systems Collaborative distributed systems. Classification of a system as centralized or decentralized refers to communication and control organization, primarily.

79 Film and picture library Client 1 Client 2 Client 3 Client 4 Wide-bandwidth network Catalogue server Video server Picture server Hypertext server Catalogue Film clip files Digitized photographs Hypertext web Oscar Nierstrasz ESE Software Architecture ESE Ian Sommerville 2000

80 Traditional Client-Server Processes are divided into two groups (clients and servers). Synchronous communication: requestreply protocol In LANs, often implemented with a connectionless protocol (unreliable) In WANs, communication is typically connection-oriented TCP/IP (reliable) High likelihood of communication failures

81 Client-Server Architectures A client-server architecture distributes application logic and services respectively to a number of client and server sub-systems, each potentially running on a different machine and communicating through the network Advantages Distribution of data is straightforward Makes effective use of networked systems. May require cheaper hardware Easy to add new servers or upgrade existing servers Disadvantages No shared data model so sub-systems use different data organisation. Data interchange may be inefficient Redundant management in each server May require a central registry of names and services it may be hard to find out what servers and services are available Oscar Nierstrasz ESE Software Architecture ESE 10.81

82 C/S Architectures General interaction between a client and a server.

83 Layered (software) Architecture for Client-Server Systems User-interface level: GUI s (usually) for interacting with end users Processing level: data processing applications the core functionality Data level: interacts with data base or file system Data usually is persistent; exists even if no client is accessing it File or database system

84 Examples Web search engine Interface: type in a keyword string Processing level: processes to generate DB queries, rank replies, format response Data level: database of web pages Stock broker s decision support system Interface: likely more complex than simple search Processing: programs to analyze data; rely on statistics, AI perhaps, may require large simulations Data level: DB of financial information Desktop office suites Interface: access to various documents, data, Processing: word processing, database queries, spreadsheets, Data : file systems and/or databases

85 IT System Architectures Distributed processing systems Client-Server Computing 2-tier architecture 3-tier architecture N-tier architecture Web-Based Computing Peer-to-Peer Computing Copyright 2010 John Wiley & Sons, Inc. 2-85

86 Architecture categories Two-tiers architecture Three-tiers architecture Service oriented architecture 86

87 Two-tiers architecture The server handles both application and database duties 87

88 Two-tiers architecture Benefits Easy-to-use and access to information and services Low cost in terms of infrastructure requirements High performance with a limited number of workstations Drawbacks Inflexible in terms of adding more clients and software Requires expensive middleware for integration Changes or modifications in database affect applications Limited flexibility in moving program functionality from one server to another 88

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91 Three-tiers architecture Data Tier (Data Management) Business Tier (Business logic of functional modules) Presentation Tier (End-User Interface GUI) 91

92 The logical 3-tier architecture Client Presentation Application Data Display information to the user. Format information for display. Translate UI events into application events. Execute application logic. Store and provide access to persistent data. The conceptual distinction between the tiers is important Really only an N-tier architecture if carried through into the implementation architecture

93 Multitiered Architectures (3 Tier Architecture) An example of a server acting as client.

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100 Three-tiers architecture in business systems Benefits End-users have access to ERP applications over the Web. Easily integrate ERP applications with existing systems. Server-centric No complex, expensive client software installation. Client-centric Architecture has better response time because user requests are mostly processed on the client s computer. Web-based architectures also allow better system-to-system integration. Drawbacks Client-centric architectures lack security 100

101 Business Application Architecture Copyright 2010 John Wiley & Sons, Inc

102 Client/Server security Network environment has complex security issues. Networks susceptible to breaches of security through eavesdropping, unauthorised connections or unauthorised retrieval of packets of information flowing round the network. Specific security issues include: System-level password security user names and passwords for allowing access to the system. Password management utilities Database-level password security - for determining access privileges to tables; read/update/insert/delete privileges Secure client/server communication - via encryption but encryption can negatively affect performance

103 Middleware From Wikipedia, middleware is computer software that provides services to software applications beyond those av ailable from the operating system. Middleware can be described as "software glue". Thus middleware is not obviously part of an operating system, not a database management system, and neither is it part of one software application. Middleware makes it easier for software developers to perform com munication and input/output, so they can focus on the specific purp ose of their application.

104 System Architecture Mapping the software architecture to system hardware Correspondence between logical software modules and actual computers Multi-tiered architectures Layer and tier are roughly equivalent terms, but layer typically implies software and tier is more likely to refer to hardware. Two-tier and three-tier are the most common

105 Infrastructure Software Layering Uniprocessor Operating System Separating applications from operating system code through a microkernel. Distributed Systems 105

106 Distributed Operating System Tightly-coupled operating system for multi-processors and homogeneous multi-computers. Strong transparency. Distributed Systems 106

107 Network Operating System Loosely-coupled operating system for heterogeneous multi -computers (LAN and WAN). Weak transparency. Distributed Systems 107

108 Middleware System Additional layer on the top of NOS implementing general-purpose services. Better transparency. Distributed Systems 108

109 Middleware Examples Examples: Sun RPC, CORBA, DCOM, Java RMI (distribu ted object technology) Built on top of transport layer in the ISO/OSI 7 layer re ference model: application (protocol), presentation (sema ntic), session (dialogue), transport (e.g. TCP or UDP), net work (IP, ATM etc), data link (frames, checksum), physical (bits and bytes) Most are implemented over the internet protocols Masks heterogeneity of underlying networks, hardware, operating system and programming languages so provides a uniform programming model with standard services Distributed Systems 109

110 3 types of middleware: Transaction oriented (for distributed database applications) Message oriented (for reliable asynchronous communication) Remote procedure calls (RPC) the original OO middleware

111 Thin & Fat Clients Thin client = Network computer Typically no local storage has only presentation function(= user interface) Fat Client = Desktop PC, Workstation has both presentation function and logic function (=application) Motivation for Thin Clients Hidden costs of System administration and supports Networks computers move toward centralized system Admin., but local processing at client Java(mobile code) an enabling technology E.g. PDA,. Distributed Computing & Database Lab 111

112 File Server Architecture FAT CLIENT

113 Database server architecture Thinner clients DBMS only on server

114 Three-tier architecture Thinnest clients Business rules on separate server DBMS only on DB server

115 Application Layering The simplified organization of an Internet search engine into three different layers.

116 Key Technology Infrastructure Components Principles of Information Systems, Seventh Edition 116

117 Internet Architecture: Internet Network Architecture

118 THE INTERNET The Domain Name System

119 Google: System Architecture Provide powerful, fast search capability for material on the Internet Derive income from advertising that is targeted to each user based on their searches Basic requirements Capable of responding to millions of simultaneous requests from all over the world Perform a web crawl of the Internet retrieve and organize data Establish ranking of results with appropriately targeted advertising High reliability of the system System is easily scalable and cost effective Copyright 2010 John Wiley & Sons, Inc

120 Google Data Center Search Application Architecture Copyright 2010 John Wiley & Sons, Inc

121 Simplified Google System Hardware Architecture Copyright 2010 John Wiley & Sons, Inc

122 The Future of Network Computing More Tier, More Functional Server Powerful One Server(2 Tier) Functions, Flexibility of Systems Mobile Server Distributed Systems

123 Summary of Class Computer System Data Presentations Analog/ Digital Data /Systems Data/ Computer Communications System, Software Architecture Layering Structure Protocols Networks Computing Client/Server 2.3, N Tier Networks