GB2250894A

GB2250894A - Providing redundancy in digital transmission equipment

Info

Publication number: GB2250894A
Application number: GB9120928A
Authority: GB
Inventors: Reino Osmo Ilmari Talarmo; Jukka Tapio Ruosteoja; Harri Juhani Lahti; Esa Tapio Toermae
Original assignee: Telenokia Oy
Current assignee: Nokia Oyj
Priority date: 1990-10-01
Filing date: 1991-10-01
Publication date: 1992-06-17
Anticipated expiration: 2011-10-01
Also published as: FI904834A0; FI87123B; GB9120928D0; FI904834A; DE4132729C2; DE4132729A1; FI87123C; GB2250894B

Description

22 503 ^4 1 System for providing redundancy for the baseband main channels

of digital transmission equipment This invention relates to a system for combining the main channel interfaces of duplicated transmission equipments, such as radio links.

Duplicated transmission equipments, typically comprising two similar transceivers connected in parallel, such as radio links, and a baseband branching device connected to them (so-called 1+1 redundancy), operate both in the receive and transmit direction of a telecommunication network. The choice of the radio equipment to be used in each particular case usually depends on which equipment produces a signal of superior quality.

In prior art arrangements, the branching function between the two changeovertransmission equipments is integrated in either one of the duplicated equipments, such as radio links. The branching device thereby contains and is dependent on one of the transmission equipments and its active components, the failure rate of which af f ects directly the failure rate of the branching device. The disconnection of a faulty equipment for repair may totally break the connection for the time of the replacement or repair. In addition, the structure of the equipments may vary in different conditions and with different ways of operation and be problematic in view of the production.

The object of the invention is to provide a method and a device by means of which the above disadvantages are avoided. To achieve this, the system according to the invention is characterized in that the system comprises a separate branching device in which the main channel interfaces of the transmission 57300.535 is equipments are combined, the main channel being branched in the receive direction by means of at least one transformer and connected in the transmit direction directly or by means of at least one transformer.

When a failure occurs, duplicated radio links/ transmission equipments can decide to switch the traffic to the equipment ready for use by mutual control means.

only the baseband branching device is common to the equipments. In this way, the reliability is considerably increased, which is the primary object of the invention. In prior art arrangements, many parts of the equipment remain unduplicated.

In the invention, the reliability of the connection in case of malfunction is increased almost independently of the basic radios. The transmission equipments may be identical in structure and their structure is not dependent on the way of operation, that is, similar equipments as in non-redundant systems can be used. Due to the separate branching device, the system is simpler than prior art systems both in view of production and in view of the customer's choice of equipment.

Other preferred embodiments of the invention are characterised by what is disclosed in the accompanying claims.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Figure 1 shows a duplicate pair of transmission equipments in which a prior art technique is applied;

Figure 2 shows a duplicated radio link station according to an embodiment of invention; Figure 3 shows a branching device according to 3 one embodiment of the invention; and - Figure 4 shows a branching device according to another embodiment of the invention.

In the prior art arrangement shown in Figure 1, two transmission equipments, in this particular case radio links 1 and 2, are connected to a digital main channel, that is, a telecommunicltion network A. In addition to a link equipment 5 itself, the radio link 1 comprises a required interface, that is, a G.703 interface 3, and a changeover switch 4 which ensures maintenance of connection both when a failure occurs in one of the link equipments 2, 5 and when disturbances occur in the propagation of the signal received by the equipments by changing over to the other equipment e.g. when the quality of the received signal is inferior. The G.703 interface is a standard interface used in telecommunication networks, its specifications and properties being obvious to one skilled in the art. On the side of the transmission path B, when the transmission equipments are radio links, as in this specific example, the antenna cables of the radio links can, for instance, be connected to an antenna branching device 6 for further transmission by means of an antenna 7.

In other words, the branching device in the conventional arrangement is an intelligent changeover switch 4 realized by active components and the required interface 3 is constructed in connection with the radio link 5.

Figure 2 shows a duplicated radio link station corresponding to that of Figure 1 but according to an embodiment Of the invention. The radio link station comprises a baseband branching device 8, two radio linls 9 and 10 and, similarly as above, an optional antenna branching device 6 4 and an antenna 7. The radio links 9 and 10 comprise the actual transmission equipments, i.e. radio links 11 and 12, and modified G.703 interfaces 13 and 14 comprising improved receive direction attenuation tolerance, switching of the inactive output to a proper idle state, adaption of the transmit direction to the baseband branching device 8, and a radio link processor program portion which causes the outputs of the G.703 interface to be switched to the right state when a changeover command is received. The interface parts 13, 14 of the radio links have to be designed for co-operation with the baseband branching device 8. Signal attenuation caused by a transformer provided in the inputs (see Figure 3 and 4) has to be taken into account in the design of the corresponding input in the transmission equipment in such a way that this input tolerates the attenuation caused by the branching device in addition to normal attenuation.

As the baseband branching device 8 is able to connect the outputs of the transmission equipment galvanically together (see Figure 3), the outputs 13, 14 of the transmission equipment 11,12 have to be designed so as to make this possible. The control unit of the transmission equipment causes the outputs to be switched to the right state depending on which one of the equipments is in use. Since only one of the outputs is in an active state, a data transmission connection 15 has to be provided between the control units of the transmission equipments. This is also necessary for the propagation redundancy of the signal, as this function is not performed bythe baseband branching device in this embodiment of the invention; instead, it is performed by the radio links 9 and 10. A duplicate equipment switch 17a, l7b passes the signal to an active propagation redundancy switch 18a or 18b which changes the path of propagation of the signal to the other link whenever required, e.g. when the signal received from the transmission path B is weak. The switches 17a, 17b, 18a and 18b are electronic switches controlled by the control units (not shown) of the transmission equipments. In general, only one of the interfaces 13 and 14 is active at a time, that is, the signal passes only via the interface of one radio link through the baseband branching device until the other interface is made active due to a failure or for some other reason.

The radio links 9 and 10 are identical devices, and the branching device 8 is completely separate from them, effecting solely the provision of redundancy for the link station, that is, the disconnection of the faulty link (9 or 10) from the network in case of failure. Now in the data transmission to and from the radio links in the telecommunication network A, the number of common unduplicated components in the duplicated pair formed by the radio links 9 and 10 is minimized, the only common component being the branching device 8 comprising mainly passive parts. This arrangement according to the invention increases considerably the reliability of the radio link station.

Figure 3 shows a branching device according to one embodiment of the invention, operating at a rate of 2 Mbit/s. In this branching device, which is completely passive, the receive direction is realized by a transformer 21 having two windings on its secondary side, and the transmit direction is realized by simply connecting the wires of the transmission equipments galvanically 22 together.

6 Figure 4 shows a branching device according to another embodiment of the invention, designed to operate at a rate of 34 Mbit/s. At a rate of this order, amplifiers 19, 20 have to be provided in the receive direction of the branching device so as to amplify signals coming from the transformer 21; in the transmit direction, an impedance matching transformer 23 is also usually needed. A standby power supply 16 has to be provided for the active parts of the 34Mbit/s branching device (Figure 2).

It is obvious to one skilled in the art that the different embodiments of the invention are not restricted to the above examples, but may vary within the scope of the accompanying claims. Accordingly, the telecommunication network connected to the branching device may be a fixed network, such as a telephone network, radio path or telecommunication terminal station, such as a PAD computer. The transmission path utilized by the transmission equipments may also be a fixed network or an optical transmission path as well as a radio path. Without deviating from the invention, the signal divided by the baseband branching device may also propagate over geographically different paths, e.g. in the two different directions of a loop formed by branching repeater stations, whereby the same redundancy is provided as with transmission equipments operating in parallel (i.e. utilizing the same geographical path).

57300.535

Claims

1. System for combining substantially identical main channel interfaces of duplicated transmission equipments, such as radio links, in such a manner that only one of the interfaces is in an active state at a time, characterised in that the system comprises a separate branching device in which the main channel interfaces of the transmission equipments are combined, the main channel being branched in the receive direction by means of at least one transformer and connected in the transmit direction directly or by means of at least one transformer.

2. System according to claim 1, characterised in that active amplifiers are coupled to the secondary side of the transformer of the branching device dividing the 20 main channel in the receive direction.

3. Transmitting and receiving apparatus comprising, a pair of transmitting/receiving means, each said transmitting/receiving means having associated therewith a respective channel interface; a branching device connecting a main channel to said channel interfaces; and switching means for selectively interconnecting one of said channel interfaces with one of said pair of transmitting/receiving means.

Transmitting and receiving apparatus as claimed in claim 3 wherein in the receiving direction said branching device comprises a transformer, and wherein in the transmitting direction said branching device 35 comprises a direct connection or a transformer.

5. Transmitting and receiving apparatus as claimed in - 8 claim 4 wherein amplifiers are coupled to the secondary side of the transformer in the receiving direction.

6. Transmitting and receiving apparatus as claimed in claim 4 or 5 wherein in the transmitting direction the branching device comprises an impedance matched transformer.

7. Transmitting and receiving apparatus as claimed in any of claims 3 to 6 wherein said transmitting/receiving means are connected via a second branching device to a single antenna.

8. Transmitting and receiving apparatus substantially is as hereinbefore described with reference to Figures 2 to 4 of the accompanying drawings.