Information Technology Reference
In-Depth Information
All the signaling standards and communication methods discussed in the previous section
typically focus around the connection to one massive voice network, known as the PSTN.
If you have ever made a call from a home telephone, you have experienced the results of
the traditional telephony network. This network is not unlike many of the data networks
of today. Its primary purpose is to establish worldwide pathways to allow people to easily
connect, converse, and disconnect.
Pieces of the PSTN
When the phone system was originally created, individual phones were wired together to
allow people to communicate. If you wanted to connect with more than one person, you
needed multiple phones. As you can imagine, this solution was short lived as a more scala-
ble system was found. The modern PSTN is now a worldwide network (much like the In-
ternet), built from the following pieces, as shown in Figure 1-9:
Analog telephone:
Able to connect directly to the PSTN and is the most common
device on the PSTN. Converts audio into electrical signals.
■
Key
To p i c
Local loop:
The link between the customer premises (such as a home or business)
and the telecommunications service provider.
■
CO switch:
Provides services to the devices on the local loop. These services include
signaling, digit collection, call routing, setup, and teardown.
■
Trunk:
Provides a connection between switches. These switches could be CO or
private.
■
CO Switch
Trunk
Trunk
Local Loop
Trunk
CO Switch
CO Switch
Analog Telephone
Trunk
Private Switch
Digital Telephone
Figure 1-9
PSTN Components
