Chapter 11

Wireless networksISM frequencies, LANs, PANs, MANs

Contents

• Business role of wireless LANS (WLANs)• ISM frequency bands• 802.11a/b/g/n – WLANs/ Wi-Fi• 802.15 – Bluetooth Personal area networks• 802.16 – WiMax

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ISM 802.15 802.16802.11Utility

Business role of wireless networks

• Quick and easy networking

• In conjunction with laptops, networking everywhere

• Pilot programs on city-wide LANs• Historical buildings

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Concerns with wireless

• Primary concern is security

• Health

• Speed and reliability

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ISM 802.15 802.16802.11Utility

ISM frequency bands

• Wireless LANs are possible because of a very special category of wireless frequencies

• Normally, licenses needed for wireless transmission

• ISM bands are available for free, unlicensed use

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ISM 802.15 802.16802.11Utility

ISM frequency bands

• Most of the popular ISM bands are not commercially useful– Energy absorption by water vapor, foliage

• Microwave ovens operate at 2.45 GHz

• In the U.S., ISM bands are defined in part number 18, title 47 of the FCC rules– Code of federal regulations

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ISM frequency bandsISM frequency Band (tolerance)

6.78 MHz ±15.0 KHz

13.56 MHz ±7.0 KHz

27.12 MHz ±163.0 KHz

40.68 MHz ±20.0 KHz

915 MHz ±13.0 MHz

2.45 GHz ±50.0 MHz

5.8 GHz ±75.0 MHz

24.125 GHz ±125.0 MHz

61.25 GHz ±250.0 MHz

122.5 GHz ±500.0 MHz

245 GHz ±1.0 GHz

RC

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LAN

s

W i- M A X

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Wireless network categories

• Three categories– Local area networks

• 802.11 (wi-fi)

– Personal area networks• 802.15 (Bluetooth)

– Metropolitan area networks• 802.16 (Wi-max)

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ISM 802.15 802.16802.11Utility

wireless vs wired LANs

• No defined boundaries in wireless LANs– Geographical location does not define LAN

membership• Very unreliable medium

– Boundary is unobservable and can shift• Unprotected from co-existing signals on the

medium• All stations cannot hear each other

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ISM 802.15 802.16802.11Utility

Wireless LAN architecture

• Wireless LANs appear to higher layers (IP) as wired LANs– All imperfections of the medium are handled by the

physical layer itself

• Large WLANs are built from small blocks– Basic service set (BSS) covering a basic service area

(BSA)– BSSs are connected through distribution system

(DS) to create larger WLAN (extended service set)10

ISM 802.15 802.16802.11Utility

Wireless LAN architecture

DS

BSS 1

BSS 2

AP

AP

Laptop (station 1)

Laptop (station 4)

Station 2

Station 3

802.3 LAN

Portal

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Basic service set (BSS)

• When a wireless station moves from one BSS to another, upper layers are not aware of the change

• BSSs may overlap for redundancy• BSSs may be physically separated to

obtain coverage in selected areas12

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Access point (AP)

• An access point (AP) acts like a station on the BSS and enables access to the DS to associated wireless stations

• Stations (e.g. laptops) need to become associated with an access point (AP)

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Distribution system (DS)

• The DS directs traffic between multiple BSSs• 802.11 does not specify how DS should

distribute messages between APs• A DS can combine multiple BSSs to create a

wireless network of arbitrary size– Called a ESS (Extended service set)– DS not considered part of ESS

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Portal

• Data enters and leaves ESS at a portal

• When DS determines that destination is not in the ESS, it directs traffic to the portal

• All required frame format changes occur at the portal

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ISM 802.15 802.16802.11Utility

Security

• Unlike wired LANs, any receiver near the BSS can listen to traffic

• 802.11 defines three cryptographic techniques to protect data– WEP, TKIP, CCMP

• Default encryption mode is unencrypted

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MAC frame format

Data from IP layerand

Padding FC

S

0-2304 Bytes

4 Bytes

Direction of data flow

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A

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Seq

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con

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SS

AP

a

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ress

QoS

co

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2 Bytes

2 Bytes

6 Bytes 6 Bytes 6 Bytes 6 Bytes2 Bytes 2 Bytes

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802.11 Physical layer

• MAC layer in wireless LANs is designed to be independent of physical layer technology used

• Unlike other technologies, wireless LAN physical layer adds header to account for unreliable transmission

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Physical layer format

MAC layer data

Syn

c

He

ad

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err

or

che

ck

SF

D

Le

ng

th

Da

ta r

ate

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Popular 802.11 technologies

• 802.11 b/g (ch 14,15,18/ 19 in 802.11 standard)– 2.4 GHz– Upto 11 Mbps (b)/ 54 Mbps (g)– Frequency hopping spread spectrum, direct

sequence spread spectrum (b)/ DSSS-OFDM (g)• 802.11 a (ch 17 in 802.11 standard)

– 5 GHz– Upto 54 Mbps data rates– Orthogonal frequency division multiplexing

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802.11n

• Expected to be finalized in December 2009• Aims to provide upto 600 Mbps data rate

• Primary innovation is MIMO (multiple input multiple output)

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802.11n evolution

• http://grouper.ieee.org/groups/802/11/Reports/tgn_update.htm

• 4 candidate technologies voted in Nov ’04• TGn obtained required majority in Mar ’07• Technical and editorial issues in the standard

are being resolved

• Draft-n products on market today

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802.15 - Personal area networks

• Bluetooth– Communication over short distances (< 10m)

• Called personal operating space (POS)• All receivers within visual range

– Private, intimate group of participant devices– Focus on small, power-efficient, inexpensive

solutions

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Bluetooth vs. WLAN

• Not intended for dedicated computing devices

• Little or no direct connectivity to the world outside the link

• No infrastructure necessary (e.g. AP, DS)• Focus on long battery life and low cost

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Bluetooth architecture

• 2.4 GHz band• Data rate of 1 Mbps• Frequency hopping spread spectrum (FHSS)

modulation• Network unit is piconet

– One device, master, provides synchronization clock– All other devices are piconet slaves– All devices on a piconet share the same physical

channel

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Piconet architecture

• A number of independent piconets may exist in one location

• A device may be a slave on multiple piconets

• But master on only one piconet at a time• Participation in a scatternet does not imply

the ability to route between piconets

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Piconet architecture

• Each piconet has a different physical channel• Physical channel defined by

– Unique frequency hopping sequence– Slot timing of transmissions– Access code– Packet header encoding

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Bluetooth frame structure

Channel access code

Packet headerIncludes flow control, seq number, header error check (HEC)

Payload headerIncludes data length,

transport link ID

PayloadUser data such as IP packet, possibly

segmented by BluetoothCRC

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Device discovery

• Special physical channel for inquiry requests and responses

• Devices looking for nearby devices are called inquiring devices

• Devices willing to be found are called discoverable devices

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Device connection

• Once a pair of devices discover each other, connection procedure begins

• One device must be connectable

• Other device must page on connection channel of connectable device

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WLAN and WPAN co-existence

• 802.11b/g and 802.15 operate at 2.45GHz• Bluetooth signals interfere with WLAN• IEEE 802.15.2

– Two kinds of co-existence mechanisms to minimize interference

• Collaborative– 802.15 and 802.11 system communicate with each

other

• Non-collaborative

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WLAN and WPAN co-existence

• Collaborative– MAC layer

– Physical layer

• Non-collaborative– Transmitters sense channel conditions before

transmitting, avoid busy frequencies

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Bluetooth categories

• Normal data rate– 1 Mbps (802.15.1)

• High data rate– 20 Mbps (802.15.3)

– Efficient physical layer encoding techniques• Low data rate

– Remote control devices, home automation33

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Wireless MAN

• IEEE 802.16• Worldwide Interoperability for Microwave Access (WIMAX)

– Popular in developing countries for rural phone connectivity

• Original design goals– High-speed alternative to cable and DSL– Fixed base and subscriber stations– 20+Mbps upto 10+ miles

• Technology can now support mobile stations

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WIMAX goals

• Delivery of last mile wireless broadband access

• Fixed, nomadic, portable broadband connectivity• Typically, up to 40 Mbps per channel, for fixed and

portable access applications up to 6 miles– Enough bandwidth to simultaneously support hundreds of

businesses with T-1 speed connectivity– And thousands of residences with DSL speed connectivity

• Support for direct mobile access added (802.16e-2005)

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Fixed WIMAX data rates

QPSK32-45 Mbps

QAM 1664-90 Mbps

QAM 6496-134 Mbps

Base station

Subscriber station 1

Subscriber station 2

Subscriber station 3

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WIMAX vs WLAN

• Metropolitan area network vs LAN• Assumes a point-to-multipoint topology• Controlling base station• Subscriber stations not connected to each

other

• WIMAX may use both licensed and unlicensed frequencies

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Summary

• Why wireless networks are useful• Why different categories of wireless networks• ISM frequency bands• Comparisons between WLAN, WPAN and

WMAN

Case study – Oil industry

• Vertically integrated• Monitoring fuel levels in gas stations• Improved monitoring of pipelines

– Equivalent to adding 2% - 5% of refining capacity• Improved monitoring of remote oil pumps

Hands-on exercise

• AirPCap and Wireshark

Network design

• LAN network in Amsterdam– Technology choice