Chapter 2: Wireless LANs and PANs
 Introduction
 Fundamentals of WLANs
 IEEE 802.11 Standard
 HIPERLAN Standard
 Bluetooth
 HomeRF
1
Characteristics of wireless LANs
 Advantages
•
•
•
•
Flexibility: very flexible within the reception area
Planning: Ad-hoc networks without previous planning possible
Design: (almost) no wiring difficulties (e.g. historic buildings, firewalls)
Robustness: more robust against disasters like, e.g., earthquakes, fire or users
pulling a plug
• Cost: Adding additional users to a wireless network will not increase the cost.
 Disadvantages
• Quality of service: typically very low bandwidth compared to wired networks
(1-10 Mbit/s)
• Proprietary solutions: many proprietary solutions, especially for higher bitrates, standards take time (e.g. IEEE 802.11). Now, 802.11g is a popular
solution.
• Restrictions: products have to follow many national restrictions if working
wireless, it takes long time to establish global solutions like, e.g., IMT-2000
• Safety and security: Precautions have to be taken to prevent safety hazards.
Secrecy and integrity must be assured.
2
Fundamentals of WLANs
 Differences between wireless and wired transmission
•
•
•
•
Address is not equivalent to physical location
Dynamic topology and restricted connectivity
Medium boundaries are not well-defined
Error-prone medium
 Use of WLANs
• Users can access the Internet on the move.
• WLANs are handy in areas affected by earthquakes or other disasters.
• WLANs are good solutions in places where wiring may not be permitted.
3
Design goals for wireless LANs
 Operational simplicity
 Power-efficient operations
 License-free operation: no special permissions or licenses needed
to use the LAN
 Tolerance to interference
 Global usability
 Security: security (no one should be able to read my data), privacy
(no one should be able to collect user profiles),
 Safety requirement (low radiation)
 Quality of service requirements
 Compatibility with other technologies and applications
4
Comparison: Infrastructure vs. Ad-hoc
networks
 WLANs can be classified into two types:
• Infrastructure networks contains access points (APs) and mobile station
(STAs).
• Ad hoc LANs do not need any fixed infrastructure.
 Infrastructure networks
• Provide access to other networks
• Include forwarding functions
• Medium access control
 Ad-hoc networks is a group of computers each with wireless
adapters, connected as an independent wireless LAN.
• Each node can communicate with other nodes
5
Comparison: infrastructure vs. ad-hoc
networks
Infrastructure
Network
AP
AP
Wired network
AP: Access Point
AP
Ad-hoc network
6
802.11 Services
 Distribution Services (for APs)
• Association – mobile stations connect themselves to base stations
• Reassociation – a station may change its preferred base station
• Disassociation – the station or base station breaks the association
Distribution – determines how to route frames sent to the base station
• Integration – handles the translation from the 802.11 format to the format
of the destination network
 Intracell Services (for STAs and APs)
• Authentication – a station must authenticate itself before permitted to send
data.
• Deauthentication – a authenticated station wanting to leave the network is
deauthenticated.
• Privacy – manages the encryption and decryption. The algorithm specified
is RC4 by Ronald Rivest of MIT.
• Data Delivery – not reliable.
7
IEEE 802.11 Standard
 IEEE 802.11b is known as Wi-Fi (wireless Fidelity).
 Mobile Stations (MTs) can operate two modes:
• Infrastructure mode, in which MTs can communicate with one or more APs
which are connected to a WLAN.
• Ad hoc mode, in which MTs can communicate directly with each other
without using an AP.
 IEEE 802.11 supports two medium in the physical layer:
• Infrared
• Radio wave
 The physical layer is subdivided into physical medium dependent
(PMD) sublayer and physical layer convergence protocol (PLCP).
• IEEE 802.11 used CSMA/CD for MAC.
8
802.11 - Architecture of an infrastructure
network
802.11 LAN
STA1
802.x LAN
 Station (STA)
Portal
 Basic Service Set (BSS)
BSS1
Access
Point
Distribution System
Access
Point
ESS
• terminal with access mechanisms to
the wireless medium and radio
contact to the access point
• group of stations using the same
radio frequency
 Access Point (AP)
• station integrated into the wireless
LAN and the distribution system
 Portal
BSS2
• bridge to other (wired) networks
 Distribution System
STA2
802.11 LAN
STA3
• interconnection network to form
one logical network (EES:
Extended Service Set) based
9
on several BSS
802.11 - Architecture of an ad-hoc network
802.11 LAN
 Direct communication
within a limited range
STA1
• Station (STA):
terminal with access
mechanisms to the wireless
medium
• Independent Basic Service Set
(IBSS):
group of stations using the
same radio frequency
STA3
IBSS1
STA2
IBSS2
STA5
STA4
802.11 LAN
10
IEEE standard 802.11
fixed
terminal
mobile terminal
infrastructure
network
access point
application
application
TCP
TCP
IP
IP
LLC
LLC
LLC
802.11 MAC
802.11 MAC
802.3 MAC
802.3 MAC
802.11 PHY
802.11 PHY
802.3 PHY
802.3 PHY
11
Comparison: infrared vs. radio transmission
 Infrared
• uses IR (Infra-Red) diodes,
diffuse light, multiple
reflections (walls, furniture
etc.)
• Advantages
• simple, cheap, available in
many mobile devices
• no licenses needed
• simple shielding possible
• Disadvantages
• interference by sunlight,
heat sources etc.
• many things shield or
absorb IR light
• low bandwidth
• Example
• IrDA (Infrared Data
Association) interface
available everywhere
 Radio
• typically using the license free ISM
(Industrial, Scientific, Medical) band at
2.4 GHz
• Advantages
• experience from wireless WAN and
mobile phones can be used
• coverage of larger areas possible
(radio can penetrate walls, furniture
etc.)
• Disadvantages
• limited license free frequency bands
• shielding more difficult, interference
with other electrical devices
• Example
• WaveLAN (Lucent), HIPERLAN,
12
Bluetooth
802.11 - Layers and functions
 PMD (Physical Medium Dependent) : modulation, encoding/decoding (coding)
 PLCP (Physical Layer Convergence Protocol):
• provide a uniform abstract view for the MAC sublayer
• service access point (SAP) abstract the channel that offers up to 1 or 2 Mbps
• clear channel assessment (CCA) signal (carrier sense) used for CSMA/CA
LLC
MAC
MAC Management
PLCP
PHY Management
PMD
Station Management
DLC
PHY Management: channel selection, Management Information Base (MIB)
Station Management: coordination of all management functions
MAC: access mechanisms, fragmentation, encryption
MAC Management: synchronization, roaming, authentication, MIB, power
management
PHY




13
802.11 Physical Layers
 Infrared – 1 Mbps and 2 Mbps
• 850-950 nm, infra-red light, typical 10 m range, encoded using PPM
 FHSS (Frequency Hopping Spread Spectrum) uses 79 channels,
each 1 MHz wide, starting in the 2.4 GHz band.
• A psudorandom number generator is used to produce the sequence of
frequencies hopped to.
• The amount of time spent at each frequency, dwell time, is adjustable.
• spreading, despreading, signal strength, typical 1 Mbit/s
• min. 2.5 frequency hops/s (USA), 2-level GFSK modulation, 4-level GFSK
for 2Mbit/s
 DSSS (Direct Sequence Spread Spectrum) delivers 1 or 2 Mbps in
the 2.4 GHz band.
• DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying),
DQPSK for 2 Mbit/s (Differential Quadrature PSK)
• preamble and header of a frame is always transmitted with 1 Mbit/s, rest of
transmission 1 or 2 Mbit/s
• chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)
• max. radiated power 1 W (USA), 100 mW (EU), min. 1mW
14
802.11 - Physical layer
 802.11a uses OFDM (Orthogonal Frequency Division
Multiplexing) to deliver up to 54 Mbps in the 5 GHz band.
 Orthogonal Frequency Division Multiplexing, an FDM
modulation technique for transmitting large amounts of digital
data over a radio wave. OFDM works by splitting the radio signal
into multiple smaller sub-signals that are then transmitted
simultaneously at different frequencies to the receiver
 802.11b uses HR-DSSS (High Rate Direct Sequence Spread
Spectrum) to achieve 11 Mbps in the 2.4 GHz band.
 802.11g uses OFDM to achieve 54 Mbps in the 2.4 GHz band.
 The physical layer sensing is through the clear channel
assessment (CCA) signal provided by the PLCP. The CCA is
generated based on sensing of the air interface by:
• Sensing the detected bits in the air: more slowly but more reliable
• Checking the received signal strength (RSS): faster but no so precise
15
The 802.11 Protocol Stack
Part of the 802.11 protocol stack.
16
Orthogonal Frequency Division
Multiplexing (OFDM)
 OFDM, also called multicarrier modulation (MCM), uses multiple
carrier signals at different (lower) frequencies, sending some of the
c
bits on each channel.
k3
f
t
 The OFDM scheme uses advanced digital signal processing
techniques to distribute the data over multiple carriers at precise
frequencies.
• Suppose the lowest-frequency subcarrier uses the base frequency fb. The other
subcarriers are integer multiples of the base frequency, 2fb, 3fb, etc.
• The precise relationship among the subcarriers is referred to as orthogonality.
• The result is the maximum of one subcarrier frequency appears exactly at
17 a
frequency where all other subcarriers equal zero
Orthogonal Frequency Division
Multiplexing (OFDM)

Superposition of frequencies in the same frequency range
Amplitude
subcarrier:
sin(x)
SI function=
x
f
 Properties
• Lower data rate on each subcarrier  less intersymbol interference (ISI)
• interference on one frequency results in interference of one subcarrier only
• no guard space necessary
• orthogonality allows for signal separation via inverse FFT on receiver side
• precise synchronization necessary (sender/receiver)
 Advantages
• no equalizer necessary
• no expensive filters with sharp edges necessary
• better spectral efficiency (compared to CDM)
 Application: 802.11a, 802.11g, HiperLAN2, DAB (Digital Audio Broadcast),
18
DVB (Digital Video Broadcast), ADSL
802.11 FHSS PHY Packet Format
 Synchronization: synch with 010101... pattern
 SFD (Start Frame Delimiter): 0000110010111101 start pattern
 PLW (PLCP_PDU Length Word): length of payload incl. 32
bit CRC of payload, PLW < 4096
 PSF (PLCP Signaling Field): data of payload (1 or 2 Mbit/s)
 HEC (Header Error Check): CRC with x16+x12+x5+1
80
synchronization
16
12
4
16
variable
SFD
PLW
PSF
HEC
payload
PLCP preamble
bits
PLCP header
19
802.11 DSSS PHY Packet Format
 Synchronization: synch., gain setting, energy detection,
frequency offset compensation
 SFD (Start Frame Delimiter): 1111001110100000
 Signal: data rate of the payload (0A: 1 Mbit/s DBPSK; 14: 2
Mbit/s DQPSK)
 Service: future use, 00: 802.11 compliant
 Length: length of the payload
 HEC (Header Error Check): protection of signal, service and
length, x16+x12+x5+1
128
synchronization
16
SFD
PLCP preamble
8
8
16
16
signal service length HEC
variable
bits
payload
PLCP header
20
WLAN: IEEE 802.11a
 Data rate
• 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s,
depending on SNR
• User throughput (1500 byte packets):
5.3 (6), 18 (24), 24 (36), 32 (54)
• 6, 12, 24 Mbit/s mandatory
 Transmission range
• 100m outdoor, 10m indoor
• E.g., 54 Mbit/s up to 5 m, 48 up to
12 m, 36 up to 25 m, 24 up to 30m,
18 up to 40 m, 12 up to 60 m
 Frequency
• Free 5.15-5.25, 5.25-5.35, 5.725-5.825
GHz ISM-band
 Security
• Limited, WEP insecure, SSID
 Cost: Check market
 Availability
• Some products, some vendors
 Connection set-up time
• Connectionless/always on
 Quality of Service
• Typ. best effort, no guarantees
(same as all 802.11 products)
 Manageability
• Limited (no automated key
distribution, sym. Encryption)
 Special Advantages/Disadvantages
• Advantage: fits into 802.x
standards, free ISM-band,
available, simple system, uses less
crowded 5 GHz band
• Disadvantage: stronger shading
due to higher frequency, no QoS
• adapter (a/b/g combo) $70, base station
$160
21
IEEE 802.11a – PHY Frame Format
4
1
12
1
rate reserved length parity
6
16
tail service
variable
6
variable
payload
tail
pad
bits
PLCP header
PLCP preamble
12
signal
1
6 Mbit/s
data
variable
symbols
6, 9, 12, 18, 24, 36, 48, 54 Mbit/s
22
Operating channels for 802.11a / US U-NII
36
5150
40
44
48
52
56
60
64
5180 5200 5220 5240 5260 5280 5300 5320
channel
5350 [MHz]
16.6 MHz
149
153
157
161
channel
center frequency =
5000 + 5*channel number [MHz]
5725 5745 5765 5785 5805 5825 [MHz]
16.6 MHz
23
OFDM in IEEE 802.11a (and HiperLAN2)
 OFDM with 52 used subcarriers (64 in total)
 48 data + 4 pilot
 (plus 12 virtual subcarriers)
 312.5 kHz spacing
312.5 kHz
pilot
-26 -21
-7 -1 1
7
channel center frequency
21 26
subcarrier
number
24
WLAN: IEEE 802.11b
 Data rate
 Connection set-up time
• 1, 2, 5.5, 11 Mbit/s, depending on
• Connectionless/always on
SNR
 Quality of Service
• User data rate max. approx. 6 Mbit/s
• Typ. Best effort, no guarantees (unless
 Transmission range
polling is used, limited support in
• 300m outdoor, 30m indoor
products)
• Max. data rate ~10m indoor
 Manageability
 Frequency
• Free 2.4 GHz ISM-band
 Security
• Limited, WEP insecure, SSID
 Cost: Check market
• Adapter $30, base station $40
 Availability
• Many products, many vendors
• Limited (no automated key distribution,
sym. Encryption)
 Special Advantages/Disadvantages
• Advantage: many installed systems, lot
of experience, available worldwide, free
ISM-band, many vendors, integrated in
laptops, simple system
• Disadvantage: heavy interference on
ISM-band, no service guarantees, slow
relative speed only
25
IEEE 802.11b – PHY Frame Formats
Long PLCP PPDU format
128
16
synchronization
SFD
8
8
16
16
signal service length HEC
PLCP preamble
bits
variable
payload
PLCP header
192 µs at 1 Mbit/s DBPSK
1, 2, 5.5 or 11 Mbit/s
Short PLCP PPDU format (optional)
56
short synch.
16
SFD
8
8
16
16
signal service length HEC
PLCP preamble
(1 Mbit/s, DBPSK)
variable
bits
payload
PLCP header
(2 Mbit/s, DQPSK)
96 µs
2, 5.5 or 11 Mbit/s
26
Channel Selection (Non-overlapping)
Europe (ETSI)
channel 1
2400
2412
channel 7
channel 13
2442
2472
22 MHz
2483.5
[MHz]
US (FCC)/Canada (IC)
channel 1
2400
2412
channel 6
channel 11
2437
2462
22 MHz
2483.5
[MHz]
27
WLAN: IEEE 802.11g
 Data rate
• OFDM: 6, 9, 12, 18, 24, 36, 48, 54
Mbit/s CCK: 1, 2, 5.5, 11 Mbit/s
• User throughput (1500 byte packets):
5.3 (6), 18 (24), 24 (36), 32 (54)
• 6, 12, 24 Mbit/s mandatory
 Transmission range
• 300m outdoor, 30m indoor
• E.g., 54 Mbit/s up to 5 m, 48 up
to 12 m, 36 up to 25 m, 24 up to
30m, 18 up to 40 m, 12 up to 60
m
 Frequency
• Free 2.4 – 2.497 GHz ISM-band
 Security
• Limited, WEP insecure, SSID
 Cost: Check market
• Adapter $50, base station $50
 Availability
• more products, more vendors
 Connection set-up time
• Connectionless/always on
 Quality of Service
• Typ. best effort, no guarantees (same
as all 802.11 products)
 Manageability
• Limited (no automated key
distribution, sym. Encryption)
 Special Advantages/Disadvantages
• Advantage: fits into 802.x standards,
free ISM-band, available, simple
system
• Disadvantage: heavy interference on
ISM-band, no service guarantees
28
Wireless LAN Standard
Standard Modulation
Spectrum
Max physical Working
Rate
distance
2 Mbps
≈100 m
802.11a
WDM, FHSS 2.4 GHz
DSSS
OFDM
5 GHz
54 Mbps
≈ 50 m
802.11b
HR-DSSS
2.4 GHz
11 Mbps
≈ 200 m
802.11g
OFDM
2.4 GHz
54 Mbps
≈ 200 m
802.11
29
Wireless LANS Devices
 wireless router
 wireless network
30
card
Medium Access Control in Wireless LANs
• Because there is higher error rate and signal strength is not
uniform throughout the space in which wireless LANs operate,
carrier detection may fail in the following ways:
• Hidden nodes:
• Hidden stations: Carrier sensing may fail to detect another station. For
example, A and D.
• Fading: The strength of radio signals diminished rapidly with the
distance from the transmitter. For example, A and C.
• Exposed nodes:
• Exposed stations: B is sending to A. C can detect it. C might want to
send to E but conclude it cannot transmit because C hears B.
• Collision masking: The local signal might drown out the remote
transmission.
 An early protocol designed for wireless LANs is MACA (Multiple Access with
Collision Avoidance).
31
Wireless LAN configuration
A
B
C
Laptops
radio obs truc tion
Palmtop
Server
D
E
Wireles s
LAN
Base station/
ac cess point
LAN
32
The 802.11 MAC Sublayer Protocol
(a) The hidden station problem.
(b) The exposed station problem.
33
MACA and MACAW
 MACAW (MACA for Wireless) is a revision of MACA.
• The sender senses the carrier to see and transmits a RTS (Request To
Send) frame if no nearby station transmits a RTS.
• The receiver replies with a CTS (Clear To Send) frame.
• Neighbors
• see CTS, then keep quiet.
• see RTS but not CTS, then keep quiet until the CTS is back to the
sender.
• The receiver sends an ACK when receiving an frame.
• Neighbors keep silent until see ACK.
• Collisions
• There is no collision detection.
• The senders know collision when they don’t receive CTS.
• They each wait for the exponential backoff time.
34
MACA Protocol
The MACA protocol. (a) A sending an RTS to B.
(b) B responding with a CTS to A.
35
802.11 MAC Sublayer
 MAC layer tasks:
• Control medium access
• Roaming, authentication, power conservation
 Traffic services
• DCF (Distributed Coordination Function) (mandatory): Asynchronous
Data Service
• Only service available in ad-hoc network mode
• does not use any kind of central control
• exchange of data packets based on “best-effort”
• support of broadcast and multicast
• PCF (Point Coordination Function) (optional): Time-Bounded Service
• uses the base station to control all activity in its cell
36
802.11 MAC Sublayer
 PCF and DCF can coexist within one cell by carefully defining
the interframe time interval. The four intervals are depicted:
• SIFS (Short InterFrame Spacing) is used to allow the parties in a single
dialog the chance to go first including letting the receiver send a CTS and
an ACK and the sender to transmit the next fragment.
• PIFS (PCF InterFrame Spacing) is used to allow the base station to send
a beacon frame or poll frame.
• DIFS (DCF InterFrame Spacing) is used to allow any station to grab the
channel and to send a new frame.
• EIFS (Extended InterFrame Spacing) is used only by a station that has
just received a bad or unknown frame to report the bad frame.
 The result MAC scheme used in 802.11 is carrier sensing
multiple access with collision avoidance (CSMA/CA) that is
based on MACAW.
• Use NAV (Network Allocation Vector) to indicate the channel is busy.
37
The 802.11 MAC Sublayer Protocol
Interframe spacing in 802.11.
38
802.11 MAC Sublayer
 Access methods
• DFWMAC-DCF (distributed foundation wireless medium access controlDistributed Coordination Function) CSMA/CA (mandatory)
• collision avoidance via randomized „back-off“ mechanism
• minimum distance between consecutive packets
• ACK packet for acknowledgements (not for broadcasts)
• DFWMAC-DCF w/ RTS/CTS (optional)
• avoids hidden terminal problem
• DFWMAC- PCF (Point Coordination Function) (optional)
• access point polls terminals according to a list
• Completely controlled by the base station. No collisions occur.
• A beacon frame which contains system parameters is periodically (10
to 100 times per second) broadcasted to invite new stations to sign up
for polling service.
39
802.11 - CSMA/CA access method
DIFS
DIFS
medium busy
direct access if
medium is free  DIFS
contention window
(randomized back-off
mechanism)
next frame
t
slot time
 Station ready to send starts sensing the medium (Carrier Sense
based on CCA, Clear Channel Assessment)
 If the medium is free for the duration of an Inter-Frame Space
(IFS), the station can start sending (IFS depends on service type)
 If the medium is busy, the station has to wait for a free IFS, then
the station must additionally wait a random back-off time
(collision avoidance, multiple of slot-time)
 If another station occupies the medium during the back-off time
40
of the station, the back-off timer stops (fairness)
802.11 - Competing Stations
DIFS
DIFS
station1
station2
DIFS
boe
bor
boe
busy
DIFS
boe bor
boe
busy
boe busy
boe bor
boe
boe
busy
station3
station4
boe bor
station5
busy
bor
t
busy
medium not idle (frame, ack etc.)
boe elapsed backoff time
packet arrival at MAC
bor residual backoff time
41
802.11 - CSMA/CA access method
 Sending unicast packets
• station has to wait for DIFS before sending data
• receivers acknowledge at once (after waiting for SIFS) if the packet was
received correctly (CRC)
• automatic retransmission of data packets in case of transmission errors
DIFS
sender
data
SIFS
receiver
ACK
DIFS
other
stations
waiting time
data
t
contention
42
802.11 – DFWMAC
 Sending unicast packets
• station can send RTS with reservation parameter (transmission duration)
after waiting for DIFS (reservation determines amount of time the data
packet needs the medium)
• acknowledgement via CTS after SIFS by receiver (if ready to receive)
• sender can now send data at once, acknowledgement via ACK
• other stations set its net allocation vector (NAV) in accordance with the
duration field.
DIFS
sender
RTS
data
SIFS
receiver
other
stations
CTS SIFS
SIFS
NAV (RTS)
NAV (CTS)
defer access
ACK
DIFS
data
t
contention
43
Fragmentation
 The deal with the problem of noisy channels, 802.11 allows frames
to be fragmented.
DIFS
sender
RTS
frag1
SIFS
receiver
CTS SIFS
frag2
SIFS
ACK1 SIFS
SIFS
ACK2
NAV (RTS)
NAV (CTS)
other
stations
NAV (frag1)
NAV (ACK1)
DIFS
data
t
contention
44
DFWMAC-PCF
 A super frame comprises a contention-free period and a
contention period.
• D for downstream
• U for upstream
• CF for an end maker
t0 t1
medium busy PIFS
point
coordinator
wireless
stations
stations‘
NAV
SuperFrame
SIFS
D1
SIFS
SIFS
D2
SIFS
U1
U2
NAV
45
DFWMAC-PCF
t2
point
coordinator
wireless
stations
stations‘
NAV
D3
PIFS
SIFS
D4
t3
t4
CFend
SIFS
U4
NAV
contention free period
contention
period
t
46
802.11 MAC Frame format
 Types
• control frames, management frames, data frames
 Sequence numbers
• important against duplicated frames due to lost ACKs
 Addresses
• receiver, transmitter (physical), BSS identifier, sender (logical)
 Miscellaneous
• sending time, checksum, frame control, data
bytes
2
2
6
6
6
2
6
Frame Duration/ Address Address Address Sequence Address
Control
ID
1
2
3
Control
4
bits
2
2
4
1
1
1
1
1
1
1
0-2312
4
Data
CRC
1
Protocol
To From More
Power More
Type Subtype
Retry
WEP Order
version
DS DS Frag
Mgmt Data
47
MAC address format
scenario
ad-hoc network
infrastructure
network, from AP
infrastructure
network, to AP
infrastructure
network, within DS
to DS from
DS
0
0
0
1
address 1 address 2 address 3 address 4
DA
DA
SA
BSSID
BSSID
SA
-
1
0
BSSID
SA
DA
-
1
1
RA
TA
DA
SA
DS: Distribution System
AP: Access Point
DA: Destination Address
SA: Source Address
BSSID: Basic Service Set Identifier
RA: Receiver Address
TA: Transmitter Address
 Ad-hoc network: packet exchanged between two wireless nodes without a
distribution system
 Infrastructure network, from AP: a packet sent to the receiver via the access point
 Infrastructure network, to AP: a station sends a packet to another station via the
access point
 Infrastructure network, within DS: packets transmitted between two access points
over the distribution system.
48
Special Frames: ACK, RTS, CTS
 Acknowledgement
ACK
bytes
2
2
6
Frame
Receiver
Duration
Control
Address
4
CRC
bytes
 Request To Send
RTS
2
2
6
6
Frame
Receiver Transmitter
Duration
Control
Address Address
bytes
 Clear To Send
CTS
2
2
6
Frame
Receiver
Duration
Control
Address
4
CRC
4
CRC
49
802.11 - MAC management
 Synchronization
• try to find a LAN, try to stay within a LAN
• Synchronize internal clocks and generate beacon signals
 Power management
• periodic sleep, frame buffering, traffic measurements
• sleep-mode without missing a message
 Roaming for Association/Reassociation
• integration into a LAN
• roaming, i.e. change networks by changing access points
• scanning, i.e. active search for a network
 MIB - Management Information Base
• All parameters representing the current state of a wireless station and an
access point are stored in a MIB.
• A MIB can be accessed via SNMP.
50
Synchronization using a Beacon
(infrastructure)
 Timing synchronization function (TSF) is needed for:
• Power management
• Coordination of the PCF and for synchronization of the hopping
sequence
 A beacon contains a timestamp and other management
information.
 The access point tries to schedule transmissions according to
the excepted beacon interval (target beacon transmission time).
beacon interval
access
point
medium
B
B
busy
busy
B
busy
B
busy
t
value of the timestamp
B
beacon frame
51
Synchronization using a Beacon (ad-hoc)
 The standard random backoff algorithm is also applied to the
beacon frames in the ad-hoc networks.
beacon interval
station1
B1
B1
B2
station2
medium
busy
busy
B2
busy
busy
t
value of the timestamp
B
beacon frame
random delay
52
Power management
 Idea: switch the transceiver off if not needed
 States of a station: sleep and awake
 Timing Synchronization Function (TSF)
• stations wake up at the same time
 Infrastructure
• Traffic Indication Map (TIM)
• list of unicast receivers transmitted by AP
• Delivery Traffic Indication Map (DTIM)
• list of broadcast/multicast receivers transmitted by AP
 Ad-hoc
• Ad-hoc Traffic Indication Map (ATIM)
• announcement of receivers by stations buffering frames
• more complicated - no central AP
• collision of ATIMs possible (scalability?)
53
Power saving with wake-up patterns
(infrastructure)
TIM interval
access
point
DTIM interval
D B
T
busy
medium
busy
T
d
D B
busy
busy
p
station
d
t
T
TIM
D
B
broadcast/multicast
DTIM
awake
p PS poll
d data transmission
to/from the station
54
Power saving with wake-up patterns (adhoc)
ATIM
window
station1
beacon interval
B1
station2
A
B2
B2
D
a
B1
d
t
B
beacon frame
awake
random delay
a acknowledge ATIM
A transmit ATIM
D transmit data
d acknowledge data
55
802.11 - Roaming
 Roaming: moving from one access point to another
 No or poor connection? Then perform:
 Scanning
• scan the environment, i.e., listen into the medium for beacon signals or send
probes into the medium and wait for an answer
 Reassociation Request
• station sends a request to one or several AP(s)
 Reassociation Response
• success: AP has answered, station can now participate
• failure: continue scanning
 AP accepts Reassociation Request
• signal the new station to the distribution system
• the distribution system updates its data base (i.e., location information)
• typically, the distribution system now informs the old AP so it can release
56
resources
WLAN: IEEE 802.11 – Current and Future
Developments
 802.11c provides required information to ensure proper bridge
operations.
 802.11d: Regulatory Domain Update – completed in 2001, amended in
2003
 802.11e: MAC Enhancements – QoS – ongoing
• Enhance the current 802.11 MAC to expand support for applications with Quality
of Service requirements, and in the capabilities and efficiency of the protocol.
 802.11f: Inter-Access Point Protocol – completed in 2003
• Establish an Inter-Access Point Protocol for data exchange via the
distribution system.
 802.11h: Spectrum Managed 802.11a (DCS, TPC) – completed in 2003
 802.11i: Enhanced Security Mechanisms – completed in 2004
• Enhance the current 802.11 MAC to provide improvements in security and replace
57
Wired Equivalent Privacy (WEP).
ETSI - HIPERLAN
 ETSI standard
• European standard, cf. GSM, DECT, ...
• Enhancement of local Networks and interworking with fixed networks
• integration of time-sensitive services from the early beginning
 HIPERLAN family
• one standard cannot satisfy all requirements
• range, bandwidth, QoS support
• commercial constraints
• HIPERLAN 1 standardized since 1996 – no products!
higher layers
medium access
control layer
channel access
control layer
physical layer
HIPERLAN layers
network layer
data link layer
physical layer
OSI layers
logical link
control layer
medium access
control layer
physical layer
IEEE 802.x layers
58
Overview: original HIPERLAN protocol
family
Application
Frequency
Topology
Antenna
Range
QoS
Mobility
Interface
Data rate
Power
conservation
HIPERLAN 1
wireless LAN
HIPERLAN 2
access to ATM
fixed networks
HIPERLAN 3
wireless local
loop
HIPERLAN 4
point-to-point
wireless ATM
connections
17.2-17.3GHz
point-to-point
5.1-5.3GHz
decentralized adcellular,
point-tohoc/infrastructure
centralized
multipoint
omni-directional
directional
50 m
50-100 m
5000 m
150 m
statistical
ATM traffic classes (VBR, CBR, ABR, UBR)
<10m/s
stationary
conventional LAN
ATM networks
23.5 Mbit/s
>20 Mbit/s
yes
155 Mbit/s
not necessary
HIPERLAN 1 never reached product status,
the other standards have been renamed/modfied !
59
HIPERLAN - Characteristics
 Data transmission
• point-to-point, point-to-multipoint, connectionless
• 23.5 Mbit/s, 1 W power, 2383 byte max. packet size
 Services
• asynchronous and time-bounded services with hierarchical priorities
• compatible with ISO MAC
 Topology
• infrastructure or ad-hoc networks
• transmission range can be larger then coverage of a single node
(„forwarding“ integrated in mobile terminals)
 Further mechanisms
• power saving, encryption, checksums
60
Bluetooth
 Idea
• The need to interconnect computer and peripherals, handheld devices, PDAs,
cell phones – replacement of IrDA led to the emergence of personal area
networks (PANs)
• Universal radio interface for ad-hoc wireless connectivity
• Embedded in other devices, goal: $5/device (2005: $40 bluetooth headset)
• Short range (10 m), low power consumption, license-free 2.45 GHz ISM
• Voice and data transmission, approx. 1 Mbit/s gross data rate
One of the first modules (Ericsson).
61
Bluetooth
 History
• 1994: Ericsson (Mattison/Haartsen), “MC-link” project
• Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen
[son of Gorm], King of Denmark in the 10th century
(was:
• 1998: foundation of Bluetooth SIG, www.bluetooth.org
• 1999: erection of a rune stone at Ercisson/Lund ;-)
• 2001: first consumer products for mass market, spec. version 1.1 released
• Nov. 8, 2004 (Overland Park, KS): Version 2.0 + EDR (Enhanced Data
Rate) is announced. Up to 3 Mbps.
 Bluetooth Special Interest Group (SIG)
•
•
•
•
Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba
Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola
> 2500 members
Common specification and certification of products
 IEEE founded IEEE 802.15 for Wireless Personal Area Networks
(WPAN) and approved a Bluetooth-based standard.
62
)
History and Hi-Tech…
1999:
Ericsson mobile
communications AB
reste denna sten till
minne av Harald
Blåtand, som fick ge
sitt namn åt en ny
teknologi för trådlös,
mobil kommunikation.
63
…and the real rune stone
Located in Jelling, Denmark,
erected by King Harald “Blåtand”
in memory of his parents.
The stone has three sides – one side
showing a picture of Christ.
Inscription:
"Harald king executes these sepulchral
monuments after Gorm, his father and
Thyra, his mother. The Harald who won the
whole of Denmark and Norway and turned
the Danes to Christianity."
Btw: Blåtand means “of dark complexion”
(not having a blue tooth…)
This could be the “original” colors
of the stone.
Inscription:
“auk tani karthi kristna” (and
made the Danes Christians)
64
Characteristics
 2.4 GHz ISM band, 79 RF channels, 1 MHz carrier spacing
• Channel 0: 2402 MHz … channel 78: 2480 MHz
• GFSK modulation, 1-100 mW transmit power
 FHSS and TDD
• Frequency hopping with 1600 hops/s
• Hopping sequence in a pseudo random fashion, determined by a master
• Time division duplex for send/receive separation
 Two type of links:
• Voice link – SCO (Synchronous Connection Oriented)
• FEC (forward error correction), no retransmission, 64 kbit/s duplex, pointto-point, circuit switched
• Data link – ACL (Asynchronous Connectionless)
• Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s
symmetric or 723.2/57.6 kbit/s asymmetric, packet switched
 Topology: Overlapping piconets (stars) forming a scatternet
65
Protocol Specification
 The Bluetooth specification can be divided into:
• A core specification which describes the protocols from physical layer to the
data link control
• Profile specifications describe many protocols and functions need to adapt
the wireless Bluetooth technology to legacy and new applications.
 The protocol stack of Bluetooth is logically partitioned into three
layers: the core protocol group, the middleware group, and the
application group.
 The transport protocol group comprise the following elements:
• Radio: specification of the air interface – frequencies, modulation, power
• Baseband: connection establishment, packet formats, timing, QoS
• Link management protocol: link set-up and management between devices
including security functions and parameter negotiation
• Logical link control and adaptation protocol (L2CAP): adaptation of higher
layers to the baseband
• Service discovery protocol: Device discovery plus querying of service
characteristics
66
Bluetooth Specification
 The Bluetooth specification can be divided into:
• A core specification which describes the protocols from physical layer to the
data link control
• Profile specifications describe many protocols and functions need to adapt
the wireless Bluetooth technology to legacy and new applications.
 The core protocols comprise the following elements:
• Radio: specification of the air interface – frequencies, modulation, power
• Baseband: connection establishment, packet formats, timing, QoS
• Link management protocol: link set-up and management between devices
including security functions and parameter negotiation
• Logical link control and adaptation protocol (L2CAP): adaptation of higher
layers to the baseband
67
Bluetooth Specification
 The middleware protocol group comprises of:
• Radio Frequency Communications (RFCOMM) emulates a serial line
interface such as EIA-232 or RS-232
• Service discovery protocol (SDP): Device discovery plus querying of service
characteristics
• Infrared Data Association (IrDA)
• The telephony control protocol specification – binary (TCS BIN) describes a
bit-oriented protocol that defines voice and data calls between Bluetooth
devices.
• The host controller interface (HCI) provides a command interface to the
baseband controller and link manager, and access to the hardware status and
control registers.
• TCP/IP can run on PPP or Bluetooth network encapsulation protocol (BNEP).
 The application group consists of applications:
• Modem dialer
• Web-browsing client
• Calendar and business card objects (vCalendar/vCard) can be exchanged
68
using the object exchange protocol (OBEX).
Bluetooth protocol stack
audio apps.
NW apps.
vCal/vCard
TCP/UDP
OBEX
telephony apps.
AT modem
commands
IP
mgmnt. apps.
TCS BIN
SDP
BNEP PPP
Control
RFCOMM (serial line interface)
Audio
Logical Link Control and Adaptation Protocol (L2CAP)
Link Manager
Host
Controller
Interface
Baseband
Radio
AT: attention sequence
OBEX: object exchange
TCS BIN: telephony control protocol specification – binary
BNEP: Bluetooth network encapsulation protocol
SDP: service discovery protocol
RFCOMM: radio frequency comm.
69
Forming a Bluetooth Network: Piconet
 Collection of devices connected in an
ad hoc fashion
 One unit acts as master and the others
as slaves for the lifetime of the piconet
 Master determines hopping pattern,
slaves have to synchronize
 Each piconet has a unique hopping
pattern
 Participation in a piconet =
synchronization to hopping sequence
 Each piconet has one master and up to
7 simultaneous slaves (> 200 could be
parked)
P
S
S
M
P
SB
S
P
M=Master
S=Slave
SB
P=Parked
SB=Standby
70
Forming a Piconet
 All devices in a piconet hop together
• Master gives slaves its clock and device ID
• Hopping pattern: determined by device ID (48 bit, unique worldwide)
• Phase in hopping pattern determined by clock
 Addressing
• Active Member Address (AMA, 3 bit)
• Parked Member Address (PMA, 8 bit)
SB
SB
SB 
SB
SB
SB
SB
SB 
SB
S
SB
P 
S
M
P
S
P 
SB
71
Scatternet
 Linking of multiple co-located piconets through the sharing of
common master or slave devices
• Devices can be slave in one piconet and master of another
• As soon as a master leaves a piconnet, all traffic within this piconet is
suspended until the master returns.
 Communication between piconets
• Devices jumping back and forth between the piconets
P
S
S
S
P
P
M
M=Master
S=Slave
P=Parked
SB=Standby
Piconets
(each with a
capacity of
< 1 Mbit/s)
M
SB
S
P
SB
SB
S
72
Oprational States of a Bluetooth Device
unconnected
standby
detach
inquiry
transmit
AMA
park
PMA
page
connected
AMA
hold
AMA
Standby: do nothing
Inquire: search for other devices
Page: connect to a specific device
but a piconet is not formed yet.
Connected: participate in a piconet
sniff
AMA
connecting
active
low power
Park: release AMA, get PMA
Sniff: listen periodically, not each slot
Hold: stop ACL, SCO still possible, possibly
participate in another piconet
73
Radio and Baseband Layer
 The time between two hops is called a slot, which is an interval of
625 µs.
 Bluetooth transceivers use Gaussian FSK for modulation in three
classes:
• Power class 1: 1 – 100 mW, 100 m
• Power class 2: 0.25 mW – 2.5 mW, 10 m
• Power class 3: maximum 1 mW
 TDD is used for separation of the transmission directions. 1-slot,
3-slot, and 5-slot packets are available.
 The packet consists of three fields:
• Access code
• Packet header
• Payload
74
625 µs
fk
M
Frequency selection during data
transmission
fk+1
fk+2
fk+3
fk+4
fk+5
fk+6
S
M
S
M
S
M
t
fk
fk+3
fk+4
fk+5
fk+6
M
S
M
S
M
t
fk
fk+1
M
S
fk+6
M
t
75
Baseband
 Piconet/channel definition
 Low-level packet definition
• Access code
• Channel, device access, e.g., derived from master
• Packet header
• 1/3-FEC, active member address (broadcast + 7 slaves), link
type, alternating bit ARQ/SEQ, checksum
68(72)
54
0-2745
access code packet header
4
preamble
64
sync.
(4)
3
(trailer) AM address
bits
payload
4
1
1
1
8
type
flow
ARQN
SEQN
HEC
bits
76
SCO (Synchronous ConnectionOriented) payload types
 Bluetooth offers two types of links:
• Synchronous connection-oriented link for classical telephone (voice)
connections: HV (High quality Voice), DV (Data and Voice)
• Asynchronous connectionless link for typical data applications: DM1
(Data Medium rate) and DH3 (Data High rate) with 3 slots
payload (30)
HV1
audio (10)
HV2
audio (20)
HV3
DV
FEC (20)
FEC (10)
audio (30)
audio (10)
header (1)
payload (0-9)
2/3 FEC
CRC (2)
(bytes)
77
ACL (Asynchronous connectionless
Link) Payload types
payload (0-343)
header (1/2)
DM1 header (1)
DH1 header (1)
DM3
header (2)
DH3
header (2)
DM5
header (2)
DH5
header (2)
AUX1 header (1)
payload (0-339)
payload (0-17)
2/3 FEC
payload (0-27)
payload (0-121)
CRC (2)
(bytes)
CRC (2)
2/3 FEC
payload (0-183)
payload (0-224)
payload (0-339)
payload (0-29)
CRC (2)
CRC (2)
CRC (2)
2/3 FEC
CRC (2)
CRC (2)
78
Baseband data rates
ACL
1 slot
3 slot
5 slot
SCO
Type
Payload User
Header Payload
[byte]
[byte]
FEC
CRC
Symmetric Asymmetric
max. Rate max. Rate [kbit/s]
[kbit/s]
Forward
Reverse
DM1
1
0-17
2/3
yes
108.8
108.8
108.8
DH1
1
0-27
no
yes
172.8
172.8
172.8
DM3
2
0-121
2/3
yes
258.1
387.2
54.4
DH3
2
0-183
no
yes
390.4
585.6
86.4
DM5
2
0-224
2/3
yes
286.7
477.8
36.3
DH5
2
0-339
no
yes
433.9
723.2
57.6
AUX1
1
0-29
no
no
185.6
185.6
185.6
HV1
na
10
1/3
no
64.0
HV2
na
20
2/3
no
64.0
HV3
na
30
no
no
64.0
DV
1D
10+(0-9) D 2/3 D yes D
64.0+57.6 D
Data Medium/High rate, High-quality Voice, Data and Voice
79
Baseband link types
 Polling-based TDD packet transmission
• 625µs slots, master polls slaves
 SCO (Synchronous Connection Oriented) – Voice
• Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point
 ACL (Asynchronous ConnectionLess) – Data
• Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint
MASTER
SLAVE 1
SLAVE 2
SCO
f0
ACL
f4
SCO
f6
f1
ACL
f8
f7
f5
SCO
f12
f9
ACL
f14
SCO
f18
f13
ACL
f20
f19
f17
f21
80
Robustness
 Slow frequency hopping with hopping patterns determined by a
master
• Protection from interference on certain frequencies (FHSS)
• Separation from other piconets (FH-CDMA)
 Retransmission
Error in payload
(not header!)
• ACL only, very fast
 Forward Error Correction
NAK
• SCO and ACL
MASTER
SLAVE 1
SLAVE 2
A
C
B
C
D
F
ACK
H
E
G
G 81
Link manager protocol
 The link manager protocol (LMP) has the following functions:
•
•
•
•
•
•
•
Authentication, pairing, and encryption
Synchronization
Capability negotiation: negotiate
Quality of service negotiation
Power control
Link supervision
State and transmission mode change
 Major baseband states are: Standby, inquiry, page, active, low
power
 To save battery power, a Bluetooth device can go into one of three
low power states:
•
•
•
•
Active: A Bluetooth device actively participates in the piconet.
Sniff: listen periodically, not each slot
Hold: stop ACL, SCO still possible, possibly participate in another piconet
82
Park: release AMA, get PMA



















Example: Power consumption/CSR
BlueCore2
Typical Average Current Consumption (1)
VDD=1.8V Temperature = 20°C
Mode
SCO connection HV3 (1s interval Sniff Mode) (Slave)
26.0 mA
SCO connection HV3 (1s interval Sniff Mode) (Master)
26.0 mA
SCO connection HV1 (Slave)
53.0 mA
SCO connection HV1 (Master)
53.0 mA
ACL data transfer 115.2kbps UART (Master)
15.5 mA
ACL data transfer 720kbps USB (Slave)
53.0 mA
ACL data transfer 720kbps USB (Master)
53.0 mA
ACL connection, Sniff Mode 40ms interval, 38.4kbps UART
4.0 mA
ACL connection, Sniff Mode 1.28s interval, 38.4kbps UART
0.5 mA
Parked Slave, 1.28s beacon interval, 38.4kbps UART
0.6 mA
Standby Mode (Connected to host, no RF activity)
47.0 µA
Deep Sleep Mode(2)
20.0 µA
Notes:
(1) Current consumption is the sum of both BC212015A and the flash.
(2) Current consumption is for the BC212015A device only.
(More: www.csr.com )
83
Example: Bluetooth/USB adapter (2005:
$10)
84
L2CAP - Logical Link Control and
Adaptation Protocol
 Simple data link protocol on top of baseband
 Connection oriented, connectionless, and signalling channels
 Protocol multiplexing
• RFCOMM (Radio Frequency Communication), SDP (Service Discovery
Protocol), telephony control
 Segmentation & reassembly
• Up to 64 kbyte user data, 16 bit CRC used from baseband
 QoS flow specification per channel
• Follows RFC 1363, specifies delay, jitter, bursts, bandwidth
 Group abstraction
• Create/close group, add/remove member
85
L2CAP logical channels
Master
Slave
L2CAP
L2CAP
2
d
L2CAP
1
1 d d d d 1
baseband
signalling
Slave
baseband
ACL
connectionless
1
d
d
baseband
connection-oriented
 The master has a bi-directional signaling channel (CID 1).
 The master maintains a connectionless, unidirectional channel to
both slaves (CID 2).
 The master has one connection oriented channel to the left slave
and two to the right slave.
86
2
L2CAP packet formats
Connectionless PDU
2
2
2
0-65533
length
CID=2
PSM
payload
bytes
Connection-oriented PDU
2
2
0-65535
length
CID
payload
bytes
Signalling command PDU
2
2
length
CID=1
bytes
One or more commands
1
1
2
0
code
ID
length
data
87
Security
 Paring – user input a secret PIN into both devices
 Authentication – link keys are typically stored in a persistent
storage
 Encryption – the device address and the current clock are generated
for ciphering user data
 Ciphering – simple XOR of the user data and the payload key
88
Security
User input (initialization)
PIN (1-16 byte)
Pairing
PIN (1-16 byte)
E2
Authentication key generation
(possibly permanent storage)
E2
link key (128 bit)
Authentication
link key (128 bit)
E3
Encryption key generation
(temporary storage)
E3
encryption key (128 bit)
Encryption
encryption key (128 bit)
Keystream generator
Keystream generator
payload key
Ciphering
payload key
Cipher data
Data
Data
89
Middleware Protocol Group: SDP
 Bluetooth needs to know what devices or services are available in
radio proximity.
 SDP is a Inquiry/response protocol for discovering services
• Searching for and browsing services in radio proximity
• Adapted to the highly dynamic environment
• Can be complemented by others like SLP (Service Location Protocol), Jini,
Salutation, …
• Defines discovery only, not the usage of services
• Caching of discovered services
• Gradual discovery
 Service record format
• Information about services provided by attributes
• Attributes are composed of an 16 bit ID (name) and a value
• values may be derived from 128 bit Universally Unique Identifiers (UUID)
90
Middleware Protocol Group
 RFCOMM
• Emulation of a serial port (supports a large base of legacy applications)
• Allows multiple ports over a single physical channel
 Telephony Control Protocol Specification (TCS)
• Call control (setup, release)
• Group management
 OBEX (Object Exchange)
• Exchange of objects, IrDA replacement
 WAP
• Interacting with applications on cellular phones
91
Profiles
• Vertical slice through the protocol stack
• Basis for interoperability













Applications
Protocols
 Represent default solutions for a certain usage model
Generic Access Profile
Service Discovery Application Profile
Cordless Telephony Profile
Intercom Profile
Additional Profiles
Serial Port Profile
Advanced Audio Distribution
Headset Profile
PAN
Dial-up Networking Profile
Audio Video Remote Control
Basic Printing
Fax Profile
Basic Imaging
LAN Access Profile
Extended Service Discovery
Generic Object Exchange Profile Generic Audio Video Distribution
Object Push Profile
Hands Free
Hardcopy Cable Replacement
File Transfer Profile
Synchronization Profile
Profiles
92
WPAN: IEEE 802.15.1 – Bluetooth
 Data rate
• Synchronous, connection-oriented: 64
kbit/s
• Asynchronous, connectionless
• 433.9 kbit/s symmetric
• 723.2 / 57.6 kbit/s asymmetric
 Transmission range
• POS (Personal Operating Space) up to 10
m
• with special transceivers up to 100 m
 Frequency
• Free 2.4 GHz ISM-band
 Security
• Challenge/response (SAFER+), hopping
sequence
 Cost
• $30 adapter, drop to $5 if integrated
 Availability
• Integrated into some products, several
vendors
 Connection set-up time
• Depends on power-mode
• Max. 2.56s, avg. 0.64s
 Quality of Service
• Guarantees, ARQ/FEC
 Manageability
• Public/private keys needed, key
management not specified, simple system
integration
 Special Advantages/Disadvantages
• Advantage: already integrated into several
products, available worldwide, free ISMband, several vendors, simple system,
simple ad-hoc networking, peer to peer,
scatternets
• Disadvantage: interference on ISM-band,
limited range, max. 8
devices/network&master, high set-up
latency
93
WPAN: IEEE 802.15 – Current
Developments
 802.15.2: Coexistance
• Coexistence of Wireless Personal Area Networks (802.15) and Wireless
Local Area Networks (802.11), quantify the mutual interference
 802.15.3: High-Rate
• Standard for high-rate (20Mbit/s or greater) WPANs, while still lowpower/low-cost
• Data Rates: 11, 22, 33, 44, 55 Mbit/s
• Quality of Service isochronous protocol
• Ad hoc peer-to-peer networking
• Security
• Low power consumption
• Low cost
• Designed to meet the demanding requirements of portable consumer imaging
and multimedia applications
94
WPAN: IEEE 802.15 – Current
Development
 802.15-4: Low-Rate, Very Low-Power, approved in May 2003
• Low data rate solution with multi-month to multi-year battery life and very
low complexity
• Potential applications are sensors, interactive toys, smart badges, remote
controls, and home automation
• Data rates of 20-250 kbit/s, latency down to 15 ms
• Master-Slave or Peer-to-Peer operation
• Support for critical latency devices, such as joysticks
• CSMA/CA channel access (data centric), slotted (beacon) or unslotted
• Automatic network establishment by the PAN coordinator
• Dynamic device addressing, flexible addressing format
• Fully handshaked protocol for transfer reliability
• Power management to ensure low power consumption
• 16 channels in the 2.4 GHz ISM band, 10 channels in the 915 MHz US ISM
95
band and one channel in the European 868 MHz band
History of HomeRF
 HomeRF is the technique that aimed at offering voice, data and
video image at home or small scale office with a low cost by radio
frequency instead of wiring.
 The HomeRF standard was developed by HomeRF Working Group
that is composed of major companies such as Compaq, Intel,
Motorola, National Semiconductor, Proxim and Siemens.
 The HomeRF standard diverged from the original 802.11 FHSS
standard and incorporated the Digital Enhanced Cordless
Telephone (DECT) technology used for cordless telephones in
Europe.
 HomeRF follows shared wireless access protocol (SWAP).
 SWAP is used to set up a network that provides access to a public
network telephone, the Internet (data), entertainment networks
(cable television, digital audio, and video), transfer and sharing of
data resources (disks, printer), home control, and automation. 96
History of HomeRF and Infrared
 The SWAP can support up to 127 devices, each identified by a 48bit network identifier.
• Connection point is a gateway to the public switched telephone network
(PSTN).
• Asynchronous data node is used to communicate with other nodes.
 The demise of HomeRF
• In 2001, Intel has started the process of abandoning the HomeRF standard for
in-home networking and is switching to IEEE 802.11b.
• Eventually, HomeRF lost its supporters and market and HomeRF Working
Group disbanded in 2003.
 The infrared technology (IrDA) has the following characteristics:
•
•
•
•
•
The infrared rays can be blocked by obstacles.
The effective range of infrared communications is about one meter.
The power consumed by infrared devices is extremely low.
Data rates of 4 Mbps are easily achievable.
The cost of infrared devices is low.
 Despite the restriction of line of sight (LoS), infrared devices are
very popular because they cost less and consume less power.
97
HomeRF Standard
 Data rate
• 0.8, 1.6, 5, 10 Mbit/s
 Transmission range
• 300m outdoor, 30m indoor
 Frequency
• 2.4 GHz ISM
 Security
• Strong encryption, no open
access
 Cost
• Adapter ?, base station ?
 Availability
• Several products from different
vendors
 Connection set-up time
• 10 ms bounded latency
 Quality of Service
• Up to 8 streams A/V, up to 8 voice
streams, priorities, best-effort
 Manageability
• Like DECT & 802-LANs
 Special Advantages/Disadvantages
• Advantage: extended QoS support,
host/client and peer/peer, power
saving, security
• Disadvantage: future uncertain due to
DECT-only devices plus 802.11a/b for
data
98
RFID – Radio Frequency Identification
 RFID (radio frequency identification) is a technology that
incorporates the use of electromagnetic or electrostatic coupling in
the radio frequency (RF) portion of the electromagnetic spectrum
to uniquely identify an object, animal, or person.
 RFID is coming into increasing use in industry as an alternative to
the bar code.
 The advantage of RFID is that it does not require direct contact or
line-of-sight scanning.
 An RFID system consists of three components: an antenna and
transceiver (often combined into one reader) and a transponder (the
tag).
 The antenna uses radio frequency waves to transmit a signal that
activates the transponder. When activated, the tag transmits data
back to the antenna.
99
RFID – Radio Frequency Identification
 The data is used to notify a programmable logic controller that an
action should occur. The action could be as simple as raising an
access gate or as complicated as interfacing with a database to
carry out a monetary transaction.
 Low-frequency RFID systems (30 KHz to 500 KHz) have short
transmission ranges (generally less than six feet). High-frequency
RFID systems (850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz)
offer longer transmission ranges (more than 90 feet). In general, the
higher the frequency, the more expensive the system.
 RFID is sometimes called dedicated short range communication
(DSRC).
100
RFID – Radio Frequency Identification
 Data rate
• Transmission of ID only (e.g., 48 bit,
64kbit, 1 Mbit)
• 9.6 – 115 kbit/s
 Transmission range
• Passive: up to 3 m
• Active: up to 30-100 m
• Simultaneous detection of up to, e.g.,
256 tags, scanning of, e.g., 40 tags/s
 Frequency
• 125 kHz, 13.56 MHz, 433 MHz, 2.4
GHz, 5.8 GHz and many others
 Security
• Application dependent, typ. no crypt.
on RFID device
 Cost
• Very cheap tags, down to $1 (passive)
 Availability
• Many products, many vendors
 Connection set-up time
• Depends on product/medium access
scheme (typ. 2 ms per device)
 Quality of Service
• none
 Manageability
• Very simple, same as serial interface
 Special Advantages/Disadvantages
• Advantage: extremely low cost, large
experience, high volume available, no
power for passive RFIDs needed,
large variety of products, relative
speeds up to 300 km/h, broad temp.
range
• Disadvantage: no QoS, simple denial
of service, crowded ISM bands, typ.
one-way (activation/ transmission of
ID)
101
RFID – Radio Frequency Identification
 Function
• Standard: In response to a radio interrogation signal from a reader (base
station) the RFID tags transmit their ID
• Enhanced: additionally data can be sent to the tags, different media access
schemes (collision avoidance)
 Features
• No line-of sight required (compared to, e.g., laser scanners)
• RFID tags withstand difficult environmental conditions (sunlight, cold, frost,
dirt etc.)
• Products available with read/write memory, smart-card capabilities
 Categories
• Passive RFID: operating power comes from the reader over the air which is
feasible up to distances of 3 m, low price (1€)
• Active RFID: battery powered, distances up to 100 m
102
RFID – Radio Frequency Identification
 Applications
• Total asset visibility: tracking of goods during manufacturing, localization of
pallets, goods etc.
• Loyalty cards: customers use RFID tags for payment at, e.g., gas stations,
collection of buying patterns
• Automated toll collection: RFIDs mounted in windshields allow commuters
to drive through toll plazas without stopping
• Others: access control, animal identification, tracking of hazardous material,
inventory control, warehouse management, ...
 Local Positioning Systems
• GPS useless indoors or underground, problematic in cities with high
buildings
• RFID tags transmit signals, receivers estimate the tag location by measuring
the signal‘s time of flight
103
RFID – Radio Frequency Identification
 Security
• Denial-of-Service attacks are always possible
• Interference of the wireless transmission, shielding of
transceivers
• IDs via manufacturing or one time programming
• Key exchange via, e.g., RSA possible, encryption via, e.g., AES
 Future Trends
• RTLS: Real-Time Locating System – big efforts to make total asset visibility
come true
• Integration of RFID technology into the manufacturing, distribution and
logistics chain
• Creation of „electronic manifests“ at item or package level (embedded
inexpensive passive RFID tags)
• 3D tracking of children, patients
104
RFID – Radio Frequency Identification
 Devices and Companies
•
•
•
•
•
•
•
•
•
•
AXCESS Inc., www.axcessinc.com
Checkpoint Systems Group, www.checkpointsystems.com
GEMPLUS, www.gemplus.com/app/smart_tracking
Intermec/Intellitag, www.intermec.com
I-Ray Technologies, www.i-ray.com
RF Code, www.rfcode.com
Texas Instruments, www.ti-rfid.com/id
WhereNet, www.wherenet.com
Wireless Mountain, www.wirelessmountain.com
XCI, www.xci-inc.com
 Only a very small selection…
105
RFID – Radio Frequency Identification
 Example Product: Intermec RFID UHF OEM Reader
• Read range up to 7m
• Anticollision algorithm allows for scanning of 40 tags per second regardless
of the number of tags within the reading zone
• US: unlicensed 915 MHz, Frequency Hopping
• Read: 8 byte < 32 ms
• Write: 1 byte < 100ms
 Example Product: Wireless Mountain Spider
•
•
•
•
•
Proprietary sparse code anti-collision algorithm
Detection range 15 m indoor, 100 m line-of-sight
> 1 billion distinct codes
Read rate > 75 tags/s
Operates at 308 MHz
106
RFID – Radio Frequency Identification
 ISO Standards
• ISO 15418
• MH10.8.2 Data Identifiers
• EAN.UCC Application Identifiers
• ISO 15434 - Syntax for High Capacity ADC Media
• ISO 15962 - Transfer Syntax
• ISO 18000
•
•
•
•
•
Part 2, 125-135 kHz
Part 3, 13.56 MHz
Part 4, 2.45 GHz
Part 5, 5.8 GHz
Part 6, UHF (860-930 MHz, 433 MHz)
• ISO 18047 - RFID Device Conformance Test Methods
• ISO 18046 - RF Tag and Interrogator Performance Test Methods
107
RFID – Radio Frequency Identification
 Relevant Standards
• American National Standards Institute
ANSI, www.ansi.org, www.aimglobal.org/standards/rfidstds/ANSIT6.html
• Automatic Identification and Data Capture Techniques
• JTC 1/SC 31, www.uc-council.com/sc31/home.htm,
www.aimglobal.org/standards/rfidstds/sc31.htm
• European Radiocommunications Office
• ERO, www.ero.dk, www.aimglobal.org/standards/rfidstds/ERO.htm
• European Telecommunications Standards Institute
• ETSI, www.etsi.org, www.aimglobal.org/standards/rfidstds/ETSI.htm
• Identification Cards and related devices
• JTC 1/SC 17, www.sc17.com, www.aimglobal.org/standards/rfidstds/sc17.htm,
• Identification and communication
• ISO TC 104 / SC 4, www.autoid.org/tc104_sc4_wg2.htm,
www.aimglobal.org/standards/rfidstds/TC104.htm
• Road Transport and Traffic Telematics
• CEN TC 278, www.nni.nl, www.aimglobal.org/standards/rfidstds/CENTC278.htm
• Transport Information and Control Systems
• ISO/TC204, www.sae.org/technicalcommittees/gits.htm,
www.aimglobal.org/standards/rfidstds/ISOTC204.htm
108
ISM band interference
 Many sources of interference
•
•
•
•
Microwave ovens, microwave lightning
802.11, 802.11b, 802.11g, 802.15, Home RF
Even analog TV transmission, surveillance
Unlicensed metropolitan area networks
OLD
NEW
 Levels of interference
• Physical layer: interference acts like noise
• Spread spectrum tries to minimize this
• FEC/interleaving tries to correct
© Fusion Lighting, Inc.
• MAC layer: algorithms not harmonized
• E.g., Bluetooth might confuse 802.11
109
802.11 vs. 802.15/Bluetooth
 Bluetooth may act like a rogue member of the 802.11 network
(separated by
installation)
100
byte
802.15.1
79 channels
SIFS
ACK
DIFS
500 byte
SIFS
ACK
100
byte
802.11b
3 channels
DIFS
DIFS
SIFS
ACK
SIFS
ACK
DIFS
100
byte
DIFS
DIFS
100
byte
500 byte
SIFS
ACK
SIFS
ACK
100
byte
DIFS
SIFS
ACK
1000 byte
500 byte
DIFS
DIFS
DIFS
f [MHz]
2480
SIFS
ACK
• Does not know anything about gaps, inter frame spacing etc.
(separated by
hopping pattern)
2402
 IEEE 802.15-2 discusses these problems
t
• Proposal: Adaptive Frequency Hopping
• a non-collaborative Coexistence Mechanism
 Real effects? Many different opinions, publications, tests,
formulae, …
• Results from complete breakdown to almost no effect
• Bluetooth (FHSS) seems more robust than 802.11b (DSSS)
110