WIRELESS TECHNOLOGY
WIRELESS TECHNOLOGY
• Wireless local area network (WLAN)
communication is one of the fastest growing
technologies.
• It is a cellular computer network that transmits and
receives data with radio signals instead of wires.
• Innovative ways to utilize WLAN technology are
helping people to work and communicate more
efficiently. Increased mobility and the absence of
cabling and other fixed infrastructure have proven
to be beneficial for many users.
USES OF WIRELESS NETWORKING
• Communication with mobile stations, which precludes the use of
fixed cabling, or for mobile users who roam over large distances,
such as sales reps with laptops that have cellular modems.
• Work areas in which it is impractical or expensive to run cabling,
such as older buildings that are costly to renovate. In this case, two
solutions are possible:
1. Create a wireless LAN (WLAN) that uses no cabling between stations.
2. Create a combination of traditional wired local area networks (LANs) and
as many wireless stations as needed.
• Networking buildings on a campus using a wireless bridge or router. You
can typically use wireless bridges or routers over distances up to 25 miles.
They might support point-to-point or multipoint connections and often
support Internet Protocol (IP) or Internetwork Packet Exchange (IPX)
routing using static routing or the Routing Information Protocol (RIP).
TYPES OF UNBOUNDED WIRELESS
MEDIA
A. RADIO WAVES
B. MICROWAVES
C. INFRARED
RADIOWAVES
• Radio Waves have frequencies between 10 kHz and 1 GHz.
Most radio frequencies used around the world are regulated. To
gain permission to use a regulated frequency can take a long
time and large amount of money.
• There are, however that are not regulated that anyone can use.
These bands are 902-928 MHz, 2.4 GHz (internationally
unregulated) and 5.72-5.85 GHz. The problem with unregulated
frequencies is that they can get saturated. To ease this, there
have been limits set on the amount of power that devices can
broadcast in these frequencies. While letting more people use
the frequencies, this cuts down on the usable range.
MICROWAVES
Microwaves travel at high frequencies (within the
frequency range of 1Ghz and above) than radio
waves and uses licensed frequencies. It has
relatively higher cost compared to radio wave system
because of licensed frequencies. It provides better
throughput as a wireless network media. Microwave
transmission requires the sender to be within sight of
the receiver. Numerous transmission systems use
microwaves including line-of-sight between buildings
and across vast distances, communications satellites,
PCS cellular systems and wireless LANs.
Satellite Microwave
• LEO - Low Earth Orbit - 100 miles to 1000 miles.
Used for pagers, wireless e-mail, special mobile
telephones, spying, videoconferencing.
• MEO - Middle Earth Orbit - 1000 to 22,300 miles.
Used for GPS and government.
• GEO - Geosynchronous Orbit - 22,300 miles. Used
for weather, television, and government operations.
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Satellite Microwave
HEO – Highly Elliptical Orbit
– A fourth type of orbit used by the military for
spying and by scientific organizations for
photographing celestial bodies.
– When satellite is far out into space, it takes
photos. When satellite is close to earth, it
transmits data.
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INFRARED
• INFRARED is just below visible light and
allows high-speed data transmissions.
Infrared transmissions can be affected by
objects obstructing the sender or receiver
and by interference from light sources but
immune to EMI and can be successfully
where certain types of cable media fail.
Two Leading Wireless Technology
• IEEE802.11 (Wi-Fi)
• Bluetooth
LAN Technologies
802.11 Wireless LAN
Desktop
with PCI 802.11 LAN card
Network
connectivity
to the
legacy Access Point Laptop
with PCMCIA 802.11 LAN card
wired LAN
Provides network connectivity over wireless media
An Access Point (AP) is installed to act as Bridge
between Wireless and Wired Network
The AP is connected to wired network and is
equipped with antennae to provide wireless
connectivity
LAN Technologies
802.11 Wireless LAN
Range ( Distance between Access Point and WLAN
client) depends on structural hindrances and RF
gain of the antenna at the Access Point
To service larger areas, multiple APs may be
installed with a 20-30% overlap
A client is always associated with one AP and when
the client moves closer to another AP, it associates
with the new AP (Hand-Off)
Three flavors:
802.11b
802.11a
802.11g
LAN Technologies
Multiple Access with Collision
Avoidance (MACA)
other node in other node in
sender receiver
sender’s range receiver’s range
RTS
CTS
data
ACK
Before every data transmission
Sender sends a Request to Send (RTS) frame
containing the length of the transmission
Receiver respond with a Clear to Send (CTS) frame
Sender sends data
Receiver sends an ACK; now another sender can
send data
When sender doesn’t get a CTS back, it assumes
collision
LAN Technologies
WLAN : 802.11b
The most popular 802.11 standard currently in
deployment.
Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4
GHz ISM (Industrial-Scientific-Medical) band
LAN Technologies
WLAN : 802.11a
Operates in the 5 GHz UNII (Unlicensed National
Information Infrastructure) band
Incompatible with devices operating in 2.4GHz
Supports Data rates up to 54 Mbps.
LAN Technologies
WLAN : 802.11g
Supports data rates as high as 54 Mbps on the 2.4
GHz band
Provides backward compatibility with 802.11b
equipment
BLUETOOTH
• Bluetooth is the industry standard wireless technology used for
Wireless Personal Area Network (WPAN). Bluetooth devices in
WPAN operate in a range up to 30 feet away.
• A Bluetooth LAN is an ad hoc network, which means that the
network is formed spontaneously; the devices, sometimes called
gadgets, find each other and make a network called piconet.
• A Bluetooth LAN can even be connected to the internet if one of
the gadgets has this capability.
• A Bluetooth LAN, by nature, cannot be large. If there are many
gadgets that try to connect, there is a chaos. Bluetooth
technology has several applications. Peripheral devices of a
computer can communicate with the computer through this
technology (wireless mouse or keyboard).
Repeater, HUB, Bridge & Switch
REPEATER, HUB, BRIDGE AND
SWITCH
Repeater, Hub, Bridge & Switch
Repeater
A repeater receives a signal, regenerates it, and
passes it on.
It can regenerate and retime network signals at the
bit level to allow them to travel a longer distance on
the media.
It operates at Physical Layer of OSI
The Four Repeater Rule for 10-Mbps Ethernet
should be used as a standard when extending LAN
segments.
This rule states that no more than four repeaters can
be used between hosts on a LAN.
This rule is used to limit latency added to frame
travel by each repeater.
Repeater, Hub, Bridge & Switch
Hub
Hubs are used to connect
multiple nodes to a single
physical device, which
connects to the network.
Hubs are actually multiport
repeaters.
Using a hub changes the
network topology from a
linear bus, to a star.
With hubs, data arriving over
the cables to a hub port is
electrically repeated on all
the other ports connected to
the same network segment,
except for the port on which
the data was sent.
Repeater, Hub, Bridge & Switch
Bridge
Bridges are used to logically separate
network segments within the same
network.
They operate at the OSI data link layer
(Layer 2) and are independent of higher-
layer protocols.
The function of the bridge is to make
intelligent decisions about whether or
not to pass signals on to the next
segment of a network.
When a bridge receives a frame on the
network, the destination MAC address is
looked up in the bridge table to
determine whether to filter, flood, or
copy the frame onto another segment
Broadcast Packets are forwarded
Repeater, Hub, Bridge & Switch
Switch
Switches are Multiport Bridges.
Switches provide a unique network segment on each
port, thereby separating collision domains.
Today, network designers are replacing hubs in their
wiring closets with switches to increase their network
performance and bandwidth while protecting their
existing wiring investments.
Like bridges, switches learn certain information about
the data packets that are received from various
computers on the network.
Switches use this information to build forwarding
tables to determine the destination of data being sent
by one computer to another computer on the network.
Repeater, Hub, Bridge & Switch
Switches: Dedicated Access
Hosts have direct A
connection to switch
C’ B
Full Duplex: No collisions
Switching: A-to-A’ and B-to-
B’ simultaneously, no switch
collisions
Switches can be cascaded to
expand the network C
B’ A’
