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A local area network (LAN) is a data

communication system connecting a number

of devices to each other.

The size of a LAN is limited to the radius of a

few miles.

Its physical size is usually limited to a

building, campus, or site.

Local Area NetworkLocal Area Network

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A local area network is a combination of

hardware and software.

The hardware is the part of the network that

is tangible.

The software is a collection of programs that

allows the use of the physical components of

the network.

Local Area NetworkLocal Area Network

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The hardware used in a LAN can be divided into

three categories :

Stations

Transmission media

Connecting devices

HArdWAREHArdWARE

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STATIONS

The purpose of LAN is to connect stations such

as computers, printers, and modems.

These stations are sometimes referred as nodes.

A station needs extra hardware and software

tools to be capable of being connected to the

network to perform tasks such as sending and

receiving data and monitoring the network.

HArdWAREHArdWARE

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The hardware used is generally a Network

Interface Card (NIC), which is commonly installed

inside the station.

It contains the necessary circuitry ( in the form

of chips) to perform network functions.

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TRANSMISSION MEDIA

It is the path that allows communication

between stations.

LANs can either use guided or unguided

transmission media.

Wired LANs can use guided media such as

twisted pair cable, coaxial cable, and fibre optic

cable.

HArdWAREHArdWARE

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CONNECTING DEVICES

Two categories of connecting devices are used in

LANs.

One category consists of devices that connect

transmission media to the stations.

(Transceivers and transceiver cables)

The second category consists of devices that

connect segments of a network together.

( Repeaters and Bridges)

HArdWAREHArdWARE

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SOFTWARESOFTWARE

Software run on LAN can be divided into two large

groups :

Network operating system software

Application programs

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NETWORK OPERATING SYSTEM (NOS)

A network operating system is a program that

allows the logical connection of stations and

devices to the network.

It enables users to communicate and share

resources.

Eg. Novell Netware, UNIX, Linux, Windows 2000

SOFTWARESOFTWARE

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APPLICATION PROGRAMS

Application programs allow users to solve special

problems.

They are not specific to LANs; they are also used

by the stand alone computers.

Eg. Program to calculate taxes.

SOFTWARESOFTWARE

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From a users point of view, a LAN can be

configured either as a client -server LAN or a

peer-to-peer LAN.

LAN MODELSLAN MODELS

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LAN APPLICATIONSLAN APPLICATIONS

Some of the common applications of local area

networks are :

Office networks

Industry networks

Backbone networks

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OFFICE NETWORKSOFFICE NETWORKS

The most commonly used application of a local

area network is in the office environment.

LANs are used in the office for three purposes :

Sharing

Interoffice communication

Internet communication

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Some LAN architectures are suitable for

automated manufacturing and production.

For eg, a LAN can be used in the automobile

industry to coordinate activities such as

controlling robots, material handling, or

warehouse inventory.

INDUSTRY NETWORKSINDUSTRY NETWORKS

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ADVANTAGES

It would be too expensive to use one high

speed LAN to connect each individual user.

It improves the reliability of the system i.e if

one of the LAN fails, the rest will continue to

function.

It isolates the load on one network from others.

BACKBONE NETWORKSBACKBONE NETWORKS

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LAN & WAN are the technologies used for the

internet.

However, internet is not made of a single LAN or a

single WAN & there must be a way to join these

LANs & WANs together.

These joining tools are known as connecting

devices.

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Connecting devices include: RepeatersHubs

Bridges

Routers

Switches

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Operates only in the physical layer.

Receives a signal, & before it becomes too weak or

corrupted, it regenerates the original bit-pattern.

Can extend the physical length of a network.

The cable can be divide into segments to extend the cable

length and repeaters can be installed between them.

Portion of the network between repeaters are called

segments.

A repeater acts as a two interface node & forwards every

packet but has no filtering capability.

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Is actually a multi-port repeater which is

normally used to create connection

between stations in a physical startopology.

Also used to create multiple levels of

hierarchy. The hierarchical use of hubs removes the

length limitation of 100 mts.

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Operates in both the physical & data link layer.

As a physical layer device, it regenerates the

signals it receives.

As a data link layer device, the bridge can check

the physical addresses contained in the packet.

Has no physical address & acts only as filter, i.e.,

not as an original sender to a final destination.

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A bridge has filtering capability, i.e., can

check the destination address of a packet and

decide if the packet should be forwarded or

dropped. If the packet is to be forwarded, the decision

must specify the interface.

A bridge uses a table in filtering decisions. Connects segments of a LAN together.

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A Router is a three layer device:

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Router is an inter-networking device. It can connect :

LANS together

WANS together

LANS and WANS together

Two networks (LANS or WANS) connected by a

router becomes an internetwork or an internet

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A two-layer switch is a bridge with many

interfaces and better(faster) performance.

Due to having many interfaces , it may beable to allocate a unique interface to each

station, with each station on its own

independent segment. This means no traffic and no collision .

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A three-layer switch is a router with an

improved design to allow better

performance. It can receive , process and dispatch a

packet much faster than a traditional router

even though the functionality is the same.

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Backbone networkallows several LANs to

be connected together.

No station is directly connected to the

backbone.

Stations are part of LAN and backbone

connects LANs.

Uses a LAN protocol like Ethernet

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Logical topology of the backbone is a bus.

Physical topology can be a bus or a star.

Protocol that supports the logical bus are 10BASE5,

10BASE2, 10BASE-T OR 100BASE-T

Normally used as a distribution backbone to connectdifferent buildings in an organization.

Each building can be comprised of either a single LAN or

another backbone. (normally a logical star backbone)

To connect logical bus backbone uses:-

Bridge based

Router based

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LANs are connected to the backbone through

bridges.

Delivery of the frame uses the Data Link layer

address of the frame.

Each bridge connected to the backbone has a table

that shows the station on the LAN side of the

bridge. The blocking or delivery of a frame is based on the

contents of this table.

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LAN

LAN

LAN

LAN

BRIDGE

BRIDGE

BRIDGE

BRIDGE

BACKBONE

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LANs are connected to the backbone through

routers.

Delivery of the frame uses the network layer

(IP) address of the packet encapsulated

inside the frame.

System is viewed as several sub-networks

with each LAN and the backbone each

forming a subnet.

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Each router connected to the backbone has a routingtable that shows how to route the frame to the

appropriate router.

The blocking or delivery of the frame is based on the

content of this table.

After the router finds the IP address of the destination

router, it uses either static or dynamic mapping to find

the data link layer address of the destination router.

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LAN

LAN

LAN

LAN

ROUTE

R

ROUTER

ROUTE

R

ROUTE

R

BACKBONE

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Also called as collapsed or switched backbone

Logical topology of the backbone is a star.

The backbone is just one switch that connects the

LAN together.

No need of bridges or routers.

Switch-acts as backbone as well as connects LANs

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Delivery of frames can be based on the data link layer ornetwork layer addresses.

If the backbone switch is a two layer switch, delivery is

based on the data link layer address, means wholesystem is still one single network.

If the switch is a three layer switch acting a multiport

router, the delivery is based on the network layer

addresses, means each LAN acts as a subnet.

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Mostly used as a distribution backbone

inside a building.

In a multi-floor building, one LAN serves the

whole floor.

Logical star backbone connects these LANs

Switch can be set at one place and separate

cables can run from the switch to each LAN.

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LAN

LAN

LAN

LAN

BACKBONE

SWITCH

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Two token rings are provided for possible backup

in case the primary ring fails.

The primary ring offers up to 100 Mbps capacity.

When a network has no requirement for the

secondary ring to do backup, it can also carry

data, extending capacity to 200 Mbps.

The secondary ring makes FDDI self-healing.

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NODE

NODE

NODENODE

PRIMARY RING

SECONDARYRING

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