Page 189 - CISSO_Prep_ Guide

from the other bytes. This becomes especially challenging when
the network is multiplexing many channels together into one
data stream. For example, with a T1 line, 24 channels or
individual communications can be transmitted through the
network at once, at a speed of 1.544 megabits per second. The
receiving end must be able to demultiplex the traffic back into
individual channels, while a clocking signal is used to maintain
the correct timing of the two endpoints so that they can combine
and separate the channels correctly. This is an example of
synchronous communications.

A fax machine is an example of asynchronous communications.
A fax machine sets up a connection on demand - when required,
and when the two devices initially begin to communicate, they
have to determine the best speed to use. Some machines will
have the ability to operate at higher speeds than others, and
sometimes the network will only permit a certain speed. Once
the speed has been established, the data itself will be sent as
individual pieces, often as individual characters, and each
character will be wrapped with a start and stop bits to signal the
start and end of each character (each piece of data).

Carrier Sense Multiple Access with Collision Detection
(CSMA-CD)
When several devices are sharing the same communications
media (or carrier), it is necessary to manage the traffic so that
the data transmission from one device does not disrupt the data
being sent by other devices. There are several ways to manage
network communications. The first of these is through carrier
sense - or, in other words, the ability to sense or listen to traffic
on the carrier medium. When a device wants to transmit data, it