Transcript COM347J1 Networks and Data Communications L1

COM319J1
Networks and Data Communications
Lecture 9: Wireless Networks
Ian McCrum
Room 5B18
Tel: 90 366364 voice mail on 6th ring
Email: [email protected]
Web site: http://www.eej.ulst.ac.uk
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IEEE
•The IEEE is an international organization that develops standards
for hundreds of electronic and electrical technologies
•Uses a series of numbers, like the Dewey Decimal system in
libraries, to differentiate between the various technology families.
•The 802 committee develops standards for local and wide area
networks (LANs and WANs)
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802.3 committee develops standards for Ethernet -based wired networks
802.15 group develops standards for personal area networks,
802.16 group develops standards for WiMAX
802.11 committee develops standards for wireless local area networks
(LAN).
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802.11 ABC’s
Layer
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Description
a
PHY
54 Mb/s in 5 GHz bands
b
PHY
11 Mb/s direct sequence in 2.4 GHz band
c
MAC
Bridging operation
d
PHY
International domains
e
MAC
Quality of service (QoS) (late ’04)
f
both
Access point interoperability
g
PHY
54 Mb/s at 2.4 GHz (802.11b compatible)
h
both
Coordination with European HiperLAN2 standards
i
MAC
Security (mid ’04)
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802.11 ABC’s: Continued
Layer
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Description
j
both
Additional Japanese bands at 4.9 and 5 GHz
k
both
Radio resource measurement enhancements
m
both
Maintenance of earlier standards
n
both
High throughput (>100 Mb/s)
p
MAC
Vehicular hand-off
r
MAC
Fast roaming
s
both
Mesh networking
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Wi-Fi Terms
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AP: Access Point
SSID: Service Set Identifier (Network)
Wi-fi: Wireless Fidelity
WEP: Wired Equivalent Privacy
WLAN: Wireless Local Area Network
Ad-Hoc (mode): device to device
Infrastructure (mode): device to Access Point
RFID: Radio Frequency Identifiers
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802.11a
• Operates in 5GHz radio
band
• Maximum throughput per
channel -54Mbps
• Supports up to 12 separate
non-overlapping channels
• Pros
– 12 channels @ 54Mbps
• Cons
– Incompatible with
existing 802.11b & g
– Equipment more
expensive
– Limited range
• Range -80 feet
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802.11b
• Operates in 2.4Ghz
spectrum (cordless
phones)
• Maximum throughput per
channel -11Mbps
• Supports 3 nonoverlapping channels
• Pros
– Inexpensive Equipment
– Compatible with newer
faster 802.11g
• Cons
– Three channels per access
point
– Slow
– Easily hacked
• Range: 328 feet
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802.11b: Be careful abroad
• The 802.11b standard defines a total of 14 frequency channels.
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FCC allows channels 1 through 11 within the U.S. Most of
Europe can use channels 1 through 13. In Japan, only 1 choice:
channel 14.
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Channel represents a center frequency. Only 5 MHz separation
between center frequencies of channels.
5 MHz
Channel
1
2.412
2
3
4
2.417
2.422
2.427
5
6
2.432
2.437
7
2.442
8
2.447
9
2.452
10
11
2.457
2.462
Center
Frequency
(GHz)
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802.11b: Get Close to the Tx
• Ideally, 802.11b supports wireless
connections between an access
point and a wireless device at four
possible data rates: 1 Mbps, 2
Mbps, 5.5 Mbps, and 11 Mbps.
• Specifically, as terminal travels
farther from its AP, the connection
will remain intact but connection
speed decreases (falls back).
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2 Mbps
5.5 Mbps
11 Mbps
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802.11g
• Operates in the same
crowded 2.4 GHz
• Maximum throughput per
channel: 54Mbps
• Range: 328 feet
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• Pros
– Faster than 802.11b
– Interoperability with
802.11b
• Cons
– Three channels per access
point
– Slower than wired
networks
– Questionable Security
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Comparing .11a and .11g (both high speed)
• 802.11a operates in underused 5 GHz band; 802.11g operates in heavily used
2.4 GHz band.
• 11g systems experience interference from other 2.4 GHz devices such as
cordless phones, microwave ovens, satellites, etc.
• Both 802.11a and 802.11g offers up to 54Mbps speeds in the lab.
• In the field, 802.11a delivers about 20Mbps.
• 802.11b's 11Mpbs theoretical speed is more often 4Mbps in practice.
• The realistic data rates quoted for 802.11g thus far range from 6 Mbps to 20
Mbps.
• 11g has to contend with more interference in the 2.4 GHz range as compared
to 11a in the 5 GHz band.
• Range will depend on antenna gain, transmit power applied to the antenna, the
receive sensitivity of the radio card and the obstacles between path ends.
• 802.11a has range 150-300 ft in practical scenarios. 11g has range
comparable to 11b (approximately 1000 ft).
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802.11i
• Enhanced security
• Emerge in the second quarter of 2004
• Wi-Fi Protected Access (WPA)
– Enhancements to strongly increase the level of data
protection (encryption)
– access control (authentication) for existing and future
Wi-Fi wireless LAN systems.
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Wi-Fi Security
• WEP
– SSID
– Broadcast
– MAC (Media Access Control)
• WPA (Wi-Fi Protected Access)
• AES (Advanced Encryption Standard)
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Cellular technology
• 2G (Second Generation)
– Began in the 1990s,
– Digital voice encoding.
– Steadily improved, with increased bandwith, and the introduction
of multimedia.
• 2.5G –current state of mobile wireless
– Between 40k & 60K through put
• 3G –reach maturity between 2003-2005
– Up to 2mbps (not available in the US)
– Enable multimedia (voice, data,video)
• Ubiquitous
• Timeline
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Satellite Technology
• Viable for rural areas
• Cumbersome
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200/300 Kbps download speeds
128 Kbps upload
Encryption
VPN
Expensive
Susceptible to environmental factors
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Infrared (IR)
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Widely available on PDA’s, Cell Phones, Laptops
Short Range (1-2 Meters at maximum of 4MB/s)
Non-visible light based
Critical alignment
9600 bps to 4 Mbps
Direct RS-232 replacement
Line of sight – no obstructions
Bright sunlight can disrupt
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Bluetooth
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A short-range (30 feet) wireless specification
Technology to remove cables
Name comes from 10th-century Danish King Harald
Blåtand (Bluetooth), who unified Denmark and Norway.
Radio Frequency – 2.4 GHz
Frequency hopping spread spectrum
1Mbsp up to 10 meters
Ad hoc session
Interferes with WiFi
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Home Wireless Networks
• Need/Desire for multiple devices to connect to broadband (high
speed) internet
• Relatively inexpensive
• Easy setup
• Flexible
• Secure (can be)
• Laptops and PDAs with embedded wireless
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Corporate Wireless
• Eliminates cabling to end user devices, thus reducing cost (new
construction only)
• Provides flexibility for growth, contraction, relocation
• Enhances creativity and collaboration through mobility
• Requires thought and planning (site survey)
• Allows for security if configured properly
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Corporate Wireless (for visitors)
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Member access to internet, e-mail, corporate network
Presentation from internet or corporate network
Vendor access to web for demos
Separate from corporate network (VLAN)
Visitors are expecting wireless
Provides collaboration at conferences and meetings
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Connecting to a Hotspot
• There are actually two steps to making a connection.
• The first is to have your notebook "talk" to the hotspot, which
means that the hardware and hotspot must recognize each
other. This should happen automatically as long as your
wireless hardware is turned on and new.
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Connecting to a Hotspot (Cont’d)
• On the newest machines, an 802.11 card will automatically
connect with an 802.11 hotspot and a network connection will be
established. As soon as you turn on your machine, it will connect
and you will be able to browse the Web, send email, etc. using
WiFi.
• On older machines you often have to go through a simple 3-step
process to connect to a hotspot.
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Connecting to a Hotspot (Cont’d)
• Access the software for the 802.11 card -- normally there is an
icon for the card down in the system tray at the bottom right of the
screen.
• Click the "Search button" in the software. The card will search for
all of the available hotspots in the area and show you a list.
• Double-click on one of the hotspots to connect to it.
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Connecting to a Hotspot (Cont’d)
• On ancient 802.11 equipment (more than 2-3 years old), there is
no automatic search feature.
• You have to find what is known as the SSID of the hotspot
(usually a short word of 10 characters or less) as well as the
channel number (an integer between 1 and 11) and type these two
pieces of information in manually.
• All the search feature (in newer equipment) is doing is grabbing
these two pieces of information from the radio signals generated
by the hotspot and displaying them for you.
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Connecting to a Hotspot (Cont’d)
• On most notebook models, you will see some sort of signal icon
on the bottom right hand corner of your screen or a lit indicator on
the notebook itself, which will give you feedback for "On" and
signal strength (a red screen means your radio is Off; a green
screen indicates it is On).
OFF
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ON
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Connecting to a Hotspot (Cont’d)
• You can also see the quality of the signal by clicking on the
radio icon (may vary by system):
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Connecting to a Hotspot (Cont’d)
• Your next step is to sign up with a wireless Internet service
provider and configure your notebook according to their
instructions.
• Most of the time, this is a matter of simply launching your web
browser. It will automatically go to the wireless service
provider's sign-in page.
• Keep in mind that different hotspot locations work with
different service providers, but each hotspot location should
provide easy and clear instructions on how to connect.
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Connecting to a Hotspot (Cont’d)
• If you don't subscribe to a service, chances are you will need to
use your credit card to pay for access every time you want to
connect.
• Always make sure you know what the service provider charges, as
there can be a wide range of prices.
• After this, you will end up at the log-on page of the wireless
provider (or, in some cases, the wireless location).
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Connecting to a Hotspot (Cont’d)
• If so, simply follow the instructions to sign up for the service,
or enter your user name and password if you are already a
customer.
• Once you successfully log on, you should see the following
icon in your tool bar, indicating the connection has been made:
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WiFi Security
• WiFi hotspots can be open or secure.
• If a hotspot is open, then anyone with a WiFi card can access
the hotspot.
• If it is secure, then the user needs to know a WEP key to
connect.
• WEP stands for Wired Equivalent Privacy
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WiFi Security (Cont’d)
• WEP is an encryption system for the data that 802.11 sends
through the air.
• Encryption system prevents any non-authorized party from
reading or changing data.
• Specifically, it is the process of encoding bit stream in such a
way that only the person (or computer) with the key (a digital
sequence) can decode it.
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WEP
• WEP has two variations: 64-bit encryption (really 40-bit) and 128bit encryption (really 104-bit).
• 40-bit encryption was the original standard but was found to be
easily broken.
• 128-bit encryption is more secure and is what most people use if
they enable WEP.
• For a casual user, any hotspot that is using WEP is inaccessible
unless you know this WEP key.
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WEP (Cont’d)
• If you are setting up a hotspot in your home, you may want to
create and use a 128-bit WEP key to prevent the neighbors
from casually eavesdropping on your network.
• Whether at home or on the road, you need to know the WEP
key, and then enter it into the WiFi card's software, to gain
access to the network.
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Setting up a Hotspot at Home
• If you already have several computers hooked together on an
Ethernet network and want to add a wireless hotspot to the mix,
you can purchase a Wireless Access Point and plug it into the
Ethernet network.
Wireless Access Point
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Setup #1
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Alternate Setup using a Wireless Router
• If you are setting up a network in your home for the first time, or
if you are upgrading, you can buy a Wireless Access Point Router.
• This is a single box that contains:
– 1) a port to connect to your cable modem or DSL modem,
– 2) a router,
– 3) an Ethernet hub,
– 4) a firewall and
– 5) a wireless access point.
• You can connect the computers in your home to this box either
with traditional Ethernet cables or with wireless cards.
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Alternate Setup (Cont’d)
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WiFi Range
• Regardless of which setup you use, once you turn your Wireless
Access Point on, you will have a WiFi hotspot in your house.
• In a typical home, this hotspot will provide coverage for about 100
feet (30.5 meters) in all directions, although walls and floors do
cut down on the range.
• Even so, you should get good coverage throughout a typical home.
For a large home, you can buy inexpensive signal boosters to
increase the range of the Hotspot.
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One Type of Amplifier
Or a directional
antenna can be
used to give
better range in
a particular
direction.
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Another Way to Amplify WiFi Signals
A WiFi repeater
is installed to
extend
coverage.
Wireless
Access Point
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Configuring a Hotspot
• Most wireless access points come with default values built-in.
• Once you plug them in, they start working with these default
values.
• However, you may want to change things.
• You normally get to set three things on your access point.
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Things to Configure in a Hotspot
• The SSID -- Service Set IDentifier is a sequence of
charactersthat uniquely names a WLAN.
– It will normally default to the manufacturer's name (e.g.
"Linksys" or "Netgear").
– You can set it to any word or phrase you like.
• The channel – the radio link used by access point/router to
communicate to wireless devices.
– Normally it will default to channel 6.
– However, if a nearby neighbor is also using an access point
and it is set to channel 6, there can be interference. Choose
any other channel between 1 and 11.
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Things to Configure (Cont’d)
• The WEP key -- The default is to disable WEP.
– If you want to turn it on, you have to enter a WEP key and
turn on 128-bit encryption.
– WEP can be in text format.
Access points come with simple instructions for changing
these three values. Normally you do it with a Web browser.
Once it is configured properly, you can use your new hotspot
to access the Internet from anywhere in your home.
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Infrastructure versus Ad Hoc
• All the connections that we have talked about today require a
connection from a device equipped with a wireless network
interface card (NIC) to a wireless access point.
• Generally, all such connections are operating in what is known as
the infrastructure mode. Here the wireless network resembles a
cellular architecture.
• Wireless devices can also communicate directly with each other,
i.e., it is not required that they communicate with an access point
first.
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Infrastructure versus Ad Hoc
• When devices with NIC cards communicate directly with each
other, the wireless network operates in ad hoc mode.
• Essentially peer-to-peer communication is enabled.
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Ad Hoc Mode
• Ad Hoc connections can be used to share information directly
between devices. This mode is also useful for establishing a
network where wireless infrastructure does not exist.
• Some uses,
– Synchronize data between devices.
– Retrieve multimedia files from one device and “play” them
on another device.
– Print from a computer to a printer without wires.
• There are many applications of ad hoc networking in the
military and in specialized networks.
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Security Threats
• Wireless technology doesn’t remove any old security
issues, but introduces new ones
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Viruses, Trojans and stuff like that are still there
Eavesdropping
Man-in-the-middle attacks
Denial of Service
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Eavesdropping
• Easy to perform, almost impossible to detect
• By default, everything is transmitted in clear text
– Usernames, passwords, content ...
– No security offered by the transmission medium
• Different tools available on the internet
– Network sniffers, protocol analysers . . .
– Password collectors
• With the right equipment, it’s possible to eavesdrop
traffic from few kilometers away
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Man in the middle attacks
•
In a MITM attack, the attacker funnels victim’s traffic
through a point controlled by the attacker
• Allows data analysis and
manipulation
– Tools available on the internet
• Can target secure higher level
protocols
• MITM attacks are also
possible in wired networks
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Man in the middle attacks
The attacker can terminate victim’s SSL/TSL session at her host and reconnect
to the actual site. This allows the attacker to see everything in clear text
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Wireless MITM Attack
1.
2.
3.
Attacker spoofes a disassociate
message from the victim
The victim starts to look for a new
access point, and the attacker
advertises his own AP on a different
channel, using the real AP’s MAC
address
The attacker connects to the real AP
using victim’s MAC address
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Denial of Service
• Frequency jamming
– Not very technical, but works
• Spoofed deauthentication / disassociation messages
– can target one specific user
• Attacks on higher levels
– SYN Flooding
– Ping of death
– ...
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Other Wireless networking
• WiMax “Wider_fi” is described in 802.16
• 10-100 Mb/s and several (up to 40)km range
• Also “Mobile-fi” 802.20
• 16 Mb/s and several km range, allows fast hand-offs
• Personal Area Networking (PANs) 802.15
• 3G mobile telephone products,
• Bluetooth, Hiperlan, Zigbee etc etc…
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WiMax
• WiMax, short for Worldwide Interoperability for
Microwave Access, is the latest of the wireless "last
mile" broadband technologies.
• ISP see WiMax as a means of connecting rural or remote
areas with broadband service, something that would be
technically, physically or economically difficult to do by
burying wire for DSL or cable connections.
• Laying wires is especially difficult in hilly areas like
County Down.
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Benefits over Satellite
• In rural areas, the real competition to WiMax would be
satellite data services.
• The benefit that WiMax offers over satellite is that satellite
offers limited uplink bandwidth (upload data rates are not as
high as download data rates).
• Further, satellite suffers with high latency.
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WiMax (Cont’d)
• In congested cities, WiMax products could shift traffic to
help relieve heavy demand on broadband networks.
• WiMax will work with other shorter-range wireless
standards, including Wi-Fi, which has taken off as an
easy way to provide Internet access throughout a home
or business.
• Eventually, advocates hope to see the standard evolve
into a mobile wireless Internet service similar to cellular
data technologies. It may not ever be as wide-area as
cellular but will offer higher data rates.
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WiMax Protocols
• The protocols that govern WiMax have been
standardized. They are collectively referred to as
802.16.
• Like Wi-Fi = 802.11, WiMax = 802.16.
• Overall vision for 802.16 is that carriers (e.g., ISP)
would set up base stations connected to a public (wired)
network. This is like cellular.
• Each base station would support hundreds of fixed
subscriber stations. Fixed means that subscriber stations
do not move. Plans to expand the standard to include
mobile stations is in the working.
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More on WiMax
• Base stations will use the 802.16 protocols to dynamically
allocated uplink/downlink bandwidth to subscriber stations based
on their demand.
• 802.16 has been developed for several frequency bands (various
licensed frequencies in 10-66 GHz, also licensed and unlicensed
frequencies in 2-11 GHz).
• In the unlicensed bands, 802.16 can be used as a backhaul for wifi systems or a longer-range alternative, i.e., replacing hotspots
with hotzones.
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Some Technical Specs on WiMax
• The radio technology is based on OFDM.
• 802.16 standards incorporate use of adaptive antenna arrays,
which can be used to create dynamic beams in desired directions.
• Standards offer option for a mesh mode network topology.
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Mesh Networking in WiMax
• When a subscriber unit is not in line of sight with the base station
(does not have a good signal strength), then it may be able to make
a peer-to-peer connection to a neighbor, i.e., hop to a neighbor’s
subscriber unit.
• The neighbor’s unit may be in line of sight with the base station,
in which case this neighbor would serve as a relay station (a
repeater).
• If the neighbor’s unit is not in line-of-sight then another hop can
be made.
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Mesh Mode
Residential
Business
Trunk
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Trunk
(Wired)
Network
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WiMax Costs
• Analysts estimate that subscriber stations for home access will
initially cost up to $300.
• Base stations will cost as little as $5,000 but will reach $100,000,
depending on their range. Each base station may be able to
support up to 60 T1 class subscriber lines.
• In some cases, consumers would lease subscriber stations from
carriers the way they do with cable set-top boxes as part of their
service plans.
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WiMax Predictions
• Base stations will be able to connect to other base
stations within a range of up to 30 miles with data
transfer speeds of up to 75 megabits per second.
• Subscriber stations, the set-top box-like devices, will
connect to base stations with ranges of up to three miles
and transfer speeds of up to 15 megabits per second.
• WiMax T1 class lines may cost 10% of wired T1 costs.
• Products will start being available 2005-2006.
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