Systems Architecture, Fourth Edition1 Internet and Distributed Application Services Chapter 13

Systems Architecture, Fourth Edition 1

Internet and Distributed Application Services

Chapter 13


Objectives

• 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, named 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 LDAP standard


Chapter Topics


Distributed Computing

• Client-server architecture is the current dominate architecture for distributed computing.



Client-server architecture is the current dominate architecture for 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.



3-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




Network Resource Access

Protocol Stacks:

– Software that implements the lowest five levels of the OSI model.



Advantages of Protocol Stacks:• divide the task of network interaction into several

well-defined pieces that can be separately implemented and installed

• provide the flexibility needed to keep up with rapid protocol standard evolution

• insulate application programs and many portions of the operating system from details of low-level network communication protocols.





Accessing Remote Resources:

• A static connection is initialized by the user or system administrator prior to accessing a remote resource.

• A dynamic connection is created by the interaction between a resource locator and a primary resource registration repository.






Interprocess Communication



Peer-to-peer protocol:

• Socket

• Named Pipe

• Remote Procedure Call



Socket:

• 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)





Named Pipe:

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.





Remote Procedure Call:

With a remote procedure call protocol, a process on one machine can call a process on another machine.



Remote Procedure Call: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.


Technology Focus


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 only by a limited set of internal users.


The Internet

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.


The Internet

Uniform Resource Locator:• 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.


The Internet







In later versions of HTML, program code or scripts can be embedded within HTML documents.






Components and Distributed Objects

Component-Based Software:

A component is a standardized and interchangeable software module that:– Is executable– Has a unique identifier– Has a well-known interface– Similar to objects within an OO program



CORBA - Industry-wide component specifies the middleware used by objects to interact across the network.Two components:– Object Request Broker (ORB)– Internet Inter-ORB Protocol (IIOP)

COM+ - a Microsoft specification for component interoperability.



Differences between CORBA and COM+:

• Components are not assigned a permanent identifier.

• Components are registered in the Windows Registry of the client machine.





Simple Object Access Protocol (SOAP):

SOAP is a standard for distributed object interaction that attempts the shortcomings of both CORBA and COM+.




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.


Directory Services


Technology Focus


Technology Focus


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.

• Distributed processes must communicate with one another to exchange data and synchronize their activities.


Summary

• The Internet is a global network based on TCP/IP and many other protocols.

• 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.

Documents

Systems Architecture, Fourth Edition1 Internet and Distributed Application Services Chapter 13