Lesson 28 - Devi Ahilya Vishwavidyalaya , Indore · specifying Complementary Code Keying (CCK) 2008...

2008 Chapter-3 L28: "Embedded Systems - " , Raj Kamal, Publs.: McGraw-Hill Education 1

DEVICES AND COMMUNICATIONBUSES FOR DEVICES NETWORK––

LessonLesson--28:28: WIRELESS AND MOBILE WIRELESS AND MOBILE SYSTEM PROTOCOLSSYSTEM PROTOCOLS── IEEE802.11IEEE802.11


Wireless Personal Area Network (WPAN)Wireless Personal Area Network (WPAN)

� IrDA (Infrared Data Association)� Bluetooth 2.4 GHz� 802.11 WLAN and 802.11b WiFi� ZigBee 900 MHz


� IEEE standards 802.11a to 802.11g� 802.11a data transfer rates─ 1 Mbps

and 2 Mbps� 802.11b data transfer rates─ 5.5 Mbps

and 2 Mbps� FHSS or DSSS or Infrared 250 ns

802.11 Wireless LAN connected devices


802.11b802.11b� Called wireless fidelity (WiFi)� 802.11b support data rates of 5.5 Mbps

by mapping 4 bits � 11 Mbps mapping 8 bits simultaneously

during modulation.


Basic service set (BSS)Basic service set (BSS)• Has one wireless station, which

communicates to an access point, also called hotspot.

• BSS support ad-hoc network, which as and when node come nearby in range of access point it forms the network through extended service set (ESS).

• A node free to move from one BSS to another.


BSS [Basic Service Set] WLANBSS [Basic Service Set] WLAN

802.11 protocol embedded device or computer

Wireless Access Point

802.11 protocol embedded

printer




To ESSTo ESS

Ad hoc network


Independent basic service set (IBSS)Independent basic service set (IBSS)

� No access point. � Does not connect to the distribution system. � May have multiple stations, which also

cannot communicate among themselves.� IBSS support ad-hoc network, which as and

when nodes come nearby in range they form the network


802.11 IBSS LAN802.11 IBSS LAN802.11 IBSS LAN

802.11 Computer

802.11 protocol

embedded device to connect to

another BSS

802.11 protocol embedded device at a piconet boundary

802.11embedded

device

802.11Printer

802.11embedded

fixed network device

Ad hoc network


LANLAN--station accessstation access--points networked togetherpoints networked together

� Called extended service set (ESS)� Backbone distribution system. � A backbone set may network through

Internet� ESS support fixed infrastructure

network


802.11 ESS LAN802.11 ESS LAN802.11 ESS LAN

802.11 Computer

802.11 protocol

embedded device to connect to

another BSS

802.11 protocol embedded device at a piconet boundary

802.11embedded

device

802.11Printer

802.11embedded

fixed network device

To BSSTo BSS

Fixed network


802.11 Backbone802.11 Backbone802.11 backbone network to Internet

BSSC

BSSB

802.11 protocol

embedded device

To Internet

To Internet

Multipoint relay node Base station

gateway

BSSA


� 802.11 provides specifications for physical layer and data link layers

802.11 protocol 802.11 protocol


802.11 physical and data link layers 802.11 physical and data link layers

Physical layer─ Physical Medium Dependent (PMD) protocol, Physical Layer Convergence Protocol (PLCP)802.11b additional sub-layer for specifying Complementary Code Keying (CCK)

Data link layer─MAC layer for power management, handover and registration of roaming mobile node

within the backbone network at a new BSS within the ESS


• Specifies a MAC layer• MAC layer specifies power

management, handover and registration of roaming mobile node within the backbone network at a new BSS within the ESS

802.11 protocol 802.11 protocol data link layer data link layer


802.11 802.11 packet for MACpacket for MAC� Packet called request to send

(RTS), which is first sent� If other end responses by the

packet called clear to send (CTS), then the layer data is transmitted.


MAC layerMAC layer• Uses carrier sense multiple access and

collision avoidance (CSMA/CA) protocol. • A station listens to the presence of carrier

during a time interval is called distributed inter-frame spacing (DIFS) interval.

• If carrier is not sensed (detected) during DIFS then the station backs off for a random time interval to avoid collision and retries after that interval.


• A receiver always acknowledges within a short inter-frame spacing (SIFS)

• Acknowledgment after successful CRC (cyclic redundancy check)

• If there is no acknowledgement within SIFS, then transmitter retransmits and upto 7 retransmission attempts are made

802.11 protocol MAC Acknowledgment802.11 protocol MAC Acknowledgment


802.11 Physical Layer 802.11 Physical Layer communication methods communication methods � Three─ FHSS or DSSS or Infrared 250

ns pulses. � 802.11a Physical layer has two sub-

layers� One is Physical Medium Dependent

(PMD) protocol, Physical Layer Convergence Protocol (PLCP)

� 802.11b additional sub-layer for specifying Complementary Code Keying (CCK)


Physical Medium Dependent (PMD) Physical Medium Dependent (PMD) protocol 802.11 protocol 802.11 sublayersublayer

• Specifies the modulation and coding methods.


Physical Layer Convergence Protocol Physical Layer Convergence Protocol (PLCP) 802.11 sub(PLCP) 802.11 sub--layerlayer

Specifies the header and payload for transmission. It specifies the sensing of the carrier at receiver. It specifies how packet formation takes place at the transmitter and packets assemble at the receiver. It specifies ways to converge MAC (Medium Access Control) to PMD at transmitter and separate MAC (Medium Access Control) from PMD at the receiver.


An additional subAn additional sub--layer in 802.11blayer in 802.11b

• Specifying Complementary Code Keying (CCK).


SummarySummary


We learntWe learnt� IEEE standard 802.11a to g protocols� FHSS or DSSS or IR 259 ns� BSS with wireless access point and

IBSS without access point � ESS between several BSSs� ESS backbone connects to Internet


We learntWe learnt� MAC� PMD� PLCP� CCK


End of Lesson 28 of Chapter 3End of Lesson 28 of Chapter 3

Lesson 28 - Devi Ahilya Vishwavidyalaya , Indore · specifying Complementary Code Keying (CCK) 2008...

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