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Part 3 – Packet Switching and
Network Technologies
Wireless Networking
Technologies
Gail Hopkins
Part 3 – Packet Switching and
Network Technologies
Introduction
Here we will be discussing wireless
communication technologies for a range of
distances
Wireless has multiple technologies Many have similar characteristics
Wide range of networks and distances
Partly due to Government regulations that make
specific ranges of the EM spectrum available for
communication
This lecture will cover some of these
technologies
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Part 3 – Packet Switching and
Network Technologies
Taxonomy of Wireless
Networking Technologies
Wireless Networks
Local Area Networks (LANs)
Metropolitan Area Networks
(PANs)
Wide Area Networks (WANs)
Personal Area Networks (PANs)
From Comer, 2009
Part 3 – Packet Switching and
Network Technologies
Personal Area Networks (PANs)
Type Purpose
Bluetooth Communication over a short distance
between a small peripheral devices such
as a headset or a mouse and a system
such as a mobile phone or a computer
InfraRed Line-of-sight communication between a
small device, often a hand-held
controller, and a nearby system such as
a computer or entertainment centre
ISM wireless Communication using frequencies set
aside for Industrial Scientific and
Medical devices, an environment where
EM interference may be present
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Part 3 – Packet Switching and
Network Technologies
ISM Wireless Bands Used by
LANs and PANs
From Comer, 2009
Part 3 – Packet Switching and
Network Technologies
Wireless LAN Technologies and
Wi-Fi IEEE Standard Frequency Band Data Rate
Original 802.11 2.4 GHz 1 or 2 Mbps
Original 802.11 InfraRed 1 or 2 Mbps
802.11a 5.725 GHz 6 to 54 Mbps
802.11b 2.4 GHz 5.5 and 11 Mbps
802.11g 2.4 GHz 22 and 54 Mbps
Different standards may use:
Different modulation techniques (e.g. PSK)
Different multiplexing techniques
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Part 3 – Packet Switching and
Network Technologies
Spread Spectrum Techniques
Spread spectrum transmission uses multiple frequencies to send data Sender spreads data across multiple frequencies
Receiver combines information from these frequencies to rebuild the original data
Different techniques use different ways of doing this
Two alternative reasons for using spread spectrum: Increase overall performance
Make transmission more immune to noise
Part 3 – Packet Switching and
Network Technologies
Other Wireless LAN Standards
Many standards created by IEEE! For different types of communication
Each standard specifies: Frequency range
Modulation technique
Multiplexing technique
Data rate
Different standards have different advantages, e.g.: 802.11i – enhanced security
802.11n – data rate > 100Mbps to handle video applications
802.11r – improved reliability to roam among access points without losing connectivity
Latest standards – 802.11ac, 802.11ad!!!!
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Part 3 – Packet Switching and
Network Technologies
Wireless LANs
Three key parts to a wireless LAN:
Access points
Aka base stations
Switch or router
Used to connect access points
Set of wireless hosts
Aka wireless nodes or wireless stations
Part 3 – Packet Switching and
Network Technologies
Wireless LANs (2) 802.11 standard (WiFi), works in 2 modes:
Infrastructure
Wireless host only communicates with an access point
Access point relays all packets
Ad hoc
Wireless hosts communicate among themselves without a base station
Infrastructure with base station Ad hoc networking
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Part 3 – Packet Switching and
Network Technologies
Achieving Mobility with a
Wireless LAN
Wireless Access
Point
Switch or router
Basic Service
Set (BSS) 1
BSS 2
Part 3 – Packet Switching and
Network Technologies
Overlap and Association
Multiple access points are used to cover a large area
The network consists of multiple cells
If a pair of access points are too far apart
Dead zone
If too close together
Overlap
If a client is within range of multiple access points it has
to associate with a single access point
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Part 3 – Packet Switching and
Network Technologies
Overlap and Association (2)
If a client is within range of multiple access points it has to associate with a single access point
The 802.11 frame format therefore also carries the MAC address of the access point
From Comer, 2009
Part 3 – Packet Switching and
Network Technologies
Coordination Among Access
Points
Early more complex access points
coordinated among themselves to handoff
as a wireless device moved from one access
point’s region to another
E.g. Some used a measure of signal strength
Alternatively, lower cost access points
operate independently
Rely on wireless devices to change their
association from one access point to another
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Part 3 – Packet Switching and
Network Technologies
PAN Technologies Example -
Bluetooth Short distance wireless connection technology
Replacement for cables, for linking devices within a small area
Up to 5 metres (variations extend range to 10 or 50m)
Operates at 2.45 GHz
Spread spectrum frequency hopping
1600 hops per second across chosen frequencies
Voice 64 Kbps, data up to 721 Kbps
Part 3 – Packet Switching and
Network Technologies
Bluetooth Architecture
Basic unit – piconet
Master node, up to 7 active slaves, up to 255 parked nodes (low-power state)
Centralised TDM system
All communication is between master and slave
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Part 3 – Packet Switching and
Network Technologies
Wireless WAN Technologies
Example – Cellular Communication
Systems Originally designed for providing voice
services to mobile phone customers
Now used heavily for data too
System consists of cells, each containing a
transmitter (Base Station Controller (BSC))
Cells placed side-by-side to cover large areas
Group of cells connected to a Mobile Switching
Centre (MSC)
Part 3 – Packet Switching and
Network Technologies
Achieving Mobility with Cellular
Telephony
Mobile Switching
Centre (MSC)
Cell
Base station
Gateway MSC
GSM 850-1900 MHz
3G (UMTS) – 2.1 GHz
Base Station
Controller (BSC)
BSC
PSTN
Mobile Switching
Centre (MSC)
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Part 3 – Packet Switching and
Network Technologies
Cellular Communications
Adjacent cells use different frequencies to
prevent interference
When a user moves between cells that
connect to the same MSC, the MSC handles
the change-over (handoff)
When a user moves between different
geographic regions, two MSCs handle the
change-over
Part 3 – Packet Switching and
Network Technologies
Cellular Communications (2)
In theory, the cells are hexagonal-shaped
In practice they aren’t!
Also, obstructions and electrical interference
can attenuate a signal or cause an irregular
pattern
In built up areas, more cells are used which are
more tightly packed together
In rural areas, cells cover a larger area
Lower density of subscribers
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Part 3 – Packet Switching and
Network Technologies
Generations of Cellular
Technologies
Four generations:
1G, 2G, 3G, 4G
With intermediate versions; 2.5G, 3.5G
Part 3 – Packet Switching and
Network Technologies
Generation Date Purpose
1G Late 1970s through 1980s Used analogue signals to carry
voice
2G and 2.5G Early 1990s, still used today Uses digital signals to carry voice.
2.5G extends 2G to include some
3G features
3G and 3.5G 2000s Addition of higher speed data
services. Download rates of
400Kbps to 2Mbps. Intended to
support web browsing, photo
sharing, etc.
4G 2008 onwards Support for real-time multimedia,
e.g. TV programs/high-speed video
download. Includes multiple
connection technologies, e.g. Wi-Fi
and satellite. Phone chooses best
connection technology at any time.
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