Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-03-06
2001-03-27
Felber, Joseph L. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S542000
Reexamination Certificate
active
06208670
ABSTRACT:
TECHNICAL FIELD
The present invention is related generally to a digital carrier telephony system and, more particularly described, is directed to a digital carrier system for supporting the delivery of telephony and data services to a limited set of subscribers in remote locations, such as rural regions.
BACKGROUND OF THE INVENTION
Local telephone companies have used many different systems to provide Plain Old Telephone System (POTS) services to subscribers in rural areas. For a selected POTS application, a particular system may be implemented because it can overcome the limitations or problems that are commonly associated with rural telephone service delivery. Typical problems associated with the delivery of telephony and data services to a small number of subscribers in a rural location include a shortage of available copper wire pairs for carrying signals, an extended distance between the Central Office (CO) and the subscriber, a lack of available electrical power to operate components of the telephony system, and certain communication technology limitations. Representative systems for addressing at least some of these problems include an analog “direct connection” system, an analog carrier system, a universal digital loop carrier (UDLC) system, an integrated digital loop carrier (IDLC) system, and an add-drop multiplexing system. These prior telephony systems will be described in more detail below in connection with
FIGS. 1
,
2
,
3
and
4
.
Direct Connection System
FIG. 1
illustrates an analog direct connection system
1
for connecting a subscriber's telephone
5
to a CO switch
3
via a local loop
2
comprising copper wire pairs. This direct connection system can be implemented for a rural application unless the existing set of copper wire pairs for carrying telephony signals is smaller than the numbers of subscribers to the telephony service. In the event that the local loop
2
extends for a distance greater than approximately 40 kft., the CO switch
3
is typically equipped with battery voltages in excess of the nominal −48Vdc, and amplifiers
4
can be used within the local loop
2
to increase the level of the telephony signal. The direct connection system is not appropriate for applications involving a distance between the CO switch and the subscriber's telephone that is outside the limits of switch capability.
In contrast to the direct connection system described above, multiplex systems can be used to transport two or more telephone conversations or data links between a subscriber's premises and a telephone terminal or CO switch. As described below in connection with
FIGS. 2
,
3
and
4
, prior multiplexing systems have used a variety of transmission techniques and multiplexing and encoding schemes, and delivered a variety of telephony services.
Amplitude Modulated Telephone Carrier System
U.S. Pat. No. 4,087,639 describes a representative amplitude modulated telephone carrier system that supports the delivery of POTS for both single and multiple party lines over a single pair of copper wires. The system, which is powered from the CO, modulates an analog speech signal onto a single carrier in the very low frequency (VLF) or low frequency (LF) bands to complete a telephony transmission. Subscriber terminals can be placed at any location along the telephone line by using a bridged tap connection. Carrier signals can be regenerated at prescribed intervals along the telephone line by using bidirectional amplifiers.
Referring now to
FIG. 2
, which illustrates a typical amplitude modulated telephone carrier system
6
, a multiband analog double sideband modulated carrier is carried on a single pair line
7
. Subscriber drops
8
can be placed at any location along the line
7
between a Central Office Terminal (COT)
10
and a termination network
11
. The subscriber's telephone
5
is connected to one of the subscriber drops
8
via a wire pair
9
. Each subscriber drop
8
is powered from the line
7
and is connected to that line by a bridged tap splice in a conventional “T” connection. A bidirectional repeater
12
can be inserted along the line
7
to amplify the carrier signals on an as needed basis. The COT
10
is located at the CO
3
and is typically powered by a local −48V dc source via an interface cable
13
. The COT
10
can house plug-in cards
18
for converting the analog carrier on the line
7
to a conventional 2-wire POTS signal for distribution to the CO
3
via an interface
19
.
For a typical amplitude modulated telephone carrier system, the maximum distance between the CO switch and a subscriber's telephone can exceed 100 kft. In contrast, the distance between subscriber drops and the subscriber premise associated bridge-tap connections is commonly two or three kft. However, the distance ‘d’ between any two bridge tap connections, as shown in
FIG. 2
, can range from 0 feet to approximately 50 kft.
The amplitude modulated telephone carrier system can support limited data services, but cannot deliver these services by means other than low speed (nominally 4800 bps) analog modems. Furthermore, this analog-type carrier system cannot support the delivery of CLASS features, such as caller identification, call forwarding and call waiting, to subscribers. This effectively limits the growth of possible services that can be offered by a telephone company that relies on this analog transmission system. The limited data services and the absence of CLASS functions are a direct result of the analog component implementation of the amplitude modulated telephone carrier system. In addition, the telephone company must maintain the signal characteristics of an amplitude modulated telephone carrier system, including impedance levels, current levels, and voltage levels, because of the analog implementation of this system. For example, this system requires a terminating impedance at the end of the subscriber loop.
Universal Digital Loop Carrier System
A typical universal digital loop carrier system, also described as a UDLC system, uses a digital multiplexer, placed between the subscriber's telephone and the CO, to combine subscriber channels into a single high speed digital line signal for transmission to a de-multiplexer or a COT. Because a multiplexed digital line cannot carry signals as far as a corresponding analog line, the digital line often requires a number of digital repeaters to boost signal level. A typical digital multiplex system will carry from 24 to 3000 POTS circuits.
FIG. 3
illustrates the components of a typical UDLC system
16
, which represents a point-to-point multiplex system. A remote terminal (RT)
17
, connected to voice and data channels, places voice and data signals in a digital format and time-division multiplexes these digital signals onto a single digital carrier for transmission. The digital carrier is transmitted by a carrier line
18
extending between the RT
17
and a COT
19
. One or more bidirectional repeaters
20
can be placed in the line
18
to boost the level of the digital carrier. The line
18
is terminated at the COT
19
, which performs the inverse function of the RT
17
. In particular, the COT
19
maps individual channels on a one-for-one basis and reproduces the channels in original form. Channel grooming and interchange, however, are not performed by the COT
19
. The number of channels supported by the RT
17
is the same as that of the corresponding COT
19
.
The customer premises equipment (CPE)
5
is connected to a POTS line card
21
in the RT
17
via a copper local loop
22
having a length of typically less than 12 kft. The RT
17
is typically powered by a local AC source via an interface cable
23
a
. A channel card
24
of the COT
19
is connected to the CO
3
via a copper pair
25
. The COT
19
is typically powered from a local −48Vdc power supply, typically located at the CO
3
, via an interface cable
19
a.
Integrated Digital Loop Carrier System
Although IDLC systems have evolved from the UDLC system design shown in
FIG. 3
, IDLC sy
Kilgore John M.
Milliron David B.
Poirier Dean C.
Conklin Corporation
Felber Joseph L.
King & Spalding
LandOfFree
Digital carrier system for rural telephone and data... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital carrier system for rural telephone and data..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital carrier system for rural telephone and data... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2530631