GB1581803A - Data transmission system - Google Patents

Description

(54) DATA TRANSMISSION SYSTEM (71) We, STANDARD TELE PHONES AND CABLES LIMITED, a British Company of 190 Strand, London W.C.2. England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a multi-'station data transmission system in which the stations served are interconnected by optical fibre transmission links.

An' object of the present invention is to provide a system- of the above type which has a high degree of system security.

According to the invention there is provided a data transmission system having a number of stations between which data is conveyed via optical fibre transmission links, in which each station has an optical transmission coupler to which it is coupled, the couplers being interconnected serially by the optical fibre links, in which each said coupler interconnects at least three incoming links and at least three outgoing links, in which for each said coupler one of the incoming links and one of the outgoing links provide the coupling between that coupler and its said station. in which for each said coupler each of the other incoming links and each of other outgoing links comes from or goes to another one of the couplers of the system, and in which the couplers and each of the links which interconnects two couplers of the system are so arranged that there are at least two communication paths including optical fibres between the couplers of any pair of non-adjacent stations Embodiments of the invention will now be described with reference to the accompanying highly schematic Figures 1 to 3.

Optical fibre transmission systems may be of the closed loop type. and the arrangements described herein are in fact of this type. However, the invention is also applicable to multi-station systems which are not of the closed loop type. A further point to notice is that in transmission systems which use optical fibre transmission links, repeaters may be needed to deal with problems caused by attenuation in the fibres. Such repeaters, however, have not been shown in the drawings as they are not relevant to the present invention. However a typical repeater has a receiving device such as a phototransistor which responds to light incoming via an optical fibre which feeds electronic circuitry which in response to the phototransistor output produces an amplified version of the incoming signal.This amplified version is then applied via a laser or a lightemitting diode to the outgoing optical fibre.

Figure 1 shows a multi-station communicating system with three fibre communication links serving the stations. At each station there is transmission coupler or mixer such as M which is connected as shown to the station's equipment S. Each of these couplers has three fibres entering one of its ends and three leaving its other end so that light arriving at such a coupler on one fibre is distributed over the three fibres at the other end of the coupler.

Thus three outgoing fibres leave the "transmit" end of each coupler, one of which goes to the appropriate station equipment such as S, while a second fibre goes to the next station's coupler, e.g. N, and a third fibre goes to the next-but one station's coupler 0. In a similar way, at the "receive" end we have three fibres, one from the station equipment, one from the next station and one from the next but one station.

Thus it will be seen that in a closed loop system there are at least two optical paths between any pair of optical couplers. with the exception of pairs of adjacent couplers.

Thus for a multi-station system there is no problem of different path delays, and at worst only one terminal will be affected by the failure of any one fibre or coupler.

In the absence of repeaters such as referred to above, the maximum number of stations in the loop depends on the losses introduced by the couplers, and the inherently unbalanced way in which even perfect components would distribute the optical power.

Optical couplers such as described in our Application No. 15530/77 (Serial No 1558643) can be used in systems embodying the present invention.

The balance of the system, and hence the maximum number of stations which it can accommodate, can be improved by extending the principle to couplers with more than three ways, i.e. each with more than three input fibres and more than three output fibres. Figure 2 shows such a system, which is similar to Figure 1 except that it has a four-way coupler at each of its stations.

Note that in Figure 2 the station equipments are not actually shown. Thus each coupler in the system of Figure 2 has four incoming optical fibres, one from its own station equipment, one from the immediately preceding station's coupler, one from the nextbut-one preceding station's coupler and one from the next-but-two preceding station's coupler. Similarly each of these couplers has four outgoing optical fibres, one to its own station equipment, one to the immediately succeeding station's coupler, one to the next-but-one succeeding station's coupler and one to the next-but-two succeeding station's coupler. Since the couplers for only three stations are shown in Figure 2, not all of these connections actually appear therein.

As will be seen from Figure 3. in which again we do not show the station equipments, it is simple to introduce a new station into the system by breaking the fibres at the dotted lines shown and connecting the fibres to a new station as shown in the lower half of Figure 3.

WHAT WE CLAIM IS: 1. A data transmission system having a number of stations between which data is conveyed via optical fibre transmission links, in which each station has an optical transmission coupler to which it is coupled, the couplers being interconnected serially by the optical fibre links. in which each said coupler interconnects at least three incoming links and at least three outgoing links, in which for each said coupler one of the incoming links and one of the outgoing links provide the coupling between that coupler and its said station. in which for each said coupler each of the other incoming links and each of the other outgoing links comes from or goes to another one of the couplers of the system. and in which the couplers and each of the links which interconnects two couplers of the system are so arranged that there are at least two communicating paths including optical fibres between the couplers of any pair of nonadjacent stations.

2. A system as claimed in claim 1, in which each said coupler has three incoming fibres, one from the station equipment with which that coupler is associated, one from the coupler at the immediately preceding station and one from the coupler at the next-but-one preceding station, and in which each said coupler has three outgoing optical fibres one to the station equipment with which that coupler is associated, one to the coupler at the immediately succeeding station and one to the coupler at the next-but-one succeeding station.

3. A system as claimed in claim 1, in which each said coupler has four incoming optical fibres, one from the station equipment with which that coupler is associated, one from the coupler at the immediately preceding station, one from the coupler at the next-but-one preceding station and one from the coupler at the next-but-two preceding station, and in which each said coupler has four outgoing optical fibres, one to the station equipment with which that coupler is associated, one to the coupler at the immediately succeeding station, one to the coupler at the next-but-one succeeding station and one to the coupler at the next-but-two succeeding station.

4. A data transmission system substantially as described with reference to Figure 1, 2 or 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. worst only one terminal will be affected by the failure of any one fibre or coupler. In the absence of repeaters such as referred to above, the maximum number of stations in the loop depends on the losses introduced by the couplers, and the inherently unbalanced way in which even perfect components would distribute the optical power. Optical couplers such as described in our Application No. 15530/77 (Serial No 1558643) can be used in systems embodying the present invention. The balance of the system, and hence the maximum number of stations which it can accommodate, can be improved by extending the principle to couplers with more than three ways, i.e. each with more than three input fibres and more than three output fibres. Figure 2 shows such a system, which is similar to Figure 1 except that it has a four-way coupler at each of its stations. Note that in Figure 2 the station equipments are not actually shown. Thus each coupler in the system of Figure 2 has four incoming optical fibres, one from its own station equipment, one from the immediately preceding station's coupler, one from the nextbut-one preceding station's coupler and one from the next-but-two preceding station's coupler. Similarly each of these couplers has four outgoing optical fibres, one to its own station equipment, one to the immediately succeeding station's coupler, one to the next-but-one succeeding station's coupler and one to the next-but-two succeeding station's coupler. Since the couplers for only three stations are shown in Figure 2, not all of these connections actually appear therein. As will be seen from Figure 3. in which again we do not show the station equipments, it is simple to introduce a new station into the system by breaking the fibres at the dotted lines shown and connecting the fibres to a new station as shown in the lower half of Figure 3. WHAT WE CLAIM IS:

1. A data transmission system having a number of stations between which data is conveyed via optical fibre transmission links, in which each station has an optical transmission coupler to which it is coupled, the couplers being interconnected serially by the optical fibre links. in which each said coupler interconnects at least three incoming links and at least three outgoing links, in which for each said coupler one of the incoming links and one of the outgoing links provide the coupling between that coupler and its said station. in which for each said coupler each of the other incoming links and each of the other outgoing links comes from or goes to another one of the couplers of the system. and in which the couplers and each of the links which interconnects two couplers of the system are so arranged that there are at least two communicating paths including optical fibres between the couplers of any pair of nonadjacent stations.

2. A system as claimed in claim 1, in which each said coupler has three incoming fibres, one from the station equipment with which that coupler is associated, one from the coupler at the immediately preceding station and one from the coupler at the next-but-one preceding station, and in which each said coupler has three outgoing optical fibres one to the station equipment with which that coupler is associated, one to the coupler at the immediately succeeding station and one to the coupler at the next-but-one succeeding station.

3. A system as claimed in claim 1, in which each said coupler has four incoming optical fibres, one from the station equipment with which that coupler is associated, one from the coupler at the immediately preceding station, one from the coupler at the next-but-one preceding station and one from the coupler at the next-but-two preceding station, and in which each said coupler has four outgoing optical fibres, one to the station equipment with which that coupler is associated, one to the coupler at the immediately succeeding station, one to the coupler at the next-but-one succeeding station and one to the coupler at the next-but-two succeeding station.

4. A data transmission system substantially as described with reference to Figure 1, 2 or 3 of the accompanying drawings.