Transcript Document

Wireless LAN Technology
Wireless LANs
• A wireless LAN uses wireless transmission medium.
• Used to have high prices, low data rates, occupational
safety concerns, and licensing requirements.
• Problems have been addressed.
• Popularity of wireless LANs has grown rapidly.
2
Wireless LAN Applications
•
•
•
•
LAN Extension
Cross-building interconnect
Nomadic Access
Ad hoc networking
LAN Extension
• Wireless LAN linked into a wired LAN on same
premises
– Wired LAN
• Backbone
• Support servers and stationary workstations
– Wireless LAN
• Stations in large open areas
• Manufacturing plants, stock exchange trading floors,
and warehouses
• Saves installation of LAN cabling
• Eases relocation and other modifications to network
structure
• However, increasing reliance on twisted pair cabling for
LANs
– Most older buildings already wired with Cat 3 cable
– Newer buildings are prewired with Cat 5
• Wireless LAN to replace wired LANs is beginning to
happen, but most popular as a team
• In some environments, role for the wireless LAN
– Buildings with large open areas
• Manufacturing plants, stock exchange trading
floors, warehouses
• Historical buildings
• Small offices where wired LANs not economical
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Applications of Wireless LANs
Single Cell Wireless LAN (typical)
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Applications of Wireless LANs
Multi-Cell Wireless LAN
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Cross-Building Interconnect
• Connect LANs in nearby buildings
– Wired or wireless LANs
• Point-to-point wireless link is used
• Devices connected are typically bridges or routers
Ad Hoc Networking
• Temporary peer-to-peer network set up to meet
immediate need
• Example:
– Group of employees with laptops convene for a
meeting; employees link computers in a
temporary network for duration of meeting
Infrastructure Wireless LAN
Applications of Wireless LANs
Ad Hoc Networking
•Peer-to-peer network,
•No centralised server,
•No infrastructure,
•Temporary nature.
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Wireless LAN Requirements
THROUGHPUT –
should make efficient
use of medium
NUMBER OF
NODES- hundreds of
nodes across multiple
cells
CONNECTION TO
BACKBONE LAN –
use of control
modules
SERVICE AREA –
coverage area of 100
to 300m
BATTERY POWER
CONSUMPTION –
reduce power
consumption while not
in use
TRANSMISSION
ROBUST AND
SECURITY– reliability
and privacy/security
COLLOCATED
NETWORK
OPERATION –
possible interference
between LANs
LICENSE-FREE
OPERATION – not
having to secure a
license for the
frequency band used
by the LAN
HANDOFF/ROAMING
– enable stations to
move from one cell to
another
DYNAMIC
CONFIGURATIONaddition, deletion,
relocation of end
systems without
disruption
IEEE 802.11 Wireless LANs
 IEEE 802.11 (also known as Wi-Fi) defines a standard for
the physical and the data link layers of wireless LANs.
 The standard is defined for the license-free Industrial,
Scientific, Medical (ISM) bands.
ISM Bands
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ISM Bands
14
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IEEE 802 Protocol Layers
Protocol Architecture
• Functions of physical layer:
– Encoding/decoding of signals
– Preamble generation/removal (for
synchronization)
– Bit transmission/reception
– Includes specification of the transmission
medium
Protocol Architecture
• Functions of medium access control (MAC)
layer:
– On transmission, assemble data into a frame with
address and error detection fields
– On reception, disassemble frame and perform address
recognition and error detection
– Govern access to the LAN transmission medium
• Functions of logical link control (LLC)
Layer:
– Provide an interface to higher layers and perform flow
and error control
IEEE 802.11 Protocol Stack
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IEEE 802.11 Architecture
IEEE 802.11 Architecture
• Distribution system (DS)
• Access point (AP)
• Basic service set (BSS)
– Stations competing for access to shared wireless
medium
– Isolated or connected to backbone DS through AP
• Extended service set (ESS)
– Two or more basic service sets interconnected by DS
IEEE 802.11 – Architecture
• Smallest building block is basic service set (BSS)
– Number of stations
– Same MAC protocol
– Competing for access to same shared wireless
medium
• May be isolated or connected to backbone distribution system
(DS) through access point (AP)
– AP functions as bridge and a relay pt
• MAC protocol may be distributed or controlled by central
coordination function in AP
• BSS generally corresponds to cell
• DS can be switch, wired network, or wireless network
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BSS Configuration
• Simplest: each station belongs to single BSS
– Within range only of other stations within BSS
• Can have two BSS’s overlapping
– Station could participate in more than one BSS
• Association between station and BSS dynamic
– Stations may turn off, come within range, and
go out of range
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Extended Service Set (ESS)
• When two or more BSS are interconnected by DS
– Typically, DS is wired backbone but can be any
network
• Appears as single logical LAN to LLC (logical Link
Control)
• In BSS, client stations do not communicate
directly with each other, must pass through an AP
• In IBSS stations all communicate directly, no AP
is required
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Access Point (AP)
• Logic within station that provides access to DS
– Provides DS services in addition to acting as
station
• To integrate IEEE 802.11 architecture with wired
LAN, portal used
• Portal logic implemented in device that is part of
wired LAN and attached to DS
– E.g. Bridge or router
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IEEE 802.11 Protocol Stack
802.11 network standards
802.11 Releas
protocol
e
version
Freq.
(GHz)
Bandwidt
h
(MHz)
Data rate per
stream
(Mbit/s)
Allowable
MIMO
streams
Modulati Approxim Approxima
on
ate
te outdoor
indoor
range(m)
range(m)
97
Jun
1997
2.4
20
1, 2
1
a
Sep
1999
5
20
6, 9, 12, 18,
24, 36, 48, 54
1
b
Sep
1999
2.4
20
5.5, 11
1
DSSS
38
140
g
Jun
2003
2.4
20
6, 9, 12, 18,
24, 36, 48, 54
1
OFDM,
DSSS
38
140
n
Oct
2009
2.4/5
20
7.2, 14.4, 21.7,
28.9, 43.3,
57.8, 65, 72.2
15, 30, 45, 60,
90, 120, 135,
150
4
OFDM
70
250
70
250
3.7
40
DSSS,
FHSS
20
100
OFDM
35
120
—
5,000
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802.11n
• IEEE 802.11n has enhancements in three general
areas:
– multiple-input-multiple-output (MIMO) antenna
architecture
• most important enhancement
– radio transmission scheme
• increased capacity
– MAC enhancements
• most significant change is to aggregate multiple MAC
frames into a single block for transmission
IEEE 802.11 MAC Sublayer
CSMA/CD cannot be used in wireless LANs.
Because not all stations are within the radio range of each other.
It is also not possible to detect collision while transmitting
because most stations are half-duplex.
(a) The hidden station problem. (b) The exposed station problem
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IEEE 802.11 MAC Sublayer
•IEEE 802.11 MAC algorithm is called Distributed Foundation
Wireless MAC (DFWMAC).
•DFWMAC defines two sublayers. Distributed Coordination Function
(DCF) and Point Coordination Function (PCF).
•DCF is distributed with an optional centralised access control that
works on top of that (i.e., PCF).
•DCF is based on CSMA/CA (CSMA with Collision Avoidance) or
MACAW.
•All frame transmissions are acknowledged with ACK packets. This is
the way collision is avoided.
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IEEE 802.11 MAC Sublayer
DCF/MACAW
Virtual sensing
A
C
B
D
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Summarise DCF
•
•
•

No Central Control
Stations Compete for Time, just as in Ethernet
2 types
(a) When a station wants to transmit it senses the
channel- if idle, sends frame, it does not sense
while transmitting- data may be destroyed. If
busy defers some time (t) using Ethernet binary
exponential back-off.
 (b) as discussed on previous slide- channel sensing
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Distributed Coordination Function
• DCF sublayer uses CSMA
if station has frame
to send it listens to
medium
if medium is idle,
station may transmit
else waits until
current transmission
is complete
• no collision detection since on a wireless network
• DCF includes delays that act as a priority scheme
IEEE 802.11 MAC
Sublayer
More on Distributed Coordination
Function (DCF)
IFS: InterFrame Space
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IEEE 802.11 MAC Sublayer
Point Coordination Function (PCF)
•The access point periodically broadcasts beacon frames that
contains system parameters and invites stations to request
bandwidth.
•The access point can provide guaranteed bandwidth to stations
that are working in PCF mode.
•PCF allows the transport of real-time traffic over the wireless
LAN.
•PCF is not very well defined in the standard, and not commonly
implemented in most commercial access points. However, it
exists in the standard specification.
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Point Coordination Function (PCF)
alternative access
method implemented
on top of DCF
polling by centralized
polling master (point
coordinator)
uses PIFS when
issuing polls
if point coordinator
receives response, it
issues another poll
using PIFS
when poll issued,
polled station may
respond using SIFS
point coordinator polls
in round-robin to
stations configured
for polling
if no response during
expected turnaround
time, coordinator
issues poll
coordinator could lock
out asynchronous
traffic by issuing polls
have a superframe
interval defined
802.11 MAC Frame Format
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WiFi’s future: faster, smarter, and fewer cables
IEEE 802.11ac: Standard finalization is in late 2012, with
final 802.11 Working Group approved in Feb 2014.
Theoretically, this specification will enable multi-station
WLAN throughput of at least 1 gigabit per second and a
maximum single link throughput of at least 500 Mbit/s. This
is accomplished by extending the air interface concepts
embraced by 802.11n: wider RF bandwidth (up to 160
MHz), more MIMO spatial streams (up to 8), multi-user
MIMO, and high-density modulation (up to 256 QAM).
IEEE 802.11ac™-2013 2014 INTERNATIONAL CES, LAS VEGAS,
USA, 7 January 2014 - See more at:
http://standards.ieee.org/news/2014/ieee_802_11ac_ballot.html#sthash.o
IzisTd8.dpuf
802.11ac alone may be fast enough (7Gbps) to begin
making wired networks redundant.
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WiGig- Wireless Gigabit Alliance
IEEE 802.11 ad
• In June 2011, WiGig announced the release of its
certification-ready version 1.1 specification.
• The WiGig specification will allow devices to communicate
without wires at multi-gigabit speeds.
• 60GHz, (microwave Wi-Fi), low power, very high
performance – possibly 7Gbps – but over only very short
ranges, perhaps one to 10 metres, within a single room
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IEEE 802.11ac And 802.11ad?
IEEE 802.11ac and 802.11ad both provide much higher
data throughputs than their predecessors. Yet they
have much different potential uses.
 IEEE 802.11ac is an evolution of previous WLAN
capability. It gives the “unwired office” the ability to
compete directly with gigabit wired systems while
offering much better layout and connection flexibility.
In contrast,
 IEEE 802.11ad is a new solution that provides adhoc short-range connectivity in support of extremely
high data rates.
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Super Wi-Fi (802.11 af) White-Fi
 Standard was approved in February 2014
 Cognitive radio technology is used
 Employs unused TV spectrum at frequencies between 54MHz and
790MHz, over very long ranges (possibly several miles)
 It can offer reasonable throughput, perhaps 26.7Mb/s for 6 and 7
MHz channels and 35.6 Mbit/s for 8 MHz channels.
 With four spatial streams and four bonded channels, the maximum
data rate is 426.7 Mbit/s in 6 and 7 MHz channels and 568.9 Mbit/s
for 8 MHz channels.
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802.11ah Low Power Wi-Fi
standard is expected to be finalized and arrive in 2016
will provide bandwidth for sensors and monitors in gadgets and
appliances that will join up to create the Internet Of Things.
900MHz, large coverage, garages, back yards, attics, buildings,
factories, malls
Relay Access Point (AP)
Power saving
https://www.qualcomm.com/i
nvention/research/projects/wifi-evolution/80211ah
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WirelessHD(WiHD)
• The specification was finalized in January 2008.
• Developed by Intel, LG Electronics, Panasonic, Philips, Samsung,
Silicon Image, Sony, and Toshiba,
• The WirelessHD specification is based on a 7 GHz channel in the
60 GHz Extremely High Frequency radio band. It allows either
lightly-compressed (proprietary wireless link-aware codec) or
uncompressed digital transmission of high-definition video and
audio and data signals, essentially making it equivalent of a wireless
HDMI. First-generation implementation achieves data rates from 4
Gbit/s, but the core technology allows theoretical data rates as
high as 25 Gbit/s (compared to 10.2 Gbit/s for HDMI 1.3 and 21.6
Gbit/s for DisplayPort 1.2), permitting WirelessHD to scale to
higher resolutions, color depth, and range. The 1.1 version of the
specification increases the maximum data rate to 28 Gbit/s,
supports common 3D formats, 4K resolution, WPAN data, lowpower mode for portable devices, and HDCP 2.0 content protection.
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Specification Summary
 operating in the unlicensed and globally available 60 GHz frequency band
 a secure, quick and easy way to wirelessly connect and share data or play their HD
content among a wide range of devices, e.g. laptops, tablets, televisions, Blu-ray players,
DVRs, camcorders, gaming consoles, adapter products
 Supports data transmission rates at 10-28 Gbps, more than 20x faster than the highest
802.11n data rates.
 3D supported.
 4K resolution
 Data support. file transfers at faster than 1 Gbps for portable and fixed devices.
 Hollywood approved content protection with DTCP and HDCP2.0 over WirelessHD
technology, meaning WirelessHD systems will have full access to the most important
premium digital content
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Product list
WirelessHD (aka WiHD)
technology provides the
only Full HD wireless
video link with perfect
video quality and no
gaming lag for a stellar
gaming experience.
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http://www.portablehifi.com/dvdo-air-wireless-hd-connectionsystem/
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• William Stallings, “Data and Computer
Communications”, chapter 13, 14.
• A. S. Tanenbaum, “Computer Networks”, chapter 4.
•
http://iamwww.unibe.ch/~rvs/lectures/SS98/cn/applets/Ethernet/et
hernet.htm (CSMA/CD applet)
• http://www.wi-fiplanet.com/
• http://www.vicomsoft.com/knowledge/reference/wir
eless1.html
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