WO1992008302A1

WO1992008302A1 - Fiber optic telecommunications network

Info

Publication number: WO1992008302A1
Application number: PCT/US1991/008097
Authority: WO
Inventors: Philip E. Gunn
Original assignee: The Ohio Bell Telephone Company
Priority date: 1990-11-05
Filing date: 1991-11-01
Publication date: 1992-05-14
Also published as: AU9026991A

Abstract

An optical communications network comprising a transmitter (28b) for transmitting a message along a plurality of transmitting paths, a receiver (28a) for receiving a message from a plurality of receiving paths, and first and second couplers (34) for facilitating optically coupling a plurality of paths, wherein one of the transmitting paths is optically coupled to one of the receiving paths through the second coupler, and the other transmitting and receiving paths form the same path. A method of communicating between a central office and a subscriber comprising the steps of transmitting an optical message along a first path (22) between the subscriber (16) and the central office (12), simultaneously transmitting the message along a second path to an intermediate location, optically coupling the message transmitted and third paths establish a path between the subscriber and the central office, and receiving the message from the first path and the path established by the second and third paths.

Description

Tide: FIBER OPTIC TELECOMMUNICATIONS NETWORK

FIELD OF THE INVENTION The present invention relates generally to communications networks, and, more particularly, to an optical fiber network providing redundant telephone service.

BACKGROUND OF THE INVENTION

Telephone networks providing services ranging from voice to data communications are well known and have been available for many, many years. However, with businesses developing more data intensive communication needs, as well as the desire for uninterrupted service, the current copper conductor technology has become a limiting factor in a telephone network the availability of many desirable services. To expand telecommunications capabilities optical fibers, which provide a greater data transmission rate with less noise than copper conductors, have been used with increasing frequency.

Further, to provide uninterrupted .service to many businesses relying on consistent voice and data transmission capabilities, networks have been developed that will link a subscriber to one or more central offices through separate paths. Consequently, if one path providing service to the subscriber is severed or otherwise becomes inoperable, communication to the primary central office can be had over the other path. Similarly, if a central office becomes inoperable, such as due to a fire, communication paths may be made available to a separate central office.

However, many optical fiber telecommunications networks to date have been expensive and very inflexible. For example, to change the capabilities of an installed optical network such as to provide redundant service to an interexchange carrier, such as AT&T, MCI, Sprint, etc. , often requires extensive modifications and installations of additional hardware which may be quite expensive and impractical.

It would be desirable that a telecommunications network provide redundant service to one or more central offices while mainώning the flexibility to be modified to provide additional services or to change services relatively easily and inexpensively. SUMMARY OF THE INVENTION The present invention provides a redundant optical fiber telecommunication network that employs a splice hub to facilitate flexible operation. Through the splice hu a subscriber may be provided with service protection to a single central office or to second or third central office, as well as to an interexchange carrier.

According to one aspect of the invention, an optical communications networ includes transmitting means for transmitting a message along a plurality of transmittin paths; receiving means for receiving a message from a plurality of receiving paths, an coupling means for facilitating optically coupling of a plurality of paths; wherein on transmitting path is optically coupled to one receiving path through the coupling means and the other transmitting and receiving path form the same path.

According to another aspect of the invention, a method of communicating betwee a central office and a subscriber includes the steps of transmitting an optical messag along a first path between the subscriber and the central office; simultaneousl transmitting the message along a second path to an intermediate location; opticall coupling the message transmitted to the intermediate location to a third path; wherein th s^econd and third paths establish a path between the subscriber and the central office; an receiving the message from the first path and the path established by the second and thir paths. In another aspect of the invention including an optical telecommunication metho comprises the steps of passing a first set of at least four optical fibers from a centr office to a splice hub along a route in the vicinity of a subscriber; passing a second s of at least four optical fibers from the central office to the splice hub; coupling the fir set of optical fibers to the second set of optical fibers in the splice hub; and severing least two fibers of the first set of optical fibers and coupling the severed ends to subscriber, while leaving at least two other fibers of the first set of fibers unsevered.

In another aspect of the present invention a method of providi telecommunications services from a user serviced by a primary central office in existing copper network to a secondary central office includes the steps of passing at lea two optical fibers between the secondary central office and the primary central offic severing two fibers of the at least two optical fibers at an intermediate location; a optically coupling the user at the intermediate location to the severed ends of the tw optical fibers of the at least two optical fibers extending towards the central office.

These and other objects, advantages, features and aspects of the present inventio will become apparent as the following description proceeds. To the accomplishments of the foregoing and related ends, the invention, the comprises the features hereinafter fully described in the specification and particularl pointed out in claims, the following description and the annexed drawings setting fort in detail a certain illustrative embodiment of the invention, this being indicative however, of but one of the various ways in which the principals of the invention may b employed. It will be appreciated that the scope of the invention is to be determined b the claims and the equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings: Figure 1 is a schematic representation of a redundant communications networ employing one centra office in accordance with one aspect of the present invention;

Figure 2 is a schematic representation of a redundant communications networ employing one central office and a redund-ant communications path to the interexchang carrier; Figure 3 is a schematic representation of a redundant communications networ employing communications paths to two central offices;

Figure 4 is a schematic representation of a redundant communications networ employing communications paths to two central offices as well as a redundan communications path to the interexchange carrier; Figure 5 is a schematic illustration of a redundant communications network including two central offices each providing redundant paths to an interexchange carrier; and

Figure 6 is a schematic representation of a communications network employing a diversity hub to provide selected subscribers on an already existing network access to a second central office. DETAILED DESCRIPTION OF THE INVENTION With reference now to the several figures in which like reference numerals depict like items, and initially to Figure 1, there is shown a redundant communications network 10 configured in accordance with one aspect of the present invention. The network 10 includes a central office 12 which handles communication between subscribers on the network and other local users or to long distance users through -an interexchange carrier 14, a number of locations housing subscribers 16, 18, a splice hub 20 and main and protect cables 22, 24, respectively, establishing communications paths between the central office, the subscriber locations, and the splice hub. As shown in Figure 1 each of the subscriber locations may be a separate building, such as an office building, preferably located in relatively close proximity to each other and to the central office as would be typical in a city or on a college campus. It will be appreciated that each subscriber location may include and usually does include several separate users and exchange numbers. The main cable 22, which preferably consists of a number of optical fibers, for example ninety-six, is laid from the central office 12 along a path which would cause it to pass in close proximity to a number of potential subscriber locations, for example, the buildings denoted as 16 and 18 in Figure 1, to splice hub 20. The main cable 22 then terminates in the splice hub 20. Optical communication from the splice hub 20 to the central office 12 is accomplished over the protect cable 24 preferably following the shortest convenient path between the splice hub and the central office. The protect cable 24 further preferably includes the same numbe of optical fibers as the main cable, in this inst^ce ninety-six, although it may contai more or fewer.

The central office 12 and the splice hub 20 are physically connected to each fibe of the main and protect cable 22, 24 through a light guide frame 26. The light guid frame 26 facilitates easy physical and optical coupling between the optical fibers of cable and a separate optical fiber for providing the optical signal to a separate device cable, etc. of the system. In the central office 12 the individual optical fibers of the mai and protect cables 22, 24 terminating in the light guide frame 26 are optically couple to a fiber optic terminal 28a, 30a devoted to communication with the subscriber locatio from which the particular optical fiber supplied optical communication. A fiber opti terming takes an electrical signal, multiplexes it, and converts the resultant signal to a optical signal for distribution over the fiber optic cable. Working in reverse, the same fiber optic terminal takes an optical signal received over the fiber optic cable, converts it to an electrical signal and demultiplexes for communication to the intended user. In the subscriber locations 16, 18 the optical fibers providing a communication path for the users in that location are coupled directly to a fiber optic terminal 28b, 30b, respectively, located in each subscriber location. Consequently, there will be a fiber optic terminal 28a, 30a in the central office 12 corresponding to a fiber optic terminal 28b, 30b in each subscriber location 16, 18. For example, the fiber optic terminal 28a in the central office 12 will communicate via fibers in the main or protect cable 22, 24 with a fiber optic terminal 28b in subscriber location 16, while fiber optic terminal 30a will communicate with a corresponding fiber optic terminal 30b in subscriber location 18, etc. It is noted that while the networks shown in the embodiments of Figures 1-4 specifically depict two subscriber locations, this is merely illustrative. A typical network embodying the invention could include several subscriber locations with the central office including a separate fiber optic terminal devoted to communication with each.

The network 10 illustrated in Figure 1 provides redundant paths for communications between the central office 12 and the individual subscriber locations. For instance, for a user in subscriber location 16 to send a telephone call to the central office 12 for transmission to another person or business, the call, or message, will be provided as an electrical signal to the channel bank 32 which will route the electrical signal to the fiber optic terminal 28b. The fiber optic termini 28b will multiplex the electrical signal, possibly with other messages travelling to the central office 12 at the same time, and convert the multiplexed electrical signal to an optic signal. The optical message will then be simultaneously sent out over a pair of designated optical fibers following separate paths to the central office 12.

As us-ed herein it will be appreciated that the usage of the word "message" refers to the transmission of voice, data, or video communications of any length and duration. One path carries the message over the main cable 22 only, and provides a direct optical path to the central office 12. This path will be referred to herein as the "primary path", and the message following the primary path will be referred to herein as the

"primary message". The other path also initially occurs over the main cable 22, but in the direction of the splice hub 20. At the splice hub 20 the message will be placed on an optical fiber of the protect cable 24 through the light guide frame 26, by a physical connection or by optical switching, and the message will complete the path to the central office 12 over the protect cable. This secondary path to the cential office will be referred to herein as the "protect path", and the message following the protect path will be referred to as the "protect message".

The primary message sent out over the main cable 22 will travel directly to the central office 12 where a fiber optic terminal 2.8a devoted to communication with subscriber location 16 will decode the message and pass it along to other devices in the central office, as will be described more fully below, to complete the transmission of the message to the intended recipient whether that recipient is on the network or not.

The protect message, arriving at the central office 12 over the protect cable 24, will also be routed through the light guide frame 26 to the fiber optic terminal 28a devoted to communication with subscriber location 16. Provided that the primary message that travelled directly to the central office 12 over the main cable 22 reached the central office and that the fiber optic terminal 28a was able to decode the primary message, the protect message is disregarded. If, however, there is a break in the main cable 22 between subscriber location 16 and the central office 12, or for some other reason the message was not able to be properly delivered or decoded, the protect message, which followed a separate path to the central office, will be decoded by the fiber optic terminal 28a and transmitted to the intended recipient.

As it is one of the objects of providing redundant communications that if communication over one path fails, then communications over the other path will not, the primary and protect paths are preferably physically separated. Consequently, if, for example, a road crew accidently severs a section of the main cable 22, a physically remote protect cable 24 would not likely also be severed. Further, it is preferable that the primary and protect paths into a subscriber location and the central office 12 are also physically separated to prevent both being severed or otherwise impaired from the .same event.

Each subscriber location located along the path of the main cable 22 is provided service on the network 10 by splicing into a number of fibers in the main cable.

Considering the subscriber location 16 as an example, the optical fibers in the main cable 22 passing near the location 16 are exposed at a point 34 and eight of the ninety-six optical fibers are severed. The remaining 88 optical fibers remain unbroken. The eigh severed optical fibers extending towards the central office 12 .are then placed into optica communication with eight optical fibers 36 exiting the subscriber location 16 at the poin 38 .and running to the splice at the point 34. Six of the eight optical fibers 36 ar 5 allocated for present or future use via the central office 12 or a second central office an two fibers are allocated for auxiliary services such as SONET (Synchronous Optical Network) communications. Note that in Figure 1, the main and protect cables 22, 2 have been illustrated as relatively thick lines and smaller sets of optical fibers, such as the eight fibers 36, have been illustrated as relatively thinner lines to facilitate 10 differentiation of the respective cables and fiber groups.

To establish communication with the central office 12 each subscriber location 16, 18, etc., requires a pair of optical fibers; one fiber for receiving optical communication from the central office, and one optical fiber for transmitting optical communication to the central office. Consequently, the six optical fibers provide three possible pairs o 15 communication lines between a central office and the subscriber location 16 upon which multiplexed communication may occur.

In the embodiment illustrated in Figure 1 , two fibers 40 of the eight fibers 36 are placed in communication with a fiber optic terminal 28b located in the subscriber location 16 and provide optical communication with the corresponding fiber optic terminal 28a 20 located in the central office 12. The two auxiliary fibers 42 will be coupled to other fibers in communication with the main cable 22 to provide a continuous path around the network 10. The remaining two optical fiber pairs are .set aside for future uses, such as communication with a .second central office or for accommodating a video terminal.

At a point located preferably a short distance away from the first splice 34 the 25 optical fibers of the main cable 22 are exposed at a second location 44, and the eight fibers which have been severed at the point 34 are again severed. The severed ends corresponding to the fibers which extend to the splice hub 20 are optically coupled with a s-econd set of eight fibers 46 leading to the subscriber location 16. Preferably, this

♦ second set of optical fibers 46 enters the building housing the subscriber at a separate 30 point 48 from the set of optical fibers 36 to provide additional protection against both sets of fibers 36, 46 being accidentally severed. Two fibers 50 of the eight fibers 46, corresponding to the fiber pair 40 of the fiber set 36 coupled to the fiber optic terminal 28b, are also optically coupled to the fiber optic terminal 28b. The pair of fibers 50 establish an optical path between the fiber optic terminal 28b and the splice hub 20. Another four fibers, corresponding to those fibers of the fiber set 36 reserved for future communications, are also set aside for future communications with a second central office, etc. The remaining two optical fibers of the set of fibers 46 are optically coupled with the two auxiliary wires 42 from the first set of optical fibers 36. Consequently, this set of two optical fibers, as a result of the coupling of the corresponding fibers in the fiber sets 36 and 46, establish a complete optical path between the central office 12 and the splice hub 20, while passing into the building housing the subscriber 16. The six optical fibers of the main cable 22 in communication with the six optical fibers of the optical fiber set 46 allocated for communication with a central office are optically coupled with six optical fibers from the protect cable 24 through a light guide frame 26 in the splice hub 20. The two optical fibers of the protect cable 24 terminating in the light guide frame 26 of the central office 12 which are in optical communication with the fiber optic terminal 28b are placed into communication with the fiber optic terminal 28a of the central office 12. As a result, a separate optical communication path is established from the fiber optic terminal 28b of the subscriber location 16 to the corresponding fiber optic terminal 28a in the central office 12, through the splice hub 20 and protect cable 24. As discussed above, this second path, or the protect path, provides redundant service to the subscriber location 16 in the event that the main service is disrupted as a result of a disturbance along the main path. The two auxiliary fibers in the main cable 22 are optically coupled to a corresponding pair of fibers of the protect cable 24 through the light guide frame 26 of the splice hub 20. Consequently, an unbroken path is established around the network 10. As the same corresponding eight optical fibers in the main cable 22 were severed at locations 34 and 44 and only the ends providing communication to the central office 12 and splice hub 20, respectively, were coupled to other optical fibers, eight fibers severed at both ends will remain uncoupled in the main cable 22 between locations 34 and 44. Since six optical fibers have been spliced for communication between the central office 12 and the subscriber location 16 and two optical fibers have been spliced to provide auxiliary services, eighty-eight unspliced fibers are left of the ninety-six fibers in the main cable 22 to provide communication between the central office 12 and the remaining subscribers on the network 10. The next subscriber location on the network

10, for example, subscriber location 18, would be connected to the main cable 22 in much the same way as was subscriber location 16.

5 At a point 52 near the building housing the subscriber location 18, the fibers of the main cable 22 are again exposed. Six previously unspliced optical fibers are severed along with the two fibers which, via the fiber sets 36, 42 and 46, pass through the subscriber location 16. These eight fibers are optically coupled to eight fibers 54 entering the building housing the subscriber location 18 at the point 56. Two fibers 58

10 of the six fibers coupled to the previously unsevered fibers of the main cable 22 are optically coupled to the fiber optic terming 30b, completing the prim.ary communications path to the corresponding fiber optic terminal 30a in the central office 12. Four of the six fibers are reserved in the subscriber location 18 for future communication with the central office 12 or another central office. The optical fibers of the main cable 22 are

15 again exposed at a location 60 and the eight fibers corresponding to the fibers severed at point 52 are again severed. These fibers are coupled to eight fibers 62 which are provided to the subscriber location 18 through the point 64 and are optically coupled to the auxiliary fibers or the fiber optic terminal 30b as discussed above relative to subscriber location 16. This completes the protect communication path by which a

20 message from the fiber optic terminal 30b may pass over the main cable 22 in the direction of the splice hub 20 where it is optically coupled to corresponding fibers in the protect cable 24 at the light guide frame 26. The message then travels to the central office 12 where it is coupled to the fiber optic terminal 30b through the light guide frame

26, providing the redundant communication path for subscriber location 18.

25 Other subscriber locations located on the main cable 22 would be connected in much the same way as subscriber locations 16 and 18, using six previously unspliced fibers and the two auxiliary fibers. It is also possible to connect subscriber locations to the protect cable 24. Subscriber locations will be connected to the protect cable in the

, same way as the locations discussed above were connected to the main cable 22.

30 However, in this case, the protect cable 24 would serve as the primary communication t path, and the protect path would follow the reverse route and travel to the central office

12 through the protect cable 24, the splice hub 20 and the main cable 22. The completion of the communication path between a user in a subscriber location and another person or business is accomplished in the central office 12. Once an optical message has been converted to an electrical signal and demultiplexed by a fiber optic terminal, the signal is provided to the digital cross-connect panel 68. The digital cross- connect panel 68 consists of a number of physical connections allowing direct communication with another fiber optic terminal servicing a subscriber location or to a user not located on the network 10 by a digital cross-connect system 70. The digital cross-connect system 70 provides electronic switching allowing the electrical signal message to be routed to a local user, through the path indicated by the line 72, or to a long-distance user. If the communication is intended for a long distance user via the interexchange carrier 14, the message is preferably provided to the interexchange carrier over a fiber optic cable 74. The digital cross-connect system 70 would then provide the electrical message through the digital cross-connect panel 68 to a fiber optic terminal 76a which would multiplex the message and convert it to .an optical signal for communication over the fiber optic cable 74, from which it would be received by a corresponding fiber optic terminal 76b in the interexchange carrier 14. The fiber optic terminals 76a, 76b encode and decode messages for transmission over the fiber optic cable 74 much in the same way as the fiber optic terminals 28, 30 discussed above.

It will appreciated that while the above discussion provides an example of redundant communication originating in a subscriber location and being transferred to the central office 12, the network also provides a redundant path from the central office 12 to the subaScriber locations. In such an instance a message will be transferred from the central office 12 to the appropriate fiber optic terminal 28a, 30a and then over both the main and protect cables 22, 24. The message following the primary path will travel over the main cable 22 and will be received by a corresponding fiber optic termini 28b, 30b in the recipient subscriber location. Simultaneously, the message following the protec path will travel over a devoted optical fiber in the protect cable 24 to a correspondin optical fiber in the main cable 22 through an optical connection in the light guide fram 26 of the splice hub 20. The protect message will then arrive at the recipient subscribe location over the main cable 22, but from the reverse direction as did the primar message, where it will be received by the fiber optic terminal. Provided that the primar message was received properly, the protect message will be disregarded. Referring now to Figure 2 there is shown .an alternate embodiment 10' of the communications network 10 of Figure 1 including a redundant path to the interexchange carrier 14. As discussed above, the prim∑iry path for a message intended for transfer to the interexchange carrier 14 is over the fiber optic cable 74. A protect path is provided using the existing protect cable 24 and existing splice hub 20 and by providing an optics path between the fiber optic terminal 76a .and the protect cable 24 and between the fiber optic termini 76b and the splice hub. The fiber optic terminal 76a is optically coupled to a pair of fibers of the protect cable 24 through the light guide frame 26 and a pair of optical fibers 78 running from the fiber optic terminal 76a to the light guide frame. The pair of fibers of the protect cable 24 in communication with the fiber optic terminal 76a are then coupled through the light guide frame 26 of the splice hub 20 to a pair of fibers in a second protect cable 80. The protect cable 80 runs from the splice hub 20 to the interexchange carrier 14 where the fibers in optical communication with the fiber optic terminal 76a are coupled to the fiber optic terminal 76b. Accordingly, a protect path is established between the fiber optic terminus 76a, 76b over the pair of optical fibers 78, the protect cable 24 and the second protect cable 80.

In this instance, a pair of optical fibers of the protect cable 24 are devoted to connection at the light guide frame 26 with a corresponding pair of optical fibers in the protect cable 80. While in this embodiment it is only ne-cessary for the protect cable 80 to include two optical fibers, typically, several more would be included to maintain the flexibility of the network 10'. For example, if the interexchange carrier 14 is housed in an office building along with other potential users of the network, fiber optic termin-als may be included in the building to provide service to these users over the network 10'.

This redundant service to the interexchange caπier 14 is accessible not only by users on the network 10' , but also by other local users having access to the central office 12, such as over the line 72. Also note that regardless of whether the user desiring to access the interexchange carrier 14 is on the network 10' or is an external lcxaJ user, communication with the interexchange carrier will be the .same. If the user is housed in a subscriber location on the network, such as subscriber location 16, access to the interexchange carrier 14 will be through the central office 12. The user would place a message over the network 10' on the main and protect cables 22, 24. The message would be then received in the central office 12 at the light guide frame 26 where the message would be converted to an electrical signal and demultiplexed by the fiber optic terming 28a. The electrical signal message would then be provided to the digital cross- connect system 70 via a physical connection in the digits cross-connect panel 68. The digital cross-connect system 70 would then electronically switch the electrical message to follow a separate physical connection in the digital cross-connect panel 68 to the fiber optic terminal 76a. The fiber optic terminal 76a will then encode the message and convert it to an optic^ signal for optical transmission over the fiber optic cable 74 to the fiber optic terminal 76b in the interexchange carrier 14. Simultaneously, the optical message would also be transferred from the fiber optic terminal 76a over an optical fiber 78 to a corresponding optical fiber of the protect cable 24 through the light guide frame

26. By nature of the optical connection between the corresponding fiber of the protect cable 24 and a corresponding fiber of the protect cable 80 in the light guide frame 26 at the splice hub 20, the message will be transferred to the fiber optic terminal 76b in th interexchange carrier 14. Referring now to Figure 3 there is shown an illustration of an optica communications network 10" providing redundant service between subscriber location and two central offices. In this embodiment a second central office 90 is configure much in the same way as the central office 12 with a light guide frame 26, fiber opti terminals 92a, 94a, a digital cross-connect panel 68 and a digital cross-connect syste 70. The second central office 90 is preferably a nearby central office providin telephone .services to its local users. The central office 90 is placed in communicatio with the splice hub 20 through a main cable 96, and in communication with the centra office 12 through a protect cable 98. Preferably, the main cable 96 and the protect cabl 98 are fiber optic cables having typically the same number of optical fibers as the mai and protect cables 22, 24, i.e., 96 optical fibers.

The network 10" illustrated in Figure 3 provides redundant communication path between two central offices 12, 90 and the subscriber locations 16 and 18 Communication between the subscriber locations 16, 18 and the central office 12 i accomplished in the same manner as was discussed above relative to Figure 1. Th subscriber locations 16, 18 are, however, provided with an additional fiber optic termin

92b. 94b, respectively for communication with the fiber optic terminals 92a, 94a of th central office 90. Con.sequently, if communication through the central office 12 i disabled for some rearøn, such as due to a fire in the central office 12 or other equipment malfunction, the subscriber locations can communicate with other persons or businesses on or off of the network 10" through the second central office 90.

Considering the subscriber location 16 again, as an example, an outgoing message from the user will be provided to the fiber optic terminal 92b by the channel bank 100.

The message will then be multiplexed and converted to an optical signal which will be simultaneously sent out over a pair of designated optical fibers in the main cable 22 with the final destination as the central office 90. The prim-aiy path to the central office 90 follows the main cable 22 in the direction of the arrow 102 toward the splice hub 20. At the splice hub 20 the message is optically coupled to the m.ain cable 96 leading to the central office 90. At the central office 90 the message is transferred through the light guide frame 26 to a fiber optic terminal 92a corresponding to the fiber optic terminal 92b in the subscriber location 16. Simultaneously, the message is also sent along the protect path. The protect message will follow the main cable 22 in the direction of the arrow 104 toward the central office 12. At the central office 12, through an optical coupling in the light guide frame 26, the message is transferred to the protect cable 98 and travels the final distance to the central office 90. At the central office 90 the message is transferred through the light guide frame 26 to the fiber optic terminal 92a devoted to communication with the subscriber location 16. Provided that the primary message that traveled in the direction of the arrow 102 over the main cable 22 and main cable 96 reached the fiber optic terminal 92a and was properly decoded, the protect message will be disregarded. In the event that the primary message was not received by the fiber optic terminal 92a for some reason, such as break in the cable 96, the protect message following the main cable 22 in the direction of the aiτow 104 and protect cable 98 will be decoded by the fiber optic terminal 92a and transmitted to the intended recipient.

Again, it is preferable that the protect cable 98 and the main cable 96 follow different routes to the central office 90. It is .also preferable that the protect cable 98 and main cable 96 enter the building housing the central office 90 at different physical locations to reduce the likelihood that an accident severing one of the cables will also severe the other.

The fiber optic terminal 28b in the subscriber location 16 providing communications to the central office 12 is optically coupled to the main cable 22 in the same way as described above relative to Figure 1. As will be remembered with reference to the discussion accompanying Figure 1, a total of eight fibers 36 were coupled to the main cable 22 and provided to the subscriber location 16. Two of these fibers were designated for auxiliary services; two fibers were coupled to the fiber optic terminal 28b in communication with the central office 12, and two pairs of fibers were left unused. Of the two pairs of fibers left unused, one pair 106 will now be coupled to the fiber optic terminal 92b. .An unused pair of fibers 108 of the set of eight fibers 46 will also be coupled to the fiber optic terminal 92b. The two optical fibers 108 of the eight fibers 46, which are optically coupled to the main cable 22 at the location 44, provide the primary path to the central office 90. The corresponding two fibers of the main cable 22 will be connected to two corresponding fibers in the main cable 96 through the light guide frame 26 in the splice hub 20. The corresponding two fibers in the main cable 96 are then optically coupled to the fiber optic terminal 92a through the light guide frame 26 in the central office 90, thus completing the primary communication path between the subscriber location 16 and the central office 90.

The two fibers 106 of the set 36 optically coupled to the fiber optic terminal 92b in the subscriber location 16 provide the protect service to the central office 90. These two fibers 106 of the eight fibers 36 are optically coupled to the main cable 22 at the location 34 and provide communication in the direction of arrow 104. The corresponding two fibers in the main cable 22 will thus provide the protect service to the central office 12. At the central office 12 these two fibers are placed into optical communication through the light guide frame 26 with two corresponding fibers in the protect cable 98. At the cential office 90 the two fibers of the protect cable 98, providing the protection service from the fiber optic terminal 92b in the subscriber location 16, are provided to the fiber optic terminal 92a in the central office 90 throug the light guide frame 26, thus completing the protect path to the central office 90. Th subscriber location 18 via the fiber optic terminals 94a, 94b, as well any other subscribe locations on the network 10", may be provided redundant service to the central offic 90 in much the same manner. Consequently, a subscriber location on the network illustrated in Figure 3 i provided with main and protect service to two different central offices 12, 90. If one o the cables, 22, 24, 96, 98 is severed, communication can still be had to both centra offices 12, 90. Further, if one central office 12, 90 is disabled for some reason, the service may be provided to the other central office.

As will be appreciated, the modifications to the network 10 shown in Figure 1 t produce the network 10" shown in Figure 3 are facilitated Uirough the connections in th splice hub 20 occurring in the light guide frame 26. Optical fibers of the m∑tin cable 2 may be easily placed into optical communications with corresponding fibers of the mai cable 96, providing service to the central office 90, or with fibers of the protect cabl 24 providing protect service to the central office 12. Consequently, the splice hu provides a very flexible optical telecommunication network allowing available service to be tailored to meet the needs of the users in the different subscriber locations. Th splice hub 20 may also be provided with optical switching capabilities when optica switching becomes commercially practical, thus increasing the flexibility of the system. Optical switching would permit the same optical fibers of the main cable 22, for instance to communicate with optical fibers in either the protect cable 24 or the main cable 9 depending on the commands provided to the switch. This could possibly reduce th number of fibers which must be devoted to provide certain services, thus increasing th number of users which may be attached to the network or the number of services whic may be provided.

Turning now to Figure 4, there is shown a telecommunications network 10' similar to that shown in Figure 3 with a redundant communications route to a interexchange carrier shown. In this instance, communications between the subscribe location 16, 18 to the central office 12 or central office 90 will be accomplished in th same way as described relative to Figure 3. Communication between the subscribe locations and the interexchange carrier 14 is accomplished only through the central offic 12, with the fiber optic terminal 76a providing access to the fiber optic terminal 76b i the interexchange carrier 14 over the fiber optic cable 74. Similarly, protect service i provided from the central office 12 to the interexchange carrier 14 over the protect cabl 24 and protect cable 80. The small number of modifications required to the network 10" shown in Figure 3 to accomplish the redundant communication with the interexchang carrier 14 illustrates, again, the flexibility of the network provided by the splice hub 20.

To modify the network 10" of Figure 3 to provide redund.ant communications t interexchange carrier 14 simply requires running an optical cable 80 from the fiber opti terminal 76b of the existing interexchange caπier 14 to the existing splice hub 20, and providing a pair of optical fibers 78 from the existing fiber optic terminal 76a to the existing light guide frame 26. In the central office 12 the pair of optical fibers 78 will be optically coupled through the light guide frame 26 to a pair of fibers of the protect cable 24. This pair of optical fibers in the protect cable 24 will then be optically coupled through the light guide frame 26 in the splice hub 20 to corresponding fibers in the protect cable 80 which are in communication with the fiber optic terminal 76b. This provides a complete redundant path between the central office 12 and the interexchange c-arrier 14 with very little modifications required to the network 10" of Figure 3. Communication between the interexchange carrier 14 and the subscriber locations 16, 18 would then be achieved as described above relative to Figure 2.

With reference now to Figure 5, there is shown a network 10"" providing redundant communications between the subscriber locations 16, 18 and the two central offices 12, 90, redundant paths between each central office and the interexchange carrier 14, and redundant service to subscribers located in the building housing the interexchange carrier. In this embodiment, the cable 80', which in Figure 4 provided redundant service to the fiber optic terminal 76b in the interexchange carrier 14, is extended to the central office 12. Consequently, the cable 80' runs between the central office 12 and the splice hub 20 while passing by the building housing the interexchange carrier 14. Preferably, the cable 80' includes several optical fibers, such as 96, for example.

In this embodiment corresponding fiber optic terminals 110a, 110b are placed in the central office 90 and the interexchange carrier 14, respectively. In the central offic 90 the fiber optic terminal 110a is placed into communication with two fibers of the main cable 96 and the protect cable 98 through the light guide frame 26. The two fibers o the main cable 96 are placed into optical communication with two fibers of the cable 80' through the light guide frame 26 with the splice hub 20. At a point 112 near th interexchange carrier 14, the optical fibers of the cable 80' are exposed and the tw fibers in communication with the fiber optic terminal 110a are severed and opticall coupled with the fiber optic terminal 110b in the interexchange carrier. Redund.ancy i provided by optically coupling the fiber optic terminal 110b with the two severed optica fibers in the section of the cable 80 extending towards the central office 12. At th central office 12 these two fibers are placed into optical communication with the protec cable 98 through the light guide frame 26. Consequently, a reduno^nt path from the central office 90 is established to the interexch.ange carrier 14. Whether the interexchange carrier 14 received the long-distance communication from the fiber optic termini 76b or the fiber optic terminal 110b is irrelevant to the tiansmission of the message by the interexchange carrier over its long-distance network.

In many inst^ces an interexchange carrier may be located in a building, such as an office building, including several tenets, many of which may desire to be placed on the network 10"". In this case, corresponding fiber optic terminals 116a, 116b are placed in the central office 12 and in the building housing the interexchange carrier 14, respectively. The fiber optic terminal 116b in the building housing the interexchange carrier 14 is optically coupled to the cable 80', preferably in two physically separate locations, to provide optical communications in two directions over the cable 80'. One direction, which is towards the central office 12, provides the primjuy communication path between the fiber optic terminal 116b, and the fiber optic terminal 116a. The other direction, which is towards the splice hub 20, provides the protect path. The protect path follows the cable 80' to the splice hub 20 where the optical fibers devoted to servicing the users in the building housing the interexchange carrier 14 are optically coupled through the light guide frame 26 to corresponding fibers in the protect cable 24. These corresponding fibers in the protect cable 24 are then provided to the light guide frame 26 of the central office 12, where the fiber pair optically coupled to the fiber optic termini 116b is placed into optical communication with the fiber optic terminal 116a. While only two optical fibers are needed in the cables 80' and 24 to establish communication between the fiber optic terminal 116a and the fiber optic terminal 116b, preferably eight optical fibers will be devoted to the users in the building housing the interexchange carrier 14 to provide the flexible services available to the subscriber locations 16, 18, for example.

Note that the addition of the fiber optic terminals 1 10b and 116b to the building housing the interexchange carrier 14 does not affect the functioning of the fiber optic terminal 76b or its connections to the cable 80'. Further, while the fiber optic terminals in the building housing the interexchange carrier 14 are shown as spliced into the cable

80' at five different locations, it will be appreciated that preferably only two paths will exist between the building and the cable 80', although one, three or more actual splice locations may be chosen. It will also be appreciated that once the cable 80' is provided in the vicinity of the building housing the interexchange carrier 14, and a number of fibers must be spliced to provide services to a device in the interexch∑uige carrier, at the same time other fibers will preferably be spliced and provided to the building housing the interexchange carrier to facilitate the connection of other devices at a future time.

With reference now to Figure 6, there is shown an embodiment of the present invention particularly applicable to users in a non-urban environment employing a diversity hub 118. The diversity hub 118 is analogous to the splice hub 20 discussed above and includes a light guide frame or some other optical connection mechanism. In Figure 6, there are illustrated three central offices 120, 122, 124, denoted as squares in the figure, each servicing a number of discrete users illustrated as circles. The locales 126, 128, 130 and users provided service by the individual central offices 120, 122, 124, respectively, are generally indicated by the vertical and horizontal dashed lines 132, 134. As is conventional, a copper cable 136 runs from each of the central offices to the area of each of the corresponding users serviced by that central office. The cable will contain discrete copper conductors dedicated to each user served by the central office. A copper cable 138, 140, 142 also runs between each central office providing for communication between users serviced by different central offices. While this conventional telephone network provides acceptable telephone services to many users, some users would like the security of having a communication path available to a separate central office in the event that the central office which they are served by becomes inoperable. However, due to the relatively low density of users in non-urban areas, the cost of connecting each user in a network as discussed relative to Figures 1-5 above is often prohibitive. The embodiment of the invention illustrated in Figure 6 provides service to a second central office for selected users in a low density area through a diversity hub 118 and a number of fiber optic cables.

In the figure, the cables 136, 138, 140 represented as solid lines are conventional copper cables, while fiber optic cables are represented by dashed lines. The cable 142 illustrated as alternating lines and dashes would be a copper cable carrying conventional interoffice communications and a fiber optic cable providing servic-es between selected users and a s^ond central office. Alternatively, the communication carried over the copper cable could be handled by the fiber optic cable and the copper cable could eliminated or used to provide partial redundant services.

Considering as an example the central office 120, there are illustrated thr exemplary users 146, 148, 150 serviced by the centi l office 120. While the u.ser 1 is provided service by the central office 120 only, the users 148, 150 are provided acce to the central office 120 and the central office 124 in the event that the central office 1 somehow becomes disabled. This is done through the diversity hub 118.

A fiber optic cable 142 is laid between the central offices 120, 124 and pass near the diversity hub 118. The fiber optic cable 142 may follow the same route as th followed by the copper cable 142 or preferably a different route when the cables 142 a u.sed to provide redundant interoffice communication. The remote ends of the individu optical fibers of the fiber optic cable 142 terminate in respective light guide frames each central office 120, 124. At a location 152 ne^ the diversity hub 118, the optic fibers of the fiber optic cable 142 are exposed and those fibers not devoted to interoffi communication are severed. Both ends of each severed fiber are optically coupled to corresponding fiber terminating in a light guide frame in the diversity hub 118. T fibers leading to the diversity hub 118 in optical communication with the sep∑irate centr offices 120, 124 may follow separate paths 154, 156, respectively, to the diversity hu

Each user desiring the protection of service by a second central office is placed in optical communication with the diversity hub and corresponding fiber optic terminus a placed in the user location and the secondary central office. Through appropria connections in the diversity hub 118, optical communication between the correspondin fiber optic terminals in the user location and the secondary central office is th accomplished. For example, user 148, having primary service provided by the centr office 120, can be provided protect service with the central office 124 by locating corresponding fiber optic terminal in each, and running a fiber optic cable 158 to t diversity hub 118. A pair of optical fibers of the cable 158 would then be coupled to t fiber optic terminal serving the user 148 and, through the light guide frame in t diversity hub 118, coupled to a pair of fibers in the optical cable 142 in communicati with the corresponding fiber optic terminal in the central office 124, thus establishing secondary path. If the central office 120 or the primary copper path thereto is disable for some reason, then the user 148 will communicate with the central office 124 via t diversity hub 118. The user 150, provided primary service by the central office 120, as well as the users 160, 162, provided primary service by the cεntial office 124, may be coupled through the diversity hub 118 in similar manners to provide communications with a second central office. In .another embodiment the cables 158, 164 coupling the users 148, 150, respectively, with the diversity hub 118 may be ordinary copper conductors. In this case a fiber optic terminal will be placed in the diversity hub 118 corresponding to a fiber optic termin∑d in the central office 124. Communication from the users 158, 164 via their respective copper cables 158, 164 will then be multiplexed by the fiber optic terminal in the diversity hub 118 and converted to an optical signal for transmission over the fiber optic cable 142 to the corresponding fiber optic termini in the central office 124. Consequently, both users 148, 150 may communicate with the central office 124 via the same fiber optic terminal located in the diversity hub 118. It will be appreciated that other combinations are also available and are included within the scope of the invention.

STATEMENT OF INDUSTRIAL APPLICATION The present invention finds applications broadly in providing communications between a plurality of users. Particularly, the invention provides a very flexible optical network and method for providing telephone communications to users desiring redundancy, access to a secondary central office, and other features.

Claims

What is claimed is:

1. .An optical communications network; comprising: transmitting means for transmitting a message along a plurality of transmitting paths; receiving means for receiving a message from a plurality of receiving paths, and first and second coupling means for facilitating optically coupling a plurality of paths; wherein one of such transmitting paths is optically coupled to one of such receiving paths through said second coupling means, and the other of such transmitting and receiving paths form the same path.

2. The apparatus of claim 1, wherein said second coupling means includes a splice hub, said splice hub comprising a light guide frame.

3. The apparatus of claim 1 , including a central office and a subscriber, each including both said transmitting means and said receiving means.

4. The apparatus of claim 3, wherein said transmitting means and said receiving means each include multiplexing means for multiplexing a plurality of messages.

5. The apparatus of claim 1, wherein such message is an optical signal.

6. The apparatus of claim 5, wherein such transmitting and receiving paths are optical paths.

7. The apparatus of claim 6, wherein said optical paths include optical fibers.

8. A method of communicating between a central office and a subscriber; comprising the steps of: a) transmitting an optical message along a first path between such subscriber and such central office; b) simultaneously transmitting such message along a second path to an intermediate location; c) optically coupling such message transmitted to such intermediate location to a third path; wherein such second and third paths establish a path between such subscriber and such central office; .and d) receiving such message from such first path and such pat established by such second and third paths.

9. The method apparatus of claim 8, wherein said transmitting step include multiplexing such message.

10. The method of claim 9, wherein said receiving step include demultiplexing such message.

11. An optical telecommunication method; comprising the steps of: a) passing a first set of at least four optical fibers from a central offic to a splice hub along a route in the vicinity of a subscriber; b) passing a second set of at least four optical fibers from such centra office to such splice hub; c) coupling such first set of optical fibers to said second set of optic fibers in such splice hub; and d) severing at least two fibers of such first set of optical fibers an coupling such severed ends to a subscriber, while leaving at least two other fibers of suc first set of fibers unsevered.

12. The method of claim 11, wherein such at least two severed fibers form tw optical paths between such central office and such subscriber; one of said two optic paths occurring over at least two fibers of said second set of optical fibers, the other said two optical paths occurring only over at least two fibers of said first set of optic fibers.

13. The method of claim 11, wherein such first and such second sets of fibe follow physically separate routes.

14. The method of claim 11, including the steps of passing a set of at least t optical fibers between such splice hub and a second central office and optically coupli such set of at least two fibers with at least two fibers of such first set of optical fibers

15. The method of claim 14, including the steps of passing a second set of least two optical fibers between said second central office and said first central offic and coupling said second set of at least two optical fibers with at least two fibers of sa first set of at least four optical fibers.

16. A method of providing telecommunications services from a user serviced by a primary central office in an existing copper network to a seconα^ry central office, comprising the steps of: a) passing at least two optical fibers between such secondary central office and such primary central office; b) severing two fibers of such at least two optical fibers at an intermediate location; and c) optically coupling such user at such intermediate location to the severed ends of such two severed optical fibers extending towards such secondaiy central office.

17. The method of claim 16, wherein said step of optically coupling includes placing a fiber optic terminal at the location of such user and a corresponding fiber optic terminal in such second-ary central office and establishing an optical path between such fiber optic terminzils via such two severed optical fibers.

18. The method of claim 16, wherein said step of optically coupling includes placing a first fiber optic terminal at such intermediate location and a corresponding second fiber optic terminal at such secondary central office, further including the steps of optically coupling the unsevered ends of such two severed optical fibers to said second fiber optic terminal, optically coupling the severed ends of such two severed optical fibers to such first fiber optic terminal, and placing such first fiber optic terminal and such user in communication.

19. The method of claim 18, wherein such communication between such user and such first fiber optic terminal is optical.

20. The method of claim 18, wherein such communication between such user and such first fiber optic terminal is electrical.