Abstract:
A plurality of telecommunications connections are installed in a distribution network by connecting a series of distribution points using a multicore cable comprising a plurality of cores having a common enclosure, some of the cores carrying fiber tubes into which optical fiber may later be introduced, and other cores carrying an electrical power supply. One or more cores may be diverted from a longer cable run to serve a local distribution point by rupturing a web connecting the core to the rest of the cable, thus allowing the remaining cores to be uninterrupted at the point of divergence. An alternative embodiment intended for underground use provides for apertures to be opened in a protective sheath to expose the individual cores required to be diverted to a local distribution point.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a National Phase entry of PCT Application No. PCT/GB2015/051707, filed on 10 Jun. 2015, which claims priority to GB Patent Application No. 1411408.6, filed on 26 Jun. 2014, which are hereby fully incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to cable connections for use in a telecommunications network, and in particular in the distribution network. The distribution network comprises the physical link between each end user installation and the switching node in the network through which all calls or sessions to and from that user are routed. 
       BACKGROUND 
       [0003]    For most of the history of telecommunications, these physical links have comprised wire pairs (usually of copper, and often referred to as the “copper” network) over which electrical signals (which have included both analogue and digital systems at different stages of development) are carried. 
         [0004]    The wires themselves are usually either suspended from poles or routed through underground conduits. Both types require some protection from their environment—in particular, overhead wiring requires reinforcement to support its own weight and the forces imposed on it by the wind, or any birds, ice, or debris that land on it. Underground wiring is protected from these forces, but requires protection against damage from ground movements and from excavation by animals or humans. Both types also require waterproofing, and electrical insulation between the two wires in each pair and from any other wire pairs using the same routing. 
         [0005]    With the development of fiber optic communication systems in the distribution network, more complex arrangements are becoming necessary. In particular, it is more difficult to connect individual lengths of optical fiber. Instead, hollow tubes are provided, linked together as necessary to provide the complete connection from exchange to end user (or intermediate fiber/wired interface) through which an optical fiber may be introduced to make the actual connection, for example using the process described in European Patent 0108590. 
         [0006]    Where a fiber network is being installed, it is often also necessary to make provision for “legacy” copper systems, either for “lifeline” backup services or because it is not possible or desirable to convert all customer premises from copper to fiber at the same time. It is therefore common for copper and fiber connections to be installed in parallel over much of the distribution network. The provision of both types of connection adds to the number of cables required to be provided in the underground ducting or on high-level connections between poles, requiring additional infrastructure and installation costs. 
         [0007]    It is often necessary to provide electrical power to operate equipment at one or other end of the connection or at intermediate distribution points, such as an optical/copper interface. Traditionally, power was provided from the exchange, over the copper network. More recently, greater power requirements within the network have made it inefficient to use the traditional copper pairs for power supply from the exchange, so power injection over the copper network from the customer end, or from intermediate points, is becoming more common. The increasing use of optical fiber connections, which require electrical power to generate light signals but cannot be used to deliver electrical power, also increases the requirement for electrical connection to intermediate points in the network. 
         [0008]    However, this increases the number of power connections required, increases exposure to tampering with the power supply at intermediate points in the network, and can be unpopular with customers. Moreover, if reliance is placed on collecting power from the customer to power the communications system, the customer&#39;s communications connection will fail if the power fails, making it difficult to report that failure to the power supplier. 
         [0009]    It is therefore often desirable to provide an electrical connection, primarily configured to deliver electrical power, between the exchange and some point in the distribution network. By configuring it specifically for power rather than communications, some of the inefficiencies described above caused by carrying power over the traditional wire pairs can be avoided. In particular it is possible to use higher voltages, thereby reducing losses in the cable. However, this again requires extra installation work, and extra space in underground ducts or overhead cable installations. 
         [0010]    Although topologically each connection (optical, power, or traditional “copper pair”) is a single run from the exchange to the customer premises, in practice it may be made up of two or more lengths in series, connected together at distribution points. Individual wire pairs or fiber tubes may be bundled into the same cable over some of these lengths, for example from the exchange to a first distribution point, at which point some or all of the individual connections may continue over different routings. 
         [0011]    As distribution points are being placed deeper into the access network, running a separate, dedicated, cable all the way from the exchange to each distribution point is becoming impractical. In many cases such a cable would pass close to other distribution points, and it is therefore preferred to use a single multicore cable for the path to the first distribution point, at which point a second cable, using fewer cores, is connected to the first to provide a connection to the next distribution point. Several distribution points may be “daisy-chained” in this way. However, this requires the multicore cable to be cut and re-spliced at each distribution point, leading to multiple potential failure points in the cable. 
       SUMMARY 
       [0012]    The present disclosure provides a multicore cable comprising a plurality of cores having a common enclosure, at least one of the cores being arranged to carry optical fiber and at least one other core being arranged to carry an electrical power supply, and arranged such that the enclosure may be disrupted over part of its length such that one or more cores may diverge from the other cores, wherein at least one of the cores of the multicore cable is a hollow tube through which optical fiber can be inserted. 
         [0013]    The present disclosure also provides a method of installing a plurality of telecommunications connections in a distribution network by connecting a series of distribution points using a multicore cable comprising a plurality of cores having a common enclosure, at least one of the cores being arranged to carry optical fiber and at least one other core being arranged to carry an electrical power supply, and arranged such that the enclosure may be disrupted over part of its length such that one or more cores may diverge from the other cores, and that each of a series of distribution points passed by the multicore cable is connected to one or more of the cores diverging from the cable, wherein at least one of the cores of the multicore cable is a hollow tube through which optical fiber can be inserted 
         [0014]    In addition to the provision for power and fiber optics, the multicore cable may also carry one or more a wire pairs for telecommunications, either in the same core as one of the fiber or power connections, or in a separate dedicated core. 
         [0015]    A wire pair primarily configured for power supply rather than plain telecommunications can be optimized for high voltages, for example standard domestic mains voltages of 110 or 230V, requiring more insulation but a smaller cross-section of wire: such a configuration can be both lighter and cheaper than standard telecommunications wiring configured for operation at about 48V. Distribution points having suitable downconverters installed can then be supplied with power by these connections, without requiring modification to any other distribution points which require traditional low-voltage telecommunications connections, for which separate wire pairs for electric telecommunications services may also be included in the cable. By combining the power and fiber cores in one and the same cable, both infrastructure and installation costs can be reduced. In particular, smaller ducts are required for underground installation, fewer suspension points are required on each fixing point for overhead installation, and in both cases installation can be done more quickly and efficiently, and installation staff exposed for less time to hazardous conditions, such as working at height or in confined spaces. 
         [0016]    The designs of the multicore cables would depend on their intended use: in particular whether they are intended to be used for overhead applications or for subterranean applications. In an embodiment for use in an overhead application, in which the cable is suspended from elevated suspension points on poles or other structures, the cable can comprise a strengthening core capable of withstanding any forces acting on the cable, including its own weight, around which are arranged a number of other cores, each comprising one or more wire pairs, or one or more fiber tubes, or a mixture of both in the same core. The strengthening core and each of the other cores are connected by frangible webs which are integral with at least an outer encapsulation of each core. 
         [0017]    In use, such a multicore cable can be attached to a run of suspension points on structures such as buildings, or poles installed for the purpose, passing a number of distribution points. At the closest suspension point to each individual distribution point, the required number and type of cores can be peeled off the central core by cutting the frangible web back to the desired branch point. The cut only needs to be made to the length necessary to connect the required cores to the distribution point, which will typically be located on or close to the structure supporting the suspension point, but at a lower, more accessible, level. Typically, the branch, being the same length as the multicore cable from which it has been peeled, would require cutting to the much shorter length required to reach the distribution point from the branch point (typically the height of the suspension point above the distribution point itself). However, unlike the prior arrangements in which all the other cores would have to be cut and spliced at each branch point, only the core or cores to be terminated there need to be cut at this point. 
         [0018]    In some embodiments, a number of individual cores are attached in a common enclosure or encapsulation, connected by a shared web to the rest of the multicore cable, and only some of those cores are required to be terminated at the distribution point. In such a case the remaining cores can be spliced back in to the continuation of the multicore. However, again only those cores sharing encapsulation with the terminated cores need to be spliced in this way. 
         [0019]    In an underground embodiment, the individual cores are all enclosed in a sheath of a material and structure suitable for protecting the cores from damage by excavation, water ingress, ground movements etc. The sheath is designed such that apertures may be opened in it to gain access to the individual cores within. The sheath may be designed in such a way that such an aperture may be created at any required point, or there may be special locations at intervals along its length, in which case the user selects and opens whichever one of the special locations is closest to the optimum branch point. Having opened the aperture, the user can then extract a core by withdrawing a loop of the core from the sheath until sufficient length has been extracted to form the branch, and then cutting to length. This process can be repeated for as many cores as are required to be terminated at that point. 
         [0020]    In both cases the unused length of each core beyond the termination point may be discarded, or it may remain attached in order to preserve the rigidity and strength of the remaining cable run. It is of course desirable that the individual cores are readily distinguishable from each other—e.g. by different colored coverings, or by means of continuity tests, to ensure that a core selected to be connected at a branch point is not the disconnected surplus of a core that has been branched off closer to the exchange, or conversely that a core to be branched off and severed at one location is not already in use to serve another location further from the exchange. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of the disclosure will now be described, by way of example and with reference to the drawings, in which: 
           [0022]      FIG. 1  is a schematic depiction of a first prior art arrangement. 
           [0023]      FIG. 2  is a schematic depiction of a second prior art arrangement. 
           [0024]      FIG. 3  is a schematic depiction of a section of cable according to an embodiment of the disclosure, intended for subterranean installation. 
           [0025]      FIG. 4  is a schematic depiction of a distribution network using cables configured according to an embodiment of the disclosure. 
           [0026]      FIG. 5  is a schematic depiction of a cross section of a cable according to an embodiment of the disclosure, intended for overhead installation. 
           [0027]      FIG. 6  is a schematic depiction of a section of the cable of  FIG. 5 , in use. 
           [0028]      FIG. 7  is a schematic depiction of an alternative embodiment. 
           [0029]      FIG. 8  is a schematic depiction of an alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    In the prior art arrangement shown in  FIG. 1 , a number of distribution points  20 ,  21 ,  22 ,  23 ,  24 ,  25  are each served by a respective cable  30 ,  31 ,  32 ,  33 ,  34 ,  35  connecting the distribution point to an exchange (switch)  1 . As shown, some of the distribution points  20 ,  21 ,  22  are mounted on poles  40 ,  41 ,  42 , and the cables  30 ,  31 ,  32  are suspended from the poles. In particular, some poles, e.g. pole  40 , support cables serving more distant distribution points  21 ,  22  as well as terminating a cable  30  at the distribution point  20  mounted on or near that pole. 
         [0031]      FIG. 1  also depicts an underground conduit  43  carrying a plurality of cables  33 ,  34 ,  35  each serving a respective distribution point  23 ,  24 ,  25  located within or accessible from the conduit. 
         [0032]    It will be recognized that installing a separate cable to serve each distribution point would be cumbersome. Moreover, because of changes in technology, and differing customer needs, it is often necessary to provide several types of communications connection to each distribution point, and different combinations of connections may be required at each. For example, some distribution points may require more fiber optic connections than others. Some distribution points may also require a power supply from the exchange  1 . This can result in several cables being run between each distribution point and the exchange  1 . 
         [0033]      FIG. 2  illustrates an alternative prior art arrangement, in which several distribution points  20 ,  21 ,  22  (or  23 ,  24 ,  25 ) are connected to the exchange  1  and each other by a series of lengths of multicore cable  50 ,  51 ,  52 ,  53 ,  54 ,  55 . One length  50  of cable connects the exchange  1  to a first pole-mounted distribution point  20 , and respective further lengths  51 ,  52  connect the first distribution point  20  to the second distribution point  21 , and the second distribution point  21  to the third distribution point  22 . 
         [0034]    Similarly, in the conduit system  43 , one length of cable  53  connects the exchange  1  to a first distribution point  23 , and respective further lengths  54 ,  55  connect the first distribution point  23  to the second distribution point  24 , and the second distribution point  24  to the third distribution point  25 . 
         [0035]    Typically cable is made in very long lengths, and it is preferable to minimize the number of joints or splices in them, in order to avoid structural weakness or electrical or optical impairment at the joints. However, in arrangements such as depicted in  FIG. 2 , it is necessary to install multiple short lengths of cable  50 ,  51 ,  52  (or  53 ,  54 ,  55 ) to reach the more remote distribution points  21 ,  22 ,  24 ,  25  in order to serve the other distribution points  20 ,  23  passed on the way. This requires the cable to be severed at each distribution point passed. 
         [0036]    The present disclosure uses a novel design of cable which avoids the problems described above. Different embodiments of such cable are configured for overhead and underground use. 
         [0037]    Referring first to  FIG. 3 , a section of multicore cable  8  is depicted. This comprises a number of individual cores  93 ,  94 ,  95 ,  96  enclosed in a protective sheath  89 . Although only four cores are depicted, in practice many more may be included. Typically some of the cores  96  will carry wire pairs, either for power supply or communications, and others  93   94 ,  95  will be fiber tubes, through which optical fiber may be inserted after the complete end-to-end run is installed. Each core may itself carry a number of wire pairs or fiber tubes, or a combination of both. 
         [0038]    The sheath  89  is arranged such that apertures  83  ( 84 ,  85 ) may be opened in it at intervals along its length. The material of the sheath may be such that an aperture may be opened with a suitable cutting tool at any point along its length, or special weakened sections may be included at intervals to allow such apertures to be created. The individual cores  93 ,  94 ,  95 ,  96  are accessible to an operative through these apertures  84 . 
         [0039]    The installation process of the subterranean cable will now be described, with reference to  FIG. 3  and  FIG. 4 . As shown in  FIG. 4 , the cable  8  is first installed in the conduit  43 , passing the distribution points  23 ,  24 ,  25  that are to be connected to the exchange  1 . In the vicinity of each distribution point  23 ,  24 ,  25 , an aperture ( 83 ,  84 ,  85 ) is opened in the sheathing material  89 . The operative can then grasp a core  93  by hand or with a suitable tool, and draw a loop of the core through the aperture  83  until a length of the core  93  has been withdrawn that is sufficient to be connected to the distribution point  23 . Any surplus length  98  of the core  93  can then be cut off ( 99 ). Thus a branch  93  has been formed in the multicore cable  8 , without severing any of the other cores  94 ,  95 ,  96  not terminating at the distribution point. 
         [0040]    Similar branches to other distribution points  24 ,  25  may be created by opening further apertures  84 ,  85  and extracting the required cores  94 ,  95 , as shown in  FIG. 4 . 
         [0041]    If required, and as shown in  FIG. 4 , two or more cores  95 ,  96  may be branched off the cable  8  through one aperture  85 . In the example shown in  FIG. 4 , a distribution point  25  is to be powered from the exchange  1  and therefore requires an associated power input  26 , capable of converting a 110V/230V supply delivered by the exchange to the voltages required by the distribution point  25  itself. The power can be delivered by connecting a power core  96  to the power input  26  associated with the distribution point  25 . This core  96 , together with the optical fiber core  95  connected to the distribution point  25 , are both accessed through an aperture  85 . 
         [0042]    Further embodiments will now be described, with reference to  FIG. 4 ,  FIG. 5 ,  FIG. 6 ,  FIG. 7  and  FIG. 8 . This embodiment is intended for overhead installation. 
         [0043]      FIG. 5  depicts a cross section of a multicore cable  6  for use in embodiments of the disclosure. This cable comprises a number of cores  60 ,  61 ,  62 ,  63 ,  64  all surrounded by a common enclosure  69 . The enclosure  69  defines a plurality of lobes  60 ,  61 ,  62   63  forming individual cores, connected by integral frangible webs  70 ,  71 ,  72 ,  73  to a central core  64  forming a strengthening member. In this embodiment three of the cores  60 ,  61 ,  62  each contain eight wire pairs, and a fourth core contains twelve fiber tubes, but this is only illustrative and the number and structure of individual cores can be varied. 
         [0044]    This cable may be produced by a series of extrusion processes, first to generate the individual cores  60 ,  61 ,  62   63  and then, bunched together, extrude through a further extrusion die to encase the individual cores in an outer layer  69  incorporating the webs  70 ,  71 ,  72 ,  73 . Alternatively the outer parts of the individual cores  60 ,  61 ,  62 ,  63  may be softened, and then deformed and adhered together to become a single outer layer incorporating the webs. 
         [0045]      FIG. 6  depicts a short section of the cable  6 . As can be seen, one of the cores  60  has been partially separated from the central member  64  by tearing the web  70 . 
         [0046]    The installation of the overhead cable  6  will now be described, with reference to  FIG. 4 . As shown in  FIG. 4 , the cable  6  is first connected to a number of poles  40 ,  41 ,  42 . Distribution points  20 ,  21 ,  22  that are to be connected to the exchange  1  are mounted on, or close to, at least some of these poles. 
         [0047]    The core or cores  60  which are to be connected to a particular distribution point  20  are separated from the main core  64  over the distance between the required branching point  80  and a convenient point some distance further from the exchange  1 —this can typically be the next pole top  81 —and the core can then be cut to length at that point. Thus a branch  60  has been formed in the multicore cable  8 , without severing any of cores  61 ,  62 ,  63  not terminating at the distribution point  20 . The newly free end of the core  60  can then be connected to the distribution point  20 . 
         [0048]    Similar branches to other distribution points  21 ,  22  may be created by peeling off the required cores  61 ,  62 , as shown in  FIG. 4 . 
         [0049]    If required, and as shown in  FIG. 4 , two or more cores  62 ,  63  may be branched off the cable  6  at the same suspension point  82 . In the example shown in  FIG. 4 , a distribution point  22  is to be powered from the exchange  1  and therefore requires an associated power input  27  capable of converting a 110V/230V supply delivered by the exchange to the voltages required by the distribution point  25  itself. The power can be delivered by connecting a power core  63  to the power input  27  associated with the distribution point  22 . This core  63 , together with the optical fiber core  62  connected to the distribution point  22 , are separated from the central core  64  by rupturing the respective webs  73 ,  72 . 
         [0050]    An alternative embodiment is depicted in  FIG. 7 , in which the cores  60 ,  61 ,  62 ,  63  are arranged side-by-side instead of around a central strengthening core  64 , with each core connected to its neighbors by a frangible strip  70 ,  71 ,  73 . The required core (e.g. core  60 ) can then be separated from its neighbor by tearing the respective frangible strip  70 . In this embodiment, each of the cores  60 ,  61 ,  62  containing power cables also carries a wire pair  68  suitable for conventional telecommunications. 
         [0051]    A further embodiment is depicted in  FIG. 8 , in which each core  65 ,  66  comprises a single fiber tube ( 65 ) or power connection ( 66 ), each core being connected by webs  75 ,  76  to the central strength member  64 . One of the cores  65  is shown partially separated from its neighbors in order to diverge from the main cable run to serve a nearby distribution point. A separate core  69  carries a wire pair for conventional telecommunications. 
         [0052]    These embodiments can be formed in a similar way to that described for the embodiment of  FIGS. 5 and 6 , by means of a suitably shaped die for the extrusion process.