Post on 09-Jun-2015
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Convergence Technology
Module 11 – Learning Outcomes 5 and 6Wi-Fi - Explain the various wireless access technologies related to PAN, HAN, LAN, CAN, MAN, and WAN networks, including associated cellular and wireless network architectures. Describe signaling and its importance to wireless telecommunications.
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What is a Wireless LAN? WLANs use infrared light (IR) or radio
frequencies (RFs). RF is more popular for its longer range,
higher bandwidth, and wider coverage. WLANs use the 2.4-gigahertz (GHz) and 5-
GHz frequency bands. These bands are reserved in most of the world for unlicensed devices.
However, wireless systems are not completely wireless.
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Wireless Evolution
The wireless vendors in 1991 formed Wireless Ethernet Compatibility Alliance (WECA) which proposed and built a standard based on contributed technology.
WECA was later changed to Wi-Fi.
In June 1997 IEEE release the first standard for wireless
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Unlicensed Frequency Bands
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Why Wireless Standards Based:
IEEE 802.11 committee and the Wi-Fi Alliance have diligently worked to make wireless equipment standardized and interoperable
Increased Data Rates:Wireless technology will now support the data rates and interoperability necessary for LAN operation.
Cost Effective:The cost of wireless devices has decreased greatly, making it an affordable option.
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Wireless
Cost to install wireless between two buildings will have a one time incur cost of several thousand dollars.
To install a T1 with less bandwidth, that wireless will cost hundreds of dollars per month.
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Benefits
User Mobility Scalability Flexibility Cost Savings Installation advantages Reliability Site to site connectivity (up to 25 miles)
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802.11 WLAN Media Infrared light 2.4-GHz radio transmission
Frequency hopping spread spectrum (FHSS) Direct sequence spread spectrum (DSSS) Orthogonal frequency-division multiplexing (OFDM) 802.11g
5-GHz frequencyOrthogonal frequency-division multiplexing (OFDM) 802.11a
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Wireless
Spread Spectrum is a modulation technique developed in 1940s.
It spreads a transmission signal over a broad range of radio frequencies.
It is used for data communications because
• less susceptible to radio noise
• crate little interferences
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CellularCellular System Topology
MSC
MSC - Mobile Switching Center- Base Transceiver Station (BTS)
Types:• TDMA• CDMA• GSM
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Components and Technology
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Cisco Aironet 802.11b Client Adapters 2.4 GHz
802.11b11 Mbps
IncludePC Card PCI CardLMC CardMini PCI
No antenna
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Example of wireless adapter5 GHz/802.11a
54 MbpsRate Shifting
6, 9, 12, 18, 24, 36, 48, or 54Fixed data rates
User configurable option5 dBi Patch AntennaCardBus interfaceTransmit power settings:
20 mW, 10 mW, and 5 mW
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WLAN Topologies
A typical use of wireless technology as an add-on to a traditional LAN.
Building to building wireless connectivity can be more cost effective and can avoid obstacles faced by wired connections.
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WAN SolutionsFour main requirements for WLAN solution:
1. High availability
• Through system redundancy
• Redundant AP automatic rate negotiation
2. Scalability
• using multiple APs per coverage area
• using multiple frequencies
• AP using load balancing
3. Manageability (diagnostic tools)
4. Open Architecture
• 802.11a
• 802.11b
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Challenges and Issues
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Interference from other Sites
Interference from other sites since the 802.11 standards use unlicensed spectrum.
Interference cannot always be detected until the link is actually implemented.
Changing channels is the best way to avoid interference.
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Power ManagementPower consumption is always an issue with laptops.
There are 3 modes of power for Cisco PC cards:
1.Constant Awake Mode (CAM)
Mode is best when power is not an issue such as when AC power is available to the device. Default mode
2. Power save mode (PSP)
Mode is used when power conservation is the utmost importance. The wireless NIC card will go to ‘sleep’ after a period of inactivity & periodically awake to retrieve buffered data from the AP.
3. Fast power save mode (FastPSP)
Combination of CAM & PSP. For clients who switch between AC & DC power.
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Interference from other Devices
Other devices use these frequencies. Physical objects also cause interference. In unlicensed bands, the potential for interference from
another unlicensed user is becoming greater. The unlicensed bands are allocated on a shared basis.
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Interoperability Interoperability issues might influence an
admin to use a single vendor for all wireless needs.
Closed networks, such as corporate sites, might choose a single-vendor solution in order to benefit from increased management utilities and vendor accountability.
In an open network such as a college campus, the admin cannot usually dictate hardware selection, and must support a variety of hardware solutions.
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Network Security As wireless networks grow, the threat of intruders
from the inside and outside is great. Attackers called war drivers are continually driving around searching for insecure WLANs to exploit.
IEEE Wired Equivalent Privacy (WEP) with Temporal Key Integrity Protocol (TKIP) provides robust authentication options with 802.1X to make 802.11-based wireless LANs secure.
IEEE has adopted the use of the Advanced Encryption Standard (AES) to the data-privacy section of the proposed 802.11i standard.
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Installation & Site Design Issues
Obstructions to visual link:Topographic featuresCurvature of the EarthBuildingsTrees
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Installation and Site Design Issues—WLAN
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HotSpots
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Wi-Fi Manufactures
• Intel – Wi-Fi chips
• Microsoft
• Cisco; 60% of wired computer networks
• 1999 bought Aironet Wireless Communications for $800 million.
• 2003, paid $480 million for Linksys.
• is now the leading maker of Wi-Fi gear
• Netgear
• Milpitas, Calif.; 58% share of chip market
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Health Issues In general, living things should not be subjected to
RF energy unnecessarily. Antenna guidelines
Do not touch an active antenna.Do not stand in front of, or close to, an antenna that is radiating a signal.Stand to the back or side of any dish-type antenna. Always assume that any antenna is currently energized.Small-sized antennas operate at higher frequencies, which are more potentially hazardous.Maintain at least 5 cm (2 in.) between yourself and a laptop antenna.
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New Standards 802.11g
Operates in the 2.4 GHz rangeHigher speeds than 802.11b (54 Mbps)Uses OFDM modulationBackwardly compatible with 802.11b
Vendor interoperability and standards alignment.
Increased security and reliability.
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Questions: Feel free to contact the creator of this material John Perrine, Professor, Collin County
Community College, jperrine@ccccd.edu
This material is based upon work supported by the National Science Foundation under Grant No. 0402356. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation