UNIT 5 Wireless LAN

Contents  Introduction  Benefits of WLANs  Design and principle of operation  WLAN configuration  Micro-cells and roaming  Types of WLANs  WLAN customer consideration  Wireless LAN standards  IEEE 802.1, b and a  Selecting the WLAN  Microwave LANs

Benefits of WLAN  Improved productivity and service  Installation speed and simplicity  Installation flexibility  Reduced cost of ownership  Scalability

Wireless LAN Applications  Medical Professionals  Education  Temporary Situations  Airlines  Security Staff  Emergency Centers

Overview of Wireless LANs  use wireless transmission medium  key application areas:  LAN extension  Cross-building interconnect  Nomadic access  Ad hoc networking

Wireless LANs: Characteristics  Types  Infrastructure based  Ad-hoc  Advantages  Flexible deployment  Minimal wiring difficulties  More robust against disasters (earthquake etc)  Historic buildings, conferences, …  Disadvantages  Low bandwidth compared to wired networks (1-10 Mbit/s)  Proprietary solutions  Need to follow wireless spectrum regulations

infrastructure network ad-hoc network AP wired network AP: Access Point Source: Schiller

Components/Architecture  Station (STA) - Mobile node  Access Point (AP) - Stations are connected to access points.  Basic Service Set (BSS) - Stations and the AP with in the same radio coverage form a BSS.  Extended Service Set (ESS) - Several BSSs connected through APs form an ESS.

 temporary peer-to-peer network

Microcells and Roaming

Single Cell LAN Extension

Multi Cell LAN Extension

Wireless LAN Features  throughput - efficient use of wireless medium  no of nodes - hundreds of nodes across multiple cells  connection to backbone LAN - using Access Points  service area to 300 m  low power consumption - for long battery life on mobiles  transmission robustness and security  license-free operation  handoff/roaming  dynamic configuration - addition, deletion, and relocation of end systems without disruption to users

Cross-Building Interconnect  connect LANs in nearby buildings  point-to-point wireless link  connect bridges or routers

Nomadic Access  link LAN hub & mobile data terminal  laptop or notepad computer  enable employee to transfer data from portable computer to server  also useful in extended environment such as campus or cluster of buildings  users move around with portable computers  may wish access to servers on wired LAN

Protocol Architecture

Design and principle of operation  WLANs use Electromagnetic airwaves to communicate.  Electromagnetic Carriers: Radio Infrared  Radio waves are transmitted on different radio frequencies Thus avoiding interference And requires tuning at receiver side

 Access Point (AP): Transmits Receives Buffers Transmits data between WLAN and Wired networks Repeater(increasing range of communication)  Supports a small group of people  Range: about 100s of feet  Usually mounted high to cover greater region

 End users access WLAN through:  Wireless LAN adapters Implemented as PC cards in notebook computers Adapters provide interface between client Network Operating System(NOS) and the airwaves(via an antenna)  ISA or PCI adapters In Desktop computers  Fully integrated devices within hand-held computers

WLAN configuration  Independent WLANs any time 2 or more wireless adapters within range can setup an independent network  Extended-Range Independent WLANs Using AP or Repeater  Infrastructure WLANs APs link the WLANs to Wired network and allow users to share network resources APs allows the mediation of traffic to immediate neighborhood Increased coverage

Technology  infrared (IR) LANs  individual cell of IR LAN limited to single room  IR light does not penetrate opaque walls  spread spectrum LANs  mostly operate in ISM (industrial, scientific, and medical) bands  no Federal Communications Commission (FCC) licensing is required in USA  narrowband microwave  microwave frequencies but do not use spread spectrum  some require FCC licensing

Infrared LANs  constructed using infrared portion of spectrum  strengths  spectrum virtually unlimited hence high rates possible  unregulated spectrum  infrared shares some properties of visible light reflection covers room, walls isolate networks  inexpensive and simple  weaknesses  background radiation, e.g. sunlight, indoor lighting  power limited by concerns for eye safety and power consumption

Infrared LANs Transmission Techniques  directed-beam IR  point-to-point links  range depends on power and focusing  for indoor use can set up token ring LAN  IR transceivers positioned so data circulates in ring  omnidirectional  single base station with line of sight to other stations  acts as a multiport repeater  other stations use beam directed towards it  diffused configuration  stations focused / aimed at diffusely reflecting ceiling

Spread Spectrum LAN Configuration  usually use multiple-cell arrangement  adjacent cells use different center frequencies  configurations:  hub connected to wired LAN connect to stations on wired LAN and in other cells may provide automatic handoff  peer-to-peer no hub MAC algorithm such as CSMA used to control access for ad hoc LANs

Spread Spectrum LANs Transmission Issues  licensing regulations differ between countries  USA FCC allows in ISM band:  spread spectrum, very low power (0.5W) MHz (915-MHz band) GHz (2.4-GHz band) GHz (5.8-GHz band)  2.4 GHz also in Europe and Japan  interference  many devices around 900 MHz: cordless telephones, wireless microphones, and amateur radio  fewer devices at 2.4 GHz; microwave oven  little competition at 5.8 GHz

WLAN customer consideration  Range/Coverage Distance over which RF waves can communicate is a function of: Transmitted power Receiver Design Propagation path Under 100 feet to more than 500 feet  Throughput Setup dependent Airwave congestion(no. of users) Type of WLAN Bottlenecks on Wired portion Data rates: 1-11 Mbps

 Integrity and reliability  Simplicity/Ease of use  Security  Scalability  Ad Hoc WLAN  Interoperability with Wired Infrastructure  Ethernet(IEEE 802.3)  Token Ring(IEEE 802.5)  WLAN nodes are supported by NOS like any other Wired node via Drivers

 Interoperability with Wireless Infrastructure  Depends on Technology choice Vendor implementation  Goal is to allow compliant products to interoperate without explicit collaboration between vendors  Interference and Coexistence  Cause: ISM band being used for many other applications  Microwave ovens are potential concern  Co-location of multiple WLAN system

 Cost  Infrastructure cost: Wireless Access Point  User cost: WLAN adapters  Cost depends on: no. of APs deployed Required coverage region No. and types of users  Compared to Wired LANs Eliminates direct cabling costs Eliminates labor associated costs for installation & repair Simplified in terms of: Movement, addition& changes

Wireless LAN standards   b  a

IEEE  Defines a wireless LAN that can have fixed or mobile workstations  Operating up to 2Mbps  It requires the wireless LAN to be totally transparent to upper layers

IEEE b  Faster WLAN  Higher data rate was added to original standard  Provides two higher speeds of 5.5Mbps and 11 Mbps  This new addition affected only the physical layer

IEEE ,802.11b and a

IEEE Protocol Layers  Layer1-PHY-Physical Layer Specifies modulation scheme Signaling characteristics for transmission through RF  Layer2-MAC-Media Access Control layer Defines means for accessing the physical layer Services related to radio resource and mobility management

 Physical Layer Characteristics are divided into three categories:  One Infrared transmission method  Two RF transmission methods DHSS FHSS

Selecting the WLAN  Proprietary versus Standard  Radio-based versus Infrared  Coverage Area  Battery life for mobile Platforms  Safety

Microwave LANs  Connects distances upto 20 miles or more  Provides full bandwidth Ethernet LAN connectivity  High reliability  Reasonable payback periods(6 months-2yrs)  Microwave links are:  Absolutely transparent  Fully compatible with Ethernet standard

 It has 3 components: Indoor data interface unit Provides interface IEEE to LAN Offers bridging or routing functions Radio unit Placed near antenna Modulates the data and places it on higher microwave frequencies Parabolic antenna Focuses the microwave signal over a narrow beam which is radiated towards the receiving antenna

Advantages  Reliable  Fast  Easy to install & maintain  Requires only 2.5 inch post to be mounted to operate effectively  Reduces installation time  Reduces cost

 Line of sight between antennas  Affected by environmental & atmospheric factors at high frequencies  Prevalent factor: Rain  Rain has adverse property of absorbing microwaves Attenuating signal path  Other factors: snow, fog, smog, temp inversion etc

Contents  Introduction  Benefits of WLANs  Design and principle of operation  WLAN configuration  Micro-cells and roaming  Types of WLANs  WLAN customer consideration  Wireless LAN standards  IEEE 802.1, b and a  Selecting the WLAN  Microwave LANs

UNIT:- 5 Q. 1 ) Explain the WLAN configuration. Q. 2 ) Discuss the WLAN issue related to customer consideration. Q. 3 ) Explain LAN standard IEEE b in detail. Q. 4 ) What are various benefits and weaknesses of WLAN ? Q. 5 ) Explain the design and principal of operation of WLAN. Q. 6 ) Explain the concept of microcells roaming related to WLAN. Q. 7 ) Write a note on :- IEEE standard Home RF Q. 8 ) Explain the criteria for selecting a WLAN.

HomeRF  Initially called as SWAP  Was a wireless networking specification for household devices.  Was developed in 1988 by Home Radio Frequency Working Group  It allowed PCs, peripherals, cordless phones and other consumer devices to share and communicate voice and data in and around the home  Works in 2.4GHz ISM band  Uses FHSS (IEEE family, and Bluetooth)  Max datarate=10Mbits/s  Range=50m  Type of network = PAN