Optical fiber is commonly deployed in the trunk parts of networks, and this use is gradually extending into the access network, with fiber-to-the premises (FTTP) bringing an optical connection all the way to end user customers. One method of serving FTTP customers is by way of a passive optical network (PON), a point-to-multipoint system using an unpowered optical splitter which links a number (commonly 32 to 128) of customers to a telecommunications exchange via a single optical fiber.
A typical exchange in the UK can serve up to a large number of customers, which can range from a few hundred to tens of thousands or even more, and the building itself may be a vast space over a number of floors. The building would house a large variety and quantity of electronic and other equipment, which provide services required by customers. Such equipment is typically located on equipment racks, and are interconnected to each other in a complex network, as well as to and from customer premises via the external telecommunications network.
This task of carrying the cables in a manner allowing for any piece of equipment to interconnect with any other piece of equipment within the exchange premises is presently carried out by apparatus sometimes known as flexibility racks. The term “interconnection” in this description includes the creation of an interconnection or link or connection by splicing fibers together, or by use of a mechanical or other connector. The terms “cable” and “fiber” denote one and or the other as the context permits. The “flexibility” function arises from their serving as junction or distribution points within the exchange so that a fiber or cable of the external network entering (or exiting) the building can be interconnected to a piece of equipment regardless of where the equipment is located.
In modern exchanges, these racks carry almost exclusively optical fiber, and so are termed optical flexibility, or fiber, racks (OFRs). The racks are typically deployed in pairs forming a “flexibility suite”. The flexibility suite comprises a network or line (“L”) side rack which receives the network cables and fibers. The other rack in the pair is the exchange or equipment (“E”) side receives fiber travelling to and from typically a single equipment rack. The racks include numbers of fiber trays which accommodate and protect the join of spliced fibers. For those L and E side fibers which need interconnection, the respective ends are spliced on trays of the respective racks to a separate jumper or patch cord serving as an intermediary between the two racks which completes the link between the network fiber and the fiber of the equipment rack.
Fibers arriving at the flexibility suite from the network and the equipment rack may arrive singly (e.g. in a point-to-point connection), although it is more and common for them to arrive in a cable which contains a number of individual fibers. For example, each cable optical fiber (COF) used with the flexibility racks contains 144 individual optical fibers. Specifically, the COF comprises a bundle of 12 cable elements, each of which in turn contains 12 fibers. Where not all the fibers of a particular COF require interconnection, those not requiring interconnection are designated and spliced on a fiber tray on the E or L side racks (depending on which side the cables and fibers are arriving from). The unused fiber is thus stored until it is needed for interconnecting by jumpering as described above.
Such conventional methods are commonly known and described in e.g. “Modular Optical Plant for Access Network: Operational Aspects” by D. Brewer et. al (Proc. EFOC & N (Technology and Infrastructure) 1995, at pages 164-167).
With the sheer numbers of customers served by the exchange and the quantity of equipment involved, it can be appreciated that massive amounts of cabling is involved. Work on the fibers include the creation of new interconnections, the re-routing of existing interconnections, the breaking of interconnections which are no longer needed, the identification of what a particular cable interconnects, and so on. Such work with large numbers of cables snaking in all directions throughout the exchange building is very likely to generally give rise to logistical and other problems over time. These problems are brought on and exacerbated by customer number growth, equipment replacement and upgrading, and other such changes within the exchange and in the external network leading to the customer premises.
Current OFRs, such as the exchange racks manufactured by Prysmian S.p.A., have the capacity to accommodate hundreds of fibers in trays, and great numbers of these racks are deployed in exchange buildings both to accommodate and to route fibers and cables. They tend however, to become fully populated quickly, due in part to the need to store unused (i.e. unpatched) fibers on the racks. Over time, severe congestion can occur at the OFRs, which hampers the identification and other dealings with the fibers. It is the experience of the applicants that such unused fibers spliced in fiber trays in the racks often end up never being used. There are many reasons for this: for example, if the customer served by a particular L side fiber never wants a particular service, the need to interconnect that fiber to the relevant equipment rack never arises. In the situation of an overcrowded OFR or exchange, it may be that the fibers requiring interconnection simply cannot be accurately identified or located, and so the safest and most expedient solution is simply to provide another L and E side fiber for interconnection, which of course adds to the congestion.
A solution to the problems raised by cable and fiber overcrowding in the exchange would be desirable.
The method of interconnecting fibers by splicing demands considerable expertise and precision. This already-difficult task is impeded if the engineer has to work in a large, rigid tangle of cables, making the task even more time-consuming and complicated. Another problem with fiber overcrowding at OFRs is that cables and fibers are routed across each other in close proximity, often directly onto each other, so that fibers located under the weight of others above it suffer an increased risk of circuit failure through optical loss and fiber breakage. This problem becomes even more critical as higher bit rate systems are employed, as these tend to be more sensitive to increases in optical loss.
Another determinant of transmission quality is the number of interconnections introduced into the optical link between its transmission and reception ends. Each interconnection introduced into the link, whether it takes the form of a splice, using a connector or otherwise, degrades the quality of the optical transmission across that link. This is the case even if the interconnection is made well. Current exchange cabling methods in exchanges typically involve the interconnection of several lengths of optical fiber interconnected by means of connectors and/or splices. It is rare for a link between the CCJ and an equipment rack to contain fewer than twelve interconnections. Typically, the further the location of a piece of service equipment in the exchange from the incoming fiber of the network, the longer the optical link path, and the greater the number of interconnections in that link. This is because a longer path involves the passing of the link through a greater number of OFR suites which route the link to its destination equipment rack, and the link is spliced twice at each OFR suite: once on each rack making up the suite.
A solution to reduce the number of interconnections required to link a fiber of the external network, to a particular piece of service equipment within the exchange, would be desirable.
A related issue is the growth in the types of services which have become available, which require different equipment types. For example, a PON system serves a number of customer (e.g. 32) per fiber, so the equipment providing this service must include multiplexing in the form of e.g. a wavelength-division multiplexing (WDM). In the current flexibility systems, the splice trays on which the fibers are spliced pre-dedicates the fibers to a certain type of service. Where a particular fiber is to be interconnected to PON service equipment and the splice tray does not support WDM, that splice will have to be broken and the fiber re-routed to another tray, or even another rack, which is WDM-capable.