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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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Peer-to-Peer Wireless Mode (Fig 14.1)
Server with
wireless cardLaptop with
wireless card
Palm pilot
PDA
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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Client/Server Wireless Configuration (Fig 14.2)
Wireless LAN access pointWired
network
Wireless card
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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Wireless Distributed Network (Fig 14.3)
Station
Access
point
Wired
network
Access
point
Distributed
system
Access
point
Station
StationStation
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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Key Features of Ricochet Modem
V.34, 28,800 bps access.
Good Availability
Unlimited access.
Flexible pricing.
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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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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Copyright 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
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