Line signaling is a class of
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
signaling protocols
Protocol may refer to:
Sociology and politics
* Protocol (politics), a formal agreement between nation states
* Protocol (diplomacy), the etiquette of diplomacy and affairs of state
* Etiquette, a code of personal behavior
Science and technology ...
. Line signaling is responsible for
off-hook In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing th ...
,
ringing signal, answer,
ground start {{refimprove, date=January 2008
In telephony, ground start is a method of signaling from a terminal of a subscriber local loop to a telephone exchange, where one side of a cable pair is temporarily grounded to request dial tone. Most middle 20th-c ...
,
on-hook In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing th ...
unidirectional supervision messaging in each direction from
calling party
The calling party (in some contexts called the "A-Number") is a person who (or device that) initiates a telephone call. The person who, or device that, receives a telephone call is the called party (or callee or B-party).
In some countries, it ...
to
called party
The called party (in some contexts called the "B-Number") is a person who (or device that) answers a telephone call. The person who (or device that) initiates a telephone call is the calling party.
In some situations, the called party may number m ...
and vice versa. After an off-hook, line signaling initiates
register signaling
In telecommunications, register signaling provides addressing information, such as the calling and/or called telephone number. R2 register signaling is an example.
This is contrasted with line signaling
Line signaling is a class of telecomm ...
to accomplish the exchange of
telephone numbers of called party and in more modern line-signaling protocols, the calling party as well. While register signaling occurs, line signaling remains quiescent unless the calling party goes on-hook or an abnormal cessation of the call occurs, such as due to equipment malfunction or shutdown or due to
network outage upstream in that call-attempt's series of spanned trunks.
Line signaling can be conveyed in a single
DS0 channel of a
trunk. In modern
PCM telecommunications, line signaling is represented by the ABCD bits in DS0 #16 of an
E1 or a selected DS0 within a
T1.
Line signaling can also be conveyed within the channels being supervised, as in the original T1 scheme which used one out of every eight bits for supervision, or with
robbed bits of a
superframe format, or as
in-band signaling, e.g. as in L1 signaling where 2280 Hz tone pulses are used.
References
{{DEFAULTSORT:Line Signaling
Telephony signals