KR0135491B1 - Telemetering access arrangement - Google Patents

Abstract

None.

Description

A telephone exchange system and a method of accessing a customer premises device from a data access device.

1 is a block diagram showing a customer meter and a connection for accessing various devices.

2 through 6 are flow charts of the connection settings of FIG. 1 and the operations for performing access to the meter and various devices.

＊ Explanation of symbols for main parts of drawing

10: personal computer 20: central sphere service unit

21,22: exchanger 30: meter interface unit

40: protection circuit

The present invention relates to a customer's access to a meter via a telecommunications line and to a method and apparatus for controlling a customer's device.

It was necessary to periodically read utility meters (common services such as electricity and gas), which was previously done primarily through manual devices. In addition, recently, as a means of preventing a power saving and a power failure state, it is also required to be able to control the electrical load on the customer side by the power utility. For that need, the prior art has only been made in part by telemetering of the devices involved in accessing telephone customer lines and by the use of a carrier system connected to the power distribution line. In those devices, the utility meter at home or at the workplace of the customer's telephone is accessed through the telephone customer's line when the telephone customer's line is not used for a telephone call. The method of accessing the telephone customer's line includes a central office that monitors and controls the customer's meter reading interface and the customer's off-hook / on-hook supervisory state. It should include a direct metallic path between the service units in the (). Access from the central office's exchange to the customer is provided through a no-test, i.e. the use of a trunk that can access the customer's line even when the customer's line is already off-hook. do. The trunk uses a no-test connection, which typically uses a special metallic connection that bypasses the switched telephone connection and connects without performing a test during the call. The metallic connection passes through a direct current signal.

No-test trunks are used to gain access to the meter without calling the customer's line, which is typically made for all dial-up connections. After such access, the meter is triggered and several signals are transmitted by the no-test connection in response to the trigger, each of which is a burst of tones of one of 13 frequencies in the phone's voice band. It consists of a burst. Using such a structure, a connection is established to the customer's line, and the service unit tests whether the customer is busy. If the customer is not in a call, the service unit is connected to the customer's meter interface. The meter interface is alerted by one of its 13 frequencies to respond to a data signal originating from the controller of the service unit or utility service and transmitted through the service unit. These data signals can be either dual tone multi-frequency (DTMF) signals or binary data signals with frequency shift keyed signals. After the wait signal is transmitted to the meter interface unit, the exchange of signal information is performed between the controller and the meter interface unit.

Use the exchange of signals to trigger readings of the meter, to send readings of the meter's presence, to report the current status of those meters, or to control devices such as air conditioning units in the residential or workplace of the called customer. .

By the function of such device control, the utility company can control the maximum load of the cooling device by temporarily shutting off a part of the provided heating and cooling device based on the possible order. The actual reading of the meter is performed by a reading mechanism that interfaces with the meter interface used. The meter's status information may include tampering with the device, a drop in battery indication, or a need for service. After the complete cycle of the meter's read operation and / or device control operation ends, the no-test connection is interrupted and allows the customer to start a new call.

While the customer's line is connected to the service unit, the customer's line monitoring is performed by the central station service unit connected by the metallic access connection providing current sense monitoring from the central station service unit (C.O. service unit).

5ESS manufactured by ATT Company, listed in the ATT Technical Journal, July / August 1985. In current digital switching systems, such as exchangers, since no metallic access connections are provided through the voice communication network, no test trunks are needed to monitor direct current. When the customer's telephone is off-hook, a DC current of 20 mA or more is detected by the central station service unit, and the central station service unit stops the telemetry call. In some cases, the monitoring may be performed from the customer's meter interface unit sending a break signal to the central station service unit for stopping the telemetry call.

Such a structure has several disadvantages. The no-test trunk is a facility where very few numbers are available at the central station, the number of which is limited by the no-test access structure. Primarily, a no-test trunk runs a check on a customer on a line that is reported to be busy for too long, runs a resistance test between two lines on the customer line, and performs a manual check on one line. Is used. In a typical exchange, such as a 5ESS exchange, only two no-test trunks can be used for an entire exchange that can provide up to hundreds of thousands of customer lines in one exchange. In a typical meter reading cycle, the time required for reading the meter and controlling the device may vary from 10 seconds to 20 seconds. It is clear that two no-test trunks are inadequate to meet the meter reading and device control needs of all customers of the 5ESS exchange. In addition, the need for a direct metallic path to provide current sensing supervision, while not directly connected to the exchange, makes it difficult to access a connected line through a subscriber line carrier system such as SLC 96 (subscriber line carrier) manufactured by ATT. do. The reason is that such SLC systems typically cannot provide a metallic path for voice connection. In addition, invoice recording for calls of no-test trunks is done separately from invoice recording for voice calls or data calls, thereby causing administrative problems.

Also, in the conventional architecture, if the customer wants to initiate a call at the same time as the reading of the meter occurs, there is a slight structure that the customer blocks, and a little that the customer blocks for 1-2 seconds until the no-test connection is stopped. Structure exists.

Due to the small number of no-test trunks, limited no-test access, and the need for no-test trunks for their intended purpose, the number of meters that can be monitored and the number of devices that can be controlled are generally Much less than the number of such meters and the number of devices provided by the large local central office. Since the metallic access units provided for such no-test trunks are expensive, it is expensive to add a large number of extra no-test trunks in a digital exchange such as 5ESS that does not provide a metallic access voice switching network. Thus, the problem with the prior art is that a large number of central stations, in particular digital central stations that cannot provide a direct metallic path for dial-up, read a large number of meters by a customer line connecting the central station to telephones and telemetry devices. And there is no device that enables access to the device control interface in a reasonable time.

The above problem can be solved unlike the prior art, for example, solved by providing the structure described below. That is, a standard interoffice trunk that can be controlled by special software of the connected switching system is connected to a customer premises device (such as a meter interface unit (MIU)) from a data access device such as a utility meter reader / device controller. premises devices are used for access by analogue customer lines, the standard trunks of which are connected via a call suppression signal connection through a communications signaling network used for voice signals to access the analogue line of the customer connected to the MIU. It has a structure that can be connected to the line.

The device thus configured does not require additional, high-angle, no-test trunks to simultaneously access different meter interface units, and can use multiple circuits.

Current digital switching systems, such as 5ESS exchangers, cannot provide metallic connections to pass DC signals. Metallic access facilities are expensive at digital exchanges because they bypass the digital network used to pass voice signals for telephony calls. The exchange network is C.O. It is not necessary to provide metallic access from the service unit to the line, because indication supervision is performed on the line circuit and the interface between the switching network and the customer's line, and the detected indication is sent to the software controlled processor. Passed through trunk connected by CO This is because it passes through the service unit. Trunks such as known E M trunks or trunks using common channel signals or trunks such as known E M trunks include devices for communicating monitoring state changes from one end of the trunk to the other. Such a device may provide a change in C.O. Since it is used to transmit to the service unit, if the customer goes off-hook, the connection of the unit can be disconnected.

In the prior art, the only way to gain access to a customer's line using a standard switched network or exchange structure was to call the customer's line and monitor monitoring from the circuit circuit in the exchange. Unlike the prior art, a new type of call connection is made. The new call connection suppresses calls in order to avoid monitoring the customer, monitors the indications by the exchange, and sends them to the monitoring central office unit by software controlled processor and trunk monitoring signaling technology. The meter interface provides a new service for calls from the utility, so that a waiting signal is generated without calling the customer from a connection through the central exchange's standard exchange structure, and the new service is characterized by a connection made without such a call. Doing. In this case, such a service is a kind of service in terms of invoking and affects the nature of the invoking set up. The meter interface unit has a C.O. The tone transmitted via the service unit, or alternatively by the utility service controller via the service unit, indicates that a connection to the meter interface is desired. The interface unit receives those tones on-hook and processes those tones without sending off-hook signals back to the central station.

Billing records are created in the usual way that the billing records are made for calls over the switching network. Such a call connection establishes a common exchange architecture to continue using normal customer monitoring from the switching network, providing the call suppression needed to access the customer's line and also access the meter interface without disturbing the customer. It is available.

Today subscriber line carriers (SLCs) cannot establish a connection unless they detect a call. The exception to this rule is for connections from no-test trunks that are recognized by the subscriber line carrier and are later provided with a special tone that provides a metallic bypass of the SLC. According to one aspect of the invention, when a meter interface unit access call is established over a subscriber line carrier, a short burst of calls is given to that connection. In response to a short burst of the call, the carrier of the subscriber line establishes a connection to the called customer whose meter interface unit is accessed inside its own exchange structure. The call burst is short enough so that subscriber line carriers that repeat any call signal detected at the input do not actually repeat the call signal for that customer's line at all.

Thus, troublesome customers can be avoided only when the meter interface unit is accessed.

The central station service unit interfaces between a utility controller, such as a personal computer, at a public enterprise and a meter interface unit connected via a voice signal exchange network. In response to the signal from the utility controller, the central station service unit sends an indication of the called customer to the exchange to establish a call suppression connection to the desired meter interface unit. The central station service unit or utility controller sends a wait indication signal to the meter interface unit. The central station service unit detects the off-hook signal from the exchange for signal transmission for premature call disconnection, and sends a signal to the exchange for meter reading and disconnection of the device control connection in response to the meter interface unit disconnect signal. do. The central station service unit has trunks between multiple offices that communicate with customers connected to other switching systems, and at the same time communicate to read several meters simultaneously in parallel for the customers in their switching systems.

In addition, the service station service unit can be connected to a number of utilities for simultaneous use via different trunks.

In accordance with one aspect of the present invention, a D-channel is used to communicate with a meter and a controllable device for a Primary Rate Interface or Basic Rate Interface and an Intergrated Services Digital Network (ISDN) connected through a digital circuit. It can also be used for communication signaling networks to provide access to the customer's circuits, and high bandwidth (64 or 16 kb./sec.) D-channels can be used for communication with meters and devices. have. Here, supervision is detected at the customer's premises device and transmitted via the D-channel by data signal.

Accordingly, the present invention provides data using a suppressed call connection through a voice signal switching network of an optical communication switching system.

A method and apparatus are provided for accessing a customer premises device from an access device.

1 is an operation block diagram of the present invention. Terminals such as the personal computer 10 in the public interest office are connected via a line or connected to the telephone exchange 21 by a trunk between the secretariat. When the access number is dialed from the PC 10 and received at the exchange 21, a connection is established to the central station service unit 20. FIG. The central station service unit is located here in a first central station which comprises a switching system (exchange) 21. In an alternative arrangement, the central station service unit disconnects the PC 10 and protects the PC 10 for protection against meter reading and tampering from unauthorized sources of control processing of the apparatus. Dial in reverse to access it. The central office (C.O.) service unit 20 is connected to a number of central station exchanges, such as exchanges 21 and 22, by utility telemetering trunks in the trunk between the simple offices. Each of the switches 21 and 22 may be housed in different wiring centers, each of which transmits a communication signal such as a voice signal and a communication signal comprising the meter reading and device control signals of the present invention. Each includes. Each of the exchanges includes control processor means 26 that operate under the control of a program 28 stored in memory 27 to control the operation of the exchange. In response to the signal received from the PC 10, the C.O. The service unit 20 sends a signal of the same kind of transmitted signal to an appropriate one of the exchanges 21 or 22 to establish a call between the central stations to request a utility service connection.

In this particular embodiment, the method used to signal as a request to be connected via a customer's line to a particular meter interface unit (MIU) such as MIU30, MIU32 or MIU35 is a series of multi-frequency ( MF) Sends a string of digits. Such a digit string consists of a key pulse signal KP, a 4, 5, 7 or 10 digit directory number and a start (ST) signal. In response to receipt of those digits, an exchange, such as exchange 21, translates the received directory number, identifies a meter interface, such as meter interface unit 30, and establishes a customer line at MIU 30, 32, or 35. A connection is established by the utility telemetry trunk (UTT) between the central station service unit 20 via the switching network 23 or 24.

The utility telemetry trunk contains a particular service that identifies whether the requested connection is connected to an exchange that is supposed to make a call suppression. In response to the directory number received from the UTT, the switch 21 suppresses the call and establishes a connection at the MIU 30. The fact that the call suppression connection is different from the normal voice connection means that the call signal is not transmitted, that the line is not stopped or monitored for the management signal for the trip call, and that the call signal actually flows on the analog line. Note that no check is made. The call signal and accompanying checks are basically essential parts of any dial-up. For example, even when the facsimile call is complete, no audible ring tone can be heard, and the circuit of the facsimile device responds to the call signal sent from the exchange.

When a suppressed call connection to the MIU has been established, the MIU 30 is set to C.O. It is connected to the service unit 20 and receives the wait instruction beep from the PC 10 through the service unit or from the service unit to trigger the MIU in the telemetry mode. According to the principles of the present invention, a device on the customer side includes a voice or other communication device and a MIU, usually the call signal usually gives an indication to the communication device, where the device is a voice device, and by the voice device Sending a wait indication signal to the customer, the tone signal transmitted over the suppressed call connection gives the MIU a wait indication. Telemetry and control signals are described in C.O. The data is exchanged between the service unit 20 or the utility controller 10 and the MIU 30, and the data received from the MIU 30 is transferred to the C.O. It is transmitted from the service unit 20 to the PC 10.

Similarly, a utility control signal is sent from the PC 10 to the C.O. Sent to service unit 20 to control various devices in the customer's home. If the customer picks up the phone's handset and communication between the service unit and the meter and / or various devices at the customer's location proceeds, their communication is quickly terminated and the regular service is returned to the customer.

However, the incoming call receives a busy signal if a utility access call is in progress.

UTT is a trunk between common offices, such as an EM trunk or a common channel signaling trunk. Such a trunk has several devices, which are structured so that an indication change at one end is transmitted to the other end by a tone (EM), or by a tone or data signal other than a band. Such a trunk passes an indication signal detected in a circuit circuit, and is executed by the exchange processor processor at one end of the trunk and the C.O. 2 to execute disconnection of the unit when the customer goes off-hook in the middle of the utility access call. Pass the indication signal to the service unit.

That C.O. The service unit is connected to the trunk by the C.O. It extends from the service unit to a plurality of exchanges such as the exchanges 21, ..., 22, and is connected to each such exchange by a plurality of trunks (trunk groups). In some cases, several trunk groups can be connected to one exchange, for example, to handle calls for other groups of SLC. In addition, such C.O. The service unit is connected to a number of utilities, but only one of them is shown, and he sets up calls to other customers at the same time.

In the above embodiment, the utility access unit PC 10 is connected to the MIU via the service unit, but an alternative arrangement may be that the utility access unit is directly connected to the switching network via a trunk for access to the MIU.

The particular embodiment of FIG. 1 uses an analog line to transmit voice band signals, call or tone alerting signals, and to use direct current detection of the indication. Here, the term ringing used is used for reasons of convenience and convenience, but is meant to describe any processing of a customer's wait indication signal, including, for example, transmission of a customer tone wait indication signal. In an Integrated Sevices Digital Network (ISDN) line, the management and customer wait indication signals are transmitted as data signals over the D-channel of the customer line.

1 is a detailed view of a meter interface unit. The protection circuit 40 is used to protect parts other than the meter interface unit 30 against damage caused by electrical signals that transmit very high energy. In practice it is used for overvoltage protection. Such protection circuits are already known in the art. The wait indication circuit 42 is used to detect an initial wait indication tone that is used to convey the random connection request signal to the meter interface communication circuit 46. The wait indicating circuit continuously monitors the circuit when the circuit is on-hook to detect such a signal. When such an initial waiting indication beep is detected, the meter interface communication circuit communicates with the PC 10 to exchange control information for controlling the device 48, control information on the meter 50, and reading information from the meter. Do it. The control and read cycles are C.O. When finished with the determined by the service unit 20, the C.O. The service unit is in an on-hook state that triggers the switch 21 to send a 300 millisecond minimum open-loop signal to the MIU to convey a disconnect signal.

In some cases, an SLC of the same kind as the SLC 96 of the ATT does not carry a forward split (open) signal.

In many cases, it carries its forward split signal. If the split signal is not a forward split signal, the MIU detects the end of the data transfer, and the C.O. Notifies the service unit, and C.O. The service unit detects the end of the data transmission and disconnects the trunk connection. Depending on the status of the channel unit inventory, the telephone service provider may want to allow off-hook transmission. In this case, the MIU detects the off-hook signal of the end user to convey the disconnect signal of the inhibited call connection. This means in any case to provide forward separation signals through the appropriate channel unit.

While the meter interface unit 30 provides an impedance in excess of about 10 k ohms for the circuit, the central station will treat the circuit as on-hook. While the communication between the PC and the meter interface unit is in progress, when the customer picks up his handset, the exchange 21 detects an off-hook condition and terminates the connection to complete the C.O. It sends a disconnect signal to the MIU, sending its on-hook status signal to the service unit, stopping the communication between the PC and the meter interface unit.

Devices for communication with on-hook devices such as meter interface unit 30 are already known in the art and are defined, for example, in Bellcore Technical Reference TR-TSY-000030, dated June 1, 1988.

2-6 are flow diagrams illustrating call processing operations that occur while processing utility telemetry calls. 2 shows a first step in response to a seizure from a utility telemetry trunk. As shown in FIG. 1, a utility telemetry trunk, which is a trunk between ordinary offices, is made accessible to other exchanges. The trunk is initially in an idle state. The trunk is off-hook at block 203 and a wink start signal is received from the trunk at block 205. This is accompanied by a digit receive state at block 207. 3 is a flowchart in response to receiving a digit. If the trunk is brought on-hook during or upon receipt of the digit at block 311, then the call is left at block 313 and the trunk is taken down at block 315, and block 317. Return to the idle state. When it is not a received digit as determined by the time-out or timing test between digits at block 321, the call at block 341 is considered to be left unattended, the trunk is released at block 343, and the block In 317, the operation returns to the idle state. If the digit is properly received, the digit is analyzed at block 323. If the ST signal is determined at block 325 as the standard ST signal STO, then the path order proceeds to block 329. Alternatively, an alternative form of ST signal ST1, ST2 or ST3 is used to determine the length of the required call burst, which needs to be applied after the connection of the required meter interface unit is established.

In this particular example, the burst lengths are 20, 40 and 60 ms. In addition, other experiments may exhibit different lengths, such as, for example, 50, 100, and 150 ms, and it may be desirable to consider modifications, for example, in the ability to control the length of the burst. The best device is that the length of the burst is controllable by the translation recent change facility of the latest exchange. If more than two different lengths (plus zero length) are required, different groups of utility trunks can be used for different groups of call burst lengths, e.g. group A can be used for 0, 20, 40, or 60 ms bursts. While used, group B can be used for 0, 80, 100 and 120 ms bursts. The burst of calls is used by the SLC to allocate time slots for access to the customer's MIU, but short enough to terminate before the connection is actually made. Thus, no call signal is sent to the MIU at all.

Thereafter, the routing sequence 329 is executed. 4 is a flowchart showing the steps of a routing sequence. First, at block 401 it is determined whether the call is a call between exchanges. If it is a call between exchanges, an error is shown at block 403 since the utility telemetry trunk used in the call is assumed to be connected to the exchange that governs the required interface unit. If the call is not a call between exchanges, block 405 determines whether the called customer associated with the requested meter interface unit is busy or out of service. If on the call or outside the service area, the state on the call or outside the service area returns to the trunk control program, and another operation is executed as shown in FIG. If the called customer's line is not busy or outside of the service area, the connection is blocked at block 409 using a shortened call if necessary, such as at block 327. When the call is blocked for the end user, the trunk off-hook signal is sent to C.O. Return to the service unit 20. The trunk then proceeds to a telemetry data wait state at block 413. 5 illustrates the operation performed at block 407 when the called customer associated with the requested meter interface unit is busy or outside the service area. In block 501 the C.O. The service unit 20 on-hook signal is sent and the trunk is released at block 503. The trunk is then idle at block 317.

In the telemetry data wait state, it is necessary to respond to a signal from the utility controller or to trigger internally to inform the MIU of the wait state. The role of the service unit. Using today's devices, the MIU is given a standby indication by one of thirteen frequencies. If a wait indication is given to the MIU, another signal, such as a frequency shift key data signal, may be used for communication with the MIU. The end user cannot give the MIU a wait indication. This is because the device on the user's side does not include a generator for generating the frequency signal of any of the above 13, and the call is released when the end user is off-hook.

6 is a flow chart of operations performed in response to various time-out states and disconnect signals. The exchange is in standby state 413 during the telemetry connection at block 413. If the maximum duration of 10 or 20 seconds is exceeded at block 611, the customer line is disconnected, a signal is sent to the MIU at block 613, and at block 615 on-hook via the utility telemetry trunk. Signal CO The trunk is sent to the service unit, and the trunk is released at block 617 and returns to idle state 317. The same detach function is executed when the telemetry access call completes. Thereafter, the bill record is created in the same way as the bill record is made for a conventional call. If an on-hook signal is detected on the utility telemetry trunk at block 621, the disconnect from the utility side is instructed, and then the line connected to the metering interface unit is disconnected at block 623, and at block 625 An on-hook signal is sent to the utility telemetry trunk, which is released at block 627 and returns to idle state 317. If an overload or other condition in the exchange is detected at block 631, it indicates that the telemetry operation should be temporarily stopped, and then the customer's line is disconnected at block 633 and on-hook through the utility telemetry trunk. A signal is sent at block 635, and the trunk is released at block 637 and returns to idle state 317. If the end user is off-hook in the telemetry period because the end user wants to make a call at block 641, then the line is disconnected from the telemetry connection, and at block 643 a disconnect signal from the exchange to the MIU. Is sent, an on-hook signal is sent to the utility telemetry trunk at block 645, and the trunk is released at block 647. The end user is then ready to receive the dial tone and process it in the normal manner of dialing and calling the appropriate digit (state 649).

It can be seen that the above description is only one of the preferred embodiments of the present invention. Various other devices may be invented by those skilled in the art within the scope of the present invention. Accordingly, the invention is not limited to the appended claims.

Claims (5)

A voice band signal exchange network for interchangeably interconnecting a plurality of inlets for connecting to interoffice telecommunications trunks and a plurality of outlets for connecting to an analog customer line. A method of accessing a customer premises device from a data access device through a telecommunications exchange system, wherein the service type for a first incoming connection to the data access device is necessary for establishing a compressed call connection. Determining cognition; Establishing a compressed call connection from the incoming line to the outgoing line of the voice band signal switching network for connecting the data access device to an analog customer line connected to a station equipment of a customer; Transmitting a signal over the compressed call connection to access the customer premise device from the data access device over the analog customer line, wherein the setting step includes whether the terminal is connected through a subscriber loop carrier. Determine and transmit a short spurt over the connection so that the subscriber loop carrier can establish a random connection to the terminal without transmitting a substantial call signal to the terminal, if connected via the loop carrier. And an access method. 2. The method of claim 1 wherein the determining step includes determining a length of the short spurt for the terminal. 3. The method of claim 2, wherein determining the length comprises determining the type of subscriber loop carrier used to access the terminal. A telephone exchange system comprising: a switching network interconnecting a plurality of telecommunication trunks and a plurality of analog customer lines; At least one of said trunks accessible to a utility data access device for accessing a customer premises device; A processor means for analyzing a service type of at least one of said plurality of trunks and operating under control of a program for establishing a connection over said switching network without transmitting a call signal to any analog customer line in response to said analysis; One of said customer lines is connected to a customer premises device via a subscriber loop carrier, and said processor means is connected to said customer line so that said subscriber loop carrier can establish a connection to one device of said customer. And operate under the control of a program transmitting a short spurt of the call signal. A method of accessing a customer premises device from a data access device via a telecommunications switching system comprising a voice band signal exchange network interconnecting a plurality of telecommunication systems and analog customer lines, said data access device and a central station service unit. Establishing a connection between them; Establishing a connection from the central station service unit to the switching network through a trunk between central stations; Establishing a compressed call connection from the trunk via the switching network to an analog customer line connected to a meter interface unit of a customer terminal connected to a controllable device; Accessing the controllable device via a tone signal transmitted to the meter interface unit via the connection, comprising: controlling the controllable device via the connection; Creating an invoice record for the compressed call connection in substantially the same manner as an invoice record for the voice call; Detecting an off-hook signal on the compressed call connection; In response to detecting the off-hook signal, disconnecting the compressed call connection; The establishing of the compressed call connection may include determining whether the terminal is connected via a subscriber loop carrier, and if connected via that subscriber loop carrier, allowing the subscriber loop carrier to establish a connection to the terminal. Transmitting a short spurt of a call signal via the method, wherein the determining comprises determining the length of the short spurt for a subscriber loop carrier connection to the terminal. CLAIMS 1. A method of accessing a customer premises device connected to a customer terminal by a telecommunications exchange system, comprising: 6. determining whether the call connection required by the terminal is a compressed call connection; Determining that the terminal has become accessible to the switching system via a subscriber loop carrier, upon determining that the requested call connection is a compressed call connection; If the terminal is accessible through a subscriber loop carrier unit, establishing a connection from the switching system to the subscriber loop carrier unit; Transmitting a short spurt of a call signal from the switching system over the connection; Upon receiving a short spurt of the call signal, extending the connection from the switching system to the terminal via the subscriber loop carrier without transmitting any call signal to the terminal. .