uol wn bs w15 w4( nadeem )
DESCRIPTION
Wireless networkTRANSCRIPT
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Semester: Spring 2015Team: Dr. Arshad Ali & Nadeem Akhtar
CS & IT DepartmentThe University of Lahore
Email: [email protected]:-https://sites.google.com/site/bcdecsuoledupkwns15/home
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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
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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
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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
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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
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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
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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
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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