by Dinesh Thakur Category: Computer Network

what is lan: It actually stands for local area network. A network is a group of computers and other devices connected together so they can pass information back and forth. 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.

Lan Definition

The personal computers and workstations in the offices are interconnected via LAN to share resources. The resources to be shared can be hardware like a printer or softwares or data. 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.  The data rates for LAN range from 4 to 16 Mbps with the maximum of 100 Mbps.

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 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).Local Area Network

Types of lan

Ethernet is the most common type of LAN. Different Lan can be differentiated on the behalf of following characteristics.

Topology: The topology is the geometric arrangement of a network elements. For example, Network devices can be interconnected in a ring topology or in a bus topology or linear bus.

Protocols: It is a guidelines for communicating data between two devices. The protocols also determine type of error and data compression.
Media: The cable used in Lan to connect devices are twisted-pair wire, coaxial cables, or fiber optic.

Wan vs Lan

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. Two or more interconnects different smaller networks are called a wide-area network (WAN).The difference between a LAN and WAN is that the WAN spans a relatively large geographical distance such as across cities, states, or countries.

Example of 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.

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 share 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.

About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.

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