Wireless LAN

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Wireless LAN

• Organisations and standards
• Wireless devices and topologies
• Authentication and association
• The radio wave and microwave spectrums
• Modulation
• Signals and noise on a WLAN
• Wireless security

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Organisations and standards (Enables
interoperable of networks)
IEEE is the prime issuer of standards IEEE802.11
Direct Sequence Spread Section (DSSS) wireless
devices - 1 to 2Mbps - 2.4 GHz IEEE802.11b -
Increased transmissions to 11Mbps Also known as
Wi-Fi or High speed wireless. DSSS operates at
1,2,5.5 and 11 Mbps. Backward compliant. Uses
different coding techniques Normally operates at
2 to 4Mbps - 2.4 GHz
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Organisations and standards (Enables
interoperable of networks)
IEEE 802.11a - Increased transmissions to 5 GHz
Isnt interoperable with 802.11b - operates at
2.5GHz Capable of 54Mbps Normally operates at 20
to 26Mbps Using proprietary technology (rate
doubling) can operate at 108Mbps IEEE 802.11g -
Same throughput as 802.11a Backward compatible
with 802.11b High-rate extension to 802.11b
allowing for data rates up to 54 Mbps in the
2.4-GHz ISM (Industrial, Scientific and Medical)
band
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Organisations and standards (Enables
interoperable of networks)
IEEE 802.15.1 Wireless Personal Area Network
standard based on the Bluetooth
specification, operating in the 2.4-GHz ISM
band. IEEE 802.11e Enhance the 802.11 Medium
Access Control (MAC) to improve and manage
Quality of Service, provide classes of service,
and enhanced security and authentication
mechanisms. These enhancements should provide the
quality required for services such as IP
telephony and video streaming.
.
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Organisations and standards (Enables
interoperable of networks)
IEEE 802.11f Develop recommended practices for an
Inter-Access Point Protocol (IAPP) which provides
the necessary capabilities to achieve
multi-vendor Access Point interoperability across
a Distribution System supporting IEEE P802.11
Wireless LAN Links. IEEE 802.11h Enhance the
802.11 Medium Access Control (MAC) standard and
802.11a HighSpeed Physical Layer (PHY) in the
5GHz band. Objective is to make IEEE 802.11ah
products compliant with European regulatory
requirements
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Organisations and standards (Enables
interoperable of networks)
IEEE 802.11i Enhance the 802.11 Medium Access
Control (MAC) to enhance security and
authentication mechanisms
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Organisations and standards (Enables
interoperable of networks)
IEEE 802.15 TG2 (802.15) Developing Recommended
Practices to facilitate coexistence of Wireless
Personal Area Networks and Wireless Local Area
Networks (802.11). IEEE 802.15 TG3 Draft and
publish a new standard for high-rate (20Mbit/s
or greater) WPANs IEEE 802.15 TG4 Investigate a
low data rate WPAN solution with multi-month to
multi-year battery life and very low complexity
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Task 1 Standards
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Wireless devices and topologies
Wireless network may consist of as few as two
devices. Equipped with wireless NICs, an ad
hoc network could be established which compares
to a peer-to-peer wired network Both devices act
as servers and clients in this environment. Altho
ugh it does provide connectivity, security is at
a minimum along with throughput. Another
problem with this type of network is
compatibility. Many times NICs from different
manufacturers are not compatible. Q Do you
visualise this concept???
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Wireless devices and topologies
To solve the problem of compatibility, an access
point (AP) is commonly installed to act as a
central hub for the WLAN infrastructure mode.
AP is hard wired to the cabled LAN APs are
equipped with antennae and provide wireless
connectivity over a specified area referred to
as a cell. The range will be from xxx to xxx
meters (xxx to xxx feet). Q Do you visualise
this concept???
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Wireless devices and topologies
To solve the problem of compatibility, an access
point (AP) is commonly installed to act as a
central hub for the WLAN infrastructure mode.
AP is hard wired to the cabled LAN APs are
equipped with antennae and provide wireless
connectivity over a specified area referred to
as a cell. The range will be from 91.44 to 152.4
meters (300 to 500 feet). Q Do you visualise
this concept???
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Wireless devices and topologies
To service larger areas, multiple access points
may be installed with a degree of overlap. The
overlap permits roaming between cells. This is
very similar to the services provided by
cellular phone companies. Overlap, on multiple AP
networks, is critical to allow for movement of
devices within the WLAN. Although not addressed
in the IEEE standards, a 20-30 overlap is
desirable. This rate of overlap will permit
roaming between cells, allowing for the
disconnect and reconnect activity to occur
seamlessly without service interruption.
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Wireless devices and topologies
When a client is activated within the WLAN, it
will start listening for a compatible device
with which to associate. This is referred to as
scanning and may be active or passive. Active
scanning causes a probe request to be sent from
the wireless node seeking to join the
network. The probe request will contain the
Service Set Identifier (SSID) of the network it
wishes to join. When an AP with the same SSID is
found, the AP will issue a probe response. The
authentication and association steps are
completed.
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Wireless devices and topologies
Passive scanning nodes listen for beacon
management frames (beacons), which are
transmitted by the AP (infrastructure mode) or
peer nodes (ad hoc). When a node receives a
beacon that contains the SSID of the network it
is trying to join, an attempt is made to join
the network. Passive scanning is a continuous
process and nodes may associate or disassociate
with APs as signal strength changes.
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Wireless devices and topologies
After establishing connectivity to the WLAN, a
node will pass frames in the same manner as on
any other 802.x network. WLANs do not use a
standard 802.3 frame. Therefore, using the term
wireless Ethernet is misleading. There are three
types of frames control management data.
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Wireless devices and topologies
Since radio frequency (RF) is a shared medium,
collisions can occur just as they do on wired
shared medium. The major difference is that
there is no method by which the source node is
able to detect that a collision occurred. For
that reason WLANs use Cxxxxxx Sxxxx Mxxxxx
Axxxx/Cxxxxxxxx Axxxxxxxx (CSMA/CA). This is
somewhat like Ethernet CSMA/CD.
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For that reason WLANs use Carrier Sense Multiple
Access/Collision Avoidance (CSMA/CA). This is
somewhat like Ethernet CSMA/CD.
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Wireless devices and topologies
When a source node sends a frame, the receiving
node returns a positive acknowledgment (ACK).
This can cause consumption of 50 of the
available bandwidth. This overhead when
combined with the collision avoidance protocol
overhead reduces the actual data throughput to a
maximum of 5.0 to 5.5 Mbps on an 802.11b wireless
LAN rated at 11 Mbps.
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Wireless devices and topologies
Performance of the network will also be affected
by signal strength and degradation in signal
quality due to distance or interference. As the
signal becomes weaker, Adaptive Rate Selection
(ARS) may be invoked. The transmitting unit
will drop the data rate from 11 Mbps to 5.5
Mbps, 5.5 Mbps to 2 Mbps 2 Mbps to 1 Mbps.
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Authentication and association
WLAN authentication occurs at Layer 2. It is the
process of authenticating the device not the
user. Association, performed after
authentication, is the state that permits a
client to use the services of the AP to transfer
data.
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Authentication and association
Authentication and Association types
Unauthenticated and unassociated The node is
disconnected from the network and not associated
to an access point. Authenticated and
unassociated The node has been authenticated on
the network but has not yet associated with the
access point. Authenticated and
associated The node is connected to the network
and able to transmit and receive data through
the access point.
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Authentication and association
Methods of authentication IEEE 802.11 lists two
types of authentication processes. Open
connectivity standard in which only the SSID must
match. This may be used in a secure or
non-secure environment although the ability of
low level network sniffers to discover the
SSID of the WLAN is high. Shared key. Process
requires the use of Wireless Equivalency Protocol
(WEP) encryption. WEP is a fairly simple
algorithm using 64 and 128 bit keys. The AP is
configured with an encrypted key and nodes
attempting to access the network through the AP
must have a matching key. WEP keys provide a
higher level of security than the open system
but are definitely not hack proof.
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The radio wave and microwave spectrums
The process of altering the carrier signal that
will enter the antenna of the transmitter is
called modulation. There are three basic ways
in which a radio carrier signal can be
modulated. Amplitude Modulated (AM) Frequency
Modulated (FM) In WLANs, a third type of
modulation called phase modulation is used to
superimpose the data signal onto the carrier
signal that is broadcast by the transmitter.
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Wireless security
EAP-MD5 Challenge Extensible Authentication
Protocol is the earliest authentication type,
which is very similar to CHAP password protection
on a wired network. LEAP (Cisco)
Lightweight Extensible Authentication LEAP
provides security during credential exchange,
encrypts using dynamic WEP keys, and supports
mutual authentication. User authentication
Allows only authorized users to connect, send
and receive data over the wireless network.
Encryption Provides encryption services
further protecting the data from intruders.
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Wireless security

• Data authentication Ensures the integrity
• of the data, authenticating source and
  destination
• devices.
• VPN technology effectively closes the wireless
  network
• since an unrestricted WLAN will automatically
  forward traffic
• between nodes that appear to be on the same
  wireless
• network.

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Task 2 Wireless devices
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The Wireless Road Show
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The Wireless Road Show
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The Wireless Road Show
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The Wireless Road Show
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Task 3 Do you know the answers