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Wireless LAN Basics
Wireless Standards (802.11 a/b/g/n/ac/ad)
Wireless LAN and Technology,
Wireless application protocols Architecture
Wireless application protocols application
Wireless LAN Basics
Wireless Standards (802.11 a/b/g/n/ac/ad)
Wireless LAN and Technology,
Wireless application protocols Architecture
Wireless application protocols application
LANs provide connectivity for interconnecting computing resources at the local levels of an organization
Wired LANs
Limitations because of physical, hard-wired infrastructure
Wireless LANs provide
Flexibility
Portability
Mobility
Ease of Installation
Types◦ Infrastructure based
◦ Ad-hoc
Advantages◦ Flexible deployment
◦ Minimal wiring difficulties
◦ More robust against disasters (earthquake etc)
◦ Historic buildings, conferences, trade shows,…
Disadvantages◦ Low bandwidth compared to wired networks (1-10 Mbit/s)
◦ Proprietary solutions
◦ Need to follow wireless spectrum regulations
Access point (AP): A station that provides access
to the DS.
Basic service set (BSS): A set of stations controlled
by a single AP.
Distribution system (DS): A system used to
interconnect a set of BSSs to create an ESS.
Extended service set (ESS):Two or more BSS
interconnected by DS
Hidden terminals◦ A and C cannot hear each other.◦ A sends to B, C cannot receive A. ◦ C wants to send to B, C senses a “free” medium (CS fails)◦ Collision occurs at B.◦ A cannot receive the collision (CD fails).◦ A is “hidden” for C.
Solution? (MAC layer)◦ Hidden terminal is peculiar to wireless (not found in wired)◦ Need to sense carrier at receiver, not sender!◦ “virtual carrier sensing”: Sender “asks” receiver whether it can
hear something. If so, behave as if channel busy.
BA C
Loss of frames due to noise, interference, and propagation effects
Frame exchange protocolSource station transmits dataDestination responds with acknowledgment (ACK)If source doesn’t receive ACK, it retransmits frame
Four frame exchange for enhanced reliabilitySource issues request to send (RTS)Destination responds with clear to send (CTS)Source transmits dataDestination responds with ACK
Asynchronous data service (DCF)CSMA/CARTS/CTS
Time bounded service (PCF)
Polling
Inter-frame spacing (IFS)
DIFS
PIFS
SIFS
CSMA/CD – CSMA/Collision detectionFor wire communication
No control BEFORE transmission
Generates collisions
Collision Detection-How?
CSMA/CA – CSMA/Collision AvoidanceFor wireless communication
Collision avoidance BEFORE transmission
Why avoidance on wireless?
Difference in energy/power for transmit & receive
Difficult to distinguish between incoming weak signals, noise, and effects of own transmission
802.11 avoids the problem of hidden terminals
◦ A and C want to send to B
◦ A sends RTS to B
◦ B sends CTS to A
◦ C “overhears” CTS from B
◦ C waits for duration of A’s transmission
A B C
RTS
CTSCTS
DIFS: Distributed IFS(Inter Frame Space) RTS: Request To SendSIFS: Short IFSCTS: Clear To SendACK: AcknowledgementNAV: Network Allocation VectorDCF: Distributed Coordination Function
Defined length of time for control
SIFS - Short Inter Frame Spacing
Used for immediate response actions
e.g ACK, CTS
PIFS - Point Inter Frame Spacing
Used by centralized controller in PCF scheme
DIFS - Distributed Inter Frame Spacing
Used for all ordinary asynchronous traffic
DIFS (MAX) > PIFS > SIFS (MIN)
Wireless LAN Basics
Wireless Standards (802.11 a/b/g/n/ac/ad)
Wireless LAN and Technology,
Wireless application protocols Architecture
Wireless application protocols application
In response to lacking standards, IEEE developed the first
internationally recognized wireless LAN standard – IEEE 802.11
IEEE published 802.11 in 1997, after seven years of work
Most prominent specification for WLANs
Scope of IEEE 802.11 is limited to Physical and Data Link Layers.
Appliance Interoperability
Fast Product Development
Stable Future Migration
Price Reductions
The 802.11 standard takes into account the following significant differences between wireless and wired LANs:
Power Management
Security
Bandwidth
IEEE 802.3
CarrierSense
IEEE 802.4
TokenBus
IEEE 802.5
TokenRing
IEEE 802.11
Wireless
IEEE 802.2Logical Link Control (LLC)
PHYOSI Layer 1(Physical)
Mac
OSI Layer 2(Data Link)
802.11-1997 (802.11 legacy) 802.11a (OFDM Waveform) 802.11b 802.11g 802.11-2007 802.11n 802.11-2012 802.11ac 802.11ad 802.11af 802.11ah 802.11ai 802.11aj 802.11aq 802.11ax
•Operating in 2.4 GHz ISM band
•Lower cost, power consumption
•Most tolerant to signal interference
Frequency-
hopping spread
spectrum
•Operating in 2.4 GHz ISM band
•Supports higher data rates
•More range than FH or IR physical layers
Direct-sequence
spread
spectrum
•Lowest cost
•Lowest range compared to spread spectrum
•Doesn’t penetrate walls, so no eavesdropping
Infrared
Spread spectrum is a form of wireless communications in
which the frequency of the transmitted signal is
deliberately varied. This results in a much greater
bandwidth than the signal would have if its frequency
were not varied
This technique decreases the potential interference to
other receivers while achieving privacy.
Two types- FHSS and DSSS
Signal is broadcast over seemingly random series of radio frequenciesSignal hops from frequency to frequency at
fixed intervalsReceiver, hopping between frequencies in
synchronization with transmitter, picks up messageAdvantages
Efficient utilization of available bandwidthEavesdropper hear only unintelligible blipsAttempts to jam signal on one frequency succeed only at knocking out a few bits
Each bit in original signal is represented by multiple bits in the transmitted signalSpreading code spreads signal across a wider
frequency band DSSS is the only physical layer specified for
the 802.11b specification802.11a and 802.11b differ in use of chipping method 802.11a uses 11-bit barker chip
802.11b uses 8-bit complimentary code keying (CCK) algorithm
FH systems use a radio carrier that “hops” from frequency to frequency in a pattern known to both transmitter and receiver◦ Easy to implement
◦ Resistance to noise
◦ Limited throughput (2-3 Mbps @ 2.4 GHz)
DS systems use a carrier that remains fixed to a specific frequency band. The data signal is spread onto a much larger range of frequencies (at a much lower power level) using a specific encoding scheme.◦ Much higher throughput than FH (11 Mbps)
◦ Better range
◦ Less resistant to noise (made up for by redundancy – it transmits at least 10 fully redundant copies of the original signal at the same time)
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
30
IEEE 802.11 standards :
IEEE 802.11 b
31
Frequency = 2.4 GHz (ISM band)
Maximum Speed =11 Mbps
Range = about 38meters(Varies)
Encoding Scheme = DSSS
Modulation Technique= BPSK(1 Mbps),
DQPSK(2 Mbps), CCK(5.5 Mbps,11Mbps)
www.cisco.com
IEEE 802.11 standards :
IEEE 802.11 b
32
Pros of 802.11b - lowest cost; signal range is good and not easily obstructedCons of 802.11b - slowest maximum speed; home appliances may interfere on the unregulated frequency band
www.cisco.com
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
33
IEEE 802.11 standards :
IEEE 802.11 a
34
Frequency = 5 GHz
Maximum Speed = 54 Mbps
Range = about 35 meters(Varies)
Encoding Scheme = OFDM
www.cisco.com
IEEE 802.11 standards :
35
IEEE 802.11 a
Multipath Effect(Multipath Fading)
is simply a term used to describe the multiple
Paths the radio wave may follow between
transmitter and receiver
IEEE 802.11 standards :
36
IEEE 802.11 a
Orthogonal Frequency Division Multiplexing(OFDM)
OFDM a digital multi-carrier modulation method. A large
number of closely-spaced orthogonal sub-carriers are used to
carry data.
OFDM is popular for wideband communications today by way
of low-cost digital signal processing components
Ultra-high spectrum efficiency◦ 5 GHz band is 300 MHz (vs. 83.5 MHz @ 2.4 GHz)
◦ More data can travel over a smaller amount of bandwidth
High speed◦ Up to 54 Mbps
Less interference◦ Fewer products using the frequency 2.4 GHz band shared by cordless phones, microwave
ovens, Bluetooth, and WLANs
Standards and Interoperability
◦ Standard not accepted worldwide
◦ Not compatible or interoperable with 802.11b
Legal issues
◦ License-free spectrum in 5 GHz band not available worldwide
Market
◦ There is limited interest for 5 GHz adoption
Cost◦ 2.4 GHz will still has >40% cost advantage
Power consumption◦ Higher data rates and increased signal require more power
OFDM is less power-efficient than DSSS
Building-to-building connections
Video, audio conferencing/streaming video,
and audio
Large file transfers, such as engineering
CAD drawings
Faster Web access and browsing
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
40
IEEE 802.11 standards :
IEEE 802.11 g
41
Frequency= 2.4 GHz
Maximum Speed = 54 Mbps
Range = about 38 meters(Varies)
Encoding Scheme = OFDM
Backward compatibility with 802.11 b devices
www.cisco.com
IEEE 802.11 standards :
IEEE 802.11 g
42
•Pros of 802.11g -
fast maximum speed;
signal range is good and not easily obstructed
•Cons of 802.11g -
costs more than 802.11b;
appliances may interfere on the unregulated
signal frequency
Provides higher speeds and higher capacity requirements for applications
Leverages Worldwide spectrum availability in 2.4 GHz
Less costly than 5 GHz alternatives
Provides easy migration for current users of 802.11b WLANs◦ Delivers backward support for existing 802.11b
products
Provides path to even higher speeds in the future
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
44
IEEE 802.11 standards :
IEEE 802.11n
45
Frequency = 5 GHz,2.4 GHz
Modulation = OFDM
Addition of MIMO (Multiple Input Multiple Output)
Speed = 54 Mbit/s to 600 Mbit/s
Range = about 70 meters(Varies)
Encoding Scheme = OFDM
IEEE 802.11 standards :
IEEE 802.11 n
Multiple Input Multiple Output(MIMO)
46
In radio, Multiple-input and
Multiple-output is used of
multiple antennas at both the
transmitter and receiver to
improve communication
performance.
IEEE 802.11 standards :
47
Pros of 802.11n -•fastest maximum speed and best signal range;• more resistant to signal interference from outside sources
Cons of 802.11n -•standard is not yet finalized; •costs more than 802.11g; •the use of multiple signals may greatly interfere with nearby 802.11b/g based networks.
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
48
IEEE 802.11 standards :
IEEE 802.11ac
49
Frequency = 5 GHz
Modulation = OFDM
Addition of MIMO (Multi User-Multiple Input Multiple Output)
Speed = 433.3 Mbit/s per spatial stream, 1.3 Gbit/s
total
IEEE 802.11 standards :
IEEE 802.11ac - Features
50
Extended channel bindingMore MIMO spatial streamsMultiple STAs, each with one or more antennas, transmit or receive independent data streams simultaneouslyModulation- 256-QAMBeamforming with standardized sounding and feedback for compatibility between vendors
IEEE 802.11 standards :
IEEE 802.11ac Applications
52
Highly interactive video gaming, video conferencing, High definition video streaming andMany more applications that need data at rates that push the boundaries of exiting Wi-Fi systems.
IEEE 802.11 standards :
IEEE 802.11 standards
IEEE 802.11 b
IEEE 802.11 a
IEEE 802.11 g
IEEE 802.11 n
IEEE 802.11 ac
IEEE 802.11 ad
53
IEEE 802.11 standards :
IEEE 802.11ad
54
Frequency = 60GHz
Speed = 7Gbps
Antenna Technology = Uses Beamforming
Modulation = OFDM
Wireless LAN Basics
Wireless Standards (802.11 a/b/g/n/ac/ad)
Wireless LAN and Technology,
Wireless application protocols Architecture
Wireless application protocols application
WAP Introduction
Architecture overview
Components of WAP architecture
Applications, Advantages & Disadvantages of WAP
o WAP stands for Wireless Application Protocol o WAP is an application communication protocol o WAP is used to access services and information o WAP is inherited from Internet standards o WAP is for handheld devices such as mobile
phones o WAP is a protocol designed for micro browsers o WAP enables the creating of web applications
for mobile devices. o WAP uses the mark-up language WML (not
HTML) WML is defined as an XML 1.0 application
The basic AIM of WAP is to provide a web-like experience on small portable devices- like mobile phones and PDAs
Purpose of WAP
To enable easy, fast delivery of relevant information andservices to mobile users.
Type of devices that use WAP
Handheld digital wireless devices such as mobile phones,pagers, two-way radios, smart phones and communicators-- from low-end to high-end.
Type of OS that use WAP
It can be built on any operating system including Palm OS,EPOC 32, Windows CE, FLEXOS, OS/9, Java O
WAP works with most Wireless networks such as:
CDPD, CDMA, GSM, PDC, PHS, TDMA, FLEX, ReFLEX, iDEN, TETRA, DECT, DataTAC, Mobitex.
WAP Introduction
Architecture overview
Components of WAP architecture
Applications, Advantages & Disadvantages of WAP
WWW programming model is optimized and
extended to match characteristics of the wireless
environment
Utilizes proxy technology to connect between the
wireless domain and WWW
CGI, Scripts,Etc.
Content
Web Server
Client
WAEUserAgent
Request(URL)
Response(Content)
Gateway
EncodersAnd Decoders
EncodedRequest
EncodedResponse
WAP Device
- Is used to access WAP applications and content. It might be a PDA,
handheld computer.
WAP Client
- Entity that receives content from Internet via a WAP Gateway. This is
usually the WAP Browser.
WAP Content/Origin/Application Server
- Element in the network where the information or web/WAP
applications resides.
WAP Proxy
- Acts both as a client and as a server in the network . Typically has
◦ Protocol gateway : translates requests from the WAP protocol stack
to WWW protocol stack
◦ Content encoders and decoders : translate WAP content into compact
encoded formats to reduce the size of data over the network
WAP Gateway
- Intermediary element used to connect two different types of network. It receives request directly from the clients as if it actually were the origin server that clients want to receive the information form. The clients are usually unaware that they are speaking to the Gateway.
WAP Browser
◦ Software running on the WAP device that interprets the WAP content arriving from the internet and decides how to display it on WAP device.
WML
o WML – Wireless Markup Language
o Is a tag language that allows the text portions of Web Pages to be presented on cellular phones and Personal Digital Assistants (PDAs) via wireless access.
o WML is used for delivering data to WAP devices, and is HTML- like in its appearance.
WAP Introduction
Architecture overview
Components of WAP architecture
Applications, Advantages & Disadvantages of WAP
Other ServicesAnd Applications
Transport Layer (WDP)
Security Layer (WTLS)
Transaction Layer (WTP)
Session Layer (WSP)
Application Layer (WAE)
GSM CDMA PHS IS-136 CDPD PDC-P FLEX Etc…
Bearers :
General-purpose application environment based on
a combination of WWW and mobile telephony
technologies.
It defines the user interface on the phone. It
contains WML and WTA (Wireless Telephony
Application).
Primary objective – interoperable environment.
WAE includes a micro-browser .Various
components of WAE are:
◦ Addressing model –uses URL & URI
◦ WML- similar feature like HTML
◦ WML script –For user I/P validation
◦ WTA(Wireless Telephony Application)
◦ Content formats
The WAP session protocol (WSP) layer provides a lightweight session layer to allow efficient exchange of data between applications.
Application layer with a consistent interface for two session services◦ Connection-oriented service that operates
above the transaction layer protocol (WTP)◦ Connectionless service that operates above a
secure or non-secure datagram service (WDP)
Optimized for low-bandwidth bearer networks with long latency
Establish and releasing a reliable session between client and server
Exchange content between client & server using compact encoding
Suspend & resume session
Provide HTTP 1.1 functionality
Exchange client & server session headers
Interrupt transactions in process
Push content from server to client in an unsynchronized manner
Light weight transaction-oriented protocol suitable for “ thin client”
Provides reliability to the datagram service through the use of unique transaction identifier , acknowledgements, retransmission duplicate removals
Basic unit of exchange is entire message
Allows asynchronous transaction
Three classes of transaction services Class 0: Unreliable one-way requests
Class 1: Reliable one-way requests
Class 2: Reliable two-way request-reply transactions
Based on industry-standard Transport Layer Security (TLS) protocol
Provides Transport layer security between WAP client & WAP Gateway/Proxy
WTLS can be used with both connectionless & connection oriented mode.
Optimized for use over narrow-band communication channels
Features:
◦ Data integrity
◦ Privacy
◦ Authentication
◦ Denial-of-service protection
Provides services and common interface to the upper layer
protocols and hence they function independent of the underlying
wireless network.
Services offered are
oApplication addressing by port numbers
ooptional segmentation and reassembly
ooptional error detection
The WAP datagram protocol (WDP) is the Transport layer that sends
and receives messages via any available bearer network, including
SMS, USSD, CSD, CDPD, IS–136 packet data, and GPRS.
Differing levels of quality of service with respect to
throughput, error rate, and delays
WAP protocols are designed to compensate for or
tolerate these varying levels of service :
o Short Message Service(SMS)
o Circuit Switched Data (CSD)
o Unstructured Supplementary Services Data (USSD)
o General Packet Radio Service(GPRS)
WAP Introduction
Architecture overview
Components of WAP architecture
Applications, Advantages & Disadvantages of WAP
Accessing Internet from mobile phones
Application to locate WAP customer geographically
Playing Games from mobile devices over wireless devices
Corporate Applications: Sales force automation where sales people
use their WAP enabled handsets to get instant, direct access to the
latest pricing, latest news, competitive information any time,
anywhere.
Online Services:
o Banking: Users can get their current balance, transfer funds
between accounts and receive fax of a mini-statement.
o Electronic Commerce: Subscribers can use their handset just like
their PC to purchase products and services over the Web.
Tele services
Prepaid Services: With a WAP-enabled phone, prepaid
subscribers can see their current balance with the press of a button.
By pressing another button, they can also recharge their account by
entering a credit card or voucher number into the handset.
Personal Productivity
Email: Using WAP users can keep track of their email right from
their handset.
- Others include: Interactive Chat,Auctions,Games
Most modern mobile devices support WAP
Real time send/receive data
Multiplatform functionality
open standard, vendor independent
network-standard independent
transport mechanism–optimized for wireless data bearers
Easy to write a program and control of web page appearance
application downloaded from the server, enabling fast service
creation and introduction, as opposed to embedded software
Low speed, security and very small user interface
Not very familiar to other users
Small screens: For web phones, there's an incredibly small viewing area; palmtops are barely better.
Speed of access: All devices have slow access.
Business model is expensive
Third party is included
Lack of user habit: It takes some patience and overcoming the learning curve to get the hang of it -- connecting, putting in an address, typing. Users just aren't used to the idea and protocol yet.