In general, a computer network composed of one or more servers, workstations, network interface cards, active and passive hub, routers, bridges, gateways, modem, software components like network operating systems, and other application software. The following components widely used for the construction of networks.
Server It is the most powerful computer in the network. In a local area network, usually, a powerful microcomputer or a super microcomputer with the power of a minicomputer is used as a server. There are two types of servers typically employed in a local area network. They are dedicated servers and non-dedicated servers.
In a dedicated server, the server computer performs the functions and services of the whole network. It helps to run user applications efficiently and increases the overall system cost. Users cannot run their applications directly in a dedicated server. It provides e-mail service, sharing of multiple hard disks, and sharing of other resources and faster response time. For more extensive networks with a heavy load, dedicated servers usually employed.
In a non-dedicated server, apart from the role of a network controller, a server also acts as an individual workstation — the server equipped with a prodigious memory. Network operations demand only a portion of server memory. The remaining portion of the memory may use for the user applications. Under light load conditions, it is advisable to use a non-dedicated server. Some servers can operate on both modes, according to the requirement of the user.
These are the devices used to interconnect the components of the network, basically the network cards, the cabling between servers and workstations, as well as the cables to connect the peripherals.
Resources to Share
They are resources of both Software and Hardware devices. The most common hardware devices are printers, hard drives, drives, CD ROM drives. Among the Software resources that are shared are programs, files, applications, etc.
The primary goal of a computer network is to share data among several users. They also make their attached disk drives, printers, modems, and unique communication links available to the various client stations. Providing one computer with one or more hard disks facilitates this. All client stations share these hard disks. Clients can make their requests to access any of the shared facility to the server. The file server is a powerful computer, which runs special software. It provides the files and other shared resources to different users in the network. It provides facilities like user authentication, security to various user programs, and data. It can access through a network operating system (NOS). Typical configurations of a server are Pentium 4 machine with 128MB or higher capacity RAM, 40 GB or higher capacity hard disk, to serve up to 10 nodes or workstations.
All activities of a file server can be monitored and controlled from the monitor called console. The network administrators gave special privileges. They gave supervisory passwords. They perform the network administration operation for the entire network. Any user of the network needs to get a new network service; they have to contact the network administrator and make a request for the specific service they need. The file server has a prodigious memory, which used for caching directories and files and hashing directories. Novell Netware and Windows NT are the two network operating systems that run on a server machine.
Another critical component of a network is the workstation or a client. A workstation is an individual computer with capabilities to communicate with other machines. It must equip with the hardware and software necessary to connect to a LAN. Usually, a Network Interface Card (NIC) or an Ethernet card or an Arc net card use for this purpose. Part of the network operating system is also available in the workstation. A workstation can communicate with other workstations or to the server. The hardware requirement for a workstation depends on the application and the size of the network. In a typical LAN of a university computer center, a Pentium III system with 64MB RAM and 4 to 8GB hard disk capacity, with necessary network interface card can use for a typical workstation. In general, c the memory and hard disk capacity of a workstation are much less than that of the server.
Network Operating Systems
Network operating systems (NOS) is the logical component that controls communications, shared resources on the network, and provides distributed processing capacity. At first, the network operating systems only allowed to share printers and disks. A single station could access a disk volume at a time. Currently, network operating systems provide the basis for creating client/server applications, integrating different types of computers, and forming workgroups.
In most networks, the operating system works in conjunction with the computer's operating system. The computer's operating system first processes system commands. When a local request made, a command that only specifies the resources/devices of the station, this is done at the user station. When a request is made that requires the participation of the logical equipment or network devices, it passed to the network operating system for processing.
Network Interface Unit
Every computer on the network needs one add-on card called the Network Interface Card (NIC) or Ethernet adapter or Network Interface Adapter. The role of NIC is to move the serial signals on the network cables or media into parallel data stream inside the Pc. In some cases, two or more such NIC’s are used in the server to split the load. These interface units also have important jobs of controlling access to the media. It includes activities known as carrier sense (listen before transmit), following station number, and token passing. The above activities are known as Media Access Control.
The data signal travels through this medium. There are two general categories. They are bounded (guided) and unbounded (unguided) medium. Twisted pair, coaxial cable, and fiber optic cables are all bounded media. The data signals travel within the boundaries of the transmission media. On the other hand, microwave and satellite transmissions, both travel through the air, which has no boundaries, hence called unbounded transmission.
The network hub is a centralized distribution point for all data transmission in a network. Hub may also refer to as a concentrator Data packet from a NIC arrives at the hub. The hub receives and rebroadcasts them to other computers connected to it. In general, the hub network is a passive device. It does not know the destination of a received data packet. Hence, it is required to send copies to all the hub connections. Hubs can classify into the following three categories.
• Stackable and non-stackable hubs
• Active and passive hubs
• Intelligent and non-intelligent hubs
Stackable hubs are hubs that can be stacked or interconnected to make a single hub appearance. They are useful for vendors to make hubs of a size suitable to customer requirement. Non-stackable hubs cannot be interconnected. They always provided only a fixed number of connections.
The hubs that connect to the network backbone are known as active hubs. The hubs, which connect only to active hubs, are known as passive hubs.
Intelligent hubs contain a special firmware that can be accessed by remote workstations. The firmware is known as the Simple Network Management Protocol (SNMP). Network performance and Network status data read from SNMP.
A repeater is a communication device that connects two segments of the network cable. It retimes, regenerates, strengthens the digital data, and sends them on their way again. Repeaters are often used to extend the cable length to enlarge LANs. Wide area network contains many repeaters. Ethernet also frequently uses repeaters to extend the length of the bus.
A bridge interconnects two networks using the same technology (such as Ethernet or Arc net). The bridge is more sophisticated than a repeater. A modern bridge reads the destination address of the received packet and determines whether the address is on the same segment of the network cables of the originating station. If the destination is on the other side of the bridge, the bridge transmits the packet into the traffic on that cable segment. Local bridges are used to connect two segments of the same LAN. Remote bridges are used to link local LAN cables to thin long distance cables to link two physically separated networks. Network administrators often use bridges to split the big networks into several small networks. Bridges are easy to install. They provide an easy way to perform network management functions.
A router transfers data between networks. It is also possible for a router to transfer data between different compatible network technologies such as Ethernet and IBM token ring. Since the Internet consists of thousands of different network technologies, routers are an integral part of the Internet. A router has the address on the network. A bridge does not have an address. Hence, a router can act as an intermediate destination. In other words, a computer can send a data packet to the router of another network. The router transfers the packet to the other network.
On the other hand, the bridge must examine all the packets to determine which packets to transmit between networks. As such, computers never send packets directly to a bridge. A router examines a packet only if it contains the router's address.
A router also can act as a bridge. Such a router is known as a router. The router receives the packet and examines whether it supports the protocol used by the packet. If not, it only drops the packet. The packet is bridged using the physical address information.
Two different networks can be connected using a gateway. For example, a mainframe can be connected and accessible to a PC network using a gateway. Unlike routers, a gateway converts the format of the data sent between two networks. A router adds only addressing information to the data packet. Routers never change the content of the message. However, a gateway has to identify the protocols used in the networks, and recognize the data format and convert the message format into a suitable format to be accepted by the other network. Wide area networks often use gateways because there is a large number of different networks present in a WAN. Gateways provide excellent connectivity to different kinds of networks on the Internet.
Another significant network component is modern. The term Modem is the shortened version of the name modulator-demodulator. Modern provides two-way communication facility between a computer network and telephone network. As Wide Area Network uses the existing telephone network to connect to a distant network, it always uses a modern to dial-up the telephone network. The modem converts the digital data from the computer into useful analog signals that can transmit through a telephone network. Similarly, signals from the telephone channels are converted back into digital data s1suitable for a computer.