servers:-
The server is a special computer that contains more disk space and memory than are found on client workstations. The server has special software installed that allows it to function as a server. This special software can provide file and print services (to allow sharing of files and printers), provide web pages to clients, or provide e-mail functionality to the company.
Workstations :-The workstation also is known as a client, which is just a basic computer running a client operating system such as Windows XP or Linux. These users typically store their files on a central server so that they can share the files with other users on the network.
Hosts:-The term host refers to any computer or device that is connected to a network and sends or receives information on that network. A host can be a server, a workstation, a printer with its own network card, or a device such as a router. We can summarize by saying that any system or device that is connected to the network is known as a host.
Types of Networks:-Organizations of different sizes, structures, and budgets need different types of networks. Networks can be divided into one of two categories: peer-to-peer or server-based networks.
1. Peer-to-Peer Network 2. Server-Based NetworksPeer-to-Peer Network:-
A peer-to-peer network has no dedicated servers instead; a number of workstations are connected together for the purpose of sharing information or devices. When there is no dedicated server, all workstations are considered equal; any one of them can participate as the client or the server. Peer-to-peer networks are designed to satisfy the networking needs of home networks or of small companies that do not want to spend a lot of money on a dedicated server but still want to have the Capability to share information or devices. For example, A small peer-to-peer network will allow these three computers to share the printer and the customer information with one another .The extra cost of a server was not incurred because the existing client systems were networked together to create the peer-to-peer network. A big disadvantage of peer-to-peer networking is that you can‘t do your day-today administration in a single place.
Server-Based Networks:-
Usually after four or five systems have been networked, the need for a dedicated server to store all of the user accounts and data files becomes apparent—this is a server-based network. The advantage of a server-based network is that the data files that will be used by all of the users are stored on the one server. This will help you by giving you a central point to set up permissions on the data files, and it will give you a central point from which to back up all of the data in case data loss should occur. With a server-based network, the network server stores a list of users who may use network resources and usually holds the resources as well. The server in a server-based network may provide a number of different services. The services it will offer to the network usually are decided by the server‘s role.
There are a number of different roles that a server could play on a network:1. File and print Servers
2.Application servers
3.Web servers
4.Directory servers
1. File and print servers:-
File and print servers control and share printers and files among clients on the network. File and print servers were the original reason to have a network; a large number of users needed access to the same files, so the files were placed on a server, and all clients were connected to the server when they needed to work with the files.
2. Application servers:-Application servers are servers that run some form of special program on the server. A good example of an application server is a server that runs the company‘s e-mail server. The e-mail server software is special software that can be run on a server operating system. Another example of software that would run on an application server is a database server product such as Microsoft SQL Server. A database server is a server that holds the company‘s core business data and typically gives this data to custom applications that run on the workstations.
These are some applications that you might find on an application server:1. Microsoft SQL Server
2.Oracle
3.Microsoft Exchange Server
4.IBM Lotus Domino
3. Web servers:-
Web servers are servers that run the Hypertext Transfer Protocol (HTTP) and are designed to publish information on the Internet or the corporate intranet. Web servers are popular in today‘s businesses because they host web applications (web sites) for the organization. These web applications could be designed for internal use, or they could be used to publish information to the rest of the world on the Internet. Examples of web server software are Microsoft‘s Internet Information Services that runs on Windows or Apache web server software that runs on UNIX/Linux, Novell NetWare, and Windows.
4. Directory servers:-Directory servers hold a list of the user accounts that are allowed to log on to the network. This list of user accounts is stored in a database (known as the directory database) and can store information about these user accounts such as address, city, phone number, and fax number. A directory service is designed to be a central database that can be used to store everything about such objects as users and printers.
Network Media and Connectors:-Cabling is the medium for the transmission of data between hosts on the LANs. LANs can be connected together using a variety of cable types, such as unshielded twisted-pair, coax, or fiber. Each cable type has its own advantages and disadvantages, which you will examine in this section. There are three primary types of cable media that can be used to connect systems to a network—coaxial cable, twisted-pair cable, and fiber-optic cable. Transmission rates that can be supported on each of these physical media are measured in millions of bits per second, or megabits per second (Mbps).
Coaxial Cable:-Coaxial, or coax, cable looks like the cable used to bring the cable TV signal to your television. One strand (a solid- core copper wire) runs down the middle of the cable. There are two types of coax cabling: thinnet and thicknet. The two differ in thickness and maximum cable distance that the signal can travel.
Twisted-Pair Cable:-Coaxial cable is not as popular today as it was a few years ago; today the popularity contest has been dominated by twisted-pair cabling. Twisted-pair cabling gets its name by having four pairs of wires that are twisted to help reduce crosstalk or interference from outside electrical devices. (Crosstalk is interference from adjacent wires.) there are two forms of twisted-pair cabling—unshielded twisted-pair (UTP) and shielded twisted-pair (STP).
Fiber-Optic Cable:-The third type of cabling that we want to discuss is fiber-optic cabling. Fiber-optic cabling is unlike coax and twisted-pair, because both of those types have a copper wire that carries the electrical signal. Fiber-optic cables use optical fibers that carry digital data signals in the form of modulated pulses of light. An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. There are two fibers per cable-one to transmit and one to receive. The core also can be an optical-quality clear plastic, and the cladding can be made up of gel that reflects signals back into the fiber to reduce signal loss.
There are two types of fiber-optic cables: single-mode fiber (SMF)and multimode fiber (MMF).
1. Single-mode fiber Uses a single ray of light, known as a mode, to carry the transmission over long distances.
2. Multimode fiber Uses multiple rays of light (modes) simultaneously, with each ray of light running at a different reflection angle to carry the transmission over short distances