Computer networking
Computer networking concepts
Introduction to the Concept of Networking:
A computer network is an interconnection of various computer systems located at the same or different places. The interconnection is done through a communication link also known as the physical layer of the network and this link is such that it is totally transparent to the users of the network. The transparency of the communication link is brought about by the interfacing software known as protocols which enables a user in one location to freely access a computer system/database/process/software in another location.
However, if the computers in the network operate together as a single unit which to the user appears as a single computer, albeit physically dispersed, then the complete system is more accurately described as a distributed system. Therefore, although any interconnected set of computers often conveniently referred to as a ??computer network??, the use of the term often implies an interconnected set of independent computers and not a distributed system. However, it may be useful when considering a distributed system to be able to recognize the particular type of network on which it is based.
Network Architecture:
In communications, data is transferred wither on parallel or serial mode. Parallel communication is faster but requires more wires. Serial communications is much slower but requires fewer wires. Serial is more practical for communication with remote sites, and the existing telephone networks use serial communications for linking computers.
Local Area Network (LAN):
Networks used to interconnect computers in a single room or rooms within a building or buildings are normally called Local Area Network (LAN). LAN??s normally transmit data in a digital form with typical transmission speeds of up to several megabytes per second. These speeds can be achieved using parallel transmission where a cable with multiple core is used, or serial transmission, making use of high frequency carriers, using coaxial cables, fiber optics or even a simple pair of wires because distances are short. Modems are not normally required although some mechanism for converting from parallel to serial transmission and back again may be needed. The terminals and workstations are able to connect to either one of the two ??host?? computers at will. The network also has a file server and a print server. The former is a special computer which provides a form of auxiliary storage which can be used by any other computer on the network and the latter is a special computer which can receive data from other computers on the network and print it. There is also an external communication server on the LAN, which enables communication between equipment on the network and system elsewhere.
Local Area Network link computers in the same area for the purpose of sharing information and hardware. Usually the computers are within 300 meters of each other, because they must be connected by a cable hookup, which can be expensive. People at the work stations in a LAN gain more capabilities in work processing, data processing, information retrieval and communication without duplication of equipment, databases and activities. LAN has become popular. Many businesses are installing LAN in order to improve the efficiency of office functions and to facilitate office automation. The configuration of the LAN can be a star or a ring topology or simply devises attached along a length of cable.
The typical LAN connects computers located within half a mile of each other. The attached computers may be different typed and be performing variety of functions such as data processing, word processing and electronic mail. The two main purposes of the local network are to link workstations within an area so that they may share peripherals (such as magnetic disks holding the database) and to allow workstations to communicate with each other.
Advantages of Local Area Networks over Conventional Systems:
To facilitate communication: Where key personnel are scattered on offices on several floors and perhaps in several buildings, conferences may be inconvenient. Telephone calls may also prove frustrating if the participants cannot express their difficulties accurately. One solution may be the use of electronics mail, in which individuals use a LAN a leave, written messages to a number of subordinate for example a memo ?V it may also be possible to keep a computerized distribution line and use electronic mail and a LAN for this purpose.
| |
To improve communications, speed and accuracy: It is uncommon for the inter-office mail of even fairly small companies to take several days for delivery. In contrast, sending messages through LAN is virtually instantaneous and there is also less chance of the message being lost. Communications may also be more accurate because no ambiguous messages are taken by the other and because word processors can be used to compose the message.
To share Computer Equipment: Letter-quality printers and large hard-disk drives can be expensive. Local area networks enable users to share equipment by networking microcomputers or workstations together. For example, a company with twenty microcomputer users, each requiring only limited hard-disk space and occasional printing, might save substantial amount in equipment costs through networking. Savings may also be achieved by buying less expensive terminals or disk-less microcomputers, rather than fully configured stand-alone equipment.
To Share Computer Files: LAN enables the users to share files with each other. This advantage is invaluable (for example, to word-processing personnel who need access to filed documents or to managers using electronic mail). Corporate databases, important policy or procedure statements, and even local classified advertisements can call be stored on shared computer files.
To Save Software Costs: The purchase or lease of most software products includes a licensing agreement that restricts copying softwares. Whereas some software companies require buyers to purchase separate copies for each computer or microcomputer, others offer ??site-licensing agreement?? that permits purchasers to pay a single one time fee per LAN. Since many commercial software packages are costly, the savings for companies with local area networks can be considerable.
To Enable unlike Computer Equipment's to Communicate: It is not uncommon for the typical company to purchase incompatible microcomputers or peripheral equipment. However, most microcomputers have standard RS232C (serial) output ports that can be used to network unlike machines together. Whereas, the swapping of computer programs may not be possible because of operating system differences, the ability to share files and send messages may be sufficient for implementing a LAN.
Wide Area Network (WAN):
The term wide area network (WAN) is used to describe a computer spanning a region or global area. A large company may use the WAN to connect its regional computers, manufacturing centers, distribution centers and regional accounting centers. They are connected to national headquarters, and therefore to each other for communication purposes.
Difference between LAN & WAN:
1. A LAN is restricted to a limited geographical coverage of few kilometers, but a WAN spans greater distance and many operate nationwide or even worldwide.
2. The cost to transmit data in a LAN is negligible since the transmission medium is usually owned by user organization. However, in case of a WAN, this cost may be very high because the transmission medium used are leased lines or public systems such as telephone lines, microwave and satellite links.
3. In a LAN, the computer terminals and peripherals devices are usually physically connected with wired and coaxial cables. Whereas, in a WAN there may not be a direct physical connection between various computers.
4. Data transmission speed is much higher in LAN than in a WAN. Typical transmission speeds in LAN are 0.1 to 100 bits per second. On the other hand, in a WAN the data transmission speed is normally of the order of 1800 to 9600 bits per second.
5. Fewer data transmission error occurs in case of LAN as compared to a WAN. This is mainly because in the case of a LAN, the distance covered by the data is negligible as compared to WAN.
Metropolitan Area Networks (MAN):
As implied by their names, Metropolitan and Wide area networks have wider geographical reaches than Local area networks. While MAN usually spans over a city, the reach of a WAN extends over one or more computers and possibly the whole world. Despite the differences in their geographical reach, MAN??s and WAN??s of today generally use the same technology. For example if the computers of an Insurance Company spread all over the country are connected together and information / data travels from operating offices to controlling office and vice versa then we can say that WAN is implemented in the company.