Dharma-Chapt-14 - Redes Inalmbricas LANs y PANs-2002

7/28/2019 Dharma-Chapt-14 - Redes Inalmbricas LANs y PANs-2002

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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved

Wireless LANs and PANs

Chapter 14


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IEEE 802.11

It is the standard for wireless LANs.

It specifies MAC procedures and operate in 2.4 GHz rangewith data rate of 1Mbps or optionally 2Mbps.

User demand for higher bit rates and international

availability of 2.4 GHz band has resulted in development

of a high speed standard in the same carrier frequencyrange.

This standard called 802.11b, specifies a PHY layer

providing a basic data rate of 11Mbps and a fall back rateof 5.5Mbps.

802.11a uses OFDM in packet based communication.


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IEEE 802.11

The IEEE 802.11 and 802.11b standards can beused to provide communication between a number

of PSs (Peer Stations) as an adhoc network using

peer to peer mode(Fig 14.1)

As a client server wireless configuration (Fig 14.2)

Complicated distributed network (Fig 14.3)


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Peer-to-Peer Wireless Mode (Fig 14.1)

Server with

wireless cardLaptop with

wireless card

Palm pilot

PDA


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Client/Server Wireless Configuration (Fig 14.2)

Wireless LAN access pointWired

network

Wireless card


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Wireless Distributed Network (Fig 14.3)

Station

Access

point

Wired

network

Access

point

Distributed

system

Access

point

Station

StationStation


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IEEE 802.11 The keys behind all the above networks are the wireless cards and

wireless LAN access points. These cards are PCMCIA card

In an ad hoc network mode , there is no central controller, thewireless access cards use CSMA/CA protocol to resolve shared

access.

In client server model, many PCs or laptops physically close to

each other (20-500m) can be linked to a central hub (access point).

This access point acts as a bridge between the wireless and wired

network.

A large area can be covered by installing several access points inthe building.

Fig 14.3 shows how LANs are interconnected using access points.


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Ricochet

A mobile data access service that is always on,

provides high speed, secure mobile access to thedesktop from outside the office.

It allows to link to the internet or the corporate

network without needing phone lines or cableconnections.

The Ricochet service is provided by Metricom.


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Ricochet

The Ricochet service is a wide area wireless system using

spread spectrum packet switching data.

The network operates within 902-928 MHz portion of RF

spectrum.

The Ricochet wireless Micro Cellular Data Network

(MCDN), consists of shoebox sized radio receivers, calledMicro cell radios (Fig 14.5)

Micro cells are typically mounted to street poles.

Micro cells require a small power from the street lights.

Each Micro cell radio employs 162 frequency hopping

channels.


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The Ricochet Mobile Communication Network (Fig 14.5)

Network interconnection facilityMicrocell radios on

street lights, utility poles

Wireless access point

Name server

Router

Gateway

Gateway to Internet, Intranets,

LANS, Compuserve, AOL andother on-line servicesComputer device

Modem radio


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The Ricochet Wireless Modem

It weighs 13 ounces.

Has the general dimensions of a small paperback

book, plugs directly into a desktop.

When a Ricochet modem is configured to operate

in bridge mode, it translates signals from other

Ricochet modems into signals that a wired modem

can receive.


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Services Provided by Ricochet

Provides immediate, dependable and secure

connections without the cost and complexities ofland based phone lines.

Sending E-mails, access to documents in home

networks. Many real estate agents use this to search for

property listings while on road.


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Key Features of Ricochet Modem

V.34, 28,800 bps access.

Good Availability

Unlimited access.

Flexible pricing.


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Home RF

Two kind of networks: Home RF (for home), Hiper LAN (for business

workspace).

43 million US homes now contain more than one PC. A home network typically consists of one high speed internet access port

providing data to multiple networked nodes.

Home networking allows all computers in a home to simultaneously

utilize the same high speed ISP account. Home networking allows two options: wired solution and wireless

solution.

Wired Solutions such as Ethernet, phone line offers a fast reliable secure

connections, but the cost of wiring and installation is high. Wireless networks such as PC-Centric Data offer more mobility to the

users of the network.


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Advantages of Wireless Home RF

Mobility

Flexibility: Simultaneous internet access while sharing asingle internet connection with other PCs.

Simple: Installation time is small.

Economical: Less than $100 for each networked PC. Secure

Based on industry Standards: Enables interoperability

between many different manufacturers.


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Home RF Technology

In Home RF all the devices can share the same connections

for voice and data. Provides the foundation for a broad range of interoperable

consumer devices.

A specification for wireless communications in the homecalled Shared Wireless Access Protocol (SWAP) has been

developed.

A typical home network is shown in Fig 14.6.


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Architecture of HomeRF system (Fig 14.6)

Baby Monitor

Phone - Connection

Cell Phone

Main- PC

Clock

PalmTop

Wireless Headset

Satellite Dish

Fridge Data Pad

TelevisionHandheld

Communicator Laptop

2nd PC

Cable

Modem


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Home RF Network

A network consists of Resource providers, which are

gateways to different resources like cordless phones,

printers, fileservers and TV.

The goal of Home RF is to integrate all of them in to a

single Network suitable for all applications and also

remove all wires and utilize RF links in the network. This will support the mobility of devices.

With Home RF, cordless phone can connect to PSTN

ordinarily, but can also connect through a PC for enhanced

services.


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HiperLAN

It Stands for High Performance LAN.

It can support Multimedia data and asynchronous data

effectively at high rates (23.5 Mbps). It is specifically designed to support as hoc computing for

multimedia systems, where there is no requirement to deploycentralized infrastructure.

It employs 5.15 GHz and 17.1 GHz frequency bands, with acoverage of 50m and mobility

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Dharma-Chapt-14 - Redes Inalmbricas LANs y PANs-2002