GB1570969A - Automatic isolating device for telephone junctors - Google Patents

Description

(54) AUTOMATIC ISOLATING DEVICE FOR TELEPHONE JUNCTORS (71) We, INTERNATIONAL STANDARD ELECTRIC C:ORPOX ON, a Corporation organised and existing under the Laws of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- This invention relates to a device whereby junctors in a PCM (Pulse Code Modulation) switching centre can be isolated by automatic means.

When a fault originates in a signalling chain serving a group of junctors, the junctors do not continue to assume their correct mode of operation. This fault is detected by a central control unit which takes the necessary steps. so as not to use that group of junctors any more. This fault is not detected by the other centres to which the junctors are also connected, so they may try, without success, to use the free incoming junctors for new calls.

An object of the invention is to provide an automatic isolating device for junctors allowing the other centres of the network not to be perturbed.

According to the invention there is provided a time division multiplex telecommunications switching centre, in which the lines served are each connected at the centre to a junctor with the junctors connected in groups to time division multiplex highways via multiplexing equipment, in which each said group of junctors is served by a scanning device which executes a scanning operation on the junctors of that group at preset intervals, in which each said scanning operation is initiated in response to the reception of a scan order from control equipment, in which control means monitors the scanning device to check whether that device receives scan orders from the control equipment, said control means causing the production of an isolating signal if no such orders are received by the scanning device during a period whose length at least equals a preset multiple of the duration of said preset interval, and in which a said isolating signal is applied to the junctors of the group served by that scanning device to prevent them from being taken into use for a call even if they are free, the isolating signal having no effect on a junctor which is already in use.

The device according to the invention has the advantages of being simple and not needing special signalling orders on the multiplex junctions.

An embodiment of the invention will now be described in connection with the attached drawings, in which: Figure 1 shows an example of how the junctors are connected to their centre; Figure 2 represents the lay-out of the junctors and of their scanner-driver; Figure 3 represents a form of automatic isolating device for junctors.

Figure 1 represents an example of connecting the junctors to their PCM centre identified by C. This centre is connected to p multiplex junctions J(0) to J(p-1), each conveying m=32 time channels V(0) to V(31) each having a duration of t=3,9 ys.

Thus a junction successively transmits m=32 codes of b=8 bits during one repetition period or frame T=125 ,us. The time channels V(0) and V(16) are reserved respectively for synchronization and for line signalling, according to the standards defined by the "Comite Europeen des Postes et Telecommunications" (C.E.P.T.). The (m-2)=30 time channels remaining are used for the transmission of speech between subscribers. Each multiplex junction is connected to the voice frequency network via a conversion circuit MUX, which does the demultiplexing of the time channels and the digital-to-analog conversion of the speech codes in the PCM -network e voice frequency network direction, and reciprocally in the voice frequency network o PCM network direction.Each unit MUX is connected to (m-2) voice frequency lines L via (m-2) junctors JCT. These junctors are controlled by a scanner-driver JSD. connected to the unit MUX, so as to receive the order messages and to return results on the signalling time channel V(16). Each message comprises several codes of b bits, and thus needs several consecutive frames to be transmitted (multi-frame structure).

Addressing of the junctors to be controlled is carried out by "label", i.e. by association of an address code with the signalling message.

In place of the type of addressing by "label", the line siginalling can also be of the "channel by channel" type, by time association on a multi-frame base (C.E.P.T.

format). The address of the junctor to be controlled is determined, not by a particular code included in the signalling message, but by the position in the time of the message within a multi-frame. In this case, the scanner-driver is located inside the PCM centre, before the multiplex junctions, and controls an image-memory representing the state of the junctors.

The operating principle of the automatic isolating device for the junctors will be explained in connection with figure 2, which represents the lay-out of the junctors and of the scanner-driver associated with a multiplex junction, e.g. the junction J(0).

We find again the elements described in figure 1, i.e. conversion circuit MUX, the (m-2) voice frequency lines which we call L(1) to L(15) and L(17) to L(31), and the (m-2) junctors. The later include outgoing junctors OJCT (1) to OJCT (15), and incoming junctors IJCT(17) to IJCT(31). The outgoing junctors are used for setting up connections from the PCM centre to an outside centre, while the incoming junctors are used for connections from an outside centre to the PCM centre. Each junctor has access points which are scanning points, and driving points. The scanner-driver JSD receives, from the conversion circuit MUX via the link LMUX, four different types of order: (i) A cyclical scanning order, which enables a given scanning point in each junctor to be read. This order is received periodically by the scanner-driver JSD, e.g. every period x=25 ms.

(ii) A driving order, which enables the state of the driving points of the addressed junctor to be controlled.

(iii) An on-demand order, which enables the state of the scanning points and the driving points of the addressed junctor to be read.

(iv) A scanner-driver testing order, which allows the operation of the scanner-driver to be checked.

The scanner-driver JSD decodes the order messages and controls the junctors via links LJCT.

The isolating device is inside the scannerdriver, and its operating principle is to detect the absence of a correct cyclical scanning order message for a given period, e.g., ranging about 200 ms, and thereupon sending an isolating signal ISL to all the incoming junctors IJCT(17) to IJCT (31), via the link LISL. This isolating signal ISL is removed as soon as the device receives a correct cyclical scanning order message.

The presence of this isolating signal on the incoming junctors causes a blocking signal to be sent on the lines L(17) to L(31) so as to warn the outside centre that these junctors are unable to receive another call.

The presence of the signal ISL does not affect the driving points of the junctors, and so does not affect calls in progress. The blocking signal can, for example, consist in opening the line; this is effected in known manner, e.g. by opening a relay contact in the line, the relay being controlled by a photo-coupler which receives the isolating signal ISL. Thus a fault in the line signalling chain, which results in a degradation of the signalling messages, and thus in an incorrect reception of the cyclical scanning order messages or no reception at all according to the type of fault, causes automatically, without any action of the central control unit, the isolation of the incoming junctors.The isolating device is controlled by the signals already existing in the scanner-driver JSD and does not require a special link with the conversion unit MUX or with the central control unit, but operates by means of the signalling links already existing.

Figure 3 shows the automatic isolating device of the junctors, and comprises a counter 1 of c bits, advancing under the control of clock pulses H with a period x, received at the clock input CK. The c outputs S(0) to S(c-l) of the counter are connected to the inputs of a decoder 2 which delivers an isolating signal ISL when the counter has advanced by a certain number of steps q. The presence of the signal ISL blocks the advance of counter 1, via the inhibition input EN. The counter is reset to zero due to the presence of a signal CYS at its resetting input CL. The signal CYS is produced by the scanner-driver when it receives a correct cyclical scanning order message. It is not used solely by the isolating device, but is also used for the control of the junctors, this use having no connection with the invention.Thus, when the signal CYS is absent for a period y between (q-l).x and q.x, the isolating signal ISL is delivered and remains until another signal CYS appears, which corresponds to the correct reception of another cyclical scanning order message. The exact value of the period y, between (q-l).x and q.x, depends on the position of the signal CYS with respect to the clock pulses H. Thus, as an example, for q=9 steps and x=25 ms, the period y will be between 200 and 225 ms.

Up to the moment, one has seen that the isolating device, permits the automatic isolation of the incoming junctors in case of a fault in the signalling chain. In fact, this isolation can also be obtained, not only in the case of a fault, but if desired, it can be controlled from the central control unit, by suppressing the cyclical scanning order messages. This possibility can be used in the initialization phase, for testing the operation of the scanner-driver and the junctors without disturbing the outside centres.

Although the present invention has been described with the aid of a particular example, it is clearly not limited to that example, and is capable of variants or modifications still lying within its scope. In particular, the device can operate as well in the case of "channel by channel" line signalling with time association. In this case, the device according to the invention is located inside the PCM centre and controls the incoming junctors, not directly, but by sending a particular blocking code to the signalling channel V(16) of the incoming junctors.

1. A time division multiplex telecommunications switching centre, in which the lines served are each connected at the centre to a junctor with the junctors connected in groups to time division multiplex highways via multiplexing equipment, in which each said group of junctors is served by a scanning device which executes a scanning operation on the junctors of that group at preset intervals, in which each said scanning operation is initiated in response to the reception of a scan order from control equipment, in which control means monitors the scanning device to check whether that device receives scan orders from the control equipment, said control means causing the production of an isolating signal if no such orders are received by the scanning device during a period whose length at least equals a preset multiple of the duration of said preset interval, and in which a said isolating signal is applied to the junctors of the group served by that scanning device to prevent them from being taken into use for a call even if they are free, the isolating signal having no effect on a junctor which is already in use.

2. A time division multiplex telecommuuication switching centre, in which the lines served are each connected at the centre to a junctor with the junctors connected in groups of time division multiplex highways via multiplexingi demultiplexing equipment, in which each said group of junctors is served by a scanning device which executes a cyclical scanning operation on the junctors of that group at preset intervals, in which each said cyclical scanning operation is initiated in response to the reception of a cyclical scan order from control equipment, in which a said scanning device also receives from the control equipment other order messages each of which causes scanning or testing of one or more of said junctors, in which control means monitors the scanning device to check whether that device receives cyclical scan orders or other order messages from the control equipment, said control means causing the production of an isolating signal if no such correct orders are received by the scanning device during a period whose length at least equals a preset multiple of the duration of said preset interval, and in which a said isolating signal is applied to the junctors of the group served by that scanning device to prevent them from being taken into use for a call even if they are free, the isolating signal having no effect on a junctor which is already in use.

3. A switching centre according to claim 2, and in which the presence of the isolating signal causes a blocking signal to be sent to other switching centres.

4. A switching centre according to claim 2 or 3, and in which said control means includes a counter advancing under the control of clock pulses H of period x and reset to zero by a signal CYS, which signal CYS is present each time a correct order message for a cyclical scan has been detected by the scanning means, the outputs of said counter being connected to the inputs of a decoder delivering the isolating signal when the counter has advanced by q steps, the presence of the isolating signal block the advance of the counter.

5. A switching centre as claimed in claim 1, 2, 3 or 4, and in which the intelligence when conveyed in time division multiplex manner is expressed in pulse code modulation form.

6. A time division multiplex switching centre substantially as described with reference to the accompanying drawings.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. control of the junctors, this use having no connection with the invention. Thus, when the signal CYS is absent for a period y between (q-l).x and q.x, the isolating signal ISL is delivered and remains until another signal CYS appears, which corresponds to the correct reception of another cyclical scanning order message. The exact value of the period y, between (q-l).x and q.x, depends on the position of the signal CYS with respect to the clock pulses H. Thus, as an example, for q=9 steps and x=25 ms, the period y will be between 200 and 225 ms. Up to the moment, one has seen that the isolating device, permits the automatic isolation of the incoming junctors in case of a fault in the signalling chain. In fact, this isolation can also be obtained, not only in the case of a fault, but if desired, it can be controlled from the central control unit, by suppressing the cyclical scanning order messages. This possibility can be used in the initialization phase, for testing the operation of the scanner-driver and the junctors without disturbing the outside centres. Although the present invention has been described with the aid of a particular example, it is clearly not limited to that example, and is capable of variants or modifications still lying within its scope. In particular, the device can operate as well in the case of "channel by channel" line signalling with time association. In this case, the device according to the invention is located inside the PCM centre and controls the incoming junctors, not directly, but by sending a particular blocking code to the signalling channel V(16) of the incoming junctors.

1. A time division multiplex telecommunications switching centre, in which the lines served are each connected at the centre to a junctor with the junctors connected in groups to time division multiplex highways via multiplexing equipment, in which each said group of junctors is served by a scanning device which executes a scanning operation on the junctors of that group at preset intervals, in which each said scanning operation is initiated in response to the reception of a scan order from control equipment, in which control means monitors the scanning device to check whether that device receives scan orders from the control equipment, said control means causing the production of an isolating signal if no such orders are received by the scanning device during a period whose length at least equals a preset multiple of the duration of said preset interval, and in which a said isolating signal is applied to the junctors of the group served by that scanning device to prevent them from being taken into use for a call even if they are free, the isolating signal having no effect on a junctor which is already in use.

2. A time division multiplex telecommuuication switching centre, in which the lines served are each connected at the centre to a junctor with the junctors connected in groups of time division multiplex highways via multiplexingi demultiplexing equipment, in which each said group of junctors is served by a scanning device which executes a cyclical scanning operation on the junctors of that group at preset intervals, in which each said cyclical scanning operation is initiated in response to the reception of a cyclical scan order from control equipment, in which a said scanning device also receives from the control equipment other order messages each of which causes scanning or testing of one or more of said junctors, in which control means monitors the scanning device to check whether that device receives cyclical scan orders or other order messages from the control equipment, said control means causing the production of an isolating signal if no such correct orders are received by the scanning device during a period whose length at least equals a preset multiple of the duration of said preset interval, and in which a said isolating signal is applied to the junctors of the group served by that scanning device to prevent them from being taken into use for a call even if they are free, the isolating signal having no effect on a junctor which is already in use.

3. A switching centre according to claim 2, and in which the presence of the isolating signal causes a blocking signal to be sent to other switching centres.

4. A switching centre according to claim 2 or 3, and in which said control means includes a counter advancing under the control of clock pulses H of period x and reset to zero by a signal CYS, which signal CYS is present each time a correct order message for a cyclical scan has been detected by the scanning means, the outputs of said counter being connected to the inputs of a decoder delivering the isolating signal when the counter has advanced by q steps, the presence of the isolating signal block the advance of the counter.

5. A switching centre as claimed in claim 1, 2, 3 or 4, and in which the intelligence when conveyed in time division multiplex manner is expressed in pulse code modulation form.

6. A time division multiplex switching centre substantially as described with reference to the accompanying drawings.