Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1998-11-23
2001-10-30
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S493000, C375S222000, C375S260000
Reexamination Certificate
active
06310894
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of data communications. More specifically, the present invention concerns a method and apparatus for simultaneously delivering different communication services to physically separated subscribers over a single, shared pair of communication wires, as well as inverse multiplexing multiple physical links into a single, higher bandwidth virtual link.
BACKGROUND OF THE INVENTION
Communication systems, such as the telephone system (e.g., the Public Switched Telephone Network or PSTN) typically employ bridged taps, which are open circuit cable pair segments constructed such that multiple branches of a single pair share a common origin. Bridged taps are provided so that a common pair of wires can serve different subscribers. The common pair of wires passes more than one subscriber location, with each location having an access point for connecting the subscriber's service drop wire to the common pair. Bridged taps are commonly incorporated into telephone distribution networks in order to provide plant flexibility for future additions, or for changes in service demands.
FIGS. 1 and 2
illustrate two different types of bridged tap constructions. Shown in
FIG. 1
is a tree-type topology bridged tap construction in which a number of cable pairs (collectively bundle
102
) emanate from respective line cards at the central office
104
. At point
106
, bridged tap
107
connects to cable pair
109
. Bridged tap
107
is a cable pair within bundle
108
, which includes a number of cable pairs, only one of which is shown in the drawing. Bridged tap
112
, which is within bundle
110
, is shown as a continuation of cable pair
109
. Similar to bundle
108
, bundle
110
contains a number of cable pairs, only one of which is shown (
112
). Connected to cable pair
112
is a drop cable which provides service access for subscriber
114
. The topology of
FIG. 1
is “tree-type” in that the bridged taps resemble interconnecting branches of a tree. In contrast, the bridged tap construction of
FIG. 2
is a bus-type construction in that the distribution path from the central office is a single path, with no branching paths.
Such bridged tap construction results in a cable layout having one or more cables starting at a common origin. Each of these cables may have branches, and the branches may in turn have additional branches. The resulting topology is the tree-type topology having branching cables with no closed loops. Alternatively, where there is no branching, the topology may reduce to a bus-type topology in the case of a single cable with one or more subscribers attached to the shared common line.
A class of digital subscriber line transmission methods (e.g., ADSL, VDSL) use a single pair of wires to provide both narrowband and broadband services to a subscriber using frequency division multiplexing. This is illustrated in FIG.
3
. At the network side of the line, narrowband and broadband services are coupled onto the line at the same location (e.g., at the central office or at a remotely located service node). Specifically, narrowband services are coupled via line card
120
, while broadband services are coupled via ADSL modem
122
. The narrowband and broadband services are coupled onto cable pair
112
within bundle
102
via respective service filters
124
and
126
. Alternatively, the narrowband and broadband services may be coupled onto the line at different locations on the network side of the line (e.g., Plain Old Telephone Service POTS coupled onto the line at the central office and ADSL coupled onto the line at a remotely located service node).
At the subscriber side of the line, the services are separated at the end of the drop at the customer premises
128
using respective service filters
130
and
132
. The service filters used in combining and separating services may be such as those described in U.S. Pat. Nos. 5,627,501 and 5,528,630, the contents of which are incorporated herein by reference. For example, a filter may be located at the end of the drop wire which couples the telephone service onto the existing in-premises telephone wiring and isolates the broadband service from the telephone wire pairs. Alternatively, the two service filters
130
,
132
at the customer premises
128
may be combined into one apparatus, for example, a POTS-type splitter. A metallic wire pair has information carrying capacity (bandwidth) available in the unused frequency spectrum of the channel. In the case of a POTS line, the frequency spectrum from 0-4 kHz may be used for POTS, while the upper portion may be used for ISDN, ADSL or VDSL.
The number of metallic wire pairs in adequate condition may be insufficient to support full market deployment of broadband services using the existing telephone network infrastructure, because certain limitations exist on the number and quality of wire pairs in the distribution cables. The number of wire pairs that pass each premises is usually limited. For example, in the case of residential premises, the number of wire pairs that pass the premises is typically two pairs, with a minimum of one and a maximum of about five pairs. It is estimated that the number of pairs available may be insufficient to meet the demand for services.
Several aspects of the existing telephone network infrastructure limit the information carrying capacity (bandwidth orbit rate) of the individual lines. These factors include: (1) the type of cables and the use of bridged taps; (2) the condition of the plant; and (3) the noise picked up by the network. Also, a reduction in capacity may result from restricted use of particular frequency bands (e.g., amateur radio bands) because of potential radio frequency interference. These factors will reduce either the usable bandwidth available for broadband service (bit rate) or the length of the working line (reach).
SUMMARY OF THE INVENTION
The present invention allows the simultaneous delivery of different services to physically separated subscribers over a shared single pair of wires. Service is provided to one or more subscribers by connecting them to an open-circuited branch or directly with the working portion of the shared line. Service filters are used at appropriate locations in the network topology to couple or isolate the different communication channels. The wire pairs are used to simultaneously carry different services to physically separated subscribers, i.e., a portion of a common line carries one service to one location and a second service to another location. Telecommunication services are partitioned to occupy separate frequency bands in the spectrum of the transmission line using frequency division multiplexing (FDM) techniques. The location of the terminating point for each service is different and flexible as facilitated by the use of bridged taps, service drop connections and appropriate filtering.
Inverse multiplexing is a method of combining multiple physical links (e.g., telephone lines) into a single, virtual communication link with increased transmission bandwidth. For example, three T1 lines each having a capacity of 1.544 Mbps may be multiplexed to provide an aggregate capacity of 4.6 Mbps between two telephone offices. Similarly, other types of services may be multiplexed, such as ADSL or VDSL.
The simultaneous delivery of different telecommunication services over a common line to physically separated subscribers may be used in conjunction with inverse multiplexing to increase and/or vary the transmission bandwidth to individual subscribers.
The present invention leverages existing bridged tap construction to free up additional wire pairs in the distribution cable for service delivery.
REFERENCES:
patent: 5512937 (1996-04-01), Beierle
patent: 5539777 (1996-07-01), Grube et al.
patent: 5627836 (1997-05-01), Conoscenti et al.
patent: 5668857 (1997-09-01), McHale
patent: 5784683 (1998-07-01), Sistanizadeh et al.
patent: 5790550 (1998-08-01), Peeters et al.
patent: 5796424 (1998-08-01), Ely et al.
patent: 5812786 (1998-09-01), Seazholtz
Hyun Soon-Dong
Nguyen Chau
Suchyt Leonard Charles
Verizon Laboratories Inc.
Weixel James K.
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