4.4 WIRELESS LANS
4.4.1 The 802.11 Architecture
• The main wireless LAN standard is 802.11.
• Informally the technology is called WiFi (wireless
fidelity).
• 802.11 networks can be used in two modes.
– infrastructure mode.
– ad hoc mode.
• Infrastructure mode is the most popular mode
which is used to connect clients, such as laptops
and smart phones, to another network, such as a
company intranet or the Internet.
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Infrastructure Mode
• In infrastructure mode, each client is associated
with an AP (Access Point) that is in turn
connected to the other network. The client sends
and receives its packets via the AP.
• Several access points may be connected together,
typically by a wired network called a distribution
system, to form an extended 802.11 network. In
this case, clients can send frames to other clients
via their APs.
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4.4.1 The 802.11 Architecture
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Ad Hoc Mode
• The ad hoc mode is a collection of computers
that are associated so that they can directly
send frames to each other.
• There is no access point. Since Internet access
is the killer application for wireless, ad hoc
networks are not very popular.
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4.4.1 The 802.11 Architecture
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4.4.1 The 802.11 Protocol Stack(Data
Link Layer)
• The data link layer In 802.11 as well as in all the
802 protocols is split into two or more sublayers:
– the MAC (Medium Access Control) sublayer
determines how the channel is allocated, that is, who
gets to transmit next.
– Above it is the LLC (Logical Link Control) sublayer,
whose job it is to
• hide the differences between the different 802 variants
technologies
• and make them indistinguishable as far as the network layer
is concerned (provide an interface to the network layer).
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4.4.1 The 802.11 Protocol Stack
(physical layer)
• Several transmission techniques have been
added to the physical layer as 802.11 has
evolved since it first appeared in 1997.
– infrared in the manner of television remote
controls.
– frequency hopping in the 2.4-GHz band.
– direct sequence spread spectrum at 1 or 2 Mbps
in the 2.4-GHz band, It is now known as 802.11b.
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4.4.1 The 802.11 Protocol Stack
• To give wireless junkies a much-wanted speed boost,
new transmission OFDM (Orthogonal Frequency
Division Multiplexing)scheme introduced in 1999 and
2003.
– 802.11a and uses a different frequency band, 5 GHz.
– 802.11g with 2.4 GHz. Both give rates up to 54 Mbps.
• Most recently, transmission techniques that
simultaneously use multiple antennas at the
transmitter and receiver for a speed boost were
finalized as 802.11n in Oct. 2009. With four antennas
and wider channels, the 802.11 standard now defines
rates up to a startling 600 Mbps.
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4.4.1 The 802.11 Protocol Stack
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4.4.5 Services
• The 802.11 standard defines the services that
the clients, the access points, and the network
connecting them must be a conformant
wireless LAN. These services cluster into
several groups.
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4.4.5 Services
• The association service
– Used by mobile stations to connect themselves to APs.
– It is used just after a station moves within radio range
of the AP.
– The capabilities include
•
•
•
•
the data rates supported
security arrangements
power-saving capabilities
quality of service support, and more.
– The station sends a request to associate with the AP.
The AP may accept or reject the request.
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4.4.5 Services
• The Reassociation service
– lets a station change its preferred AP.
– useful for mobile stations moving from one AP to
another AP in the same extended 802.11 LAN, like
a handover in the cellular network.
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4.4.5 Services
• The Authentication service
– Stations authenticate before they can send frames via
the AP, but authentication is handled in different ways
depending on the choice of security scheme. If the
802.11 network is ‘‘open,’’ anyone is allowed to use it.
Otherwise, credentials are needed to authenticate.
– The recommended scheme, called WPA2 (WiFi
Protected Access 2)
– With WPA2, the AP can talk to an authentication
server that has a username and password database to
determine if the station is allowed to access the
network.
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4.4.5 Services
• The integration service
– handles any translation that is needed for a frame
to be sent outside the 802.11 LAN, or to arrive
from outside the 802.11 LAN.
– The common case here is connecting the wireless
LAN to the Internet.
• Data delivery service.
– This service lets stations transmit and receive data
using the protocols described earlier.
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4.4.5 Services
• The privacy service
– Wireless is a broadcast signal. For information
sent over a wireless LAN to be kept confidential, it
must be encrypted.
– manages the details of encryption and decryption.
– The encryption algorithm for WPA2 is based on
AES (Advanced Encryption Standard).
– The keys that are used for encryption are
determined during the authentication procedure.
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4.4.5 Services
• QOS traffic scheduling service.
– To handle traffic with different priorities, It uses
the protocols we described to give voice and video
traffic preferential treatment compared to besteffort and background traffic.
• A companion service
– provides higher-layer timer synchronization. This
lets stations coordinate their actions, which may
be useful for media processing..
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4.4.5 Services
• The transmit power control service
– gives stations the information they need to meet
regulatory limits on transmit power that vary from
region to region.
• The dynamic frequency selection service
– give stations the information they need to avoid
transmitting on frequencies in the 5-GHz band
that are being used for radar in the proximity.
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4.5 BROADBAND WIRELESS
broadband
• broadband refers to telecommunication in
which a wide bandwidth of frequencies that
are available to transmit information.
• Broadband can allow remote stations(devices)
to connect to a central station at high speeds.
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Broad Band Technologies
• Telephone System Broad Band Technologies
– Plain old telephone service (POTS)
– Integrated Services for Digital Network (ISDN)
– Digital subscriber line (DSL)
• Cable Television Technology
• Satellites Technology
• Cellular Communication Technology
– (BroadBand Wireless)
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4.5 BROADBAND WIRELESS
• The problem is that running fiber or coax to millions
of homes and businesses is prohibitively expensive.
What is a competitor to do?
• The answer is broadband wireless. Erecting a big
antenna on a hill just outside of town is much easier
and cheaper than digging many trenches and
stringing cables.
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4.5 BROADBAND WIRELESS
• Thus, companies provide multimegabit wireless
communication services for voice, Internet, movies
on demand, etc.
• The Broadband Wireless standard metropolitan area
network (MAN) is 802.16.
• Informally the technology is called WiMAX
(Worldwide Interoperability for Microwave Access).
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4.5.1 Comparison of 802.16 with
802.11 (similarities)
• At this point you may be thinking: why devise a
new standard? Why not just use 802.11?
– Like 802.11, WiMAX connect devices to the Internet at
megabit/sec speeds wirelessly, instead of using cable
or DSL. The devices may be mobile, or at least
portable.
– The packets may carry traffic, VoIP calls, or streaming
media to support a range of applications.
– Also like 802.11, 802.16 is based on OFDM technology
to ensure good performance in spite of wireless signal
different problems.
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4.5.1 Comparison of 802.16 with
802.11 (differences)
• However, WiMAX unlike 802.11. WiMAX achieves
high capacity by the efficient use of spectrum, so
that a large number of subscribers in a coverage
area can all get high throughput. How?
– WiMAX base stations are more powerful than 802.11
Access Points (APs)( The typical distances are at least
10 times larger than for an 802.11 network).
– The WiMAX base station uses more power and better
antennas, and it performs more processing to handle
errors and weaker signals over larger distances.
– WiMAX maximizes throughput, by carefully schedules
transmissions by the base station for each particular
subscriber.
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4.5.2 The 802.16 Architecture
• The 802.16 architecture : Base stations connect
directly to the provider’s backbone network,
which is in turn connected to the Internet.
• The base stations communicate with stations
over the wireless air interface. Two kinds of
stations exist:
– Subscriber stations remain in a fixed location, for
example, broadband Internet access for homes.
– Mobile stations can receive service while they are
moving, for example, a car equipped with WiMAX.
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4.5.2 The 802.16 Architecture
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4.5.2 The 802.16 Protocol Stack
(Physical Layer)
• The general structure is similar to that of the
other 802 networks, but with more sublayers.
• The bottom layer (physical layer) deals with
transmission, and here we have shown only
the popular offerings of 802.16, fixed and
mobile WiMAX.
– There is a different physical layer for each offering.
Both layers operate in licensed spectrum below 11
GHz and use OFDM, but in different ways.
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4.5.2 The 802.16 Protocol Stack
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4.5.2 The 802.16 Protocol Stack (Data
Link Layer)
• The data link layer consists of three sublayers.
– Security layer
– MAC common layer
– The service-specific convergence sublayer
• The bottom one (Security layer) deals with
privacy and security, which is far more crucial
for public outdoor networks than for private
indoor networks. It manages encryption,
decryption, and key management.
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4.5.2 The 802.16 Protocol Stack (Data
Link Layer)2
• The MAC common sublayer. This part is where the
main protocols, such as channel management, are
located.
• the base station completely controls the system; It can
schedule the downlink (i.e,base to subscriber) channels
very efficiently and plays a major role in managing the
uplink (i.e., subscriber to base) channels as well.
• An unusual feature of this MAC sublayer is that, (unlike
those of the other 802 protocols), it is completely
connection oriented, in order to provide quality of
service guarantees for telephony and multimedia
communication.
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4.5.2 The 802.16 Protocol Stack (Data
Link Layer)3
• The service-specific convergence sublayer
takes the place of the logical link sublayer in
the other 802 protocols. Its function is to
– provide an interface to the network layer.
– Different convergence layers are defined to
integrate seamlessly with different upper layers.
(hide the differences between the different 802
technologies)
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4.6 BLUETOOTH
Wireless Networks
PAN
802.15.x
10m
LAN
802.11
100m
MAN
802.16
2-6km
WAN
2G, 3G
2km/link
national
areas
Overview of wireless networks
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Bluetooth
• Bluetooth wireless technology is a short-range communications
technology intended to replace the cables connecting portable
and/or fixed devices while maintaining high levels of security.
• The key features of Bluetooth technology are
– Short Range and Small Networks
– robustness,
– low power,
– and low cost.
• IEEE 802.15 is the 15th working group of the IEEE 802 which
specializes in Wireless PAN (Personal Area Network including
Bluetooth) standards.
• The Bluetooth specification defines a uniform structure for a wide
range of devices to connect and communicate with each other.
www.bluethooth.com
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Bluetooth Application Areas
• Data and voice access points
– Real-time voice and data transmissions
• Cable replacement
– Eliminates need for numerous cable attachments for
connection
• Ad hoc networking
– Device with Bluetooth radio can establish connection
with another when in range
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What does Bluetooth do for you?
Landline
Cable
Replacement
Data/Voice
Access Points
Personal Ad-hoc
Networks
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4.6.1 Bluetooth Architecture
• The basic unit of a Bluetooth system
is a piconet;
– A Piconet: it consists of a master node
(for synchronization purposes) and up to
seven active slave nodes within a
distance of 10 meters.
• Multiple piconets can exist in the
same (large) room and can even be
connected via a bridge node that
takes part in multiple piconets;
– A Scatternet : is interconnected
collection of piconets.
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4.6.1 Bluetooth Architecture
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4.6.1 Bluetooth Architecture
• In addition to the seven active slave nodes in a
piconet, there can be up to 255 parked nodes
in the net. These are devices that the master
has switched to a low power state to reduce
the drain on their batteries.
• In parked state, a device cannot do anything
except respond to an activation or signals
from the master.
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4.6.1 Bluetooth Architecture
• The reason for the master/slave design is that the
designers intended to facilitate the
implementation of complete Bluetooth chips for
under $5.
• The consequence of this decision is that the
slaves are fairly dumb, basically just doing
whatever the master tells them to do.
• All communication is between the master and a
slave; direct slave-slave communication is not
possible.
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Features of Bluetooth Technology
•
Bluetooth is based upon small, high performance integrated radio
transceivers, each of which is allocated a unique 48-bit address derived from
the IEEE 802 standards.
•
It operates in the unrestricted 2.4 GHz ISM "free band", which is available
globally, although slight variation of location and width of band apply.
•
Bluetooth uses the unlicensed ISM (Industrial, Scientific and Medical) band,
2400 - 2483.5 MHz, thereby maximizing communication compatibility
worldwide
•
The range is set at 10 meters to optimize for target market of mobile and
business user. The range can, however, be increased to 100 meters.
•
Gross data rate is 1Mbit/s, with second generation providing increase to
2Mbit/s, and further to 3Mbits/s
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