31/08/2012

INSTITUCION UNIVERSITARIA DE

ENVIGADO

Tecnología en Gestión de Redes 2012-1

Wireless LAN

What Are Wireless LANs?

They ARE:• Local, not wide area

• In-building or campus area coverage

• Up to several kilometers for point-to-point (LAN to LAN)

• Radio or infrared

• Mincomunicaciones licenses not required (ICM bands)

• Customer owns the equipment (no usage charges)

They ARE NOT:

• Cellular phones

• Pagers

• PCS

ISM (ICM) Unlicensed

Frequency Bands

Extremely

Low

Very

Low

Low Medium High Very

High

Infrared Visible

Light

Ultra-

violet

X-Rays

Audio

AM Broadcast

Short Wave Radio FM Broadcast

Television Infrared wireless LAN

Cellular (840MHz)NPCS (1.9GHz)

902-928 MHz

26 MHz

5 GHz

(IEEE 802.11)

HyperLAN

HyperLAN2

2.4 – 2.4835 GHz

83.5 MHz

(IEEE 802.11)

Ultra

High

Super

High

900MHz v.s. 2.4GHz v.s. 5GHz

900MHz band 2.4GHz band 5GHz band

PROs

CONs

Greater range than 2.4 GHz band ( for in-building LANs)

Global market

IEEE 802.11

Higher data rates (10+Mbps)

Global market

IEEE 802.11

Higher data rates (20+Mbps)

Less range than 900 MHz (for in-building LANs)

Maximum data rate 1 Mbps

Limited bandwidth

Crowded band

Much less Range than 900MHz or 2.4GHz

Higher cost RF components

Small objects interference

IEEE 802.11

Spread Spectrum Approaches

Both technologies are viable.

Direct Sequence Frequency Hopping

22

FREQUENCY

P

O

W

E

R

2.402 GHz 2.483 GHz

1 MwMhz

100 MwMhz

1 Ms

1 Sec

DS Spread Spectrum

Channels- 802.11 DS

(11) 22 MHz wide stationary channels

X “chips per bit” means each bit sent redundantly

11Mbps data rate

3 non-overlapping channels

3 Access Points can occupy same area

1 2 3 4 5 6 7 8 9 10 11

1

2

3

4

5

6

7

8

9

10

11

Channel

Frequency

2400 24832441

Frequency Hopping Spread

Spectrum

Frequency2.400 GHz 2.483 GHz

12

34

56

78

9

Tim

e

Frequency Hopping

• 79 channels, 1MHz

each

• Changes frequency

(hops) at least every

0.4 seconds

• Synchronized hopping

required

Time

DS v.s. FH: A Summary

on Interference Handling

FH system hops around interference

Lost packets are re-transmitted on next hop

Data may be decoded from redundant bits

Can move to an alternate channelto avoid interference

12

3F

req

uen

cy

2.4

00 G

Hz

2.4

83

5 G

Hz Direct Sequence

Channel 11

Channel 1

Channel 6

Fre

qu

en

cy

2.4

00 G

Hz

2.4

83

5 G

Hz

Frequency Hopping

Wireless “Ad Hoc” Network

Local Area Network (LAN)

Hub

Server Switch

Internet

Access PointHub

Wireless LAN (WLAN) as an

extension to wired LAN

Work Group Bridge

Access Point

Antennas

Radiation Pattern

Access Point Coverage

1Mbps DSSS

5.5Mbps DSSS

11Mbps DSSS

2Mbps DSSS

Channel Setup

Site Survey Channel Example

Channel 1

Channel 6

Channel 11

Channel 1

Channel 6

Channel 11

Channel 11

Channel 1

Channel 6

Channel 11

RF BarriersRF Barrier Attenuation Example

Air minimum

Wood Low Partitions

Plaster Low Office partitions

Synthetic Material Low Office patitions

Glass Low Windows

Water Medium Damp wood, aquarium

Bricks Medium Walls

Marble Medium Walls

Paper High Paper rolls

Concrete High Floors / Walls

Metal Very High Desk / partitions / elevator

Outdoor Wireless Bridges:

Applications

Companies•Connect buildings on corporate campus

•Cheaper than E1 (fast ROI)

•Cheaper than fiber

•Backup system for when cables get cut

Education•Public school system sharing WAN link

•Colleges expanding into leased facilities

•Connecting temporary classrooms

Municipal governments•Connect police, fire, city hall

•Public transportation (e.g. buses, metro cars, cable cabins)

Temporary broadband link•Construction sites

•Outdoor events

Interbuilding Bridges

Wireless LAN-to-LAN

• Wire line bypass

• Up to 54Mbps

• Faster than E1

• Line-of-sight up to 40 kms

• Point-to-Point

OR

• Point-to-Multipoint

• Supports Repeaters

Cost effective alternative to leased line/E1Rapid, simple deployment and re-deployment

No government license required

Point-to-Point Configuration

0 to 40 kms(Line of Sight)

Ethernet

Bridge

Directional

Antenna

Building A Building B

Directional

Antenna

Ethernet

Bridge

Point-to-Multipoint

Configuration

Omni-Directional

Antenna

Directional

Antenna

Ethernet

Bridge

Building B Building C

Ethernet

Bridge

Building A

WLAN “Alphabet Soup”:

IEEE 802.11 Standards Activities

802.11a: 5 GHz, 54 Mbps

802.11b: 2.4 GHz, 11 Mbps

802.11d: Multiple regulatory domains

802.11e: Quality of Service (QoS)

802.11f: Inter-Access Point Protocol (IAPP)

802.11g: 2.4 GHz, 54 Mbps

802.11h: Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC)

802.11i: Security

802.11k: Measurement

WECA

www.wirelessethernet.org

WECA certifies Interoperability between products.

This provides assurance to customers of migration and integration options.

Several Vendors are members of WECA.

Certified products can be found at www.wi-fi.com

WLAN Speeds & Frequencies

802.11g

2.4 GHz – OFDM/CCK

54 Mbps

Proprietary IEEE 802.11a/b

Ratified

802.11a

5 GHz – OFDM

54 Mbps

802.11b

2.4 GHz – CCK

11 Mbps

Jan’99 Jan’00 Jan’01 Jan’02 Jan’03 Jan’04

802.11a

Data rates supported: 54, 48, 36, 24, 12, and 6 Mbps•Client will automatically “downshift” to lower data rate when it gets further from AP

5 GHz band has more channels than 2.4 GHz band•UNII-1 + UNII-2 = 8 channels (vs. 3 channels for 2.4 GHz)

•However, depending on distance between APs, you may only be able to use half of the 5 GHz channels due to adjacent channel interference

5 GHz band subject to less interference than 2.4 GHz band

•However, 2.4 GHz interference not a major problem in most business environments

BW vs Distance

802.11g

2.4 GHz, up to 54 Mbps,

Full forward/backward compatibility with 802.11b

Wireless Technologies

PAN(Personal Area

Network)

LAN(Local Area Network)

WAN(Wide Area Network)

MAN(Metropolitan Area Network)

PAN LAN MAN WAN

Standards Bluetooth802.11

HiperLAN2802.11

MMDS, LMDSGSM, GPRS,

CDMA, 2.5-3G

Speed < 1Mbps 11 to 54 Mbps 11 to 100+ Mbps 10 to 384Kbps

Range Short Medium Medium-Long Long

ApplicationsPeer-to-Peer

Device-to-DeviceEnterprise networks

T1 replacement, last mile access

Mobile Phones, cellular data

IEEE WLAN Standandards

IEEE 802.11 vs HiperLAN 2

Sitios de Interés

www.wlana.org

www.wirelessethernet.org

www.cwne.com

www.54g.org

www.hiperlan2.com