Semester: Spring 2015Team: Dr. Arshad Ali & Nadeem Akhtar

CS & IT DepartmentThe University of Lahore

Email: nadeem.akhtar@cs.uol.edu.pkURL:-https://sites.google.com/site/bcdecsuoledupkwns15/home

The contents of these slides are mostly from the material and slides of the book Wireless

Communication & Networks by William

Acknowledgment

Communication & Networks by William Stallings

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Wireless LAN and 802.11 WLAN Standard

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A typical LAN

A typical WLANIts a hub without wires

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Wireless LAN (WLAN)?Wireless LAN provides all the features and benefits of

traditional LAN technologies such as Ethernet and Token Ringbut without the limitations of wires or cables

WLAN provides wireless network communication over short WLAN provides wireless network communication over short distances using radio or infrared signals instead of traditional network

cabling like UTP

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Wireless LANA WLAN typically extends an existing wired LANThe access point (AP) is attached to the edge of the wired

network to built a WLANa wireless network adopter enables clients to

communicate with the AP communicate with the AP similar in function to a traditional Ethernet adapter

WLANs use the 900 MHz, 2.4 GHz and 5-GHzfrequency bands.

ISM (Industry, Scientific, Medical) license-free (unlicensed) frequency bands

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Audio

AM Broadcast

Short-Wave Radio FM Broadcast

Television Infrared Wireless LANCellular (840MHz)

NPCS (1.9GHz)

Extremely Very Low Medium High Very Ultra Super Infrared Visible Ultra- X-Rays

ISM Unlicensed Frequency BandsISM radio bands (portions of the radio spectrum) are reserved internationally for the use of radio frequency (RF) energy for industrial, scientific and medical purposes other than telecommunications

ExtremelyLow

VeryLow

Low Medium High VeryHigh

UltraHigh

SuperHigh

Infrared VisibleLight

Ultra-violet

X-Rays

902928 MHz26 MHz

902928 MHz26 MHz

5 GHz(IEEE 802.11)

HyperLANHyperLAN2

5 GHz(IEEE 802.11)

HyperLANHyperLAN2

2.42.4835 GHz83.5 MHz

(IEEE 802.11)

2.42.4835 GHz83.5 MHz

(IEEE 802.11)7M.Nadeem Akhtar

Wireless LANsHow are WLANs Different?

They use specialized physical and data link protocols They integrate into existing networks through access points

which provide a bridging functionwhich provide a bridging function They let you stay connected as you roam from one coverage

area to another They have unique security considerations They have specific interoperability requirements They require different hardware They offer performance that differs from wired LANs

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Wireless network componentsMuch like a traditional wired LAN a WLAN is a grouping

of computers and peripheral devices that share a common communications backbone.

A WLAN allows users to connect to the LAN wirelessly A WLAN allows users to connect to the LAN wirelessly via radio transmission.

WLAN hardware componentsAccess pointsClient adoptersBridgeAntennas

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Wireless access pointsA small box with one or more aerials. Access points allow wireless networks to join an existing wired

networkHas a connector to attach it to the rest of wired LANHas a connector to attach it to the rest of wired LAN

In home networking, a single access point (or router) possesses sufficient range to span most residential buildings.

Businesses in office buildings often must deploy multiple access points and/or routers depending on its range and the composition of any walls/floors between the access point and wireless network card.

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Wireless access points operates within a specific frequency spectrum and uses an 802.11 standard

specified modulation technique informs the wireless clients of its availability and authenticates and associates

wireless clients to the wireless network coordinates the wireless clients' use of wired resources Serves as a connection point for wireless users to connect to the wired LAN Serves as a connection point for wireless users to connect to the wired LAN half-duplex device

RF medium uses half-duplex communication that allow for only one radio card to be transmitting at any given time

AP is simply a hub with a radio card and an antenna. It needs multiple radios to operate in full-duplex mode Contention-based

The radio card inside an access point must contend for the half-duplex medium .

Physical/Data Link layer device.

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Wireless access points It increases the effective range of a wireless network and

provides additional network management and security featuresWireless networks of three or fewer PCs do not require an

access point for ad hoc networkingaccess point for ad hoc networking Access points handle the receiving and transmission of data to

all the wireless devices in their area They can handle many different connections between different

devices all talking to each other simultaneously, But the more devices working with an access point, the

slower they will operate.

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Wireless access point example

Servers

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Access point and routerAccess Point is a radio transmitter/receiver that is most widely used to bridge

wireless and a wired (Ethernet) network it only provides an interface/portal for wireless clients to connect to

existing LANThis enables computers and devices to connect to a

wired network wirelesslywired network wirelessly

A Router is a device that connects a LAN to a WAN provided by ISP

Thus routes traffic between two different networks, usually the Internet on the WAN side, and your local area network on the LAN side

It provide DHCP service to assign IP addresses to devices on the LAN may also provide WiFi access have a Ethernet switch built in

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Access point and routerwireless router has routing function. works as a gateway and a wireless access point wireless access point is just a wireless switch that has no routing

function. don't have built-in technology for sharing Internet

connections. To share an Internet connection, you must plug an

access point into a router or a modem with a built-in router.

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Network interface card (NIC)/client adapter

A PC or workstation uses a wireless NIC to connect to the wireless network

The NIC scans the available frequency spectrum for The NIC scans the available frequency spectrum for connectivity and associates it to an access point or another wireless client

The NIC is coupled to the PC/workstation operating system using a software driver

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wireless adapters are incorporated as a built-in feature of the system in all newer laptop computers but with desktop PCs you may need to install one

This adopter acts as the radio receiver/transmitter for a

Network interface card (NIC)/client adapter

This adopter acts as the radio receiver/transmitter for a specific computer

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Bridgeused to connect multiple LANs (both wired and wireless) at the

Media Access Control (MAC) layer level Used in building-to-building wireless connections, wireless bridges can cover longer distances than APs (IEEE

802.11 standard specifies 1 mile as the maximum coverage range 802.11 standard specifies 1 mile as the maximum coverage range for an AP)

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Antenna It radiates the modulated signal through the air so that wireless

clients can receive it Characteristics of an antenna are defined by

propagation pattern (directional versus omnidirectional), Antenna gain

The relative increase in radiation at the maximum point expressed as a value in dB above a standard

The relative increase in radiation at the maximum point expressed as a value in dB above a standard

For example: the basic antenna, a -wavelength dipole by which all other antennas are measured (standard)

The reference is known as 0dBD (zero decibel referenced to dipole)

An antenna with the effective radiated power of twice the input power would therefore have a gain of 10*log(2/1) = 3dBD. transmit power, and so on.

Antennas are needed on both the AP/bridge and the clients

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Campus AntennaExample

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Wireless LANs: CharacteristicsAdvantages

very flexible within the reception area Ad-hoc networks without previous planning possible (almost) no wiring difficulties (e.g. historic buildings, (almost) no wiring difficulties (e.g. historic buildings,

firewalls)more robust against disasters like, e.g., earthquakes, fire

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Wireless LANs: CharacteristicsDisadvantages

typically very low bandwidth compared to wired networks many proprietary solutions, especially for higher bit-rates,

standards take their time (e.g. IEEE 802.11)products have to follow many national restrictions if working products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions like, e.g., IMT-2000, IMT-Advanced

IMT-2000 (International Mobile Telecommunication) a family of technologies for 3rd Generation mobile

communications defined by ITU

The objectives: an assurance of global roaming and interoperability between the various technologies

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IEEE 802.11 StandardsOriginal IEEE 802.11 standard

Published in 1999Reaffirmed in 2003

Revised publication in 2007 incorporates the amendments into 1999 version IEEE Std 802.11a-1999 IEEE Std 802.11a-1999 IEEE Std 802.11b-1999 and IEEE Std 802.11b

1999/Corrigendum 1-2001, IEEE Std 802.11d-2001, IEEE Std 802.11g-2003, IEEE Std 802.11h-2003, IEEE Std 802.11i-2004, IEEE Std 802.11j-2004 and IEEE Std 802.11e-2005

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IEEE 802.11 StandardsThe current Revised publication in 2012 incorporates the following

amendments into the 2007 version IEEE Std 802.11k-2008: Radio Resource Measurement of Wireless LANs

(Amendment 1) IEEE Std 802.11r-2008: Fast Basic Service Set (BSS) Transition (Amendment 2) IEEE Std 802.11y-2008: 36503700 MHz Operation in USA (Amendment 3) IEEE Std 802.11w-2009: Protected Management Frames (Amendment 4)

IEEE Std 802.11n-2009: Enhancements for Higher Throughput (Amendment 5) IEEE Std 802.11n-2009: Enhancements for Higher Throughput (Amendment 5) IEEE Std 802.11p-2010: Wireless Access in Vehicular Environments (Amendment 6) IEEE Std 802.11z-2010: Extensions to Direct-Link Setup (DLS) (Amendment 7) IEEE Std 802.11v-2011: IEEE 802.11 Wireless Network Management

(Amendment 8) IEEE Std 802.11u-2011: Interworking with External Networks (Amendment 9) IEEE Std 802.11s-2011: Mesh Networking (Amendment 10)After this revision, all of the previously published amendments and revisions

stand retired

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IEEE 802.11 StandardsAmendments to IEEE 802.11 2012 IEEE Std 802.11aa-2012: MAC Enhancement for Robust Audio

Video Streaming (Amendment 2) IEEE Std 802.11ad-2012: Enhancements for Very High

Throughput in the 60 GHz Band (Amendment 3) IEEE Std 802.11ae-2012: Prioritization of Management Frames IEEE Std 802.11ae-2012: Prioritization of Management Frames

(Amendment 1) IEEE Std 802.11ac-2012: Enhancements for Very High Throughput

for Operation in Bands below 6 GHz (Amendment 4) IEEE Std 802.11af-2012: Television White Spaces (TVWS)

Operation (Amendment 5)

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IEEE 802.11 In IEEE 802.11 std, the addressable unit is station (STA)

Station (STA): a device that has the capability to use the 802.11 protocol

STA may be fixed, mobile or portable

According to IEEE 802.11-2007 : A STA is any device that contains an IEEE 802.11-conformant media access control (MAC) contains an IEEE 802.11-conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM).

One requirement of IEEE 802.11 is to handle mobile as well as portable STAs.

A portable STA is one that is moved from location to location, but that is only used while at a fixed location.

Mobile STAs actually access the LAN while in motion.

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Components of IEEE 802.11 architecture The basic service set (BSS) is the basic building block of an IEEE 802.11

LAN. Each of BSS1 and BSS2 has two STAs that are their members of the BSS. Think of the ovals as coverage area of a BSS within which the member STAs

may remain in communication. This area is called the Basic Service Area (BSA).

If STA moves out of its BSA, it can no longer directly communicate with other STAs present in the BSA.STAs present in the BSA.

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Components of IEEE 802.11 architecture Two type of BSS: Independent and Infrastructure BSS Every BSS has an id called the BSSID, it is the MAC address of

the access point servicing the BSS Independent BSS (IBSS) is simply comprised of one or more Stations

which communicate directly with each other (ad-hoc network) They contain no Access Points. they can not connect to any other basic service set they can not connect to any other basic service set

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Components of IEEE 802.11 architecture In Infrastructure BSS, STAs communicate with each other through

Access Points. Infrastructure BSS can communicate with other stations not in the

same basic service set by communicating to each other through Access Points

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Components of IEEE 802.11 architectureAn Extended Service Set (ESS) is a set of connected BSSAccess Points in an extended service set are connected by a

distribution system. Each ESS has an ID called the SSID

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Components of IEEE 802.11 architectureDistribution system (DS)(ESS) connects Access Points in an

extended service set. A distribution system is usually a wired LAN but can be a wireless

LANThe architectural component used to interconnect infrastructure

BSSs is the DSBSSs is the DSPortal bridge to other (wired) networks

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Components of IEEE 802.11 architecturePortal bridge to other (wired) networks A portal is the logical point at which MSDUs (MAC service data units) from an

integrated non-IEEE-802.11 LAN enter the IEEE 802.11 DS In other words, All data from non-IEEE-802.11 LANs enter the IEEE 802.11 architecture via a portal

It is possible for one device to offer both the functions of an AP and a portal (IEEE 802.11 2012)

The portal logic is implemented in a device such as bridge or router, that is part of the wired LAN and that is attached to the DS

Distribution System

Portal

802.x LAN802.11 LAN

BSS1AccessPoint

802.11 Architecture: infrastructure networkStation (STA)

terminal with access mechanisms to the wireless medium and radio contact to the access point

Basic Service Set (BSS) group of stations using the same

radio frequencyAccess Point

STA1

Distribution System

AccessPoint

802.11 LAN

BSS2

Access Point station integrated into the wireless

LAN and the distribution systemPortal

bridge to other (wired) networksDistribution System

interconnection network to form one logical network (EES: Extended Service Set) based on several BSS

STA2 STA3

ESS

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802.11 Architecture: ad-hoc networkDirect communication within a limited range

Station (STA):terminal with access mechanisms to the wireless medium

Independent Basic Service Set (IBSS):group of stations using the same radio frequency without

802.11 LAN

IBSS1

STA1

STA2

STA3

same radio frequency without a controlling access point

802.11 LAN

IBSS2

STA4

STA5

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IEEE standard 802.11mobile terminal

access point

server

fixed terminal

application application

infrastructure network

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLCLLC LLC

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IEEE 802.11 Services IEEE 802.11 defines services that need to be provided by the

WLAN in order to provide functionality equivalent one which is inherent to wired LAN

The service provider can be either the STA or DSMAC Service Data Unit (MSDU) delivery Service

MSDU is block of data passed down from the MAC user to the MAC MSDU is block of data passed down from the MAC user to the MAC layer

If MSDU is too large to be transmitted in a single MAC frame, it may be fragmented and transmitted in a single MAC frame

Distribution of Messages Within a DSDistribution service

Used to exchange MAC frames from station in one BSS to station in another BSS

Integration service Integration serviceTransfer of data between station on IEEE 802.11 LAN and

station on integrated IEEE 802.x LAN Integrated refers to a wired LAN physically connected to

DS and whose stations may be logically connected to an IEEE 802.11 LAN via the integration service

Transition Types Based On MobilityNo transition

Stationary or moves only within BSSBSS transition

Station moving from one BSS to another BSS in same ESSStation moving from one BSS to another BSS in same ESSDelivery of data to the station requires that the addressing

capability be able to recognize the new location of the station

ESS transitionStation moving from BSS in one ESS to BSS within another

ESS

Association-Related Services Association

The identity of address of a STA must be known before it can transmit or receive frames on a wireless LAN

Establishes initial association between station and AP within a particular BSS

The AP can then communicate this information to other APs within ESS to facilitate routing and delivery of addressed frames

Reassociation Reassociation Enables transfer of association from one AP to another, allowing

station to move from one BSS to another Disassociation

Association termination notice from station or AP A STA gives notification before leaving ESS or shutting down MAC management facility protects itself against STAs that

disappear without notifications

Access and Privacy Services

AuthenticationEstablishes identity of stations to each other

Deathentication Invoked when existing authentication is terminated Invoked when existing authentication is terminated

PrivacyPrevents message contents from being read by unintended

recipientThe standard provides for the optional use of encryption to

assure privacy