Method and apparatus for service multiplexing over telephone networks which employ bridged tap construction

A method and apparatus for service multiplexing over telephone networks which employ bridged tap construction to allow 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, a method of combining multiple physical links (e.g., telephone lines) into a single, virtual communication link, is used to increase transmission bandwidth. 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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 4 is a block diagram illustrating the simultaneous delivery of
 different services to physically separated subscribers over a shared
 single pair of wires in a bus-type network topology. At the network side
 of the line, narrowband and broadband services via line card 120 and ADSL
 modem 122, respectively, are coupled onto a wire pair (112) within bundle
 102. While the broadband service is illustrated in this example as being
 an ADSL modem, it should be understood that other types of services may be
 used, such as, for example, VDSL. The narrowband service may be POTS
 service. The coupling of the different services is accomplished using
 service filters 124 and 126 which act to insert an information signal into
 and/or extract a received information signal from a particular frequency
 band. The service filters prevent the different frequency band signals
 from interfering with each other. Such couplers are well known in the art
 and typically utilize some form of transformer coupling along with
 variable impedances in the different frequency ranges to selectively
 transmit (or impede the transmission of) signals in different portions of
 the frequency spectrum. Specific reference may be made to U.S. Pat. Nos.
 5,528,630 and 5,627,501 for details regarding exemplary service filters.
 The narrowband service is ultimately delivered to customer premises 140,
 while the broadband service is delivered to a different customer premises
 142. At the customer side, drop cables 144 and 146 are connected between
 wire pair 112 and the customer premises 140 and 142, respectively. Drop
 cable 144 is connected to customer premises 140 via service filter 148.
 Similarly, drop cable 146 is connected to customer premises 142 via
 service filter 150. The service filters 148, 150 may be located at the
 point connecting the drop cables to the distribution cable (110), or
 between the end of the drop cable and the in-premises wiring at each of
 the customer premises 140, 142, or they may be connected as part of the
 in-premises wiring. Service filter 148 prevents the broadband signal from
 interfering with the signal and equipment at customer premises 140.
 Similarly, service filter 150 prevents the narrowband signal from
 interfering with the signal and equipment located at customer premises
 142.
 FIG. 5 is a block diagram illustrating the simultaneous delivery of
 different services to physically separated subscribers over a shared
 single pair of wires, similar to FIG. 4. However, in FIG. 5, the
 communication services are delivered over a tree and branch topology. One
 of the main distinctions between the topology of FIG. 5 and that of FIG.
 4, is that in FIG. 5 the drop cable (144) is connected between cable
 bundle 170 and customer premises 140. Cable bundle 170 is itself a bridged
 tap emanating from cable bundle 102, and drop cable 144 is connected to
 wire pair 172 within cable bundle 170. Drop cable 146 is similarly
 connected between wire pair 162 of bridged tap 160 and customer premises
 142. Essentially, in the tree and branch topology of FIG. 5, one branch of
 the distribution network (bridged tap 170) provides customer premises 140
 with narrowband service, while a second branch (bridged tap 160) provides
 customer premises 142 with broadband service.
 A general model for "n" services, i.e., the distribution of "n" services to
 different customer premises, is illustrated in FIG. 6. As shown in FIG. 6,
 there are "n" service filters 180 (SF-1, SF-2, . . . SF-n) connected to a
 common wire pair at the feeder side (central office) of the network, and
 "n" service filters 182 (SF- 1, SF-2, . . . SF-n) connected to the same
 common wire pair at the customer premises side of the network. Different
 services, such as POTS, ISDN (Integrated Services Digital Network) and
 ADSL are generated and received at service transceivers located at the
 feeder side (190) and customer premises side (192) of the network. The
 service transceivers are denoted "TXRX-n" or "xDSL-n", the latter
 indicating the applicable class of digital subscriber line. The term
 "xDSL" includes ADSL, VDSL and other DSL (digital subscriber line) which
 utilize the frequency spectrum above the standard POTS voice channel,
 i.e., above 4 kHz. In the example shown in FIG. 6, there are "n"
 transceivers 190 on the feeder side of the network, and "n" transceivers
 192 on the customer premises side of the network. For each communication
 service being provided, there is one transceiver 190 supporting that
 service at the feeder side of the network and one transceiver 192
 supporting the service at the customer premises side of the network.
 The equipment connected to the feeder network (e.g., service filters 180,
 transceivers 190) may be located at the central office or at locations
 remote from the central office. The equipment connected to the customer
 premises (e.g., service filters 182, transceivers 192) is flexible in
 relation to the drop cable and premises wiring for that particular
 customer premises. However, each service filter 182 and transceiver 192 is
 dedicated to a single communication service being delivered to that
 customer premises.
 According to the present invention, inverse multiplexing may be used in
 conjunction with frequency division multiplexing employing service
 filters, as described above, to increase the transmission bandwidth to a
 particular customer premises. Inverse multiplexing refers to the
 capability to combine multiple physical links (e.g., multiple telephone
 lines) into a single virtual link. An example of inverse multiplexing is
 shown in FIG. 7 where three T1 lines (202, 204, 206), each having a
 bandwidth of 1.544 Mbps are used to deliver approximately 4.6 Mbps
 full-duplex communication over a virtual link. In this manner, inverse
 multiplexing may be used to combine the service capacity of two or more
 digital subscriber lines.
 A specific application of the concept shown in FIG. 7 is shown in FIG. 8,
 whereby broadband service is delivered over two xDSLs to a customer
 premises at one location, while narrowband (standard telephone service) is
 delivered to a different customer premises at a different location.
 Referring now to FIG. 8, a multiplexer 210 is located at the central
 office side of the network wiring and is connected to an aggregate
 "virtual" link on one side and to two xDSL modems 212, 214 on the other
 side. The signals through xDSL modems 212, 214 are isolated via service
 filters 216, 218 and then connected to wire bundle 224. Also at the
 central office side of the network wiring, narrowband service may be
 provided via line card 220 and service filter 222 connected to wiring
 bundle 224. According to the present invention, the narrowband signal (via
 service filter 222) and an xDSL signal (via service filter 218) are
 connected to the same wire pair 228 within bundle 224. An additional xDSL
 signal (via service filter 216) is connected to wire pair 229 within
 bundle 224. The signals travel through wire bundle 224 onto bridged tap
 226 which is located at the customer side of the network wiring.
 At the customer side of the network wiring, a drop cable (230) connects
 from the wiring pair 228 to a first customer premises 234 in order to
 deliver the narrowband service to customer premises 234. Connected between
 drop cable 230 and customer premises 234 is a service filter 232 which is
 used to isolate the signal being delivered to customer premises 234.
 Similarly, drop cables 236 and 238 connect from the wiring pairs 229 and
 228, respectively, to a second customer premises 244 in order to deliver
 the xDSL (or other broadband) signals on those wire pairs to customer
 premises 244. Each of the drop cables 236, 238 is connected to a
 respective service filter 240, 242 for signal isolation. From the service
 filters 240, 242, the broadband signals pass through respective modems
 246, 248 and onto a multiplexer 250 which presents at its output an
 aggregate "virtual" link at customer premises 244. In this way, narrowband
 service is delivered to a first customer location and broadband service as
 an aggregate "virtual" link is delivered to a different customer location,
 using the same wiring pair.
 In the example shown in FIG. 8, the various service filters may be located
 at the point connecting the drop cable to the bundle, or between the end
 of the drop cable and the in-premises (customer) wiring, or as part of the
 in-premises wiring. In the preferred embodiment according to the present
 invention for inverse multiplexing xDSL service, the service filters are
 located between the end of the drop cable and the building (customer)
 wiring. Also, the xDSL modem and multiplexing functions may be implemented
 using the same network apparatus. At the central office side of the
 network wiring, the xDSL modem/multiplexer may be located at the central
 office or at locations remote from the central office. At the premises
 side of the network wiring, the xDSL modem/multiplexer may be located at
 the end of the drop cable, typically at the customer premises itself.
 In the example illustrated in FIG. 8, if each xDSL carries 1 Mbps to
 customer premises 244, then the aggregate virtual link capacity to the
 customer premises is approximately 2 Mbps. Of course, more than two xDSL
 signals may be multiplexed into an aggregate virtual link, depending on
 the particular system requirements and needs.
 FIG. 9 illustrates a general model for "n" services, i.e., the distribution
 of "n" services to different customer premises, similar to that
 illustrated in FIG. 6. However, in FIG. 9, some of the services utilize
 the principle of inverse multiplexing set out above. For example, as shown
 in FIG. 9, a service or signal 300 at the feeder or central office side of
 the network wiring may in fact represent an aggregate virtual link of "m"
 different xDSL signals which is delivered to a customer premises as
 follows. First, a multiplexer 302 separates the aggregate signal 300 for
 handling by "m" separate xDSL modems 304 (designated xDSL1-1 through
 xDSL1-m). Each xDSL modem 304 is connected to a respective service filter
 306 (designated SF1-1 through SF1-m) for signal isolation. The signals
 from the service filters 306 are transmitted in much the same fashion as
 discussed above in connection with FIG. 6 and FIG. 8.
 At the customer premises side of the network wiring, service filters 322
 (designated SF1-1 through SF1-m) direct the individual xDSL signal streams
 to respective xDSL modems 324 (designated xDSL1-1 through xDSL1-m) for
 processing. The signals are then provided to a multiplexer 326 which
 outputs an aggregate virtual signal 328 to the customer premises.
 In the composite model of FIG. 9, a service may use one or more digital
 transmission lines (xDSL) for inverse multiplexing. There are "n" such
 services in the example of FIG. 9, with each service having anywhere from
 1 to "m" transceivers on each side of the network wiring (i.e., the
 central office side and the customer premises side) to transmit and
 receive signals on each line. The transceivers may be xDSL modems, ISDN
 modems, telephone line codecs, or any device used for providing a service
 over a metallic wire pair. Similar to FIG. 6, the transceivers are denoted
 either as TXRX-n or xDSL-n, the latter indicating the applicable class of
 digital subscriber lines. For each service, there are also 1 to "m"
 service filters on each side of the network wiring in order to isolate the
 service from other services that may share the same line.
 While the invention has been particularly shown and described with
 reference to a preferred embodiment thereof, it will be understood by
 those skilled in the art that various changes in form and details may be
 made therein without departing from the spirit and scope of the invention.