Friday, February 4, 2011

Wireless Network

Wireless Networks
        A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier. The last link with the users is wireless, to give a network connection to all users in a building or campus. The backbone network usually uses cables

Common Topologies:
         The wireless LAN connects to a wired LAN. There is a need of an access point that bridges wireless LAN traffic into the wired LAN.The access point (AP) can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes. 
         The physical size of the network is determined by the maximum reliable propagation range of the radio signals. Referred to as ad hoc networks are self-organizing networks without any centralized control Suited for temporary situations such as meetings and conferences.

How do wireless LANs work?
          Wireless LANs operate in almost the same way a wired LANs, using the same networking protocols and supporting the most of the same applications.

How are WLANs Different?

        They use specialized physical and data link protocols.They integrate into existing networks through access points which provide a bridging function. They let you stay connected as you roam from one coverage area to another.They have unique security considerations .They have specific interoperability requirements. They require different hardware .They offer performance that differs from wired LANs.

Physical and Data Link Layers:

Physical Layer:
        The wireless NIC takes frames of data from the link layer, scrambles the data in a predetermined way, then uses the modified data stream to modulate a radio carrier signal.

Data Link Layer:
        Uses Carriers-Sense-Multiple-Access with Collision Avoidance (CSMA/CA).
Integration With Existing Networks:
         Wireless Access Points (APs) - a small device that bridges wireless traffic to your network. Most access points bridge wireless LANs into Ethernet networks, but Token-Ring options are available as well.
         Users maintain a continuous connection as they roam from one physical area to another Mobile nodes automatically register with the new access point.
Methods: Mobile IP
        IEEE 802.11 standard does no  address roaming, you may need to purchase equipment from one    vendor if your users need to roam  from one access point to another.

  • PC Card, either with integral antenna or with external antenna.
  • ISA Card with external antenna connected by cable.
  • Handheld terminals.

A family of wireless LAN (WLAN) specifications developed by a working group at the Institute of Electrical and Electronic Engineers (IEEE)
Versions: 802.11a, 802.11b, 802.11g, 802.11e, 802.11f, 802.11i
802.11a offers speeds with a theoretically maximum rate of 54Mbps in the 5 GHz band
802.11b offers speeds with a theoretically maximum rate of 11Mbps at in the 2.4 GHz spectrum band.
802.11g is a new standard for data rates of up to a theoretical maximum of 54 Mbps at 2.4 GHz.
Access Point Placement and Power:
Typically – mounted at ceiling height.Between 15 and 25 feet (4.5m to 8m)The greater the height, the greater the difficulty to get power to the unit. Solution: consider devices that can be powered using CAT5 Ethernet cable (CISCO Aironet 1200 Series).Access points have internal or external antennas.

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