wireless lan (wlan)
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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