7 WiFi Technology

7/31/2019 7 WiFi Technology

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Introduction

Wi-Fi Technologies

Wi-Fi Architecture

Wi-Fi Network Elements How a Wi-Fi Network Works

Wi-Fi Network Topologies

Wi-Fi Configurations

Applications of Wi-Fi


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Wireless Technology is an alternative to WiredTechnology, which is commonly used, forconnecting devices in wireless mode.

Wi-Fi (Wireless Fidelity) is a generic term that

refers to the IEEE 802.11 communicationsstandard for Wireless Local Area Networks(WLANs).

Wi-Fi Network connect computers to each other, to

the internet and to the wired network. Wireless Network

Design Radio Modes

Bridged Networking


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ny wireless network can be thought of as a combinationof one or more of these types of connections:

1. Point-to-Point

2. Point-to-Multipoint

3. Multipoint-to-Multipoint


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he simplest connection is the Point-to-Point link. Theselinks can be used to extend a network over greatdistances.


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hen more than one computer communicates with acentral point, this is a Point-to-Multipoint network.


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hen any node of a network may communicate with anyother, this is a multipoint-to-multipoint network(alsoknown as an ad-hoc or mesh network).


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i-Fi cards can be operated in one of these modes:

aster(Access Point) Managed(also known as client orstation) Ad-hoc.

onitor.

ther proprietary modes(e.g. Mikrotik Nstreme).

adios may only operate in one mode at a time.


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aster mode (also called AP or infrastructure mode) isused to create a service that looks like a traditionalaccess point.

he wireless card creates a network with a specifiedname (called the SSID) and channel, and offers

network services on it.

ireless cards in master mode can only communicate

with cards that are associated with it in managedmode.


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anaged mode is sometimes also referred to as clientmode.

ireless cards is managed mode will join a networkcreated by a master, and will automatically changetheir channel to match it.

lients using a given access point are said to beassociated with it.


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d-hoc mode creates a multipoint-to-multipointnetwork when there is no master or AP available.

n ad-hoc mode, each wireless card communicatesdirectly with its neighbors.

odes must be in range of each other to communicate,and must agree on a network name and channel.


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onitor mode is used by some tools (such as Kismet)to passively listen to all radio traffic on a givenchannel.

his is useful for analyzing problems on a wireless linkor observing spectrum usage in the local area.

onitor mode is not used for normal communications.


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n a simple local area wireless network, a bridgedarchitecture is usually adequate.

dvantages:

Very simple configuration Roaming works very well.

isadvantages:

Increasingly inefficient as nodes are added.


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arge networks are built by applying routing betweennodes.

tatic routing is often used on point-to-point linksDynamic routing (such as RIP or OSPF) can be used onlarger networks, although they are not designed to

work with imperfect wireless links Mesh routingProtocols (OLSR, HSLS,AODV) work very well withwireless networks, particularly when using radios inad-hoc mode.


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Wi-Fi Networks use Radio Technologies to transmit &receive data at high speed:

1. IEEE 802.11b

2. IEEE 802.11a

3. IEEE 802.11g


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Appear in late 1999

Operates at 2.4GHz radio spectrum

11 Mbps (theoretical speed) - within 30 m Range

4-6 Mbps (actual speed) 100 -150 feet range

Most popular, Least Expensive

Interference from mobile phones and Bluetooth

devices which can reduce the transmission speed.


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Introduced in 2001

Operates at 5 GHz (less popular)

54 Mbps (theoretical speed)

15-20 Mbps (Actual speed) 50-75 feet range

More expensive

Not compatible with 802.11b


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Introduced in 2003

Combine the feature of both standards (a,b)

100-150 feet range

54 Mbps Speed 2.4 GHz radio frequencies

Compatible with b


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There are three sublayers in physical layer:

1. Direct Sequence Spread Spectrum (DSSS)

2. Frequency Hoping Spread Spectrum (FHSS)3. Diffused Infrared (DFIR) - Wide angle


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Direct sequence signaling technique divides the2.4 GHz band into 11 22-MHz channels. Adjacentchannels overlap one another partially, with threeof the 11 being completely non-overlapping. Data

is sent across one of these 22 MHz channelswithout hopping to other channels.


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The data link layer consists of two sublayers :

Logical Link Control (LLC)

Media Access Control (MAC).

802.11 uses the same 802.2 LLC and 48-bitaddressing as other 802 LANs, allowing for very

simple bridging from wireless to IEEE wirednetworks, but the MAC is unique to WLANs.


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Carrier Sense Medium Access with collision avoidanceprotocol (CSMA/CA) Listen before talking Avoid collision by explicit Acknowledgement (ACK)

Problem: additional overhead of ACK packets, soslow performance

Request to Send/Clear to Send (RTS/CTS) protocol Solution for hidden node problem

Problem: Adds additional overhead by temporarilyreserving the medium, so used for large sizepackets only retransmission would be expensive


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Power Management

MAC supports power conservation to extend the battery lifeof portable devices

Power utilization modes

Continuous Aware Mode Radio is always on and drawing power

Power Save Polling Mode

Radio is dozing with access point queuing any datafor it

The client radio will wake up periodically in time toreceive regular beacon signals from the accesspoint.

The beacon includes information regarding whichstations have traffic waiting for them

The client awake on beacon notification and receive


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Fragmentation

CRC checksum

Each pocket has a CRC checksum calculated andattached to ensure that the data was not corruptedin transit

Association & Roaming


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Access Point (AP) - The AP is a wireless LAN transceiver orbase station that can connect one or many wireless devices

simultaneously to the Internet.

Wi-Fi cards - They accept the wireless signal and relayinformation. They can be internal and external.(e.g. PCMCIA Card

for Laptop and PCI Card for Desktop PC)

Safeguards - Firewalls and anti-virus software protect networksfrom uninvited users and keep information secure.


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Basic concept is same as Walkie talkies.

A Wi-Fi hotspot is created by installing an access pointto an internet connection.

An access point acts as a base station.

When Wi-Fi enabled device encounters a hotspot thedevice can then connect to that network wirelessly.

A single access point can support up to 30 users andcan function within a range of 100 150 feet indoorsand up to 300 feet outdoors.

Many access points can be connected to each othervia Ethernet cables to create a single large network.


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1. AP-based topology (Infrastructure Mode)

2. Peer-to-peer topology (Ad-hoc Mode)

3. Point-to-multipoint bridge topology


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The client communicate through Access Point. BSA-RF coverage provided by an AP.

ESA-It consists of 2 or more BSA.

ESA cell includes 10-15% overlap to allow roaming.


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AP is not required.

Client devices within acell can communicate

directly with each other. It is useful for setting up

of a wireless networkquickly and easily.


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This is used to connect a LAN in one building to aLANs in other buildings even if the buildings aremiles apart. These conditions receive a clear lineof sight between buildings. The line-of-sight range

varies based on the type of wireless bridge andantenna used as well as the environmentalconditions.


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Home

Small Businesses or SOHO

Large Corporations & Campuses

Health Care Wireless ISP (WISP)

Travellers


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Thank

You

7 WiFi Technology

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