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by Dinesh Thakur Category: Computer Network

LAN looks like an acronym that a board of directors spent a lot of money and time trying to create, but it actually stands for any generic local area network. A network is a group of computers and other devices connected together so they can pass information back and forth.

                 

           Local Area Network

• The local area network (LAN) is a network which is designed to operate over a small physical area such as an office, factory or a group of buildings. LANs are very widely used in a variety of applications.

• LANs are easy to design and troubleshoot. The personal computers and workstations in the offices are interconnected via LAN.




• The exchange of information and sharing of resources becomes easy because of LAN.

• Local Area Network technology connects people and machines within a site.

A LAN is a form of local (limited-distance), shared packet network for computer communications.

• In LAN all the machines are connected to a single cable. Different types of. Topologies such as Bus, Ring, Star, Tree etc. are used for LANs.

• LAN uses a layered architecture and they are capable of operating at hundreds of Mbits/sec.

• A local area network (LAN) is usually a privately owned and links the devices in a single office, building or campus of upto a few kilometers in size.

• Depending on the needs of an organization and the type of technology used, a LAN can be as simple as two personal computers and a printer in someone's office or home or it can extend throughout a company and include voice, sound and video peripherals.

• LAN s are widely used to allow resources to be shared between personal computers or workstations. The resources to be shared can be hardware like a printer or softwares or data.

• A common example of a LAN found in many business organizations, links a work group of task related computers, e.g. accounting and finance PCs, administrative PCs or engineering workstations.

• One of the computer in a network can become a server serving all the remaining computers called clients. Software can be stored on the server and it can be used by the remaining clients.

• In a LAN its size can be determined by licensing restrictions on the number of users per copy of software or by restricting the number of users licensed to access the operating system.

• LAN's are also distinguished from MAN's and WAN's based on the transmission media they use and topology. In general a given LAN will use only one type of transmission medium. The most common topologies used are bus, ring and star.

• The term LAN can also refer just to the hardware and software that allows you to connect all the devices together. In this sense, Local Talk is one kind of LAN, Ethernet is another. (AppleTalk is the protocol for Local Talk.)

The data rates for LAN range from 4 to 16 Mbps with the maximum of 100 Mbps.

 

The components used by LANs can be divided into cabling standards, hardware, and protocols. Various LAN protocols are Ethernet, Token Ring: TCP/IP, 5MB, NetBIOS and NetBeui, IPX/SPX, Fiber Distributed Data Interchange (FDDI) and Asynchronous Transfer Mode (ATM).

LAN Applications and Benefits

LANs are used almost exclusively for data communications over relatively short distances such as within an office, office building or campus environment. LANs allow multiple workstations to snare access to multiple host computers, other workstations, printers and other peripherals, and connections to other networks. LANs are also being utilized for imaging applications, as well. They are also being used for video and voice communications, although currently on a very limited basis.

 

LAN applications include communications between the workstation and host computers, other workstations, and servers. The servers may allow sharing of resources. Resources could be information, data files, e-mail, voice mail, software, hardware (hard disk, printer, fax, etc.) and other networks.

 

LAN benefits include the fact that a high-speed transmission system can be shared among multiple devices in support of large number of active terminals and a large number of active applications in the form of a multi-user, multi-tasking computer network. LAN-connected workstations realize the benefit of decentralized access to very substantial centralized processors, perhaps in the form of mainframe host computer and storage capabilities (information repositories). Additionally, current technology allows multiple LANs to be inter-networked through the use of LAN switches, routers and the like.

 

Disadvantages of LANs include concern for security of files and accounts.

LAN topologies:

Various topologies are possible for the broadcast LANs such as bus topology or ring topology.

                               LAN topologies

Bus topology:

• Bus topology is shown in Fig. In this topology at any instant only one computer acts as master and it is allowed to transmit (broadcast). The others are supposed to listen.

• If two or more machines want to transmit simultaneously then an arbitration mechanism has to be used for resolving the conflict.

• It is possible to have a centralized or distributed type arbitration mechanism.

• The most popular example of bus topology is Ethernet (IEEE 802.3). It has a decentralized control and it operates at 10 or 100 Mbps.

Computers on Ethernet can transmit whenever they want. If collision of their packets takes place, then they wait for a random time and retransmit their packets.

Ring topology:

• This is another broadcast topology.

• In a ring each bit propagates around on its own without waiting for the rest of the packet to which it belongs.

• Since it is a broadcast system, some rules are essential for arbitrating the simultaneous access to the ring.

• An example of ring based LAN is IEEE 802.5 (IBM token ring) operating at 4 and 16 Mbps.

Static and dynamic broadcast networks:

• The broadcast networks are further classified into two types namely,

 

1. Static networks and

2. Dynamic networks.

 

• This classification is based on how the channel is allocated.

• In static allocation, each machine is allowed to broadcast only in its allotted time slot.

• But static allocation wastes the channel capacity when a machine does not want to transmit in its allotted time slot.

• Hence most of the systems try to allocate the channel dynamically i.e. on demand.

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