DE716346C - Circuit to prevent the intrusion of unauthorized stations on busy lines in telephone dialing systems - Google Patents

Description

Circuit to prevent the intrusion of unauthorized call stations on busy lines in telephone systems The invention is a Circuit arrangement to prevent the intrusion of unauthorized call stations on. Busy lines - in telephone dialing systems with one in the preselection level generated differentiator.

There are known circuits in which automatically by switching means the intrusion is prevented when the call is through switching means in the exchange is marked as outgoing tone for an unauthorized subscriber. Have so In some arrangements, all preselectors have special contact arms for authorized users Connections are dead, for 'unauthorized connections but in the occupied number recipient energize a relay, which for unauthorized connections one only for authorized connections Connections permissible switching measure, e.g. B. Turning in 'a line selector an outside line, prevented. Such arrangements to prevent intrusion for unauthorized participants are almost only for internal traffic; z. B. within a control center, usable and in this case also offer sufficient security against Fraud measures to enforce the intrusion, - -this is because -the intrusion criterion or blocking criterion, is transmitted locally; for example only via the -c wire or d-core runs within an office. -Significant difficulty. -step but on, if you are also in: interconnection traffic, a faultless connection want to prevent an unauthorized participant with simple means. In this In case one must sleitung the criterion over the connection pass on; but then there is the risk that this will affect the signaling of the intrusion authorization calling station within the switching center certain criterion of a vicious or malicious one. Participant at his call station: is simulated.

Since the modern telephone systems mostly with moving feeder bridge trained, so is the likelihood of a malicious participant gets to his goal, even bigger. But the same also applies to systems to which the switching criteria generated at the intercom are implemented, because they are also used in normal operation, e.g. B. to initiate queries and the like, to be used.

However, there are also arrangements of this type in connection traffic known where the preferred participants after connecting through Sending a series of impulses consisting of more than ten impulses that Activate intrusion on the busy line. This ringing is achieved by a switching device provided on the connecting line, e.g. B. by a follow-up drive. On the other hand, the preferred subscriber stations must have a be equipped with a special current impulse termination device, by means of which eleven current impulses can send out one after the other.

This arrangement in no way offers sufficient security against malicious measures of a subscriber who is not authorized to intrude; because for this one it is relatively easy to switch to the usual ten power surges by loop interruption an additional current surge: add and thus force the ringing. Except for the particular surge transmitter that each preferred subscriber station This arrangement is also quite complicated and takes for the connection take a considerable amount of time.

The subject of the invention avoids this disadvantage and has not achieved it a proper prevention of a subscriber who is not authorized to intrude Use of a distinguishing feature already generated in the preselection stage in that the distinguishing feature immediately after setting the next Elective stiffness is passed on as a current surge over the voice line in such a way that in of the following optional level switching devices for interrupting the connection circuit come into action or switch devices of any Influence by this distinguishing feature is withdrawn before the connection line the calling station to the connection device equipped with the switching devices is effectively switched through.

The invention is described below with reference to the figures in several exemplary embodiments, namely the exemplary embodiment works according to the Abtr. r to 3 according to the first-mentioned principle, while the embodiments according to Fig. q. to 6 and 7, f; it is based on the second principle. 'In Fig. xa shows a connection path consisting of a call sixcher AS and a group selector GW, which is accessible to both subscribers who are authorized to display and to subscribers who are not authorized to display. The subscribers authorized to intrude are identified by earth on the relevant contact of the call seeker arm. The line selector LW shown in Fig. A can be reached via the group selector NW. Fig: 3 shows another embodiment for the line selector.

When the receiver is picked up at a calling station, a free call searcher AS- is started in a known manner, which adjusts itself to the calling line. Relay C responds via the c-wire and switches on relay R with its contact c2. The number current surges are received by the relay A in the usual way. As soon as the group selector has found a free line in the selected decade, the test relay P responds in series with the relay C in Fig. -, blocks by short-circuiting the high-resistance winding P II on its contact pi and switches on its contacts p2 and p3 the speech wires through to the line selector, which is set in a known manner with the aid of the relay A in the figure. During the series of impulses, a delay relay VB (not shown) responds, which prevents ringing at its contacts vbl and vb2 during this time. If the desired subscriber line is free, the relay P (Fig. 2-) responds and switches through to the called subscriber at its contacts p2 and ps, so that the feed relay Y responds after reporting. If, on the other hand, the desired subscriber is busy, the calling subscriber is connected to the busy line after the drop of the - mentioned VB relay via x2, the listening capacitor Kl, vbi or x3, the listening capacitor K2, vb. The creation of this connection circuit depends on the X differential relay. However, this relay is inevitably made to respond in the following way if the call originated from a call station that was not authorized to access: If the calling subscriber is not authorized to access, his dI # -, contact - no earth, so that the relay AU does not respond and at a21 the earth can be switched off from the a-wire. As a result, the a-wire is briefly earthed via the contacts sui, ri, p4 during the release time of the relay R, the circuit of which is opened when the test relay P responds. Through this inevitably transmitted earth current surge, the winding II of the X relay in the line selector is short-circuited, so that the relay X responds via its winding I and holds itself via its winding III: In this way, the contacts: x2, x3- for the The entire duration of the connection is kept open so that eavesdropping is impossible in this case.

However, if the connection originated from an authorized intercom, the AU relay in Fig. As a result, relay X is not energized, and the connection to the busy subscriber therefore comes about automatically after the relay VB drops out of the earth criterion can never lead to an intrusion, since: 'the earth criterion, as mentioned, precisely: prevents the intrusion.

The circuit shown in Fig. Ia would be considered a malicious one Participants still have a distant opportunity to avoid eavesdropping, namely by the fact that he has a grounded battery on the b-wire of his -connection line creates, -. and: at the same moment, when in the office Tiber the contact yi, p4 the earth criterion is transmitted. Through this measure the participant could the -De-excitation -of the winding-II of the relay lX and thus the response of this relay impede. Such a fraud attempt is also shown in Fig. Ib Embodiment made impossible. As can be seen from this figure, it becomes Simultaneous earthing of both speech wires is carried out via the normally closed contact, so the voice line short-circuited. Under these circumstances, every intervention is. pointless at the intercom.

The line selector ALV shown in Fig. 3 is switched so that no automatic connection to a busy line. brought about after the end of the Sirom thrust series, but the activation of a special switching measure at the subscriber station is made dependent. The special relay XI-I serves this purpose. As in the case Fig. 2 does not become an earth criterion when a call is made by a call station authorized to intrude given over the voice line, so that # the relay X does not respond. If now after - unsuccessful check - of the desired participant the relay T113 drops out, the connection circuit is still at the contacts x2. and x3 open. Of the Subscribers who are authorized to intrude can now connect by pressing the earthing button, which is available on his speaking machine, provide listening, because yes through this switching measure the relay X is made to respond, so that the contacts Close x2 and x3 while the button is pressed. An excitation of the relay XH through the contact xi is not possible - because the voter after leaving his. Rest position the mechanical contact is unoccupied and thus the excitation circuit of relay XH has opened.

Grounding of the subscriber station at an unauthorized intercom station can however not lead to the goal; because when calling such an intercom is about the quiescent crital <: t, tzt "in Fig. i immediately after checking the Group selector GW the earth criterion has been transmitted, which - the relay X in Fig. 3 - makes it respond. In this case, however, the relay can be energized. XH come about via contact x1; since eler contact -k still in the rest position is. The relay XH therefore opens the listening circuit at its contacts xh and xhs and keeps himself through his contact -xhi for the duration of the connection. In order to switching on is impossible once and for all, because even if. now the subscriber who is not authorized to intrude on his speech line in any way earths and thereby energizes relay X in Fig. 3: although contacts x2, x, closed, _ but the connection remains. at the contacts x122 and xhs prevented.

The exemplary embodiment according to FIGS. 4 and 6 works as mentioned; according to your second principle; d. H. This prevents unauthorized eavesdropping, that the switching devices which are authorized to switch between authorized and non-authorized Record or evaluate the different switching criterion, any Influence through this switching criterion. be withdrawn before the connection line the calling station to the connection device; of the switching devices are assigned, is switched through.

Is used at a calling station Nst in Fig., Q.,: It can where z: ,, B. to the 1 extension in a private branch exchange Bandeln, the handset is picked up, a free call seeker AS stands on the calling Line on; so that finally the feed relay A via its two windings is excited. In the supply circuit is shown in Fig. Q. another differential relay X, the z. B. can be used to switch to another traffic facility (office) can. This is indicated by the contact x located in the c-core, by the the test circuit of the caller AS interrupted and this connection path to Triggering is brought.

When the A-relay responds, the drop-out delay relay VA is made to respond at contact a1, which is held at its contact val for the duration of the connection. If the group selector GW has found a free line after setting it to the desired decade, the test relay P responds, blocks its contact p1 in a known manner and switches the speech wires to the line selector LW shown in Fig. 5 at its contacts p2 and p3 by. In this Tiber speaks earth, b4, p2, u-arm of the GTI ', AI (Fig. 5); Battery to relay A and switches on the delay relay T7A (Fig. 5) at its contact a1, which is maintained at va, during the -duration of the connection and at its contact vag the b-wire from the -battery winding of the AU relay switches to the earth winding II of the A relay. As a result, in Fig. Q. via earth (Fig. 5), AII, vag, b-arm of the GW, p3, au " b5, BI, battery energizes the B-relay, which with bi continues until it is triggered, with b5 its winding I switches off, at b4 disconnects the earth from the a-wire and at b = and b3 makes the connection.

In the line selector, the number current impulses sent by the calling station are then picked up by the A relay in Fig. 5 and lead to the setting of the line selector to the desired station. During the series of impulses, the short circuit of the relay VB is canceled at a1, so that this relay responds for the duration of the series of impulses and disconnects the monitoring circuit at its contacts vbl and vb. If the desired intercom is free, the P relay responds and switches through its contacts p2 and p3. If the desired subscriber line is busy, however, as can be seen from Fig. 5, a ringing is only established when the switching relay AU has the opportunity to address and close its contacts au2 and off. The response of the relay AU -depends on whether the calling station is authorized or not, as in the following. will be shown.

If the calling station is authorized to listen in, the call seeker is earthed at the d-contacts assigned to it, so that the relay AU in Fig. Q. come to the address and at his contact au., earth can put on the outgoing b-wire. When the test relay P of the group selector responds, the winding I of the AU relay in the line selector in Fig. 5 is excited via the contacts au and p3, so that this relay is maintained via its contact au and its winding II. and listening to the contacts au, and may allow from. When the P relay of the group selector is triggered, the AU relay in Fig. Q. immediately brought back to waste, so that the b-wire on the rest side of the contact au., switched through and thereby the excitation of the winding I of the relay B is possible in the manner described above.

If the calling station is not authorized to switch the ring, the AU relay in Fig. 4 cannot respond and consequently also the AW relay in Fig. 5, as in this case the ring wire in the group dialer is not earthed. Since the ground criterion for the authorization of the calling subscriber is characteristic of this circuit (i.e. the opposite of the exemplary embodiments according to Fig would be to simulate the earth criterion in good time by means of a switching measure on your call station. - But it is not able to do this, because the through contacts b2, b3 in Fig. Q. are inevitably only closed when the relay AU in Fig. 5, which is used to record the activation criterion, has already been withdrawn from the influence of the line by switching the contact: vag; because the relay B in the group selector is only energized when this contact is moved, thus causing the connection. Unauthorized ringing is definitely prevented in this way.

The line selector shown in Fig. 6 differs from the one according to Fig.5 in that the ringing is made dependent on the will of the calling subscriber. Also in the embodiment according to Fig. 6, the relay AU is separated from the b-wire by a contact va, of the delay relay Ü A and instead the earthed winding II of the relay A is switched on, so that the B relay in the group selector (Fig . r1) responds and connects the speech wires to the line selector. If the call originates from an authorized subscriber and the AU relay in the line selector has been energized in time as a result, this relay comes to hold via the contact au, on its contacts au, and aua it cancels the short circuit of the differential relay X and prepares at au, and from. the connection via the monitoring capacitors K3: and K4 before: The connection only becomes effective when the subscriber who is authorized to connect presses his earth button. and thereby brings the relay X to respond, so that he can overhear a busy subscriber for the duration of the key press via the contacts x1 and x2 on the line.

Tried one. Participants who are not authorized to intrude the listening option to enforce by applying earth to his connection line, so it is for him possible to move the contacts xl, -x @ by energizing the X-relay, an increase but still does not come about because the monitoring circuit through the contacts au4 and off is not prepared. In this embodiment, too, is unauthorized activation is excluded.

Also in the example shown in Fig. 7 and 8, the relay in the line selector serving to receive the switch-off criterion is withdrawn from the influence of the line before the calling station is effectively switched through to the line selector. However, in this embodiment, the backward surprise of a signal is; which indicates to the group selector that this relay has been switched off in the line selector, avoided. If a calling subscriber lifts the receiver in Fig. 7, a free call seeker AS adjusts itself to the calling connection line, so that the feed relay A responds. The delay relay V is switched on at contact a; so that: the contacts v1 and v2 toggle = `. After setting the group selector, the test relay P is activated on a free connection line, which blocks the line reached at p1 and its contacts pg, p4 and p. kills. In the test circuit, relay A in the line selector (Fig. 8) is activated via its winding -I, so that at a, the delay relay VA is activated. Relay VA stays at va for the duration of the connection, switches both windings of the A relay to the voice wires at va4 and va'5 and also switches the voice wires on its contacts va, and va3 - from winding I des, which responds to alternating current Relay AU from and to the monitoring circuit. The participant sends out power surges in a known manner with the help of his dial; which are picked up by relay A in the line, meter and set this selector to the contacts of the desired participant. During the series of current impulses, relay VB responds, which - at vbi and vv., Opens the listening circuit. If the desired subscriber line is free, relay .P responds and switches through to the called party. However, if the desired line is busy, the connection is made via the contacts vbi and vb of the relay VB which drops out after the end of the series of impulses. comes about, provided the contacts au "and au, are closed. The response of the relay AU depends, however, on whether the caller is authorized to intrude or not.

If it is a question of a subscriber who is authorized to listen in, -so it is due to his d-call seeker contacts ip of the call seeker level earth, so that the relay AU is energized after the call seeker has been set. After the first turning step of the group selector, shaft contact where (GW) opens, -Relay AU remains on its contact au, and contact d (GW) of the group selector rotary magnet for the duration of the series of impulses. At au, any source of alternating current, e.g. B. a pole changer; started, so that alternating current is sent simultaneously over the speech wires via the contacts aub and v after the group selector has been checked (p-contacts closed). This alternating current reaches the relay AU of this selector via the capacitors G1 and C2 in the line selector (Fig. $); so that this relay binds to its contact aua via its second winding and prepares the connection with aui and au. A short time later, the AU relay in the group selector switches to drop, since contact d (GW) finally opens. The alternating current surge transmitted via the voice wires to the line selector therefore only lasts for a brief moment. The chronological sequence is that first the relay VA in the line selector responds and removes the influence of the line in the manner described at va, and vag the relay ° AU (Fig. 8). Only when this has happened is the connection at the contacts v1 and v2 (Fig, 7) completed, in that the relay A, which controls the circuit of the delay relay V, is brought to drop out at the contacts p and p3. This chronological sequence can be adhered to effortlessly, since only for switching off the relay AU in the line selector. the response time of relay VA is decisive; while the switchover in the group selector at contacts v1 and v is only completed after the fall time of relay A and that of relay T have elapsed. This ensures that the connection line of the calling subscriber to the line selector only becomes effective when the winding I of the relay AU in the line selector is definitely switched off from the line. Even if an unauthorized subscriber were to try to simulate the Mmultaneous alternating current criterion from his speech set using any alternating current source, such an attempt does not lead to the intrusion, since the subscriber has no access to the line selector before the contacts v and v2 are switched back and after these contacts have been switched back, the AU relay in the line selector has already been switched off by the line.

It should be noted that in the execution forums after Fig. S the capacitors Cl, C2 initially serve as blocking capacitors to block the direct current from the earthed winding I of the etU relay, and then after moving the contacts vag` and va, can be used as monitoring capacitors.

Claims (7)

PATENT CLAIMS i. Circuit to prevent the intrusion of unauthorized stations on busy lines in telephone dialing systems -with a distinguishing feature generated in the preselection stage, characterized in that the IT distinguishing feature immediately after setting the next dialing level, z. B. group voter, is passed on as a power surge on the speakerphone in such a way that in the following election level, z. B. Line Voters; Switching devices (relay X, - Fig. 2; XH, Fig. @ 3) to interrupt the connection circuit come into operation or switching devices (relay AU, Fig. 5, 6 and 8) that evaluate this current surge are withdrawn from the influence of this T-Tnterscheidtingsmerkinat before the connecting line of the calling station to the connecting device equipped with the switching devices is effectively switched through. 2. Circuit according to claim i, characterized in that that the switching devices (X, 'Fig. 3) receiving the blocking criterion switch on by a subsequent broadcast by an unauthorized intercom Prevent switching criterion. 3. Circuit according to claim 2, characterized in that that the blocking criterion is of the same type and from the same switching devices (X, Fig.3) is recorded like the 'if the blocking criterion is not transmitted (the calling station is authorized) the switching criterion causing the intrusion (in both cases earthing of the speech line). 4 .. Circuit according to claim 3, characterized characterized that from the solvohl the blocking criterion as the switching criterion taking up Switching device (X) a switching device (XH, Fig. 3) depends only when it is influenced before the setting of the associated Voter (LW) can be made to speak and hold. 5. A circuit according to claim i, characterized by switching means (B, Fig. 4) at the outgoing end of the connection line, which effect the effective connection of the calling station to the subsequent connection devices only after a switching criterion has been recorded, which is determined by the switching devices (AU, Fig 5, 6) of the subsequent connection devices (LTU) is transmitted backwards over the connection line in order to report that these switching devices have been withdrawn from the influence of the speech cores. are. 6 .. Circuit according to claim 5, characterized by a switching means (VA, Fig. 5, 6) at the incoming end of the connecting line, which removes the switching devices (AU) from the influence of the line and at the same time applies the rear switching criterion (earth to A II) creates the speech wires of the connection line. 7. A circuit according to claim 5 and 6, characterized in that the switching devices (AU, Fig. 6) at the incoming end of the connecting line further switching means (X) at this end of the connecting line for receiving an authorized call station for the purpose of connection to an occupied line enable the switching criterion to be sent out (when au "off). ß. Circuit according to claim 5, characterized by switching means. (A, TI, Fig. 7), which delay the switching through of the calling station to the following connection devices until the switching devices ( AU, Fig. 8) at the incoming end of the connection line are withdrawn from the influence of the voice line.g.Circuit according to claims i to ä, characterized in that the switching criterion which distinguishes between authorized and non-authorized voice stations and transmitted via the connection line consists of an alternating current surge , the simultaneous over the speech wires of the connecting line sent out. will. -io. Circuit according to Claim 9, characterized in that the capacitors (C,., C2) used to isolate the switching device (AU, Fig. 8) receiving the alternating current surge from direct current are switched over (by vag, va ") that they serve as monitoring capacitors.