OPTICAL FIBER NETWORK

Abstract: In an optical fiber network for connecting individual subscribers (105) a local switch unit (101) is provided. The unit is connected between the subscribers and a central conventional unit (109) such as a router. The switch unit can be connected to the central unit through a ring network (107) providing a redundant communication path from the switch unit to the central unit. In the switch unit preferably a local switching circuit board is arranged comprising a packet switch (213) for locally switching traffic between different subscribers and between the subscribers and the central unit. Various filters can be arranged in the switch unit for avoiding that a subscriber can gain access to information intended for another subscriber.

Description: OPTICAL FIBER NETWORK TECHNICAL FIELD The present invention relates to an optical fiber network and in particular to an optical fiber network for connection to a plurality of subscribers such as individual apartments in a building. It also relates to a local device, also called switch unit or traffic distribution unit, used in such networks. STATE OF THE ART It is previously known to arrange optical fiber networks for buildings, in which individual apartments are connected by optical fibers to a central unit, for example a router. This central unit is then in turn connected to a transport network for transferring information from individual apartments to said transport network, for example the Internet. The same type of network and network connection can be used for e.g. a group of private homes. In U.S. patent 5.872.644 an optical fiber access system for optical communication between private subscribers and a central unit is disclosed in which each subscriber is connected by optical fibers to one of an array of optical transmitter modules (Tx) and to one of an array of optical receiver modules (Rx) which are connected to a communication switch. In U.S. patent 5,349,457 and the article by Kazunari Irie et al. , "Large Capacity Multiplex-Port Brouter with SDH Interface for Regional PC Communication Network System, Communications, 1997; Towards the Knowledge Millennium, Proceedings of ICC '97 - International Conference on Communications, Montreal, Que. , Canada. 8-12 June 1997, optical communication systems are disclosed having simple splitting/combining units for fixed connections placed near the subscribers or individual user terminals. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber network connected to a subscriber having an improved structure. This object is achieved by arranging a switch unit locally adjacent to a subscriber. This unit is thus connected between an individual subscriber and a conventional central unit, such as a router. The traffic in such a network is preferably packet switched, for example according to the standard IEEE 802. Preferably the switch unit is connected to the central unit through a network loop or ring network and thereby a redundant communication path from the switch unit to the central unit is obtained. In the switch unit a local switching circuit board is provided for switching traffic going between different subscribers connected to the same switch unit and various filters for avoiding that a subscriber connected to a considered switch unit can gain access to information intended for another subscriber connected to the switch unit or interfere with traffic intended for other subscribers. The switch unit, which is also called a traffic distribution unit, is thus generally arranged to distribute signals carrying information, called traffic, in an optical fiber network comprising a plurality of subscriber terminals and a central unit. In the conventional way the traffic distribution unit has subscriber connectors for optical fibers connected to the subscriber terminals and network connectors for optical fibers in an optical transport network connected to the central unit. The traffic distribution unit has paths for conducting traffic between the subscriber connectors and the network connectors. It also comprises a controllable switch for controlled local switching of traffic between the subscriber connectors. Thereby traffic between subscriber terminals connected to the traffic distribution unit are allowed to pass only through the traffic distribution unit and not to the optical transport network connected to the traffic distribution unit. The switch can also switch traffic between the subscriber connectors and the network connectors in order to work as a conventional splitter/combiner node. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail with reference to the accompanying drawings in which: - Fig. 1 is a schematic view of an optical fiber network connected to an individual subscriber, - Fig. 2 is a block diagram of a switch unit for local switching of signals in the network shown in Fig. 1. - Fig. 3 is a perspective view of a housing unit that can be used to enclose the unit according to Fig. 2 and includes a passive part and an active part, and - Figs. 4a - 4d are detail views of an organiser used in the encapsulating cupboard of Fig. 3. DETAILED DESCRIPTION Fig. 1 shows an optical fiber network for connection to a subscriber. The fiber network consists of a local device, a switch unit 101 connected through pairs of optical fibers 103 to individual subscriber terminals of subscribers/apartments/private homes 105 and also connected to a local optical fiber loop or fiber ring 107. The local optical fiber loop 107 comprises a ring of a pair of optical fibers for traffic in opposite directions. The fiber ring, which can be considered a local optical transport network is in turn connected to a central unit 109. which can be connected to a wide area transport network 111 such as the Internet in the conventional way. By providing the local switch unit 101 advantages are obtained compared to a conventional optical fiber network for connection to a subscriber, these networks generally called "Fiber To The Home" (FTTH). Hence it is not necessary to install pairs of optical fibers from each individual subscriber to the central unit 109. This implies that a smaller amount of optical fiber must be installed since the total length of the fiber lines becomes shorter. Furthermore, connection of new subscribers is simplified since it is only necessary to install a new optical fiber from a new subscriber to the switch unit 101. The switch unit can be placed significantly closer to the subscriber, for example in the cellar of a building holding a plurality of apartments, instead of installing optical fibers from the subscribers all the way up to the central unit. Furthermore, the local switch unit 101 is preferably built into a robust housing so that it without any risk of damages to its electronic circuits can be placed in a cellar or in an attic of the building. Furthermore, switching is achieved at a local level resulting in that the traffic load to the central unit 109 is reduced since all traffic communicated between subscribers 105 connected to the same switch unit 101 will never be transferred to the central unit but can be switched in the local switch unit. In the block diagram Fig. 2 components of the switch unit 101 are shown. The switch unit can comprise a fixed cross connection unit CPX 201 for cross connecting in a predetermined or fixed way signals to/from different subscribers 10 5 connected to the switch unit and also to/from the central unit 109. The CPX 201 has thus at one side, called a connector side, ports or connectors connected to the fibers pairs 103 extending to the subscribers and to the fibers of the fiber loop 107 connected to the central unit and at an opposite, internal side it is connected to optoelectrical converters such as the diodes of a PIN-diode array 203 and to electrooptical converters such as the lasers of a VCSEL-laser array 205. The PIN-diode array receives through the cross connection unit 201 signals which are sent from the subscribers 105 and the central unit 109 and the VCSEL-laser array 205 transmits signals which through the cross connection unit are sent to the subscribers and to the central unit, on the respective fibers of the fiber pairs 103 and of the loop 107. The PIN-diode array 203 and the VCSEL-laser array 205 are connected to the cross connect unit 205 through optical ribbon fibers. In the CPX the paths of the signals transmitted on individual fibers of the ribbon fibers are cross-connected so that on the connector side of the cross connect unit 205 pairs of ports are formed, each port pair including one port for signals from the switch unit 101 and one port for signals to the switch unit. The port pairs are connected to fiber pairs 103 extending to a subscriber, except at least one port pair that is connected to the fibers of the loop 107 for communication with the central unit. In the case of connection to a fiber ring or loop 107 two port pairs are required for the communication with the central unit 109. The PIN-diode array 203 is on its output side connected to an amplifier 207, which in turn is connected to a conventional packet handling unit 209 providing amplified signals thereto. The packet handling unit 209 is connected to output signals to a unit 211 5 comprising a distribution switch, suitable filters and preferably also support for handling a Virtual Local Area Network (VLAN). The unit 211 is connected to provide signals to a packet switch 203 which is a controllable device switching, as controlled by either external signals or by the information found in the packets, traffic from any of its inputs to any of its outputs. The packet switch 213 provides the switched signals to a buffer 215 ιo in which packets received from the packet switch are stored waiting to be forwarded from the switch unit 101. Preferably the buffer 215 has support for handling different priorities of the packets that are to be forwarded. The buffer 211 is connected to transmit its packets to a conventional packet handler 217 and an amplifier 219, which in turn is connected to the input of the VCSEL-laser array is 205. In a preferred embodiment the switch unit 101 comprises filters, included in the unit 211, for preventing information sent to/from an individual subscriber 105 from being received by another subscriber connected to the same switch unit. Filtering the information is also made to prevent a subscriber from interfering with another subscriber connected to the 20 same switch unit. Further, by arranging virtual networks, the VLANs mentioned above, different subscribers can be given different qualities of their connections. Since the packet switch 213 is arranged in the switch unit 101 switching at a local level can be performed, i.e. traffic to/from subscribers 105 connected to the same switch unit can be connected at a local level in the switch unit. 25 In a preferred embodiment the switch unit 101 and associated peripheral equipment can be arranged in a robust housing provided with optical connectors as an interface to incoming and outgoing optical fibers. In the perspective view of Fig. 3 an example of an encapsulated box arrangement is shown that is designed to among other things enclose the components of the switch unit 30 101 as shown in Fig. 2. The box arrangement has two parts 1A and IB which have doors or lids 2A and 2B that in the figure are shown in open positions. The boxes can e.g. be made from 1.5 mm steel and aluzinc plate. In the first box 1A only passive components are housed, such as eight cassettes 3 arranged for handling or connecting a maximum of 96 incoming individual optical fibers or 48 incoming two-fiber ribbons. Incoming multiduct cables and/or micro duct cables including optical fibers from for example different apartments in a building are connected in the passive box 1A. On a rear side of the first box 1A holes 4 are provided for introducing ducts/pipes enclosing the optical fibers from the apartments. The ends of the different ducts/pipes are placed in an organiser 5, see also the detailed views of Fig. 4, in order that the optical fibers in the ducts or pipes will be organised and thereby more easily handled when making the connection of the optical fibers extending from the ends of the pipes to the cassettes 3. The organiser 5 can as is shown in the example of Fig. 4 be a holder for individual pipes or pipe ends. It is in the example an upstanding rail having a cross-section of a U including two opposite sides, the legs of the U, joined by a web portion. In the two opposite sides recesses 17 are provided in which the pipe ends can be placed in parallel, on top of each other. Optical fibers blown into/sucked into the pipes using FTTH ("Fiber To The Home") or FFTH ("Fiber From The Home") technology are numbered preferably according to a special numbering scheme, for example using marker tags or similar things in order to ensure a simple and accurate handling of the optical fibers. In each cassette 3 for example six two-fiber ribbons on the subscriber side can be spliced to for example a 12-fiber ribbon on the switch or cross-connect side. In the topmost and last cassette also single mode splices for the fibers of the loop 107 carrying traffic to and from the central unit 109 can be placed. The cassettes 3 have the shape of low or thin boxes comprising two winding cores around which excess lengths of optical individual fibers and ribbon fibers can be wound. On the front side of the first box 1A holes 6 are provided for the fibers for communication with the central unit 109. Around the edges of the lid 2 A of the first box 1A a sealing strip 7 is provided to make the box tight. On the bottom side of the first box 1A a rail 8 can be mounted for attaching the box to some fixed base such as a cellar wall or similar thing. In the second box IB the active components needed for the switch unit are provided including a switch module 9 being e.g. a printed circuit board, to which the active components of the switch unit 201 are mounted, as described above with reference to Fig. 2. The switch circuit board is in the figure illustrated lifted perpendicularly up from its position inside the active box IB. Also, the active box is drawn to be positioned at some distance of the passive box, but actually they should be mounted directly at each other. Furthermore, the second box houses a DC-converter 10 and fans 12. An external electrical network cable 11 is connected to the switch module 9. The door opening is here provided with specially made conducting silicon gaskets 13 and all other openings are optimised to stop electromagnetic radiation to make the box conform with EMC-requirements . The switch module 9 could, in a suitable design, be easily mounted in the box IB without any tool using for example a weak manual pressure, using locking clips, not shown, for the attachment thereof. On the top side of the switch module 9 the fixed cross connection unit 201 can be mounted, e.g. comprising a panel and long 12-fiber ribbons 14 having clamps for absorbing tensile forces. From the cross connect unit 201 for example eight such fiber ribbons, also called pigtails, having a length of 1.8 m each, can extend to the cassettes 3 and for example two or preferably four single fiber pigtails can extend for the traffic with the central unit 109. All pigtails can be introduced through one or several bores in a intermediate piece placed between the passive box 1A and the active box IB, preferably through a bore 16 having a diameter of at most 5 mm to fulfil the EMC-requirements. The pigtails are spliced to the optical fibers of the pipes or ducts inside the cassettes 3, in which also most of the lengths of the fibers and pigtails are housed, wound around the winding cores of the cassettes. By marking all pigtails with suitable numbers, for example using marker tags or similar things, the mounting on intended places in the respective splice cassette 3 can be facilitated. On the bottom side of the active box IB a rail 15 can be mounted for attaching the cupboard to a base such as a cellar wall or similar thing. By separating the components of the switch unit 101 , so that the optical connectors or input ports are located in one first box 1A and the other components in a second box lb, the mounting and connection of the entire switch unit can be made only requiring that the first box 1A is opened to make the optical connections. Also, by providing different keys, not shown, to the locks of the lids of the boxes, only authorized persons can gain access to either one of the two boxes. The invention is of course not limited to the embodiments described above and illustrated in the drawings but can be modified within the scope of the appended claims.

Claims: CLAIMS 1. An optical fiber network comprising a central unit connected through a local device to a plurality of subscriber terminals, the local device placed adjacent to the subscriber terminals, each of the subscriber terminals connected by a pair of optical fibers to the local device and the central unit connected by an optical transport network to the local device, characterized in that the local device comprises a controllable switch for switching traffic internally between the subscriber terminals and between the subscriber terminals and the central unit. 2. An optical fiber network according to claim 1 , characterized in that the optical transport network connecting the central unit to the local device comprises a ring network. 3. A traffic distribution unit for distributing traffic in an optical fiber network comprising a plurality of subscriber terminals and a central unit, the traffic distribution unit comprising subscriber connectors for optical fibers connected to the subscriber terminals and network connectors for optical fibers in an optical transport network connected to the central unit, the traffic distribution unit conducting traffic between the subscriber connectors and the network connectors, characterized by a controllable switch for controlled local switching of traffic between the subscriber connectors, allowing traffic between subscriber terminals connected to the traffic distribution unit to pass only through the traffic distribution unit and not to an optical transport network connected to the traffic distribution unit. 4. A traffic distribution unit according to claim 3 , characterized in that the controllable switch is arranged to also switch traffic between the subscriber connectors and the network connectors. 5. A traffic distribution unit according to claim 3, characterized by an optical cross connect unit for fixed connections between ports on first side of the cross connect unit and ports on a second side, the ports on the first side connected to or including the subscriber and network connectors. 6. A traffic distribution unit according to claim 5, characterized in that the ports on the second side are connected to optoelectrical and electrooptical converters for traffic incoming to and going out from the traffic distribution unit respectively, the optoelectrical converters connected to the controllable switch to provide electrical signals thereto and the electrooptical converters connected to the controllable switch to receive electrical sisnals therefrom. 7. A traffic distribution unit according to claim 3, characterized by electronic logical filters to prevent traffic intended for one of the subscriber terminals from being received by other ones of the subscriber terminals by filtering away such information. 8. A traffic distribution unit according to claim 7, characterized in that the electronic logical filters are also arranged to filter traffic from one of the subscriber terminals so that the traffic cannot interfere with traffic to or from other ones of the subscriber terminals. 9. A traffic distribution unit according to claim 3, characterized by hardware and software for supporting handling of virtual networks (VLANs). 10. A traffic distribution unit according to claim 3, characterized by a housing including a first box and a second box, the first box enclosing the subscriber and network connectors and the second box enclosing remaining components of the traffic distribution unit. 11. A traffic distribution unit according to claim 10, characterized in that the first box includes a plurality of cassettes in which the subscriber and network connectors are placed. 12. A traffic distribution unit according to claim 1 1 , characterized in that the cassettes include two winding cores around which excessive length of optical fibers and fiber ribbons can be wound.

Inventors: EKLUND HANS, HOLMBERG JOHAN, NILSSON LARS, RADOJEVITC GOJKO, RENGMAN JACOB, SJOELINDER SVEN, WRIF KENNETH, EKLUND, HANS, HOLMBERG, JOHAN, NILSSON, LARS, RADOJEVITC, GOJKO, RENGMAN, JACOB, SJOELINDER, SVEN, WRIF, KENNETH
Applicants: EKLUND HANS, ERICSSON TELEFON AB L M, HOLMBERG JOHAN, NILSSON LARS, RADOJEVITC GOJKO, RENGMAN JACOB, SJOELINDER SVEN, WRIF KENNETH, EKLUND, HANS, HOLMBERG, JOHAN, NILSSON, LARS, RADOJEVITC, GOJKO, RENGMAN, JACOB, SJOELINDER, SVEN, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL), WRIF, KENNETH
Application year: 2001
Main classification: H04B10
IPC codes: H04B10, H04Q11