Wireless LAN (WLAN)

• Wireless Ethernet

• Bluetooth

Introduction Demand for wireless device

connection has been growing WLAN is generally used in campus,

office as well as in cafe, petrol station etc.

WLAN can also be fixed at home for usage of Internet connection in other mobile devices

IEEE 802.11IEEE 802.11

802.11 standard define specification that cover physical and data link layer for WLAN Architecture Physical layer Media Access Control Layer (MAC) Addressing mechanism

WLAN architecture: Basic Service Set (BSS) BSS defined as building block of WLAN Made of mobile wireless stations and

an optional central base station (access point -AP)

BSS without an AP is stand alone network and cannot send data to other BSSs. (called: ad-hoc architecture)

Stations can locate one another and agree to be part of BSS

WLAN architecture : Extended Service Set (ESS)

WLAN Architecture: Extended Service Set (ESS) ESS is made of >= 2 BSSs with APs Generally, BSSs are connected through a

distribution system (wired LAN) Distributed system connects the APs in the BSSs. IEEE 802.11 doesn’t restrict the distribution

system : It can be any IEEE LAN (such as Ethernet)

Stations in ESS: mobile & stationary Mobile: normal stations inside a BSS Stationary: AP stations that are part of a WLAN

When BSSs are connected, this architecture called infrastructure network, and stations in BSS no need AP to communicate one another

However communication between 2 stations from 2 difference BSSs normally occur through 2 APs

Stations types IEEE 802.11 defines 3 type of

stations based on their mobility: No-transition

Stationary or moving only inside a BSS BSS-transition

Move from one BSS to another, but the movement is confined inside one ESS

ESS-transition Move from one ESS to another but IEEE

802.11 doesn’t guarantee that communication is continuous during the move

Physical Layer Specification IEEE 802.11 defines specification

to convert bit to signal (physical layer)

There are 5 type of specification in radio frequency domain

Frequency Hopping Spread Spectrum Generating signal in 2.4 GHz ISM band Data transmission using 1 frequency carrier

for certain period and hop to another frequency and so on.

After N hops, loop will be repeated. If initial bandwidth signal is B, spread

spectrum bandwidth is : N x B data rate: 1 @ 2 Mbps, use FSK modulation at

1M baud/s

Direct Sequence Spread Spectrum Also in 2.4-GHz ISM band (industrial, scientific,

medical) Each bit that sent replaced with bit sequence (chip

code) To prevent the use of buffer, the time to send a chip

code should = time to send original bit If number of bit in each chip code = N, data rate to

send code chip = N x original stream bit data rate Not same as CDMA because this is physical layer

implementation bit sequence use overall band Data rate 1 @ 2 Mbps, use PSK modulation at

1Mbaud/s

MAC sub-layer in IEEE 802.11 standard

2 MAC sub-layer Distributed coordination function(DCF) Point coordination function (PCF) –

more complex for just infrastructure network

Acess method: CSMA/CA

CSMA/CA and Network Allocation Vector NAV is CA implementation method

When RTS is sent by 1 station (including time period that needed to use channel)

Other station will start respective NAV– waiting time before checking channel status

Distributed IFS and Short IFS are waiting time between frames

MAC sub-layer frame format The wireless environment is very noisy; a

corrupt frame has to be retransmitted The division of a large frame into smaller

ones. (fragmentation)

Sub-field in FC fieldSub-field in FC field

Field Explanation

VersionVersion The current version is 0.The current version is 0.

TypeType Type of information: management (00), control (01), or data (10).Type of information: management (00), control (01), or data (10).

SubtypeSubtype Defines the subtype of each type (see ).Defines the subtype of each type (see ).

To DSTo DS Defined later.Defined later.

From DSFrom DS Defined later.Defined later.

More flagMore flag When set to 1, means more fragments.When set to 1, means more fragments.

RetryRetry When set to 1, means retransmitted frame.When set to 1, means retransmitted frame.

Pwr mgtPwr mgt When set to 1, means station is in power management mode.When set to 1, means station is in power management mode.

More dataMore data When set to 1, means station has more data to send.When set to 1, means station has more data to send.

WEPWEP Wired equivalent privacy. When set to 1, means encryption Wired equivalent privacy. When set to 1, means encryption implemented. implemented.

RsvdRsvd Reserved.Reserved.

Control FrameControl Frame

Sub-field value in control frameSub-field value in control frame

Subtype Meaning

1011 Request to send (RTS)Request to send (RTS)

1100 Clear to send (CTS)Clear to send (CTS)

1101 Acknowledgment (ACK)Acknowledgment (ACK)

Sub-field in FC fieldSub-field in FC field

ToToDSDS

FromFromDSDS

AddressAddress11

AddressAddress22

AddressAddress33

AddressAddress44

00 00 DestinationDestinationstationstation

SourceSourcestationstation BSS IDBSS ID N/AN/A

00 11 DestinationDestinationstationstation

SendingSendingAPAP

SourceSourcestationstation N/AN/A

11 00 ReceivingReceivingAPAP

SourceSourcestationstation

DestinationDestinationstationstation N/AN/A

11 11 ReceivingReceivingAPAP

SendingSendingAPAP

DestinationDestinationstationstation

SourceSourcestationstation

Addressing Mechanism Pengalamatan : kes 1 Addressing in 802.11 very complex because it involve

many APs Addr 1 : next device Addr 2 : previous device Addr 3 : final destination if it is not defined by Addr 1 Addr 4 : original source if it is not the same as Addr 2

Figure 15.12 Addressing mechanism: case 2

Figure 15.13 Addressing mechanism: case 3

Figure 15.14 Addressing mechanism: case 4

BluetoothBluetooth WLAN technology designed to connect

devices of different functions such as telephone, PDA, camera, printers, mouse, earpiece etc.

It is an ad hoc network– formed spontaneously

Bluetooth devices/gadgets find each other and make a network called a piconet

Bluetooth LAN can even be connected to the Internet if one of the gadgets has this capability

Standard : IEEE 802.15 that defines wireless personal area network (PAN) operable in an area the size of a room or a hall

Network architecture: Piconet Piconet can have up to 8 station with one of them

function as master The slave devices synchronize their clocks and

hopping sequence (hop) with the master Communication between master-slave can be 1-1 or

1-many Slave can change from active to parked state and

vice versa

Network architecture: Scatternet

Piconet 1

Piconet 2

Scatternet Piconet can be combined to form

scatternet Station slave in a piconet can be

master in another piconet This Station can receives message

from master (first piconet) and acting as master (second piconet ) to deliver them to slave in second piconet

Bluetooth device Bluetooth device has short distance

radio transmitter Data rate: 1Mbps with bandwidth 2.4-

GHz, therefore may be disruption can happen between WLAN IEEE 802.11b and LAN Bluetooth

Bluetooth layer Bluetooth uses layers that do not exactly match

TCP/IP model Radio layer ~ physical layer Bluetooth devices are lo-power and have a range of

10 m Band: use 2.4-GHz ISM band divided into 79

channels of 1 MHz each

Bluetooth layer Bluetooth use FHSS method in the physical

layer to avoid interference from other devices or networks

Bluetooth hops 1600 per second, which means that each device changes its modulation frequency 1600 times per second

To transform bits to a signal, use GFSK modulation(Gaussian)

Baseband layer: equivalent to MAC sublayer in LAN with access method is Time Divison Duplexing-TDMA (half-duplex communication)

Communication only between master-slave No direct communication between slave-slave

Single-slave communication

Multiple-slave communication

Frame Format

L2CAP Packet Data Format