GB2175775A - Data transmission system - Google Patents

Abstract

In a data transmission system, e.g. a local area network, each station is connected to the next adjacent station via two fibre optic links, one of which terminates at an auxiliary receiver in the station. The other fibre link terminates at an optical splitter (OS) with two output paths. One such path goes to the station's own normally active receiver and the other to the auxiliary receiver at the next downstream station. If a station fails, the next downstream station detects this, and switches out its normally effective receiver, and switches in its own auxiliary receiver, thus bypassing the failed station. <IMAGE>

Description

SPECIFICATION Data transmission system This invention relates to a data transmission system of the serial type, such as, for instance a local area network.

In such a system it will be appreciated that a failure of a single station of the system is catastrophic since many or indeed all stations may be denied service. An object of the invention is to provide a system in which this difficulty is minimised or overcome.

According to the invention, there is provided a data transmission system, in which data are transmitted from a source station to a destination station via a data transmission medium serving a number of stations, in which a said transmission medium is connected at the input side of each said station, to a first data path to a receiver device at that station and to a second data path to an auxiliary receiver device at the next station on the transmission medium, so that the medium is duplicated with each said station having two such media arriving at its input, in which in normal operation the auxiliary receiver device at a said station, although receiving data from the next preceding station, is ineffective, in which if a failure occurs at a said station the detection of that failure at the next adjacent station causes the connection of that next adjacent station's auxiliary receiver device instead of its normally effective receiver device, so that the faulty station is bypassed.

The accompanying drawing shows schematically a fibre optic communication system of the closed loop type embodying the invention, but it should be noted that the invention is applicable to other types of serial systems.

As can be seen from the drawing, each station is connected to the next station by two fibre optic paths, each of which terminates at an optical receiver, i.e. an opto-electronic converter O-E. The uppermost fibre optic path at each station terminates, as can be seen, at a normally disconnected, i.e. ineffective, receiver O-E.

The lower-most path is connected in each station to an optical splitter (OS) via the upper output path of which it is connected to the normally disconnected receiver of the next station in the downstream direction. The lower output path from the splitter is connected to the station's normally effective receiver OE. This gives access to the station's electrical interface, which is also connected to an electro-optical converter (transmitter) EO.

In normal operation, with the switches, which could be electronic switches, set as in the drawing, data pass from Station 1 to Station 2 over fibre link 1D-2B, and then to Station 3 via link 2D-3B.

If Station 2 develops a fault, Station 3 stops receiving valid data, which is detected by electronics (not shown) in Station 3. This causes the switch at Station 3 to be reversed so that the upper receiver thereat is selected.

Data then pass from Station 1 to Station 2 over fibre 1D-2B (as before), and then via the optical splitter in Station 2 and fibre 2C-3A to Station 3. Thus Station 2 is bypassed. In addition an alarm indication is given at Station 3, and sent over the data transmission path to notify other stations, and maintenance personnel, that a fault has occurred in Station 2.

As a result of the above operations, the only component in Station 2 still in the transmission path is the optical splitter. This is a passive component, and so its failure propensity is very low or even non-existent.

Where the system uses an electrical medium, the splitter could be a transformer or the like.

1. A data transmission system, in which data are transmitted from a source station to a destination station via a data transmission medium serving a number of stations, in which a said transmission medium is connected at the input side of each said station, to a first data path to a receiver device at that station and to a second data path to an auxiliary receiver device at the next station on the transmission medium, so that the medium is duplicated with each said station having two such media arriving at its input, in which in normal operation the auxiliary receiver device at a said station, although receiving data from the next preceding station, is ineffective, in which if a failure occurs at a said station the detection of that failure at the next adjacent station causes the connection of that next adjacent station's auxiliary receiver device instead of its normally effective receiver-device, so that the faulty station is bypassed.

2. A system as claimed in claim 1, in which the media are optical fibres and the normally effective medium is connected at each said station to the two paths via an optical splitter.

3. A system as claimed in claim 1, in which the media are electrical conductors and the normally effective medium is connected at each said station to an electrical transformer.

4. A data transmission system substantially as described with reference to the accompanying drawings.

5. A station for use in a system as claimed in claim 1, 2, 3 or 4.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Data transmission system This invention relates to a data transmission system of the serial type, such as, for instance a local area network. In such a system it will be appreciated that a failure of a single station of the system is catastrophic since many or indeed all stations may be denied service. An object of the invention is to provide a system in which this difficulty is minimised or overcome. According to the invention, there is provided a data transmission system, in which data are transmitted from a source station to a destination station via a data transmission medium serving a number of stations, in which a said transmission medium is connected at the input side of each said station, to a first data path to a receiver device at that station and to a second data path to an auxiliary receiver device at the next station on the transmission medium, so that the medium is duplicated with each said station having two such media arriving at its input, in which in normal operation the auxiliary receiver device at a said station, although receiving data from the next preceding station, is ineffective, in which if a failure occurs at a said station the detection of that failure at the next adjacent station causes the connection of that next adjacent station's auxiliary receiver device instead of its normally effective receiver device, so that the faulty station is bypassed. The accompanying drawing shows schematically a fibre optic communication system of the closed loop type embodying the invention, but it should be noted that the invention is applicable to other types of serial systems. As can be seen from the drawing, each station is connected to the next station by two fibre optic paths, each of which terminates at an optical receiver, i.e. an opto-electronic converter O-E. The uppermost fibre optic path at each station terminates, as can be seen, at a normally disconnected, i.e. ineffective, receiver O-E. The lower-most path is connected in each station to an optical splitter (OS) via the upper output path of which it is connected to the normally disconnected receiver of the next station in the downstream direction. The lower output path from the splitter is connected to the station's normally effective receiver OE. This gives access to the station's electrical interface, which is also connected to an electro-optical converter (transmitter) EO. In normal operation, with the switches, which could be electronic switches, set as in the drawing, data pass from Station 1 to Station 2 over fibre link 1D-2B, and then to Station 3 via link 2D-3B. If Station 2 develops a fault, Station 3 stops receiving valid data, which is detected by electronics (not shown) in Station 3. This causes the switch at Station 3 to be reversed so that the upper receiver thereat is selected. Data then pass from Station 1 to Station 2 over fibre 1D-2B (as before), and then via the optical splitter in Station 2 and fibre 2C-3A to Station 3. Thus Station 2 is bypassed. In addition an alarm indication is given at Station 3, and sent over the data transmission path to notify other stations, and maintenance personnel, that a fault has occurred in Station 2. As a result of the above operations, the only component in Station 2 still in the transmission path is the optical splitter. This is a passive component, and so its failure propensity is very low or even non-existent. Where the system uses an electrical medium, the splitter could be a transformer or the like. CLAIMS

1. A data transmission system, in which data are transmitted from a source station to a destination station via a data transmission medium serving a number of stations, in which a said transmission medium is connected at the input side of each said station, to a first data path to a receiver device at that station and to a second data path to an auxiliary receiver device at the next station on the transmission medium, so that the medium is duplicated with each said station having two such media arriving at its input, in which in normal operation the auxiliary receiver device at a said station, although receiving data from the next preceding station, is ineffective, in which if a failure occurs at a said station the detection of that failure at the next adjacent station causes the connection of that next adjacent station's auxiliary receiver device instead of its normally effective receiver-device, so that the faulty station is bypassed.

2. A system as claimed in claim 1, in which the media are optical fibres and the normally effective medium is connected at each said station to the two paths via an optical splitter.

3. A system as claimed in claim 1, in which the media are electrical conductors and the normally effective medium is connected at each said station to an electrical transformer.

4. A data transmission system substantially as described with reference to the accompanying drawings.

5. A station for use in a system as claimed in claim 1, 2, 3 or 4.