CHAPTER 13 Internet and Distributed Application Services

I. Distributed Computing  Client-Server Architecture Network printing services implemented with client- server architecture Service request Response Document Fig.13-2

Three-layer Architecture User request View layer Information request Business Logic layer Unformatted response Data layer Database query Query response Fig. 13-3

 N-Layer Client-Server Architecture  The data layer manages stored data, usually in one or more databases  The business logic layer implements the rules and procedures of business processing  The view layer accepts user input and formats and displays processing results

II. Network Resource Access  Protocol stacks  They divide the task of network interaction into several well-defined pieces that can be separately implemented and installed  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 and physical network implementation, which ensures software portability across a wide range of network protocols and transmission media

Two upper-level stacks sharing a single NIU and driver OSI Session layer Transport Layer Interface Sockets OSI Transport layer Sequenced Packet Exchange Transmissio n Control Protocol OSI Network layer Internet Packet Exchange Internet Protocol Logical network interface driver Open Data Interface OSI Data Link layer (Physical Network Interface Driver) 10-Mbps Ethernet OSI Physical layerTwisted-pair copper wire Layer description Stack 1Stack 2 Fig. 13-4

 Accessing 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

Software layers to access local and remote resources Application program Local service layer Fig Resource locator Service provider Local device driver Local hardware device Service call Service request Low-level protocol stack Network messages

Resource Locator has two important tasks: The locator resources referred to in service requests from local or remote users and programs Route service requests to the appropriate service provider

III. Interprocess Communication OSI Application layer DCE RPC Named Pipes OSI Session layerSockets OSI Transport layer Transmission Control Protocol OSI Network layer Internet Protocol Fig.13-7  Peer-to-peer protocols layered over TCP/IP

TCP/IP layer  Sockets Fig  Multiple Processes communicating through sockets Client process 0|1|2|3|4|5|6 Sockets ( ) Physical layer 0|1|2|3|4|5|6 Sockets TCP/IP layer ( ) Physical layer Network Computer A Computer B

 Named Pipes  A name that is permanently placed within a file system directory  The ability to communicate among processes on different computers

Fig  Two processes communicating through a named pipe Sending process I/O buffer Named pipe Service I/O buffer Named pipe Service 0|1|2|3|4|5|6 Sockets 0|1|2|3|4|5|6 Sockets TCP/IP layer Physical layer Computer A Computer B File I/O Service calls File I/O Service calls Network

 Remote Procedure Calls  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

IV. The Internet The Internet is a global collection of networks that are interconnected using TCP/IP The World Wide Web(www), also called the Web, is a collection of resources(programs, files, and services) that can be accessed over the Internet by standard protocols such as the File Transfer Protocol(FTP) and Hypertext Transfer Protocol(HTTP) An Intranet is a private network that uses Internet protocols but is accessible only by a limited set of internal users(usually members of the same organization or workgroup). It also describes a set of privately accessible resources that are organized and delivered via one or more Web protocols over a TCP/IP network

 Standard Web Protocols and Services  Protocol- an optional header specifying the resource access protocol ( is the default value)  Host- the P number or registered name of an Internet host computer or device  Port- an optional port number that, together with the IP address, specifies a socket as described in Chapter 9 (if omitted, a standard port number for the protocol is assumed)  Resource- the complete path name of a resource on the host (if omitted, the host can be configured to supply a default value)

http: // averia.unm. edu :8 0/ default. htm Fig  URL components Optional protocol header and separator Optional port number and separator IP address or host name Optional resource name on IP host

Fig  Web protocols CategorySample Protocols Formatted and linked documents Hypertext Markup Language (HTML) and Extensible Markup Language (XML) File and document transferFile Transfer Protocol (FTP) and Hypertext Transfer Protocol (HTTP) Remote login and process execution Telnet, tn3270, and Remote Procedure Call (RPC) Mail and MessagingSimple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), and Internet Message Access Protocol (IMAP) Executable programsJava, JavaScript, and Visual Basic Script (VBScript)

Fig  Telnet Connection Telnet client Network protocol stack O/S command layer Telnet server Network protocol stack Local host Remote stack

 The Internet as an Application Platform

Fig  A distributed Web-based application Database server Web server Payroll database Payroll update application Database server software Web server software Web browser software Home or office microcomputer User

Although sockets, named pipes, HTTP, and HTML are adequate to implement distributed applications, they’re not optimal for the following reasons: With lower-level protocols, server addresses are stored in client configuration files or source code. I server resources are moved, the clients must be reconfigured or recompiled. Breaking up server-side processes into small manageable pieces is difficult. Each new distributed piece requires a new set of hard- coded connections. Developers usually create large complex server processes to avoid the complexity of large numbers of connections between many smaller server processes. But doing so reduces the chances that server processes can be incorporated into multiple distributed applications.

V. Components and Distributed Objects Component- Is executable Has a unique identifier Has a well-known interface

 Component-Based Software  The developers of another word processing program want to incorporate the existing grammar-checking function into their product  The developers of the grammar-checking function modify it to improve speed and accuracy

 Components and objects  Connection Standards and Infrastructure

Fig  Standard connectors and infrastructure enable communication between telephones Telephone infrastructure

Two important issues protocols don’t address: Format and content of valid messages and responses Means of uniquely identifying each component on the internet and routing messages to and from that component

 CORBA  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

 COM+  Components are not assigned a permanent identifier and their internal states cannot be stored permanently. COM+ components can’t remember information from one invocation to the next. COM+ components are similar to functions or subroutines. CORBA components are objects  COM+ Components are registered in the Windows Registry of the client machine on which they’re installed. The Windows Registry stores information other than component registrations, including hardware configuration, software configuration, and user profile information. A CORBA ORB is dedicated to component services

VI. Directory Services Stores the name and network address of distributed resources Responds to directory queries Accepts directory updates Synchronizes replicated or distributed directory copies 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

 Lightweight Directory Access Protocol (LDAP)

Fig  An LDAP hierarchy of objects and container objects O = School of ManagementO = School of Law O = Faculty O = Workstations O = Servers DN = AGUILA DN = ASM DN = AVERIA DN = Ranjit BoseDN = Stephen Burd Directory root C = Mexico C = USA C = Canada OU = University of New MexicoOU = New Mexico State University O = School of Arts and Sciences