Elnasr Technical College
IT Department
Level (4)
“Network Administration”
Lecture #3
By:
Mohamed A. Goumaa
M.Sc. in Computer Architecture and Networking
University of Khartoum
4. Wireless Architecture Facts
The following table describes details of a wireless networking architecture.
Characteristic Description
FHSS uses a narrow frequency band and 'hops' data signals in
a predictable sequence from frequency to frequency over a
Frequency
wide band of frequencies. Because FHSS hops between
Hopping Spread
frequencies, it can avoid interference on one cable as it shifts
Signaling Spectrum (FHSS)
to another. Hopping between frequencies increases
Method transmission security.
Direct-Sequence The transmitter breaks data into pieces and sends the pieces
Spread Spectrum across multiple frequencies in a defined range. DSSS is less
(DSSS) secured then FHSS.
Works in peer-to-peer mode without a WAP (the
wireless NICs in each host communicate directly with
one another)
Ad hoc Uses a physical mesh topology
Cheap and easy to set up but cannot handle more than
four hosts
Topology
Use a WAP
Uses a physical star topology
You can easily add hosts without increasing
Infrastructure
administrative efforts (scalable)
Allows you to connect easily to a wired network
Wireless networks use Carrier Sense Media Access/Collision Avoidance
(CSMA/CA) to control media access and avoid (rather than detect) collisions.
Collision avoidance involves implementing the following practices:
If a host detects traffic on the network, it experiences a longer back-off
Media Access
time than hosts on a wired network before attempting to transmit again.
Every transmission must be acknowledged. As every frame is
acknowledged by the receiving host, other hosts receive a message
indicating that they must wait to transmit.
Devices on a wireless network include:
A wireless NIC for sending and receiving signals.
Devices A wireless access point (WAP) is the equivalent of an Ethernet hub. The
wireless NICs connect to the WAP and the WAP manages network
communication.
A wireless bridge connects two wireless WAPs into a single network or
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connects your wireless WAP to a wired network. Most WAPs today
include bridging features.
Note: Many wireless access points include ports (or hubs, switches, or routers) to
connect the wireless network to the wired portion of the network.
5. Wireless Standards
Radio frequency wireless networking standards are specified by various IEEE 802.11
committees. Three of the most common are listed below.
Specification Standard
802.11a 802.11b 802.11g
Frequency 5 GHz 2.4 GHz 2.4 GHz
Speed 54 Mbps 11 Mbps 54 Mbps
Range** 150 Ft. 300 Ft. 300 Ft.
Signal DSSS DSSS DSSS
Note: Some newer 802.11g devices can use multiple channels (dual-band) to effectively double
the data transfer rate to 108 Mbps. However, dual-band wireless is especially susceptible from
interference from other wireless devices (such as phones).
Wireless equipment does not come with enabled security features. You should enable the types
of security you want to implement. The table below describes common wireless security
features.
Feature Description
The SSID is used to group several wireless devices and Access Points as part
of the same network and to distinguish these devices from other adjacent
wireless networks. The SSID is also commonly referred to as the network
name.
The SSID is a 32-bit value that you assign to both the WAP and the
host's NIC.
SSID (Service Set The SSID is part of the header of every frame that travels on the
Identification) network.
In order to communicate across the network, the data frames from a
host must include an SSID in the header that matches the WAP's
SSID.
The SSID name is case-sensitive.
Most WAPs come with a default SSID, which you should change as part of
your security implementation. Even after you change the SSID, it is still only
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a minimal security feature. There are two type of SSIDs:
BSSID (Basic Service Set Identification) is used by an ad-hoc
wireless network with no access points.
ESSID (Extended Service Set Identification), or ESS Identifier, is
used in an infrastructure wireless network that has access points.
WEP is a 64- or 128-bit encryption mechanism. WEP was designed to
provide wireless networks the same type of protection that cables provide on
a wired network. WEP has two implementations:
Open System uses encryption but does not require authentication.
Shared Key encrypts the SSID and the data. You must configure all
devices with a shared key (the key is not case-sensitive).
WEP (Wireless
WEP suffers from the following weaknesses:
Equivalent
Privacy)
The key is static. Because it doesn't change, it can be captured and
broken.
Every host on the network uses the same key.
On a wireless network that is employing WEP (Wired Equivalent Privacy),
only users with the correct WEP key are allowed to authenticate through the
WAP (Wireless Application Protocol) access points. WEP is intended to
prevent unauthorized users by employing a wireless session key for access.
WPA is a security mechanism that attempts to address the weaknesses of
WEP in the following ways:
WPA uses dynamic keys that change periodically.
Each host uses a unique key which is generated from a passphrase
(the passphrase is case-sensitive).
WPA (Wi-Fi WPA requires authentication.
Protected Access)
Despite its increased strength, WPA has the following disadvantages:
It is not widely implemented.
It is more difficult to configure than WEP.
All wireless equipment on the wireless network must support WPA.
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6. Bluetooth Facts
The Bluetooth standard was designed to allow people to connect in PAN (personal area network)
configurations using cell phones, PDAs (personal digital assistants), printers, mouse, keyboards
and other Bluetooth equipped devices. Bluetooth is a proposed standard of the IEEE 802.15
committee:
Bluetooth
Specification
(proposed 802.15)
Frequency 2.45 GHz
Speed 1 or 2 (2nd generation) Mbps
Range 30 Ft.
Signal FHSS
Bluetooth devices take the following steps to form a PAN:
Step Description
1. Device Discovery A Bluetooth device broadcasts its MAC address when it starts up.
The device identifies itself using a name the user previously
2. Name Discovery
configured.
3. Bonding
The device joins the PAN.
(Association)
4. Service Discovery The device tells other devices what services it provides.
Bluetooth uses a 128-bit proprietary encryption mechanism to encrypt its signals.
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