JP3001534B1 - ISDN service method in multi-way multiplex communication system - Google Patents

Abstract

A slot allocation for a B channel, which is not always necessary, is omitted. A first slave station that has received a message transmitted from an originating ISDN terminal belonging to the first slave station among the plurality of slave stations to a first slave station has a time slot of a D channel. Requests the base station 2 connected to the ISDN network to allocate a time slot for the B channel, and establishes a D-channel between the originating ISDN terminal,
A channel time slot and a B channel time slot are allocated. By monitoring the first message 101, the stations 2 and 3 detect whether the first slave station 3 to which the calling ISDN terminal 61 belongs and the second slave station to which the called ISDN terminal belongs are the same station. If the stations are the same, no B-channel time slot is allocated between the base station 2 and the first slave station 3. The time slot thus omitted is released for a third party.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ISDN service method in a multi-directional multiplex communication system, and more particularly, to an ISDN service method.
The present invention relates to an ISDN service method in a multi-way multiplex communication system in which a predetermined number of B-channel and D-channel time slots are allocated to SDN terminals and TDMA (time division multiplex) communication is performed between subscribers.

[0002]

2. Description of the Related Art An ISDN service in a multi-way multiplex system is a TD between a slave station and a base station connected to an ISDN network.
This is a communication service in which information is transmitted between subscribers having an ID, which is a terminal in a child station, using two channels according to the MA system. The basic interface of ISDN is one user
Two B channels and one D on the network interface
This interface has channels and can be used in common for various telephone and non-telephone services. A plurality of time slots are assigned to the two channels at the time of bidirectional communication. In other words, the ISDN service in which such a communication line between the base station and the slave station is provided regardless of the presence or absence of the communication is based on a pre-assigned line setting method. In such a pre-assignment type line setting method, the number of communication lines between the base station and the slave station is equal to the number (N) of accommodated ISDN basic interfaces.

[0003] As described above, in the pre-assignment type line setting method, a communication line is always allocated between terminals that are not performing communication. Although the user can use a terminal such as a telephone, a facsimile, and a data terminal, the traffic at the time of use can be considered to be smaller than when using a dedicated line. In this way, as long as the call volume is considered to be small, the pre-assignment type line setting method of allocating communication lines regardless of the presence or absence of communication limits the number of subscribers accommodated, and promptly responds to an increase in subscribers. It is difficult to deal with the problem, and there is a problem that the use efficiency of the communication line is extremely reduced.

In a multi-way multiplex system, the ISDN service employs a demand assignment system for allocating / releasing a communication line between a base station and a slave station in response to generation and termination of a call, thereby improving communication line utilization efficiency. It is preferred in terms of. That
Such as demand-assigned multi-way multiplex communication system
Allocating and releasing a transmission channel between a base station and a terminal accommodated in a slave station, including a base station and a plurality of slave stations, in response to the generation and termination of a call. The ISDN service of the multi-directional multiplex communication system accommodating the ISDN basic interface is considered,
Further, the base station terminates the layers up to layer 2 in the ISDN network, and the slave station terminates the layers up to layer 2 in the ISDN terminal. The step of monitoring the messages in layer 3 includes the steps of: recognition to, and the step of allocating and opening the transmitting channel between the base station and the terminal
Can be considered. Such a new technology can increase the efficiency of using the D channel and the B channel,
It is believed that there is yet another common problem.

Looking at such a common problem in correspondence with FIG. 7, when a call is made from the terminal 61 to the terminal 62, first, when the terminal 61 makes a call, a time slot for the D channel and the B channel is used. Is assigned, the layer 3 message from the terminal 61 is transmitted to the ISDN 1 via the assigned D-channel time slot 101 and a call is established, and the voice from the terminal 61 is assigned. It is relayed by the B channel time slot 102. In the case of an incoming call, when the base station detects an incoming call to the terminal 62, the time slot 10 for the D channel is used.
3. The incoming process is performed on the terminal 62 by allocating the time slot 104 for the B channel, and the terminal 61 and the terminal 62 enter a talking state when the terminal 62 responds.

The technique envisaged in this way is indispensable when a call is made between ISDN subscribers accommodated in different slave stations, and therefore, when two subscribers make a call, two techniques are required for the D channel. It is essential that a maximum of four time slots be allocated for each channel and the B channel, but it is also essential that the same number of time slots be allocated when subscribers accommodated in the same slave station make a call. Not always.

As described above, by allocating a time slot for the B channel, a time slot for a maximum of four B channels is secured, so that other subscribers may not be able to use the time slot. Use efficiency decreases. The time slot for the D channel is indispensable for transmitting a layer 3 message between the terminal and the ISDN network, but information of the B channel such as voice and data between the terminals is transmitted through the ISDN network. It is considered that it is not essential to allocate the time slot for the B channel, transmit the information of the B channel to the ISDN network, and return to the same slave station again.

[0008] From the ISDN network to which the base station is connected, B
It is known from Japanese Patent Application Laid-Open No. 10-191445 that the channel is omitted to increase the use efficiency of the B channel. This known technique also has the above-mentioned problems in common.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ISDN service method in a multi-directional multiplex communication system which can increase the B channel utilization efficiency by omitting slot allocation of a B channel which is not always necessary. To provide. Another object of the present invention is to eliminate the B channel slot allocation, which is not always necessary, by using the layer 3 message monitoring function between the terminal and the network as the conventional technology. It is an object of the present invention to provide an ISDN service method in a multi-way multiplex communication system capable of improving the use efficiency of the ISDN. Another object of the present invention is to provide a multi-directional multiplex communication system capable of improving the use efficiency of the B channel by omitting slot allocation of the B channel, which is not always necessary, and being applicable to the demand assignment system as it is. To provide an ISDN service method.

[0010]

Means for solving the problem are indicated in the following description in which the means for solving the problem are expressed according to the claims. It shows that it corresponds to the member, the process, and the operation of at least one of a plurality of forms of the present invention. However, the solution means of the present invention is to be interpreted as being limited to the members of the embodiment indicated by those numerals. It is not a thing, but to clarify the correspondence.

[0011] The ISDN service method in the multi-directional multiplex communication system according to the present invention is a method for providing a first one of a plurality of slave stations.
Transmitting a first message (101) from an originating ISDN terminal (61) belonging to the slave station (3) to the first slave station (3); ) Requests the base station (2) connected to the ISDN network (1) to allocate a D-channel time slot and a B-channel time slot, and the base station (2) ), Allocating a D-channel time slot and a B-channel time slot among the originating ISDN terminal (61), the first slave station (3), and the base station (2) in response to the allocation request A plurality of second slave stations (no corresponding number) and a plurality of first slave stations via a station comprising a first slave station (3) and a base station (2). ISDN service in one-way multiplex communication system In the method, the at station (2,3) 1
By monitoring the message (101), it is determined whether the first slave station (3) to which the calling ISDN terminal (61) belongs and the second slave station to which the called ISDN terminal (62) belongs are the same station. The step for detecting in (2, 3), and if the first and second slave stations (3) and (2) are the same station, a step between the base station (2) and the first slave station (3); And a step for setting a B channel path between the first slave station (3) to which the originating ISDN terminal (61) belongs and the receiving ISDN terminal without assigning a B channel time slot to.

When the terminals belong to the same slave station, the time slot of the B channel is not allocated between the base station (2) and the first slave station (3), so that the time slot is saved. The time slots thus saved are released for other subscriber terminals.

The base station (2) may be used as a station for detecting whether the first mobile station (3) and the second mobile station are the same, or, as will be described later, the mobile station (3). ). The first slave station is assigned the second message (101 ') in which the destination number is added to the first message (101) received from the originating ISDN terminal (61) by the time slot of the D channel already assigned. (3) transmitting to the base station (2).

The base station (2) reads and stores the destination number, transmits the destination number to the ISDN (1), and makes a call from the originating ISDN terminal (61) to the destination ISDN terminal (62). Is established, the base station (2) receives the source number of the calling ISDN terminal (62) from the ISDN (1). A search is made for an originating subscriber corresponding to the originating number, and then a further search is made for an incoming subscriber corresponding to the stored destination number.

The fact that the originating subscriber and the terminating subscriber belong to the same slave station and that the first slave station (3) and the second slave station are the same station coincide with each other. is there. Furthermore,
A third message (1
06) to the same slave station (3) by the base station (2). Further, based on the time slot allocation request of the first slave station (3) for the D channel only, the base station (2) is switched to the receiving side ISDN.
The time slot of the D channel of the terminal (62) is allocated. Further, when the incoming call is established, the originating ISDN (6
The station releases the time slot allocated to the B channel in 1). The time slot thus released can be assigned to a third party.

It is technically possible to make the first slave station (3) a station that detects whether the first slave station (3) and the second slave station are the same station. In this case, the B-channel time slot is not allocated before the incoming call to the called ISDN terminal (62) is established, and the B-channel time slot is not assigned after the incoming call to the called ISDN terminal (62) is established. The call path is set in the same slave station. Incoming IS
Until the incoming call to the DN terminal is established, the same slave station is the originating IS.
It is necessary to make the DN terminal (61) hear the bell. The call bell will be described in the embodiments.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with FIG. 1, a first embodiment of an ISDN service method in a multi-directional multiplex communication system according to the present invention includes a base station 2 and a base station 2 connected to an ISDN network 1. And a slave station 3 connected thereto. Network-side lines 51 and 52 of the ISDN 1 are connected to the base station 2. The slave station 3 provides the U-point of the ISDN basic interface to the network terminating devices 71 and 72 accommodating the terminals 61 and 62. The child-station-side lines 53 and 54 accommodated by the child station 3 correspond to the network-side lines 51 and 52.

The communication line between the slave station 3 and the base station 2 is set by demand assignment line control for allocating and releasing according to the occurrence and termination of a call. Communication by the communication line is performed by the B channel and the D channel. The B channel is a channel for performing communication relating to call information between the terminals 61 and 62, and the D channel is a channel for controlling communication of the call information.

As described above, the demand-assigned multi-directional multiplex communication system includes a base station 2 and a plurality of slave stations 3, and the base station 2 and the slave stations 3 correspond to the occurrence and termination of a call. This is an ISDN service of a multi-directional multiplex communication system that accommodates an ISDN basic interface by allocating and releasing a transmission channel between the accommodated terminals 61 and 62. This service provides the base station 2 with the ISDN network 1
Terminate the layers up to the layer and set the slave station 3 to the ISDN terminal 6
1 and 62, the step of terminating the layers up to the second layer, the step of monitoring the messages of the third layer, and the transmission and reception between the base station 2 and the terminals 61 and 62 by recognizing the occurrence and termination of the call. And the step of allocating and releasing a dedicated channel, and can improve the use efficiency of the D channel and the B channel.

In a service provided by such a demand assignment type multidirectional multiplex communication system, the base station 2 and the slave station 3
Can be smaller than the number of subscribers accommodated by the system.

FIG. 2 shows the system configuration of Embodiment 1 of the ISDN service method in the multidirectional multiplex communication system according to the present invention. The base station 2 has an ISDN network 1
Are accommodated. The slave station 3 is performing time division multiplexing (TDMA) communication. Between the base station 2 and the slave station 3, TDM is performed for the D channel and the B channel according to the occurrence and termination of the call.
A time slot (hereinafter, time slot) is provided by demand assignment line control which is allocated and released as a communication line. The C channel 100, which is a frame structure of a signal transmitted and received between the base station 2 and the slave station 3 and is given as a common control channel, controls the time slot allocation between the base station 2 and the slave station 3. It is used for exchanging information with the D channel information of the basic interface.

The base station 2 and the slave station 3 are composed of a first layer, a second layer
First layer termination circuits 21 and 31 and second layer termination circuits 22 and 32 for terminating layers are provided respectively. The first layer termination circuits 21 and 31 and the second layer termination circuits 22 and 32 establish synchronization of the first layer between the base station 2 and the ISDN network 1 and between the slave station 3 and the ISDN terminals 61 and 62, The link establishment of the second layer can be individually performed, and the messages of the third layer above the second layer can be monitored.

The first layer terminating circuits 21 and 31 and the second layer terminating circuits 22 and 32 are well-known circuits in the ISDN communication system, and the conventional circuits are used as they are. Such circuits can be easily realized using an LSI conforming to the CCITT standard.
On the other hand, each of the slave stations 61 and 62 can transmit and receive voice and data using the transmission / reception function of the C channel and the time slot designated by the base station 2.

The interface between the slave station 3 and the terminals 61 and 62, and the interface between the base station 2 and the ISDN 1 are respectively at the U point of the ISDN basic interface as shown in FIG. is there. The base station 2 has a function of managing time slots in addition to the transmission / reception function of the C channel, and refers to the time slot management table 23 for the D channel and the B channel upon generation of a call, and specifies a necessary time slot. Can be assigned. ISDN
Network-side lines 51 and 52 corresponding to terminals 61 and 62 are accommodated in base stations.

FIG. 3 shows a sequence showing the operation of the first embodiment. In particular, a call is issued from a terminal 61 accommodated in the slave station 3 and another terminal 62 accommodated in the same slave station.
5 shows a sequence operation on the calling side and the called side when there is an incoming call. The vertical axis in FIG. 3 is a time axis that is positive downward.

(1) Operation on the Calling Side When the terminal 61 accommodated in the slave station 3 makes a call, a second call between the terminal 61 and the slave station 3 and between the base station 2 and the ISDN network 1 It is assumed that the layer link has already been set by the demand assignment control described above. When a call is originated from the terminal 61, the SETUP (I
(Frame) message 101 is transmitted.

The SETUP message 101 is a third layer message for notifying a call. The slave station 3
The monitoring function for monitoring the third layer message 101 detects the SETUP message from the terminal 61 and sends a time slot (represented by TS in the figure) allocation request 102 to the base station 2 using the C channel 100. Send out. The time slot allocation request 102 is a message for requesting the terminal 61 accommodated in the own station to allocate a time slot for the D channel and the B channel.

The slave station 3 further transmits a SETUP message 1
The number of time slots requested is checked based on the information in 01, and the number is added to the time slot allocation request 102 as information (not shown). Upon receiving the time slot assignment request 102 from the slave station 3, the base station 2 adds the requested number of time slot numbers to the time slot assignment response 103 with reference to the time slot management table 23, and The time slot assignment response 103 to which the slot number is added is transmitted to the slave station 3.

When the slave station 3 receives the message which is the time slot assignment response 103 from the base station 2,
Time slots for the D channel and the B channel from the ISDN 1 to the terminal 61 are established. The slave station 3 uses the time slot for the assigned D channel to
SETUP message 101 received from terminal 61
To the base station 2 as a D channel setup message 101 ′. The D-channel setup message 101 'is a message in which the destination number received from the terminal 61 by the slave station 3 is added.

At the time of this transmission, even if the protocol between the slave station 3 and the base station 2 does not conform to the ISDN, the conventionally used protocol can be used as it is. Received D channel message 1
01 is converted into a message 101 ′ between the slave station 3 and the base station 2 and is transmitted as a D channel information message to the base station 2.
Sent to.

The base station 2 reads and stores the called party number (called party number) added to the received SETUP message 101 ′ of the D channel information, and transmits the called number to the ISDN 1. . Thereafter, the terminal 61 receives the ISDN 1
Layer message 104 (CAL) sent from
L PROC, ALERT, and CONNECT) are relayed by the frame in the time slot for the D channel under the control of the base station 2 in the same manner as in the case of the SETUP message, and transmitted to the terminal 61. The call is established by this transmission.

(2) Operation on the Called Side In this way, when a call is established and a call is received to the terminal 62, first, the line 52 corresponding to the terminal 62 on the side of the base station 2 SETUP message 1 from ISDN network 1
05 is sent. The SETUP message 105 contains I
It is a third layer message indicating an incoming call from the SDN network 1 side. The base station 2 receives the SETU received from the ISDN 1
Source number (c) added in P message 105
By using the "alling party number", it is checked whether the caller is a subscriber accommodated in the own system, and if the caller is a subscriber accommodated in the own system, it is checked whether the caller is in a calling state.

If the call is in the calling state, it is further checked whether it matches the destination number stored at the time of calling, and if all match, the connection between the terminal 61 and the terminal 62 is connected to the B channel time. Judging that the slot is not necessary, slave station 3
The D channel information message 106 in which information for connecting the B channel between the terminal 61 and the terminal 62 in the own station is included in the SETUP message to the C channel 100.

The slave station 3 receives the D channel information message 1
When the SETUP message and the connection information within the local station of the B channel are detected in 06, a time slot allocation request 107 for requesting the time slot allocation of only the D channel is transmitted. The base station 2 allocates a time slot for the D channel of the terminal 62, and
08 is transmitted to the slave station 3. The slave station 3 transmits the SETUP message 108 in the received D channel information 106 to the terminal 62. Thereafter, a third layer message 110 (CALL PROC,
ALERT) is transmitted to the ISDN 1 via the base station 2 in the time slot allocated for the D channel, and the call is established.

When the incoming call is established, the time slot allocated for the B channel of the terminal 61 is released, and the base station 2 receives the third layer message (CONN) indicating the subscriber's response from the terminal 62. When do. The reason is that until the terminal 62 responds, the terminal 61
This is because it is necessary to hear the Ring Back Tone from the network 1.

If the response from the terminal 62 is received, the time slot of the B channel of the terminal 61 is released according to the instruction of the base station 2, and the communication path of the B channel of the terminal 61 and the terminal 62 is set in the slave station 3. At this time, the third channel on the D channel
The layer message is transmitted via the assigned time slot for the D channel and the base station 2 via the base station 2.
The state is transmitted to the SDN network 1.

FIG. 4 shows a system image diagram of the first embodiment in a call state. This image shows that the control signal is still performed on the D channel between the base station 2 and the slave station 3 and the terminals 61 and 62 connected by the ISDN network. The B channel between and is not connected and is omitted, and the B channel is connected only between the terminal 61 and the terminal 62 in the same child station. Channel B is ISD for the amount omitted
The network is open to other terminals (users) for use in the N network.

Corresponding to FIG. 5, there is shown the sequence of the second embodiment of the ISDN service method in the multi-way multiplex communication system according to the present invention. Embodiment 2
The second embodiment differs from the first embodiment in that a step in which the slave station 3 itself checks the destination number at the time of calling is provided in the slave station 3. Not the base station 2 but the slave station itself reads the destination number in the third layer message 101 received from the terminal 61, and if the destination is a subscriber in the own station, the slave station is referred to D
A time slot allocation request 102 'for only the channel is transmitted to the base station. After the incoming call to the destination is established, the slave station 3 sets a communication path of the B channel in the own station 3. By such local settings, allocation of the time slot for the B channel to the calling side can be omitted.

The sequence shown in FIG. 5 of the second embodiment will be described next in comparison with the sequence shown in FIG. 3 of the first embodiment in the case where a call is made from terminal 61 to terminal 62. You. Slave station 3 receives S from terminal 61
When receiving the ETUP message 101, the slave station 3 of the first embodiment issues a time slot assignment request for the B channel and the D channel, but the slave station 3 of the second embodiment performs a time slot assignment for the D channel only. Make a slot allocation request.

The base station 2 responds from the terminal 62 (CON
N), in the first embodiment, when receiving B
Although there is a sequence for releasing a time slot for a channel, such a sequence is naturally unnecessary in the second embodiment.

The system according to the second embodiment is similar to the system according to the first embodiment.
As compared with, the use efficiency of the time slot is further improved, and an unnecessary sequence is eliminated, so that the processing speed is improved. Instead, since the time slot for the B channel is not allocated to the calling side, the slave station needs to have a sound source for allowing the calling side to hear the Ring Back Tone until the called side answers. Become. The sequence for generating such a bell is shown in FIG.
Is shown in The ALERT 111 transmitted by the terminal 62 that has received the call signal arrives at the terminal 61 via the slave station 3, the base station 2, the ISDN network 1, the base station 2, and the slave station 3 as a call bell signal, and the base station The terminal bell 61 allows the terminal 61 to hear the bell. When the terminal 62 responds, the CONN 112 reaches the terminal 61 as the release signal 113, and the ringing stops. At this stage, B
The channel is opened and released.

[0042]

According to the ISDN service method in the multi-way multiplex communication system according to the present invention, if the originating subscriber and the terminating subscriber are accommodated in the same slave station, it is not necessary to allocate a B-channel time slot. By using the communication line between the base station and the slave station more effectively, the line use efficiency is further improved, and the number of accommodated subscribers can be further increased. Such an effect is further exhibited when used in combination with the demand assignment method.

[Brief description of the drawings]

FIG. 1 is a net diagram showing a communication network according to a first embodiment of a multidirectional multiplex communication system according to the present invention.

FIG. 2 is a net diagram showing the communication net of FIG. 1 in more detail;

FIG. 3 is a time chart showing a sequence of a communication method of the multi-directional multiplex communication system according to the present invention.

FIG. 4 is a diagram showing a system in a call state according to the first embodiment;
It is a network diagram showing an image.

FIG. 5 is a time chart showing a sequence of a communication method according to a second embodiment of the multidirectional multiplex communication system according to the present invention.

FIG. 6 is a time chart showing a sequence of generating a bell in the second embodiment.

FIG. 7 is a net diagram showing a communication network of a communication method of a known multi-way multiplex communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... ISDN network 2 ... Base station 3 ... First slave station 61 ... Calling side ISDN terminal 62 ... Calling side ISDN terminal 101 ... 1st message 101 '... 2nd message 106 ... 3rd message

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04Q ^7/ 00-7/38 H04M 3/42

Claims (11)

(57) [Claims] 1. A step of transmitting a first message from an originating ISDN terminal belonging to a first slave station of a plurality of slave stations to a slave station, wherein the first slave station having received the first message includes: Requesting a base station connected to an ISDN network to allocate a D-channel time slot and a B-channel time slot; and wherein the base station responds to the allocation request of the slave station by Allocating the time slot of the D channel and the time slot of the B channel among the originating ISDN terminal, the first slave station, and the base station, comprising the slave station and the base station. Through the bureau, multiple second
An ISDN service method in a multi-way multiplex communication system for performing multi-way communication between a slave station and the first slave station, wherein the first message to which the originating ISDN terminal belongs belongs by monitoring the first message at the station. A step of detecting whether the slave station and the second slave station to which the called ISDN terminal belongs are the same station, and if the first slave station and the second slave station are the same station. If
The B channel time slot is not allocated between the base station and the slave station, and the B channel path is set between the first slave station to which the calling ISDN terminal belongs and the called ISDN terminal. And an ISDN service method in a multi-way multiplex communication system. 2. The ISDN service method according to claim 1, wherein the first mobile station and the second mobile station detect whether or not the same mobile station is the same base station as the base station. 3. The time slot of the D-channel according to claim 2, wherein a second message in which a destination number is added to the first message received from the originating ISDN terminal is already assigned. Transmitting the first mobile station to the base station by the first mobile station. 4. The method according to claim 3, wherein said base station reads and stores a destination number, transmits said destination number to an ISDN network, and makes a call from said originating ISDN terminal to said destination ISDN terminal. And establishing the originating IS from the ISDN network.
Receiving the source number of the DN terminal by the base station.
N service methods. 5. The method according to claim 4, further comprising: a step of retrieving that there is a calling subscriber corresponding to the source number; and a step of retrieving that there is a receiving subscriber corresponding to the stored destination number. The fact that the originating subscriber and the terminating subscriber belong to the same slave station coincides with the fact that the first slave station and the second slave station are the same station. IS in directional multiplex communication system
DN service method. 6. The multidirectional multiplex communication system according to claim 5, further comprising the step of: said base station notifying said same slave station of a third message for setting said path of said B channel. ISD
N service methods. 7. The base station according to claim 6, further comprising:
Allocating a time slot of a channel to establish an incoming call. 8. The multi-way multiplex communication system according to claim 7, further comprising the step of releasing, by the station, a time slot assigned to the B channel of the originating ISDN when the incoming call is established. ISDN service method. 9. The ISDN service in a multi-directional multiplex communication system according to claim 1, wherein the station for detecting whether the first and second slave stations are the same station is the first slave station. Method. 10. The method according to claim 9, further comprising the step of setting B before the incoming call to the called ISDN terminal is established.
A time slot of a channel is not allocated, and after a call to the called ISDN terminal is established, a step of setting a B-channel communication path in the same slave station.
N service methods. 11. The multidirectional multiplexing method according to claim 10, further comprising the step of: allowing said same slave station to call said calling ISDN terminal for a call bell until an incoming call to said called ISDN terminal is established. An ISDN service method in a communication system.