WIRELESS LANS. By: M. Habibullah Pagarkar Mandar Gori Rajesh Jaiswal

Transcription

1 WIRELESS LANS By: M. Habibullah Pagarkar Mandar Gori Rajesh Jaiswal

2 Introduction Why wireless? World will become fully mobile Increase in wireless devices usage Wireless will succeed; integrates into many devices and can meet a variety of needs

3 WLANs What are WLANs? Primarily b and HiperLAN Application areas LAN extension Cross building interconnect Nomadic Access Ad-hoc networks

4 Advantages of WLANs Cheaper Convenient Easy to install Expandable

5 Disadvantages of WLANs Not TRULY Mobile Device limitations small LCD screens Data rates WML instead of HTML Compatibility issues Cannot use and Bluetooth in the same device.yet!

6 Techniques WLANs Infrared Spread Spectrum Narrowband Microwave Diffused Directed Frequency Hopping Direct Sequence

7 Comparison Chart Infra-red Spread Spectrum Microwave Diffused I.R. Directed I.R. Frequency Hopping Direct Sequencing Data rate (Mbps) Range (m) Detectable Negligible Little Some Modulation ASK FSK QPSK QPSK Radiated Power - < 1 W 25 mw Access Methods CSMA Token Ring CSMA CSMA CSMA

8 Examples of Networks Peer to Peer Transmitter/Receiver

9 Overview of IEEE is an extension of into wireless communication Allows roaming computers to talk to other devices (peer to peer) or connect to a wired network (transmitter/receiver) Interoperability between multiple vendor products

10 Comparison With OSI Model

11 IEEE Architecture protocol covers MAC & Physical layer Access method CSMA/CA (802.3 uses CSMA/CD)

12 IEEE Architecture contd. Extended Services Set IEEE 802.x LAN Distribution System Portal AP STA 1 STA 2 STA 3 STA 4 Basic Services Set AP STA5 STA 7 STA 6 Basic Service Set

13 IEEE Terminology Access Point (AP) Basic Services Set (BSS) Coordination Function Distribution System (DS) Extended Service Set (ESS) MAC protocol data unit (MPDU) MAC service data unit (MSDU) Station

14 IEEE Services MSDU Distribution of Messages within a DS Distribution Integration Association related services Association Re-association Disassociation

15 IEEE Services contd.. Access & privacy services Authentication De-authentication Privacy

16 IEEE MAC Reliable Data Delivery Access Control Security Distribution Coordination Function (DCF) uses CSMA (diagram on next slide) Point coordination function (PCF) on top of DCF

17 Medium Access Control Logic Wait for transmit Y Idle? Wait IFS Still Idle? N Y N Transmit frame Wait IFS Wait till transmission ends N Still Idle? Y Exponential backoff Transmit frame

18 MAC Frame Frame Control Duration Id Sequence Control FCS Address 1 Address 2 Address 3 Address 4 Frame Body MAC Header

19 Frame Format 3 types of frames Data Frames data transmission Control Frames control access to medium; assist in reliable delivery Management Frames not forwarded to upper layers Each type is further divided into sub-types

20 Physical Layer 2 types of transmission media -Micro-wave Radio(SS/NB) -Infrared 1.DS-SS 2.FHSS 1.Direct Beam 2.Omnidirection 3.Diffused

21 Variations IEEE has a veritable alphabet soup a 6-54 Mbps 5 GHz band Uses OFDM instead of FHSS or DSSS Interference b (also called as Wi-Fi) Mbps 2.4 Ghz band DSSS only Physical layer combines CCK & PBCC

22 Variations contd g a b -OFDM from a & CCK-PBCC from b -Facilitate development of DUAL-BAND radio e -Not a protocol but a technology -Can move 2 a new frequency if interference -Used in time sensitive applications (voice & multimedia)

23 Variations contd f -deals with communication among AP 2 -supports roaming i -advanced ENCRYPTION standard for better PRIVACY

24 Power Saving Battery power is a scarce resource Two power saving modes Continuous aware mode Power save polling mode

25 Security Uses Wired Equivalent Privacy (WEP) protocol There are 2 issues -access control (ESSID & mac addr.) -encryption mechanism(rc4prng-rsa) WEP slows WLAN by 20-50%

26 References Wireless Communication & Networks Stallings IEEE Spectrum September 2002 IEEE Communications Magazine