Page 69 - DCAP311_DCAP607_WIRELESS_NETWORKS

Unit 4: Wireless Networks Types and PAN Technologies

Types of Wireless LAN Notes

The Project 802.11 committee distinguished between two types of wireless LAN : “ad-hoc” and
“infrastructred” networks.
Figure 4.1: Infrastructred Wireless LAN; (b) Ad-hoc Wireless LAN

Source: http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol2/mjf/article2.html

z z Ad-hoc Networks: Figure 2b shows an ad-hoc network. This network can be set up by a
number mobile users meeting in a small room. It does not need any support from a wired/
wireless backbone. There are two ways to implement this network.

z z Broadcasting/Flooding: Suppose that a mobile user A wants to send data to another user
B in the same area. When the packets containing the data are ready, user A broadcasts the
packets. On receiving the packets, the receiver checks the identification on the packet. If
that receiver was not the correct destination, then it rebroadcasts the packets. This process
is repeated until user B gets the data.

z z Temporary Infrastructure: In this method, the mobile users set up a temporary
infrastructure. But this method is complicated and it introduces overheads. It is useful
only when there is a small number of mobile users.

z z Infrastructure Networks: Figure 2a shows an infrastructure-based network. This type of
network allows users to move in a building while they are connected to computer resources.
The IEEE Project 802.11 specified the components in a wireless LAN architecture. In an
infrastructure network, a cell is also known as a Basic Service Area (BSA). It contains a
number of wireless stations. The size of a BSA depends on the power of the transmitter and
receiver units, it also depends on the environment. A number of BSAs are connected to each
other and to a distribution system by Access Points (APs). A group of stations belonging to
an AP is called a Basic Service Set (BSS). Figure 4.2 shows the basic architecture for wireless
LANs.

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