Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
2000-08-28
2001-05-01
Kizou, Hassan (Department: 2662)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S216000, C370S395430, C370S244000, C714S002000
Reexamination Certificate
active
06226261
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to providing redundancy for switching operations regularly carried out in telecommunications systems. In particular, the invention relates to switching elements backed up by redundant units, and specifically to redundant switching networks. In this context, a switching element refers to any unit or system that carries out a switching operation.
BACKGROUND OF THE INVENTION
For example at telephone exchanges, a switching network is the most important single component whose failure may, in the worst case, paralyse the telephone services of a larger number of subscribers. Therefore it is vital that the operation of the switching network can be efficiently controlled and that the operating personnel are immediately notified of any malfunctions to ensure that such malfunctions are quickly located and repaired.
Traditionally, the operation of the switching network has been protected by using two parallel switching networks that serve as mutual spare units.
FIG. 1
illustrates this type of switching network arrangement with two parallel switching networks, SWF_A and SWF_B. Normally, the data received at the switching network are connected to the input ports of both switching networks (INAi and INBi, i=1,2, . . . n), and both switching networks operate all the time carrying out switching operations in the same way. As a result, the data fed to the output ports (OUTAi and OUTBi, i=1,2, . . . n) are in normal operation identical. However, only one of the switching networks is, at any given time, selected as the active switching network whose output signals are forwarded.
The operation of an individual switching network (SWF_A or SWF_B) is monitored by performing internal comparative testing controlled by the switching network control unit (CU_A, CU_B). This comparison is carried out (see arrows) by branching off the data of selected output channels (time slots) and that of corresponding input channels (time slots) to the control unit which compares the two sets of data for the duration of several frames. Considering the total number of time slots, the actual number of channels being compared simultaneously is normally very low to ensure that the system does not become too complicated.
One drawback of such a redundant system is that whenever a minor fault occurs in the equipment that induces errors in the data passing through the switching network, this is not noticed until the internal compare test of the switching network happens to compare the input and output channels of that particular switching operation. For example, in a switching network with a maximum capacity of 2048 PCM circuits (2048 2048-kbit/s PCM signals, PCM=Pulse Code Modulation), it takes tens of seconds to identify an error in any single channel.
Another known method of providing redundancy is to use three switching networks in parallel and to compare the output data of all the switching networks. By applying the majority vote principle, the system identifies the switching network(s) that work(s) correctly. However, this is an expensive solution because it requires three identical switching networks.
SUMMARY OF THE INVENTION
The purpose of the invention is to eliminate the said drawbacks and to provide a solution that allows the operation of a switching network or other switching element to be tested quickly and reliably without having to resort to costly hardware.
This goal is achieved by using the solution defined in the independent patent claims.
The idea of the invention is to provide redundancy for a switching network (or other switching element) by doubling and to test the operation of the switching networks by comparing data in corresponding output channels, preferably on a continuous basis. If this first comparison shows that the data in certain corresponding output channels are not identical, one of the switching networks is not operating correctly. Then, an internal compare test is carried out in at least one of the two switching networks. Because the first compare test has already identified the output channel where the error occurred, the internal compare test can be carried out on that particular channel and the corresponding input channel data. Thus, the actual internal compare test is carried out using a known method, but now the affected channels can be selected for comparison immediately. As a result, the outcome of the compare test is obtained immediately and the passive switching network can be quickly activated, if the compare test(s) show(s) that the currently active switching network is faulty.
Another advantage offered by the solution in accordance with the invention is that the inter-network compare test to be added to a known switching network arrangement that uses an internal compare test can be carried out very simply. This is due to the fact that the comparison between the switching networks can be performed without having to save the comparison data because the corresponding output channels are concurrently present at corresponding outputs of the switching networks.
In one preferred embodiment of the invention, the validity of the connection information of both switching networks is checked after the inter-network compare test has revealed a discrepancy relative to the output data from the switching networks. For example, this can be effected by having the control unit read the connection information used by the switching network and compare this information against its own connection information. If the connection information of both switching networks is correct, this is followed by an internal compare test in at least one of the switching networks. If not, an attempt may be made to replace the incorrect connection information by correct data, and failing that, an alarm can be given.
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International Search report for PCT/FI99/00175.
Hurtta Ari
Ruuskanen Markku
Tuominen Antti
Altera Law Group LLC
Kizou Hassan
Mehra Inder Pal
Nokia Networks Oy
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