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WIRELESS LOCAL AREA WIRELESS LOCAL AREA NETWORKSNETWORKS
Ian F. AkyildizIan F. AkyildizBroadband & Wireless Networking LaboratoryBroadband & Wireless Networking Laboratory
School of Electrical and Computer EngineeringSchool of Electrical and Computer Engineering
Georgia Institute of TechnologyGeorgia Institute of Technology
Tel: 404-894-5141; Fax: 404-894-7883 Tel: 404-894-5141; Fax: 404-894-7883
Email: [email protected]: [email protected]
Web: http://www.ece.gatech.edu/research/labs/bwnWeb: http://www.ece.gatech.edu/research/labs/bwn
2IFA’2004
WIRELESS LANsWIRELESS LANs
Infrastructure Network
Ad-hoc Network
APAP
AP
wired network
AP: Access Point
3IFA’2004
Wireless LAN - IEEE 802.11 Wireless LAN - IEEE 802.11 Reference ArchitectureReference Architecture
The terminology and some of the specific The terminology and some of the specific features are unique to this standard and features are unique to this standard and are not reflected in all commercial are not reflected in all commercial products.products.
However, it is However, it is useful to be useful to be familiar with the familiar with the standard since its standard since its features are features are representative of representative of the Wireless LAN the Wireless LAN capabilities capabilities required. required.
4IFA’2004
Reference Architecture of Reference Architecture of Wireless LANsWireless LANs
Station (STA)Station (STA)– terminal with access terminal with access
mechanisms to the wireless mechanisms to the wireless medium and radio contact to medium and radio contact to the access pointthe access point
Basic Service Set (BSS)Basic Service Set (BSS)– group of stations using the group of stations using the
same radio frequencysame radio frequencyAccess PointAccess Point
– station integrated into the station integrated into the wireless LAN and the wireless LAN and the distribution systemdistribution system
PortalPortal– bridge to other (wired) bridge to other (wired)
networksnetworksDistribution SystemDistribution System
– interconnection network to interconnection network to form one logical network (ESS: form one logical network (ESS: Extended Service Set) based Extended Service Set) based on several BSSon several BSS
Distribution System
Portal
Access Point
BSS2
BSS1
Access Point
STA1
STA2
STA3
ESS
5IFA’2004
Reference ArchitectureReference Architecture
The smallest building block of a wireless LAN is a The smallest building block of a wireless LAN is a basic service set (BSS), which consists of some basic service set (BSS), which consists of some number of stations executing the same MAC number of stations executing the same MAC protocol and competing for access to the same protocol and competing for access to the same shared medium.shared medium.
A basic service set may be isolated or it may A basic service set may be isolated or it may
connect to a backbone distribution system through connect to a backbone distribution system through an access point. an access point.
The access point functions as a bridge. The access point functions as a bridge. The MAC protocol may be fully distributed or The MAC protocol may be fully distributed or
controlled by a central coordination function controlled by a central coordination function housed in the access point. housed in the access point.
6IFA’2004
Reference ArchitectureReference Architecture
The basic service set generally corresponds The basic service set generally corresponds to what is referred to as a cell in the to what is referred to as a cell in the literature.literature.
An extended service set (ESS) consists of An extended service set (ESS) consists of two or more basic service sets two or more basic service sets interconnected by a distribution system. interconnected by a distribution system.
Typically, the distribution system is a wired Typically, the distribution system is a wired backbone LAN. backbone LAN.
The extended service set appears as a single The extended service set appears as a single logical LAN to the logical link control (LLC) logical LAN to the logical link control (LLC) level.level.
7IFA’2004
Reference ArchitectureReference Architecture
The standard defines three types of stations The standard defines three types of stations based on mobility:based on mobility:
No transition:No transition: A station of this type is either stationary A station of this type is either stationary or moves only within the direct communication range or moves only within the direct communication range of the communicating stations of a single BSS.of the communicating stations of a single BSS.
BSS transition:BSS transition: This is defined as a station movement This is defined as a station movement from one BSS to another BSS within the same ESS. In from one BSS to another BSS within the same ESS. In this case, delivery of data to the station requires that this case, delivery of data to the station requires that the addressing capability be able to recognize the new the addressing capability be able to recognize the new location of the station.location of the station.
ESS transition:ESS transition: This is defined as a station movement This is defined as a station movement from a BSS in one ESS to a BSS within another ESS. from a BSS in one ESS to a BSS within another ESS. This case is supported only in the sense that the This case is supported only in the sense that the station can move. station can move.
8IFA’2004
Protocol ArchitectureProtocol Architecture
mobile terminal
access point
fixedterminal
application
TCP
PHY
MAC
IP
802.3 MAC
802.3 PHY
application
TCP
802.3 PHY
802.3 MAC
IP
MAC
PHY
LLC
infrastructurenetwork
LLC LLC
9IFA’2004
Protocol Layers and Protocol Layers and FunctionsFunctions
PLCP PLCP Physical Layer Convergence ProtocolPhysical Layer Convergence Protocol
clear channel assessment signal clear channel assessment signal (carrier sense)(carrier sense)
PMD PMD Physical Medium DependentPhysical Medium Dependent
modulation, codingmodulation, coding
PHY ManagementPHY Managementchannel selection, MIBchannel selection, MIB
Station ManagementStation Managementcoordination of all management coordination of all management
functionsfunctions
PMD
PLCP
MAC
LLC
MAC Management
PHY Management
MACMAC– access mechanisms, access mechanisms,
fragmentation, encryption fragmentation, encryption MAC ManagementMAC Management
– synchronization, roaming, synchronization, roaming, MIB, power managementMIB, power management
PH
YD
LC
Sta
tion
Man
agem
ent
10IFA’2004
Basics of Wireless Basics of Wireless LANsLANs
Coverage area, data rate, and battery Coverage area, data rate, and battery consumption.consumption.
Characterized by small coverage areas Characterized by small coverage areas (~200m), but relatively high (~200m), but relatively high bandwidthsbandwidths
(data rates) (upto 50Mbps currently)(data rates) (upto 50Mbps currently) Major standardsMajor standards
– WLAN: IEEE 802.11 and HIPERLAN.WLAN: IEEE 802.11 and HIPERLAN.– WPAN: IEEE 802.16 (Bluetooth) and WPAN: IEEE 802.16 (Bluetooth) and
HomeRFHomeRF
11IFA’2004
Advantages of WLANs
– Very flexible within the reception area Very flexible within the reception area
– Users can access high speed multimedia applications Users can access high speed multimedia applications anywhere at anytime, with easy implementation, low cost, anywhere at anytime, with easy implementation, low cost, and wide user acceptanceand wide user acceptance
- Generally works in industrial, scientific, and- Generally works in industrial, scientific, and medical (ISM) band, which is un-licensed andmedical (ISM) band, which is un-licensed and available for public. available for public.
– (Almost) no wiring difficulties (e.g. historic buildings, (Almost) no wiring difficulties (e.g. historic buildings, firewalls)firewalls)
12IFA’2004
WLANs – Advantages WLANs – Advantages
Buildings with large open areas, such Buildings with large open areas, such as manufacturing plants, stock as manufacturing plants, stock exchange trading floors, and exchange trading floors, and warehouseswarehouses
Historical buildings with insufficient Historical buildings with insufficient twisted pair and where drilling holes twisted pair and where drilling holes for new wiring is prohibitedfor new wiring is prohibited
Small offices where installation and Small offices where installation and maintenance of wired LANs is not maintenance of wired LANs is not economicaleconomical
13IFA’2004
Disadvantages of WLANsDisadvantages of WLANs
– Typically very low bandwidth compared to Typically very low bandwidth compared to wired networks (1-10 Mbit/s)wired networks (1-10 Mbit/s)
– Many proprietary solutions, especially for Many proprietary solutions, especially for higher bit-rates, standards take their time.higher bit-rates, standards take their time.
– Products have to follow many national Products have to follow many national restrictions if working wireless, it takes a very restrictions if working wireless, it takes a very long time to establish global solutions.long time to establish global solutions.
– Interference ProblemsInterference Problems
14IFA’2004
Family of Wireless LAN Family of Wireless LAN (WLAN) Standards (WLAN) Standards 802.11802.11
– 802.11a - 5GHz- Ratified in 1999802.11a - 5GHz- Ratified in 1999– 802.11b - 11Mb 2.4GHz- ratified in 1999802.11b - 11Mb 2.4GHz- ratified in 1999– 802.11d - Additional regulatory domains802.11d - Additional regulatory domains– 802.11e - Quality of Service802.11e - Quality of Service– 802.11f - Inter-Access Point Protocol (IAPP)802.11f - Inter-Access Point Protocol (IAPP)– 802.11g - Higher Data rate (>20mBps) 802.11g - Higher Data rate (>20mBps)
2.4GHz2.4GHz– 802.11h - Dynamic Frequency Selection and 802.11h - Dynamic Frequency Selection and
Transmit Power Control mechanismsTransmit Power Control mechanisms– 802.11i - Authentication and security802.11i - Authentication and security
15IFA’2004
WLANs – WLANs – Current Current UseUse
Home wireless networks.Home wireless networks. Enterprise wireless networks. Enterprise wireless networks. Public access. Public access. Hospitals. Hospitals. Warehouses. Warehouses. Consulting and audit teamsConsulting and audit teams Dynamic environments, ad agencies, etc.Dynamic environments, ad agencies, etc. UniversitiesUniversities Historic buildings, older buildings. Historic buildings, older buildings. Meeting rooms. Meeting rooms. Retail storesRetail stores Restaurants and car rental agenciesRestaurants and car rental agencies Data backup. Data backup.
16IFA’2004
In-Building Deployment – In-Building Deployment – Service ObjectivesService Objectives
Greater coverageGreater coverage High-speed ratesHigh-speed rates Scalable and manageable bandwidthScalable and manageable bandwidth Enable new (high-end) services (and keep running Enable new (high-end) services (and keep running
the good old ones)the good old ones) Service differentiationService differentiation Smooth deployment and low maintenanceSmooth deployment and low maintenance Interoperable systemsInteroperable systems Plug & PlayPlug & Play Extends the local area networkExtends the local area network Freedom to access the corporate networkFreedom to access the corporate network Comparable to those of wired networksComparable to those of wired networks Secure access to important information (e-mail, Secure access to important information (e-mail,
corporate data, Internet)corporate data, Internet)
17IFA’2004
Some FactsSome Facts
By 2005, more than 1/3By 2005, more than 1/3rdrd of Internet users will of Internet users will have Internet connectivity through a wireless have Internet connectivity through a wireless enabled device (750 million users)!!! (Source: enabled device (750 million users)!!! (Source: Intermarket group)Intermarket group)
By the end of 2001, more than half of the By the end of 2001, more than half of the workforce in the US uses a wireless net device – workforce in the US uses a wireless net device – primarily cellular phones! (Source: Cahners Intat primarily cellular phones! (Source: Cahners Intat Group)Group)
By the year 2004 revenue from wireless data will By the year 2004 revenue from wireless data will reach $34B, and by the year 2010 the number of reach $34B, and by the year 2010 the number of wireless data subscribers will hit 1B!!wireless data subscribers will hit 1B!!
18IFA’2004
Design Goals for Wireless Design Goals for Wireless LANsLANs
– Global, seamless operation (must sell in all countries)Global, seamless operation (must sell in all countries)– Low power for battery use (power saving modes and Low power for battery use (power saving modes and
power management functions)power management functions)– No special permissions or licenses needed to use the No special permissions or licenses needed to use the
LAN LAN – Robust transmission technology (avoid interference)Robust transmission technology (avoid interference)– Simplified spontaneous cooperation at meetings Simplified spontaneous cooperation at meetings – Easy to use for everyone, simple management Easy to use for everyone, simple management – Protection of investment in wired networks Protection of investment in wired networks
(interoperable with wired LANs)(interoperable with wired LANs)– Security (no one should be able to read my data), Security (no one should be able to read my data),
privacy (no one should be able to collect user privacy (no one should be able to collect user profiles), safety (low radiation)profiles), safety (low radiation)
19IFA’2004
TopologiesTopologies- - Single-Cell Wireless LANSingle-Cell Wireless LAN
20IFA’2004
TopologiesTopologies- - Single-Cell Wireless LANSingle-Cell Wireless LAN
In Figure there is a backbone wired LAN, such as Ethernet, that In Figure there is a backbone wired LAN, such as Ethernet, that supports servers, workstations, and one or more bridges or supports servers, workstations, and one or more bridges or routers to link with other networks. routers to link with other networks.
In addition, there is a control module (CM) (Access Point (AP) In addition, there is a control module (CM) (Access Point (AP) before) that acts as an interface to a wireless LAN. (CM = AP)before) that acts as an interface to a wireless LAN. (CM = AP)
The control module includes either bridge or router functionality The control module includes either bridge or router functionality to link the wireless LAN to the backbone. to link the wireless LAN to the backbone.
In addition, it includes some sort of access control logic, such as a In addition, it includes some sort of access control logic, such as a polling or token-passing scheme, to regulate the access from the polling or token-passing scheme, to regulate the access from the end systems. end systems.
Note that some of the end systems are stand-alone devices such Note that some of the end systems are stand-alone devices such as a workstation or a server. as a workstation or a server.
In addition, hubs or other user modules (UM) (PORTAL before) that In addition, hubs or other user modules (UM) (PORTAL before) that control a number of stations off a wired LAN may also be part of control a number of stations off a wired LAN may also be part of the wireless LAN configuration.the wireless LAN configuration.
21IFA’2004
TopologiesTopologies- - Multiple Cell Wireless Multiple Cell Wireless LANLAN
Figure 2
22IFA’2004
TopologiesTopologies- - Multiple Cell Wireless Multiple Cell Wireless LANLAN
In this case there are multiple control In this case there are multiple control modules interconnected by a wired LAN.modules interconnected by a wired LAN.
Each control module supports a number Each control module supports a number of wireless end systems within its of wireless end systems within its transmission range. transmission range.
For example, with an infrared LAN, For example, with an infrared LAN, transmission is limited to a single room; transmission is limited to a single room; therefore, one cell is needed for each therefore, one cell is needed for each room in an office building that requires room in an office building that requires wireless support.wireless support.
23IFA’2004
WLANs – 802.11 WLANs – 802.11 Protocol Protocol ArchitectureArchitecture
Physical Layer (PHY)
Distributed Coordination Function (DCF)
Point Coordination Function (PCF)
Normal Data Traffic(Asynchronous)
Real Time Traffic
MAC
24IFA’2004
IEEE 802.11IEEE 802.11- - Physical Medium Physical Medium SpecificationSpecification
Three Physical Media:Three Physical Media: INFRAREDINFRARED
Narrowband MicrowaveNarrowband Microwave
Spread SpectrumSpread Spectrum
25IFA’2004
InfraredInfrared
Infrared signals used to transmit data (similar to TV Infrared signals used to transmit data (similar to TV remotes!)remotes!)
Higher data rates possible (than spread spectrum)Higher data rates possible (than spread spectrum)
Line of sight point-to-point configuration required (or Line of sight point-to-point configuration required (or reflection surface that reflects signals)reflection surface that reflects signals)
Too sensitive to obstacles, line-of-sight requirement, etc. Too sensitive to obstacles, line-of-sight requirement, etc.
850-950 nm, diffuse light (to allow point-to-multipoint 850-950 nm, diffuse light (to allow point-to-multipoint communication)communication)
10 m maximum range with no sunlight or heat interfere10 m maximum range with no sunlight or heat interfere
26IFA’2004
Narrowband Narrowband MicrowaveMicrowave
Typically used to link two WLANs together (for Typically used to link two WLANs together (for example, to link WLANs in two buildings)example, to link WLANs in two buildings)
Microwave dishes required at both ends of linkMicrowave dishes required at both ends of link
Unlike spread spectrum which operates in the Unlike spread spectrum which operates in the unlicensed ISM band, narrowband microwave unlicensed ISM band, narrowband microwave requires FCC licensingrequires FCC licensing
Exclusive license typically effective within a Exclusive license typically effective within a 17.5 mile radius17.5 mile radius
27IFA’2004
Spread SpectrumSpread Spectrum
Distributed signals over multiple frequencies (to Distributed signals over multiple frequencies (to avoid eavesdropping or jamming)avoid eavesdropping or jamming)
Frequency Hopping Spread Spectrum (FHSS)Frequency Hopping Spread Spectrum (FHSS)– Sender transmits over a seemingly random series of frequenciesSender transmits over a seemingly random series of frequencies– Intended receiver aware of sequence of frequencies and hops Intended receiver aware of sequence of frequencies and hops
accordingly accordingly – Allows the coexistence of multiple networks in the same area by Allows the coexistence of multiple networks in the same area by
using different hopping sequencesusing different hopping sequences
Direct Sequence Spread Spectrum (DSSS)Direct Sequence Spread Spectrum (DSSS)– Sender transmits redundant information called “chips” between Sender transmits redundant information called “chips” between
actual data bitsactual data bits– Intended receiver aware of spread removes redundant Intended receiver aware of spread removes redundant
information accordinglyinformation accordingly– Preamble and header of a frame is always transmitted with 1 Preamble and header of a frame is always transmitted with 1
Mbit/s, rest of transmission 1 or 2 Mbit/sMbit/s, rest of transmission 1 or 2 Mbit/s
28IFA’2004
Wireless LAN Wireless LAN ClassificationClassification
Infrared (IR) LANsInfrared (IR) LANs– An individual cell of an IR LAN is limited to a single An individual cell of an IR LAN is limited to a single
room, since infrared light does not penetrate opaque room, since infrared light does not penetrate opaque walls.walls.
Spread Spectrum LANsSpread Spectrum LANs– In most cases these LANs operate in the ISM In most cases these LANs operate in the ISM
(industrial, scientific, and medical) bands, so no FCC (industrial, scientific, and medical) bands, so no FCC licensing is required for their use in the United licensing is required for their use in the United States.States.
Narrowband Microwave LANsNarrowband Microwave LANs– These LANs operate at microwave frequencies but do These LANs operate at microwave frequencies but do
no use spread spectrum. Some of these products no use spread spectrum. Some of these products operate at frequencies that require FCC licensing; operate at frequencies that require FCC licensing; others use one of the unlicensed ISM bands. others use one of the unlicensed ISM bands.
– Table 1 summarizes some of the key characteristics Table 1 summarizes some of the key characteristics of these three technologies; the details are explored of these three technologies; the details are explored in the next three subsections.in the next three subsections.
29IFA’2004
Comparison: Comparison: Infrared vs. Radio Infrared vs. Radio TransmissionTransmission
InfraredInfrared– uses IR diodes, diffuse light, uses IR diodes, diffuse light,
multiple reflections (walls, multiple reflections (walls, furniture etc.)furniture etc.)
AdvantagesAdvantages– simple, cheap, available in simple, cheap, available in
many mobile devicesmany mobile devices– no licenses neededno licenses needed
DisadvantagesDisadvantages– interference by sunlight, heat interference by sunlight, heat
sources etc.sources etc.– many things shield or absorb many things shield or absorb
IR light IR light – low bandwidthlow bandwidth– Line of Sight ProblemLine of Sight Problem
ExampleExample– IrDA (Infrared Data IrDA (Infrared Data
Association) interface available Association) interface available everywhere: PDAs, calculators, everywhere: PDAs, calculators, laptops, mobile phones...laptops, mobile phones...
RadioRadio– typically using the license typically using the license
free ISM band at 2.4 GHz free ISM band at 2.4 GHz AdvantagesAdvantages
– experience from wireless experience from wireless WAN and mobile phones can WAN and mobile phones can be used be used
– coverage of larger areas coverage of larger areas possible (radio can possible (radio can penetrate walls, furniture penetrate walls, furniture etc.) etc.)
DisadvantagesDisadvantages– very limited license free very limited license free
frequency bands frequency bands – shielding more difficult, shielding more difficult,
interference with other interference with other electrical deviceselectrical devices
ExampleExample– WaveLAN, HIPERLAN, WaveLAN, HIPERLAN,
BluetoothBluetooth
30IFA’2004
Overview of WLAN ClassificationOverview of WLAN Classification
31IFA’2004
Wireless LAN MACWireless LAN MAC
CSMA as Wireless MAC?CSMA as Wireless MAC?
Hidden and Exposed TerminalHidden and Exposed Terminal Problems Problems make the use of CSMA make the use of CSMA an inefficient techniquean inefficient technique
32IFA’2004
Hidden Terminal Hidden Terminal ProblemProblem
A talks to BA talks to B C senses the channelC senses the channel C does not hear A’s transmission C does not hear A’s transmission (out of range)(out of range) C talks to BC talks to B Signals from A and B collide Signals from A and B collide
A B C
Collision
33IFA’2004
Exposed Terminal Exposed Terminal ProblemProblem
B talks to AB talks to A C wants to talk to DC wants to talk to D C senses channel and finds it to be C senses channel and finds it to be
busybusy C stays quiet (when it could have C stays quiet (when it could have
ideally transmitted)ideally transmitted)
A B C D
Notpossible
34IFA’2004
Hidden and Hidden and Exposed Terminal Exposed Terminal ProblemsProblems
Hidden TerminalHidden Terminal– More collisionsMore collisions– Wastage of resourcesWastage of resources
Exposed TerminalExposed Terminal– Underutilization of channelUnderutilization of channel– Lower effective throughputLower effective throughput
35IFA’2004
MACA - Collision AvoidanceMACA - Collision Avoidance
MACA (Multiple Access with Collision Avoidance) uses MACA (Multiple Access with Collision Avoidance) uses short signaling packets for collision avoidanceshort signaling packets for collision avoidance– RTS (request to send): a sender request the right to RTS (request to send): a sender request the right to
send from a receiver with a short RTS packet before send from a receiver with a short RTS packet before it sends a data packetit sends a data packet
– CTS (clear to send): the receiver grants the right to CTS (clear to send): the receiver grants the right to send as soon as it is ready to receivesend as soon as it is ready to receive
Signaling packets containSignaling packets contain– sender addresssender address– receiver addressreceiver address– packet sizepacket size
Variants of this method can be found in IEEE802.11 as Variants of this method can be found in IEEE802.11 as DFWMAC (Distributed Foundation Wireless MAC)DFWMAC (Distributed Foundation Wireless MAC)
36IFA’2004
Hidden Terminal Hidden Terminal Revisited …Revisited …
A sends RTSA sends RTS B sends CTSB sends CTS C overheads CTSC overheads CTS C inhibits its own transmitterC inhibits its own transmitter A successfully sends DATA to BA successfully sends DATA to B
A B CRTS CTS
DATACTS
37IFA’2004
Hidden Terminal Hidden Terminal RevisitedRevisited
How does C know how long to wait How does C know how long to wait before it can attempt a transmission?before it can attempt a transmission?
A includes length of DATA that it A includes length of DATA that it wants to send in the RTS packetwants to send in the RTS packet
B includes this information in the CTS B includes this information in the CTS packetpacket
C, when it overhears the CTS packet, C, when it overhears the CTS packet, retrieves the length information and retrieves the length information and uses it to set the inhibition timeuses it to set the inhibition time
38IFA’2004
Exposed Terminal Exposed Terminal RevisitedRevisited
B sends RTS to A (overheard by C)B sends RTS to A (overheard by C) A sends CTS to BA sends CTS to B C cannot hear A’s CTSC cannot hear A’s CTS C assumes A is either down or out of rangeC assumes A is either down or out of range C does not inhibit its transmissions to DC does not inhibit its transmissions to D
A B C DRTS RTS
CTS Cannot hear CTSTx notinhibited
39IFA’2004
CollisionsCollisions
Still possible – RTS packets can collide!Still possible – RTS packets can collide!
Binary exponential backoff performed by Binary exponential backoff performed by stations that experience RTS collisionsstations that experience RTS collisions
RTS collisions not as bad as data RTS collisions not as bad as data collisions in CSMA (since RTS packets are collisions in CSMA (since RTS packets are typically much smaller than DATA typically much smaller than DATA packets)packets)
40IFA’2004
DrawbacksDrawbacks
Collisions still possible if CTS Collisions still possible if CTS packets cannot be heard but packets cannot be heard but carry enough to cause significant carry enough to cause significant interferenceinterference
If DATA packets are of the same If DATA packets are of the same size as RTS/CTS packets, size as RTS/CTS packets, significant overheadssignificant overheads
41IFA’2004
WLANs – 802.11 WLANs – 802.11 Protocol Protocol ArchitectureArchitecture
Physical Layer (PHY)
Distributed Coordination Function (DCF)
Point Coordination Function (PCF)
Normal Data Traffic(Asynchronous)Contention Service
Real Time Traffic Contention Free Service
MAC
42IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
– Distributed Mode: Distributed Coordination Function (DCF) Distributed Mode: Distributed Coordination Function (DCF) * Based on CSMA/CA protocol * Based on CSMA/CA protocol * Uses a contention algorithm to provide access to all traffic.* Uses a contention algorithm to provide access to all traffic. * Ordinary asynchronous traffic uses DCF directly.* Ordinary asynchronous traffic uses DCF directly.
– Coordinated Mode: Point Coordination Function (PCF) Coordinated Mode: Point Coordination Function (PCF) * Supports real time traffic * Supports real time traffic * Based on polling which is controlled by a centralized point * Based on polling which is controlled by a centralized point
coordinator.coordinator. * Uses a c* Uses a centralized MAC algorithm and provides contention-free entralized MAC algorithm and provides contention-free
service.service. * PCF is built on top of DCF and exploits features of DCF to assure * PCF is built on top of DCF and exploits features of DCF to assure
access for its users. access for its users.
NOTE: NOTE: Both the DCF and PCF can operate concurrently Both the DCF and PCF can operate concurrently within the same BSS to provide alternative contention within the same BSS to provide alternative contention and contention-free periodsand contention-free periods
43IFA’2004
802.11 - MAC Layer 802.11 - MAC Layer OverviewOverview
– DFWMAC-DCF CSMA/CA (Mandatory)DFWMAC-DCF CSMA/CA (Mandatory)(Distributed Foundation Wireless Medium Access (Distributed Foundation Wireless Medium Access Control - Distributed Coordinated Function Control - Distributed Coordinated Function CSMA/CA)CSMA/CA)
– DFWMAC-DCF w/ RTS/CTS (Optional)DFWMAC-DCF w/ RTS/CTS (Optional)Distributed Foundation Wireless MACDistributed Foundation Wireless MACAvoids Hidden Terminal problemAvoids Hidden Terminal problem
– DFWMAC- PCF (Optional)DFWMAC- PCF (Optional)Access point polls terminals according to a listAccess point polls terminals according to a list
44IFA’2004
802.11 - CSMA/CA 802.11 - CSMA/CA Access Method DFWMAC-DCF Access Method DFWMAC-DCF CSMA/CACSMA/CA
– A station with a frame to transmit senses the A station with a frame to transmit senses the medium. medium.
– If the medium is idle, it waits to see if the medium If the medium is idle, it waits to see if the medium remains idle for a time equal to IFS. If so, the remains idle for a time equal to IFS. If so, the station may transmit immediately.station may transmit immediately.
– If the medium is busy (either because the station If the medium is busy (either because the station initially finds the medium busy or because the initially finds the medium busy or because the medium becomes busy during the IFS idle time), medium becomes busy during the IFS idle time), the station defers transmission and continues to the station defers transmission and continues to monitor the medium until the current transmission monitor the medium until the current transmission is over.is over.
– Once the current transmission is over, the station Once the current transmission is over, the station delays another IFS.delays another IFS.
– If the medium remains idle for this period, the If the medium remains idle for this period, the station backs off using a binary exponential station backs off using a binary exponential backoff scheme and again senses the medium. backoff scheme and again senses the medium.
– If the medium is still idle, the station may transmit.If the medium is still idle, the station may transmit.
45IFA’2004
802.11 - CSMA/CA 802.11 - CSMA/CA Access Method IAccess Method I
slot time
direct access if medium is free DIFS
t
medium busy
DIFSDIFS
next frame
contention window(randomized back-offmechanism)
46IFA’2004
802.11 - CSMA/CA Access Method 802.11 - CSMA/CA Access Method IIII Interframe Spaces (IFS)Interframe Spaces (IFS)
Priorities– Defined through different inter frame spaces
– SIFS (Short Inter Frame Spacing)highest priority, for ACK, CTS, polling response
– PIFS (PCF IFS) - Point Coordination Function Inter-Frame spacingmedium priority, for real time service using PCFSIFS + one slot time
– DIFS (DCF, Distributed Coordination Function IFS)lowest priority, for asynchronous data serviceSFIS + two slot times
47IFA’2004
Interframe Spaces (IFS)Interframe Spaces (IFS)
t
medium busySIFS
PIFS
DIFSDIFS
next framecontention
direct access if medium is free DIFS
48IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
In Figure we illustrate the use of these time
values.
49IFA’2004
802.11 - CSMA/CA 802.11 - CSMA/CA Access Method IIAccess Method II
– Station has to wait for DIFS before sending dataStation has to wait for DIFS before sending data– Receivers acknowledge at once (after waiting for SIFS) if the packet Receivers acknowledge at once (after waiting for SIFS) if the packet
was received correctly (CRC))was received correctly (CRC))– Automatic retransmission of data packets in case of transmission Automatic retransmission of data packets in case of transmission
errorserrors
t
SIFS
DIFS
data
ACK
waiting time
otherstations
receiver
senderdata
DIFS
contention
50IFA’2004
802.11 – DFWMAC 802.11 – DFWMAC w/ RTS/CTSw/ RTS/CTS
– Station can send RTS (request to send) with reservation Station can send RTS (request to send) with reservation parameter after waiting for DIFS (reservation determines parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium) amount of time the data packet needs the medium)
– Every node receiving the RTS has to set its Net Allocation Every node receiving the RTS has to set its Net Allocation Vector (NAV) in accordance with the duration of the field Vector (NAV) in accordance with the duration of the field (NAV specifies the earliest point at which the station can (NAV specifies the earliest point at which the station can try to access the mediumtry to access the medium
– If receiver receives RTS, it sends CTS (Clear to Send) after If receiver receives RTS, it sends CTS (Clear to Send) after SIFS. CTS again contains duration field and all stations SIFS. CTS again contains duration field and all stations receiving this packet need to adjust their NAVreceiving this packet need to adjust their NAV
– Sender can now send data after SIFS, acknowledgement Sender can now send data after SIFS, acknowledgement via ACK by receiver after SIFSvia ACK by receiver after SIFS
51IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Clear to Send (CTS)Clear to Send (CTS)– A station can ensure that its data frame will get A station can ensure that its data frame will get
through by first issuing a small request to send through by first issuing a small request to send (RTS) frame. (RTS) frame.
– The station to which this frame is addressed should The station to which this frame is addressed should respond immediately with a CTS frame if it is ready respond immediately with a CTS frame if it is ready to receive. to receive.
– All other stations receive the RTS and defer using All other stations receive the RTS and defer using the medium until they see a corresponding CTS or the medium until they see a corresponding CTS or until a timeout occurs.until a timeout occurs.
– PIFS is used by the centralized controller in issuing PIFS is used by the centralized controller in issuing polls and takes precedence over normal contention polls and takes precedence over normal contention traffic. traffic.
– However, those frames transmitted using SIFS have However, those frames transmitted using SIFS have precedence over a PCF poll. precedence over a PCF poll.
– Finally, the DIFS interval is used for all ordinary Finally, the DIFS interval is used for all ordinary asynchronous traffic.asynchronous traffic.
52IFA’2004
802.11 – DFWMAC 802.11 – DFWMAC w/ RTS/CTSw/ RTS/CTS
t
SIFS
DIFS
data
ACK
defer access
otherstations
receiver
senderdata
DIFS
contention
RTS
CTSSIFS SIFS
NAV (RTS)NAV (CTS)
53IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Point Coordination FunctionPoint Coordination Function– PCF is an alternative access method PCF is an alternative access method
implemented on top of the DCF. implemented on top of the DCF. – The operation consists of polling with the The operation consists of polling with the
centralized polling master (point centralized polling master (point coordinator). coordinator).
– The point coordinator makes use of PIFS The point coordinator makes use of PIFS when issuing polls. when issuing polls.
– Because PIFS is smaller than DIFS, the Because PIFS is smaller than DIFS, the point coordinator can seize the medium point coordinator can seize the medium and lock out all asynchronous traffic while and lock out all asynchronous traffic while it issues polls and receives responses.it issues polls and receives responses.
54IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Point Coordination Function (Cont.)Point Coordination Function (Cont.)– A wireless network is configured so that a number A wireless network is configured so that a number
of stations with time-sensitive traffic are controlled of stations with time-sensitive traffic are controlled by the point coordinator while remaining traffic by the point coordinator while remaining traffic contends for access using CSMA. contends for access using CSMA.
– The point coordinator could issue polls in a round-The point coordinator could issue polls in a round-robin fashion to all stations configured for polling. robin fashion to all stations configured for polling.
– When a poll issued, the polled station may respond When a poll issued, the polled station may respond using SIFS. using SIFS.
– If the point coordinator receives a response, it If the point coordinator receives a response, it issues another poll using PIFS. issues another poll using PIFS.
– If no response is received during the expected If no response is received during the expected turnaround time, the coordinator issues a poll.turnaround time, the coordinator issues a poll.
55IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Point Coordination Function (Cont.)Point Coordination Function (Cont.)
Figure 18 illustrates the use of the superframe.Figure 18 illustrates the use of the superframe.
Figure 18
56IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Point Coordination Function (Cont.)Point Coordination Function (Cont.)– At the beginning of a superframe, the At the beginning of a superframe, the
point coordinator may optionally seize point coordinator may optionally seize control and issues polls for a given control and issues polls for a given period of time. period of time.
– This interval varies because of the This interval varies because of the variable frame size issued by variable frame size issued by responding stations. responding stations.
– The remainder of the superframe is The remainder of the superframe is available for contention-based access. available for contention-based access.
57IFA’2004
IEEE 802.11IEEE 802.11- - Medium Access ControlMedium Access Control
Point Coordination Function (Cont.)Point Coordination Function (Cont.)– At the end of the superframe interval, At the end of the superframe interval,
the point coordinator contends for the point coordinator contends for access to the medium using PIFS. access to the medium using PIFS.
– If the medium is idle, the point If the medium is idle, the point coordinator gains immediate access coordinator gains immediate access and a full superframe period follows. and a full superframe period follows.
– However, the medium may be busy at However, the medium may be busy at the end of a superframe. the end of a superframe.
– In this case, the point coordinator In this case, the point coordinator must wait until the medium is idle to must wait until the medium is idle to gain access; this results in a gain access; this results in a foreshortened superframe period for foreshortened superframe period for the next cycle.the next cycle.
58IFA’2004
DFWMAC-PCF IDFWMAC-PCF I
The access mechanisms presented so far The access mechanisms presented so far cannot guarantee a maximum access delay or cannot guarantee a maximum access delay or minimum transmission bandwidth.minimum transmission bandwidth.
To provide a time bounded service, the To provide a time bounded service, the standards specify a Point Coordination standards specify a Point Coordination Function (PCF) on top of the DCF mechanisms.Function (PCF) on top of the DCF mechanisms.
Using PCF requires an access point that can Using PCF requires an access point that can controls medium access and polls the single controls medium access and polls the single nodes. Ad Hoc networks cannot use this nodes. Ad Hoc networks cannot use this functionfunction..
59IFA’2004
DFWMAC-PCF IDFWMAC-PCF I
At time tAt time t00 the contention-free period should the contention-free period should start, but another station is transmitting datastart, but another station is transmitting data
After the medium has been idle, the PCF has to After the medium has been idle, the PCF has to wait for PIFS before accessing the medium.wait for PIFS before accessing the medium.
The point coordinator now sends data DThe point coordinator now sends data D11 to the to the first station. The station can answer after SIFS. first station. The station can answer after SIFS. After waiting for SIFS, the point coordinator can After waiting for SIFS, the point coordinator can poll the second station by sending Dpoll the second station by sending D22. .
The second station replies with UThe second station replies with U22
60IFA’2004
DFWMAC-PCF IDFWMAC-PCF I
PIFS
stations‘NAV
wirelessstations
point coordinator
D1
U1
SIFS
NAV
SIFSD2
U2
SIFS
SIFS
SuperFramet0
medium busy
t1
61IFA’2004
DFWMAC-PCF IIDFWMAC-PCF II
tstations‘NAV
wirelessstations
point coordinator
D3
NAV
PIFSD4
U4
SIFS
SIFSCFend
contentionperiod
contention free period
t2 t3 t4
Polling continues with the third node which has nothing Polling continues with the third node which has nothing to answer.to answer.
After waiting for PIFS, the point coordinator can issue an After waiting for PIFS, the point coordinator can issue an end marker (CFend marker (CFendend), indicating that the contention period ), indicating that the contention period may start again.may start again.
The cycle starts again with the next superframeThe cycle starts again with the next superframe
62IFA’2004
WLAN: IEEE WLAN: IEEE 802.11b802.11b
Data rateData rate– 1, 2, 5.5, 11 Mbit/s, 1, 2, 5.5, 11 Mbit/s,
depending on SNR depending on SNR – User data rate max. approx. User data rate max. approx.
6 Mbit/s6 Mbit/s Transmission rangeTransmission range
– 300m outdoor, 30m indoor300m outdoor, 30m indoor– Max. data rate ~10m indoorMax. data rate ~10m indoor
FrequencyFrequency– Free 2.4 GHz ISM-bandFree 2.4 GHz ISM-band
SecuritySecurity– Limited, WEP (Wired Limited, WEP (Wired
Equivalent Privacy) insecure, Equivalent Privacy) insecure, SSIDSSID
AvailabilityAvailability– Many products, many Many products, many
vendorsvendors
Connection set-up timeConnection set-up time– Connectionless/always onConnectionless/always on
Quality of ServiceQuality of Service– Typ. Best effort, no guarantees Typ. Best effort, no guarantees
(unless polling is used, limited (unless polling is used, limited support in products)support in products)
ManageabilityManageability– Limited (no automated key Limited (no automated key
distribution, sym. Encryption)distribution, sym. Encryption) Special Special
Advantages/DisadvantagesAdvantages/Disadvantages– Advantage: many installed Advantage: many installed
systems, lot of experience, systems, lot of experience, available worldwide, free ISM-available worldwide, free ISM-band, many vendors, integrated band, many vendors, integrated in laptops, simple systemin laptops, simple system
– Disadvantage: heavy Disadvantage: heavy interference on ISM-band interference on ISM-band (Industrial, Scientific, Medical (Industrial, Scientific, Medical band), no service guarantees, band), no service guarantees, slow relative speed onlyslow relative speed only
63IFA’2004
WLAN: IEEE WLAN: IEEE 802.11a802.11a
Data rateData rate– 6, 9, 12, 18, 24, 36, 48, 54 6, 9, 12, 18, 24, 36, 48, 54
Mbit/s, depending on SNRMbit/s, depending on SNR– User throughput (1500 byte User throughput (1500 byte
packets): 5.3 (6), 18 (24), 24 packets): 5.3 (6), 18 (24), 24 (36), 32 (54) (36), 32 (54)
– 6, 12, 24 Mbit/s mandatory6, 12, 24 Mbit/s mandatory Transmission rangeTransmission range
– 100m outdoor, 10m indoor100m outdoor, 10m indoor E.g., 54 Mbit/s up to 5 m, 48 up to E.g., 54 Mbit/s up to 5 m, 48 up to
12 m, 36 up to 25 m, 24 up to 30m, 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m 18 up to 40 m, 12 up to 60 m
FrequencyFrequency– Free 5.15-5.25, 5.25-5.35, Free 5.15-5.25, 5.25-5.35,
5.725-5.825 GHz ISM-band5.725-5.825 GHz ISM-band SecuritySecurity
– Limited, WEP insecure, SSIDLimited, WEP insecure, SSID AvailabilityAvailability
– Some products, some vendorsSome products, some vendors
Connection set-up timeConnection set-up time– Connectionless/always onConnectionless/always on
Quality of ServiceQuality of Service– Typ. best effort, no Typ. best effort, no
guarantees (same as all guarantees (same as all 802.11 products)802.11 products)
ManageabilityManageability– Limited (no automated key Limited (no automated key
distribution, sym. Encryption)distribution, sym. Encryption) Special Special
Advantages/DisadvantagesAdvantages/Disadvantages– Advantage: fits into 802.x Advantage: fits into 802.x
standards, free ISM-band, standards, free ISM-band, available, simple system, uses available, simple system, uses less crowded 5 GHz bandless crowded 5 GHz band
– Disadvantage: stronger Disadvantage: stronger shading due to higher shading due to higher frequency, no QoSfrequency, no QoS
64IFA’2004
WLAN: IEEE 802.11 – WLAN: IEEE 802.11 – Future Developments Future Developments ((08/200208/2002))
802.11d: Regulatory Domain Update – 802.11d: Regulatory Domain Update – completedcompleted 802.11e: MAC Enhancements – QoS – 802.11e: MAC Enhancements – QoS – ongoingongoing
– Enhance the current 802.11 MAC to expand support for Enhance the current 802.11 MAC to expand support for applications with Quality of Service requirements, and in the applications with Quality of Service requirements, and in the capabilities and efficiency of the protocol. capabilities and efficiency of the protocol.
802.11f: Inter-Access Point Protocol – 802.11f: Inter-Access Point Protocol – ongoingongoing – Establish an Inter-Access Point Protocol for data exchange via the Establish an Inter-Access Point Protocol for data exchange via the
distribution system.distribution system. 802.11g: Data Rates > 20 Mbit/s at 2.4 GHz802.11g: Data Rates > 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM; 54 Mbit/s, OFDM – –
ongoing ongoing 802.11h: Spectrum Managed 802.11a (D802.11h: Spectrum Managed 802.11a (DCCS, TPC) – S, TPC) – ongoing ongoing 802.11i: Enhanced Security Mechanisms – 802.11i: Enhanced Security Mechanisms – ongoingongoing
– Enhance the current 802.11 MAC to provide improvements in Enhance the current 802.11 MAC to provide improvements in security. security.
Study GroupsStudy Groups– 5 GHz (harmonization ETSI/IEEE) – 5 GHz (harmonization ETSI/IEEE) – closed closed – Radio Resource Measurements – Radio Resource Measurements – startedstarted– High Throughput – High Throughput – startedstarted
65IFA’2004
WLANs – 802.11 WLANs – 802.11 CompatibilityCompatibility
802.11a and 802.11b share the same MAC layer802.11a and 802.11b share the same MAC layer Significant differences at the physical layer.Significant differences at the physical layer.
– 802.11b: 2.4 GHz, ISM band, 802.11b: 2.4 GHz, ISM band, – 802.11a: 5 GHz, U-NII band802.11a: 5 GHz, U-NII band– possible to operate both on the same possible to operate both on the same
network concurrently (using the same access network concurrently (using the same access points)points)
InteroperabilityInteroperability– WECA (Wireless Ethernet Compatibility WECA (Wireless Ethernet Compatibility
Alliance): organization behind Wi-Fi that Alliance): organization behind Wi-Fi that certifies products meeting the 802.11b certifies products meeting the 802.11b specificationspecification
66IFA’2004
WLANs – WLANs – Comparison of Comparison of TechnologiesTechnologies
Characteristic 802.11 802.11b 802.11a HiperLAN/2
Spectrum 2.4GHz 2.4GHz 5GHz 5GHz
Max Physical Rate 2Mb/s 11Mb/s 54Mb/s 32Mb/s
Max data rate layer 3 1.2Mb/s 5Mb/s 32Mb/s 32Mb/s
Medium access CSMA/MA TDMA/TDD
Connectivity Conn.-less Conn.-less Conn.-less Conn.-oriented
Multicast Yes Yes Yes Yes
QoS support No No No Yes
Frequency selection FH/DSSS DSSS Single carrier Single carrier with Dynamic Frequency
Selection
Authentication No No No NAI/IEEE address/X.509
Encryption 40bit RC4 40bit RC4 40bit RC4 DES, 3DES
Handover support No No No No
Fixed network support Ethernet Ethernet Ethernet Ethernet, IP, ATM UMTS, FireWire, PPP
Management 802.11MIB 802.11MIB 802.11MIB HiperLAN/2MIB
Radio link quality control No No No Link adaptation
67IFA’2004
WLANs – WLANs – InterferenceInterference
An important issue in all wireless systems An important issue in all wireless systems because nearby users occupy same because nearby users occupy same bandwidth and cause co-channel interference. bandwidth and cause co-channel interference.
For WLANs, in addition to co-channel For WLANs, in addition to co-channel interference, other types of interference exist interference, other types of interference exist mainly due to the use of unlicensed ISM band. mainly due to the use of unlicensed ISM band. Interference to WLANs comes from the Interference to WLANs comes from the following major sources:following major sources:– Co-channel interference. Co-channel interference. – Interference from non-wLAN devices in the Interference from non-wLAN devices in the
same frequency band same frequency band – Interference between different wLANs in Interference between different wLANs in
the same frequency band. the same frequency band.
68IFA’2004
WLANs – WLANs – Interference Interference ReductionReduction
Regulatory and standards Regulatory and standards – Change frequency segment of a channel (proposed Change frequency segment of a channel (proposed
by FCC for Bluetooth) by FCC for Bluetooth) Usage and practicesUsage and practices
– When one wLAN is working, others are banned. Not When one wLAN is working, others are banned. Not practical. Modal operation of wLANs can be a good practical. Modal operation of wLANs can be a good alternativealternative
Technical approaches. Technical approaches. – Driver layer: software above the MAC layer can be Driver layer: software above the MAC layer can be
installed for different types of wLANs. Thus, installed for different types of wLANs. Thus, software switch from one wLAN to another wLAN is software switch from one wLAN to another wLAN is required. required.
– MAC layer: more attractive but it is an on-going MAC layer: more attractive but it is an on-going research topic. research topic.
– Physical layer: signal processing techniques and Physical layer: signal processing techniques and anti-jamming schemes usedanti-jamming schemes used
69IFA’2004
WLANs – WLANs – Environmental Environmental IssuesIssues
Has been proved that WLAN is safe for healthHas been proved that WLAN is safe for health– Radiation used by this technology, fall well within the limits Radiation used by this technology, fall well within the limits
of safety guidelines (both in terms of frequency content of safety guidelines (both in terms of frequency content and power level) specified by Radio Frequency Safety and power level) specified by Radio Frequency Safety Standards and Recommendations. Standards and Recommendations.
– Radiation in this frequency range is non-ionizing (as they Radiation in this frequency range is non-ionizing (as they do not have enough energy to break the chemical bonds of do not have enough energy to break the chemical bonds of genetic material of body cells). genetic material of body cells).
– Vendors designing their products to operate within the Vendors designing their products to operate within the power limit set by the Safety Standards. power limit set by the Safety Standards.
OthersOthers– No wires to hide and maintainNo wires to hide and maintain– Looks much better and cleaner compared to the wired one. Looks much better and cleaner compared to the wired one. – Positive impact on user psychology due to user mobility, Positive impact on user psychology due to user mobility,
reduced-cost of ownership, real-time-access to information,reduced-cost of ownership, real-time-access to information,
70IFA’2004
WLANs – WLANs – Major SuppliersMajor Suppliers
Three types of products in WLANs:
– Access Point– LAN Adapters and – LAN Bridges.
71IFA’2004
WLANs –WLANs –Access Point Access Point ProductsProducts
Major Suppliers
Products Operating Frequency
Standard Throughput WEP Encryption
Agere AP-1000 2.4GHz 802.11b 11Mbps -
Avaya I/700022270 2.4GHz 802.11b 11Mbps -
Nokia A032 2.4GHz 802.11b 11Mbps 64- and 128-bit
Nortel e-mobility DSSS AP DR4000E02
2.4GHz 802.11b 11Mbps -
Intel PRO/Wireless 2011B
2.4GHz 802.11b 11Mbps 64- and 128-bit
Intel PRO/Wireless 5000
5.2 GHz 802. 11b 54 Mbs 64- and 128-bit
Siemens I-GATE 11M 2.4GHz 802.11b 11Mbps 11Mbps
3Com Access Point 6000
2.4GHz 802.11b 11Mbps 64-bit
Fujitsu MBH8MB01 2.4GHz Bluetooth 732.2kbps -
Compaq WL510 2.4GHz 802.11b 11Mbps 128bit
Agere AP-1000 2.4GHz 802.11b 11Mbps 128bit
Apple AirPort 2.4GHz 802.11b 11Mbps -
IBM AP500 2.4GHz 802.11b 11Mbps -
Cisco Aironet® 350 Series
2.4GHz 802.11b 11Mbps -
72IFA’2004
WLANs – WLANs – LAN Adapter LAN Adapter ProductsProducts
Major suppliers
Products Operating Frequency
Standard Throughput Range
Intel PRO/Wireless 2011B LAN
PC Card
2.4GHz 802.11b 11Mbps -
Intel PRO/Wireless 5000 LAN
PCI Adapter
5.2GHz 802.11a 54Mbps 100 feet
Compaq WL110 2.4GHz 802.11b 11Mbps -
Agere ORiNOCO PC Card
2.4GHz 802.11b 11Mbps -
Apple Airport Client Card
2.4GHz 802.11b 11Mbps -
Cisco Aironet® 350 Series
2.4GHz 802.11b 11Mbps -
73IFA’2004
WLANs –WLANs –Bridge Bridge ProductsProducts
Major suppliers
Products Operating Frequency
Standard Throughput Range
Intel Wireless Gateway
2.4GHz 802.11b 11Mbps -
Compaq WL310 2.4GHz 802.11b 11Mbps 160m(525feet)
Agere RG-1100 Broadband
Gateway
2.4GHz 802.11b 11Mbps 550m(1750ft)
Agere ORiNOCO PC Card
2.4GHz 802.11b 11Mbps -
Cisco Aironet® 350 Series Wireless Bridge
2.4GHz 802.11b 11Mbps 25 miles (40.2 km)
74IFA’2004
WLANs – WLANs – Market Market SegmentSegment
by Wireless LAN Association (wLANA )
75IFA’2004
WLANs – WLANs – Market Market ForecastForecast
Seen as "The Technology" of the future. Seen as "The Technology" of the future. – Trend support: Decrease of product price and Trend support: Decrease of product price and
increase of network speed, increase of network speed, – Apart from current sectors, more and more new Apart from current sectors, more and more new
markets are opening up for this technology. Some markets are opening up for this technology. Some of these are shipping and receiving area, of these are shipping and receiving area, distribution center, cafeteria, home, train, bus, distribution center, cafeteria, home, train, bus, airport, sport complexes, trade shows, coffee airport, sport complexes, trade shows, coffee shops, etc. shops, etc.
Huge market potentialHuge market potential– Make WLAN as a viable option to connect the Make WLAN as a viable option to connect the
developing nations to the developed part of the developing nations to the developed part of the world, making the concept "Global Village" a world, making the concept "Global Village" a reality.reality.
Estimated a five-fold increase in its market by 2005Estimated a five-fold increase in its market by 2005
76IFA’2004
WLANs – WLANs – Technology Technology ForecastForecast
WLAN will have higher speeds WLAN will have higher speeds – Wi-Fi5 for IEEE 802.11a up to 54Mbps Wi-Fi5 for IEEE 802.11a up to 54Mbps – 5.7-GHz band promises to allow for the next 5.7-GHz band promises to allow for the next
breakthrough data rate of 100 Mbps. breakthrough data rate of 100 Mbps. Provide multimedia and access to 3G-4G SystemsProvide multimedia and access to 3G-4G Systems
– HIPERLAN/2 to provide high speed access (up HIPERLAN/2 to provide high speed access (up to 54 Mbit/s at PHY layer) to 3G mobile core to 54 Mbit/s at PHY layer) to 3G mobile core networks, and Internet.networks, and Internet.
More security guarantees. More security guarantees. – Enhancements to Wired Equivalent Privacy Enhancements to Wired Equivalent Privacy
(WEP)(WEP)
77IFA’2004
WLANs – WLANs – Technology Technology ForecastForecast
Even more decreased size, cost, Even more decreased size, cost, power consumptionpower consumption
New approaches in handling New approaches in handling network parameters dynamically to network parameters dynamically to improve throughput. improve throughput.
Improved reliabilityImproved reliability Efficient and concurrent uses of Efficient and concurrent uses of
bandwidth via Wideband bandwidth via Wideband Orthogonal Frequency Division Orthogonal Frequency Division Multiplexing (W-OFDM)Multiplexing (W-OFDM)
78IFA’2004
WLANs – WLANs – Service Service
AnalysisAnalysis
Convergence for voice and data networksConvergence for voice and data networks– As voice, audio and video are shared As voice, audio and video are shared
among WLAN-enabled phones, MP3 among WLAN-enabled phones, MP3 players, web cameras, interactive TVs, players, web cameras, interactive TVs, etc, wireless applications will move etc, wireless applications will move beyond traditional computer networking.beyond traditional computer networking.
Replacement of proprietary cables. Replacement of proprietary cables. Portable access to wireless LAN. Portable access to wireless LAN. Multimedia over wireless networks. Multimedia over wireless networks. Wireless remote data access. Wireless remote data access. Data Backup. Data Backup.
79IFA’2004
WLANs – WLANs – Network Network Design Plan Design Plan AnalysisAnalysis
Key parameters:Key parameters:– number of expected usersnumber of expected users– area of coveragearea of coverage– quality of servicequality of service– service typesservice types
Network topology for WLAN can Network topology for WLAN can broadly be classified into:broadly be classified into:– Ad-Hoc WLAN Ad-Hoc WLAN – Client-Server based WLAN Client-Server based WLAN
80IFA’2004
WLANs – WLANs – Performance Performance
MetricsMetrics
Overall coverage area Overall coverage area – Can be evaluated in terms of received Can be evaluated in terms of received
signal strength intensity (RSSI)signal strength intensity (RSSI) Throughput Throughput
– Can be evaluated by measuring TCP Can be evaluated by measuring TCP connection throughputs since wLANs connection throughputs since wLANs establish a client-server communication establish a client-server communication link via TCP connection,link via TCP connection,
Implementations of handoff and dropping Implementations of handoff and dropping are the responsibility of manufacturers, are the responsibility of manufacturers, since they vary according to different since they vary according to different equipmentsequipments
81IFA’2004
WLANs – WLANs – Network Network Security AspectsSecurity Aspects
Service set identifier (SSID) (can be configured into 802.11 Service set identifier (SSID) (can be configured into 802.11 APs)APs)
Use VPN technologies built into or on top of WLAN productsUse VPN technologies built into or on top of WLAN products Wired equivalent privacy (WEP) of 802.11 or the common Wired equivalent privacy (WEP) of 802.11 or the common
128-bit extension128-bit extension– Uses shared keys and a pseudo random number (PRN) as Uses shared keys and a pseudo random number (PRN) as
an initial vector (IV) to encrypt the data portion of an initial vector (IV) to encrypt the data portion of network packets, but does not encrypt 802.11b header network packets, but does not encrypt 802.11b header
– Each station (clients and APs) has a number of keys to Each station (clients and APs) has a number of keys to encrypt data before it is transmitted encrypt data before it is transmitted
– Each station can only receive a packet being encrypted Each station can only receive a packet being encrypted with its appropriate key. Without proper key, the packet with its appropriate key. Without proper key, the packet will be discarded will be discarded
– Some vendors also provide key servers to implement Some vendors also provide key servers to implement centralized key management, such as Cisco.centralized key management, such as Cisco.
82IFA’2004
WLANs – WLANs – Price ComparisonPrice Comparison
Vendor Name Access Points PC card PCI Adapter Wireless Bridge
3Com $545.00 $169.00 $199.00 $1095.00
Apple $301.00 $99.00 -- --
Avaya $685.00 $144.00 $59.00 --
Cisco $717.00 $193.00 $269.00 $458.00
Compaq $729.00 $166.00 $208.00 --
Ericsson $929.00 $186.00 -- --
IBM $1015.00 $182.00 -- --
Nokia $751.00 $212.00 $199.00 --
Nortel $1065.00 $289.00 -- $638.00
Symbol $1025.00 $181.00 $271.00 $655.00
Zoom $410.00 $136.00 $136.00 $1888.00
83IFA’2004
WLANs – Total CostWLANs – Total Cost
Much smaller (around one year) payback periodMuch smaller (around one year) payback period– Even though initial capital cost for the WLAN may Even though initial capital cost for the WLAN may
be more, but the running cost for the WLAN is be more, but the running cost for the WLAN is much lessmuch less
Cost-effective large scale network deploymentCost-effective large scale network deployment– Example: organizations for around 300 users Example: organizations for around 300 users
benefited annual savings of up to $4.9 million, benefited annual savings of up to $4.9 million, which corresponds to per user saving of which corresponds to per user saving of $15,989.00.$15,989.00.
Low initial installation cost (wiring)Low initial installation cost (wiring)– University of Akron, covered their four-story University of Akron, covered their four-story
library with WLAN with a total cost of $80,000, library with WLAN with a total cost of $80,000, using Cisco Airnet 350 series and the estimated using Cisco Airnet 350 series and the estimated cost for wired network for that was $800,000 cost for wired network for that was $800,000
84IFA’2004
ConclusionsConclusions Users demand ubiquity: mergence of the Users demand ubiquity: mergence of the
wireless communication services; indoor and wireless communication services; indoor and outdooroutdoor
Greater demand for integration with Greater demand for integration with Bluetooth, wLAN and cellular system Bluetooth, wLAN and cellular system
Technology to meet these demand available Technology to meet these demand available todaytoday
Some key issues:Some key issues:– interoperability between different wireless interoperability between different wireless
network systems (MORE WORK NEEDED)network systems (MORE WORK NEEDED)– Security: More work needed. An ideal Security: More work needed. An ideal
solution: combination of VPN and IPSec solution: combination of VPN and IPSec
85IFA’2004
ConclusionsConclusions Since the needs from various enterprises and Since the needs from various enterprises and
end users are quite different, the service end users are quite different, the service providers should prepare various network providers should prepare various network deploymentsdeployments– Many issues to be considered: network Many issues to be considered: network
capacity, the connectivity to wired network, capacity, the connectivity to wired network, QoS, security, price and performance.QoS, security, price and performance.
A competitive solution provides seamless end-A competitive solution provides seamless end-to-end connectivity from mobile users to wired to-end connectivity from mobile users to wired ones.ones.
A web-based, centralized network A web-based, centralized network management is another consideration most management is another consideration most customers wantcustomers want
86IFA’2004
WLANs - WLANs - Challenging IssuesChallenging Issues
Relatively low data rate. Relatively low data rate. – Some can achieve very high data rate, e.g., the Some can achieve very high data rate, e.g., the
rate of IEEE 802.11 WLANs can be as high as rate of IEEE 802.11 WLANs can be as high as 11Mbps, while some products such as Bluetooth 11Mbps, while some products such as Bluetooth can only achieve medium speed data rate. can only achieve medium speed data rate.
Lack of support for real time services. Lack of support for real time services. – IEEE 802.11 products, which are based on the IEEE 802.11 products, which are based on the
CSMA/CA protocol, are unable to provide QoS CSMA/CA protocol, are unable to provide QoS guarantees for voice, video, and other real time guarantees for voice, video, and other real time services. (IEEE 802.11 working group E is still services. (IEEE 802.11 working group E is still working QoS enhancement)working QoS enhancement)
Interference between different types of WLANs Interference between different types of WLANs Lack of Interoperability between WLANs Lack of Interoperability between WLANs
