IE45958B1

IE45958B1 - Telecommunications transmission apparatus

Info

Publication number: IE45958B1
Application number: IE2646/77A
Authority: IE
Original assignee: Siemens Ag
Priority date: 1976-12-30
Filing date: 1977-12-29
Publication date: 1983-01-12
Also published as: BE862549A; IT1089195B; FR2376584B1; CH625927A5; DE2659664B1; DK585777A; DE2659664C2; JPS5384607A; NL7714549A; AU516846B2; SE7714903L; GB1598917A; IE45958L; BR7708766A; AU3183077A; FR2376584A1; AR212060A1; LU78781A1; MX143029A

Abstract

This data transmission device serves to connect a plurality of subscribers (T1 ... Tp) to a central exchange, the number of channels of the transmission device being lower than the number of subscribers. The transmission is carried out via a frequency division multiplexing device (16, 17, 18; 26, 27, 28) and, with the aid of a central control device (14), a switching device (13) connected to the exchange-side terminal is controlled directly and at least one allocation device (23) for connection set-up which is connected to a subscriber-side terminal is controlled by means of a telecontrol device (15, 25).

Description

This invention relates to telecommunications transmission apparatus for connecting a plurality of subscriber terminals of a central exchange, in particular, where the number of available channels of the transmission link is less than the number of subscribers.

In order to connect subscriber stations to a central exchange, multiplex transmission devices can be provided with a channel allocation which is either fixed or is selective to match instantaneous requirements. Channel allocation as and when required can prove particularly expedient when the resultant economy in transmission capacity leads to a substantial reduction in outlay.

In comparison to division into small, decentralised units, the retention of a central switching exchange for large area subscriber networks has the advantage that it is possible to use conventional switching devices and that when the network is extended, the basic network structure is largely retained.

It is an aim of this invention to provide telecommunications transmission apparatus for connecting a plurality of subscribers to a central exchange in such a manner that the connection between subscriber and exchange is established only when required, and in fact by allocating a channel still available at the time.

In accordance with this invention there is provided telecommunications transmission apparatus for connecting a plurality of subscribers to respective associated - 3 subscriber terminals of a central exchange in a telecommunications system, the apparatus including an exchange station connected via a frequency division multiplex transmission link to at least one subscriber end station having respective terminals for all the subscribers to be served by the subscriber end station, and frequency division multiplex allocation means for connecting selected ones of a plurality of the frequency channels of the link to respective selected ones of the subscriber terminals, the exchange station having respective subscriber terminals for all the subscribers to be served by the exchange station, being greater in number than the frequency channels of the link, and a frequency division multiplex switch arrangement for connecting selected ones of the frequency channels to respective ones of the subscriber terminals of the exchange station that are to be interconnected via a central exchange subscriber switching device to which the apparatus can be connected, a central control device being arranged to control the switch arrangement directly and the allocation means via a remote control arrangement, said control being dependent upon switching and/or subscriber requirement criteria and upon the state of seizure of the link.

In one embodiment, the allocation means takes the form of a switch arrangement interposed between the subscribers and a channel converter in which latter the frequency channels are allocated to subscriber side terminals in a fixed manner. This embodiment is particularly expedient in the case where in a subscriber end station the number of subscribers is greater than the number of channels (which corresponds to the number of subscriber-side terminals of the channel converter) - 4 459 58 although it can also be used (in a system employing a plurality of subscriber end stations and where the total number of subscribers in the system is greater than the number of transmission channels) in a subscriber end station having a number of subscriber terminals less than or equal to the number of channels available in the subscriber end station.

In a further embodiment, in a subscriber end station in which the number of subscriber terminals is at most equal to the number of frequency channels which can be provided via a channel converter of the end station, the allocation means include a carrier-frequency switch connected between a carrier-frequency supply device and the channel converter to which the respective subscribers have predetermined connections. The carrier-frequency switch, which is preferably a controllable carrierfrequency switching network, can be constructed and installed in a relatively simple fashion and only a discrete frequency requires to be allocated in respect of each transmission channel.

Furthermore, when the subscribers are telephone subscribers, the transmission apparatus can be arranged in the central exchange so that each subscriber-allocated channel can transmit dialled information, metering information, dialling tone, ringing tone, engaged tone and/or other switching signals.

On the other hand the remote control arrangement can expediently be arranged for the transmission of the criteria seize, clear, subscriber number, and/or channel number. The transmission apparatus may be arranged so that at least two groups of channels can be transmitted by means of the transmission link, the - 5 45938 channels of a group being available for allocation to at least one associated group of subscribers in the or at least one of the subscriber end stations, and a common remote control arrangement and/or central control devices being provided for all the channels of the link. These measures advantageously enable greater exploitation of components of the remote control arrangement and/or of the central control device. In particular, a central station of the remote control arrangement can effect the desired allocation of frequency-channels for a plurality of channel groups by means of t.d.m. operation. The improved exploitation is achieved both when the groups of channels are provided via respective separate transmission paths of the link and when they are provided by a common transmission path.

Furthermore, when sections of the transmission link each transmit a plurality of channel groups, the advantage is achieved that over each of these link sections the same signal channel of the remote control arrangement is assigned for all the channel groups.

Embodiments of this invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 is a block circuit diagram of an exchange of transmission apparatus embodying this invention; and Fig. 2 is a block circuit diagram of a subscriber station of transmission apparatus embodying this invention and which can be used in conjunction with the exchange shown in Fig. 1.

The exchange 1 illustrated in Fig. 1 contains channel converters 16 and 17 which are connected to a transmission link 3 via channel converter 18 which can 4S35B - 6 handle the number of channels of the link 3 which is larger than that handled by either converter 16, 17.

The low-frequency terminals of the channel converters are connected to dialling circuits E'l to E'n of the exchange unit 12 (which provides a speech signal/ signalling interface) via frequency division multiplex switch arrangement 13, which is controllable LF switching network (controlled by device 14 via lines d), and via lines b.

For each channel (including the signalling channel) the channel converters 16 and 17 possess four wire terminals and the switch arrangement 13 is likewise arranged for a four-wire switch through. The device 12 is used to achieve a transition from four-wire to two-wire transmission in each one of the dialling circuits E'l to E'n which are permanently assigned to the respective subscribers. Via the two-wire connections a, the circuits E'l to E'n are connected to subscriber circuits Al to An of switching device 11.

Central control device 14 is connected via call integrator 10 to the circuits E'l to E'n and via each of the lines £ can receive an integrated call signal from the switching device 11 as a criterion for a connection request emanating from the exchange.

The central control device 14 (which can be a micro-computer for example) is connected to the central station 15 of a remote control arrangement. Via frequency branching device 19 the station 15 provides signals on a channel, which is not available for allocation to subscribers, and which connects the station 15 to other (subsidiary) remote control stations in subscriber end stations (not showing in Fig. 1) - 7 4S9S8 connected to the exchange and forming parts of the remote control arrangement.

The common signal channel of the remote control arrangement provides a conference circuit via which the station 15 exchanges information with the other (subsidiary) remote control stations, in particular by coded t.d.m. transmission. The station 15 can operate in call-up fashion, i.e. in such a way that the station 15 calls up one subsidiary remote control station after the other and causes it to emit a message and/or command. It can prove particularly expedient to employ a remote control arrangement operating in accordance with the so-called call-up and impulse (combined impulse/interrogation) method, in which, during the call-up cycle, jump-in time gaps are kept free to allow the subsidiary remote control stations independently to interrupt the call-up cycle and emit messages when messages are to be transmitted to the central remote control station 15. Expediently the central remote control station calls up the subsidiary control stations individually and deliberately as and when required. When a flexible remote control arrangement is used for information exchange, the subsidiary remote control stations and the central remote control stations can be adapted to suit differing configurations of the subscriber networks.

The criteria seize, clear, subscriber number and channel number are transmitted with the aid of the remote control arrangement. In addition the remote control arrangement can be used for link monitoring, and other remotely controlled operations.

The frequency branching device 19 allows the channel excluded from availability for allocation to be tjt v «J Ο ·-* - 8 simultaneously used as signalling and service-channel.

It can possibly be dispensed with, particularly when an independent channel is provided for the service line and/or a remote control arrangement is used which does not permit common accommodation of a service path and signalling path in one and the same LF-channel on account of bandwidth restrictions, or when no service path is required.

The subscriber end station shown in Fig. 2 is connected via coupler Al to the transmission link 3. The coupler establishes a connection, which is low in return flux, between three four-wire paths. The subscriber end stations for further subscribers Τρ+l...Tn are not shown in detail in the Figure.

The two-wire lines emanating from the subscribers T1 to Tp. are connected to subscriber dialling circuits El to Ejq (of subscriber device 22 which provides a speech signal/signalling interface) which effect a transition from two-wire to four-wire signal paths. Channel converters 26 and 27, connected to the dialling circuits via line f_, each combine twelve LF-channels to form a primary group. In channel converter 28, which are connected to the coupler Al, the primary groups are used to form a transmission band comprising a greater number of channels than twelve.

Other services can be transmitted by the frequency multiplex transmission apparatus in parallel to the allocated subscriber channels, e.g. data transmission, CF-tone transmission or other signals.

The channel converters 26 and 27 each contain modulators which serve to convert the LF-band into the pre-modulation range 48 to 52 kHz . In a second stage connected to the (first stage) modulators via lines c[. 459 38 - 9 the bands are converted into different frequency positions. Carrier-frequency supply device 21 is connected via allocation device 23 (in the form of a controllable switching network) to modulators of the second converter stage.

This allocation means (comprising devices 21 and 23 and the channel converters) enables individual subscribers to be selectively allocated one of the frequency positions within the primary group. The converters 18, 28, 16 and 27 can be dispensed with if a twelve-channel transmission link is used in place of the link having a higher number of channels.

The allocation device 23 is also connected to station 25 of the remote control arrangement and control commands which are emitted by the central control device 14 and are transmitted via the remote control arrangement trigger the desired allocation in the subscriber end station.

In the dialling circuits El to En, the dialling pulses emanating from each subscriber are output-coupled t and fed via integrator 20 which serves to smooth the dialling pulses, and via lines e to the station 25, and are conveyed via the remote control arrangement to the central control device 14 which is thus caused to establish a connection for the calling subscriber.

The central control device 14 connects the calling or called subscriber, in accordance with the state of seizure of the transmission link 3, via an arbitrary member of those channels which are still available to the switching device. The transmission band of the transmission apparatus represents a telephone group with full access at all the subscriber end stations. 439 58 -ΙΟΙη order to be able to control the channel allocation in dependence upon the state of seizure of the transmission link 3 and the subscribers, the following criteria are constantly monitored in the central control device 14: a) In respect of each subscriber number and address the criteria: free, i.e. no loop closure, seized by the subscriber i.e. an outgoing call (from the subscriber) IO seized by exchange i.e. an incoming call (to the subscriber) b) In respect of each transmission channel free, connected at the subscriber end, connected at the exchange end.

If none of the transmission channels is free, it is necessary to distinguish between two situations, in dependence upon the origin of the connection establishment request: a) A seizure impulse from one of the subscribers T1 to Tn: the subscriber does not receive a dialling tone, replaces the receiver and can make a new attempt after a specific length of time. b) Seizure impulse from the exchange: the central device 14 simulates a loop closure or the “engaged state in the exchange direction also for all subscribers who are still free: the remote subscriber therefore receives engaged signals from the switching device 11. - 11 The switching criteria Seize and Clear are transmitted directly to the central control device 14 when originating in the exchange 1, and are transmitted to the device 14 via the common signal channel made available by the remote control arrangement when originating from a subscriber end station 2.

The additional waiting time between the lifting of the hand set and the reception of the dialling tone which is caused by the channel allocation is dependent upon the properties of the remote control arrangement employed.

This waiting time can be made sufficiently short with the aid of a high-speed remote control arrangement which may operate in accordance with a combined impulse/interrogation process, for example.

Following the allocation of a transmission channel, the criteria dialling signals, ringing, and possibly charge pulses are transmitted by means of the signalling channel individually assigned to the speech circuit and provided in the CF-transmission system and can be an in-band or out-band channel.

The criteria dialling tone, ringing tone, engaged tone are inserted into the speech band of the allocated channel from the exchange. 459 58 - 12 For longer multiple-channel subscriber links a section-wise protected transmission of the remote monitoring and control signals can be advantageous, in particular, by means of a 1:1 LF-switch-over device. In this case the alternative route can lead across an arbitrary, second LF or CF connection.

It is necessary to differentiate between two situations as regards making and clearing a connection: 1. The subscriber in question is the calling subscriber . 2. The subscriber in question is the called subscriber.

A preferred method of channel allocation and release is as follows: 1) Connection establishment by subscriber (i.e. the calling subscriber). la) Channel allocation.

The lifting receiver, i.e. a long loop closure is recognised as a seizure impulse by the associated subscriber circuit and by the integrator 20 for dialling pulse suppression, and is fed, together with the subscriber number and address via the remote control arrangement to the central control device 14. The integrator 20 provides a time criterion so that when the seizure impulse has been interrupted for a long period of time, e.g. 10 sec., the channel allocation impulse is cancelled. The central control device 14 seeks a free transmission channel and supplies the command connect subscriber via the remote control arrangement to the allocation device 23 of the calling subscriber - 13 station 2. When a connection has been effected at the subscriber end, an acknowledgement is sent to the central control device 14 and in the exchange 1 produces the command connect subscriber terminal at exchange end.

The connection between the switching device and calling subscriber is now established; all other switching criteria, namely dialling tone, dialling signal, ringing tone, engaged tone, charge pulses are transmitted via the allocated channel. lb) Release of the transmission channel.

A receiver replacement, i.e. a long loop interruption at the subscriber end is recognised as a clearance impulse by the subscriber circuit and by the integrator 20 and the message subscriber has replaced receiver is supplied to the central control device 14.

The central control device 14 emits the command release channel at subscriber end.

Following the reception by the device 14 of the acknowledgement channel free at subscriber end, the channel is cut off at the exchange end. Thereafter the central control device 14 stores the information channel free for the relevant channel.

Thus a transmission channel is released only as a result of the subscriber replacing the receiver. This also applies when a connection has been established by the exchange (situation 2 below). 2) Connection establishment by the switching device in the exchange; the subscriber referred to is the called subscriber . 2a) Channel allocation.

The seizure impulse subscriber is called is 459 58 - 14 obtained by the dialling circuit from the ringing signal (25 or 50 Hz) emanating from the exchange; the intervals between the ringing periods are suppressed by the call integrator.

The seizure impulse obtained in this way is fed to the central control device. When the seizure impulse is instead supplied directly from the exchange, the call integrator can be dispensed with.

The central control device 14 seeks a free transmission channel and feeds a connect command via the remote control arrangement to the subsidiary station (of the remote control arrangement) assigned to the subscriber, and the subscriber is connected to this channel; an appropriate acknowledgement is sent to the central control device 14, The central control device 14 is switched through the channel at the exchange end following the reception of the acknowledgement and the call passes via the allocated channel to the called subscriber.

The subscriber lifts the receiver to effect loop closure which is used as a hold criterion for the allocated channel; if no loop closure has occurred after a long period of time, the channel is released by the channel control device. 2b) Release The release of the transmission channel is effected as in situation lb) above as a result of the subscriber replacing the receiver, i.e. by a loop interruption.

It is to be understood that different sections of the transmission link 3 may have different number of channels to suit requirements. - 15 With the transmission apparatus described above it is possible to achieve improvements in the exploitation of the transmission capacity of carrier-frequency subscriber systems. Furthermore, the advantage is achieved that the allocation of channels as and when required can be made possible without any need to modify the components of conventional frequency multiplex transmission systems but by providing additional devices which can largely comprise conventional units. Arbitrary transmission media, such as free lines, cables and radio relays can be used for transmission link.

The allocation of channels as and when required in multiple carrier-frequency channel systems is particularly advantageous when the number of speech circuits in economically feasible transmission systems is not sufficient for the number of subscribers to be served.

Particularly advantages are achieved in the following situations: a) An existing symmetrical cable or free line is available for picking up subscribers. The cable quality permits only the use of systems having small numbers of channels (not systems having larger numbers of channels). The number of subscribers is such that if instead fixed channel allocation were to be provided, a plurality of small channel-number systems would be required. b) The sub-base band of a wide-band radio relay system or the coaxial cable is available for picking up subscribers along a link connecting a plurality of subscriber groups. The number of speech circuits which can be achieved is less than the number of subscribers.

With fixed channel allocation, at least one further radio relay or cable system would have to be used. - 16 c) Narrow-band radio relay systems need to be used for picking up the subscribers as the frequencies available preclude wider-band systems. With fixed channel allocation, two or more parallel radio relay systems would have to be qsed.

It is possible for the subscriber end station to take a different form from that shown in Fig. 2.

In one embodiment, different from that shown in Fig. 2 but similar to the arrangement shown in Fig. 1, the allocation device takes the form of a switch arrangement interposed between the subscribers and a channel converter in which latter the frequency channels are allocated to subscriber-side terminals in a fixed manner. This embodiment is particularly expedient in the case where in a subscriber end station the number of subscribers is greater than the number of channels (which corresponds to the number of subscriber-side terminals of the channel converter) although it can also be used (in a system employing a plurality of subscriber end stations and where the total number of subscribers in the system is greater than the number of transmission channels) in a subscriber end station having a number of subscriber terminals less than or equal to the number of channels available in the subscriber end station.

Claims

1. CLAIMS : 1. Telecommunications transmission apparatus for connecting a plurality of subscribers to respective associated subscriber terminals of .a central exchange in a telecommunications system, the apparatus including an exchange station connected via a frequency division multiplex transmission link to at least one subscriber end station having respective terminals for all the subscribers to be served by the subscriber end station, and frequency division multiplex allocation means for connecting selected ones of a plurality of the frequency channels of the link to respective selected ones of the subscriber terminals, the exchange station having respective subscriber terminals for all the subscribers to be served by the exchange station, being greater in number than the frequency channels of the link, and a frequency division multiplex switch arrangement for connecting selected ones of the frequency channels to respective selected ones of the subscriber terminals of the exchange station that are to be interconnected via a central exchange subscriber switching device to which the apparatus can be connected, a central control device being arranged to control the switch arrangement directly and the allocation means via a remote control arrangement, said control being dependent upon switching and/or subscriber requirement criteria and upon the state of seizure of the link.

2. Apparatus according to claim 1 wherein the subscriber end station has a speech signal/signalling interface which provides said end station subscriber terminals and is connected for speech signal transmission to the frequency division multiplex allocation means, the exchange station having a speech signal/signalling - 18 interface connected between the exchange station subscriber terminals and the frequency division multiplex switch arrangement, the central control device being arranged for receiving signals via said exchange station speech 5 signal/signalling interface and via the remote control arrangement and said subscriber end station speech signal/ signalling interface.

3. Apparatus as claimed in claim 1 or claim 2 wherein the allocation means is a switch arrangement 10 connected between the subscriber terminals and a channel converter.

4. Apparatus as claimed in claim 1, or claim 2, wherein in the or at least one of the subscriber end stations where the number of subscriber terminals is at 15 most equal to the number of frequency channels which can be provided via, a channel converter of the end station, the allocation means includes a carrier-frequency switch connected between a carrier-frequency supply device and the channel converter to subscriber-side terminals of 20 which the respective subscriber terminals have predetermined connections.

5. Apparatus as claimed in any one of the preceding claims, wherein the subscribers are to be telephone subscribers, and the exchange station is arranged in the 25 central exchange such that each channel available for allocation is arranged for transmitting dialled information, metering information, dialling tone, ringing tone, engaged tone and/or other switching signals.

6. Apparatus as claimed in any one of the preced30 ing claims, wherein the subscribers are to be telephone subscribers, and the remote control arrangement associated with the or each subscriber end station is arranged - 19 for transmitting signals representing the criteria seize, clear, subscriber number and/or channel number.

7. . Apparatus as claimed in any one of the preceding claims, wherein in respect of each subscriber terminal, a dialling circuit is provided in the exchange and in the or each subscriber end station.

8. Apparatus as claimed in claim 7, wherein a call integrator in the exchange station is connected between the dialling circuits and the central control device.

9. Apparatus as claimed in claim 7 or claim 8, wherein in the or each subscriber end station an integrator for smoothing dialling pulses is connected between the dialling circuits and a station of the remote control arrangement.

10. Apparatus as claimed in any one of claims 7 to 9, wherein the exchange station switch arrangement is connected between the dialling circuits and channel converters of the exchange station.

11. Apparatus as claimed in any one of the preceding claims wherein a signal transmission channel interconnects in a conference circuit respective stations of the remote control arrangement that are provided in the exchange station and in the or each subscriber end station, the signal transmission channel being one of the frequency-channels of the transmission link that is not available to be allocated to a subscriber.

12. . Apparatus as claimed in any one of the preceding claims, wherein the remote control arrangement provides for combined call-up and impulse operation.

13. Apparatus as claimed in any one of the preceding claims, wherein the remote control arrangement provides means for monitoring operation of the transmission apparatus. - 20

14. Apparatus as claimed in any one of the preceding claims, wherein at least two groups of channels can be handled by the transmission link, the channels of each group can be allocated to at least one associated group 5 of subscriber terminals in the or at least one of the subscriber end stations, and a common remote control arrangement and/or common central control device is or are provided for all the channels of the link.

15. Telecommunications transmission apparatus for 10 connecting a plurality of subscribers to subscriber terminals of a central exchange in a telecommunications system said apparatus being substantially. as described herein with reference to the accompanying drawings.

16. A telecommunications system including apparatus 15 according to any one of the preceding claims wherein a plurality of said subscriber end stations are interconnected with the central exchange via said link.