Page 96 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes z z Explain how to access PDAs

z z Discuss about mobile phone accessing
Introduction

A wireless network enables people to communicate and access applications and information
without wires. This provides freedom of movement and the ability to extend applications to
different parts of a building, city, or nearly anywhere in the world. Wireless networks allow
people to interact with e-mail or browse the Internet from a location that they prefer.
Many types of wireless communication systems exist, but a distinguishing attribute of a wireless
network is that communication takes place between computer devices. These devices include
personal digital assistants (PDAs), laptops, personal computers (PCs), servers, and printers.
Computer devices have processors, memory, and a means of interfacing with a particular type of
network. Traditional cell phones don’t fall within the definition of a computer device; however,
newer phones and even audio headsets are beginning to incorporate computing power and
network adapters. Eventually, most electronics will offer wireless network connections.
As with networks based on wire, or optical fiber, wireless networks convey information between
computer devices. The information can take the form of e-mail messages, web pages, database
records, streaming video or voice. In most cases, wireless networks transfer data, such as e-mail
messages and files, but advancements in the performance of wireless networks is enabling
support for video and voice communications as well.

6.1 Basics of Wireless PAN Systems

Wireless PAN is based on the standard IEEE 802.15. The two kinds of wireless technologies used
for WPAN are Bluetooth and Infrared Data Association.
A WPAN could serve to interconnect all the ordinary computing and communicating devices that
many people have on their desk or carry with them today; or it could serve a more specialized
purpose such as allowing the surgeon and other team members to communicate during an
operation.

6.1.1 Synchronization

The definition of time synchronization does not necessarily mean that all clocks are perfectly
matched across the network. This would be the strictest form of synchronization as well as the
most difficult to implement. Precise clock synchronization is not always essential, so protocols
from lenient to strict are available to meet one’s needs.
There are three basic types of synchronization methods for wireless networks. The first is relative
timing and is the simplest. It relies on the ordering of messages and events. The basic idea is to
be able to determine if event 1 occurred before event 2. Comparing the local clocks to determine
the order is all that is needed. Clock synchronization is not important.

The next method is relative timing in which the network clocks are independent of each other
and the nodes keep track of drift and offset. Usually a node keeps information about its drift and
offset in correspondence to neighboring nodes. The nodes have the ability to synchronize their
local time with another nodes local time at any instant. Most synchronization protocols use this
method.

The last method is global synchronization where there is a constant global timescale throughout
the network. This is obviously the most complex and the toughest to implement. Very few
synchronizing algorithms use this method particularly because this type of synchronization
usually is not necessary.

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