w-lan (wireless local area network)

“Wireless local area Network (WLANS)”

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Wireless LAN?

A wireless LAN or WLAN is a wireless local area network that uses radio

waves as its carrier.

The last link with the users is wireless, to give a network connection to all

users in a building or campus.

The backbone network usually uses cables

Common Topologies

The wireless LAN connects to a wired LAN

There is a need of an access point that bridges wireless LAN traffic into the wired LAN.

The access point (AP) can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes.

Common Topologies

Complete Wireless Networks

The physical size of the network is determined by the maximum reliable propagation range of the radio signals.

Referred to as ad hoc networks

Suited for temporary situations such as meetings and conferences.

How do wireless LANs work?

Wireless LANs operate in almost the same way as wired LANs, using the same

networking protocols and supporting the most of the same applications.

How are WLANs Different?

They integrate into existing networks through access points which provide a bridging function.

They let you stay connected as you roam from one coverage area to another.

They have unique security considerations (WEP,WPA,WPA-2).

They have specific interoperability requirements.

They require different hardware Ex-Wireless Routers.

They offer performance that differs from wired LANs.

Some Devices that use W-LAN

Tablets

Wireless v/s Wired networks

Wireless v/s Wired networks(continue..)

Regulations of frequencies

Limited availability, coordination is required.

useful frequencies are almost all occupied.

Bandwidth and delays(Disadvantage)

Low transmission rates

few Kbits/s to some Mbit/s.

Higher delays

several hundred milliseconds

Higher loss rates

susceptible to interference, e.g., engines, lightning

Wireless v/s Wired networks(continue..)

Always shared medium

Lower security, simpler active attacking

SSID accessible for everyone

Wireless v/s Wired networks(continue..)

$ For Wireless (WLAN) you need wireless $ You Require RJ45 jack network

network interface card. interface card for wired(LAN)

OSI- Open System Interconnection Reference

Model

OSI was developed in 1984 by the International Standard

Organization. This model was developed to subdivide a communication

system into small parts, called layers

The OSI model defines the

functionality of network

communication.

Dividing the

communication

into 7 layer

7. Application

6. Presentation

5. Session

4. Transport

3. Network2. Data Binding

1.Physical Layer

Wireless LANs

Infrared (IrDA) or radio links (Wavelan)

Advantages

– very flexible within the reception area

– Ad-hoc networks possible

– (almost) no wiring difficulties

Disadvantages

– low bandwidth compared to wired networks

– many proprietary solutions

Infrastructure v/s ad-hoc networks (802.11)

Router

Router is a device which connects different networks-frequently over

a large distances.

A router is a device that forwards data packets between computernetworks, creating an overlay internetwork.

A router is connected to two or more data lines from different networks.

When a data packet comes in on one of the lines, the router reads the

address information in the packet to determine its ultimate destination.

A data packet is typically forwarded from one router to another through

the networks that constitute the internetwork until it gets to its destination

node.

It contains a routing table in which all information about the address of

connected networks.

Router (continue..)

Router operates in network layer of OSI Model

Packets routed by routers to their destinations

Bridges

A bridge is a connecting device which has it’s own processor, memory

and two NIC cards, to connect two portions of a network

Facilitates host to host communication

Operates at the physical as well as data link layer

Importance of a Bridge

Bridge is to divide a big network in to smaller sub-networks

A bridge connects two LAN’s

5

4

3

2

1

4

3

2

1

5

Functions of a bridge

As a physical layer device it generates the signal it receives.

As a data link layer device it checks the source and destination addresses in the frame.

It send data frames only to the concerned destination.

It minimizes unwanted traffic

It minimizes network congestion

Error links can be identified and then isolated

Security features or access control can be added

It acts as a filter

Gateway

To connect two networks that use different protocols

It works at all seven layers of OSI model

Unlike a router a gateway can forward packets across different networks that may

also use different protocols

Ex. If network A is token ring network using TCP / IP and network B is a novell-

netware network, a gateway can relay frames between the two.

Application layer

Presentation layer

Session layer

Transport layer

Network layer

Data link layer

Physical layer

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W

AY

A

Physical layer

Data link layer

Network layer

Transport layer

Session layer

Presentation layer

Application layer

B

Gateway at all OSI layers

Functions of Gateways

It has abilities to translate between different frame formats and also between

different protocols

It is a very powerful computer system compared to a bridge

It is used to connect huge and incompatible networks

Routing protocols

Routing protocols Routing protocols are the set of rules used by the routers to communicate

between source & destination.

Each protocol has its own algorithm to choose the best path.

The metrics by routing protocols ,

*Number of network layer devices along with the path (hop count)

*Bandwidth

*Delay

*Load

*MTU

*Cost Routing protocols store the result of these metrics in routing table.

Types of Routing Protocols

AODV

Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol

for mobile ad hoc networks (MANETs) and other wireless ad hoc networks.

In AODV, the network is silent until a connection is needed.

Routing Protocols (continue..)

DSR

Dynamic Source Routing (DSR) is a routing protocol for wireless mesh networks.It is similar to AODV in that it forms a route on-demand when a transmittingnode requests one.

However, it uses source routing instead of relying on the routing table at eachintermediate device.

Routing Protocols (continue..)

DYMO

The DYMO routing protocol is successor to the popular Ad hoc On-Demand

Distance Vector (AODV) routing protocol and shares many of its benefits.

It is, however, slightly easier to implement and designed with future

enhancements in mind.