Page 135 - DCAP406_DCAP_207_Computer Networks

Computer Networks/Networks

Notes the low cost of 802.11b devices have made them popular for smaller establishments like home,
small offices, etc. They support a maximum data rate of 11 Mbps and are considered superior
than dial-up. Compared to the performance of 802.11b and other standards of the same family,
their performances are considered inferior.
802.11g: It came around 2003 to extend and improve the 802.11b standard. It is considered as the
latest in the series of IEEE 802.11 standards for wireless LAN (WLAN) communications. The
802.11g compatible devices provide a maximum bandwidth of 54 Mbps and uses the same
communication frequency range of 2.4 Ghz as 802.11b so that the 802.11b compatible devices
may be used along with 802.11g devices.

802.11n: It is an upcoming industry standard being developed for high-speed WiFi networking
to replace the 802.11a, 802.11b and 802.11g WiFi standards with backward compatibility for local
area networking. 802.11n intends to provide Multiple Input Multiple Output (MIMO) so that
multiple simultaneous radio signals can be transmitted and received using multiple wireless
antennas in tandem. This will lead to increase the range and throughput of a wireless network.
The 802.11n standard is expected to support bandwidth greater than 100 Mbps.

Implementing WLAN

The WLANs, as of today, operate at much higher speeds ranging from 1 Mbps to 20 Mbps due to
sharing of the spectrum by a much smaller number of hosts in a much smaller area up to a
maximum radius of about a hundred meters. These factors lead to higher throughputs because
smaller area and hosts cause less interference, distortion from the environment, reduced amount
of error to the radio signal of WLAN. The higher throughput of WLAN makes it compatible
with the existing network operating systems and applications like file and printer sharing,
database access, etc.
The different topologies for implementing WLANs are spread spectrum including direct sequence
and frequency hopping, low-power narrowband approach, HiperLAN and infrared LANs. The
maximum reliable propagation range of the radio signals determines the physical size of a
wireless network. The wireless networks are mostly used for temporary situations such as
meetings, conferences, etc and therefore are of ad hoc nature and therefore referred to as ad-hoc
networks, which connect, to an existing wired LAN. It is the access point at the edge of wireless
network to bridge WLAN traffic onto wired LAN. Sometimes, this functionality is provided by
software in a server computer that collocates both a WLAN card and a wired LAN card. However,
in general, dedicated hardware as an access point device is used for this function. Figure 8.13
shows a bridging between WLAN and wired Ethernet.

Figure 8.13: Connection between a WLAN and Ethernet

Ethernet

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