lecture1 - introduction to wireless lan

8/8/2019 Lecture1 - Introduction to Wireless LAN

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Introduction to Wireless LAN

Lecture 1

BTN 304 Wireless LAN

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Outline

y Communication Networks LAN (Local Area Network)

MAN (Metropolitan Area Network)

WAN (Wide Area Network)y Wireless Network

Popular 2.4 Ghz Standards

IEEE 802.11 Family


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Purpose of a CommunicationNetwork

y What is a data network for?

y A network is used to share things, such as: Applications

Printers

Files

y Wireless networks are used to share the same things thatwired networks do.


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Types of Communication Networks

y Traditional

Traditional local area network (LAN)

Traditional wide area network (WAN)

y Higher-speed High-speed local area network (LAN)

Metropolitan area network (MAN)

High-speed wide area network (WAN)


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Characteristics of WANs

y Covers large geographical areas

y Circuits provided by a common carrier

y Consists of interconnected switching nodes

yTraditional WANs provide modest capacity 64000 bps common

Business subscribers usingT-1 service 1.544 Mbps common

y Higher-speed WANs use optical fiber and transmissiontechnique known as asynchronous transfer mode (ATM)

10s and 100s of Mbps common


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Characteristics of LANs

y LAN interconnects a variety of devices and provides a meansfor information exchange among them

y Traditional LANs

Provide data rates of 1 to 20 Mbps

y High-speed LANS

Provide data rates of 100 Mbps to 1 Gbps


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Differences between LANs andWANs

y Scope of a LAN is smaller

LAN interconnects devices within a single building or cluster ofbuildings

y LAN usually owned by organization that owns the attacheddevices

For WANs, most of network assets are not owned by sameorganization

y Internal data rate of LAN is much greater


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The Need for MANs

y Traditional point-to-point and switched network techniquesused in WANs are inadequate for growing needs oforganizations

y Need for high capacity and low costs over large area

y MAN provides: Service to customers in metropolitan areas

Required capacity

Lower cost and greater efficiency than equivalent service fromtelephone company


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Speed and Distance ofCommunications Networks


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Wireless Network

y Can be used in any of these three types of networks:

LAN, MAN, and WAN

y Many wireless networks that are used to connect end users to

a central site as in a last mile solution are called wide areanetworks by some.

y This is not the case, despite popular usage

y Any network of that type is clearly a MAN

y

The only case where a wireless network is truly used as partof a WAN, are the long range point-to-point microwaveconnections used to span long distances


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Nature of Wireless Network

yWireless networks are fundamentally differentfrom those that use wires.

yWireless signals are unbounded and dynamic

yA wireless signals environment is quite similar to

a microclimate as used when discussing theweather


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yWeather and wireless networks are very similar,both suffer from the same problem.

y For the weather we know about the behavior of large

weather systems and climate in generalyWe can then predict that in the summer the weather

will be hot

y D

uring the monsoon, it will rain often


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y Problem with radio frequency networks as we havewith the weather network

y How radio frequency signals traverse the

environmentyWe cannot accurately predict what they will do or

not do from a base station antenna to an end userssite a few kilometers away

y The usual way of handling this problem for both theweather and radio frequency networks is a fademargin


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What Is Wireless Networking?

y The use of infra-red (IR) or radio frequency (RF)signals to share information and resources

between devices

yA hot computer industry buzzword:

Wireless Broadband, 3G wireless, 4G, WAP, iMode,Bluetooth, WiFi

y

Mobile Internet, Pervasive Computing,Nomadic Computing, M-commerce

Ubiquitous; Global; Revolutionary


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What is Wireless Networking?

y Is a network set up by usingradio signal frequency tocommunicate amongcomputers and other

network devices.

y Sometimes its also referredto as WiFi networkorWLAN.


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Two Popular 2.4 GHz Standards:

y IEEE 802.11

Fast (11b)

High Power

Long range Single-purpose

Ethernet replacement

Easily Available

Apple Airport, iBook, G4

Cisco Aironet 350

y Bluetooth

Slow

LowPower

Short range Flexible

Cable replacement


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WLANs: IEEE 802.11 Family

y 802.11 working group

Specify an open-air interface between a wireless client anda base station or access point, as well as among wireless

clients

y IEEE 802.11a

Up to 54 Mbps in the 5 GHz band

Uses orthogonal frequency division multiplexing (OFDM)


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IEEE 802.11b

y 802.11 standards 2 Mbps bandwidth not sufficientfor most network applications

y 802.11bamendment added two higher speeds (5.5

Mbps and 11 Mbps) to original 802.11 standard Uses ISM band

y Supports wireless devices up to 115 meters (375 feet)apart Radio waves decrease in power over distance

802.11b standard specifies that, when devices out of range totransmit at 11 Mbps, devices drop transmission speed to 5.5Mbps


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IEEE 802.11a

y IEEE802.11astandard specifies maximum ratedspeed of 54 Mbps

Also supports 48, 36, 24, 18, 12, 9,and 6 Mbps transmissionsusing U-NII band

y 802.11a and 802.11b published at same time

802.11a came to market later due to technical issues and highproduction cost

y

Range of 802.11a is less than that of 802.11b


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IEEE 802.11g

y Effort to combine best features of 802.11a and802.11b

Data transfer rates to 54 Mbps

Support devices up to 115 meters aparty 802.11g standard specifies that devices operate

entirely in ISM frequency


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Projected IEEE 802.11n

y Currently in evaluation stage

y Top speed of 802.11n standard will be anywhere from100 Mbps to 500 Mbps

y Ratification may not occur until 2006 Devices based on standard may appear prior to that

802.11 pre-N


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Pros and Cons of 802.11:

y Pro:

High bandwidth (up to 11 Mbps)

Two modes of operation: infrastructure vs. ad hoc

y Con: Incompatibility between old and new cards

Signal blocked by reinforced concrete or tinted glass

No standard for hand-off between base stations

Some channel numbers overlap spectrum

High power consumption in laptops


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Bluetooth

y Cable replacement technology

y Created by Ericsson

y PAN - Personal Area Network

1-2 Mbps connections 1600 hops per second FHSS

Includes synchronous, asynchronous, voiceconnections

y Small, low-power, short-range, cheap, versatileradios

y Used as Internet connection, phone, or headset

y Master/slave configuration and scheduling


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Future of Wireless

y Higher data rates

y Better security

y Wider selection of products

y Lower pricesy Zero configuration networking

y More end-user focus

y Better software

y Less visibley More popular


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Wireless Internet Technologies

y Mobile devices (e.g., laptops, PDAs, cell phones,wearable computers)

yWireless network access

Bluetooth (1 Mbps, up to 3 meters) IEEE 802.11b (11 Mbps, up to 100 meters)

IEEE 802.11a (55 Mbps, up to 20 meters)

y Operating modes:

Infrastructure mode (access point)Ad hoc mode

yWireless Web, WiFi hot spots


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Elements of a wireless network

Ad hoc mode

no base stations

nodes can only

transmit to othernodes within linkcoverage

nodes organizethemselves into a

network: routeamong themselves


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Wireless Link Characteristics

Differences from wired link . decreased signal strength: radio signal attenuates as it

propagates through matter (path loss)

interference from other sources: standardized

wireless network frequencies (e.g., 2.4 GHz) sharedby other devices (e.g., phone); devices (motors)interfere as well

multipath propagation: radio signal reflects off objects ground, arriving destination at slightly

different times. make communication across (even a point to point)

wireless link much more difficult


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Fixed Wireless

yMicrowave

Traditionally used in point-to-point communications

Initially, 1 GHz range, more recently in the 40 GHz region

y Local Multipoint Distribution Service(LMDS)

Operates around 30 GHz

Point-to-multipoint, with applications including Internetaccess and telephony


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Fixed Wireless

yMultichannel Multipoint DistributionService (MMDS)

Operates around 2.5 GHz

Initially, for TVdistribution

More recently, wireless residential Internet service


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Growth in Wireless Systems

y Rapid growth in cellular/PCS voice services overthe last decade Cell phones everywhere!

y Wireless data is a fast growing market with lots of

exciting action WLAN rapidly growing

802.11b, 802.11a, 802.11g, Bluetooth Wide area wireless data also growing

support for data in 2.5G and 3G wirelessWireless broadbandLocation-based services, WAP


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Favorable TechnologyTrends

y Availability of a pervasive data network (Internet)

y Innovative Internet-based applications and servicesparticularly useful to mobile users

personalized information retrieval, access to airline reservationssystems, online trading

y Terminal devices

compact size, low power, ease of use

next generation will have built-in wireless interfaces

y Emerging wide-area wireless packet data services aggregate data rates of several 100 kbps

TCP/IP-friendly link layer protocols


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Evolution in Information Systems

y Wiredpwireless, e.g. wired phonesp cellular

More freedom of location and timey Voice telephony, datapmultimedia

y Intelligent telecomp networked computing

Intelligence at the edges of the network

Programmable servers intermixed with switching infrastructure forrapid service deployment

y Networked computing is becoming pervasive

Personal

p

networkedp

mobilep

pervasive More flexible resource usage, more freedom of location and time,

more efficient flow of information

y Moving beyond phones and PCs

Embedded devices & sensor-based smart spaces


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WLAN Devices:Wireless Network Interface Card

y Network interface card (NIC): Connectscomputer to network so that it can send and receivedata

y Wireless NICs perform same function, but withoutwires

y When wireless NICs transmit: Change computers internal data from parallel to serial

transmission

Divide data into packets and attach sending and receivingcomputers address

Determine when to send packet

Transmit packet


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Network interface card for a wired network


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Wireless NICs for desktop computers: (a) PCI network interface

card, (b) standalone USB device, (c) USB key


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Wireless NICs for laptop computers: (a) CardBus card; (b) Mini PCI

card


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y For smaller devices, several options:

CardBus or Type II PC Card

May require a sled

CompactFlash (CF) card: Consists of small circuit boardcontaining flash memorychips and dedicated controller chip

Small and consume little power

SDIO (Secure Digital I/O) or SDIO NOW!Card:Provides high-speed data input/output with low power

consumption


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y A movement towards integrating wireless NICs

Would eliminate need for external wireless NICs

y Software drivers necessary to allow wireless NIC

and operating system (OS) to interface Windows XP and PDA OSs have built-in drivers


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WLAN Devices: Access Point

y Three major parts:

Antenna and radio transmitter/receiver

RJ-45 wired network interface

Special bridging software To interface wireless devices to other devices

y Two basic function:

Base station for wireless network

Bridge between wireless and wired networks


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An access point acts as a bridge between the wireless network and

a wired network


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y Range depends on several factors: Type of wireless network supported

Walls, doors, and other solid objects

y Number of wireless clients that single AP can supportvaries: Theoretically over 100 clients

No more than 50 for light network use

No more than 20 for heavy network use

y Power over Ethernet (PoE): Power delivered toAP through unused wires in standard unshieldedtwisted pair (UTP) Ethernet cable


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WLAN Devices: Remote Wireless Bridge

y Bridge: Connects two network segments together Even if they use different types of physical media

y Remote wireless bridge: Connects two or morewired or wireless networks together Transmit at higher power than WLAN APs

Use directional antennas to focus transmission in singledirection

Delay spread: Minimize spread of signal so that it can reachfarther distances

Have software enabling selection of clearest transmissionchannel and avoidance of noise and interference


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Point-to-point remote wireless bridge


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Point-to-multipoint remote wireless bridge


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y Four modes: Access point mode: Functions as standard AP

Root mode: Root bridge can only communicate with otherbridges not in root mode

Non-root mode: Can only transmit to another bridge in rootmode

Repeater mode: Extend distance between LAN segments

Placed between two other bridges

y Distance between buildings using remote wirelessbridges can be up to 18 miles at 11 Mbps or 25 milestransmitting 2 Mbps


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Root and non-root modes


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Repeater mode


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WLAN Devices: Wireless Gateway

y Combines wireless management and security insingle appliance

Authentication

Encryption Intrusion detection and malicious program protection

Bandwidth management

Centralized network management


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End of Lecture 1

- Introduction to Wireless LAN-

lecture1 - introduction to wireless lan

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