EP1046318A1 - Method for managing transmission channels in a digital network termination control and corresponding termination control system - Google Patents

Abstract

The invention concerns a method for managing a termination system in an integrated-services digital network (7; 20) designed to connect at least two terminals (3, 4) to a line (5) with two transmission channels of said network. The method consists in reserving the two termination system channels for setting up a connection between one of the terminals (3; 4) and a correspondent, and in searching for any request for setting up another connection for the other terminal (4; 3) so that, if such is the case, one of the termination system channels is cleared to be assigned to the other connection.

Description

 Method for managing the transmission channels of a digital subscriber control unit and corresponding control unit

The switched telephone network, PSTN, now offers subscribers wide possibilities for data transmission. We can in particular think of the INTERNET, whose access service providers are accessible by PSTN.

Given the very low cost of Internet connections, users are inclined to extend the connection time, so that the telephone line is often unavailable to receive incoming calls and must be released if someone other wants to be able to use it as an output. In short, call collisions overload the line with the number of calls to be handled. We can obviously provide a second line, but the increase in the subscription cost is not negligible for a residential subscriber.

To try to avoid this kind of problem, of collisions between calls, RTC can signal the presence of an incoming call when the line is busy, which offers the choice to refuse or accept it, but, in such cases , the new communication replaces the old one, which must therefore at least be suspended.

There are also digital links on the PSTN lines, allowing connection to digital networks, such as the Integrated Services Digital Network (ISDN). These links include two transmission channels and a signaling channel.

In the context described above, the two ISDN channels make it possible to double the speed of exchanges, with the INTERNET for example, and the signaling channel makes it possible to signal an incoming call. While this improves overall performance, and in particular shortens the time it takes to receive large image files, it does not solve the basic problem of line overload, leading to rejection of calls or interruption of communications. WO 93/23 809 teaches to allocate two B channels to the same communication and to release one if another communication is required.

This certainly improves the flexibility of operation of the channels, but still it is necessary, in the event of an incoming call waiting for a channel, that the user's telephone equipment receives from the network a corresponding signaling. In effect, the telephone network cannot authoritatively perform channel switching, which must be controlled by the user's equipment. However, the network does not always provide this incoming call signaling.

The present invention aims to allow the release of a channel which is independent of any incoming call signaling at the level of the user's equipment.

To this end, the invention relates first of all to a method for managing the transmission channels of a digital subscriber control unit, of a digital network with integrated services, arranged to connect at least two terminals to a line with two transmission channels of said network, a process in which the two control room channels are reserved to establish a connection between one of the terminals and a correspondent, any request for the establishment of another connection for the other terminal is sought and , in such a case, one of the control room channels is freed up to assign it to the other link, characterized in that, prior to the establishment of the link on the two transmission channels, the forwarding is controlled , by the network, incoming calls to a predetermined number, specific to the control room, of a transit manager of said link and, in the event of a call being forwarded, it is the manager who releases a channel.

Thus, the management is represented, with the telephone network, by the transit manager and, as the latter is accessible to receive a forwarded incoming call, the manager can release a channel to assign it to the incoming call. The invention also relates to a digital subscriber control unit, of a digital network with integrated services, for the implementation of the method of the invention, with two signal transmission channels, for the connection of at least two terminals on a digital line of said network, governed with channel management means arranged to, in the absence of occupation of the two channels, assign them both to a link for one of the terminals and comprising means for detecting requests to establish a second link for the other terminal arranged to control the release of one of the channels by the management means, characterized in that the detection means comprise a register for receiving signals from a signaling channel, associated with the two transmission channels, and decoding circuits, of call indication signals, arranged to control the management means.

The invention will be better understood with the aid of the following description of a preferred embodiment of the process of the invention, with reference to the appended drawing, in which:

- Figure 1 shows schematically a subscriber control room for the implementation of the method of the invention, connected, by the telephone network, to an INTERNET service provider, and - Figure 2 is a functional diagram of the control room.

The assembly referenced 1 comprises a subscriber control unit 2 connected, on the user side, to a telephone set 3 and to a data processing terminal, here a PC 4 and, on the other, to a line 5 connected to the switched telephone network PSTN / ISDN 7, comprising a central office 6 for line 5. This, to the ISDN basic access standard S0 and / or TO with regard to bandwidth, is intended to carry a bidirectional bit stream useful for 144 kb / s, corresponding to two B channels at 64 kb / s and one D signaling channel at 16 kb / s. To the network 7, and here to the central office 6, is attached, by MIC links to the ISDN standard primary access T2 or S2 with 32 time channels (8), equipment 10 of the Internet access service provider 20. The equipment 10 comprises circuits 12 for connection between the links 8 and the INTERNET 20 and here comprises, between the MIC (s) 8 and the circuits 12, circuits 11 for managing the B channels or time channels of lines S0 of various subscribers, channels using MIC 8.

The management of the two B channels of line 5, with regard to their allocation to traffic, is as follows:

the two B channels are reserved to establish a connection with a correspondent, any request for the establishment of another connection is examined and, in such a case, one of the B channels is freed to assign it to the other connection.

Note that the initial link can be inbound or outbound, and concern the INTERNET 20 or a correspondent connected to the PSTN / ISDN network 7.

If the PC 4 thus occupies the two B channels of line 5, the set 3 can be off-hook to signal to the control room 2 a request for the establishment of a second outgoing link. Control room 2 then releases one of the B channels and assigns it to station 3.

If it is an incoming call, signaled by the network 7 in channel D, the control room 2 likewise releases one of the channels B and signals the identity of this to the central office 6, to allow it to make it on the incoming call. Central 6 then establishes, in a conventional manner, a connection on this channel B, by signaling the fact by channel D.

The circuits 11 aim to treat the case for which the network 7 would not provide an indication of incoming call to the control room 2 in the event of occupation of the two channels B. The control room 2 then transmits, when the reservation of the two channels B for the same communication, a command for forwarding incoming calls to a number which is specific to it and which is assigned to the access provider 10, by the links 8. As a variant, provision may be made for the network 7 to automatically carry out such a pre-programmed forwarding, on total occupation of the line 5, or for the user to have programmed such forwarding a priori.

When a call thus forwarded, coming for example from a telephone set of the network 7, reaches the equipment 10, the latter identifies the management 2 according to the destination directory number. As circuits 11 are interposed in a cut-off between line 5 (and 8) and circuits 12 for access to the INTERNET 20, the call returned commands switching in circuits 11 (time matrix). This communication releases one of the two B channels of line 5, which are extended by the MIC 8. This release is transmitted to control room 2, so that the initial link folds back to the only B channel kept for this purpose, and is signaled to INTERNET 20 to indicate that the speed is reduced by half. As the PSTN / ISDN network 7 is not intended to authoritatively interrupt an established communication, it is unable to manage the allocation of the B channels, and it is therefore here the control room 2 and the circuits 11 which manage this task.

The released channel B is then used to return, to the control room 2, from the equipment 10, the incoming call which was originally sent by the central office 6 to the equipment 10. This therefore amounts to removing the effect the return by the network 7, once the associated information has been used indicating the arrival of an incoming call on the busy line 5.

It can in particular be provided that the equipment 10 directly controls, in the central office 6, the cancellation of the forwarding of the line 5, in order to avoid the maintenance of the detour or loop, by the MIC 8 links, of the channel B which has been reassigned while it is now routing a communication from network 7, for which the INTERNET 20 is foreign.

It could also be expected that the network 7 itself detects parasitic loops, such as the round trip to the equipment 10 from the central 6, and short-circuits them. It will be noted that the presence of a second network, such as the INTERNET 20, is not necessary for the implementation of the method. In fact, the PSTN / ISDN 7 and INTERNET 20 networks functionally form a single network through which links using two 64 kb / s time channels can be established.

FIG. 2 illustrates the functional structure of control room 2. This comprises a UART 25 with a pair of line interface buffer registers, ensuring in both directions the bit exchanges of the channels, 2B + D, ie an average bit rate of 144 kb / s in each direction. The registers 25 therefore comprise three zones each, 251, 252, 253 and 254, 255, 254 respectively for the channels 2B + D, respectively in transmission and in reception.

On the terminal 3 and 4 side, the control room 2 comprises a circuit 23 of a conventional analog interface for continuously supplying the station 3, making it ring and detect its on-hook / off-hook state.

The station 3 is also connected to an encoder / decoder 22 to digitize the phonic signals transmitted and restore in analogical form those received from line 5.

The PC 4 is connected to a UART 24, of the control room 2, managing inter alia the exchange of signals for the management of communications, such as outgoing call and dialing.

The time connection matrix relating to the two channels B, connecting the terminals 3 and 4 to the UART 25, it is represented in the form of relay contacts, for the purpose of clarity of the description. The side of the encoder 22 opposite the station 3 is connected to the foot of a movable blade 26 of rest / work relay allowing a bidirectional connection with one or the other of the two channels B, that is to say the zones 251 and 254 or 252 and 255. The PC 4 is for its part connected, through the UART 24, to the foot of two independent contacts, work relay 27, 28, allowing respectively to connect it to the first channel B (251, 254) and to the second (252, 255 ).

A time base 30 sequences the operation of the assembly, a central microprocessor unit 21 which it synchronizes being connected, by links not shown, to the above circuits, in order in particular to control the matrix 26, 27, 28 .

A decoder circuit 29 receives the signals, here digital, coming from the line 5, through the area 256 of the UART 25 and provides in particular, to the central unit 21, the signals coming from the central 6 and indicating that a incoming call is on hold due to lack of available B channels.

The operation of control room 2 will now be explained in more detail.

In the event of an outgoing call, and starting from a line 5 vacancy situation, circuit 23 or 24 detects a connection request by the corresponding terminal 3 or 4 and informs the central unit 21. If this concerns the station 3, a single B channel is assigned to it, by command of the matrix (26), and the central unit 21 transmits to the central 6, by the signaling transmission channel 253, the identity of the assigned B channel, at the same time time that it transmits a request for channel B in the network 7 and retransmits the numeration of the station 3, entered by the circuit 23.

If it is the PC 4 which makes a call, the central unit 21 controls the establishment of the two connections 27 and 28, which therefore affects the two channels B to the PC 4.

The processes are basically the same for incoming calls.

If, on the other hand, it is a request to establish a second connection with one of the terminals 3, 4 while the other 4, 3 is already in communication, the central unit 21 releases a channel B if both were used for the first link. This case is therefore here that for which it is the PC 4 which first established a communication on the two B channels. It will however be noted that the ISDN allows transmissions on several B channels between purely telephone terminals, such as high-quality sound or videophones, and it could therefore have been planned to assign the two B channels to station 3.

Returning to the example considered, the station 3, asking the central unit 21 for a B channel for an outgoing call, this releases one of the B channels (opening of the connection 27 or 28) and assigns it to the station 3, by appropriately controlling the inverter 26.

In the case of an incoming call, the call indication signaling is recognized by the decoder 29, which signals this to the central unit 21, and the latter releases one of the B channels and informs it central 6, specifying the free B channel. Central 6 can then route the incoming call to the called terminal, in this case extension 3.

In all cases, communication establishment, switching, or substitution, in the allocation of channels B, and communication breakdown, the central unit 21 signals it to the central 6 by zone 253 and receives signals from it. by zone 256. The circuit 29 is therefore functionally integrated into the central unit 21.

As these are bidirectional digital time links whose outward and return channels are each managed specifically, one can consider initially taking two B channels in one direction and only one in the other direction, if the bandwidth requirement is asymmetrical . For example, a single B channel in transmission may be sufficient to interrogate a server of the INTERNET 20, while two B channels are useful for receiving large files. In this case, station 3 has a channel B in transmission.

Symmetrically, if it is the two transmitting B channels that are occupied, the reception channel B still free makes it possible to receive a call from the network 7. In either case, it is then possible to release, from the as described above, the channel B in the opposite direction to that which remained free after establishment of the first link, if the second link must be bidirectional.

Claims

1.- Method for managing the transmission channels of a digital subscriber control unit (2), of an integrated service digital network (7; 20), arranged to connect at least two terminals (3, 4) to a line (5) with two transmission channels of said network, process in which the two control room channels are reserved to establish a link (8) between one of the terminals (3; 4) and a correspondent, any request is sought establishment of another link for the other terminal (4; 3) and, in such a case, one of the control room channels (2) is released to assign it to the other link, characterized by fact that, prior to the establishment of the link on the two transmission channels, the return, by the network (7), of incoming calls to a predetermined number, specific to the control room (2), is controlled by a manager (10) transit of said link (8) and, in the event of a call being returned, it is the manager (10) which frees a channel.

2.- Method according to claim 1, in which a line signaling channel (5) is monitored to detect an incoming call, one of the transmission channels is released and a signal is returned to the network (7; 20) the identity of said channel.

3.- Digital subscriber control, of a digital network with integrated services (7; 20), for the implementation of the method of claim 1, with two signal transmission channels, for the connection of at least two terminals (3, 4) to a digital line (5) of said network, governed comprising means (21) for managing the channels arranged to, if the two channels are not occupied, assign them both to a link for one (3; 4) of the terminals and comprising means for detecting (23, 24, 25, 29) requests to establish a second link for the other terminal (4; 3) arranged to control the release of one of the channels by the management means (21), characterized in that the detection means comprise a register (256) for receiving signals from a signaling channel, associated with the two transmission channels, and decoding (29), signaling circuits call indication, arranged to control the management means (21).

4.- Subscriber control system according to claim 3, in which the detection means (29) are arranged to recognize incoming call indication signals coming from the line (5).