Telephonic communications – Supervisory or control line signaling – Signal receiver
Reexamination Certificate
1999-10-12
2004-04-27
Smith, Creighton (Department: 2645)
Telephonic communications
Supervisory or control line signaling
Signal receiver
C379S093270
Reexamination Certificate
active
06728369
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the decoding of a sequence of signals. In particular, the present invention relates to the communication of signaling information, such as dual tone multiple frequency (or “DTMF”) signals, across a telecommunications network, for example, the public switched telephone network, and the receipt and decoding (or interpretation) of such signaling information.
BACKGROUND OF THE INVENTION
In telecommunications systems, signaling performs three basic functions; namely (1) supervising functions, (2) alerting functions, and (3) addressing functions. Signaling for supervising functions is used to monitor the status of a transmission line or circuit to determine the state of the line or circuit (i.e., whether it is busy, idle, requesting service, etc.). Voltage levels, tone or data bits for example, are used for supervising function signals. Signaling for alerting functions is used, for example, to indicate the arrival of an incoming call with e.g., bells, buzzers, tones, strobes, lights, etc. Signaling for addressing functions is used to route signals over the network with, for example, dial pulses, tone pulses, and data packets.
Today, most signaling is carried out “in-band” (i.e., it goes along with voice conversations, and occupies the same circuits as those which carry voice conversations). Such in-band signaling is usually carried out with multi-frequency or single frequency signals. Unfortunately, many toll calls are not completed because the called telephone (or other equipment) does not pick up or is busy. Consequently, the circuit time used in signaling, which is substantial and expensive, becomes wasteful. Out-of-band signaling (such as signaling system 7, or “SS7”) uses circuit(s) separate from voice circuits for signaling functions.
Although one skilled in the art understands the station equipment and transmission facilities used by Regional Bell Operating Companies (or “RBOCs”), a brief overview of such station equipment and transmission facilities is provided below for the reader's convenience.
FIG. 1
illustrates the use of transmission facilities by various types of services. As shown in
FIG. 1
, a number of geographically remote central switching offices
120
are coupled via “trunks”
114
and interoffice transmission facilities
118
. Various entities, such as residences
102
, businesses
104
, and private branch exchanges (or “PBXs”)
106
are coupled with a central switching office
120
via “lines”
110
,
112
and “loop transmission facilities”
108
.
Thus, a loop transmission facility (or “subscriber loop”)
108
connects telecommunication equipment at a customer premises (e.g., a residence, business, etc.) with an associated central switching office
120
. The loop transmission facility
108
is typically on the order of a few miles and usually includes paired copper wire. Interoffice transmission facilities
118
, or trunks, connect different central switching offices
120
. Interoffice transmission facilities
118
range from less than one mile to thousands of miles.
FIG. 2
is a block diagram showing the connection of two pieces of terminal equipment at customer premises served by separate central offices. Terminal equipment X
202
(such as a telephone or modem for example) is coupled with central office A
206
, via loop
208
. Similarly, terminal equipment Y
204
is coupled with central office B
210
, via loop
212
. Central office A
206
is coupled with central office B
210
via trunk lines
214
. If all of the trunk lines
214
are busy, central offices A and B,
206
and
210
, respectively, may be coupled via trunks
216
and
220
and tandem office C
218
.
The flow diagram of
FIGS. 3
a
through
3
d
illustrates steps involved with initiating a call from terminal equipment X
202
to terminal equipment Y
204
, processing the call, and terminating the call, in a system using “in-band” signaling. For the purposes of the following discussion, it will be assumed that the terminal equipment X
202
and Y
204
are telephones. However, the terminal equipment X
202
and Y
204
may be other types of equipment, such as a modem for example.
FIG. 3
a
shows actions taken at the telephone X
202
and the central office A
206
in initiating the call. First, as shown step
302
, when the handset of telephone
202
is lifted, it sends an off-hook signal to the central office A
206
via loop
208
. At central office A
206
, a change from on-hook to off-hook status is detected. More specifically, when the telephone X
202
is taken off-hook, a circuit is established and the central office A
206
detects a DC current flowing through the established circuit. As shown in step
304
, this change in status is interpreted as a request for service. Next, as shown in step
306
, assuming that an originating register is available to accept and store the digits to be dialed by telephone X
202
, the central office A
206
connects a dial tone signal to the telephone X
202
via loop
208
. Line side equipment, such as an analog line unit (or “ALU”) or an integrated digital carrier unit (or “IDCU”) for example, provides the dial tone signal. As shown in step
308
a number is then dialed at telephone X
202
. In response, as shown in steps
310
and
312
, once the first digit of the number is recognized, the dial tone is disconnected and the numbers are stored in the originating register.
FIG. 3
b
shows actions taken at the central office A
206
in processing the call. First, as shown in step
314
, control equipment at central office A
206
translates the dialed number. The control equipment performs this translation with a dual tone multiple frequency decoder (or DTMF) receiver which is discussed in more detail below. As shown in step
316
, by examining the leading digits (e.g., the first three digits) of the dialed number, the control equipment determines whether the call is to another central office (i.e., an “inter-office” call) or to a subscriber serviced by the same central office (i.e., an intra-office call). In this example, it is assumed that the call is to telephone Y
204
which is served by a separate central office; namely, central office B
210
. Next, as shown in step
318
, routing information stored in the system indicates which paths (or “trunk groups”) are appropriate and translates the desired paths to representations of physical locations of terminations of the trunks. As shown in step
320
, if the call is billable, an automatic message accounting (or “AMA”) register is requested to enable the telephone service provider to bill the appropriate parties. Next, as shown in step
322
, the call information is transferred to an outpulsing register and the originating register is released. Then, as shown in step
324
, the control equipment at central office A
206
begins scanning outgoing trunks to find an idle trunk to central office B
210
.
If an idle trunk is found, as indicated in step
326
, the call be transmitted directly from central office A
206
to central office B
210
via a free trunk
214
. If, on the other hand, all trunks
214
from central office A
206
to central office B
210
are busy, then outgoing trunks
216
to tandem switching office C
218
are scanned such that the call may be routed from central office A
206
to central office B
210
via tandem switching office C
218
.
FIG. 3
c
illustrates the actions taken to advance the call to the terminating central office; namely central office B
210
. First, as shown in step
328
, the idle trunk found in step
326
is seized. In response, as shown in steps
330
and
336
, at central office B
210
, an incoming register of a switch is seized and control equipment sends a ready signal back to central office A to indicate that the seized incoming register is ready to receive address information. In the meantime, as shown in step
332
, at central office A
206
, the line of telephone X
202
is connected, via the loop
208
and a switching network within central office A
206
, to the seized trunk. In addi
Siemens Information & Communication Networks, Inc.
Smith Creighton
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