Basic Wireless

Network 1

Chapter 5

Basic Wireless

Network 1

Wireless Networks

•Wireless Technology overview

•The IEEE 802.11 WLAN Standards

Basic Wireless

Network 1 Wireless ?

• A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier.

• The last link with the users is wireless, to give a network connection to all users in a building or campus.

• The backbone network usually uses cables

Basic Wireless

Network 1 Why Wireless LANs (WLANs)

• Mobility (portability) and Flexibility

• Places where there is no cabling infrastructure / Hard to wire areas

• Reduced cost of wireless systems

• Improved flexibility of wireless systems

• Cost

– Relatively low cost of deployment

– Continual drop in price for WLAN equipment

Basic Wireless

Network 1 Common TopologiesThe wireless LAN connects to a wired LAN

• There is a need of an access point that bridges wireless LAN traffic into the wired LAN.

• The access point (AP) can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes.

Basic Wireless

Network 1 What is 802.11?• A family of wireless LAN (WLAN) specifications developed by a working

group at the Institute of Electrical and Electronic Engineers (IEEE)

• Defines standard for WLANs using the following four technologies

• Frequency Hopping Spread Spectrum (FHSS)

• Direct Sequence Spread Spectrum (DSSS)

• Infrared (IR)

• Orthogonal Frequency Division Multiplexing (OFDM)

• Versions: 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac

Basic Wireless

Network 1 ISM Frequency Bands

ISM (Industrial, Scientific and Medical) frequency bands:

• 900 MHz band (902 … 928 MHz)

• 2.4 GHz band (2.4 … 2.4835 GHz)• 5.8 GHz band (5.725 … 5.850 GHz)

Anyone is allowed to use radio equipment for transmitting in these bands (provided specific transmission power limits are not exceeded) without obtaining a license.

Basic Wireless

Network 1 WLAN StandardsWireless

LAN

2.4 GHz 5 GHz

802.11(2 Mbps)

802.11b(11 Mbps)

802.11g(22-54 Mbps)

HiSWANa(54 Mbps)

802.11a(54 Mbps)

HiperLAN2(54 Mbps)

HomeRF 2.0(10 Mbps)

Bluetooth(1 Mbps)

HomeRF 1.0(2 Mbps)

802.11e(QoS)

802.11i(Security)

802.11f(IAPP)

802.11h(TPC-DFS)

802.11 Protocols under development

Basic Wireless

Network 1 WLAN Standards

• Several WLAN standards, e.g.:

– IEEE 802.11b offering 11 Mbit/s at 2.4 GHz

– The same radio spectrum is used by Bluetooth

• A short-range technology to set-up wireless personal area networks with gross data rates less than 1 Mbit/s

– IEEE 802.11a, operating at 5 GHz and offering gross data rates of 54 Mbit/s

– IEEE 802.11g offering up to 54 Mbit/s at 2.4 GHz.

– IEEE 802.11n up and coming standard up to 300 Mbit/s (two spatial streams; 600 Mbit/s with 4 spatial streams)

– …

Basic Wireless

Network 1 IEEE 802 wireless network technology options

Network definition

Wireless personal area network (WPAN)

Low-rate WPAN (LR-WPAN)

Wireless local area network (WLAN)

Wireless metroplitan area network (WMAN)

IEEE standard

IEEE 802.15.1

IEEE 802.15.4

IEEE 802.11

IEEE 802.16

Known as

Bluetooth

ZigBee

WiFi

WiMAX

Basic Wireless

Network 1Characteristics of selected

wireless link standards

Indoor10-30m

Outdoor50-200m

Mid-rangeoutdoor

200m – 4 Km

Long-rangeoutdoor

5Km – 20 Km

.056

.384

1

4

5-11

54

IS-95, CDMA, GSM 2G

UMTS/WCDMA, CDMA2000 3G

802.15

802.11b

802.11a,g

UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellularenhanced

802.16 (WiMAX)

802.11a,g point-to-point

200 802.11n

Dat

a ra

te (

Mb

ps) data

Basic Wireless

Network 1 WLAN : 802.11b -Expand

The first 802.11 standard deployed.

Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band

Basic Wireless

Network 1 WLAN : 802.11a -Expand

Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band

Incompatible with devices operating in 2.4GHz

Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).

Basic Wireless

Network 1 WLAN : 802.11g -Expand

Supports data rates as high as 54 Mbps on the 2.4 GHz band

Provides backward compatibility with 802.11b equipment

Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).

Basic Wireless

Network 1 WLAN : 802.11n -Expand

Supports data rates as high as 144 Mbps on the 2.4 GHz band (802.11g/n) and 300 Mbps on 5 GHz band (802.11a/n) for 2X2 stream

The maximum bandwidth per spatial stream in 802.11a/n is 150 Mbps, which means that an 802.11a/n AP outfitted with three transmit and three receive antennas can deliver maximum theoretical throughput of 450 Mbps

Supports up to 4 stream MIMO

Provides backward compatibility with 802.11a/b/g equipment

Basic Wireless

Network 1 WLAN : 802.11ac -Expand

Supports data rates as high as 1.3 Gbps (also called gigabit wireless)

Operates only in 5 GHz band

Supports 80/160 MHz channel

Supports up to 8 stream MIMO

The maximum bandwidth in 802.11ac is 433 Mbps per spatial stream, and the maximum number of spatial streams supported are eight. So the theoretical maximum throughput on an 802.11ac network will eventually be several times that of Gigabit Ethernet. First-generation devices (wave 1), however, are limited to using either two or three transmit and receive antennas to deliver a theoretical throughput maximum of 866 Mbps or 1.3 Gbps

Basic Wireless

Network 1 WLAN : MIMO

802.11 a/b/g: Supports 54 Mbps on single 20 MHz stream

802.11 n: Two stream 144 Mbps for 20MHz 2.4GHz band (802.11g/n) and 300 Mbps for 40 MHz 5GHz band (802.11a/n) or Three stream 450 Mbps for 40 MHz 5GHz band

802.11 ac: Three stream 1.3 Gbps for 80 MHz 5 Ghz band

Basic Wireless

Network 1

WLAN components

Basic Wireless

Network 1 Wireless Lan NIC

• hardware installed in computing device that enables it to communicate on a network.

Basic Wireless

Network 1 Access Points (AP)

• Allows stations to associate with it• Supports Distributed Coordination Function (DCF) and

Point Coordination Function (PCF)• Provides management features

– Join/Associate with BSS– Time synchronisation (beaconing)– Power management

• all traffic flows through APs• Supports roaming

Basic Wireless

Network 1

Acc

ess

Poi

nts

(AP

)

Basic Wireless

Network 1

Wire

less

Rou

ter

Basic Wireless

Network 1 WIFI Certification(1)• Wi-Fi certification is provided by the Wi-Fi

Alliance (http://www.wi-fi.org), a global, nonprofit, industry trade association devoted to promoting the growth and acceptance of WLANs.

• The Wi-Fi Alliance is an association of vendors whose objective is to improve the interoperability of products that are based on the 802.11 standard by certifying vendors for conformance to industry norms and adherence to standards.

Basic Wireless

Network 1 WIFI Certification(2)

• Certification includes all three IEEE 802.11 RF technologies, as well as early adoption of pending IEEE drafts, such as 802.11n, and the WPA and WPA2 security standards based on IEEE 802.11i

Basic Wireless

Network 1 WIFI Certification (3)

• The roles of these three organizations can be summarized as follows:

• ITU-R regulates allocation of RF bands.

• IEEE specifies how RF is modulated to carry information.

• Wi-Fi ensures that vendors make devices that are interoperable.

Basic Wireless

Network 1 IEEE 802.11 terminologyBasic Service Set (BSS)

– group of stations using same radio frequency

Access Point (AP)– station integrated into the wireless LAN

and the distribution systemStation (STA)

– terminal with access mechanisms to wireless medium and radio contact to access point

Distribution System (DS)– interconnection network to form one

logical network Extended Service Set (EES)

– based on several BSS

Distribution System

Portal

802.x LAN

Access Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access Point

STA1

STA2 STA3

ESS

System Architecture of an infrastructure network

Basic Wireless

Network 1

• IEEE 802.11 allows the building of ad hoc networks between stations, thus forming one or more BSSs.

– In this case, a BSS comprises a group of stations using the same radio frequency.

– Several BSSs can either be formed via the distance between the BSSs or by using different carrier frequencies.

IEEE 802.11 BSS

Basic Wireless

Network 1 IEEE 802.11 BSS

Basic Wireless

Network 1IEEE 802.11 Extended Service Set

Basic Wireless

Network 1

Divided into overlapping channels. For e.g. the 2.4000–2.4835 GHz band is divided into 13 channels each of width 22 MHz but spaced only 5 MHz apart, with channel 1 centred on 2.412 GHz and 13 on 2.472 GHz Availability of channels is regulated by country (e.g. Japan adds a 14th channel 12 MHz above channel 13). 3 channels are non overlappingGiven the separation between channels 1, 6, and 11, the signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel.

Basic Wireless

Network 1802.11 MAC (Multiple Access Control)

LLCLLC

MACMAC

PHYPHY

:

Multiple access control: Different nodes must gain access to the shared multiple (for instance a wireless channel) otherwise there will be collisions.

FDMAFDMA

TDMATDMA

CDMACDMA

CSMACSMA

Assigning channels in frequency domain

Assigning time slots in time domain

Assigning code sequences in code domain

Assigning transmission opportunities in time domain on a statistical basis

Access methods:

Basic Wireless

Network 1

• Station must be able to send and receive data at the same time.

• Collision may not be detected because of the hidden terminal problem.

• Distance between stations in wireless LANs can be great. Signal fading could prevent a station at one end from hearing a collision at other end.

Wireless LAN cannot implement CSMA/CD for 3 reasons

Basic Wireless

Network 1 Before sending a frame, source senses the medium by

checking the energy level at the carrier frequency.Backoff until the channel is idle.After the channel is found idle, the station waits for a period of

time called the Distributed interframe space (DIFS); then the station sends a control frame called request to send (RTS).

After receiving RTS, the destination waits for a period called Short interframe space (SIFS), the destination station sends a control frame, called Clear to Send (CTS) to source. This control frame indicates that the destination station is ready to receive data.

Source sends data after waiting for SIFSDestination sends ACK after waiting for SIFS.

IEEE 802.11: CSMA/CA

Slot Time 50 µsecSIFS 28 µsecDIFS SIFS + (2 * Slot Time)Operating Frequency 2.4 GHzMaximum Data Rate 2 Mbps

Basic Wireless

Network 1 IEEE 802.11: CSMA/CA

CSMA/CA Parameter

Basic Wireless

Network 1 IEEE 802.11: CSMA/CA

Design Wireless

Network 1