1. Internet and Distributed Application Services
Chapter 13
Internet and Distributed Application Services

2. Chapter 13 Internet and Distributed Application Services
Chapter Outline
Distributed Computing
Network Resource Access
Interprocess Communication
Focus – Distributed Computing Environment
The Internet
Components and Distributed Objects
Focus – Java 2 Enterprise Edition
Directory Services
Focus – Microsoft Active Directory

3. Chapter Goals
Describe client/server and multi-tier application architecture and discuss their advantages compared to centralized applications
Explain how operating systems and network protocol stacks cooperate so users and programs can access remote resources
Describe low-level protocols for interprocess communication across networks, including sockets, names pipes, RPC, and DCE
List and describe standard Internet protocols used to access distributed resources
Discuss component-based application development and describe the protocols and standards that support component-based applications
Explain the role and function of directory services and the LSAP standard

4. Chapter Topics

5. Distributed Computing
Distributing parts of an information system across many computer systems and locations
Architectural models
Client/server
Three-layer
N-layer

6. Client/Server Architecture
Manages system resources; provides access to them through a well-defined communication interface
Client
Uses communication interface to request resources; server responds to those requests
Current dominant model for distributed computing

7. Client/Server Architecture
One of the many different ways that client/server architecture can be implemented.

8. Client/Server Architecture
Three-layer architecture
Divides application software into three tiers
Data layer
Business logic layer
View layer
Simplifies distributing or replicating application software across a network
N-layer architectures
Employ more than three layers

9. Three-Layer Client/Server Architecture
The view layer acts as a client of the business logic layer, which in turn acts as a client of the data layer.

10. Multi-Layer Architectures
Require standard models and services to communicate with one another
Middleware
System software that implements communication standards and gives clients and servers the ability to interact

11. Network Resource Access
OS components enable distributed access by:
Distinguishing between local and remote resources
Interacting with distant operating systems

12. Protocol Stacks
Software that implements the lowest five levels of the OSI model
Provide several advantages for implementing network I/O and services

13. Protocol Stacks

14. Advantages of Protocol Stacks
Divide network interaction into well-defined pieces that can be separately implemented, installed, and updated
Provide flexibility to keep up with rapid protocol standard evolution
Insulate application programs and portions of OS from details of low-level network communication protocols and physical network implementation (ensures software portability)

15. Accessing Remote Resources
Static connection
Initialized by user or system administrator prior to accessing a remote resource
Difficult to initialize and maintain
Dynamic connection
Established through interaction between a resource layer and a primary resource registration repository
More flexible but requires a distributed registry of resource name and locations

16. Premises of Remote Resource Access
Location transparency
Service-oriented resource access
Resources can be moved among computer systems

17. Service-Oriented Resource Access
Layers
between service layer and device drivers
Service provider
Server interface to specific resource
Resource locator
Locates resources referred to in service requests from local or remote users and programs
Forwards service requests to appropriate service provider
Maintains a resource registry

18. Software components that support service-oriented resource access

19. Interprocess Communication
Distributed processes must communicate with one another to exchange data and synchronize activities
Peer-to-peer interprocess communication protocols
Sockets
Named pipes
Remote procedure calls
Distributed Computing Environment (DCE)

20. Peer-to-Peer Communication Protocols
Lower-level protocols that enable processes to communicate synchronously across a network
Often used by system software to exchange data and coordinate activities

21. Sockets
Unique combinations of an IP number and a port number, separated by a colon (e.g., :53)
Implement direct process-to-process communication via protocol stacks
Supported by all modern OSs, which enable programs to initialize sockets, receive messages sent to a socket, and send messages to sockets anywhere on the Internet

22. Each socket uniquely identifies a client or server process on the Internet.

23. Named Pipes
Region of shared memory that enables multiple processes executing on the same machine to exchange data
Name is permanently placed within file system directory
Able to communicate among processes on different computers

24. When a named pipe is created, the OS assigns a free socket and allocates I/O buffers to it.
Then data flowing in/out of the pipe is routed through the low-level network protocol stack.

25. Remote Procedure Calls
Allow one process to execute another
as a subroutine
with parameter passing and format translation
The calling process does the following:
1. Passes parameters to the called process
2. Waits for the called process to complete its task
3. Accepts parameters back from the called process
4. Resumes execution with the instruction following the call

26. Distributed Computing Environment
Combines all peer-to-peer approaches and adds security (Kerberos) and minimal directory services
Promotes interoperability of distributed software across operating systems and middleware products

27. Distributed Computing Environment
DCE functions are incorporated directly into an operating system or supplied as an optional component.

28. The Internet
Internet
Global collection of networks interconnected using TCP/IP
Infrastructure upon which the Web is based
WWW
Collection of resources (programs, files, services), accessible over the Internet by standard protocols (FTP, HTTP)
Organized using client/server architecture
Intranet
Private network that uses Internet protocols; accessible only to a limited set of internal users
Set of privately accessible resources, organized and delivered via Web protocols over a TCP/IP network

29. Standard Web Protocols and Services
Define valid resource formats and a standard means of requesting resources
Identified by a unique URL
Uniform Resource Locator

30. URL Components
Host
Resource
Protocol
Port

31. Web Protocols

32. Remote Login Telnet Allows access to a remote computer
as if the user was sitting in front of it!

33. The Internet as an Application Platform
Application program executes on a Web server that can be accessed from any computer with an Internet connection

34. The Internet as an Application Platform
Advantages
Disadvantages
Expands accessibility
Eliminates need to install custom client software
Cheaper to develop and deploy
Built around existing Web standards and browser software already installed on clients
Security
Performance
Reliability

35. Components and Distributed Objects
Standardized, interchangeable software module that is executable, has a unique identifier, and has a well-known interface
Distributed object
Cooperating process that implements a public interface to the services it provides

36. Component-Based Software
Enables construction of complex programs and applications from smaller previously developed parts
Requires protocols and infrastructure for component registration, discovery, and communication

37. Components and Objects
Send and respond to messages
Encapsulate internal data
Interact with other components through a well-defined interface

38. Connection Standards and Infrastructure
Interoperability requires well-defined and widely adopted standards
Standard network protocols do not address:
Format and content of valid messages and responses
Way to uniquely identify each component on the Internet and route messages to/from that computer
Additional standards provided by CORBA, COM+, SOAP, J2EE

39. CORBA Common Object Request Broker Architecture
Specifies middleware used by objects to interact across networks
Key components
Object Request Broker (ORB)
Interface Definition Language (IDL)
Internet Inter-ORB Protocol (IIOP)
Robust, scalable, independent of programming language, OS, and CPU architecture
Disadvantage: Complexity

40. Component Object Model
COM is an interface standard for software components introduced by Microsoft in 1993.
enables interprocess communication and dynamic object creation in a large range of programming languages.
A language-neutral way to implement objects to be used in other environments or machines.
Differing language requirements are overcome by making objects responsible for their own creation and destruction through reference-counting.
Although the interface standard has been implemented on several platforms, COM is primarily used with Microsoft Windows.

41. COM+ Component Object Model Plus
Like CORBA
defines component registration, message routing services, and component communication protocol
Unlike CORBA
components are not assigned permanent identifier, and are registered in Windows Registry of client machine where installed
Disadvantage
Dependence on propriety technology and limited support outside of Microsoft products

42. SOAP Simple Object Access Protocol
Attempts to address shortcomings of CORBA and COM+
Has few infrastructure requirements and relatively simple programming interface
Relies on existing Internet protocols
Disadvantage
Security and message delivery guarantees

43. SOAP Simple Object Access Protocol
Messages are encoded in XML
and transmitted using HTTP
Enables objects to be located anywhere on the Internet.

44. J2EE Java 2 Enterprise Edition
Standards for developing/deploying component-based distributed applications written in Java
Key elements follow three-layer architecture
Component interactions based on many standards
Remote Method Invocation (RMI)
Java Naming and Directory Interface (JNDI)
Java Authentication and Authorization Service (JAAS)
Java Database Connectivity (JDBC)

45. J2EE

46. Directory Services Middleware that:
Stores name and network address of distributed resources
Responds to directory queries
Accepts directory updates
Synchronizes replicated or distributed directory copies
Integral components of network operating systems

47. Information Stored in Network OS Directories
Registered users and their permissions to access directory objects
Shared hardware resources
Shared files, databases, and programs
Computer systems and specialized hardware devices

48. LDAP Lightweight Directory Access Protocol
Widely deployed directory service standard that can track users, distributed resources, and objects
Limited interoperability among different LDAP directories; does not define standard content templates
Defines several standard container types and an attribute called distinguished name (DN) which uniquely identifies the object within an objectclass

49. Container Object Types
Country (C)
Organization (O)
Organizational Unit (OU)

50. Microsoft Active Directory
Directory service and security system built into Windows server
Stores information about network resources
Every resource or container object has an access control list that describes access rights
Based on LDAP and the Internet Domain Naming Service (DNS)
Does not support distributed or component-based software directly

53. Summary Distributed computing Network resource access
Interprocess communication
The Internet
Components and distributed objects

54. Chapter Goals
Describe client/server and multi-tier application architecture and discuss their advantages compared to centralized applications
Explain how operating systems and network protocol stacks cooperate so users and programs can access remote resources
Describe low-level protocols for interprocess communication across networks, including sockets, names pipes, RPC, and DCE
List and describe standard Internet protocols used to access distributed resources
Discuss component-based application development and describe the protocols and standards that support component-based applications
Explain the role and function of directory services and the LSAP standard