Wireless LAN TechnologyWireless LAN Technology

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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.

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

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• 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 LANsSingle Cell Wireless LAN (typical)

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Applications of Wireless LANsMulti-Cell Wireless LAN

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

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Applications of Wireless LANsAd Hoc Networking

•Peer-to-peer network,

•No centralised server,

•No infrastructure,

•Temporary nature.

Wireless LAN Requirements

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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

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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

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IEEE 802.11 Protocol Stack

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

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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 Stack802.11 network standards

802.11protocol version

Release

Freq.(GHz)

Bandwidth

(MHz)

Data rate per stream(Mbit/s)

AllowableMIMO

streams

Modulation

Approximate indoor

range(m)

Approximate

outdoor range(m)

97 Jun 1997

2.4 20 1, 2 1 DSSS, FHSS

20 100

a Sep 1999

5 20 6, 9, 12, 18, 24, 36, 48,

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1 OFDM 35 1203.7 — 5,000

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,

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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

4 OFDM 70 250

40 15, 30, 45, 60, 90, 120,

135, 150

70 250

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

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IEEE 802.11 MAC SublayerCSMA/CD cannot be used in wireless LANs.

(a) The hidden station problem. (b) The exposed station problem

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.

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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

A B

CD

DCF/MACAWVirtual sensing

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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

Distributed Coordination Function

• DCF sublayer uses CSMA

• no collision detection since on a wireless network• DCF includes delays that act as a priority scheme

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IFS: InterFrame Space

More on Distributed Coordination Function (DCF)

IEEE 802.11 MAC Sublayer

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IEEE 802.11 MAC SublayerPoint 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.

Point Coordination Function (PCF)

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802.11 MAC Frame Format

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.oIzisTd8.dpuf

802.11ac alone may be fast enough (7Gbps) to begin making wired networks redundant. 

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WiGig- Wireless Gigabit AllianceIEEE 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?

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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 ad-hoc short-range connectivity in support of extremely high data rates.

Super Wi-Fi (802.11 af) White-Fi

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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.

802.11ah  Low Power Wi-Fi

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standard is expected to be finalized and arrive in 2016will 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, mallsRelay Access Point (AP)Power saving

https://www.qualcomm.com/invention/research/projects/wi-fi-evolution/80211ah

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, low-power mode for portable devices, and HDCP 2.0 content protection.

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Specification Summary

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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

Product list

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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-connection-system/

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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/ethernet.htm (CSMA/CD applet)

• http://www.wi-fiplanet.com/

• http://www.vicomsoft.com/knowledge/reference/wireless1.html