Abstract:
A communication system comprising: 
     a first multiplexing/demutliplexing stage positioned at a first locality and connected to a telephone interchange; 
     a plurality of second multiplexing/demultiplexing stage positioned in a plurality of second localities apart from said first locality; 
     a communication link, such as a transmission line or radio link which connects said first multiplexing/demultiplexing stage to each of said second multiplexing/demultipleg stages; and 
     a plurality of subscribers lines connected to each of a plurality said second multiplexing/demultiplexing stages.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to communication systems and specifically to multiplexing access lines of communication systems. 
     BACKGROUND OF THE INVENTION 
     Congestion of transmission lines is a well known, and undesirable, situation in communication art. In order to solve congestion problems multiplexing (MUX)/demultiplexing (DEMUX) systems have successfully been incorporated to transmission lines. 
     FIG. 1A illustrates a block diagram which represent a transmission system  100 , of prior art Transmission system  100  comprises two MUX/DEMUX units  102  and  104  and single line  114 , preferably an optical fiber, which connects MUX/DEMUX units  102  and  104 . Alternatively, line  114  may be a multiconductor line. Umits  102  and  104  are situated at two localities  106  and  108 , remote from each other, where a plurality of POTS  110  and  112  are interfaced to units  102  and  104  respectively. 
     In accordance with the scheme illustrated in FIG. 1A, a plurality of communications from subscribers on lines  116 , which enter MUX/DEMUX unit  102 , converted to digital signals, multiplexed and routed, through line  114 , to locality  108  by unit  102 . Unit  104  demultiplexes the signals it receives from line  114 , transforms the digital signals into electrical signals and redirects them through lines  118  towards their respective end communication devices (not shown) in locality  108 . 
     The general scheme described above enables transmission system  100  to comprise only one single line connecting localities  106  and  108  and yet handle a plurality of communications. 
     FIG. 1B illustrates a variation of the prior art illustrated in FIG. 1A. A plurality of communications are routed by a switch board  120 , through analog lines  122  to MUX/DEMUX unit  102 , then to MUX/DEMUX unit  104  and then to end communication devices  124  in the described above in conjunction with FIG.  1 A. Unit  104  is, optionaly power fed by a remote powers supply through lie  114 , which in this case may be a multiconductor. 
     FIG. 1C illustrates a digital loop carrier (DLC) of prior art wherein a switchboard  126  sends a plurality of communication signals over a digital E 1  line to a MUX/DEMUX unit  102 . MUX/DEMUX unit  102  demultiplexes the plurality of signals it received one or more E 1  lines  114  and redirects them towards respective subscribers in much the same way as described above. 
     The number of communications that can be handled by transmission lines pertaining to prior art described above, depends on the number of communications that each of the components, comprised in the lines, can support. Tie more powerful the components (i.e. components which can multiples/demultiplex greater number of signals) the greater number of communications that can be supported. 
     Transmission lines of the prior art do not allow their modular expansion. A transmission line of the prior art can be expanded by replacing the MUX/DEMUX components by more powerful MUX/DEMUX components. 
     SUMMARY OF THE INVENTION 
     It is an object of some preferred embodiments of the present invention, to provide a communication system (APIC) which has two stage multiplexing/demultiplexing capabilities. 
     In some preferred embodiments of this invention, a first multiplexing/demultiplexing stage (EU) is situated at, or in the vicinity of, a local exchange in a central office while a second, remote multiplexing/demultiplexing (RU) stage is situated at remote subscribers premises or in their vicinity. Preferably, a plurality of EU modules are comprised in a shelf so as to form a serial bus. 
     In some preferred embodiments of the present invention, a plurality of RU modules are interfaced to a single EU module. Preferably, an RU module supports 2 POTS (RU 2  nodule). Alternatively, an RU module may support  10  POTS (RU 10  module) or some number of POTS or other analog lines. Additionally, a single EU module may support RU 2  and RU 10  modules jointly. Alternatively, RU modules may support digital communication lines. Additionally, the RU modules may support POTS and digital communication lines jointly. Alternatively and/or additionally, RU modules generate preferably all necessary subscriber signals including current feed, ring, and/or metering. 
     In one aspect of the invention, the EU module comprised in some of preferred embodiments of the present invention, supports CAS protocols Additionally, the EU module may support newer CCS communication protocols like V5 communication protocol and/or ISDN-PRI protocol which enables these preferred embodiments to be connected to legacy and/or newer local exchanges. Additionally and preferably, the EU module comprises a power supply unit to remotely power the RU modules as well as the EU itself More preferably, the power supply unit comprised in the EU module comprises necessary protection and safety circuitry. 
     In one aspect of the invention, the APIC communication system does not require preliminary setup. Additionally, the APIC system. is preferably able to function independent of a central clock source. Preferably, the APIC communication system also allows for communication between any of the subscribers it serves, without connection to a central office. 
     There is thus provided, in accordance with a preferred embodiment of the invention, a communication system comprising: 
     a first multiplexing/demultiplexing stage positioned at a first locality and connected to a telephone interchange; 
     a plurality of second multiplexing/demunltiplexing stage positioned in a plurality of second localities apart from said first locality; 
     a communication channel such as a transmission line or a radio link which connects said first multiplexing/demultiplexing stage to each of said second multiplexing/demultiplexing stages; and 
     a plurality of subscribers lines connected to each of a plurality said second multiplexing/demultiplexing stages. 
     Preferably, the first stage is interfaced with said telephone exchange with a single digital interface. 
     Preferably, the digital interface comprises a plurality of logical lines wherein the total number of subscriber lines connected to said second multiplexing/demultiplexing stages is greater than said plurality of logical lines. 
     In a preferred embodiment of the invention, the subscribers include subscribers connected to said second stage by POTS lines. Alternatively or additionally the subscribers include subscribers connected to said second stage by ISDN lines. 
     There is further provided, in accordance with a preferred embodiment of the invention, communication apparatus, comprising: 
     a plurality of communication systems according to the invention; 
     a bus connecting said communications systems; 
     a control unit that mediates communication between said communication systems. 
     preferably, the switchboard connects a subscriber served by one of said second stages with a subscriber served by another of said second stages. 
     Preferably the communication apparatus includes means for grooming the switchboard. 
     There is further provided, in accordance with a preferred embodiment of the invention, a communication method comprising. 
     connecting a first multiplexing/demultiplexig stage to a telephone interchange; 
     connecting a plurality of second multiplexing/demultiplexing stage positioned in a plurality of second localities to each of said first multiplexing/demultiplexing stages; 
     connecting a plurality of subscribers to each of said second multiplexing/demultiplexing stages; 
     There is further provided, in accordance with a preferred embodiment of the invention, a communication method comprising: 
     connecting a plurality of first multiplexing/demultiplexing stages to a telephone interchange; 
     connecting a plurality of second multiplexing/demultiplexing stages positioned in a second locality to each of said first multiplexing/demultiplexing stage; and 
     connecting a plurality of subscribers to said second multiplexing/demultiplexing stage; 
     connecting said first stages via a bus; and 
     mediating between said first stages via said bus. 
     In a preferred embodiment of the invention, connecting said first stage comprises connecting said first stage to said telephone exchange with a single digital interface. 
     Preferably, the communication method comprises connecting a subscriber served by one of said second stages with a subscriber served by another of said second stages via said bus. 
     In a preferred embodiment of the invention, the subscribers include subscribers connected to said second stage by POTS lines. Alternatively or additionally,the subscribers include subscribers connected to said second stage by ISDN lines. 
    
    
     BRIEF DESCRIPTION OF FIGURES 
     The invention will be more clearly understood by reference to the following description of preferred embodiments thereof, read in conjunction with the accompanying figures. Identical structures, elements or parts that appear in more than one of the figures are labeled with the same numeral in all the figures in which they appear. 
     FIGS. 1A-1C show prior art communication systems; 
     FIG. 2 shows schematically a fully populated APIC transmission system in accordance with a preferred embodiment of the present invention; 
     FIG. 3 shows schematically details of a cabinet comprising exchange modules of an APIC transmission system, in accordance with a preferred embodiment of the present invention; and 
     FIG. 4 is a schematic block diagram of a MUX/DEMUX unit in accordance with a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to both FIG. 2 which shows schematically a fully populated APIC transmission system  20  and to FIG. 3 which shows some details of a cabinet (i.e., numeral  32  in FIG. 2) comprising exchange modules (EU), in accordance with a preferred embodiment of the present invention. 
     APIC  20 , preferably supports simultaneously basic rate ISDN and analog telephone lines. APIC  20  comprises at least one exchange unit (EU)  22 , which preferably supports CAS and newer CCS communication protocols like V5 communication protocol and/or ISDN-PRI protocol, interfaced to a local exchange  24 , through digital exchange interface (E 1 )  26 , and a plurality of remote units (RU)  28 . The operation of EU  22  performs roost of its functions via a MUX/DEMUX unit  52 , shown on FIG.  3  and described in more detail below, with respect to FIG.  4 . In some preferred embodiments of the present invention, APIC  20 , preferably uses 64 Kbps rate PCM standard for digital voice transmission between analog communication devices  40  and exchange interface  26 . 
     Preferably, each RU  28  is interfaced with a single EU module  22  by a communication line  38  such as an HSDL twisted pair. Alternatively, communication line  38  may be of ISDN type. Alternatively, communication line  38  may be of any other multi subscriber twisted pair or may be an optical transmission line. In some preferred embodiments of the present invention, each EU module  22 , may support HSDL, ISDN and other multi subscriber lines jointly. Communication line(s)  38  preferably enable(s) full duplex 784 bits connection between RU  28 , and EU  22 , modules, preferably, over existing infrastructure by combining voice channels which preferably use high rate digital 2B1Q technique. 
     In some preferred embodiments of the present invention, each RU module may be either a POTS type  28 , or an ISDN type  50 . A POTS type RU module preferably supports a plurality of analog telephones  40  (or other analog devices such as facsimile machines or modems), while an ISDN type RU module preferably supports a plurality of digital communication devices such as telephones  36 , PCs  37  and/or FAXs  39 . Alternatively, some RU modules may support a plurality of both analog and digital communication devices. RU module  28  preferably handles all necessary conversations to and from subscriber lines  30 . Each RU module  28 , may support a number of POTS and/or digital communication devices. 
     RU modules  28  and  50  may be installed in street cabinets. Alternatively, RU modules  28  and/or  50  may be wall mounted in any protected indoor location. Altenatively, RU modules  28  may be wall or pole mounted in an unprotected outdoor locality. Alteinatively, RU modules  28  and/or  50  way be installed underground. Preferably, RU modules are remotely powered via line  38 , as in some prior art embodiments, and preferably generates all necessary subscriber power and signals including current feed, ring, and/or metering. 
     EU module  22 , which preferably is a stand alone module, is plugged in an EU shelf  32  which preferably is an ETSI  19  inch compliant standard shelf In some preferred embodiments of the present invention, a fully populated EU shelf  32  consists of sixteen EU modules  22  and a shelf control unit (SCU)  34 . SCU  34 , which provides management interface between the shelf  32  and Shelf/Site OPS, controls and interfaces preferably up to sixteen EU modules  22 . EU and SCU modules are mounted on a bus  58  which is connected to a switchboard  56  in SCU  34 . 
     SCU module  34 , enables maintenance and management, preferably, via graphical user interface, preferably, on an MS windows platform. Altenatively, a higher hierarchy, preferably UNIX based network management and control unit  48  (see FIG. 2) is supported by SCU module  34 . SCU  34  handles concentration and grooming, if necessary of user interfaces towards the network (E 1 ) interfaces. It can perform these functions by running proprietary or standard protocols, such as V5.2 and using on board switchboard  56 . Two SCUs can be installed for redundancy and increased capacity. In some embodiments of the present invention, a UNIX based network management system (NMS)  48  (see FIG. 2) may control a plurality of APICs  20  through their individual SCU modules. Alternatively, APICs  20  can operate without shelf control unit  34 , if management and interface of EU modules  22 , is not required. 
     FIG. 4 shows a preferred embodiment of MUX/DEMUX unit  52  in greater detail, but still in schematic form. In general MUX/DEMUX unit  52  comprises an E 1  interface  70  a matrix and control unit  72  and a plurality of digital subscriber line (DSL) interfaces  74 . E 1  interface  70  acts as the interface to local exchange  24  and DSL interfaces  72  each connect to a digital subscriber line  38  which connects the DSL interface with an RU. Matrix and control unit  72  is a switchboard and control system that switches the lines from interfaces  74  (and the outside subscribers) to interface  70  (and the local exchange). In addition, unit  72  can also transfer data from either interface  70  or  74  to other EUs or to SCU  34  via a system bus, based on the destination of the data Matrix and control unit  72  also receives and sends timing and control signals to and from the system bus. In a preferred embodiment of the invention, MUX/DEMUX unit  52  also contains a local CPU  76  that preferably provides local control of the DSL interfaces, the E 1  interface and the matrix and control unit, preferably via a local BUS (not shown). In a stand alone mode it preferably provides full control of the EU. When the EU is integrated into a system as in FIGS. 1-3, the CPU operates under at least partial control of the SCU, via a communication bus  77 . 
     It should be understood that the present invention is useful with a large number of different interfaces and remote units. In some preferred embodiments of the invention, the number of subscribers is the same or fewer than the number of logical connections (E 1 ) to the local exchange. However, in accordance with a preferred embodiment of the invention, for SCU  34  to provide management of the connections such that the number of subscribers exceeds the number of logical connections to the local exchange. 
     The EU units  22  each preferably include a power supply  46  wich preferably contains all protection and safety circuitry. Power supply units are used to power the EUs, and preferably are utilized to remotely power RUs connected to the EU as well. 
     Shelf control unit (SCU)  34 , serves as a mediation device between EU modules  22  and management and control unit  48 . SCU  34  has, preferably, RS232/4,5 interfaces (not shown) which enables control, configuration and maintenance of BU modules  22 . Preferably, control, configuration and maintenance of EU modules  22 , is performed from a remote locality where management and control unit  48 , is positioned. Altenatively, control, configuration and maintenance of EU modules  22 , is performed directly from SCU module  34  without using management and control unit  48 . In some preferred embodiments of the present invention, control, configuration and maintenance of EU modules  22 , may be performed both directly from SCU module  34  and/or management and control unit  48 . 
     The slots of EU shelf  32 , can also be occupied, by other data communication products such as the HiWAY™ high speed Internet access product or the ExLine2™, in order to extend E 1  services from local exchange  24  to customer premises, of ECI Israel. EU shelf  32  is preferably installed at the local exchange premises. Alternatively, EU shelf  32  may be installed in a street cabinet, preferably in the vicinity of a local exchange  24 . 
     In some preferred embodiments of the present invention, a central connection panel (CCP)  54 , is installed, preferably, above EU shelf  32  CC  54 , enables connecting to shelf  32 , preferably protected−48 VDC power supply output, G.703 unbalanced (75 Ω) or balanced (120 Ω), G703/10 external clock input and output, alarm and/or management interfaces and DSL lines interfaces. 
     By implementing a two stage multiplexing/demultiplexing configuration that includes plug-in EU modules  22 , at exchange  24 , premises and separate remote subscriber units  28 , (multi point configuration) at the subscriber end, some preferred embodiments of the present invention enable flexible planning, installation, operation and/or Maintenance of the APIC transmission system  20 . In some preferred embodiments of the present invention, and due to its flexibility, new services may be introduced to the APJC  20  transmissiom system as they appear. 
     In some preferred embodiments of the present invention, APIC transmission system  20  has no“single point of failure” in the sense that failure of one of the EUs will affect only the subscribers connected to it while the rest of the transmission system continues to operate. Additionally and/or alternatively, the subscribers connected to different RUs can communicate with each other via bus  58 , through the mediation of switchboard  55 , without going through local exchange  24 . 
     In some preferred embodiments of the present invention, APIC transmission system  20  does not require any preliminary setup. Preferably, APIC  20  is fully operational by its default settings. More preferably, APIC  20  is able to function independent of a central clock source. Preferably, APIC  20  extracts its internal timing signals from its own E 1  connection. 
     While the invention has been described with reference to certain preferred embodiments, various modifications will be readily apparent t, and may be readily accomplished by persons skilled in the art without departing from the spirit and the scope of the above teachings. Therefore, it is understood that the invention may be practiced other than as specifically described herein without departing from the scope of the following claims: 
     It will be appreciated by a person skilled in the art that the present invention is not limited by what has thus far been described Rather, the present invention is limited only by the 
     Preferably, the communication method comprises connecting a subscriber served by one of said second stages with a subscriber served by another of said second stages via said bus. claims which follow. when used in the following claims, the terms“comprises”,“comprising”, “includes”,“including” or the like means “including but not limited to”.