WO1999022459A1

WO1999022459A1 - Protection switching system

Info

Publication number: WO1999022459A1
Application number: PCT/EP1998/006745
Authority: WO
Inventors: Antti Poutanen
Original assignee: Nokia Networks Oy
Priority date: 1997-10-25
Filing date: 1998-10-23
Publication date: 1999-05-06
Also published as: AU1486399A; DE19747214A1

Abstract

This invention concerns a telecommunications system having a plurality of user interface ports (interface port) connected to a switching matrix (data connection), with each user interface port being switchable between a working port (hot) and a protection port (stand-by) which can assume the function of the working port in the event of a failure of the latter, and where all the user interface ports are connected by a common wiring logic (back-plane system) to the user interfaces belonging to the respective ports. To increase security against false triggering of a switching operation in the switching means, switching means are provided at each user interface for switching between the working port and the protection port, are assigned together in groups controlled by a common higher-order controlling system (supervisor), with the higher-order controlling system (supervisor) being connected over a separate bidirectional data exchange connection to the rest of the telecommunications system, where there is information about the respective status (HOT/STAND-BY) of the connected user interface ports.

Description

PROTECTION SWITCHING SYSTEM

This invention concerns a telecommunications system and a data transmission frame for use in such a telecommunications system.

A telecommunications system of the type defined initially is known from practical use. User interface ports designed in duplicate are provided with such a system and are connected to the switching matrix provided for all the interfaces. The purpose of this duplication in design is that in the event of a failure of one user interface port (hot) , its function can be assumed by the redundant user interface port (stand-by) . This yields a fail-safe design.

The switching means known from practice for switching between the hot user interface port and the stand-by user interface port are usually designed as electromechanical relays so that overvoltage protection is achieved in combination with a high reliability. The required transmission characteristics can be achieved by electromechanical relays .

A telecommunications system usually has a plurality of user interfaces, each switched by separate switching means. Such a design therefore means that a large number of switching relays are required. The switching relays are driven over lines provided through the passive backplane logic between the user interface and the telecommunications system. The relays are usually in working position (hot) when no coil voltage is applied and in protection position (stand-by) when voltage is applied.

To reduce the number of control lines required for the relays, it is known from practice that the relays can be divided into individual groups. The groups of relays may then be driven either with assigned group activation signals or with binary-coded control signals.

However, a disadvantage of this design is that there is no feedback signal to the higher-order control unit for the relays indicating whether or not the relay driven has actually responded, i.e., whether it has triggered the switching function.

Other disadvantages include the fact that the coil voltage is applied continuously in stand-by operation, which causes a high current consumption. Furthermore, when replacing the higher-order control unit, the relays may be switched inadvertently to stand-by state by voltage pulses although there is no malfunction of the hot terminal. In addition, interference on the back-plane logic can change the level of the control signal and cause a voltage peak. The risk of such interference is especially high because the protection module is designed to be separated mechanically from the telecommunications system. Purely external interference may also occur. Furthermore, large groups of relays can contribute to the emission of interference signals because they form parallel inductors which can emit high current peaks. This risk is also high because of the mechanical isolation of the protection module from the telecommunications system. Against this background, the object of the present invention is to improve upon a telecommunications system of the type defined in the preamble so that there will be greater security against false tripping of a switching operation in the switching means.

This object is achieved with a telecommunications system of the type defined in the preamble by the fact that at each user interface there are switching means for switching between a working port and a protection port, which are paired with each other in groups and can be controlled by a common higher-order controlling system (supervisor) , and the higher-order controlling system (supervisor) is connected by a separate bidirectional data exchange connection to the rest of telecommunications system where information is available regarding the respective status (HOT/STAND-BY) of the connected user interface ports.

This object is also achieved by a data transfer frame in a telecommunications system of the type defined in the preamble, characterized in that the data transfer frame used in a serial bidirectional data exchange connection between the higher-order controlling system and the rest of the telecommunications system contains information about the prevailing status (HOT/STAND-BY) of the connected user interface ports.

This invention is characterized in that mutual information regarding the desired and actual status (HOT/STAND-BY) of the switching means or the connected user interface ports is exchanged between the telecommunications system on the one hand and the higher- order controlling system on the other hand. With this solution, a plurality of switching means can be combined in groups without putting a strain on the necessary resources of the back-plane logic, because the switching means are controlled directly by the higher-order controlling system. The plurality of switching means to be controlled is determined and limited only by the length of the bidirectionally transmitted information. On the basis of the mutual information regarding the states of the respective switching means, the telecommunications system can now monitor completely whether or not the desired switching means have received the respective coil voltage pulses. This is extremely important so that the diagnosis confirms that an actual switching operation (from hot to stand-by) has taken place. The size of the group monitored by a common controlling system can then be set at will and may also apply to the control of only one single switching means, for example. The solution according to this invention also makes it possible to form any desired subgroups with the controlling system, with the subgroups being mechanically isolated from one another, but working together with the telecommunications system over the common data exchange connection.

One particular embodiment of the invention is derived from the fact that the data exchange connection is via serial data transfer organized by frames in the form of a data bus, where the beginning of the frame is identified by appropriate coding (SEL1, SEL2) . The data transferred serially may include the respective states of the ports, i.e., within the data transfer frame a certain portion of data bits is provided for the digital states of the respective ports assigned to the groups. Another portion of the data frame transferred may be reserved for test information. According to another embodiment of this invention, another portion of the data frame may be reserved for CRC (cyclic redundancy check) checksum notation. This compares whether or not the checksum of the data received matches the calculated checksum. If the checksums do not match, the status information is not relayed to the controlling means. This serves the purpose that in the event of transient phenomena during the signaling phase, triggering of the switching means is prevented. Interference in the control lines of the switching means can also be detected by determining the CRC checksum.

Several switching means belonging to one group of user interface terminals are preferably combined in one protection module (external protection module) . Such a device can preferably be retrofitted as a whole, because it can be mounted on the existing user interface terminals .

Relays are preferred for use as the switching means, and so-called latching type relays, i.e., locking relays, have the additional advantage that they have a reduced current consumption.

Additional preferred embodiments are derived from the following subclai s .

This invention is explained in greater detail below on the basis of drawings of one embodiment, showing:

Figure 1: the basic design of a telecommunications system on which the present invention is based;

Figure 2: diagrams of group control of switching means such as those known from the state of the art; Figure 3: a block diagram of one embodiment of this invention; and

Figure 4: diagrams of the frame structure of the data transfer frames used in the embodiment according to Figure 3.

The telecommunications system shown in Figure 1 on which the present invention is based consists essentially of three blocks, the telecommunications system shown in the left part and a passive wiring system (back-plane or cabling system) which serves to connect the telecommunications system to the user interface forming the third block. The telecommunications system usually has a plurality of such units, illustrated in Figure 1, with the passive back-plane logic being shared by all units .

The telecommunications system consists of a plurality of user ports, each of which is designed in duplicate. They have a working port (hot) and a redundant protection port (stand-by) . Both ports are connected to the switching matrix (data connection) . In the event of failure of the working port, the protection port assumes its function. Therefore, switching means in the form of switchable relays which trigger a corresponding change in state are provided in the area of the user interface.

The switching means are controlled by a higher-order controlling system (supervisor) which is located in the section of the telecommunications system.

In practice, such a telecommunications system will have a plurality of user interface ports, each of which is connected via a common back-plane logic to the user interface assigned to them, and each of which has separate switching means assigned to them.

Such switching means, which are designed as relays in practice, can be arranged in groups with a plurality of port outputs, as shown in Figure 2a, for example. Through corresponding triggering of the relays in groups, it is possible by means of the higher-order controlling system to switch from hot to stand-by.

In another variant illustrated in Figure 2b, binary coding means which are assigned to the groups of relays are driven by a corresponding coding device in the higher-order controlling system such that the desired switching of ports can take place through appropriate coding information.

Figure 3 shows the design of the telecommunications system with a higher-order controlling system corresponding to the embodiment according to the present invention.

In this regard the telecommunications system also has a serial data communications port whose input (SERIN) and output (SEROUT) is connected to a protection module. The resulting serial data flow formed in this way is controlled by a microprocessor. The higher-order controlling system which is designed as a protection module consists of a receiver section (receiver) and a transmitting section (transmitter) . A shift register where the incoming or outgoing data of the data connection is processed is assigned to each area of the transmitter or receiver. The shift registers are each connected to control lines for the relays which are designed as switching means and are assigned to one group. The relays used are so-called locking relays (latching type relays) which require two items of control information which are made available by the respective outputs of a shift register. In addition to the control lines in the receiver section, diagnostic lines are provided between the input lines of the relays and the shift register of the transmitting section to monitor the status of the relays, as explained below.

In addition, a checksum testing device (CRC check) is provided within the protection device, specifically one in the receiver section and another in the transmitter section.

Furthermore, the higher-order controlling system contains a counter for the data transfer frame (frame counter) and input information for the address of the protection module used (SLOT 1, SLOT 2), since several separate protection modules which communicate over a common data bus may be provided.

Figure 4a shows the typical structure of a frame (receiver frame) received by the receiver section, and Figure 4b shows the typical structure of the transmitter frame sent by the transmitter section.

The frames shown here each contain sections in which the HOT/STAND-BY states of the individual groups are provided, and they contain other sections serving the check and CRC functions.

In addition, the frame sent by the transmitter (transmitter frame) contains a section for an alarm signal (FERF) as well as an indication of the address of the protection module addressed (SLOT 1, SLOT 2) . The device according to this invention functions as follows :

A frame to be transmitted is generated in the serial data communications port of the telecommunications system for the frame receiver of the protection module having the structure according to Figure 4b. The desired HOT and STAND-BY states are there according to the relays belonging to the individual groups. As shown in Figure 3, relays of the latching type are used to reduce power consumption as much as possible, so each relay group is controlled by first transmitting the desired A or B bits as the "HIGH" state and then transmitting the same bits as the "LOW" state. This means that each group requires two items of control information to generate a pulse for the relays.

Relays 1 through N are triggered in accordance with the desired status information (HOT or STAND-BY) . The set states are transferred over the diagnostic information lines to the transmitter area of the protection module, where the information fields of the transmitter frame provided for this purpose are filled in accordance with the states actually set.

This frame is transmitted back to the microprocessor of the telecommunications system over the serial output interface of the protection module.

It is possible there to compare only whether or not there is a corresponding match in the data bits, so that it is ensured that the desired states of relays 1 through N have in fact been achieved. In addition, bits for the CRC (cyclic redundancy check) checksum following the information bits in the frame are also provided in the receiver frames and transmitter frames .

The purpose of providing the CRC checksum in the frame is to ascertain when there is a mismatch in the system. In other words, when a comparison between the received CRC checksum with the calculated checksum does not lead to a match, the frame with its information bits is not used to control the relays.

Instead, in this case direct information (far end alarm indication) is sent to the microprocessor, so that appropriate safety functions can be initiated.

In addition, the data bits provided in the transmitter frame for characterizing the respective module (SLOT 1, SLOT 2) are also recorded in the serial communications port of the telecommunications system. The data is processed there such that the input of the frame receiver is activated according to the bits set there in the area SEL 1, SEL 2 so that the desired SLOT is activated according to the protection module selected. For example, SEL 1 here corresponds to SLOT 1, and SEL 2 corresponds to SLOT 2.

Claims

A telecommunications system with a plurality of user interface ports (interface port) connected to a switching matrix (data connection) , with each user interface port being switchable between a working port (hot) and a protection port (stand-by) which can assume the function of the working port in the event of a failure thereof, and where all the user interface ports are connected over a common wiring logic (back-plane system) to the user interfaces belonging to the respective ports, characterized in that switching means which are provided at each user interface for switching between the working port and the protection port are assigned together in groups which can be controlled by a common higher-order controlling system (supervisor) , where the higher- order controlling system (supervisor) is connected to the rest of the telecommunications system over a separate bidirectional data exchange connection, with information about the respective status (HOT/STAND-BY) of the connected user interface ports being provided there.

A telecommunications system according to Claim 1, characterized in that the data exchange connection takes place by serial data transfer (data bus) which is organized by frames, with an area of the frame being provided for the status information on the user interface ports.

3. A telecommunications system according to Claim 2, characterized in that another area of the transmitted frame is provided for additional test information (CRC check, test) .

4. A telecommunications system according to one of the preceding claims, characterized in that several switching means belonging to a group of user interface terminals are combined into one protection module (external protection module) .

5. A telecommunications system according to one of the preceding claims, characterized in that the switching means are relays.

6. A telecommunications system according to Claim 5, characterized in that the relays are locking relays (latching type relays) .

7. A telecommunications system according to one of Claims 4 through 6, characterized in that the protection module consists of a receiving device

(frame receiver) and a transmitting device (frame transmitter) , each of which has shift registers for information corresponding to the terminal states

(HO /STAND-BY) of the connected user interface ports .

8. A telecommunications system according to Claim 6, characterized in that two items of information are provided for each relay to be controlled.

9. A telecommunications system according to one of the preceding claims, characterized in that multiple protection modules are provided, each assigned to different groups of user interface ports, participating jointly in the data exchange connection.

10. A telecommunications system according to Claim 5, characterized in that the data transmission frame contains an additional identification (SEL 1) for the respective protection module.

11. A data transfer frame in a telecommunications system having a plurality of user interface ports, each connected to a switching matrix (data connection) , with each user interface port being switchable between a working port (hot) and a protection port

(stand-by) which assumes the function of the working port in the event of failure thereof, and where switching means are provided at each user interface for switching between the working port and the protection port, said switching means being assigned to one another in groups and being controllable by a common higher-order controlling system (supervisor) , characterized in that the data transfer frame used in a serial bidirectional data exchange connection between the higher-order controlling system and the rest of the telecommunications system contains information about the respective status (HOT/STANDBY) of the connected user interface ports.

12. A telecommunications system according to Claim 11, characterized in that the frame contains additional information, in particular test information.