Internet and Distributed Application Systems

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Internet and Distributed Application Systems

• SA, Chapter 13

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Summary

• Modern information systems typically are
  distributed across many computer systems and
  geographic locations.
• A network protocol enables user and applications
  to interact with resources and applications on
  remote computer systems.

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Summary

• Distributed processes must communicate with one
  another to exchange data and synchronize their
  activities.
• The Internet is a global network based on TCP/IP
  and many other protocols.

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Summary

• Component-based applications divide an
  application into many different cooperating
  processes or distributed objects.
• With directory services, users, resources, and
  components can find one another on the Internet.

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Chapter Topics

• Distributed computing
• Network resource access
• Interprocess communication
• Internet components
• Distributed objects
• Directory services

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Distributed Computing

• Client-Server Architecture
• Distributed parts of an information system across
  many computer systems and locations is called
  distributed computing.
• Client-server architecture is the current
  architecture for distributed computing.

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Distributed Computing

• Client-Server architecture divides the software
  into two classes
• Clients
• Servers

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Distributed Computing

• Client-Server Architecture
• A server manages one or more system resources and
  provides access to those resources through a
  well-defined communication interface.
• A client uses the communication interface to
  request resources from the server.

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Distributed Computing
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N-Layer Client-Server Architecture

• The software is divided into client and server
  processes called layers or tiers.
• Data layer
• Business logic layer
• View layer

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N-Layer Client-Server Architecture

• Data layer manages stored data, usually in one
  or more databases.
• Business logic layer implements the rules and
  procedures of business processing.
• View layer accepts user input and formats and
  displays processing results.

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N-Layer Client-Server Architecture
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Network Resources

• Protocol Stacks
• Accessing Remote Resources

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Network Resources

• Protocol Stacks software that implements the
  lowest five levels of the OSI model.
• Advantages of Protocol Stacks
• They divide the task of network interaction into
  several well-defined pieces that can be
  separately implemented and installed.

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Network Resources

• Advantages of Protocol Stacks
• They provide the flexibility needed to keep up
  with rapid protocol standard evolution.
• They insulate application programs and many
  portions of the operating system from details of
  low-level network communication protocols.

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Network Resources
Not OSI
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The Internet

• Internet terms
• Standard Web Protocols and Services
• The Internet as an Application Platform

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The Internet

• Internet a global collection of networks that
  are interconnected using TCP/IP.
• World Wide Web a collection of resources that
  can be accessed over the Internet.
• Intranet a private network that uses Internet
  protocols but is accessible by a limited set of
  internal users.

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The Internet URLs

• Standard Web Protocols and Services
• All resources are identifies by a unique Uniform
  Resource Locator (URL).
• The URL has four parts protocol, host, port and
  resource.

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The Internet URLs

• Protocol an optional header specifying the
  resource access protocol.
• Host the IP number or registered name of an
  Internet host computer or device.
• Port an optional port number that specifies the
  socket.
• Resource the complete path name of a resource
  on the host. Not required when?

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The Internet URLs
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The Internet - Protocols
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The Internet - Protocols

• Hypertext Markup Language (HTML) a
  device-independent document-formatting language
  in which links to other documents can be
  formatted.
• Extensible Markup Language (XML) extends HTML
  to describe the structure, format and content of
  documents.

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The Internet - Protocols

• Hypertext Transport Protocol (HTTP) a companion
  protocol to HTML and XML that specifies the
  language by which clients request documents and
  how servers respond to those requests. Related to
  FTP.
• Telnet Protocol users on one Internet host can
  interact with the operating system command layer
  of another host.

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The Internet - Protocols
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The Internet - Protocols

• Simple Mail Transport Protocol (SMTP) defines
  how text messages are forwarded and routed among
  Internet hosts.
• Multipurpose Internet Mail Extensions (MIME)
  allow non-text files to be included in mail
  messages.

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The Internet - Protocols

• Post Office Protocol version 3 standardizes the
  interaction between e-mail clients and servers so
  the client and server can execute on different
  Internet hosts.

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The Internet

• Internet scripting languages are slimmed-down
  programming languages.
• The perform many functions of programs without
  the need for compilation or link editing.
• JavaScript and VBScript are two widely used
  scripting languages.

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Network Resources

• Accessing Remote Resources
• Connections to resources can be either static or
  dynamic.
• A static connection is initialized by the user or
  system administrator prior to accessing a remote
  resource.

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Network Resources
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Remote Resources

• Operating systems, application programs, and user
  interfaces are simpler if there is no distinction
  between local and remote resource access.
• All resources potentially are shared across a
  network.
• Any computer system potentially is both a client
  and a server.
• Resources can be moved among computer systems.

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Network Resources

• Remote resource access in modern operating
  systems is based on the following premise
  (cont.)

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Network Resources
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Network Resources

• The resource locator has two important tasks
• Locate resources referred to in service requests
  form local or remote users and programs.
• Route service requests to the appropriate service
  provider.

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Network Resources

• Dynamic Connections the interaction between a
  resource locator and a primary resource
  registration repository is inherently dynamic.

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Interprocess Communication

• Sockets
• Named Pipes
• Remote Procedure Calls
• DCE
• MOM

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Interprocess Communication

• Peer-to-Peer Communication Protocols allow
  processes to use communication synchronously
  across a network.
• These protocols are used by system software such
  as operating systems and database management
  systems to exchange data and coordinate
  activities.

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Interprocess Communication
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Interprocess Communication

• Sockets
• A socket is a unique combination of an IP number
  and a port number.
• A port number is an unsigned 16-bit integer.
  (65,536 possible port numbers)

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Interprocess Communication
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Interprocess Communication

• Named Pipes
• A named pipe has a name that is permanently
  placed within a file system directory and the
  ability to communicate among processes on
  different computers.

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Interprocess Communication
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Interprocess Communication

• Remote Procedure Calls
• With a remote procedure call protocol, a process
  on one machine can call a process on another
  machine.

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Interprocess Communication

• Remote Procedure Calls
• The calling process
• Passes parameters to the called process.
• Waits for the called process to complete its
  task.
• Accepts parameters back from the called process.
• Resumes execution with the instruction following
  the call.

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Remote Procedure Call Approach
Client/Server
Single Machine
Server
Client
Find students enrolled
Print roll
Find students enrolled
Print roll
Client stub
Server stub
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RPC Sessions

• Distributes standard code modules
• Program functions distributed between client and
  server
• Stubs manage communication
• Client waits for response
• Session connected by
• service port ids addresss

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DCE Tickets and RPC

• Distributed Computing Environment

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Message Oriented Sessions

• More complex than RPC
• Each message header contains enough data to route
  and process
• Messages are queued at client
• Client may process other actions
• MOM Message Oriented Middleware

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Components and Distributed Objects

• Component-Based Software
• Components and Objects
• Connection Standards and Infrastructure
• CORBA
• Usually MOM

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Components and Distributed Objects

• Component-Based Software
• Components are ready-to-use software.
• Every component has a unique identifier, which is
  a number or symbolic name.
• A components interface is the set of services or
  tasks it performs.

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Components and Distributed Objects

• Components and Objects
• Components are similar to objects within an OO
  program because they send and respond to
  messages, encapsulate internal data, and interact
  with other components through a well-defined
  interface.

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Components and Distributed Objects

• Components and Objects
• Components are usually developed with OO software
  development tools and programming languages.

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Components and Distributed Objects

• Connection Standards and Infrastructure
• Interoperability among hardware or software
  components requires well-defined and widely
  adopted standards.
• Software components require similar standards for
  connections and services.

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Components and Distributed Objects

• Connection Standards and Infrastructure
• Connecting components located on different
  machines running different operating systems
  requires a standard network protocol.
• Internet services and protocols such as TCP/IP
  and sockets provide part of a component
  connection solution.

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Components and Distributed Objects

• CORBA - Industry-wide component specifies the
  middleware used by objects to interact across the
  network.
• Two components
• Object Request Broker (ORB) a service that
  maintains a component directory and routes
  messages among components.
• Internet Inter-ORB Protocol (IIOP) a component
  message-passing protocol.

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Components and Distributed Objects

• COM - a Microsoft specification for component
  interoperability.
• Differences between CORBA and COM
• COM components are not assigned a permanent
  identifier.
• COM components are registered in the Windows
  Registry of the client machine.

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The Internet

• The Internet as an Application Platform
• The Internet can be used to allow employees
  access to application programs.
• Implementing the application via the Internet
  expands its accessibility and eliminates the need
  to install custom client software on the
  employees laptop computers.
• The disadvantage to placing applications on the
  Internet security, performance and reliability.

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Directory Services

• Middleware that
• Stores the name and network address of
  distributed resources.
• Responds to directory queries.
• Accepts directory updates.
• Synchronizes replicated or distributed directory
  copies.

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Directory Services

• Typically, network operating system directories
  store information about
• Registered users and their permissions to access
  directory objects.
• Shared hardware resources such as printers.
• Shared files, databases, and programs.
• Computer systems and specialized hardware devices
  such as network storage appliances.

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Directory Services

• Lightweight Directory Access Protocol (LDAP)
• An LDAP directory stores information about LDAP
  objects.
• Each object is an instance of an objectclass.
• An objectclass defines the attributes common to
  all member objects.
• LDAP objects are organized in a hierarchy.

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Directory Services fig 13-17
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Directory Services MS AD

• Partitioned, replicated, synchronized