Branching accessories for fibre optic cable and methods of installation and use thereof

Abstract

Branching accessories (400; 700) are disclosed, and methods for installing a fibre optic network. The branching accessory comprises a base part (402; 702) connecting incoming and outgoing duct sections (104a, 104b) and a removable first cover part (404; 704). In a first state, the base part and first cover part define a cylindrical pathway substantially continuous with internal bores of the duct sections, allowing a plurality of fibre units (102) to be passed through the accessory without snagging. In a second state, the first cover part is removed to expose an opening in the pathway, allowing a selected fibre unit (102a) to be withdrawn. A branching cover part (424; 724) may subsequently be fitted to the base part to route the selected fibre unit to a customer premises, optionally providing an interior space (426; 726) for storing a coil of the selected fibre unit.

Description

[0001] 3702P.W0.01

[0002] 1

[0003] BRANCHING ACCESSORIES FOR FIBRE OPTIC CABLE AND METHODS OF INSTALLATION AND USE THEREOF FIELD OF THE INVENTION

[0004] The present disclosure relates to installation of cables such as telecommunications cables (e.g. optical fibres or copper wires) to a number of premises. The disclosure relates in particular to a container for storing a length of cable and to methods of deployment of cables using such a container.

[0005] BACKGROUND TO THE INVENTION

[0006] Optical fibre transmission lines can be installed through the ground, through ducts, and through service spaces within buildings by a variety of methods, including direct burying (trenching), pulling through ducts, pushing through ducts, blowing through ducts, and combinations of these. Fibre to the home (FTTH) is the generic term for broadband network architecture that uses optical fibre technology to carry data to a residential dwelling from a broadband service provider via a telecommunications cabinet located near the residential dwelling. More generally, not only homes, but office premises, antennas and other communication devices as well as backhaul communications systems are increasingly connected by optical fibres to the wider telecommunications network. Any mention of ‘customer premises’ or ‘customer terminal’ should be understood to include any termination point where the cable is terminated for use.

[0007] To facilitate the connection of a number of individual premises to the network, a type of cable is known, which comprises multiple fibre units contained loosely within an extruded tube. Once installed in the ground, or on or within a building, the extruded tube can be opened at any point along its length to access the individual fibre units, which extend loosely inside. A selected fibre unit can be accessed, retracted, and rerouted to drop directly to a home I business where fibre provision is required. Several commercial cables of this type are available, including one branded RTRYVA™ from the present applicant. They may be referred to as “pullback cable”, “retractable fibre cable”, or “mid span” / ”mid span access” cable, depending on the manufacturer and user preference. The term “pullback cable” will be used in the following description, as a convenient term for this type of product, and with the existing RTRYVA™ product as a specific known example. Pullback cable offers a number of advantages over traditional cabling solutions because several times more fibre drops can be made from an existing duct compared to traditional cables. Fibre units within pullback cable can contain3702P.W0.01

[0008] 2

[0009] multiple fibres, varying from 2 to 24 fibres per fibre unit. High speed installation and connectivity can be attained with no specialist training, and without breaking or splicing the fibres, where they branch from the pullback cable to the customer premises. GRP strength members are incorporated in the extruded tube to offer additional strength and longevity, without the need for bulky strength members in the individual fibre units.

[0010] In W02022049057A1, there is disclosed a pullback cable in which each fibre unit comprises two or more optical fibres embedded in a solid resin material to form a coated fibre bundle and an extruded polymer sheath made of a mixture of polybutylene terephthalate polymer (PBT) and at least one friction reducing additive. Adopting this form of fibre unit allows a far greater length of a selected fibre unit to be withdrawn through an opening in the extruded tube, potentially in excess of 100m.

[0011] Drop tubes can have a pre-installed draw string to aid fibre installation to the premises, or they may be short enough for installation to be completed just by pushing. Expensive installation equipment, such as fibre blowing is not required.

[0012] Despite these benefits of pullback cables, their use is restricted in some circumstances due to the relatively high purchase cost of the pullback cable for the initial phase of installation. The present disclosure aims to allow the benefits of the pullback cable technique to be realised at lower cost.

[0013] SUMMARY OF THE INVENTION

[0014] A first aspect of the present invention provides a branching accessory for use in a fibre optic cable network, the branching accessory comprising a base part and at least a first cover part, wherein:

[0015] the base part defines first and second ports, the first and second ports being adapted to connect to ends of first and second ducts respectively;

[0016] the base part further defines a channel for guiding a plurality of cable units along a pathway from the first port to the second port, said channel having an internal diameter matched to an expected internal diameter of the first and second ducts and having an open side along at least a part of its length;3702P.W0.01

[0017] 3

[0018] the first cover part by its shape and size is adapted for closing the open side of the base part and to define with said channel a substantially cylindrical bore having said internal diameter matched to an expected internal diameter of the first and second ducts.

[0019] Optionally, one or both of the first and second ports is adapted to mate with the end of the respective first or second duct by receiving the end of the respective duct into an opening in the base part, the opening having an internal diameter matched to an expected external diameter of the respective first or second duct.

[0020] In some examples, a branching cover part is adapted to engage with the base part so as to cover the open side of the channel, the branching cover part including a branching port whereby a selected fibre unit from said plurality of fibre units can be led out from within the channel through the branching port.

[0021] In some such examples, the branching port has a tubular cable guide adapted for coupling to a branching duct, the tubular cable guide having an external diameter smaller the expected external diameter of the first and second ducts.

[0022] In some such examples, the tubular cable guide of the branching port has an external diameter smaller than the internal diameter of the channel in the base part.

[0023] The tubular cable guide of the branching port may have an external diameter 14 mm or less, optionally 8 mm or less, for example 7 mm or 5 mm.

[0024] The tubular cable guide of the branching port may have an internal diameter of 10 mm or less, optionally less than 8 mm, optionally less than 5 mm.

[0025] The expected external diameter of the first and second ducts may for example be greater than 8 mm, optionally greater than 10 mm, for example 14 mm or 16 mm.

[0026] The internal diameter of the channel in the base part may for example be greater than 5 mm, optionally greater than 8 mm, for example 10 mm or 12 mm.

[0027] In some examples, the features and functions of the branching cover part and the first cover part are implemented in a dual-function cover part, the branching port communicating through an opening into said cylindrical bore when the dual-function cover part is fitted to the base part.

[0028] Optionally, the branching port extends in a direction generally perpendicular to the cylindrical bore.3702P.W0.01

[0029] 4

[0030] In some such examples, the opening into the cylindrical bore is splayed in a direction along the cylindrical bore so as to impose a minimum bend radius onto the selected fibre unit, while remaining narrow in a direction transverse to the cylindrical bore.

[0031] In other examples, the first cover part and the branching cover part are separate parts.

[0032] In some such examples, the first cover part and the branching cover part are formed such that one or the other can be fitted to the base part, but not both simultaneously.

[0033] In other such examples the first cover part and the branching cover part are formed such that both the first cover part and the branching cover part can be fitted to the base part simultaneously.

[0034] Optionally in that case, the first cover part can be removed to expose the opening into the channel without removing the branching cover part from the base part.

[0035] In some examples, the branching cover part is formed with an interior space via which the first cover part can be removed from the base part to expose the opening in the base part without removing the branching cover part from the base part, whereby a selected fibre unit from said plurality of fibre units can be led out from within the channel, through said interior space and through the branching port.

[0036] Optionally, the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit.

[0037] The interior space of the branching cover part may for example be adapted for storing a coil of the selected fibre unit having a diameter greater than 90 mm, optionally greater than 100 mm, optionally greater than 110 mm.

[0038] Optionally, the branching cover part is provided with a lid for closing the interior space, the lid being removable for access to the interior space.

[0039] In some examples, the branching cover part is provided with more than one branching port, whereby at least two selected fibres can be led out from within the channel and through respective branching ports.

[0040] In some examples, the branching accessory further includes a branch sealing gasket between the branching cover part and the base part, surrounding the location of the opening.3702P.W0.01

[0041] 5

[0042] The branch sealing gasket may be formed in one piece with a first sealing ring for sealing the first port around the first duct and a second sealing ring for sealing the second port around the second duct.

[0043] There is further disclosed a collection of branching accessories each made according to the first aspect of the invention as set forth above, wherein:

[0044] at least one of said branching accessories is of the type wherein the branching cover part and the first cover part are formed in one piece;

[0045] at least one other of said branching accessories is of the type wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit; and the base parts of all of the branching accessories in the collection are identical.

[0046] According to a second aspect of the invention, there is provided a method of installing a fibre optic network, the method comprising the steps:

[0047] (a) establishing a pathway along a route that extends from a network distribution point to an endpoint and passes a plurality of customer premises, the pathway including a series of branching accessories interlinked by a series of duct sections, each branching accessory comprising a base part and a first cover part and being connected to an incoming duct section and an outgoing duct section so as to define a cylindrical pathway substantially continuous with internal bores of the incoming and outgoing ducts, the first cover part being removable from the base part to expose an opening into said pathway; and

[0048] (b) after step (a) and while the openings of the series of branching accessories are closed by their respective first cover parts, passing at least a first plurality of individual fibre units along the pathway so that each fibre unit extends from the distribution point to the end point..

[0049] In a method where at least one of said branching accessories is of a type wherein the branching cover part and the first cover part are implemented as a dual-function cover part, the branching port communicating through an opening into said cylindrical bore when the dualfunction cover part is fitted to the base part.

[0050] In some such methods, at least one of said branching accessories is of a type wherein the first cover part can be removed to expose the opening into the channel without removing the branching cover part from the base part.3702P.W0.01

[0051] 6

[0052] In some such methods, at least one of said branching accessories is of a type wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit. Optionally, at least one other of said branching accessories is of a type wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit, and wherein the base parts of both of said branching accessories are identical.

[0053] In some methods, the branching accessories include one or more branching accessories according to the first aspect of the invention, set forth above.

[0054] The invention in a third aspect provides a method of progressing a network installation wherein steps (a) and (b) have previously been performed by a method according to the second aspect, as set forth above, the method comprising the step:

[0055] (c) removing first cover part in at least one of said branching accessories and withdrawing a length of a selected fibre unit among the plurality of fibre units, such that the selected fibre unit extends along the pathway from the distribution point as far as the branching accessory.

[0056] A method according to the third aspect may further comprise the step:

[0057] (d1) after step (c) fitting the branching cover part to the base part, with the selected fibre unit extending through the branching port and along a branch pathway towards a customer premises.

[0058] Optionally, the branch pathway is defined by a branching duct coupled to the branching port of the branching cover part.

[0059] A method according to the third aspect may further comprise the step:

[0060] (d2) after step (c), with the branching cover part fitted to the base part, coiling the withdrawn length of the selected fibre unit within an interior space of the branching cover part. The invention in a fourth aspect provides a method of further progressing a network installation wherein steps (a) to (c) and (d2) have previously been performed by a method according to the third aspect as set forth above, the method further comprising the step:

[0061] (e) after step (d2), accessing the length of the selected fibre unit coiled within the interior space of the branching cover part and extending the selected fibre unit through the branching port and along a branch pathway towards a customer premises.3702P.W0.01

[0062] 7

[0063] Optionally, the branch pathway is defined by a branching duct coupled to the branching port of the branching cover part.

[0064] According to a further aspect of the invention, there is provided a method of constructing a fibre optic network infrastructure, the method comprising the steps:

[0065] (a) establishing a pathway along a route that extends from a network distribution point to an endpoint, the pathway including a branching accessory connecting an incoming duct section and an outgoing duct section; and

[0066] (b) after step (a) and while the branching accessory is closed by a first cover part, passing a plurality of fibre units along the pathway so that the fibre units extend through the branching accessory.

[0067] These and other features of the invention will be understood from consideration of the examples described below and the dependent claims, illustrated with the appended drawings.

[0068] BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

[0070] Figure 1 is a cross-section of a known pullback cable comprising a number of loose tube fibre units surrounded by an extruded, reinforced tube;

[0071] Figure 2 illustrates the steps of (a) opening a wall of the extruded tube in a pullback cable of the type shown in Figure 1, (b) pulling back a selected fibre unit and (c) fitting a branching closure around the opened part of the pullback cable;

[0072] Figure 3 illustrates use of a pullback cable to provide optical fibre connections to user premises according to a known method;

[0073] Figure 4 illustrates steps in the connection of a user premises to an optical fibre network without preinstalling a pullback cable, using a first schematic example branching accessory made according to the present invention;3702P.W0.01

[0074] 8

[0075] Figure 5 illustrates steps in the connection of a user premises to an optical fibre network without preinstalling a pullback cable, the method being performed using a second schematic example branching accessory made according to the present invention;

[0076] Figure 6 illustrates one step in the connection of a user premises to an optical fibre network without preinstalling a pullback cable, the method being performed using a third schematic example branching accessory made according to the present invention;

[0077] Figure 7 shows a detailed example of a branching accessory made according to the second schematic example of Figure 5, in (a) top perspective view and (b) bottom perspective view; Figure 8 is an exploded view of the example branching accessory of Figure 7;

[0078] Figure 9 shows interior views of the example branching accessory of Figures 7 and 8, (a) with a first cover part in place and (b) with the first cover part removed;

[0079] Figure 10 is an external perspective view of a detailed example of a branching accessory made according to the third schematic example of Figure 6;

[0080] Figure 11 is an exploded view of the example branching accessory of Figure 10; and Figure 12 illustrates use of branching accessories according to the above examples to provide optical fibre connections to user premises according to a new method.

[0081] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0082] As mentioned in the introduction, the present application discloses a variety of branching accessories and methods for use with lightweight optical cables that will be referred to as a “fibre unit”. For the sake of example only, the fibre unit may comprise two or more optical fibres embedded in a solid resin material to form a coated fibre bundle and an extruded polymer sheath covering the coated fibre bundle. Particular examples of such fibre units are described in W02022049057A1 , wherein the extruded polymer sheath of each said fibre unit comprises a mixture of polybutylene terephthalate polymer, PBT, and at least one friction reducing additive. Other types of fibre units can of course be used in the methods described herein, provided they have suitable robustness and low surface friction.

[0083] Reference to fibre units and optical fibres does not exclude the possibility that electrical conductors are included, in a so-called hybrid cable. The fibre units in the following examples3702P.W0.01

[0084] 9

[0085] may have diameters as little as 1 mm, but the same principles can be applied with miniature cables of more substantial construction. Fibre units in other examples may have diameters of 2 mm or 3 mm. It will be understood that the dimensions of all ducts and accessories will be scaled up or down to accommodate the type of fibre units used in a given application.

[0086] Figure 1 is a schematic cross-section of a pullback cable 100, which may for example be the one known from W02022049057A1. The cable 100 in this example comprises a plurality of fibre units 102 extending in parallel with one another within an extruded polymer tube 104. The fibre units 102 are free to slide relative to one another and to the tube 104 such that a selected fibre unit 102 can be accessed and re-directed by forming an opening in a wall of the tube 104 and withdrawing a length of the selected fibre unit 102 through the opening.

[0087] Figure 2 illustrates this opening and pullback operation. A short section of the product is shown at (a), with the fibre units inside shown in broken lines. As seen at (b), an opening 120 is formed in the wall of the extruded tube 104 by cutting with a blade, which may be mounted in a special tool in a known manner. One individual fibre unit 102a is selected, for example by colour code, and pulled in a direction 122 from inside the extruded tube 104. Other fibre units 102b and 102c remain within the tube 104. At (c), a branching accessory 200 is fitted around the opened section of tube, to form a protective enclosure. Branching accessory 200 in this example comprises a box-like base part 202 with an openable lid 204. A first port 206 and a second port 208 are provided for the entry and exit of the pullback cable 100. A branching port 210 is provided, through which the selected fibre unit 102a exits the enclosure, protected by a branch duct 212. The application of this will be described further below, with reference to Figure 3.

[0088] Returning to the construction of the pullback cable 100, shown in Figures 1 and 2, each fibre unit 102 may for example comprise two or more optical fibres 106 embedded in a solid resin material to form a coated fibre bundle and an extruded polymer sheath 108 covering the coated fibre bundle. Use of other types of fibre units is not excluded. The optical fibres 106 are generally so-called primary coated optical fibres, in which the glass core and glass cladding layers are coated with layers of resin immediately upon formation, to provide buffering and to protect the surface against damage. The number of optical fibres 106 within each fibre unit 102 may vary, for example ranging from 2 to 12. All of the fibre units 102 in the illustrated example comprise two optical fibres 106, but some or all of the fibre units 102 in another example product may contain four fibres, or a different number. The number of fibres 1023702P.W0.01

[0089] 10

[0090] within each fibre unit 102 may vary between products, and some fibre units may contain different numbers of fibres 106, to provide flexibility of application.

[0091] Similarly, the number of fibre units in the pullback cable, and hence the number of optical fibres, may vary, with typical numbers being 12, 24 or 48 fibre units. Higher numbers such as 96 fibre units are possible if desired. The different fibre units 102 are made with different colours of extruded sheath 108, so that they may be identified in the finished pullback cable. Also included in the wall of the extruded tube are strength members 112. The tube wall is provided with stripes or other external markings 114, so that the locations of the strength members 112 can be identified. This allows the strength members to be avoided when making the opening 120. In a known example, stripes of different coloured polymer are co-extruded with the main wall body to provide the external markings 114. To produce the pullback cable 100, the appropriate number of fibre units 102 are prefabricated. Fibre units, strength members etc. are then bundled together and passed through an extrusion die which forms the extruded tube 104, as described in W02022049057A1.

[0092] Referring now to Figure 3, pullback cables 100 have been developed as a quick and easy solution for connecting homes and businesses to a fibre optic communications network. Within the extruded tube of the pullback cable 100, multiple fibre units are installed during manufacture. Once the pullback cable 100 is installed, duct access & branching of individual fibre units from the pullback cable 100 to individual customer access points is quick and easy and uses the minimal tools, training and installation equipment. Fibres are accessed, excess fibre is pulled back out of the duct, then branched to the customer premises through a dedicated drop duct

[0093] Referring to Figure 3(a), a length of pullback cable 100 is installed, over a route extending from a distribution point 302, such as a splicing cabinet, and passing a number of customer premises 304. In a step SO, the pullback cable 100 is pulled into a duct, or installed into an open trench along the desired route. (In multi-storey premises, the cable may be fixed into a vertical riser shaft). In the splice cabinet or other distribution point 302 the fibres are fixed in place and can be spliced at once if required, or left un-terminated, until one by one they are required.

[0094] Referring then to Figure 3 (b), suppose it is desired to make a fibre connection to the middle premises 304, which is provided with a customer access point 306. In a step S1 , a cutting tool is used to cut the extruded tube 104 (as illustrated in Figure 2 (b)) to create openings C1 and C2 as shown. At the opening C1, which is at a location beyond opening C2 a selected fibre3702P.W0.01

[0095] 11

[0096] (call it 102a, the same as in Figure 2) is identified within the open tube 104, and cut, to free its end. Then, at opening C2, the section of selected fibre unit 102a is withdrawn from the tube 104 into a coil as shown at 308. Although the coil 308 is shown loose, it will be understood that in practice it will be safely gathered in a pan or on a reel. The position of the opening C2, and the length of the withdrawn section, are such that the withdrawn section is long enough to reach the customer access point 306.

[0097] Referring then to Figure 3 (c) in a step S2, a branching duct 310 is installed from the opening C2 to the customer access point 306, and the withdrawn section of the selected fibre unit 102a is fed through the duct until it emerges at the customer access point 306 as marked. For short distances, pushing may be an adequate installation method. In other cases, pulling may be used, for example using a pulling line that has been pre-installed in the branching duct 310. With fibre units of the type disclosed in W02022049057A1, for example, pulling back installation over 100 m or even 200 m is possible, by pulling, pushing or blowing.

[0098] It will be understood that, as an alternative to installing the branching ducts 310 only at the time of need, branching ducts can be pre-installed for all the customer premises 304. At each opening C1, C2, not shown or described in detail, an enclosure 200 having suitable ports and seals, is provided to protect the opening, and the exposed ends of the branching duct or ducts, against the environment after installation. More than one branching duct can be accommodated in a typical enclosure, to serve multiple customer premises from one opening 120.

[0099] The pullback cable provides many advantages in practice. For example, the use of the pullback cable 100 provides for branching without the need to make cuts and splices of the optical fibres at the branch location. The fibre unit 102a is continuous from the distribution point 302 to the customer access point 306. Additionally, if strength members 112 are necessary to protect the fibres during installation of the cable, these can be provided in the extruded tube 104, so that little strength is required in the fibre units 102 themselves, Consequently, the overall design of a pullback cable can be very compact, compared with what would be required to accommodate the same number of fibre units as individual cables. This is a very significant advantage, given the high cost of “real estate” within the ground, within ducting, and within risers and service spaces of buildings.

[0100] While the pullback cable offers these advantages, and is popular in use, for some installations it is not economically attractive. The cable, once it has been manufactured in a length of a kilometre or more, has a certain number of fibres and fibre units in, enough for a particular3702P.W0.01

[0101] 12

[0102] street or neighbourhood. At the same time, it may be that only 5% to 25% of premises are signed up for connection during the initial connection phase. The initial cost of installing the cable includes the cost of all the fibre units, when the remaining customer premises may not be connected for weeks, months or years. In some situations, therefore, the initial cost of installing a pullback cable is prohibitive, even though savings may be realised when more customers are eventually connected.

[0103] NOVEL BRANCHING ACCESSORIES - FIRST SCHEMATIC EXAMPLE

[0104] Figure 4 illustrates steps (a) to (i) in the connection of a user premises to an optical fibre network using a novel type of branching accessory and installation technique. The novel branching accessories enable many of the benefits of pullback cables to be realised in the field, without the initial expenditure and inflexibility of specifying and installing a particular size of pullback cable. In Figures 4, 5 and 6, the key features of different example branching accessories will be presented by reference to schematic examples. More detailed examples of branching accessories will be presented further below, with reference to Figures 9, 10 and 11. The illustrations and description focus on one specific branching point. An example of using a collection of such accessories to install a fibre optic communications network between a distribution point and various customer premises will be illustrated schematically in Figure 12.

[0105] In Figure 4, a continuous tubular duct is labelled 104’, by analogy with the tube of the known pullback cable 100. In step (a) the duct 104’ is empty, but it has, for example, a similar size and structure to the extruded tube 104 of the known pullback cable. It may or may not have strength members, depending on the application. An inner surface of the duct is labelled 110’. For the sake of example, a microduct of 16 mm outer diameter and 12 mm inner diameter may be envisaged, with a low friction lining similar to what is described for the pullback cable in W02022049057A1. As the method progresses, within the duct 104’ there will be shown fibre units generally labelled 102, with specific selected fibre units labelled 102a, 102b etc.. These fibre units may be identical to the fibre units 102 in the known pullback cable.

[0106] As illustrated in step (b) of Figure 4, by cutting a short length out of the duct 104’ after it has been installed along a desired route, first and second ducts 104a and 104b are formed, with their ends spaced a short distance apart around a desired branching point. In principle, individual first and second ducts could be laid either side of the branching point.3702P.W0.01

[0107] 13

[0108] A branching accessory 400 in this schematic example comprises a base part 402, and a first cover part 404. The base part defines first and second ports 406 and 408 which are adapted to connect to ends of first and second ducts. In the illustrated example, each of the first and second ports 406, 408 is adapted to mate with the end of a respective first or second duct 104a, 104b by receiving the end of the respective duct into an opening in the base part 402. These port openings have an internal diameter matched to an expected external diameter of the respective first or second duct, for example 16 mm as mentioned above. Various arrangements for sealing and fixing the duct ends in the ports will be provided in a practical example, as seen in the detailed examples below.

[0109] In step (c) the branching accessory 400 is fitted, with its first port 406 receiving the end of the first duct 104a and its second port 408 receiving the end of the duct 104b. Dotted lines illustrate hidden parts within the body of the branching accessory 400. An interior surface 412 of base part 402 defines a channel 440 along a pathway from the first port to the second port, said channel having an internal diameter matched to an expected internal diameter of the first and second ducts (for example 12 mm). The channel in the base part 402 has an open side along at least a part of its length being the side facing upwards in Figure 4. The first cover part 404 by its shape and size is adapted for closing the open side of the base part is shown schematically. Furthermore, an interior surface 414 of the first cover part is shaped so as to define with said channel a substantially cylindrical bore having said internal diameter matched to an expected internal diameter of the first and second ducts.

[0110] In this way, the assembled branching accessory provides a continuous, unobstructed pathway from the internal bore of the first duct 104a and the second duct 104b. This can be seen in Figure 4 (c), where the dotted lines representing the interior surfaces 412 and 414 of the assembled branching accessory 400 are aligned with the inner surfaces of the first and second ducts 104a and 104b. At this point, it may be considered that a first phase of the network installation has been completed. In a next phase of installation, whether on the same day or at a later date, fibre units will be installed through the pathway. One way of doing this, as illustrated, is to feed a pushing rod 420 along the pathway in the direction indicated by arrows, as a precursor to the installation of a plurality of fibre units. In other methods, a pulling line may be pre-installed, or blown through the pathway, as desired.

[0111] In step (d) the pushing rod 420 is used to pull a bunch of fibre units 102a, 102b, 102c etc along the pathway, incoming through the first duct 104a, through the cylindrical bore of the assembled branching accessory 400 and going out through the second duct 104b. Depending3702P.W0.01

[0112] 14

[0113] on the number required, they may be pulled through in a single bunch, or a number of bunches may be pulled through in a staggered formation for example, 12 fibre units may be pulled through as a single bunch, while 30 fibre units may be pulled through in three bunches of 10. The fibre units within each bunch may be distinguished from one another by colour coding in the customary manner. The fibre units of different bunches may be provided with different ring markings every few centimetres. In addition to the fibre units, a conductive wire may be included with the bunch of fibre units, so that the pathway can be located after burial. A pulling line can also be included for additional future fibre installation. Instead of pulling the fibre units directly with the pushing rod 420, the pushing rod can be used to install a pulling line through the pathway. This pulling line can be used immediately, or left in place for use at a later date. It will be understood that the fibre units individually and collectively require certain strength and lack of frictional engagement with the interior surface 110 of the duct 104’, commensurate with the length of the pathway and any twists and turns it may involve. As taught in W02022049057A1, the particular form of fibre unit described therein and used in the present example has particularly beneficial properties on both of these counts, meaning that a bunch or bunches of fibre units can be pulled tens, and even hundreds of metres without difficulty and without damage to the delicate optical fibres within.

[0114] Figure 4 (e) shows the assembled branching accessory and the first and second ducts with the desired number of fibre units safely installed through the pathway. At this point, a second phase of the network installation is completed. It may be noted that, at this point, the state of the installation is similar to that where a conventional pullback cable has been laid. However, the number of fibre units pulled along the pathway in this example can be determined according to the needs of an individual route. Furthermore, each branching accessory serves the function of an opening, which would conventionally be formed by cutting the extruded tube 104 of the conventional pullback cable. Rather than fitting a branching enclosure 200 around the opening after it has been formed in the next phase of operation, the novel branching accessory 400, already serves to protect the fibre units in the vicinity of the opening.

[0115] Figure 4 (f) shows the beginning of a third phase of installation, which may be performed on the same day, the next day, or weeks months or years after the second phase. In this phase, the first cover part 404 of the branching accessory 400 is removed from base part 402, without disturbing the connection to the incoming and outgoing first and second ducts. With the first cover part removed, the channel formed in the base part 402 is open. As seen at (g), a selected one of the fibre units 102a can be withdrawn in the direction illustrated by an arrow, in exactly3702P.W0.01

[0116] 15

[0117] the same way as the corresponding fibre unit was withdrawn in the from the known pullback cable 100 of Figure 2 (b).

[0118] In this first schematic example, the withdrawn length of the selected fibre unit 102a will not be routed immediately to a customer premises. Rather, as seen in Figure 4 (h), a branching cover part 424 space having an interior space 426 is fitted to the base part 402 and the withdrawn length of fibre unit 102a is stored in a coil at the branching point. The branching cover part 424 engages securely with the base part 402 to seal the opening, the fibre units and the pathway from the environment. At this point, another phase of the installation process has been completed, and the withdrawn length of the selected fibre unit 102 a may be left in this stored state for a day, or for weeks, months or years. The described sealing arrangements may prevent dust ingress to the pathway. The described sealing arrangements may be air-tight and water-tight provided so that, for example, the pathway shall be prevent water ingress for at least 24 hours under at least 0.5 metres water pressure. The same sealing arrangements can serve (i) when there is no fibre in the system, (ii) when fibre has been added to the system and (iii) when fibre has been added to the system and branched to the customer.

[0119] Branching cover part 424 in this example is provided with a branching port 428. In a next phase of operation, as illustrated in Figure 4 (i), the branching point is visited again to withdraw the fibre unit 102a, so that it may be routed along a branch pathway to complete the connection to one particular premises. In this example, the branching port 428 is provided as an integral part of the branching cover part 424 from the start. The branching port may be temporarily capped or plugged to be isolated from the environment. Alternatively, during the storage phase the branching cover part may have a lid with no branching port, and be fitted with a branching port later.

[0120] In the illustrated example, the branching port 428 includes a tubular cable guide 430 projecting from the branching cover part 424. In this way, the branching port 428 is adapted for coupling to a branching duct 310’, similar to the branching duct seen in the known method of Figure 3. A standard push-fit connector 432 can be used for this. The connector includes seals to protect the inside of the ducts from the environment. In the illustrated example, each of the first and second ports 406, 408 is adapted to mate with the end of the respective first or second duct by receiving the end of the respective duct into an opening in the base part, the opening having an internal diameter matched to an expected external diameter of the respective first or second duct. In principle, any of the ports may have a different form, male or female. For example, in any of the examples, the first port and / or second port may be provided with a projecting tubular3702P.W0.01

[0121] 16

[0122] guide (not shown). Providing the first and second ports in a female form allows for a compact design, and fewer parts. Seals can be incorporated around the openings in the base part, as will be seen in the detailed examples described further below..

[0123] Returning to the branching port 428, the tubular cable guide 430 and branching duct 310’ will typically have an external diameter smaller than the expected external diameter of the first and second ducts. Indeed, the tubular cable guide of the branching port may have an external diameter smaller than the internal diameter of the first and second ports 406, 408 and the channel in the base part. The tubular cable guide 428 of the branching port may have an external diameter 14 mm or less, for example 10 mm, 8 mm, 7 mm or 5 mm. The tubular cable guide 428 of the branching port may have an internal diameter less than 5 mm. The branching duct 310’ may for example have outer / inner dimensions or 14 / 10, 12 / 8, 10 / 8, 8 / 4, 7 / 4, 7 / 3.5, 5 / 3.5. Even thinner ducts may be used, for example in in-building installations. The robustness required of the duct depends on the intended installation environment and installation method. The internal diameter required depends on the dimensions of the fibre unit or units to be carried, and the installation method.

[0124] SECOND SCHEMATIC EXAMPLE

[0125] Figure 5 illustrates steps in the connection of a customer premises to an optical fibre network without preinstalling a pullback cable, the method being performed using a second schematic example branching accessory 500. Only steps (a) and (b) are shown in Figure 5, which correspond effectively to the steps (d) and (f) in Figure 4. Other steps before and after can be the same as in Figure 4. Features of the branching accessory 500 are numbered similarly to those of the branching accessory of the first schematic example, but with prefix ‘5’ instead of ‘4’.

[0126] Branching accessory 500 in this schematic example comprises a base part 502, and a first cover part 504. The base part defines first and second ports 506 and 508 which are adapted to connect to ends of first and second duct 104a and 104b. As seen in Figure 5 (a), in this example the first cover part 504 and the branching cover part 524 are formed such that both can be fitted to the base part simultaneously. Both parts are fitted between the ends of the first and second ducts 104a, 104b from the outset. As in the previous example, an interior surface 514 of the first cover part combines with an interior surface 512 of the channel formed3702P.W0.01

[0127] 17

[0128] in the base part 502 to define a cylindrical pathway substantially continuous with the internal bores of the incoming and outgoing ducts.

[0129] As seen in Figure 5 (b), the top of the first cover part 504 is accessible from within the interior space 526 of the branching cover part 524 and can be removed so that the channel in the base part is in communication with the interior space 526 of the branching cover part. A selected fibre unit 102a can be withdrawn, stored and routed in the same way as shown in Figure 4 steps (g) to (i).

[0130] THIRD SCHEMATIC EXAMPLE

[0131] Figure 6 illustrates one step in the connection of a user premises to an optical fibre network without preinstalling a pullback cable, the method being performed using a third schematic example branching accessory. Features of the branching accessory 600 are numbered similarly to those of the branching accessory 400 of the first schematic example, but with prefix ‘6’ instead of ‘4’. In the first and second schematic examples, it will be observed that the first cover part and the branching cover part are separate parts. In the third schematic example, the features and functions of the branching cover part and the first cover part are implemented in one, dual-function cover part 636. As in the previous examples, an interior surface 614 of the cover part combines with an interior surface 612 of the channel formed in the base part 502 to define a substantially cylindrical pathway substantially continuous in diameter with the internal bores of the incoming and outgoing ducts.

[0132] At the same time, the branching port 628 in the third schematic example communicates permanently with the cylindrical pathway through a narrow opening 638, even when the cover part is fitted to the base part. As seen in broken lines, the opening 638 is splayed in a direction along the cylindrical bore so as to impose a minimum bend radius onto the selected fibre unit, while remaining narrow in a direction transverse to the cylindrical bore. In this way, large-diameter and / or stiffer items such as the pushing rod 420 and the bunch of multiple fibre units will reliably follow the pathway, while one or more individual fibre units can be withdrawn and routed through the branching port 628, when required.

[0133] It may be noted that the branching port 628 and associated tubular cable guide 630 in this example lead in a direction generally perpendicular to the cylindrical pathway. This makes the whole accessory agnostic as to which of the first and second ports is an incoming port and which port is an outgoing port. The branching port is generally smaller than the first port and3702P.W0.01

[0134] 18

[0135] second port, reflecting that it is for carrying typically one fibre unit, and not the full set of fibre units carried through the cylindrical pathway. The ducts 104a, 104b forming the pathway will likewise be bigger than the branching duct. For example, where the fibre units have a diameter in the range 1-2 mm, incoming and outgoing ducts of the pathway may have size 16 / 12 (external / internal diameter in mm) while the branching duct has size 7 / 4 or 5 / 3.5. In an example with fibre units of larger diameter, such as 2, 3 or 4 mm, the branching duct may have and external diameter as large as 14 mm, for example, and the incoming and outgoing ducts will be correspondingly larger than that.

[0136] As illustrated by arrows in Figure 6, the cover part can be removed from the base part to access the bunch of fibre units and withdraw a selected one or more. Once the selected fibre unit has been routed out through the branching port, the dual-function cover part 636 is replaced to close the channel and protect the interior space of the base part and the conduits against the environment. Effectively, the dual-function cover part 636 performs the function of the first cover part 604 in the earlier phases of a network deployment process, is removed and then replaced. After it is replaced it is performing the function of the branching cover part 624. It may be noted that the form of the base part 402 / 502 / 602 does not change between the different examples Figures 4 to 6. As will be seen from the detailed examples described in the following, a collection of different branching accessories can be designed and manufactured which all share common base part, including connection and sealing arrangements. It may also be noted that the base part and the first and second ports are symmetrical and interchangeable further simplifying the design, manufacture and use of the product in the field. In all of these examples, and in the detailed examples described below, it will be appreciated that the accessory can be made very compact, saving on the size of enclosures for example in a road surface. Where cover parts and base parts have to be assembled together in the field, with careful design these operations can be performed with one hand in a confined space.

[0137] FIRST DETAILED EXAMPLE BRANCHING ACCESSORY

[0138] Figure 7 shows a detailed example of a branching accessory made according to the second schematic example of Figure 5, in (a) top perspective view and (b) bottom perspective view. Features of the branching accessory 700 are numbered similarly to those of the branching accessory 500 of the second schematic example, but with prefix 7’ instead of ‘5’. Branching3702P.W0.01

[0139] 19

[0140] accessory 700 comprises a base part 702, and a first cover part 704. The base part defines first and second ports 706 and 708 which are adapted to connect to ends of first and second duct 104a and 104b (not shown in this drawing).

[0141] Figure 8 is an exploded view of the example branching accessory of Figure 7. Figure 9 shows interior views of the same branching accessory (a) with a first cover part 704 in place and (b) with the first cover part removed. As seen in Figures 8 and 9, in this example the first cover part 704 and the branching cover part 724 are formed such that both can be fitted to the base part 702 simultaneously. As in the previous example, an interior surface (714 not visible in Figures 8 and 9) of the first cover part combines with an interior surface 712 of the channel formed in the base part 702 to define a cylindrical pathway substantially continuous with the internal bores of the incoming and outgoing ducts.

[0142] As best seen in Figure 9 (a), the top of the first cover part 704 is accessible from within the interior space 726 of the branching cover part 724. First cover part 704 in the illustrated example is fixed in place with three screws (not shown) which pass through holes 730 in a main body of the branching cover part 724 and into the base part 702. First cover part 704 has tab portions 732 with corresponding holes. With these screws removed, the first cover part 704 can be removed (Figure 9 (b)) so that the channel 740 in the base part is in communication with the interior space 726 of the branching cover part. It will be understood that screws are only one type of fixing that could be used to hold the first cover part 704 in place over the channel 740. A selected fibre unit 102a can be withdrawn, stored as a coil and eventually routed to a premises in the same way as shown in Figure 4 steps (g) to (i).

[0143] Some further notable features of the branching accessory 700 will now be described. The first and second ports are formed in the base part, substantially as in the schematic examples presented above. Each port 706, 708 has associated with it a fastening post 742, 744 which can be used with a cable tie, to permanently fix the duct 104a, 104b in the port so it does not get pulled out. The design of the branching port is different in this detailed example than in the schematic example above. Specifically, instead of a single branching port there are two branching ports 728a and 728b, allowing two individual fibre units to be selected and routed to two different premises from the same branching point. Instead of having a projecting tubular guide for mating with a connector, each of the branching ports in this example comprises an opening for mating directly with the end of a respective branching duct (not shown).

[0144] In this example branching accessory, a bottom surface of the branching cover part 724 is provided with formations 746, 748 for engaging a flange portion of the base part 702 with a3702P.W0.01

[0145] 20

[0146] snap-fit action to assist in the retention of ducts 104a and 104b. The interior space 726 of the branching cover part is adapted for storing a coil of each selected fibre unit. Such a coil may have a diameter greater than 90 mm, optionally greater than 100 mm, optionally greater than 110 mm. It will be understood that the diameter of the interior space determines the bending radius of the coiled cable. This radius must be larger than a minimum bend radius specified for the fibre units, to avoid impairing optical performance. For fibre units of the type described herein, the minimum bend radius may be as little as 15 times the diameter of the cable. Other types of cable unit may have different specifications. In one example of the type illustrated, an overall diameter of the branching cover part 724 is around 120 mm, similar to the diameter of a compact disc.

[0147] The branching cover part 724 is provided with a lid 748 for closing the interior space 726, the lid being removable for access to the interior space. As seen in the exploded view of Figure 8, a sealing ring 750 of elastomeric material is provided between the lid and the main body of the branching cover part. One or more coiling trays 752 may be provided, to help organising the coil(s) of selected fibre unit(s) within the interior space. Cable management accessories can of course be provided within the interior space. These may include accessories such as splice or splitter inserts, which can be used for repair, upgrades and network cable reorganisation. A branch sealing gasket 754 is arranged to create a seal between the base part 702 and branching cover part 704, surrounding the opening through which the channel 740 is accessed. In this example, the branch sealing gasket 754 is integrated into one moulded piece of elastomeric material, together with a first sealing ring 756 for sealing the first port around the first duct and a second sealing ring 758 for sealing the second port around the second duct. The base part is moulded with recesses 764 receiving and retaining the elastomeric material so that the sealing rings 756, 758 surround the pathway where they will engage the ends of the first and second ducts 104a, 104b. By integrating different sealing parts in this way, a very simple and low-cost manufacture is obtained. As mentioned already, the same base part can be used with a number of different branch closing parts, further reducing cost and simplifying inventory.

[0148] SECOND DETAILED EXAMPLE BRANCHING ACCESSORY

[0149] Figure 10 is an external perspective view of a detailed example of a branching accessory made according to the third schematic example of Figure 6, and Figure 11 is an exploded view of the same branching accessory 800. Features of the branching accessory 800 are numbered3702P.W0.01

[0150] 21

[0151] similarly to those of the branching accessory 600 of the third schematic example, but with prefix ‘8’ instead of ‘6’. Thus, in this example, the features and functions of the branching cover part 824 and the first cover part 804 are implemented in one dual-function cover part 836. An interior surface 814 of the cover part combines with an interior surface 812 of the channel formed in the base part 802 to define a substantially cylindrical pathway substantially continuous in diameter with the internal bores of the incoming and outgoing ducts. A branching port 828 communicates permanently with the cylindrical pathway through a narrow opening 838, even when the cover part is fitted to the base part. As seen in the exploded view of Figure 11, the opening 838 is splayed in a direction along the cylindrical bore so as to impose a minimum bend radius onto the selected fibre unit, while remaining narrow in a direction transverse to the cylindrical bore.

[0152] As mentioned already, the same base part can be used with a number of different branch closing parts, further reducing cost and inventory complications. Accordingly, branching accessory 800 includes a branch sealing gasket 854, together with a first sealing ring 856 for sealing the first port 806 around the first duct and a second sealing ring 858 for sealing the second port 808 around the second duct, identical to the like-numbered features 754, 756, 758 of the first detailed example branching accessory 700. Formations 846 and 848 are provided on the dual-function closing part 836 for engaging of the base part 802. In this example, rather than a snap fitting, the base part 802 and closing part 836 are held together with sliding clips 860 and 862. This facilitates manual assembly and disassembly in confined spaces.

[0153] NETWORK DEPLOYMENT USING THE NOVEL BRANCHING ACCESSORIES

[0154] Figure 12 illustrates use of a branching accessories according to the above examples to provide optical fibre connections to user premises according to a new method. Features in Figure 12 have been given numbers similar to the corresponding features in Figure 3, with prefix T. Thus, the aim of the deployment is to provide optical fibre connections from a distribution point, such as a splicing cabinet, to a number of customer premises.

[0155] Figure 12 (a) illustrates an initial phase of deployment, in which a pathway is established along a route that extends from a network distribution point 1302 to an endpoint 1320, passing by a plurality of customer premises 1304a, 1304b. For the sake of conciseness and clarity, only two premises are shown, labelled 1304a and 1304b. It will be understood that a typical3702P.W0.01

[0156] 22

[0157] deployment may ultimately connect tens of premises at a time, with a corresponding number of branching accessories. On the other hand, not all customers may want to be connected on the first day. Therefore, the present method, as well as the known pullback cable method, allows customer premises to be connected individually or in groups overtime, perhaps weeks, months or years after the initial installation phase. For the sake of example, the premises illustrated are individual dwelling houses which may be distributed along a street. It will be understood that the same methods and accessories, with or without adaptation, can be deployed in other settings, for example where the individual premises are apartments within a multiple dwelling premises, and / or offices within a building premises or any device requiring a fibre connection. Sections of the route may be horizontal, as shown, or vertical, in the case of a multi-storey building.

[0158] As seen in Figure 12 (a) the pathway installed in the initial phase already includes a series of branching accessories connected by a series of duct sections 104a, 104b, 104c, each branching accessory being connected to an incoming section of duct as a first duct and an outgoing section of duct as a second duct. In the illustrated example, different types of branching accessory installed to service the first premises 1304a and the second premises 1304b. A first branching accessory 1800 is made according to the third schematic example described above, having the basic form and functionality of the branching accessory 600 of Figure 6. This branching accessory may in detail have the same form as branching accessory 800 of Figures 10 and 11. A second branching accessory 1700 is made according to the second schematic example described above, having the basic form and functionality of the branching accessory 500 of Figure 5. This branching accessory may in detail have the same form as branching accessory 700 of Figures 7 to 9.

[0159] The duct sections 104a, 104b, 104c may be installed for example in a trench dug in the ground. As described above with reference to Figure 4, these sections may be laid initially in a single length of duct 104’, and subsequently cut at the desired branching points. At each branching point a protective enclosure such as a “Toby box” is installed, which may be completely buried, or openable. A protective enclosure is provided at the endpoint 1320. While only a single length of duct is shown, installations in practice may include two or more ducts laid in the same trench. A first duct may service a first subset of premises, while a further duct serves another group of premises. The trench, in the case of a buried duct, may be a conventional open trench, or it may be conveniently a so-called micro-trench. The use of micro-trenching minimises disruption, using a kind of saw to cut a channel in the ground or pavement surface with just enough width to accept the duct 104’.3702P.W0.01

[0160] 23

[0161] At the end of this initial phase, the openings of the series of branching accessories are closed by respective first cover parts, so that a continuous, unobstructed pathway extends from the distribution point 1302 to the endpoint 1320. As shown in Figure 12 (b), a plurality of fibre units are pulled or otherwise transported along the pathway so that each fibre unit extends from the distribution point to the end point. This may be done, for example using a pushrod as illustrated in steps (c) and (d) of Figure 4. One or more bunches of fibre units may be pulled in a staggered fashion, until the desired number of fibre units is installed along the complete pathway. While it is assumed that the direction of transport leads from the distribution point to the endpoint 1320, in principle, the fibre units may be transported from the endpoint to the distribution point. In the present examples, it is assumed that all fibre units are unterminated at the time of installation, to be fitted with connectors at the distribution point 1302 and the premises, at the appropriate time. Variations of this method may be performed using preterminated fibre units, where space in the duct allows.

[0162] Regarding the installation of the ducts, it may be noted that conventional pullback cables are conveniently installed only in long splice free- lengths. By contrast, the pathway including duct sections and branching accessories as described herein can be installed in sections, then after all these sections have been joined together, the fibres can then be pulled into the ducts to complete the fibre cable system. This reduces the complexity in building fibre networks, and maximises flexibility of scheduling, including to manage disruption in the public realm.

[0163] After the initial installation of the ducts, branching accessories and fibre units, network deployment can be progressed to any or all of the premises at a later date, be it the next day, or after some weeks. Referring now to Figure 12 (c), the first branching accessory 1800 is of the type wherein the branching cover part and the first cover part are implemented as a dualfunction cover part, such as described above with reference to Figure 6 and Figures 10 and 11. This cover part is removed and a length of a selected fibre unit 1102a is withdrawn in the manner described above, so that the selected fibre unit extends along the pathway from the distribution point 1302 only as far as the branching accessory 1800. The cover part is then refitted to the base part, with the selected fibre unit extending through the branching port and along a branch pathway towards a customer premises. A branching duct 1310a is provided to protect the fibre unit along the branching pathway. Also in Figure 12 (c), another operation has been performed to store a length of a second selected fibre unit 1102b within the second branching accessory 1700. Detail of the operations at the different branching points has been described already with reference to Figures 4 to 6, and so the process is described only in outline here.3702P.W0.01

[0164] 24

[0165] Finally, in Figure 12 (d), the time has come when the customer premises 1304b is to be connected to the network. The second branching accessory 1700 is opened to access the stored length of the second selected fibre unit 1102b and to route it through the branching port of the branching accessory and along a branch pathway towards a customer access point 1306b within the second customer premises 1304b. A branching duct 1310b is provided to protect the fibre unit along the branching pathway.

[0166] CONCLUSION

[0167] Using the novel branching accessories and techniques described herein, an efficient network deployment can be achieved without the up-front cost of known pullback cables. Lengths and fibre counts can be tailored to each section of the network, without the requirement to manufacture and keep pullback cables with a range of different fibre counts. Different types of branching units can be used for different deployments, depending on the expected timing and rate of connection of customers to the network.

[0168] The example branching accessories illustrated and described above are adapted to be installed between cut ends of duct sections. In principle, the duct need only be partially cut between the incoming and outgoing duct sections, to provide an opening into the pathway within the branching accessory. Such an arrangement is not illustrated, but can be visualised as a modified version of the branching accessory shown in Figure 2, inside which a first cover is shaped so as to project into the cut opening and restore a cylindrical pathway, substantially continuous with the internal bores of the incoming and outgoing duct sections.

[0169] Details of the fibre units and the extruded tube is used as ducts in the present disclosure may be the same as those described in W02022049057A1. Depending on whether the installation is outdoors or within a building, the polymer of the duct 104’ may vary. In an example for outdoors use, polyethylene, for example high-density polyethylene (HDPE) or medium-density polyethylene (MDPE) may be selected. For indoor use (within buildings) the polyethylene tube body may be substituted by a flame resistant, zero halogen polymer. The lining of the duct may be simply the inner surface of the main body or it may be a low friction lining, as mentioned above.

[0170] While specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention, defined by the appended claims and their equivalents.

Claims

3702P.W0.0125CLAIMS1. A method of installing a fibre optic network, the method comprising the steps:(a) establishing a pathway along a route that extends from a network distribution point to an endpoint and passes a plurality of customer premises, the pathway including a series of branching accessories interlinked by a series of duct sections, each branching accessory comprising a base part and a first cover part and being connected to an incoming duct section and an outgoing duct section so as to define a cylindrical pathway substantially continuous with internal bores of the incoming and outgoing ducts, the first cover part being removable from the base part to expose an opening into said pathway; and(b) after step (a) and while the openings of the series of branching accessories are closed by their respective first cover parts, passing at least a first plurality of individual fibre units along the pathway so that each fibre unit extends from the distribution point to the end point.

2. A method as claimed in claim 1 wherein the branching accessories are branching accessories as claimed in any of claims 12 to 33.

3. A method as claimed in claim 1 or claim 2 wherein at least one of said branching accessories is of a type comprising a branching cover part in addition to the first cover part, and wherein the first cover part can be removed to expose the opening without removing the branching cover part from the base part.

4. A method of progressing a network installation wherein steps (a) and (b) have previously been performed by a method as claimed in any of claims 1 to 3, the method comprisingthe step:(c) removing the first cover part in at least one of said branching accessories and withdrawing a length of a selected fibre unit among the plurality of fibre units, such that the selected fibre unit extends along the pathway from the distribution point only as far as the branching accessory.3702P.W0.01265. A method as claimed in claim 4 further comprisingthe step:(d1 ) after step (c), fitting a branching cover part to the base part, with the selected fibre unit extending through a branching port of the branching cover part and along a branch pathway towards a customer premises.

6. A method as claimed in claim 5 wherein the branch pathway is defined by a branching duct coupled to the branching port of the branching cover part.

7. A method as claimed in claim 4 further comprisingthe step:(d2) after step (c), with a branching cover part fitted to the base part, coiling the withdrawn length of the selected fibre unit within an interior space of the branching cover part.

8. A method of further progressing a network installation wherein steps (a) to (c) and (d2) have previously been performed by a method as claimed in claim 7, the method further comprisingthe step:(e) after step (d2), accessing the length of the selected fibre unit coiled within the interior space of the branching cover part and routing the selected fibre unit through a branching port of the branching cover part and along a branch pathway towards a customer premises.

9. A method as claimed in claim 8 wherein the branch pathway is defined by a branching duct coupled to the branching port of the branching cover part.

10. A method as claimed in any of claims 4 to 9 wherein at least one of said branching accessories is of the type wherein the branching cover part and the first cover part are implemented as a dual-function cover part, the branching port communicating through an openinginto a cylindrical bore of the accessory when the dual-function cover part is fitted to the base part.

11. A method as claimed in claim 10 wherein at least one other of said branching accessories is of the type wherein the interior space of the branching cover part is3702P.W0.0127adapted for storing a coil of the selected fibre unit, and wherein base parts of both of said branching accessories are identical.

12. A branching accessory for use in a fibre optic cable network, the branching accessory comprising a base part and at least a first cover part, wherein:the base part defines first and second ports, the first and second ports being adapted to connect to ends of first and second ducts respectively;the base part further defines a channel for guiding a plurality of cable units along a pathway from the first port to the second port, said channel having an internal diameter matched to an expected internal diameter of the first and second ducts and having an open side along at least a part of its length;the first cover part by its shape and size is adapted for closing the open side of the base part and to define with said channel a substantially cylindrical bore having said internal diameter matched to an expected internal diameter of the first and second ducts.

13. A branching accessory as claimed in claim 12 wherein one or both of the first and second ports is adapted to mate with the end of the respective first or second duct by receiving the end of the respective duct into an opening in the base part, the opening having an internal diameter matched to an expected external diameter of the respective first or second duct.

14. A branching accessory as claimed in claim 12 or 13 wherein a branching cover part is adapted to engage with the base part so as to cover the open side of the channel, the branching cover part including a branching port whereby a selected fibre unit from said plurality of fibre units can be led out from within the channel through the branching port.

15. A branching accessory as claimed in claim 14 wherein the branching port has a tubular cable guide adapted for couplingto a branching duct, the tubular cable guide3702P.W0.0128having an external diameter smaller the expected external diameter of the first and second ducts.

16. A branching accessory as claimed in claim 15 wherein the tubular cable guide of the branching port has an external diameter smaller than the internal diameter of the channel in the base part.

17. A branching accessory as claimed in claim 15 or 16 wherein the tubular cable guide of the branching port has an external diameter 14 mm or less, optionally 8 mm or less, for example 7 mm or 5 mm.

18. A branching accessory as claimed in claim 15, 16 or 17 wherein the tubular cable guide of the branching port has an internal diameter of 10 mm or less, optionally less than 8 mm, optionally less than 5 mm.

19. A branching accessory as claimed in any of claims 15 to 18 wherein the expected external diameter of the first and second ducts is greater than 8 mm, optionally greater than 10 mm, for example 14 mm or 16 mm.

20. A branching accessory as claimed in any of claims 15 to 19 wherein the internal diameter of the channel in the base part is greater than 5 mm, optionally greater than 8 mm, for example 10 mm or 12 mm.

21. A branching accessory as claimed in any of claims 14 to 20 wherein the features and functions of the branching cover part and the first cover part are implemented in a dual-function cover part, the branching port communicating through an opening into said cylindrical bore when the dual-function cover part is fitted to the base part, the branching port optionally extending in a direction generally perpendicularto the cylindrical bore.

22. A branching accessory as claimed in claim 21 wherein the opening into the cylindrical bore is splayed in a direction alongthe cylindrical bore so as to impose a minimum bend radius onto the selected fibre unit, while remaining narrow in a direction transverse to the cylindrical bore.3702P.W0.012923. A branching accessory as claimed in any of claims 14 to 20 wherein the first cover part and the branching cover part are separate parts.

24. A branching accessory as claimed in claim 23 wherein the first cover part and the branching cover part are formed such that one or the other can be fitted to the base part, but not both simultaneously.

25. A branching accessory as claimed in claim 23 wherein the first cover part and the branching cover part are formed such that both the first cover part and the branching cover part can be fitted to the base part simultaneously.

26. A branching accessory as claimed in claim 25 wherein the first cover part can be removed to expose the opening into the channel without removing the branching cover part from the base part.

27. A branching accessory as claimed in any of claims 14 to 26 wherein the branching cover part is formed with an interior space via which the first cover part can be removed from the base part to expose the opening in the base part without removing the branching cover part from the base part, whereby a selected fibre unit from said plurality of fibre units can be led out from within the channel, through said interior space and through the branching port.

28. A branching accessory as claimed in claim T1 wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit.

29. A branching accessory as claimed in claim 28 wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit having a diameter greater than 60 mm, optionally greater than 90 mm, optionally greater than 100 mm, optionally greaterthan 110 mm.

30. A branching accessory as claimed in any of claims T1 to 29 wherein the branching cover part is provided with a lid for closing the interior space, the lid being removable for access to the interior space.3702P.W0.013031. A branching accessory as claimed in any of claims 14 to 30 wherein the branching cover part is provided with more than one branching port, whereby at least two selected fibres can be led out from within the channel and through respective branching ports.

32. A branching accessory as claimed in any of claims 14 to 31 further including a branch sealing gasket between the branching cover part and the base part, surrounding the location of the opening.

33. A branching accessory as claimed in claim 32 wherein the branch sealing gasket is formed in one piece with a first sealing ring for sealing the first port around the first duct and a second sealing ring for sealing the second port around the second duct.

34. A collection of branching accessories each made accordingto any of claims 12 to 33, wherein: at least one of said branching accessories is of the type wherein the branching cover part and the first cover part are formed in one piece; at least one other of said branching accessories is of the type wherein the interior space of the branching cover part is adapted for storing a coil of the selected fibre unit; and the base parts of all of the branching accessories in the collection are identical.

35. A method of constructing a fibre optic network infrastructure, the method comprisingthe steps:(a) establishing a pathway along a route that extends from a network distribution point to an endpoint, the pathway including a branching accessory connecting an incoming duct section and an outgoing duct section; and(b) after step (a) and while the branching accessory is closed by a first cover part, passing a plurality of fibre units along the pathway so that the fibre units extend through the branching accessory.

36. A method of progressing a network installation wherein steps (a) and (b) have previously been performed by a method as claimed in claim 35, the method comprising the step:3702P.W0.0131(c) removing the first cover part from the branching accessory and withdrawing a length of a selected fibre unit among the plurality of fibre units, such that the selected fibre unit extends along the pathway from the distribution point as far as the branching accessory.

37. A method as claimed in claim 36further comprisingthe step:(d1 ) after step (c), fitting a branching cover part to the branching accessory, with the selected fibre unit extending through a branching port of the branching cover part and along a branch pathway towards a customer premises.

38. A method as claimed in claim 36 further comprisingthe step:(d2) after step (c), fitting a branching cover part to the branching accessory and coiling the withdrawn length of the selected fibre unit within an interior space of the branching cover part.

39. A method of further progressing a network installation wherein steps (a) to (c) and (d2) have previously been performed by a method as claimed in claim 38, the method further comprisingthe step:(e) accessing the length of the selected fibre unit coiled within the interior space of the branching cover part and routing the selected fibre unit through a branching port of the branching cover part and along a branch pathway towards a customer premises.

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