Computer networks can be logically classified as 1) Peer-to-Peer networks and 2) Client-Server networks
A Peer-to-Peer network has no dedicated Servers. Here in Peer-to-Peer network, a number of workstations (or clients) are connected together for the purpose of sharing devices, information or data. All the workstations are considered as equal. Any one computer can act as client or server at any instance. This network is ideal for small networks where there is no need for dedicated servers, like home networks, small business networks, or retail shops. The Microsoft term for Peer-to-Peer network is “Workgroup”.
There is no limitation for the number of computers in a peer-to-peer network. But Peer-to-Peer implementations are meant for small networks. Typically a Workgroup contain less than 10 workstations.
Normal Workstation Operating Systems are Windows 95/98 (obsolete), Windows ME (obsolete), NT Workstation (obsolete), Windows 2000 professional (obsolete), Windows XP, Vista, Windows 7, Windows 8/8.1, Ubuntu Desktop, RHEL Desktop etc.
Peer-to-Peer computer networks are good for small business organizations. For example: A small pharmacy outlet, An automobile service center, A small clinic etc. The main disadvantage of Peer-to-Peer networks are listed below.
• Everything is kept distributed in different computers.
• User generated files are stored in individual computers. Data backup is extremely difficult.
• Each computer has its own user database. There is no centralized user & user privilege management. Users need to remember their user ids and passwords in every computers. Managing network users is extremely difficult.
As the organization's network grows, they must gradually upgrade their Peer-to-Peer network to Client-Server based network.
The Client/Server computer network model is made-up of Client compters and Server compters. Now we need to understand the terms Client and Server.
What is a Client? A computer which is seeking any resource from another computer is a Client Computer. You can think a client as a computer in your network, where a network user is performing some network activity. For Example: Downloading a file from a File Server, Browsing Intranet/Internet etc. The network user normally uses a client computer to perform his day to day work.
What is a Server? If a computer has a resource which is served to another computer, it is a Server computer. The client establishes a connection to a Server and accesses the services installed on the Server. A Server is not meant for a network user to browse in internet or do spreadsheet work. A Server computer is installed with appropriate Operating System and related Software to serve the network clients with one or more services, continuously without a break.
In a Client-Server network, high-end servers, installed with the Network Operating System (Server Operating System) and the related software, serve the clients continuously on a network, by providing them with specific services upon request.
Well known Server Operating System Products are Windows 2012 / Windows 2012 R2,
Unix (Oracle Solaris, IBM AIX, HP UX, FreeBSD, NetBSD, OpenBSD, SCO Unix etc), GNU/Linux (RedHat Enterprise Linux, Debian Linux, SUSE Enterprise, Ubuntu Server, CentOS Server, Mandriva, Fedora etc.
Client-Server networks require dedicated servers. Server hardware is more costlier than normal Desktop computers. Client-Server networks cost more than peer-to-peer networks. Network Operating System (Server Operating System) are also costlier than Desktop Operating Systems.
Different types of Servers used in networks are listed below.
File Server: File servers are used to store the user documents and files centrally. An ideal file server should have a large amount of memory and storage space, fast hard-disks, multiple processors, fast network adapters, redundant power supplies etc.
A File server runs FTP (File Transfer Protocol) in Windows, Linux or Unix Networks, or SMBP (Server Message Block Protocol) in Windows Networks. Well known FTP software products are Micrsoft IIS, vsftpd, Apache FTP Server etc.
The main advantage of keeping network user files and electronic documents centrally in a file server is that the network user files and documents can be managed (backup'd) easily. Think about managing network user files and electronic documents kept distributed inside user workstations in a network consists of thousands of computers! Nearly impossible.
Print Server: Print Server, which redirects print jobs from client computers to specific printers.
Mail Server: Mail Servers are used to transmit emails using email protocols. Most widely used email transmission protocol is SMTP (Simple Mail Transfer Protocol). Mail Servers exchange emails between different domains.
Most widely used Mail Server software products are Microsoft Exchange Server, SENDMAIL (now proofpoint), qmail, Postfix etc.
Application Server: Common computer applications or programs which are required by different network users can be run in a central server, which enables multiple network users to access common network applications from the network. Typically Application Servers run business logic. Which means, every business is different and the Application Server is the Server Software which controls the business process. Some examples for Application Server Software are SAP BASIS, WebLogic, WebSphere etc.
Database Server: Database Server allows authorized network clients to create, view, modify and/or delete an organization's data, stored in a common database.
Examples of Database Management Systems are Oracle 10g/11g, Microsoft SQL Server 2000/2005/2008/2012, PostgreSQL, IBM DB2, MySQL, Sybase, Informix etc.
Directory Servers: Directory Servers allows the central administration and management of network users and network resources. Directory Servers provide the basic functions of network security, Authentication, Authorization and Accounting.
Examples of Directory Servers are Microsoft Active Directory, NetIQ eDirectory, Fedora Directory Server, OpenLDAP etc.