chapter 11 wireless networks ism frequencies, lans, pans, mans
TRANSCRIPT
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Chapter 11
Wireless networksISM frequencies, LANs, PANs, MANs
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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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ISM 802.15 802.16802.11Utility
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 802.15 802.16802.11Utility
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
re m ot esW
LAN
s
W i- M A X
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ISM 802.15 802.16802.11Utility
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
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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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
MAC frame format
Data from IP layerand
Padding FC
S
0-2304 Bytes
4 Bytes
Direction of data flow
Fra
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Dur
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ID
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So
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So
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Seq
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con
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AP
a
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QoS
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2 Bytes
2 Bytes
6 Bytes 6 Bytes 6 Bytes 6 Bytes2 Bytes 2 Bytes
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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
Physical layer format
MAC layer data
Syn
c
He
ad
er
err
or
che
ck
SF
D
Le
ng
th
Da
ta r
ate
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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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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ISM 802.15 802.16802.11Utility
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
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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
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Hands-on exercise
• AirPCap and Wireshark
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Network design
• LAN network in Amsterdam– Technology choice