Wireless LANS
Justin Champion
Room C208 - Tel: 3273
www.staffs.ac.uk/personal/engineering_and_technology/jjc1
Wireless LANS
 Contents
 What is a LAN
 Types of wireless LAN
 AdHoc
 Infrastructured
 Infrared Communications
 Uses of these technologies
Wireless LANS
 What is a LAN
 There are two main types of network
infrastructures
 Local Area Network (LAN)
 Wide Area Network (WAN)
 The classification for these types of networks is
the distance that the data has to travel
 There is no exact formula to classify when a LAN
becomes a WAN in a wired network!
 Consider Staffordshire university is the email server part of a
WAN as it is located in Stoke?
 Or a LAN as it is all one network
Wireless LANS
 LAN
 The network in this campus is a example of a
LAN
 All machines are attached and located close to
each other
 Distance in network terms is classified by the number
of hops travelled between one device and another
 Hops are the stages that information has to travel
through to get to the destination.
Wireless LANS
 LAN
 Within a wireless network this is easier
 There is a physical limit to any wireless LAN
technology.
 Bluetooth – 10 Metres
 Infrared – 1 metre
 After these physical limits
 The Bit Error Rate (BER) becomes too high for realistic
communications to take place
 The BER indicates what percentage of bits sent arrive at the
destination in error
Wireless LANS
 Types of networks
 In wired networks there is always an
infrastructure
 Even if two people bring together laptops for a game,
there will be a cable and a device to repeat the signal
 A Hub, Router or Switch on Ethernet
 Wireless
 This may not be the case
 The devices may only be able to communicate for a
few seconds and then they are out of range
 People may come together for a meeting and then
move away again
Wireless LANS
 Types of networks
 AD-HOC
 No pre planning of the network takes place
 Communications may happen for hours or seconds
 Using the Nokia N-Game with friends is an example of this
 Business men in a meeting exchanging data
 Difficulty in routing data to these devices
 Infrastructured
 The network has been planned
 The structure would not change
 A office would be a good example of this
Wireless LANS
 Ad-Hoc
 These networks work as the devices come within the
transmission distance of each other
 When these devices can be used to extend a network
 In this diagram device B can not reach the printer
Printer
Device B
Device A
Wireless LANS
 Ad-Hoc
 One device can be used to reach the device you actually
require
 The packet is sent from device B to A and then to the printer
Device A
Printer
Device B
Wireless LANS
 Ad-Hoc
 These networks are an active research area
 The technology works now
 The difficulty is working out a route through the network
 The route change all of the time
 Each time a packet is sent to sort out a route this takes battery
power on all devices
 With enough devices nothing but routing information will be sent
 Ad-Hoc protocol
 Mobile Ad-hoc Networks (MANET)
 This group is standardising the IP routing protocols
 (www.ietf.org/html.charters/manet-charter.html)
Wireless LANS
 Infrastructure
 This would be used to supplement the current
network
 This allows for laptops
 Reduces the amount of cables
 This reduces infrastructure costs
 Allows workers to operate where they want in the building
 Usually combined with wired infrastructure
 Examples would be central high power printers
 Planning is required
 Remember that a radio signal from one device is just
interfering noise to another device
 The more interfering devices the less successful communications
that can take place
Wireless LANS
 Infrastructure
 Planning is required to minimise the amount of
interference
 This can be done by increasing the distance between
high users of a system
 Different rooms for the devices
 Some building materials will dampen the signal
 Staffordshire University Octagon is an example of this kind
building
Wireless LANS
The Technologies
Wireless LANS
 Before we start on this course clarification of a
widely used term the “Packet”
 All data which is transported on a network (wired
or wireless) is broken into smaller parts
 These parts are referred to as packets
 Each packet is then sent to the recipient
 The packets are then reassembled into the original data
 Packets usually consist of
 Control information
 The data which is being transported
 A checksum to ensure the packet is not corrupted
Wireless LANS
 Infrared
 Large installation base
 Most devices install these ports
 Phones
 Laptops
 Printers
 Not widely used!
 Question becomes why?
 Standards defined By
 Infrared Data Association (IRDA)
 www.irda.org
Wireless LANS
 Infrared – Operates by line of sight
Wireless LANS
 Infrared
 The data is encoded into pulses of Infrared (IR) light
 Your television remote control works in the same manner
 Technology is suited to
 Short distances with all devices within a room
 It is purposely designed to operate at about 1 meter
 This give IR security built in in respect that no one can ‘listen’ to that
conversion
 Data Rates
 Although IR is considered to be a slow technology it is developing
 Serial IR
–
115.2 Kbps
 Medium ID
–
1.152 Mbps
 Rarely Used
 Fast IR
–
4 Mbps
 Latest phones, cameras, etc support this standard
 Very Fast IR
–
16 Mbps
 Microsoft Windows XP supported only
Wireless LANS
 Infrared
 Advantage of the line of sight problem is that the
communications are not shared
 The devices need to be within a 300 arc of each other
 Once the receiver and sender have agreed a
transmission speed very little can interfere with this
 This reduces the overhead on communications
 Collisions do not need detecting
 Secure communications layer does not need adding
Wireless LANS
 What is a Stack?
 The term stack refers to the Open System
Interconnection (OSI) Stack
 This is a network standard that defines what communications




should take at which stage
There are 7 layers to the stack as shown below
Each layer carries out a specific task
Each layer can only communicate to the layer above or below
All other network protocols map to this stack
Application
 Not all layers are used with every protocol
Presentation
Session
Transport
Network
Data Link
Physical
Wireless LANS
 Communication between devices using the stack
 Packet of information going from device 1 to device 2
Device 1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Logically
Device 2
Application
Presentation
Session
Transport
Network
Data Link
Physical
Wireless LANS
 Infrared Communication Stack
 Only the layer above and below can communicate with
a point in the stack
irLAN OBEX irCOMM
IAS
TinyTP
irLMP
Optional
Required
irLAP
Physical
Wireless LANS
 Physical
 Defines encoding/decoding of data and transmission of the
signal
 IRLAP
 Link Access Protocol
 Responsible for ensuring a reliable transport of data
 IRLMP
 Link Management Protocol
 Multiplexes services and application together to use the one
connection for transport
 IAS
 Information Access Service
 Allows knowledge of the capabilities/services of the device
Wireless LANS
 Optional uses of IR
 TinyTP
 This is a version of transport protocol designed specifically for IR
 Flow control is offered ensuring that device buffers do not overflow
 Maximum packet sizes are agreed by devices
 Large packets can be broken into smaller parts
 irOBEX
 Object exchange protocol
 Allows transfer of files easily between devices
 irCOMM
 Allows emulation of serial and parallel ports
 The applications do not need to know that they are using IR
 Legacy applications will work with this a printer is an example
 irLAN
 Allows LAN access for the devices
 Mainly used to allow LAN access through a device which is already connected
to the network
Wireless LANS
 So why is not widely used
 Although newer versions of the technology are fast
the image is still for a slow technology
 Sun light
 The sun gives off IR and as such in bright light this will effect
the operation
 Makes operation in the open awkward
 Positioning
 The devices need to be in line of sight, which means that
they need moving from there normal position
 The distance between the devices can effect the rate of
transfer
 Too close can be as bad as too far!
Wireless LANS
 Summary
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


What is a LAN
OSI Stack
Packet
Infrared communications