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Switch Signaling
In order for you to make a phone call, you would need to signal the CO switch and the CO to signal back to
your telephone and vice versa. This communication back and forth is known as Signaling.There are several
types of signaling the telephone system can handle but the most common one is known as Supervisory
Signals which occur before and after a conversation has been established. These signals are known as –
On-Hook -
Known as the Normal or Inactive State and exists when your telephone is “on-
hook” and not connected to a talk path in the CO.
Off-Hook - Known as the Calling State, this signal indicates your intent to make a call but, as
yet, there is no talk path connected through the CO.
Talking - Known as the Talking State, where your phone is off-hook and a talk path exists
through the CO.
Release/Disconnect - Indicated by an on-hook signal while connected to a talk path through
the CO.
Information signal –
•
Dial Tone - Informs the subscriber that they may start to dial.
•
Ringing - Indicates that the called line has been reached and ringing has started.
•
Line Busy - Called line was reached but was already in use.
•
All Trunks Busy - Local switch paths are busy.
Control
signal – inform the CO of the call destination and are indicated by interrupting the
DC current flow on the line (pulse dialing) or by the generation of tone signals (DTMF or tone
dialing.).
Data Burst: To send information such as caller ID from the CO to your telephone. Your
telephone interprets this data and displays the appropriate information on its display. You
can hear this data burst by using your Buttset (Butt-in) and this signal is typically sent after
the first ring.
1.3.1 Connections at CO
MDF, RACK or Frame
Main Distribution Frame or Rack - The rack where a jumper cross connects from the LE/OE
to the Feeder cable going out the SAC/JWI.
HDF
Horizontal Distribution Frame is connected to the Switch/LE/OE. You may also find ADSL
connections blocks on this side of the Rack.
Figure 8: HDF Horizontal Side