AU650969B2

AU650969B2 - Bidirectional data transmission

Info

Publication number: AU650969B2
Application number: AU15939/92A
Authority: AU
Inventors: Andreas Hennig; Jurgen Schroeder; Michael Stilll
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1991-05-03
Filing date: 1992-04-30
Publication date: 1994-07-07
Anticipated expiration: 2012-04-30
Also published as: EP0521253A3; EP0521253A2; DE4114485A1; AU1593992A

Description

P/00/011 28/5/91 Regulation 3.2 650969 4 .14.

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "BIDIRECTIONAL DATA TRANSMISSION" The following statement is a full description of this invention, including the best method of performing it known to us:- This invention relates to a method for the bidirectional transmission of digital data via a. glass fibre, which enables the transmission of the data from one transmission direction via the glass fibre during transmission pauses from the other transmission direction.

Better use of existing transmission paths can be achieved with the bidirectional transmission of data via a glass fibre. Such a method is especially suitable if, in accordance with a known method, the same component part is used for the transmission and reception of the signals, which can be switched to the respective operating mode and to which the glass fibre, can be directly connected. The transmission of signals from a transmitter of a station, which is connected to a glass fibre, to the receiver of the opposite station is only possible when the transmitter of the opposite station is not transmitting. With known methods only one of the transmitters of both stations oo operates alternately in the so-called ping-pong operation. The duration of the transmit mode of the currently transmitting station determines the waiting time of the 15 other station, during which time the latter cannot transmit any data. The data i. flowing into the necessarily passive station have to be stored during receive mode, which can only be achieved with a relatively great effort.

An object of the present invention is to further develop the initially described known method in order to enable the transmission of the data from both stations at 20 each end of the glass fibre without substantial delays.

According to the present invention there is provided a method for the bidirectional transmission of digital data via a glass fibre, which enables the transmission of the data of one transmission direction via the glass fibre during transmission pauses of the other transmission direction, said method comprising the steps 25 of: reducing the bits of continuous data flow by at least a factor of 4; transmit the reduced bits of the data flow of one transmission direction in gaps resulting from reduction between the bits of the data flow of the respective other transmission direction; and elongate the bits to their original time-extension to recover the continuous data flows in the receiving stations.

The application of this method allows the transmission and reception of data C flows from both stations at the same time. The capacity of memories, which have to be provided in the stations for the incoming and outgoing data, can be kept small.

Because the data flow into opposite directions and they do not interfere with each 1 other on the glass fibre it is therefore only necessary to ensure in the transmitting and receiving devices that the incoming bits do not arrive during the transmission phase of a station. Using this method the bits are received in a moment, when the transmitter on the receiving side is not active, b-ecause its data flow is showing a gap. This is achieved through the reduction of the bits of both data flows by at least factor 4 and through the resulting gaps as well as the transmission of the bits, which is synchronised with these gaps. Collisions cannot occur.

In order that the inventic may be readily carried into effect, an embodiment thereof will now be described in relation to the drawings, in which: Figure 1 shows a continuous data flow with unreduced and reduced bits.

Figure 2 shows two data flows with reduced bits flowing into opposite directions.

1,,K Figure 3 shows a circuit for the implementation of the method based on the invention.

S 15 The data are transmitted in continuous data flows with a random binary code t as it is shown, eg. in Figure 1 above. In accordance with Figure 1 the bits of the data flows are reduced at least by factor 4 at the bottom in order to enable a simultaneous and collision-free data transmission in both directions. As a consequence their maximum time-extension is 25% of the original extension. The bits of a data flow, which is treated in this manner, are subsequently transmitted in one direction at unvaried transmission speed via a glass fibre G (Figure At the same time a data flow in the opposite direction, which is treated in the same manner, is transmitted in such a way that it's bits are respectively positioned in the gaps resulting from the reduction (one of which is marked with hatched lines in Figure 1) between the bits of the other data 25 flow. Consequently the bits transmitted from one side are received on the opposite side in the transmission pauses. Two data flows of this kind, data flow I and II, are shown in Figure 2. For better understanding the drawing of data flow I is inverted.

The bits of both data flows have to be reduced at least by factor 4 to ensure that a time-coincidence of transmitted and received signals at both ends of the transmission link is avoided at any possible length of the glass fibre G and any appertaining transit time of the data flows.

For the reduction of bits factor 4 has to be considered as a limit value, which is only valid in ideal conditions. For this purpose the bits are reduced more or a code is used, which ensures that the time-extension of the reduced bits is less than 25% of 1 their original extension, even with a factor 4 for the reduction. Such a code could be 4 a RZ-Code. When it is applied the original bits are already reduced to 50%. In that case a reduction by factor 4 results in bits with a time-extension, which is 12.5% of their original extension. Data flows of this kind in the bidirectional operation leave enough time to shift between transmit mode and receive mode.

When transmitting the data flows it is not very important that the reduced transmit-bits at each end of the glass fibre G are positioned exactly in the centre of the gaps between the received-bits. It is only important to ensure that there is enough time to distinguish between transmission phase and reception phase at the respective station in order to recognise the relevant received-bit correctly.

It is sufficient to continue the operation of the laser diode with initial current when a laser module is used as a transmission and reception component part in the reception phase. This way the incoming light can penetrate the laser diode and fall onto the monitor diode. It would, however, also be possible to switch off the laser I, diode completely.

A transmission link, which can be used for the transmission of digital data with the method based on the invention, is shown in the example of Figure 3. It consists Sof two stations STI and ST2, between which a glass fibre G is positioned. Every station includes a reducer VK, a transmitter S, a receiver E and an elongater VL.

A digital delay unit with respective linkage or a digital differential element could eg.

X 20 be used as a reducer VK. The elongater VL could, eg. be a flip-flop, which is keyed with the frequency of the original digital data flow.

The incoming bits of continuous digital data flows at station I and station II are S time-reduced in the reducer VK and transmitted to the glass fibre G by the transmitters S. The reduced bits are received by the receivers E of the respective opposite station and returned to their original time-length by the elongaters VL. The original continuous data flows are then recovered.

i

Claims

1. A method of transmitting a first data stream from a first transmit-receive station to a second transmit-receive station via an optical fibre and transmitting a second data stream from the second transmit-receive station to the first transmit-receive station via the optical fibre, the method including: reducing the duty cycle of the bits of the first and second data streams to no more than 25%; and, at the second transmit-receive station, transmitting successive reduced bits of the second data stream between the reception of pairs of bits of the first data stream; and, at the first transmit-receive station, transmitting successive reduced bits of the first data stream between the reception of successive bits of the second t" data stream.

2. A method as claimed in claim 1 including the step of restoring the duty cycle of the bits received at the first and second transmit-receive stations to the test Q t I original duration before the duty cycle was reduced.

3. A method as claimed in claim 1 or claim 2 wherein the first and second data streams are coded with an RZ-code before the duty cycle of the bits are i 0 reduced.

4. A method of bi-directional transmission via an optical fibre substantially as herein described with reference to the accompanying drawings. 2i,

5. A bi-directional transmission arrangement including a first transmit-receive S station connected to a second transmit-receive station by an optical fibre each i station including duty cycle reduction means to reduce the duty cycle of bits of its output data stream to not more than 25% and transmission means controlled to transmit successive reduced duty cycle bits in the interval between the reception of successive reduced duty cycle bits from the other transmit-receive Itests station.

6. An arrangement as claimed in claim 5 wherein each transmit-receive station includes RZ-coding means to encode the bits to be transmitted.

7. An arrangement as claimed in claim 5 or claim 6 wherein each transmit- U.1I 6 receive station includes duty cycle restoring means to restore the duty cycle of received bits.

8. An arrangement as claimed in any one of claims 5 to 7 wherein each transmit-receive station includes optical detector means to receive bits transmitted from the other transmit-receive station, each transmit-receive station including control means to switch its optical detector means oft while it is transmitting a bit.

9. A bi-directional transmission arrangement substantially as herein described with reference to the accompanying drawings. DATED THIS EIGHTH DAY OF APRIL 1994 ALCATEL N.V. r t t t t t C c CC C 1 H itEN O 4 ABSTRACT A method for the bidirectional transmission of digital data via a glass fibre, which enables the transmission of the data from one transmission direction during transmission pauses of the other transmission direction. According to the invention the bits of continuous data flows are reduced at least by factor 4 and the reduced bits of the data flow of one transmission direction are transmitted in the gaps, which re- suit from this reduction, between the bits of the data flow of the respective other transmission direction. The bits in the receiving stations are elongated to their ori- ginal time-extension in order to receiver continuous data flows. Figure 1. t tI K t c t.