Slide Master Layout: Title Text: Arial Plain, 36 pt.

1
Toronto Wireless Users Group Building a Wireless
Network

Robert Pitton October 7, 2003
2
Agenda

• Wireless Standards Overview
• Wireless Lan Components
• Small, medium, large enterprise
• Antenna Placement
• Omni directional
• directional
• RF Considerations
• Attenuation
• interference

3
Wireless LAN Components

• Infrastructure
• Access Points
• Act like shared hubs
• Attach to wired network (authentication, traffic
  aggregation)
• Consist of radio, Ethernet interface, and
  bridging software
• Wireless LAN Building-to-Building Bridge
• Long-range, cost-effective wireless connectivity
  between sites, with multiple antennae options
• Client Interfaces
• PC cards to attach wireless laptops to the
  wireless network
• PCI cards to attach wireless desktop devices to
  the wireless network
• USB devices used to attach wireless desktop
  devices when there are no PCI slots
• Firmware and Software
• Roaming and load balancing
• Security
• Network management
• Configuration and diagnostics

4
Wireless Product Categories
5
802.11 Systems Overview
6
Choose 802.11b If You

• Dont have a need for high-bandwidth
• Are price sensitive
• Want a large choice of products
• Want to give your users access to public access
  hot-spots
• Want guaranteed compatibility

7
802.11a vs. 802.11b

• Factors to consider
• 802.11a is still much more expensive than 802.11b
• Not all wireless sites need 802.11as increased
  throughput
• Three 802.11b APs can provide 33Mbps
• 802.11a is not backwards compatible with 802.11b
• 802.11b radios cannot talk to 802.11a APs

8
You may choose 802.11a over 802.11b if

• Have a dense user base confined to one coverage
  area
• Want to run high-bandwidth applications
• Voice/video, Back-up
• Need to transfer large data files
• CAD files, graphics files
• Do not need a wide coverage range
• Are not price sensitive (in the short term)
• The 2.4 GHz band is very crowded in your area
• Backwards compatibility is not an issue

9
802.11a vs. 802.11g

• Factors to consider
• 802.11a and 802.11g are specd at comparable data
  rates however 802.11a will have a higher
  effective throughput
• 802.11g is about 1 year behind 802.11a in
  development so 802.11a is a more mature
  technology
• 802.11g is backwards compatible with existing
  802.11b networks

10
You may choose 802.11g over 802.11a if

• You already have a large investment in 802.11b
• Want backward compatibility with your existing
  802.11b WLAN
• Need high-bandwidth
• Have a large coverage area

11
Antenna Placement

• Location of transmitters has a large effect on
  transmission quality and data rate
• Physical obsticals may interfere
• Electromagnetic interference may be stronger in
  some areas
• Ability to transmit around corners and down
  hallways is variable
• It is important that antennae are placed at the
  best possible location to ensure maximum
  connectivity
• Consider these questions
• Where are the transmitters and receivers (clients
  APs)
• Where is the signal going (based on antenna type)
• What is going to interfere with the signal and
  how much

12
Evaluate RF Coverage Areas

• As a part of Requirements Analysis you will want
  to consider which Access Points you will use and
  how many you will need to cover the required area
• The type of antenna used by the AP affects the
  APs coverage area
• There are two types of antennae
• Directional or high-gain
• Omni-directional or low-gain

13
Omni-Directional Radiation

• An omni-directional antenna radiates signal
  equially in all directions
• Appropriate when a wide area needs to be covered

14
Directional Radiation

• A directional antenna radiates signal more
  strongly in one directions
• Appropriate when long distances need to be covered

15
RF Reception Issues

• In order to receive a RF signal the receiver must
  be able to distinguish the signal from background
  noise
• Receivers come in varying levels of sensitivity
• Better or more sensitive receivers are able to
  distinguish weaker and more degraded signals
• Some receivers have two or more antennae in order
  to increase their sensitivity
• RF signals can be degraded by attenuation and
  interference

16
Attenuation
Walls, doors, etc.
Reduced amplitude as a result of interaction
with radio-transparent objects occurs in
free-space as path loss

• Attenuation normally occurs as the signal moves
  away from the transmitter
• Air causes relatively little attenuation
• Metals cause relatively high attenuation
• Signal Power is closely related to attenuation
• More powerfull signals travel greater distances
• 802.11 NICs usually transmit 1 30 milliwatts
• AP can transmit up to 100 millliwatts

17
Common Causes of Interference

• Microwave ovens
• Locate APs at least 20ft away
• 2.4 GHz cordless phones
• BlueTooth enabled devices
• Much lower data rate
• Interference can occur within 50ft
• Multipath interference
• Signals reflect of of walls and interferes with
  itself

18
Multipath Interference

• When a signal is transmitted it radiates in many
  directions from the antenna
• The signal may bounce off of surfaces and be
  received from multiple locations
• Reflected signals will take a longer path and
  will arrive later than the Directsignal
• Reflected signals may then interfere with the
  Direct signal.
• In indoor environments this problems may be as
  big as problem as interference from other RF
  transmitters

Access Point
Reflected Signals
Direct Signal
PC Card
19
Point to Point ConnectionsLine of Site
The area within the red ellipse needs to be free
from any object to allow the EM wave to propagate
properly
20
Conclusion

• When in doubt do a site survey
• A site survey can significantly increase the
  efficiency and capability of your wireless LAN by
  identifying potential interference before the
  equipment is installed

21
Thank You