Tema 3.- Tecnologías inalámbricas de red

Transcription

Tema 3.Tecnologías inalámbricas de red

Aspectos básicos de las comunicaciones inalámbricas
o Conceptos básicos
o Modelos de propagación
Gran escala
Pequeña escala
Redes Inalámbricas y Computación Ubicua/2006-2007
Redes Inalámbricas
Inalámbricas yy Computación
Computación Ubicua/2006-2007
Ubicua/2006-2007
Redes
Decibelios

Los dB (deciBel) son una unidad adimensional utilizada para
representar ratios y ganancias en escala logarítmica
o Las ganancias se suman en vez que multiplicarse
⎡ p2 ⎤
⎢
⎥ = 10 log
⎣ p 1 ⎦ dB

Ejemplo: cálculo de la atenuación T-R
o PT=100, PR=10
o [PT/PR]dB = 10 log(PT/PR) = 10 log(10) = 10 dB

dbm
dbm
Valores útiles:
o [1/2]dB ≈ -3 dB
o [1/1000]dB = -30 dB

Permiten expresar valores absolutos:
o [n mW]dBm = [n/mW]dB
o [n W]dBW = [n/W]dB

2
⎛ p2 ⎞
⎜
⎟⎟ = 10 (log p 2 − log p 1 )
10 ⎜
⎝ p1 ⎠
Ej.: [1mW]dBm = 0 dBm
Ej.: [1 mW]dBW = -30 dBW
De decibelios a potencia: P = 10dB/10
watt
watt
00
0.001
0.001
10
0.01
10
0.01
20
0.1
20
0.1
30
11
30
40
10
40
10
Redes Inalámbricas
Ubicua/2006-2007
Redes
3
Antenas: conceptos básicos

Non Isotropic Antenna
o Irradia la energía que recibe solo
en una sección del espacio que
la rodea.

Isotropic Antenna
o Irradia la energía que recibe en
todo el espacio que la rodea.
YAGI Directional Antenna
Redes Inalámbricas
Ubicua/2006-2007
Redes
Antenas de largo alcance
Antena Yagi exterior (13,5 dBi)
Alcance:
6 Km a 2 Mb/s
2 Km a 11 Mb/s
4
Antena Parabólica exterior (20 dBi)
Alcance:
10 Km a 2 Mb/s
4,5 Km a 11 Mb/s
Redes Inalámbricas
Ubicua/2006-2007
Redes
Más ejemplos de antenas
Horizontal Radiation
Antena dipolo diversidad para
efectos multipath
5
Antena de parche para montaje
en pared interior o exterior (8,5 dBi)
Alcance:
3 Km a 2 Mb/s
1 Km a 11 Mb/s
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bandas sin licencia en USA

Industrial, Scientific, and Medical (ISM)
o 902 – 928 MHz band.
Ahora en disuso para WLAN
o 2400 – 2483.5 MHz ISM band.

Unlicensed National Information Infrastructure (UNII):
o 5.15 – 5.25 GHz.
o 5.25 – 5.35 GHz.
o 5.725 – 5.850 GHz ISM band.
Short Wave Radio
AM Broadcast
Audio
Extremely
Low
Very
Low
Low
902 - 928 MHz
26 MHz
6
Medium
FM Broadcast
Television
Cellular (840MHz)
NPCS (1.9GHz)
High Very Ultra
High High
Super
High
2.4 - 2.4835 GHz
83.5 MHz
(IEEE 802.11)
Infrared wireless LAN
Infrared
Visible
Light
Ultraviolet
5 GHz
(IEEE 802.11)
HyperLAN
HyperLAN2
X-Rays
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bandas sin licencia en Europa

Bandas aprobadas por el CEPT (European Conference of Postal
and Telecommunications Administrations)

2400 – 2483.5 MHz, basada en la ISM.
5.15 – 5.35 GHz.
5.470 – 5.725 GHz.
Short Wave Radio
AM Broadcast
Audio
Extremely
Low
Very
Low
Low
Medium
FM Broadcast
Television
Cellular (840MHz)
NPCS (1.9GHz)
High Very Ultra
High High
Super
High
2.4 - 2.4835 GHz
83.5 MHz
(IEEE 802.11)
7
Infrared wireless LAN
Infrared
Visible
Light
Ultraviolet
5 GHz
(IEEE 802.11)
HyperLAN
HyperLAN2
X-Rays
Redes Inalámbricas
Ubicua/2006-2007
Redes
Detalles de la banda de 5 GHz
5 GHz
UNII Band
5.15
5.25
5.35
4 Channels 4 Channels
US (FCC)
12 Channels
(*can use up to
6dBi gain antenna)
Europe
19 Channels
(*assumes no
antenna gain)
UNII-1
UNII-2
40mW
200mW
5.470
5.725
11 Channels
4 Channels
UNII-3
800mW
(22 dBm EIRP) (29 dBm EIRP)
200mW
(35 dBm EIRP)
1W
UNII-1: Indoor Use, antenna must be fixed to the radio
UNII-2: Indoor/Outdoor Use, fixed or remote antenna
UNII-3: Outdoor Bridging Only (EIRP limit is 52 dBm if PtP)
*if you use a higher gain antenna, you must reduce the transmit power accordingly
8
5.825
Redes Inalámbricas
Ubicua/2006-2007
Redes
Calculo del Power Budget

Prx = Ptx+Gpa-Gtxl+Gtxa-Lpath+Grxa+Gra-Grxl
o Ptx[dBm]=Power generated by TX
o Gpa[dB]=Gain of the Power Amplifier
o Gtxa[dBi]=Gain of TX antenna
o Gtxl[dB]=Gain (loss) of transmission line
o Lpth[dB]=Loss of the transmission medium
o Grxa[dBi]=Gain of RX antenna
o Gra[dB]=Gain of the Receive Amplifier
o Grxl[dB]=Gain (loss) of receiving line
o Prx[dBm]=Power received
o Sr[dBm]=Sensivity of receiver Gtxl

(Effective Isotropically Radiated
Power) =
Ptx+Gpa+Gtxa-Gtxl
Debe valer la condición Prx > Sr
Ptx
Gpa
P
A
TX
9
EIRP
Gtxl
GTXA
Lpath
Grxa
Gra
R
A
Grxl
Sr
RX
1
0
Redes Inalámbricas
Ubicua/2006-2007
Redes
Representación grafica del power budget
Redes Inalámbricas
Ubicua/2006-2007
Redes
Características del canal inalámbrico

Theodore S. Rappaport , “Wireless Communications : Principles
and Practice”, Prentice Hall, July 1999

El canal inalámbrico sufre de los efectos de los dos siguientes
fenómenos:
o Distancia Ö Path attenuation (Large scale fading)
o Multipath (Small scale fading)
dispersión en el tiempo debida a los diferentes caminos de la señal
T
R
La
La señal
señal verde
verde recorre
recorre 1/2λ
1/2λ más
más de
de la
la línea
línea en
en
amarillo.
amarillo. El
El receptor
receptor recibe
recibe la
la señal
señal en
en rojo.
rojo.
Para
= 2,4
2,4 GHz
GHz,, λλ =
= c/f
c/f =
= 12.5cm
12.5cm
Para ff =
1
1
Redes Inalámbricas
Ubicua/2006-2007
Redes
Mecanismos/modelos de propagación

Propagación Free Space
o Solamente ondas directas. Ejemplos: regiones cerca de la fuente,
cámaras anecoicas, antenas muy elevadas.

Propagación terrestre:
o Contacto visual (tierra plana):
Refracción (Refraction): depende del tipo de los materiales conductores o
dieléctricos
o Tierra esférica:
Diffraction: zonas de Fresnel

Propagación en el espacio:
o Scattering, absorción, ...
1
2
Redes Inalámbricas
Ubicua/2006-2007
Redes
Propagación free space

Calculo de la potencia recibida cuando T&R tienen contacto visual
(LOS)
o “la atenuación de la señal que resultaría eliminando todos los efectos de
absorción, difracción, obstrucción, reflexión, dispersión.”
Pt
Pt Gt Gr λ2
=K 2
Pr (d ) =
2 2
(4π ) d L
d

Ecuación de Friis:

Valida solo para d en la región de Fraunhofer (far-field region):
“el área alrededor de una antena en la cual la radiación aparece
venir de un solo punto”
d > df = 2D2/λ;
D es la dimensión más grande de la antena
λ longitud de onda de la portadora
1
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
Difracción

La difracción ocurre cuando una onda
golpea el borde de un obstáculo
o El exceso de longitud del recorrido
produce un desplazamiento de fase
o Las zonas de Fresnel meten en
relación los desplazamientos de fase
con la posición de los obstáculos

Las zonas de Fresnel son elipses con T y R
en los focos
T
1st Fresnel zone
o L1 = L2+λ
o El campo visual (line of sight, LOS)
corresponde a la primera zona
o Si la LOS está parcialmente
bloqueada la zona 2 puede interferir
de forma destructiva
Obstruction
Path 1
Path 2
1
4
R

Aspectos básicos de las comunicaciones inalámbricas
o Conceptos básicos
o Modelos de propagación
Gran escala
Pequeña escala
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
Modelos de propagación

Gran escala (large scale): predicen el comportamiento de una señal
promediado sobre grandes distancias (» λ)
o Depende de la distancia y de las características relevantes del entorno
o Básicamente independiente de la frecuencia

Pequeña escala (small scale fading): describen las variaciones de
las señal en escala con λ
o Domina el efecto del Multipath (phase cancellation). La atenuación se
puede considerar constante
o Depende de la frecuencia y del ancho de banda
o “Fading”: representa cambios rápidos de la señal sobre pequeñas
distancia o intervalos temporales
Exponencial
Potencia
Redes Inalámbricas
Ubicua/2006-2007
Redes
Comparación
0.1 -1 m
(10-100 msecs)
Small-scale Fading
Large-scale Fading
10-100 m
(1-10 secs)
Distancia
1
7
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
Modelos de propagación a gran escala:
path loss

Se refiere al calculo de la potencia de la señal en el receptor en
base a la distancia d entre transmisor (T) y receptor (R)
T
df
d0
R
d

Calculo del path loss: PL(d) = PL (d0)+10nlog(d/d0) (dB)

PL(d0) se calcula con la ecuación de Friis, considerando Gt=Gr=L=1:
⎡ λ2 ⎤
Pt
⎡ (4π )d ⎤
= 20 log ⎢
PL(d 0 ) = 10 log = −10 log ⎢
2 2⎥
⎥
Pr
(
4
)
d
π
λ
⎣
⎦
⎣
⎦
Redes Inalámbricas
Ubicua/2006-2007
Redes
path loss Öun ejemplo

Datos: d=10km, f=900MHz,
ο λ=c/f = 3*108/9*108 = 1/3m
o d0=1km Ö
PL(d0) = 20log(4π1000/λ) = 91,5 dB
o free space n=2
PL(d) = PL (d0)+10nlog(d/ d0)
= 91,5 + 10*2*log(10000/1000)
= 111,5 dB
o ciudad n=3.5
T
1
9
n
Free space
2
Urban area
2.7-3.5
Shadowed urban area
PL(d) = PL (d0)+10nlog(d/ d0)
= 91,5 + 10*3.5*log(10000/1000)
= 126,5 dB
df
Environment
d0
Indoor LOS
1.6-1.8
Indoor no LOS
4-6
R
d
3-5
Redes Inalámbricas
Ubicua/2006-2007
Redes
2
0
Log-normal shadowing

Se consideran las variaciones del entorno a pesar de que d sea
constante
Se añade por eso una variable casual Gaussiana
⎛d ⎞
PL(d )[dB ] = PL(d ) + X σ = PL(d 0 ) + 10n log⎜⎜ ⎟⎟ + X σ
⎝ d0 ⎠
o Donde Xσ es una variable casual Gaussiana con (µ=0, σ)

Entonces:
Pr (d )[dBm] = Pt [dBm] − PL(d )[dB]
Redes Inalámbricas
Ubicua/2006-2007
Redes
modelos para exteriores

Modelos: “2-Ray” Ground Reflection
o para d >> hrht,
T
El bajo ángulo de incidencia permite a la
tierra de actuar como un reflector
La señal reflejada tiene un desfase de 180°
Pr ∝ 1/d4 (n=4)
R
ht

hr
Modelos de difracción para terrenos
montañosos (hilly terrain)
o La propagación puede pude ser LOS o
resultar en la difracción en las varias
crestas
o Si no hay LOS la difracción puede ayudar
...
2
1
Phase shift!
Redes Inalámbricas
Ubicua/2006-2007
Redes
2
2
modelos para interiores

En los modelos para interiores se puede generalizar menos:
o El entorno es más dinámico
o Las características importantes son mas pequeñas
o Distancias son más cercanas al near-field Material
Material
Concrete block
Concrete block
o Más clutters, hay scattering, menos LOS
Plywood (3/4”)

Técnicas de modelado:
Plywood (3/4”)
Plywood (2 sheets)
Plywood (2 sheets)
Plywood (2 sheets)
Plywood (2 sheets)
Aluminum siding
Aluminum siding
Sheetrock (3/4”)
Sheetrock (3/4”)
Sheetrock (3/4”)
Sheetrock (3/4”)
Turn corner in corridor
Turn corner in corridor
Loss (dB)
Loss (dB)
13-20
13-20
2
2
4
4
6
6
20.4
20.4
2
2
5
5
10-15
10-15
Frequency
Frequency
1.3 GHz
1.3 GHz
9.6 GHz
9.6 GHz
9.6 GHz
9.6 GHz
28.8 GHz
28.8 GHz
815 MHz
815 MHz
9.6 GHz
9.6 GHz
57.6 GHz
57.6 GHz
1.3 GHz
1.3 GHz
o Log-Normal, n<2 cuando hay LOS
o Log-Normal shadowing model si no hay LOS
o Atenuación debida a tabiques y al suelo
o Modelos 3D complejos basados en “ray-tracing” de los edificios y de los
factores de atenuación de los materiales
2
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
Propagación radio en un entorno cerrado
2
4
Redes Inalámbricas
Ubicua/2006-2007
Redes
Otro ejemplo
Redes Inalámbricas
Ubicua/2006-2007
Redes
2
5
Modelos de propagación a pequeña escala:
efectos del Multipath

Pequeña escala (small scale fading): describen las variaciones de
las señal en escala con λ
o Domina el efecto del Multipath (phase cancellation). La atenuación se
puede considerar constante
o Depende de la frecuencia y del ancho de banda
o “Fading”: representa cambios rápidos de la señal sobre pequeñas
distancia o intervalos temporales

Rápidas variaciones de la potencia de la señal a causa de la
cancelación de fase
Modulación de la frecuencia producida por Doppler shifts a causa
del movimiento de R o T
Redes Inalámbricas
Ubicua/2006-2007
Redes
Modelos estadísticos del fading

Los modelos de Fading modelan la probabilidad de fading en
determinadas localizaciones
Los modelos más sencillos están basados en el principio de
WSSUS
o Wide Sense Stationary (WSS)
Las estadísticas son independientes de pequeñas perturbaciones en el
tiempo y posición
Es decir, parámetros estadísticos fijos para nodos estacionarios
o Uncorrelated Scatter (US)
Los diferentes paths no están correlatos en fase o atenuación
Es decir, Las componentes multipath componentes pueden ser VC
independientes

Distribuciones comunes
o Rayleigh fading distribution
Models a flat fading signal
Used for individual multipath components
o Ricean fading distribution
2
6
Used when there is a dominant signal component, e.g. LOS + weaker
multipaths
parameter K (dB) defines strength of dominant component; for K=-∞,
equivalent to Rayleigh

Redes WLAN: IEEE 802.11
o la capa física
o
o
o
o
o
la capa MAC
calidad de servicio: 802.11e
seguridad: WAP y 802.11i
MIMO: 802.11n
herramientas de gestión

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
El estándar IEEE 802.11

En el 1997 nace el:
o IEEE Working Group for WLAN Standards:
http://grouper.ieee.org/groups/802/11/index.html

Se define el MAC y tres diferentes niveles físicos, que operan a
1Mbps y 2Mbps:
o Infrarrojos (IR) en banda base
o Frequency hopping spread spectrum (FHSS), banda de 2,4 GHz
o Direct sequence spread spectrum (DSSS), banda de 2,4 GHz

IEEE Std 802.11b (septiembre 1999):
o Extensión de DSSS; hasta 11 Mbps

IEEE Std 802.11a (diciembre 1999):
o Otro estándar de nivel físico (OFDM):
Orthogonal frequency domain multiplexing
o Hasta 54 Mbps

IEEE Std 802.11g (junio 2003)
...
PHY
Layer
Infra-Red
(IR)
802.11 IR
1 / 2 Mbit/s
2.4 GHz (FHSS)
Frequency Hopping Spread Spectrum
802.11 FHSS
1 / 2 Mbit/s
2.4 GHz (DSSS)
Direct Sequence Spread Spectrum
802.11 DSSS
1 / 2 Mbit/s
802.11b / TGb
High Data Rate Extension
5.5/11 Mbit/s
802.11b-cor1 / TGb-cor1
Corrigendum MIB
802.11g / TGg
Data Rates >20 Mbit/s
5 GHz (OFDM)
Orthogonal Frequency Division Multiplexing
802.11d / TGd
Regulatory Domain Update
802.11a / TGa
High Data Rate Extension
6/12/24 Mbit/s
Optional 9/18/36/54 Mbit/s
802.11h / TGh
Spectrum Managed
802.11a
WLANs Next Gemeration SC
Globalization &
Harmonization

Beneficios
o No se producen interferencias
con otras señales
o Mayor inmunidad al ruido
o Difíciles de interceptar

Frequency Hopping (FHSS)
o
o

Utiliza una de 78 secuencias del
salto. Salto a un nuevo canal del
1MHz (sobre un total de 79 canales)
por lo menos cada 400milliseconds
Requiere la adquisición y la
sincronización del salto
Freq.
Redes Inalámbricas
Ubicua/2006-2007
Redes
Técnicas de Spread Spectrum
f7
f6
f5
f4
f3
f2
f1
Time
Direct Sequence (DSSS)
o
Utiliza uno de los 11 canales
‘solapados’ y multiplica la señal para
una secuencia de spreading para
ensanchar datos a 1M-symbol/sec
data sobre 11MHz
Symbol time ts
“1”
“0”
X
“symbol”
=
“Barker” sequence
Result of multiplication
Chip time tc
Redes Inalámbricas
Ubicua/2006-2007
Redes
802.11 DSSS Radio Interface

1 Mbps
o 1 Msymbol/s BPSK spread by 11 chip Barker code,
o (-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz),
o IEEE 802.11

2 Mbps
o 1 Msymbol/s QPSK spread by 11 chip Barker code
o (-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz),
o IEEE 802.11

5.5 Mbps
o 2 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying
(CCK).
o IEEE 802.11b

11 Mbps
o 4 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying
(CCK).
o IEEE 802.11b

54 Mbps
o OFDM with max. 52 sub-carriers,
o IEEE 802.11a / IEEE 802.11g
Redes Inalámbricas
Ubicua/2006-2007
Redes
802.11 DSSS Frame Format

PPDU: PLCP protocol data unit
o
o
o

Durante la transmisión las MPDU son precedidas por el preámbulo y la cabecera del PLCP para crear la PPDU
El preámbulo y la cabecera del PLCP son transmitidas utilizando una modulación DBPSK a 1 Mbit/s
Todos los bits son scrambled para obtener la función de ‘data whitener’
Synchronization (SYNC) field
o
o
Field allows receiver to perform necessary SYNC operations
Also provides for:

Start Frame Delimiter (SFD) field
o

Reserved for future use. Value of 00 signifies IEEE 802.11 device compliance
LENGTH field
o

Indicates to PHY the modulation used for transmission (and reception) of the MPDU
Data rate = signal field value x 100 kbit/s
SERVICE field
o

Indicates start of PHY-dependent parameters within PLCP Preamble
SIGNAL field
o
o

gain setting, energy detection, antenna selection, frequency offset compensation
Unsigned 16-bit integer. Indicates time (in µS) required to transmit the MPDU
Header Error Check (HEC) field
o
o
SIGNAL, SERVICE, and LENGTH fields protected with a CCITT CRC-16 Frame Check Sequence (FCS)
All FCS calculations made prior to data scrambling
Redes Inalámbricas
Ubicua/2006-2007
Redes
802.11b High Rate DSSS Frame Format

Extension of IEEE 802.11 DSSS format
Additionally provides 5.5 Mbit/s and 11 Mbit/s data rates
Uses same PLCP preamble and header as DSSS
o both PHYs can co-exist in the same BSS
o can use the rate switching mechanism as provided.

Two different preambles and headers are defined:
o Long Preamble & Header
mandatory & supported
interoperates with the current 1 Mbit/s and 2 Mbit/s DSSS spec
o Short Preamble & Header
optional
where maximum throughput is desired
expected to be used only in networks of like equipment
Redes Inalámbricas
Ubicua/2006-2007
Redes
802.11b High Rate DSSS Optional Services

Mode replacing CCK modulation with packet binary convolutional
coding (PBCC)
Channel agility
HR/DSSS/short mode:
o Allows data throughput at higher rates (2, 5.5, & 11 Mbit/s) to be
significantly increased by using a shorter PLCP preamble

Can coexist with DSSS, HR/DSSS, or HR/DSSS/PBCC under
limited circumstances
o different channels
o with appropriate CCA
Redes Inalámbricas
Ubicua/2006-2007
Redes
HR/DSSS: Long Frame Format

Same format as IEEE 802.11 DSSS Frame
The only exceptions are:
o
Encoding of the rate in the SIGNAL field. Represent rate in units of 100 kbit/s
0A for 1 Mbit/s, 14 for 2 Mbit/s, 37 for 5.5 Mbit/s, 6E for 11 Mbit/s
o
SERVICE field
Rightmost bit (bit 7) used to supplement LENGTH field
–
resolve an ambiguity in PSDU length in octets, when length expressed in µS
Bit 3 used to indicate whether modulation method is CCK <0> or PBCC <1>
Bit 2 used to indicate that transmit frequency and symbol clocks are derived from same oscillator
An IEEE 802.11-compliant device shall set values of bits b0, b1, b4, b5, and b6 to 0
Redes Inalámbricas
Ubicua/2006-2007
Redes
HR/DSSS: Short Frame Format

Short Synch field
o Consists of 56 scrambled “0” bits.
o So receiver can perform necessary SYNC

Start Frame Delimiter (SFD) field
o Time reverse of long PLCP SFD field
o Not detected by non-compliant receivers

SIGNAL field
o Only 1 Mbit/s removed
o Remaining fields same as HR DSSS Long Frame format
Redes Inalámbricas
Ubicua/2006-2007
Redes
Los canales de 802.11b Overview

El estándar prevé 14 canales de 22 MHz de amplitud
o el FCC solo utiliza los primeros 11
o en España solo el 10 y el 11

3 canales que no solapan (1, 6,11)
data rate de 11 Mbps
Tres puntos de acceso pueden estar ‘cerca’ para obtener un total de 33 Mbps de
throughput agregado
Redes Inalámbricas
Ubicua/2006-2007
Redes
estándar IEEE 802.11a

5 GHz, 54 Mbps, OFDM technology
o Data rates supported: 54, 48, 36, 24, 12, and 6 Mbps
o Can “downshift” to lower data rates for longer range

Worldwide compatibility issues for 5 GHz band
o Effort underway to allow 802.11a operation in European countries
o Long-term: Worldwide usage with adoption of Transmit Power Control
(TPC) and Dynamic Frequency Selection (DFS) per 802.11h standard

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

5 GHz band subject to less interference than 2.4 GHz ISM band
o However, 2.4GHz interference not a major problem in most business
environments
Redes Inalámbricas
Ubicua/2006-2007
Redes
estándar IEEE 802.11g

Ratificado en junio del 2003 por el IEEE Standards Board
o draft standard preliminar presentado en diciembre de 2001;
o ultimo draft v8.2

Utiliza la banda de 2.4 GHz
o modulación OFDM y codificación PBCC

Compatible ‘hacia atrás con IEEE 802.11b
o Pueden co-existir en la misma WLAN

Nuevas velocidades de transmisión suportadas:
o 6, 9, 12, 18, 24, 36, 48 & 54 Mbps
Redes Inalámbricas
Ubicua/2006-2007
Redes
4
0
Ejemplo de parámetros físicos de un dispositivo real

DATA SHEET de un Cisco Aironet 802.11a/b/g CardBus Wireless
LAN Client Adapter

Link:
http://www.grc.upv.es/docencia/cosas/products_data_sheet09186a00801ebc29.html

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
Arquitecturas disponibles

Independent Basic Service Set (IBSS)
o Estructura descentralizada
o Flexible:
Redes pequeñas y grandes,
Redes transitorias y permanentes
o Control del consumo de potencia

infrastructure Basic Service Set (BSS)
o Componentes:
Estación (STA)
Access Point (AP)
o Point Coordinator (PC)
o Basic Service Set (BSS)
o Extended Service Set (ESS)

Los 5 valores de timing:
• Slot time
• SIFS: short interframe space (< slot
Servicios sin
contienda
MAC
CSMA/CA con binary
exponential backoff
El protocolo mínimo consiste de
dos tramas: los datos y el
correspondiente ACK
Point
Coordination
Function (PCF)
Distributed Coordination
Function (DCF)
time)
• PIFS: PCF interframe space (=SIFS+1slot)
• DIFS: DCF interframe space (=SIFS+2slots)
• EIFS: extended interframe space
DIFS
DIFS
ventana de contienda
PIFS
busy medium
SIFS
defer access
slot
Redes Inalámbricas
Ubicua/2006-2007
Redes
El MAC: entregas de datos fiable
Servicios con
contienda
Redes Inalámbricas
Ubicua/2006-2007
Redes
Estructura de las tramas
2
2
6
6
Frame
Duration/ / Addr. 1
Frame Duration
Addr. 1
Control
IDID
Control
prot.
prot. type subtype
type subtype
vers
vers
2
2
4
Addr.
Addr.22
6
2
Seq.
Seq.
Control
Control
Addr.
Addr.33
1
1 1
1 1 1
1
Addr.
Addr.44
0-2312
Frame
Body
4
FCS
FCS
Tipos
Tiposde
dedirecciones:
direcciones:
••Source
Sourceaddress
address(SA)
(SA)
To FromMore PowerMore
To FromMore
retry PowerMore
WEPorder
DS DS frags retrymgt data WEPorder
mgt data
DS DS frags
1
6
••Destination
DestinationAddress
Address(DA)
(DA)
••Transmitter
TransmitterAddress
Address(TA)
(TA)
bits
••Receiver
ReceiverAddress
Address(RA)
(RA)
••BSS
BSSidentifier
identifier(BSSID)
(BSSID)
• management (00)
• control (01),
• data (10),
• reserved (11)
Función
To
DS
From
DS
Addr. 1
Addr. 2
Addr. 3
Addr. 4
IBSS
0
0
RA = DA
SA
BSSDI
-
From the AP
0
1
RA = DA
BSSDI
SA
-
To the AP
1
0
RA = BSSDI
SA
DA
-
Wireless DS
1
1
RA
TA
DA
SA
Redes Inalámbricas
Ubicua/2006-2007
Redes
4
5
Addressing and DS bits
DS
TA
RA (BSSID)
SA/TA
AP
AP
SA
Client
RA
AP
DA
Client
DA
Server
Server
Función
To
DS
From
DS
Addr. 1
Addr. 2
Addr. 3
Addr. 4
IBSS
0
0
RA = DA
SA
BSSDI
-
From the AP
0
1
RA = DA
BSSDI
SA
-
To the AP
1
0
RA = BSSDI
SA
DA
-
Wireless DS
1
1
RA
TA
DA
SA
Redes Inalámbricas
Ubicua/2006-2007
Redes
Ejemplo de funcionamiento del DCF

Los intervalos de backoff son escogidos dentro de la congestion
window . Es decir en el intervalo [0, CW]
La CW puede variar entre 31 slots (CWmin) y 1023 slots (CWmax)
CW se incrementa después de una transmisión fallida y se reinicializa después de una transmisión con éxito
B1 = 25
B1 = 5
wait
data
data
B2 = 20
wait
B2 = 15
9 B1 y B2 son intervalos de backoff en las STA 1 y 2
9 CW = 31
B2 = 10
Redes Inalámbricas
Ubicua/2006-2007
Redes
Otro ejemplo

El transmisor utiliza CW = CWmin (15 slots) del 802.11a y ha seleccionado un
random backoff time de 12 slots.
Redes Inalámbricas
Ubicua/2006-2007
Redes
Situaciones problemáticas
Hidden node
Exposed node
A
A
B
B
C
C
D
Redes Inalámbricas
Ubicua/2006-2007
Redes
Hidden nodes
Obstacle
Null
The obstacle
prevents MU1 and
MU2 from hearing
one another
4
9
MU3 cannot hear
MU1 or MU2
because of the
distance
The received
signals cancel
one another
resulting in a
NULL signal
Opposite Side of AP
Redes Inalámbricas
Ubicua/2006-2007
Redes
Near-Far problem

The Near/Far problem is created when:
o A station near the AP uses high power while
o A station located far from the AP uses Low power.
o This results in corruption of the traffic from the far station.
High power
station near
the AP
5
0
Redes Inalámbricas
Ubicua/2006-2007
Redes
Mecanismo RTS/CTS

Se basa en el network allocation vector (NAV)
DIFS
fuente
data
RTS
SIFS
destino
SIFS
SIFS
ACK
CTS
DIFS
otro STA
NAV (RTS)
NAV (CTS)
defer access
ventana de contienda
Redes Inalámbricas
Ubicua/2006-2007
Redes
PCF: Point Coordination Function
PIFS SIFS
PC
SIFS
SIFS
Data+Poll
STA1
CP
STA2
STA3
Beacon
PIFS
Data+Poll
DATA+ACK
SIFS
SIFS
CF-End
Data+Poll
SIFS
(no response)
ACK
Contention Free Period
CP
NAV
Reset
Station 2 sets NAV(Network Allocation Vector)
Station 3 is hidden to the PC, it does not set the NAV.
It continues to operate in DCF.
Time
• Los beacon se utilizan para mantener la sincronización de los timers
en las estaciones y para enviar información de control
• El AP genera los beacon a intervalos regulares
• Las estaciones saben cuando llegará el siguiente beacon
¾los target beacon transmission time (TBTT) son anunciados en el
anterior beacon
Redes Inalámbricas
Ubicua/2006-2007
Redes
PCF: los superframe

Hay una alternancia de contention-free period (CFP) y contention
period (CP)
Un CFP y el siguiente CP forman un superframe.
PC
STAs
802.11 periodic Superframe
CFP(Contention Free Period)
CP(Contention Period)
CF-End
CF-Poll
Beacon
DATA
DATA
DATA
DATA
DATA
DATA
Redes Inalámbricas
Ubicua/2006-2007
Redes
Servicios

La arquitectura IEEE 802.11 define 9 servicios: para la estación y
para la distribución
Station services:
o Authentication
o Deauthentication
o Privacy Ö WEP
o Data delivery

Parecidos a conectar/desconectar
el cable en una red tradicional
Distribution services:
o Association
o Disassociation
o Reassociation
o Distribution
o integration
Ö genera una conexión entre STA y AP
Ö como association pero informando del AP anterior
Ö conexión de la WLAN con otras LANs;
uso de un portal
Redes Inalámbricas
Ubicua/2006-2007
Redes
Variables de estado y servicios
Class 1
frames
State 1:
unauthenticated,
unassociated
Successful authentication
Class 1 & 2
frames
Successful authentication
or reassociation
Class 1, 2 & 3
frames
En una IBSS no hay ni
auth., ni ass. Se
permite la
implementación del
data service
Deauthentication notification
State 2:
authenticated,
unassociated
Deauthentication notification
Disassociation notification
State 3:
authenticated,
associated
Una STA puede
estar autenticada
por varios AP pero
asociada con solo
un AP
Redes Inalámbricas
Ubicua/2006-2007
Redes
Scanning

Parámetros: BSStype, BSSID, SSID, ScanType, ChannelList,
ProbeDelay, Min/MaxChannelDelay
ScanType: Pasivo
o Las estaciones esperan beacons de los APs

ScanType: Activo
o Las estaciones envían probe requests

Se genera un scan report
La fase siguiente es la fase de joining; esta fase precede la
secuencia de acciones hasta llegar a la asociación
Redes Inalámbricas
Ubicua/2006-2007
Redes
BSSID y SSID

BSSID (Basic Service Set Identity)
o BSS: dirección MAC del AP
o Ad-Hoc: numero random de 46 bit

SSID (Service Set ID)
o Conocido como el Network Name por que básicamente es el nombre
que identifica la WLAN
o Longitud: 0~32 octetos
0: el broadcast SSID
o Gestionado manualmente o de forma automática
o identificador único de 32 caracteres
o sirve para diferenciar las WLAN entre ellas
o Los puntos de acceso y las estaciones que quieran conectarse a una
WLAN única tienen que utilizar el mismo SSID
Redes Inalámbricas
Ubicua/2006-2007
Redes
Ahorro de potencia

Los nodos que están en la modalidad de ahorro de energía (PS mode) apagan el
dispositivo radio durante un cierto intervalo de tiempo
o La mayor parte de la potencia de la batería es utilizada por los circuitos de PHY RX
el PHY puede ser apagado cuando no se este transmitiendo auque la estación sea activa
o En media la TX en una WLAN es activa menos del 2% del tiempo
o los nodos transmisores tienen que bufferizar los frames
o El aumento de la latencia causado por el PS puede ser controlado reduciendo los timeouts
en los protocolos de alto nivel

Fácil de implementar con PFC. No tan fácil en DCF
Los AP generan beacons con un time-stamp y lo transmiten cada intervalo de beaconing
(~100 ms)
o la transmisión del beacon es aplazada si el canal está ocupada
o los nodos despiertan antes de que el intervalo de beaconing termina y permanecen
despiertos hasta que el beacon es totalmente recibido
o los timestap son utilizados para actualizar los timer locales

Los nodos son sincronizados para despertar al mismo tiempo cuando el transmisor
anuncia frames buferizados
o los nodos que tienen que recibir frames están despiertos hasta que el frame es entregado
Redes Inalámbricas
Ubicua/2006-2007
Redes
El Extended Service Set (ESS)
BSS
AP
Distribution System (DS)
WLAN
LAN
9 No definido por el
estándar como realizarlo
9 Existe una propuesta de
un grupo de empresas:
Inter-acces point protocol
(IAPP)
Redes Inalámbricas
Ubicua/2006-2007
Redes
Task Group f

Scope of Project: to develop recommended practices for an Inter-Access Point Protocol (IAPP)
which provides the necessary capabilities to achieve multi-vendor Access Point interoperability
across a Distribution System supporting IEEE P802.11 Wireless LAN Links.
Purpose of Project: ... including the concepts of Access Points and Distribution Systems.
Implementation of these concepts where purposely not defined by P802.11 ... As 802.11 based
systems have grown in popularity, this limitation has become an impediment to WLAN market
growth.
This project proposes to specify the necessary information that needs to be exchanged between
Access Points to support the P802.11 DS functions. The information exchanges required will be
specified for, one or more Distribution Systems; in a manner sufficient to enable the
implementation of Distribution Systems containing Access Points from different vendors which
adhere to the recommended practices
Status: Work has been completed and is now part of the Standard as a recommended practice.
Redes Inalámbricas
Ubicua/2006-2007
Redes
Procedimiento de Handoff

Fase de ” reassociation”
Cuatro mensajes IAPP
o IAPP Latency > 4 * RTT

Los mensajes de ”Move Request” y de
”Move Response” utilizan TCP
STA
Old AP
New AP
Re a s
socia
tion
R
eque
st
Send
Ac
Secu
rity B
l oc k
ock
y Bl
t
i
r
cu
k Se
Move
Notif
y
nse
spo
e
R
e
Mov
nse
spo
e
R
n
iatio
c
o
s
s
Rea
IAPP Message
Redes Inalámbricas
Ubicua/2006-2007
Redes
6
2
Wireless Distribution System

IEEE 802.11, WDS means
o Multiple wireless “ports” inside the access-point, to wirelessly
interconnect cells (access-points connecting to other access-points)

pre-IEEE 802.11, did not support WDS:
o Three ports exist in one access-point (one Ethernet, and two wireless
cells)
o One wireless backbone extension can be made (using two radio
modules in the access-point)

WDS allows:
o Extending the existing infrastructure with wireless backbone links
o Totally wireless system without any wired backbones, needed in
locations where large areas are to be covered and wiring is not possible
6
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
Wireless Distribution System
Channel 1
Channel 11
Channel 1
Channel 6
Redes Inalámbricas
Ubicua/2006-2007
Redes
6
4
WDS Wireless Distribution System

WDS, consiste en “puentear” dos redes cableadas para obtener
conexión entre ellas, por ejemplo entre dos edificios de una misma
empresa
Redes Inalámbricas
Ubicua/2006-2007
Redes
6
5
WDS Wireless Distribution System

Repeater: Consiste en un AP en modo WDS, que simplemente va a
repetir las señales que capte de sus “compañeros” de bridge
Redes Inalámbricas
Ubicua/2006-2007
Redes
Operational processes
Traffic flow - WDS operation
Bridge learn
table
STA2
2
STA2
1
Bridge learn
table
STA2
2
STA2
1
AP-1000
AP-1000ororAP-500
AP-500
Avaya
AvayaWireless
WirelessPC-Card
PC-Card
Association table
STA1
WDS
Relay
AP-1000
AP-1000ororAP-500
AP-500
Avaya
AvayaWireless
WirelessPC-Card
PC-Card
Association table
STA2
Wireless
Backbone
Packet for STA-2
WDS
Relay
ACK
Packet for STA-2
Packet for STA-2
ACK
ACK
BSS-B
STA-1
STA-1
6
6
BSS-A
STA-2
STA-2
Redes Inalámbricas
Ubicua/2006-2007
Redes
Linksys Wireless-G Access Point
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
Limitations of the MAC standard for QoS

DCF (Distributed Coordination Function)
o Only support best-effort services
o No guarantee in bandwidth, packet delay and jitter
o Throughput degradation in the heavy load

PCF (Point Coordination Function)
o Inefficient and complex central polling scheme
o Unpredictable beacon frame delay due to incompatible cooperation
between CP and CFP modes
o Transmission time of the polled stations is unknown
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
Overview of 802.11e

Task group e formed in Sep. 1999 and Approved in March 2000
o Current version: IEEE P802.11e/D6.0, November 2003
o Backwardly compatible with the DCF and PCF

New QoS mechanism: HCF (Hybrid Coordination Function)
o Contention-based channel access
EDCA (Enhanced Distributed Channel Access)
– was Enhanced Distributed Coordination Function (EDCF)
o Controlled channel access (includes polling)
HCCA (HCF controlled channel access)

The station that operates as the central coordinator for all other
stations within the same QoS supporting BSS (QBSS) is called the
hybrid coordinator (HC).
o The HC reside inside an AP

A BSS that includes an 802.11e-compliant HC is referred to as a
QBSS.
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
Fundamental improvements

TXOP (Transmission Opportunity)
o TXOP is an interval of time during which a backoff entity has the right to
deliver MSDUs. A TXOP is defined by its starting time and duration.
An 802.11e station that obtains medium access must not utilize radio
resources for a duration longer than a specified limit.
o Can be allocated via contention (EDCA-TXOP) or granted through HCF
(polled-TXOP or HCCA-TXOP)
o The duration of an EDCA-TXOP is limited by a QBSS-wide parameter
referred to as TXOP-limit which is distributed regularly by the HC within
an information field of the beacon.

No station can transmit across a TBTT
A station is allowed to transmit frames directly to another backoff
entity in a QBSS, without involving communication with the AP
o using the direct link protocol (DLP)
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
EDCF (Enhanced DCF)

Review of DCF
o CSMA/CA
o Transmit the frame directly if the medium is found idle for DIFS (DCF
InterFrame Space)
o Otherwise, defer the transmission and start the backoff process
o Backoff_time = rand[0, CW], CWmin < CW < CWmax
o The backoff timer decreases only when the medium become idle.
o Transmit the frame once backoff timer expires

How to provide priorities
o Change the contention window size
newCW[TCi] = ((oldCW[TCi]) * PFi ) –1
PFi is the persistence factor
o Replace DIFS with AIFS (Arbitration InterFrame Space)
AIFS[i] = DIFS + TCi
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
EDCF

CSMA/CA and Exponential Backoff
Eight Traffic Categories (TCs) within one station
High priority
Low priority
DCF
TC7
TC6
TC5
TC4
TC3
TC2
TC1
TC0
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Backoff
(AIFS)
Transmission
attempt
Scheduler
(resolve virtual collisions by granting permission to highest priority)
Transmission
AIFS:Arbitration Inter-Frame Space
attempt
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
EDCA parameters for AC
¾ 4 access categories (AC),
¾ AIFS[AC] = SIFS + AIFSN[AC] * aSlotTime, AIFSN[AC] ≥ 2.
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
EDCA and AC Mapping
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
HCF: Hybrid Coordination Function

During CFP
o Poll STAs and give a station the permission to access channel
o Starting time and maximum duration of each TXOP are specified by the
HC

During CP
o Can use the EDCA rules
o HC can issue polled TXOPs in the CP by sending CF-Poll after a PIFS
idle period
o Controlled Contention
Allows STAs to request the allocation of polled TXOPs
STAs send resource request frames with the requested TC and
duration
HC sends an ACK for resource request to the STA
TXOP
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
HCF superframes
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11e
Performance

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
Wireless LAN Security Issues
Issue
Wireless sniffer can view all WLAN
data packets
Anyone in AP coverage area can get
on WLAN
802.11 WEP Solution
Encrypt all data transmitted between
client and AP
Without encryption key, user cannot
transmit or receive data
Wireless LAN
(WLAN)
Wired LAN
client
access point (AP)
Goal: Make WLAN security equivalent to that of wired LANs (Wired Equivalent
Privacy)
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP – Protection for 802.11b

Wired Equivalent Privacy
o No worse than what you get with wire-based systems.

Criteria:
o “Reasonably strong”
o Self-synchronizing – stations often go in and out of coverage
o Computationally efficient – in HW or SW since low MIPS CPUs might be
used
o Exportable – US export codes (relaxed in Jan 2000 / “Wassenaar
Arrangement”)
o Optional – not required to used it

Objectives:
o confidentiality
o integrity
o authentication
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP – How It Works

Secret key (40 bits or 104 bits)
o can use up to 4 different keys

Initialization vector (24 bits, by IEEE std.)
o total of 64 or 128 bits “of protection.”

RC4-based pseudo random number generator (PRNG)
Integrity Check Value (ICV): CRC 32
Frame header
IV
(4 bytes)
Init Vector
(3 bytes)
Data (PDU)
(≥ 1 byte)
1 byte
Pad
6 bits
Key ID
2 bits
ICV
(4 bytes)
FCS
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP Encryption Process
1)
2)
3)
4)
5)
Compute ICV using CRC-32 over plaintext msg.
Concatenate ICV to plaintext message.
Choose random IV and concat it to secret key and input it to RC4 to
produce pseudo random key sequence.
Encrypt plaintext + ICV by doing bitwise XOR with key sequence to
produce ciphertext.
Put IV in front of cipertext.
Initialization
Vector (IV)
Secret Key
Seed
WEP PRNG
Key
Sequence
Plaintext
Integrity Algorithm
Integrity Check Value (ICV)
IV
Ciphertext
Message
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP Decryption Process
IV of message used to generate key sequence, k.
2) Ciphertext XOR k Î original plaintext + ICV.
3) Verify by computing integrity check on plaintext (ICV’) and
comparing to recovered ICV.
4) If ICV ≠ ICV’ then message is in error; send error to MAC
management and back to sending station.
1)
Secret Key
IV
Message
Ciphertext
WEP PRNG
Key
Sequence
Plaintext
Seed
Integrity Algorithm
ICV’
ICV
ICV’ - ICV
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP Station Authentication

Wireless Station (WS) sends
Authentication Request to Access Point
(AP).
AP sends (random) challenge text T.
WS sends challenge response
(encrypted T).
AP sends ACK/NACK.
WS
Auth. Req.
AP
Challenge Text
Challenge Response
Ack
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
WEP Weaknesses

Forgery Attack
o Packet headers are unprotected, can fake src and dest addresses.
o AP will then decrypt data to send to other destinations.
o Can fake CRC-32 by flipping bits.

Replay
o Can eavesdrop and record a session and play it back later.

Collision (24 bit IV; how/when does it change?)
o Sequential: roll-over in < ½ day on a busy net
o Random: After 5000 packets, > 50% of reuse.

Weak Key
o If ciphertext and plaintext are known, attacker can determine key.
o Certain RC4 weak keys reveal too many bits. Can then determine RC4
base key.

Well known attack described in Fluhrer/Mantin/Shamir paper
o “Weaknesses in the Key Scheduling Algorithm of RC4”, Scott Fluhrer,
Itsik Mantin, and Adi Shamir
o using AirSnort: http://airsnort.shmoo.com/
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
Ways to Improve Security with WEP

Use WEP(!)
Change wireless network name from
default
o any, 101, tsunami

Turn on closed group feature, if
available in AP
o Turns off beacons, so you must
know name of the wireless
network

MAC access control table in AP
o Use Media Access Control
address of wireless LAN cards to
control access

Use Radius support if available in AP
o Define user profiles based on
user name and password

War Driving in New Orleans
(back in December 2001)
o Equipment
Laptop, wireless card, software
GPS, booster antenna (optional)
o Results
64 Wireless LAN’s
Only 8 had WEP Enabled (12%)
62 AP’s & 2 Peer to Peer
Networks
25 Default (out of the box)
Settings (39%)
29 Used The Company Name
For ESSID (45%)
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
War Driving in New Orleans
(back in December 2001)
Redes Inalámbricas
Ubicua/2006-2007
Redes
WEP y IEEE802.11i
802.11i Task Group Recommendations

Mutual Authentication
Dynamic Session Key
Message Integrity Check (MIC)
Temporal Key Integrity Protocol (TKIP)
o Per-packet Key Hashing
o Initialization Vector Sequencing
o Rapid Re-Keying

Future
o Stronger encryption schemes such as AES

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
0
1
IEEE802.11n
Ways to increase data rate

Conventional single tx and rx radio systems
o Increase transmit power
Subject to power amplifier and regulatory limits
Increases interference to other devices
Reduces battery life
o Use high gain directional antennas
Fixed direction(s) limit coverage to given sector(s)
o Use more frequency spectrum
Subject to FCC / regulatory domain constraints

Advanced MIMO: Use multiple tx and / or rx radios!
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Conventional (SISO): Wireless Systems
channel
Bits
DSP
Radio
TX

Bits
DSP
RX
Conventional “Single Input Single Output” (SISO) systems were favored for simplicity
and low-cost but have some shortcomings:
o Outage occurs if antennas fall into null
Switching between different antennas can help
o Energy is wasted by sending in all directions
Can cause additional interference to others
o Sensitive to interference from all directions
o Output power limited by single power amplifier
1
0
2
Radio
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
0
3
IEEE802.11n
MIMO Wireless Systems
D
S
P
Bits
TX

Radio
Radio
channel
Radio
Radio
D
S
P
Bits
RX
Multiple Input Multiple Output (MIMO) systems with multiple parallel radios improve
the following:
o Outages reduced by using information from multiple antennas
o Transmit power can be increased via multiple power amplifiers
o Higher throughputs possible
o Transmit and receive interference limited by some techniques
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
0
4
IEEE802.11n
MIMO Alternatives

There are two basic types of MIMO technology:
o Beamforming MIMO
Standards-compatible techniques to improve the range of existing data rates
using transmit and receive beamforming
Also reduces transmit interference and improves receive interference
tolerance
o Spatial-multiplexing MIMO
Allows even higher data rates by transmitting parallel data streams in the
same frequency spectrum
Fundamentally changes the on-air format of signals
– Requires new standard (11n) for standards-based operation
– Proprietary modes possible but cannot help legacy devices
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Beamforming MIMO Overview
Consists of two parts to make standard 802.11 signals “better
Uses multiple transmit and/or receive radios to form coherent 802.11a/b/g compatible
signals
o Receive beamforming / combining boosts reception of
standard 802.11 signals
D
S
P
Radio
Bits
TX
Radio
Radio
Bits
RX
Phased array transmit beamforming to focus energy to each
receiver
D
S
P
Bits
1
0
5
TX
Radio
Radio
Radio
Bits
RX
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
0
6
IEEE802.11n
Benefits of Beamforming

Benefits
o Power gain (applicable only to transmit beamforming)
Power from multiple PA’s simultaneously
(up to regulatory limits)
Relaxes PA requirements, increases total
output power delivered
o Array gain: “dynamic high-gain antenna”
o Interference reduction
Reduce co-channel inter-cell interference
o Diversity gain: combats fading effects
o Multipath mitigation
Per- subcarrier beamforming to reduce spectral nulls
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Multipath Mitigation
o Multiple transmit and receive radios allow compensation of notches on one channel by nonnotches in the other
o Same performance gains with either multiple tx or rx radios and greater gains with both multiple
tx and rx radios
1
0
7
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Spatial Multiplexing MIMO Concept

Spatial multiplexing concept:
o Form multiple independent links (on same channel) between transmitter and
receiver to communicate at higher total data rates
DSP
Bits
Bit
Split
TX
1
0
8
DSP
Radio
Radio
Radio
Radio
DSP
DSP
Bit
Merge
RX
Bits
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Spatial Multiplexing MIMO Difficulties

o However, there are cross-paths between antennas
DSP
Bits
Bit
Split
TX
1
0
9
DSP
Radio
Radio
Radio
Radio
DSP
DSP
Bit
Merge
RX
Garbage
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE802.11n
Spatial Multiplexing MIMO Reality

o However, there are cross-paths between antennas
o The correlation must be decoupled by digital signal processing algorithms
DSP
Bits
Bit
Split
TX
1
1
0
DSP
Radio
Radio
Radio
Radio
D
S
P
Bit
Merge
RX
Bits

o la capa física
o
o
o
o
o
la capa MAC
MIMO: 802.11n
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Herramientas genéricas

Existen varias herramientas de red de propósito general, que suelen estar
disponibles para la mayor parte de los sistemas operativos, y que permiten obtener
información importante relativa a conectividad, direccionamiento IP, etc. Estas son:
o
o
o
o

ipconfig / ifconfig
route
ping / traceroute
Ethereal (aplicación que no integra el S.O.)
Por otro lado están disponibles herramientas de red que sólo se aplican a las redes
locales inalámbricas, como:
o Kismet
o Airopeek
o Network Stumbler
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Ethereal

Herramienta de código abierto disponible para Linux y Windows
Permite capturar paquetes en modo promiscuo de cualquier
interface del sistema
Ofrece una descripción muy detallada de cada paquete recibido,
permitiendo visualizar las diferentes cabeceras de los protocolos
utilizados y el contenido de los datos (¡peligroso!)
Permite guardar los resultados del análisis en un fichero y
recuperarlos más tarde
Permite obtener estadísticas variadas
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Ethereal
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Kismet

Kismet es una herramienta que opera con información del nivel
MAC de 802.11.
Puede funcionar como:
o Detector de redes inalámbricas
o Sniffer (captura de paquetes en modo promiscuo)
o Sistema de detección de intrusos

Además tiene otras características que lo hacen muy interesante
como:
o compatibilidad con Ethereal y Airsnort
o detección de rango IP de la red
o Descubierta de puntos de acceso ocultos

Kismet viene con su propio programa de GPS que permite
interpolación de valores, aunque no es muy exacto:
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
gKismet
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Network Stumbler

Busca tramas de gestión 802.11
Permite guardar y exportar los datos en varios formatos distintos
Soporta GPS y permite guardar información GPS juntamente con
los demás datos
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Network Stumbler
El interface gráfico utilizado es muy intuitivo y permite
variados tipos de análisis de forma sencilla y directa:
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Network Stumbler
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Beacons

Algunos puntos de acceso permiten ajustar el intervalo entre
beacons consecutivos. Aumentar la tasa de generación de beacons
ofrece como ventajas:
o Permitir que el escaneo por parte de los clientes sea más rápido y fiable
o Permitir, además, que el roaming entre puntos de acceso se haga de
forma más rápida y eficiente.

Por otro lado, reducir la tasa de generación de beacons también
tiene algunas ventajas:
o Los beacons consumen recursos del canal, reduciendo el ancho de
banda disponible
o De forma indirecta, aumento las capacidades de ahorro de energía de
los nodos móviles
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Umbral de RTS/CTS

Si el entorno de trabajo es suficiente grande como para que existan
varios terminales inalámbricos que no están al alcance uno del otro,
pero comparten un mismo punto de acceso o terminal intermedio,
habilitar la función de RTS/CTS puede mejorar las prestaciones si la
congestión es elevada.
En general, si la red no está congestionada, activar el RTS/CTS
provocará una disminución del ancho de banda disponible.
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Umbral de fragmentación

El 802.11 ofrece soporte a la fragmentación como solución para
intentar reducir los efectos de las interferencias
En entornos donde existe ruido electromagnético en forma de
ráfagas, la fragmentación permite ajustar el nivel de robustez:
Mayores valores para el umbral de fragmentación permite aumentar
el ancho de banda en general, pero reduce la robustez ante errores
Menores valores para este umbral reduce el ancho de banda
disponible en general, pero permite obtener mejores prestaciones si
el entorno es ruidoso
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Retry limits

La mayor parte de dispositivos inalámbricos permite ajustar los
valores de los limites para reintento de transmisión.
El “short retry limit” indica el numero de reintentos para tramas de
tamaño inferior al umbral de RTS/CTS.
El “long retry limit” indica el numero de reintentos para tramas de
tamaño igual o superior al umbral de RTS/CTS.
Si aumentamos estos valores, ofrecemos más fiabilidad a las
estaciones que sufren de peores condiciones en términos de
relación señal ruido. Por otra parte, a nivel global el efecto suele ser
el de reducir el ancho de banda agregado de la red.
Si disminuimos los valores logramos menor ocupación de buffers y
por veces mejor comportamiento por parte de TCP.
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Ahorro de energía

La opción de ahorro de energía permite a las estaciones móviles
desconectar sus dispositivos inalámbricos durante ciertos periodos
Sí estamos ante una red de infraestructura (típico) el punto de
acceso deberá guardar en un buffer todos los paquetes destinados
a estaciones durmientes hasta que estas se despierten.
Problemas:
o Si el numero de estaciones en modo de ahorro de energía es elevado,
el punto de acceso puede sobrecargarse o restringir nuevas conexiones
o Para aplicaciones con requisitos de calidad de servicio, las
interrupciones causadas por el modo de ahorro de energía pueden ser
problemáticas
Redes Inalámbricas
Ubicua/2006-2007
Redes
herramientas
Optimización: Potencia de la señal

Si un punto de acceso o dispositivo inalámbrico permite ajustar la
potencia de la señal, esto permite obtener beneficios:
o Puedo aumentar de forma sencilla el área de cobertura de un punto de
acceso
o Mayor potencia en la señal recibida implica mayor robustez ante errores,
lo que reduce el numero de retransmisiones y aumenta el ancho de
banda
o El 802.11 permite ajustar el bitrate según la calidad de la señal, por lo
que puedo aumentar aún más el ancho de banda

Por otro lado también puede generar problemas:
o Aumento la interferencia con puntos de acceso / terminales cercanos
que operan en el mismo canal, pudiendo reducir el ancho de banda
agregado de la red
o Facilito la detección de los puntos de acceso por entidades exteriores
o Reduzco el tiempo de vida de los dispositivos con batería

Redes WPAN: Bluetooth
agradecimientos/acknowledgments
Foo Chun Choong, Ericsson Research / Cyberlab
Singapore, and Open Source Software Lab, ECE
Dept, NUS.
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Specifications

Bluetooth is a system solution comprising hardware, software and
interoperability requirements. The Bluetooth specifications specify
the complete system.
De facto standard - open specifications.
Two part document - Volume 1:Core and Volume 2:Profiles.
Bluetooth specs developed by Bluetooth SIG.
o February 1998: The Bluetooth SIG is formed
promoter company group: Ericsson, IBM, Intel, Nokia, Toshiba
o May 1998: The Bluetooth SIG goes “public”
o July 1999: 1.0A spec (>1,500 pages) is published
o December 1999: ver. 1.0B is released
o December 1999: The promoter group increases to 9
3Com, Lucent, Microsoft, Motorola
o February 2000: There are 1,500+ adopters

0.7 ---> 0.9 ---> 1.0A ---> 1.0B ---> 1.1 -->
November 2003: release 1.2
Currently (November 2004), release 2.0
1
2
7
o (aka EDR or Extended Data Rate) triples the data rate up to about 2
Mb/s
1
2
8
Redes Inalámbricas
Ubicua/2006-2007
Redes
release 2.0: the new partitioning
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
2
9
Bluetooth usage

Low-cost, low-power, short range radio Ö a cable replacement
technology
o Common (File transfer, synchronisation, internet bridge, conference
table)
o Hidden computing (background synchronisation, audio/video player)
o Future (PC login, remote control)

Why not use Wireless LANs?
o power
o cost
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
3
0
Bluetooth RF

1 Mb/s symbol rate
Normal range
10m (0dBm)
Optional range
100m (+20dBm)
Normal transmission power 0dBm (1mW)
Optional transmission power -30 to +20dBm (100mW)
Receiver sensitivity
-70dBm
Frequency band
2.4Ghz ISM band
Gross data rate
1Mbit/s
Max data transfer
721+56kbps/3 voice channels
Power consumption 30uA(max), 300uA(standby), ~50uA(hold/park)
Packet switching protocol based on frequency hop scheme with
1600 hops/s
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Power Class Table
Power Class
Max Output Power
Max Output Power
Expected Range
Range in
Free Space
Class 1
100mW
20dBm
42m
300m
Class 2
2.5mW
4dBm
16m
50m
Class 3
1mW
0dBm
10m
30m
Bluetooth Power Class Table
1
3
1
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Network Topology

Bluetooth devices have the ability to work as a slave or a master in
an ad hoc network. The types of network configurations for
Bluetooth devices can be three.
o Single point-to-point (Piconet): In this topology the network consists of
one master and one slave device.
o Multipoint (Piconet): Such a topology combines one master device and
up to seven slave devices in an ad hoc network.
o Scatternet: A Scatternet is a group of Piconets linked via a slave device
in one Piconet which plays master role in other Piconet. The Bluetooth standard
M
M
M
Master/Slave
S
M
S
S
1
3
2
S
S
S
i) Piconet (Pointto-Point)
S
S
ii) Piconet (Multipoint)
S
S
iii) Scatternet
does not describe any
routing protocol for
scatternets and most of
the hardware available
today has no capability
of forming scatternets.
Some even lack the
ability to communicate
between slaves of one
piconet or to be a
member of two piconets
at the same time.

Composed of protocols to allow
Bluetooth devices to locate each other
and to create, configure and manage
both physical and logical links that
allow higher layer protocols and
applications to pass data through these
transport protocols
IP
SDP
RFCOMM
Data
Audio
Transport Protocol Group
1
3
3
Applications
Source: Farinaz Edalat, Ganesh Gopal, Saswat Misra, Deepti Rao
Co
ntr
ol
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Protocol Stack
L2CAP
Link Manager
Baseband
RF
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
3
4
Transport Protocol Group (contd.)

Radio Frequency (RF)
o Sending and receiving modulated
bit streams

Baseband
o Defines the timing, framing
o Flow control on the link.

Link Manager

The Radio, Baseband and Link
Manager are on firmware.
The higher layers could be in software.
The interface is then through the Host
Controller (firmware and driver).
The HCI interfaces defined for
Bluetooth are UART, RS232 and USB.
o Managing the connection states.
o Enforcing Fairness among
slaves.
o Power Management

Logical Link Control & Adaptation
Protocol
o Handles multiplexing of higher
level protocols
o Segmentation & reassembly of
large packets
o Device discovery & QoS
BLUETOOTH SPECIFICATION, Core Version 1.1 page 543
Additional transport protocols to
allow existing and new applications
to operate over Bluetooth. Packet
based telephony control signaling
protocol also present. Also includes
Service Discovery Protocol.
IP
SDP
RFCOMM
Data
Middleware Protocol Group
Service Discovery Protocol (SDP)
¾ Means for applications to discover device info,
services and its characteristics.
TCP/IP
¾ Network Protocols for packet data
communication, routing
RFCOMM
1
3
5
Applications
¾ Cable replacement protocol, emulation of serial
ports over wireless network
Audio
Co
ntr
ol
Redes Inalámbricas
Ubicua/2006-2007
Redes
Middleware Protocol Group
L2CAP
Link Manager
Baseband
RF
Application Group
Applications
IP
Consists of Bluetooth aware as
well as un-aware applications.
SDP
RFCOMM
Data
Audio
L2CAP
Link Manager
Baseband
RF
1
3
6
Co
ntr
ol
Redes Inalámbricas
Ubicua/2006-2007
Redes
Application Group
1
3
7
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth stack: short version
Applications
RFCOMM
SDP
L2CAP
HCI
Link Manager
Baseband
RF
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
3
8
End to End Overview of Lower Software Layers to
Transfer Data
BLUETOOTH SPECIFICATION, Core Version 1.1 page 544
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
3
9
Time-Division Duplex Scheme

Bluetooth devices use a Time-Division Duplex (TDD) scheme
Channel is divided into consecutive slots (each 625 µs)
One packet can be transmitted per slot
Subsequent slots are alternatively used for transmitting and receiving
o Strict alternation of slots b/t the master and the slaves
o Master can send packets to a slave only in EVEN slots
o Slave can send packets to the master only in the ODD slots
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
4
0
Frequency Hop Spread-Spectrum
Bluetooth channel is represented by a
pseudo random hopping sequence
through the entire 79 RF frequencies
Nominal hop rate of 1600 hops per
second
Channel Spacing is 1 MHz
Area
USA
Europe
Spain
France
Japan
Frequency Band
(GHz)
2.400-2.4835
2.400-2.4835
2.445-2.475
2.4465-2.4835
2.471-2.497
Bluetooth
Channels
79
79
23
23
23
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
4
1
Physical Link Definition

Synchronous Connection-Oriented (SCO) Link
o circuit switching
o symmetric, synchronous services
o slot reservation at fixed intervals

Asynchronous Connection-Less (ACL) Link
o packet switching
o (a)symmetric,
o asynchronous services
o polling access scheme
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
4
2
ACL data rates
Packet type
Name
Symmetric
(kbps)
Asymmetric
(kbps)
1 slot + FEC
DM1
108.8
108.8
108.8
1 slot
DH1
172.8
172.8
172.8
3 slot + FEC
DM3
256.0
384.0
54.4
3 slot
DH3
384.0
576.0
86.4
5 slot + FEC
DM5
286.7
477.8
36.3
5 slot
DH5
432.6
721.0
57.6
1
4
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
Multi-slot packets
fn
Single slot
Three slot
Five slot
fn+1
fn+2
fn+3
fn+4
fn+5
1
4
4
Redes Inalámbricas
Ubicua/2006-2007
Redes
Symmetric single slot
fn
Master
Slave
fn+1
fn+2
fn+3
fn+4
fn+5 fn+6
fn+7
fn+8
fn+9
fn+10 fn+11 fn+12
1
4
5
Redes Inalámbricas
Ubicua/2006-2007
Redes
Mixed Link Example
MASTER
SLAVE 1
SLAVE 2
SLAVE 3
SCO
ACL
SCO
ACL
ACL SCO
SCO
ACL
Redes Inalámbricas
Ubicua/2006-2007
Redes
Polling on ACL links

Slave is allowed to send only after it has been polled.
Master polls slave at least Npoll slots (negotiated).
Master may send at will.
Polling algorithm is proprietary.
POLL
Data
Master
Data
Slave
Slot
TDD frame
1
4
6
time
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Connection States

1
4
7
There are four Connection states on
Bluetooth Radio:
Active: Both master and slave
participate actively on the channel by
transmitting or receiving the packets
(A,B,E,F,H)
Sniff: In this mode slave rather than
listening on every slot for master's
message for that slave, sniffs on
specified time slots for its messages.
Hence the slave can go to sleep in the
free slots thus saving power (C)
Hold: In this mode, a device can
temporarily not support ACL packets
and go to low power sleep mode to
make the channel available for things
like paging, scanning etc (G)
Park: Slave stays synchronized but not
participating in the Piconet, then the
device is given a Parking Member
Address (PMA) and it loses its Active
Member Address (AMA) (D,I)
A
H
B
C
Master
H
D
E
I
G
Bluetooth Connection States
C
F
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Forming a Piconet

1
4
8
Inquiry: Inquiry is used to find the
identity of the Bluetooth devices in the
close range.
Inquiry Scan: In this state, devices are
listening for inquiries from other
devices.
Inquiry Response: The slave responds
with a packet that contains the slave's
device access code, native clock and
some other slave information.
Page: Master sends page messages
by transmitting slave's device access
code (DAC) in different hop channels.
Page Scan: The slave listens at a
single hop frequency (derived from its
page hopping sequence) in this scan
window.
Slave Response: Slave responds to
master's page message
Master Response: Master reaches this
substate after it receives slave's
response to its page message for it.
Master
Inquiry
Slave
1
Inquiry Scan
2
3
Page
Inquiry
Response
4
5
Page Scan
Slave Response
6
Master
Response
7
Connection
Connection
Forming a Piconet Procedures
Redes Inalámbricas
Ubicua/2006-2007
Redes
Connection State Machine
Inquiry
Page
Standby
Connected
Transmit data
Park
1
4
9
Hold
Sniff
Redes Inalámbricas
Ubicua/2006-2007
Redes
SDP - Service Discovery

Focus
o Service discovery within Bluetooth environment
o Optimized for dynamic nature of Bluetooth
o Services offered by or through Bluetooth devices

Some Bluetooth SDP Requirements (partial list)
o Search for services based upon service attributes and service classes
o Browse for services without a priori knowledge of services
o Suitable for use on limited-complexity devices
o Enable caching of service information

How it works?
o Establish L2CAP connection to remote device
o Query for services
Search for specific class of service, or
Browse for services
1
5
0
o Retrieve attributes that detail how to connect to the service
o Establish a separate (non-SDP) connection to use the service
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
5
1
L2CAP packet format
16
Length
L2CAP
72
Baseband
16
Access
Code
0 - 65,535 bits
DCID
Payload
54 bits
Header
Payload
Header
Payload
CRC
Redes Inalámbricas
Ubicua/2006-2007
Redes
Packet Structure
72 bits
54 bits
Access Code Header
Payload
Control packets
ID*
Null
Poll
FHS
DM1
Guard
Data/voice packets
data
Voice
HV1
HV2
HV3
DV
•No retries
•No CRC
•FEC (optional)
1
5
2
220µs
0 - 2745 bits
(136 bits)
DH1
DH3
DH5 (2712 bits)
DM1
DM3
DM5
Header
Data
•ARQ
•CRC
•FEC (optional)
CRC
1
5
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluez
1
5
4
Redes Inalámbricas
Ubicua/2006-2007
Redes
Resultados: Prueba de Interferencia
1
5
5
Redes Inalámbricas
Ubicua/2006-2007
Redes
Resultados: Tiempo de Inquiry
1
5
6
Redes Inalámbricas
Ubicua/2006-2007
Redes
Resultados: Comparación throughput

Represents default solution for a
usage model
Vertical slice through the protocol
stack
Basis for interoperability and logo
requirements
Each Bluetooth device supports
one or more profiles
Applications
Protocols
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
5
7
Interoperability & Profiles
Profiles
Source: Dr. Chatschik Bisdikian [BT_OVERVIEW_UNIVMARYLAND_03_2001.PPT]
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth 1.0 - Usage Models

Internet Bridge
o Dial-up Networking & Fax capabilities
o Notebook or desktop computer as data terminal
o Mobile phone or cordless modem as modem

Headset
o Wireless audio capability
o Headset as audio input and output device
o Mobile Phone as audio gateway

Cordless Phone & Intercom
o Cordless phone - connection to PSTN at home or the office
incurring a fixed line charge.
calls via a voice basestation
o Intercom - connection directly to other phones
1
5
8
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
5
9
Bluetooth 1.0 - Usage Models (cont.)

File Transfer & Object Exchange
o Transfer data objects from one device to another.
Generic object types, e.g., xls, ppt, wav, jpg, doc, entire folders, …
Possibility to browse the contents of the folders on a remote device.
o Simple push and exchange operations, e.g., business card exchange

Synchronization
o Sync of PIM data - typically phonebooks, calendars, messages, and
notes

LAN Access
o Multiple data terminals use a LAN access point as a wireless connection
to a LAN
o DTs operate as connected to the LAN via dialup networking.
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
0
Next Steps of Bluetooth

Bluetooth in and around the Car
Bluetooth “Spontaneous” Networking
Still Imaging
Bluetooth Printing
Native support for richer audio/voice/video
Bluetooth Human Interface Device (HID)
1
6
1
Redes Inalámbricas
Ubicua/2006-2007
Redes
Bluetooth Profiles
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
2
Bluetooth Modules – Free2Move

Bluetooth modules add the components needed to make a working
radio: crystal, antenna, flash memory. The current generation of
modules measure about 1”x0.5” w/ antenna.

Free2Move (Sweden) has some particularly interesting modules
based on CSR BlueCore2-flash
chips with audio.

This radio offers a functioning SPP for
serial data, a 15-bit audio channel,
and another 8-bit A/D channel.
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
3
More Bluetooth Hardware
Cambridge Scientific Radio (CSR) chips (in most peripherals)
BlueCore2 chip Bluetooth v1.1, 16-bit XAP2 processor, A/D, audio options
BlueCore3 chip Bluetooth v1.1-1.2, XAP2 processor, audio DSP option
BlueCore4 chip Bluetooth V2.0, XAP2 processor
AT&T Broadcom chips (in many PC + PDAs)
BCM2040 Bluetooth v1.1-1.2, 8-bit 8051 processor
BCM2037 Bluetooth v2.0 with audio, 16-bit ARM7 processor
BCM2045 Bluetooth v2.0 host side chip
Class 2 Modules (with antenna)
Free2Move FM03AC2 Bluetooth v1.1 qualified, SPP, 15-bit audio + 8 bit A/D
Taiyo Yuden EYMF2CAMM-XX Bluetooth v1.1 qualified, serial port profile
BlueGiga WT12 Bluetooth v2.0 EDR qualified, serial port profile + PCM
Class 1 Modules (no antenna)
Free2Move FM2M03C1 Bluetooth v1.1 qualified, SPP, 15-bit audio + 8 bit A/D
BlueGiga Wrap Thor 2022 Bluetooth v1.1 qualified, SPP, DUN, OBEX, HID
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
4
Otras tecnologías

HomeRF
o HomeRF-Lite Ö Philips RF-Lite Program Ö Firefly

Zigbee

Cypress WirelessUSB

Otros estándares IEEE 802
1
6
6
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE 802 Working Group
1
6
7
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE 802.15 Working Group for WPAN
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
8
IEEE 802.15 - General

Wireless Personal Area Networks (WPANs)
o Short Range
o Low Power
o Low Cost
o Small Networks

Communication within a persons operating space
Outline:
o IEEE 802.15.1 – ”Bluetooth”
o IEEE 802.15.3 – High data rate WPAN
o IEEE 802.15.4 – Low data rate WPAN
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
6
9
IEEE 802.15.2

IEEE 802.15.2
o Coexistence between
802.15 and 802.11
o Predefined traffic
management rules for
coexistence
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
0
Broadband Wireless Access (BWA)

What is a BWA?
o High speed connection
o Uses radio waves
o Point to multipoint system
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
1
Broadband Access to Buildings

The “Last Mile”
o Fast local connection to network

Business and residential customers want it
o Data
o Voice
o Video distribution
o Real-time videoconferencing
o etc.

High-capacity cable/fiber to every user is expensive
o Construction costs do not follow Moore’s Law
Redes Inalámbricas
Ubicua/2006-2007
Redes
WirelessMAN: Wireless Metropolitan Area Network
Basestation
SOHO
customer
Residential
customer
Multi-tenant
customers
Core
network
1
7
2
repeater
Basestation
Source: Nokia Networks
SME
customer
Redes Inalámbricas
Ubicua/2006-2007
Redes
Properties of IEEE Standard 802.16

Broad bandwidth
o Up to 134 Mbit/s in 28 MHz channel (in 10-66 GHz air interface)

Supports multiple services simultaneously with full QoS
o Efficiently transport IPv4, IPv6, ATM, Ethernet, etc.

Bandwidth on demand (frame by frame)
MAC designed for efficient used of spectrum
Comprehensive, modern, and extensible security
Supports multiple frequency allocations from 2-66 GHz
o ODFM and OFDMA for non-line-of-sight applications

Link adaptation: Adaptive modulation and coding
o Subscriber by subscriber, burst by burst, uplink and downlink

Point-to-multipoint topology, with mesh extensions
Support for adaptive antennas and space-time coding
Extensions to mobility are coming next.
1
7
3
Redes Inalámbricas
Ubicua/2006-2007
Redes
WiMAX Forum

o It is a non-profit organization
o It was formed in 2003
o It has more than 110 members such as Alcatel, AT&T, Intel, Nortel,
Motorola, SBC, Siemens, and so forth..

Mission: To promote deployment of BWA by using a global standard
and certifying interoperability of products and technologies.
Principles:
o Support IEEE 802.16 above 11 GHz
o Propose access profiles for the IEEE 802.16 standard
o Guarantee known interoperability level
o Promote IEEE 802.16 standard to achieve global acceptance
o Open for everyone to participate

1
7
4
WiMAX: Worldwide Interoperability for Microwave Access
Developing & submitting baseline test specs
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
5
WiMAX
Technology

Worldwide Interoperability of Microwave Access (WiMAX)
It will provide fixed, nomadic, portable and, eventually, mobile
wireless broadband connectivity.
connectivity at rates of up to 75 Mb/sec
WiMAX 10-66 GHz technical working group
o two MAC system profile
o two primary PHY system profile

WiMAX 2-11 GHz technical working group
o defining MAC and PHY system profile for IEEE 802.16e and HiperMAN
standards.

Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
6
What is WiMAX, 802.16d and e
A
specification of 915 pages accepted in 2004. A
member of the IEEE802 family of specifications.
IEEE802.16-2004 include P2P, P2MP and mesh access
networks
2-11GHz NLOS 10-66 GHz LOS
During 2005 IEEE 802.16e includes mobility.
During 2005 MIB standardized as well
IEEE802.16 is supported by the industry group WiMAX
IEEE802.11 is supported by the industry group WiFi
1
7
7
Redes Inalámbricas
Ubicua/2006-2007
Redes
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
8
WiMAX vs. 3G, pros and cons

Cost
o Lower equipment cost for WiMAX due to certified products (compare with WiFi)
o WiMAX require new infrastructure while HSPA rides on UMTS

Coverage
o Roughly the same coverage (average ~5 km)

Performance
o Roughly the same performance (average ~2 Mb/s per user)

Market window
o HSDPA launches in 2006 while HSUPA will come in 2008?
o WiMAX standard set end of 2005 -> first products in 2007

Acceptance
o HSPA has a higher acceptance with mobile operator
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
7
9
IEEE Standard 802.16: Tutorial
IEEE Communications Magazine, June 2002
(available on 802.16 web site)
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
0
IEEE 802.20 MBWA
an overview

MBWA Working Group was approved on the 11th of December 2002
To prepare a formal specification for a packed-based air interface
designed for IP-based services with peak data rates per user in
excess of 1 Mbps
Will address MBWA in licensed bands below 3.5 GHz MBWA
Could provide commuters with reliable high-speed wireless voice
and data links from trains and cars travelling at up to 250km/h
(155miles/h).
Redes Inalámbricas
Ubicua/2006-2007
Redes
The vision of the IEEE 802.20
Mobile Broadband
Wireless Access
Home
Domain
Video Streaming Conferencing Apps
Field Service Apps
Portable Remote
Access Services
Work
Domain
Portable
Office
Seamless
Ubiquitous
Experience
High BW Connectivity
Hotel/Motel
Mobile Office (Voice
and Data Apps)
Mobile
Domain
Portable Services
Reservations-Listings
Directions Services
1
8
1
Mobile Commerce
Services
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
2
.16 and .20 comparison

IEEE 802.20 and IEEE 802.16e standards seem very similar.
But
there are some important differences !!!
802.16e
¾It is the extension of an existing
standard
802.20
¾It is starting from scratch
¾It operates in the 2 to11 GHz
licensed spectrum
¾It operates in the licensed band below
3.5 GHz
¾ Speeds of 75 to 93 miles/h
¾Speeds of 155 miles/ h
Redes Inalámbricas
Ubicua/2006-2007
Redes
Wireless Broadband Access Technology
WAN
3GPP, EDGE
(GSM)
IEEE 802.20
(proposed)
IEEE
802.16/16a/16e
Wireless MAN
IEEE
802.11/11a/11b/11g
Wireless LAN
IEEE 802.15
Bluetooth
1
8
3
MAN
LAN
PAN
ETSI HiperMAN &
HIPERACCESS
ETSI
HiperLAN
ETSI
HiperPAN
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
4
802.21

Approved as a full IEEE WG Feb 27th
Has been meeting as an ECSG for 1 year
Initial charter to study handover between
o 802.x Ù 802.x (where handover not supported)
o 802.x Ù 802.y (where x may not equal y)
o 802.x ÙNon 802 (e.g. cellular)
Now has approved PAR (Project Authorization Request) for ‘Media
Independent Handover Services’
Motivations:
o Multi-Interfaced Devices
o Session maintenance
Across heterogeneous media
Redes Inalámbricas
Ubicua/2006-2007
Redes
Relevant Elements in Network
L3 Network
AR
AP
802.y
AP
802.x
AP
802.x
AR
AR
AP
802.x
AP
802.y
Potential links
802.x
One or more
802 interfaces
1
8
5
802.y
Mobile Device
y=x | y!=x
Redes Inalámbricas
Ubicua/2006-2007
Redes
IEEE Standards
RAN
IEEE 802.22
40 km
sec
µ
25 w
o
sec
in d
µ
W
2.2 tion
)
orp refix
5
s
2
0. h ab lic p
a t yc
ltip (C
0.8 Mu
18 Mbps
BW= 6,7,8 MHz
54 - 862 MHz
1
8
6
“Regional Area
Network”
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
7
IEEE 802.22
Project Authorization Request (PAR)

Wireless Regional Area Networks (WRAN)
802.22 is to define:
o MAC: Cognitive Wireless RAN Medium Access Control
o PHY: Physical Layer specifications
o Policies and procedures for operation in the TV Bands

“This standard specifies the air interface, including the medium
access control layer (MAC) and physical layer (PHY), of fixed pointto-multipoint wireless regional area networks operating in the
VHF/UHF TV broadcast bands between 54 MHz and 862 MHz.”
Redes Inalámbricas
Ubicua/2006-2007
Redes
1
8
8
IEEE 802.22
Project Authorization Request (PAR)

Purpose: “This standard is intended to enable deployment of
interoperable 802 multivendor wireless regional area network
products, to facilitate competition in broadband access by providing
alternatives to wireline broadband access and extending the
deployability of such systems into diverse geographic areas,
including sparsely populated rural areas, while preventing harmful
interference to incumbent licensed services in the TV broadcast
bands.”
Reason: “There is a large, untapped market for broadband wireless
access in rural and other unserved/underserved areas where wired
infrastructure cannot be economically deployed. Products based on
this standard will be able to serve those markets, taking advantage
of the favorable propagation characteristics in the VHF and low UHF
TV bands and increase the efficiency of spectrum utilization in
spectrum currently allocated to, but unused by, the TV broadcast
service.”