Telephonic communications – Having light wave or ultrasonic link for speech or paging... – Including fiber optic link within telephone network
Reexamination Certificate
1999-12-20
2002-05-21
Legree, Tracy (Department: 2681)
Telephonic communications
Having light wave or ultrasonic link for speech or paging...
Including fiber optic link within telephone network
C379S413000, C307S066000
Reexamination Certificate
active
06393105
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to telephony service on a hybrid fiber-coax (HFC) network, and more particularly to an improved power arrangement for ensuring reliable lifeline telephony service on an HFC network.
Background Art
There are primarily three types of physical media utilized in wired communication systems: (1) fiber optic cable, (2) coaxial cable, and (3) twisted copper pair cable (“twisted pair”). Presently, twisted pair cable predominates in the access local loop portion of existing telephone networks. Coaxial cable has been used widely by cable television companies, and both telephone companies and cable companies have made use of fiber optics for main or trunk line signal distribution.
Fiber optic cable can carry more information over greater distances than coaxial cable, while coaxial cable can carry more information over greater distances than twisted pairs. Because twisted pair is the predominant local loop technology in the telephone industry, new network architectures have been developed that work with twisted pair wire to increase information carrying capacity. In the cable industry, an HFC network employs a combination of broadband linear fiber optics and coaxial cable. Such a network also allows delivery of many advanced two-way services in a cost-effective manner when compared with total conversion to a baseband digital optical network with significant time-division multiplex hardware included in the access plant.
In addition to requiring two-way communication, voice telephony service has two other requirements not necessarily addressed by video distribution networks: lifeline service powering and privacy of voice communication. In video networks, the power to operate a subscriber television set for example, is provided by the subscriber, i.e., a subscriber merely plugs a television into an electrical outlet at the subscriber location. In the event of a power outage, the user is unable to view the delivered video services.
In contrast, telephony subscribers expect working telephone service whether or not electricity is available. Because basic telephone service is always expected to be available, the telephone distribution network typically provides to a subscriber location what is referred to as “talk battery” along with electric power utilized for conventional voice telephony signaling and supervision to ensure the availability of such “lifeline” services.
Basic HFC two-way capability requires the addition of reverse-path node laser transmitters and headend receivers, and activation of two-way amplifiers in the coaxial port on of the network. Node power and all locally powered amplifiers require appropriate uninterruptible power supplies (UPS) in order to bring basic HFC system reliability to the proper level for support of lifeline telephony service availability.
Conventional tap devices do not pass power to the drop cable. In some HFC networks, reverse-path filters are used to mitigate noise ingress in the reverse spectrum, and the maximum value of through current may only be 4 to 6 amperes at 48 volts AC. Such through current and relatively low voltage is inadequate to provide the necessary reserve power for cable telephony remote hardware in HFC networks being upgraded for lifeline telephony services.
Providing power for “talk battery” and emulation of conventional telephony signaling and supervision on HFC networks is usually accomplished in one of two ways, either as steady-state power supplied only from the network as shown in
FIG. 1
, or as Exclusive-OR local rectifier/battery arrangements at or near a customer residence as shown in FIG.
2
.
More specifically, the hybrid fiber/coaxial (HFC) cable network of
FIG. 1
includes a cable head-end/central office
10
incorporating a central office switch
12
connected to a two-way digital interface or head-end digital terminal (HDT)
14
. HDT
14
modulates the digital signals from the line side of switch
12
to generate appropriate modulated RF carriers
16
for transmission on a fiber optic cable
18
by a combiner/optical transceiver
20
, and to demodulate RF carriers received by optical transceiver
20
from cable
18
.
Central office
10
further includes a bank of RF modulators
22
for generating modulated video/audio signals from baseband signals received from an external baseband video service
24
. Optical transceiver
20
is arranged to transmit the modulated video signals onto cable
18
. Baseband special services equipment
26
is also connected to the network via HDT
14
and transceiver
20
.
An optical node
28
includes a suitable optical transceiver
30
coupled to fiber optic cable
18
and a coaxial cable
32
for providing a link for communications between the central office
10
and television units
34
and cable telephony service platform (CTSP) equipment
36
connected to telephone units
37
located at one or more customer premises
38
. In the network power only arrangement, electrical power is generated by a protected power supply
40
located at a node, and powers amplifiers
42
, and all equipment in a network interface unit (NIU)
44
located at or near a customer's premises via a power passing tap
46
and a drop cable
47
. Power supply
40
also provides power for lifeline “talk battery” along with electric power utilized for conventional voice telephony signaling and supervision.
FIG. 2
illustrates the typical local power arrangement for an HFC network, wherein elements identical to those described in connection with
FIG. 1
have been denoted with like reference numbers. As shown, a conventional tap
49
, i.e., a nonpower passing tap, is employed in the network so that NIU
44
does not receive equipment power from node
28
. Instead, electric power for talk battery and conventional voice telephony signaling and supervision is provided by an AC power converter/battery charger unit
48
connected to a conventional AC power source
50
and a back-up battery
52
. In the event of power loss from AC power source
50
, CTSP
36
within NIU
44
will receive power from battery
52
.
Regarding the network-only power arrangement, safety regulations in certain countries limit voltage on a coaxial cable plant to a typical value of 48 vAC, and certain active and passive devices pass only about one-third of the current required to support cable telephony lifeline service applications. Thus, network power source arrangements have not proven satisfactory in certain situations.
With respect to the local power arrangement, reliability is dependent on considerations external to the network like AC power source reliability or user interaction to maintain properly charged batteries. In addition, a common practice in certain countries is to turn off all circuit breakers and unplug all appliances prior to departing on month-long holidays. Therefore, inadvertent or deliberate disconnection of ordinary lead-acid batteries servicing cable telephony network interface units (NIU) on customer premises are deprived of a constant float voltage for extended periods, which in turn leads to likely battery damage or destruction well before the rated operational life expectancy of the battery.
As such, a need exists for an apparatus and method of reliably enabling the electrical form of talk battery, signaling, and supervision in an HFC network which can support telephony lifeline service applications in a cost effective manner while also minimizing the need for customer interaction at the customer location, and power drawn from network optical node or other network uninterruptible power supplies.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an apparatus and method for reliably enabling the electrical form of talk battery, signaling, and supervision in an HFC network which fully supports lifeline telephony service while overcoming the above-noted deficiencies of network-only power source and local-only power source arrangements.
It is another object of the present invention to provide an apparatus and method for poweri
Brooks & Kushman P.C.
Legree Tracy
MediaOne Group Inc.
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