28-07-2012, 12:09 PM
Wireless LAN
Wireless LAN.ppt (Size: 163 KB / Downloads: 27)
Wireless Technology
Market for wireless communications has enjoyed tremendous growth.
Today wireless technology is capable of reaching virtually every location on the face of the earth.
Uses of wireless technology
Wide use in IT industry.
Health and Medicine.
Factories.
Shopping Malls.
Chemical industry.
Wireless LAN
Wireless LAN is the same standard LAN without a hard-wired connection.
Increased mobility.
Increased flexibility.
When and why to use WLAN?
WLAN is suitable for networks where the terminals are not stationary at one place.
Can provide connectivity in places where wired LAN is impractical.
Temporary networks required in conference or demonstrations.
Mobile IP
Initially Mobile IP was suggested as a means to attain wireless networking.
IP address of the mobile machine does not change.
Forwarding routine is implemented, as in the case of mobile phones.
Drawbacks in Mobile IP
Depending on how far the mobile agent moves, there may be need for some store and forwarding of packets.
Mobile IP works only for IPv4 and does not take advantage of the features of the newer IPv6.
IEEE 802.11
In 1997 the IEEE adopted IEEE Std. 802.11, the first wireless LAN (WLAN) standard.
In IEEE's proposed standard for wireless LANs, there are two different ways to configure a network: ad-hoc and infrastructure.
Ad-Hoc network
In the ad-hoc network, computers are brought together to form a network “on the fly”.
Infrastructure Network
This architecture uses fixed network access points with which mobile nodes can communicate.
Layers
The 802.11 standard defines the media access control (MAC) and 3 physical (PHY) layers for a LAN with wireless connectivity.
The 802.11 MAC must appear to the upper layers of the network as a ‘standard’ 802 LAN. This forces functionality into the 802.11 MAC layer that is typically handled by upper layers.
MAC
Allows reliable data delivery for the upper layers over the wireless PHY media.
Provides a controlled access method to the shared wireless media called (CSMA/CA).
Protects the data being delivered by providing security and privacy services.
PHY
Physical layer (PHY) is the interface between the MAC and the wireless media where frames are transmitted and received.
Provides an interface to exchange frames with the upper MAC layer for transmission and reception of data.
It uses signal carrier and spread spectrum modulation to transmit data frames over the media.
Provides a carrier sense indication back to the MAC to verify activity on the media.
PHY operation
Can use either direct sequence spread spectrum, frequency-hopping spread spectrum, or infrared (IR) pulse position modulation.
Data rates of either 1 Mbps or 2 Mbps, and calls for operation in the 2.4 - 2.4835 GHz frequency band
300 - 428,000 GHz for IR transmission.
Limitations
Range limitations and unreliable media, dynamic topologies where stations move about, interference from outside sources
Larger geographic coverage is handled by building larger LANs from the smaller fundamental building blocks or by integrating the smaller WLANs with an existing wired network
Important
Mobility of wireless stations may be the most important feature of a wireless LAN.
A WLAN would not serve much purpose if stations were not able to move about freely from location to location either within a specific WLAN or between different WLAN ‘segments’.
Conclusion
Although 802.11 provides a reliable means of wireless data transfer, some improvements to it have been proposed.
Continuous research is being done to enhance the 802.11 standard.