Chapter One An Introduction to Networking

Networks and Standalone Computers Network Group of computers and other devices connected by some type of transmission media Group of computers and other devices connected by some type of transmission media Networks enable users to share devices and data, collectively called a network’s resources Networks enable users to share devices and data, collectively called a network’s resources Standalone computer Uses programs and data only from its local disks and is not connected to a network Uses programs and data only from its local disks and is not connected to a network

Standalone Computers Method of sharing data by copying it to a disk and carrying the disk from computer to computer Figure 1-1: Data sharing before the advent of networks

Network Network A Network is an Any-to-Any Communication System Can connect any station to any other Can connect any station to any other

Advantages of a Network in an Office Setting A Recourse Sharing - All office members can share computer files - Laser printers can be shared -Software applications are more easily shared and upgraded A Electronic mail can be implemented A Office computers can be backed up over the network A Working groups can share information within the each group ASaving money :- In a distributed network computers have a better price/performance ratio as compared to large ones. E.g. Mainframes are 10 times faster than personal computers, but they cost 1000 times more.

Basic Components of Network AWorkstations ANetwork Operating System ACabling

Basic Network Components

Networking Basics Workstation Computer that typically runs a desktop operating system and connects to a network Computer that typically runs a desktop operating system and connects to a network Client/server architecture Networking model in which clients use central server to share applications, devices, and data Networking model in which clients use central server to share applications, devices, and data Network operating system Special software designed to manage data and other resources on a server for a number of clients Special software designed to manage data and other resources on a server for a number of clients

Terminal-Host Systems (Mainframe Architecture) Central host computer does all the processing Central host computer does all the processing Terminal is dumb--only a remote screen and keyboard Terminal is dumb--only a remote screen and keyboard Host are mainframes Host are mainframes TerminalsHost

Distributed Networks (Client/Server Architecture) The Most Common Platform in Organizations Based on Client/Server Architecture Based on Client/Server Architecture Allows PCs to share resources Allows PCs to share resources Network Client PC Client PC PC Server PC File Server

Client / Server Networked Computers Client User (PC, Workstation, Laptop) Requires Data, Application, Communications It Does Not Have User (PC, Workstation, Laptop) Requires Data, Application, Communications It Does Not HaveServer Component (Computer) Having Desired Data, Application, Communications Component (Computer) Having Desired Data, Application, Communications

Client/Server Processing Cooperation Through Message Exchange Client program sends Request message, such as a database retrieval request Client program sends Request message, such as a database retrieval request Server program sends a Response message to deliver the requested information or an explanation for failure Server program sends a Response message to deliver the requested information or an explanation for failure Client MachineServer Client Program Server Program Request Response

PC Network Components File Servers Store files (data files and programs) Store files (data files and programs) The most common type of server in PC networks The most common type of server in PC networks Almost all file servers are themselves PCs Almost all file servers are themselves PCs File Server

File Server Program Access File Server Program Access is the Most Common Way to Execute Programs in PC Networks Program files are stored on the file server Program files are stored on the file server But downloaded (copied) to client PC for execution But downloaded (copied) to client PC for execution Executed on client PC, not on file server Executed on client PC, not on file server File Server Client PC Stored on the File Server Download Executed on Client PC

LANs – WANs - MANs Networks Have Different Geographical Scopes Local Area Networks (LANs) Small Office Small Office Office Building Office Building University Campus University Campus Wide Area Networks (WANs) Connect Customer and Supplier across various building within a city. Connect Customer and Supplier across various building within a city. Metropolitan Area Network (MAN) Connect corporate sites across cities Connect corporate sites across cities

Local Area Network (LAN) Network of computers and other devices confined to relatively small space LANs involving many computers are usually server-based On a server-based network, special computers (known as servers ) process data for and facilitate communication between other computers on the network (known as clients ) On a server-based network, special computers (known as servers ) process data for and facilitate communication between other computers on the network (known as clients )

Figure 1-3: LAN with a file server

Small Peer-Peer PC Network No dedicated (full- time) server User PCs supply services to each other So user PCs act both as clients and as servers

Small Peer-Peer PC Network File Sharing Each PC can make certain disk drives or directories available to to other user PCs Can allow others read-only or full access to files there Can require password for access

Small Peer-Peer PC Network Printer Sharing Each PC can make one or more printers attached to it available to others Windows 95 can be used as for Peer – to – peer network. Windows NT can also be used but it is designed to work in a centralized networking model

Small Peer-Peer PC Network Advantage No dedicated server to purchase and maintain

Small Peer-Peer PC Network Disadvantages If someone turns off their PC or crashes it, people using its files or printer are cut out

Small Peer-Peer PC Network Disadvantages (Cont.) Users often set up security poorly giving access to unauthorized people Special problem if home network is connected to the Internet Experience slow response if heavily loaded.

Small Peer-Peer PC Network Overall Beyond about 5 users, problems become pronounced Beyond about 10 users, very bad idea

MANs and WANs Metropolitan area network (MAN) Network connecting clients and servers in multiple buildings within limited geographic area Network connecting clients and servers in multiple buildings within limited geographic area Wide area network (WAN) Network that spans large distance and connects two or more LANs Network that spans large distance and connects two or more LANs The Internet is an example of a very intricate and extensive WAN that spans the globe The Internet is an example of a very intricate and extensive WAN that spans the globe

WAN Figure 1-5: A simple WAN

Elements Common to All Server-Based Networks Client In addition to referring to a computer on the network, may also refers to human user of client workstation In addition to referring to a computer on the network, may also refers to human user of client workstation Server – It runs the NOS ( Eg. UNIX, NT4.0) Cabling Network interface card (NIC) Enables workstation to connect to the network and communicate with other computers Enables workstation to connect to the network and communicate with other computers

Elements Common to All Server-Based Networks Figure 1-6: A network interface card (NIC)

Servers Provide services to client PCs Provide services to client PCs Usually PCs themselves Usually PCs themselves Most PC nets have multiple servers Most PC nets have multiple servers Require a NIC Require a NIC Require a server operating system (SOS) Require a server operating system (SOS) Require application software Require application software

Server Operating System (SOS) Servers need operating systems more reliable than client PC operating systems Servers need operating systems more reliable than client PC operating systems Windows NT/2000 Server, Novell NetWare, UNIX, LINUX Windows NT/2000 Server, Novell NetWare, UNIX, LINUX Application Software Provides the services offered by the servers Provides the services offered by the servers , word processing, file sharing, etc. , word processing, file sharing, etc. More expensive than the SOS More expensive than the SOS

Novell NetWare SOS Once dominant, but market share has shrunk Once dominant, but market share has shrunk Excellent file and print service Excellent file and print service Excellent directory service (later) Excellent directory service (later) Until recently, was not sufficiently robust and scalable for servers other than file servers Until recently, was not sufficiently robust and scalable for servers other than file servers

Microsoft Windows Server Operating System More robust than desktop Windows (Win 95, Win 98, Win 2000 Professional, etc.) More robust than desktop Windows (Win 95, Win 98, Win 2000 Professional, etc.) All 32-bit code All 32-bit code Microsoft Windows NT Server before 2000 Microsoft Windows NT Server before 2000 Newer Microsoft Windows 2000 Server Newer Microsoft Windows 2000 Server Versions in order of increasing functionality: Windows 2000 Server, Advanced Server, DataCenter Server New

Microsoft Windows Server Operating System Easy to install, learn, and use because resembles desktop Windows Easy to install, learn, and use because resembles desktop Windows Becoming dominant for small business and small department servers Becoming dominant for small business and small department servers

UNIX Powerful workstation servers run UNIX Powerful workstation servers run UNIX Extremely reliable Extremely reliable Workstation servers running UNIX dominate the enterprise server market Workstation servers running UNIX dominate the enterprise server market

UNIX Expensive to buy Expensive to buy Must retrain staff or hire UNIX staff Must retrain staff or hire UNIX staff Many versions of UNIX exist Many versions of UNIX exist Most run the same application software However, have different management utilities, etc., requiring training for each version used Not for Small PC Networks Not for Small PC Networks

Server Application Software File Service Allows File Sharing File server stores program and data files File server stores program and data files Shared file be accessed by any user with access rights Shared file be accessed by any user with access rights Built into most SOSs Built into most SOSs File Server Access Rights No Access Rights

Server Application Software File Service For sharing application program files also For sharing application program files also No need to install applications on each PC No need to install applications on each PC Greatly reduces installation labor File Server

Server Application Software File Server Program Access Program is STORED on the file server Program is STORED on the file server File Server

Server Application Software File Server Program Access But program is EXECUTED on the client PC But program is EXECUTED on the client PC Limited by power of client PCs, which do not get very large Limited by power of client PCs, which do not get very large File Server

Server Application Software Print Service Also built into SOSs Also built into SOSs Print jobs go to shared printers Print jobs go to shared printers But they first go to the file server But they first go to the file server Not directly to the print server! Not directly to the print server! File Server Print Server Shared Printer Client PC

Server Application Software Print Service File server stores print job in a print queue until print server is ready to print it File server stores print job in a print queue until print server is ready to print it File server sends the print job to the print server File server sends the print job to the print server File Server Print Server Shared Printer

Server Application Software Print Server Print server feeds the print job to the printer Print server feeds the print job to the printer Print servers are simple and inexpensive because the file server does most of the work Print servers are simple and inexpensive because the file server does most of the work Low print server cost allows shared printers can be scattered throughout the office Low print server cost allows shared printers can be scattered throughout the office File Server Print Server

Server Application Software Typical Application Software Word processing, , etc. Word processing, , etc. Must buy multiuser versions, not just a single copy from a retail store Must buy multiuser versions, not just a single copy from a retail store License will limit the number of users License will limit the number of users Will cost more than the SOS Will cost more than the SOS

Server Application Software Remote Access Service (RAS) User dials into a remote access server User dials into a remote access server Server authenticates the user (user must prove identity) Server authenticates the user (user must prove identity) If authenticated, user may use internal servers If authenticated, user may use internal servers Client PC needs RAS software Client PC needs RAS software LAN Internal Server RAS Dial-In Client Dial-Up Telephone Line RAS Client Software

Server Application Software Directory Servers Problem: Most networks have many servers Problem: Most networks have many servers To use a resource, must know the server To use a resource, must know the server To send , address is Files must be accessed on particular servers

Server Application Software Directory Servers Directory server knows all resources on all servers Directory server knows all resources on all servers Can send mail to user Can send mail to user Can search for a specific file across servers Can search for a specific file across servers Directory Server

Server Application Software Directory Servers Know user access rights on all servers Know user access rights on all servers Single login to directory server Single login to directory server After that, get access to all other servers where user has access rights After that, get access to all other servers where user has access rights Directory Server Single Login

Elements Common to All Server-Based Networks Topology Physical layout of computer network Physical layout of computer network Figure 1-7: Commonly used network topologies

An Ethernet Bus Network

The Ring Topology

Ethernet Star Topology with a Concentrator

Elements Common to All Server-Based Networks Protocol Rules network uses to transfer data Rules network uses to transfer data A ANetBEUI (native to NT Server) A ATCP/IP (important for networks with UNIX, Internet communications) A AIPX/SPX (for communications on networks with Novell Netware) Data Packets The distinct units of data transmitted from one computer to another on a network The distinct units of data transmitted from one computer to another on a network

Elements Common to All Server-Based Networks Addressing Scheme for assigning unique identifying number to every workstation on network Scheme for assigning unique identifying number to every workstation on network The number that uniquely identifies each workstation and device on a network is its address The number that uniquely identifies each workstation and device on a network is its address

Elements Common to All Server-Based Networks Transmission media Means through which data are transmitted and received Means through which data are transmitted and received Figure 1-8: Examples of network transmission media

How Networks Are Used Services Features provided by a network Features provided by a network File and print services Communications services Mail services Internet services Management services

Network Services File services Refers to capability of a server to share data files, applications, and disk storage space Refers to capability of a server to share data files, applications, and disk storage space Server that provides file services is called a file server Server that provides file services is called a file server Print services Allows printers to be shared by several users on a network Allows printers to be shared by several users on a network

Network Services Communications services Allow remote users to connect to a network Allow remote users to connect to a network Remote user Person working on a computer in a different geographical location from the LAN’s server Person working on a computer in a different geographical location from the LAN’s server Communications server Communications server Server that runs communications services Also referred to as access servers and remote access servers

Network Services Mail services Coordinate storage and transfer of between users on a network Coordinate storage and transfer of between users on a networkGateway Combination of software and hardware enabling two different kinds of networks to exchange data Combination of software and hardware enabling two different kinds of networks to exchange data Internet services Enable networks to communicate with the Internet Enable networks to communicate with the Internet

Network Services Management services Centrally administer and simplify complicated management tasks on the network Centrally administer and simplify complicated management tasks on the network Numerous services fall under category of network management Numerous services fall under category of network management