Telephonic communications – Plural exchange network or interconnection – Interexchange signalling
Reexamination Certificate
1998-12-23
2001-08-14
Matar, Ahmad (Department: 2742)
Telephonic communications
Plural exchange network or interconnection
Interexchange signalling
C370S225000, C370S228000, C379S230000, C379S235000, C379S236000, C379S237000, C379S240000, C379S221040
Reexamination Certificate
active
06275578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the field of signaling systems for a telecommunications network and, more particularly, to a method and apparatus for reverting to in-band signaling in the event of the detection of a failure of presently conventional out-of-band signaling systems.
2. Description of the Relevant Art
In the United States, it became prevalent in the telecommunications arts to provide in-band signaling between switching centers through the middle of the twentieth century. Referring to
FIG. 1
, there is shown a simplified block diagram of the telecommunications network in the United States circa 1970.
FIG. 1
is used by way of example to describe in-band signaling; it is not intended to comprise a thorough study of telecommunications networks, and the reader is referred to well-known telecommunications textbooks for further insight. While Local Exchange Carrier (LEC) was a term not known in the art in the middle of this century, LEC
180
signifies one of the several Bell telephone operating companies or independent telephone companies serving a local geographic area. Of course, in the middle of this century, there was only one toll carrier, American Telephone and Telegraph Company (AT&T), signified as toll carrier
190
. At a time after the middle of this century, competition in toll services was permitted and other toll carriers entered the market. Other toll carriers would be shown as separate network clouds
190
. Of course, there exists several LEC's
180
, and each LEC connects to the several toll carriers, the LEC's providing service in their respective geographic areas.
A local subscriber
100
in a local exchange area is connected, according to the system of
FIG. 1
, by typically a two wire facility
110
to an end office
130
. A second end office
135
is shown within the local area
180
connected to end office
130
by trunk/trunk group
140
for completion of local calls. The two wire facility
110
connecting a subscriber to an end office
130
is typically a copper wire pair and the end office
130
,
135
, typically, a No. 5 cross-bar switch manufactured by, then, Western Electric Company, and still supported today by Lucent Technologies, Inc. Generally, these crossbar type common-controlled switches of end offices
130
,
135
and even older vintage switches such as step-by-step switches have been replaced for the most part by electronic switching systems. Typically, two or four wire trunk facilities
140
connect end office
130
of LEC
180
with other end offices, such as end office
135
, in the local exchange carrier's network
180
. These may be N carrier, T carrier, copper wire or other facilities then prevalent. A two wire or four wire facility
150
(a four wire facility is shown) is typically used to connect an end office
130
to an originating toll switch (OTS)
170
. An originating toll switch
170
, in turn, is typically connected to other toll switches of a toll network
190
by four wire facilities. By four wire facility is intended the use of tip and ring leads for each direction of transmission or simulated four wire facilities such as carrier facilities. Trunks
150
may be one way (such as originating or terminating trunks or trunk groups) or two-way (both originating and terminating at end office
130
; two-way trunks may be seized and busied out by either end office
130
or originating toll switch (OTS)
170
). Long distance trunks
155
are shown leaving originating toll switch
170
for connection to other toll switches (not shown) in toll network cloud
190
. In the 1970's, analog L carrier facilities were typically utilized for long distance trunks
155
, either via land line or microwave. Since then, these have been substantially replaced by digital trunk facilities (T
1
, T
3
, . . . hierarchy) in time division multiplex arrangement.
A customer
100
in the United States typically dials a toll/directory number (DN) given by a three digit area code and a seven digit address of a called party within the dialed area code to reach a called party outside the calling party's area code. (In some states such as Maryland, one must dial the area code and telephone number to make a local call.) The signaling data is provided to end office
130
via dial pulse or tone signals originating from a rotary dial switch or a tone signaling pad of a telecommunications terminal respectively of calling party
100
. These are carried via two wire facility
110
to end office
130
. In a toll call or a local call involving more than one office, the end office
130
,
135
may repeat the so-called dial pulse (DP) address signals or generate different tone address signals as appropriate. In the latter case, for example, there is a translation of “touch-tone” to dual tone multifrequency (MF) signals at end office
130
,
135
for transmission on trunk
150
,
140
.
Thus, for each trunk between switching centers, such as end office
130
and originating toll switch
170
, there is a respective supervisory signaling and a DP or MF address signaling capability directly associated therewith. This direct association of a signaling path for supervisory and address message signaling with a voice/data trunk
150
is what is intended herein by in-band signaling. In-band signaling was prevalent and out-of-band signaling unknown in the telecommunication arts until the 1970's.
Referring to
FIG. 2
, and by way of example, there is shown a typical in-band signaling arrangement for T
1
carrier. T carrier, developed in the late 1960's, has replaced analog carrier systems such as N and L carrier over time. T
1
carrier utilizes a digital pulse code modulation scheme and permits the transmission of 24 voice/data channels over a 1.544 megabit per second data stream. A T
1
carrier system comprises 24 individual voice/data channels. In a simple example, each channel may comprise one trunk connecting two end points.
Associated with each channel, according to prior art T
1
systems, there would be, for example, the digital equivalent of an E and M (Ear and Mouth) lead or other supervisory signaling and an MF address signaling capability. Supervisory signaling comes in several varieties such as ground start and wink start depending, for example, on how and which office initiates the signaling. Each channel provides a digital bitstream for a voice or data channel and an in-band signaling data and a maintenance data path as will be further explained below.
Signaling for supervisory and address messages requires little bandwidth while voice/data consumes much greater bandwidth of a channel. Consequently, to utilize an entire voice/data channel for supervisory and address signaling came to be recognized as a waste of the voice/data bandwidth of the channel. There was recognized a need in the telecommunications art to preserve the bandwidth requirements. Also, the end-to-end links from a calling party
100
to a called party might involve tying up trunks connecting as many as nine switching centers of LEC
180
, toll carrier
190
and a terminating LEC (not shown) according to the prior art. For example, a voice/data bandwidth signaling path would be required from End Office
130
of
FIG. 1
all the way through a hierarchy of switching centers in a local/toll network configuration to reach a terminating end office (not shown). The waste of bandwidth per channel, thus, was further compounded by the unnecessary reservation of trunks and service circuits all across the country when it might be learned from the terminating end office that the called party would be “busy” or a switching center in the path would be otherwise unable to provide a link through the office, a service circuit or a trunk to the next office. Finally, the problem with in band signaling was further complicated by a problem with black box long distance line fraud. The black box could be used by a service pirate to steal telephone service by emulating the tones of MF signaling. Once a long distance line was seized via a toll-f
De Trana Nicholas D.
DeCaluwe Craig L.
Eslambolchi Hossein
Fischer Patrick H.
Kohler Joseph C.
AT&T Corp.
Matar Ahmad
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