JP2885922B2 - Extension communication system between home terminals and network termination device - Google Patents

Description

The present invention relates to an extension communication system between home terminals,
For example, the present invention relates to an extension communication method between a plurality of terminals accommodated in the same basic interface of ISDN and a network terminating device thereof.

(Prior Art) A user / network interface in ISDN (Digital Service Integrated Network) is constructed based on the rules of CCITT Recommendation I.400.

Among them, ISDN terminals are connected to a network via a network terminating device having a layer 2 and layer 3 terminating function. Layer 2 defines the function of each unit for transferring data. Layer 3 defines the function of each unit for performing call control. The connection point between the network terminating device and the ISDN terminal is positioned as an S / T point. This S / T point is a reference point in the user / network interface of the basic interface. A plurality of ISDN terminals can be connected to this S / T point by bus connection. The network terminating device and the terminal are connected by a 2B + D channel.

Conventionally, in a case where such a plurality of terminals perform communication between terminals in the same house connected to one network terminating device, that is, when performing so-called extension communication, the following is performed.

When a communication request is issued from a certain terminal to another terminal, the terminal sends a call setup message to the network via the network terminating device as in the case of the line communication. In this call setup message, for example, a request for using the B1 channel as a used channel, a station number for designating a terminal as a destination (in this case, the own station number), a subaddress of the destination terminal, etc. Are added as information elements. The network receives the call setup message, recognizes the destination terminal based on the information element in the message, and sends the call setup message to the partner terminal via the network terminating device. In the call setup message, for example, an information element such as B2 channel assignment is added. At this time, the network sends a call setup acceptance message to which information elements such as B1 channel assignment are added to the calling terminal. The called terminal receiving the call setup message returns a call setup acceptance message to the network via the network terminating device, and then sends a call message to the network. The network receiving the call message from the called terminal sends the call message to the calling terminal. Thereafter, when the called terminal is a telephone, for example, if the call is answered off-hook or the like, the called terminal sends a response message to the network. The network receiving this sends a response message to the calling terminal, and further returns a response confirmation message to the called terminal. Thus, after the response confirmation message is transmitted and received between the calling terminal and the network, communication is performed between the two terminals via the network. At this time, the communication fee is charged in the network. When the communication is completed, for example, a disconnection message is sent from the calling terminal to the network, and the network that receives the message returns a release message to the calling terminal, and further sends a release message to the called terminal. Send a disconnect message. The called terminal that has received the disconnection message sends a release message to the network, and the network that has received the message returns a release completion message to the called terminal. The calling terminal that has received the release message from the network returns a release completion message to the network. When transmission / reception of the release completion message is completed between the network and both terminals, the call is released and charging ends at the same time.

(Problems to be Solved by the Invention) By the way, since extension communication is performed in the same house because of its short distance, the communication may be frequently performed.
However, as described above, conventional extension communication between in-home terminals is performed via a network in the same communication scheme as that of general office line communication. Instead, the signal is transferred to a terminal in the same home via a subscriber transmission path and further via a network switch. Therefore, there is a problem that the line use efficiency is poor. In addition, there is a problem that the internal processing of the exchange in the network is increased, and the processing efficiency is deteriorated.

The present invention solves such disadvantages of the prior art, and can process communication between terminals in the same house without performing the communication via a network. Therefore, it is possible to increase line use efficiency, and It is an object of the present invention to provide an extension communication method between home terminals and a network termination device that can reduce the load on a network.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a network termination device having a function of terminating a subscriber transmission line accommodated in a network, in which a plurality of terminals are provided with two uplinks and two downlinks. A control message transmitted from these terminals when performing extension communication between terminals in an extension communication system between home terminals accommodated by sharing a communication channel and one control channel for each of uplink and downlink. Is returned to the network terminating device without sending it to the network side, so that the control message is transmitted to other terminals to control the extension communication between the terminals, and when the extension communication is performed, the communication channel of the communication channel is controlled. It is characterized in that an extension communication is performed in the same house by returning a signal at the network terminating device without transmitting the signal to the network side.

In this case, the extension communication request message sent from the calling terminal and the called terminal that has received the extension communication request message are included in the layer 3 control message in the control channel between the network terminating device and the terminal. An extension communication enable message, an extension communication release request message sent from the calling terminal or the called terminal after the communication is completed, and an extension release acceptance message returned from the called terminal or the calling terminal that received the extension communication cancellation message And an extension communication control message including an extension communication control message, and when performing extension communication between the terminals, by using these extension communication control messages at each terminal, a network terminating device that loops back these extension communication control messages. Control of extension communication between terminals in the same home by distinguishing between communication via office lines and extension communication. It is characterized in.

Also, in this case, after receiving the extension communication request message from the calling terminal, the network terminating device controls the control transmitted from the terminal until the extension communication is released from when the extension communication is received from the called terminal until the extension communication is released. It is characterized in that a message is transmitted to the network side as an insignificant signal.

Further, after receiving the extension request message from the calling terminal, the network terminating device activates a loopback function that loops back the communication channel signal when receiving the extension communication enable message from the called terminal, and initiates the call. After receiving an extension communication cancellation request message from one of the terminal and the called terminal, the loopback function is canceled when an extension communication cancellation request message is received from the other.

Further, the extension communication control message is composed of a plurality of frames, respectively, and an escape code for distinguishing between the communication by the office line and the extension communication is set in the first octet defining the message type therein, The second octet is characterized in that the message type of the extension communication control message, the return state of the communication channel in the network terminating device, and the communication channel transmission / reception use conditions in the calling / calling terminal are included.

In addition, the transmission / reception use conditions of the communication channel in the calling / receiving terminal include half-duplex communication in which communication is performed using the same channel and full-duplex communication in which communication is performed using different channels. It is characterized by.

In this case, if half-duplex communication is set as the transmission / reception use condition of the communication channel at the calling / receiving terminal, set the destination sub-address to the address of a plurality of terminals or set the destination sub-address to the global address specifying all terminals. By doing so, a broadcast-type extension communication is performed.

Further, the network terminating apparatus according to the present invention, when performing extension communication between the terminals, control signal return means for returning a control message of the uplink control channel to a downlink control channel, and a terminal for the extension communication Signal generation means for sending a control message transmitted from the network as a meaningless signal to the network side, and communication signal return means for returning an upstream communication channel signal to a downstream communication channel at the time of extension communication. It is characterized by the following.

(Operation) According to the extension communication method between home terminals according to the present invention, a network terminating device having a function of terminating a transmission path accommodated in a network is provided with a communication channel return function, and A processing function for controlling the extension communication at the layer 3 level is added to the terminal firmware, so that when the extension communication between the terminals in the same house is performed, the signal of the communication channel is transmitted to the network. Without being sent to the network termination device.

(Embodiment) Next, with reference to the attached drawings, an embodiment of an extension communication system between home terminals and a network termination device according to the present invention will be described in detail.

In this embodiment, as shown in FIG. 1, the network termination unit (DSU) 10 has a function of returning a control signal of the control channel D at the time of extension communication and a function of returning a signal of the communication channels B1 and B2. When extension communication is performed between the terminals (TE1, TE2) accommodated in the network terminating device 10, the extension communication is performed only in the home system without transmitting the extension communication signal to the network side. This is a major feature.

In FIG. 1, a calling terminal TE1 and a called terminal TE2 are connected to a passive bus 20 having two communication channels B1 and B2 each for uplink and downlink, and one control channel D for each uplink and downlink. . This passive bus 20
Are housed in the network terminating device 10.

The passive bus 20 has a plurality of connection terminals, and can accommodate a plurality of terminals TE1 to TEn as shown in FIG. For example, up to eight terminals can be connected.

As shown in FIG. 2, the network terminating device 10 is a device connected to the subscriber transmission line 35 accommodated in the network 30 and managing the layer 2 and layer 3 terminating functions. As described above, the network terminating device 10 in this embodiment includes the communication channels B1, B
It has a function of returning the signal of No. 2 and a function of returning the signal of the control channel D. The internal configuration of the network termination device 10 will be described in more detail with reference to FIG. This network terminating device 10 is used for layer 2 and layer 3 for extension communication.
An extension communication control unit 12 for controlling the level, a loopback circuit 14 for turning back signals of the communication channels B1 and B2 to the inside of the house at the time of extension communication, and a loopback circuit 14
JK flip-flop (FFI) 16 for activating and deactivating the loopback function, an OR circuit for transmitting a control signal to the network side as an insignificant signal at the time of extension communication, and an OR circuit 18 for activating the function And a JK flip-flop (FF2) 19 for stopping.

The extension communication control unit 12 is connected to an uplink control channel D of the passive bus 20, receives a control message transmitted on the control channel D, and converts the control message into a control message for extension communication. This is a control circuit that starts or stops the loop-back circuit 14 and the OR circuit 18 by determining whether or not there is, and setting or resetting the JK flip-flops 16 and 19. More specifically, when an extension communication request message, which will be described later, is received, and when an extension communication enable message transmitted thereafter is received, the J terminal of the JK flip-flop 19 is turned on, and the OR circuit 18 is activated to activate the network. After generating an insignificant signal to the side and receiving an extension communication release acceptance message to be described later, the K terminal of the JK flip-flop 19 is turned on to perform a layer 3 level control for stopping the insignificant signal generation function of the OR circuit 18. Similarly, when the extension communication control unit 12 receives the extension communication enable message from the control channel D, the extension communication control unit 12 turns on the J terminal of the JK flip-flop 16 to activate the loopback function of the loopback circuit 14 and accepts the extension communication cancellation. When a message is received, the K terminal of the JK flip-flop 16 is turned on to perform a layer 2 level control for stopping the loopback function of the loopback circuit 14.

The loopback circuit 14 is configured by a selection circuit including two AND circuits 14a and 14b and one OR circuit 14c for each of the downstream communication channels B1 and B2.
The AND circuit 14a has one input terminal connected to the upstream communication channel B1 (or B2) and the other input terminal connected to the other input terminal.
The Q terminal of the JK flip-flop 16 is connected. The AND circuit 14b has a subscriber transmission line 35 at one input terminal.
The downstream communication channel B1 (or B2) is connected, and the Q terminal of the JK flip-flop 16 is connected to the other input terminal so that the signal is inverted. AND circuit 14a,
The output terminals of the OR circuit 14c are connected to the input terminals of the OR circuit 14c, respectively. Therefore, the output terminal of the OR circuit 14c receives the upstream communication channel B1 (B2) from the home or the upstream of the subscriber transmission line 35. The communication channel B1 (B2) is configured to be selectively output as a downstream communication channel B1 (B2) to the home.

In the OR circuit 18, when one of the input terminals is connected to the upstream control channel D inside the house, the other input terminal is connected to the Q terminal of the JK flip-flop 19, and the Q terminal is on. In this configuration, an insignificant signal which is all "1" is transmitted to the network side, and when the Q terminal is off, the signal of the upstream control channel is directly output to the network side.

When the set signal is supplied to the J terminal from the extension communication control unit 12, the JK flip-flops 16 and 19 turn on the Q terminal, and when the reset signal is supplied to the K terminal,
Turn off the terminal and clock until each state changes
It operates in synchronization with the CLK signal.

Further, in the terminating device 10, the downlink control channel D and the uplink control channel D are wired-connected at a point T before the OR circuit 18. As a result, the signal of the uplink control channel D of the passive bus 20 is directly returned to the echo bit E of the downlink control channel D. This control channel loopback function is originally used when performing communication on office lines.
Since the control channel D is shared by the plurality of terminals TE1 to TEn, the content of the uplink control channel D is returned as it is to the echo bit E of the downlink control channel D as it is in order to determine the contention. Bit E is set to each terminal TE1
The use right of the control channel D is obtained by detecting the control signal received by .about.TEn and transmitted by itself. In this embodiment, this control channel return function is used to transfer the control message to each of the terminals TE1 to TEn when performing extension communication.

In this embodiment, an extension communication control message dedicated to extension communication is used as a layer 3 control message on the control channel D in order to perform communication without the intervention of the network 30. This extension communication control message is, for example, the third
As shown in the figure, an extension communication request message 40 sent from the calling terminal (TE1), an extension communication enable message 42 sent from the called terminal (TE2), and an extension communication request message 40 sent from the calling terminal or the called terminal. An extension communication cancellation request message 44 and an extension cancellation reception message 46 sent from the called terminal or calling terminal are used.

The extension communication request message 40 is a message for making an extension communication request when a communication request is issued from a certain terminal to another terminal in the same house. This extension communication request message 40 is sent out when an extension is dialed at the calling terminal, is returned by the network terminating device 10 and is received by the designated receiving terminal (TE2), Termination device 1
It is sent to the network 30 via 0. Upon receiving the extension communication request message 40, the network 30 updates a table for monitoring the use state of the communication channels B1 and B2,
Monitor its usage. The network 30 receives the extension communication request message 40 and monitors its use state, so that, for example, when a call is received by a central office line, if all the channels are in use, the A message such as busy is returned to the caller, and if at least one B channel is vacant, an empty B channel can be allocated to the called side. The extension communication possible message 42 is a message indicating that the called terminal (TE2) is in a receivable state that is transmitted when the extension communication request message 40 is received. This extension communication possible message 42 is transmitted from the called terminal (TE2) by off-hook or the like, and
At the calling terminal (TE1). While the signal is being transmitted, the extension communication possible message 42 is transmitted from the network terminating device 10 to the network as an insignificant signal that is all "1", and the network 30 enters a frame error state. Is not received. The called terminal (TE2) shifts to the communication channel transmission / reception processing when the extension communication possible message 42 is transmitted. Upon receiving the extension communication possible message 42, the calling terminal (TE1) shifts to transmission / reception processing of the communication channels B1 and B2. The extension communication release request message 44 is a message transmitted from the calling terminal (TE1) or the called terminal (TE2) when terminating the extension communication. This extension communication release request message
44 is transmitted from the terminal by on-hook or the like, looped back by the network terminating device 10, received by the partner terminal, and received by the network 30 as an insignificant signal. The extension communication cancellation acceptance message 46 is a message for canceling the extension communication transmitted from the called terminal (TE1) or the calling terminal (TE2) that has received the extension communication cancellation request message. The network terminating device 10 transmits the extension communication release acceptance message
Upon receipt of 46, the function of returning the communication channel loopback function and the function of transmitting the control channel signal to the network 30 as an insignificant signal are released.

These extension communication control messages are composed of a plurality of frames 50 to 58, as shown in FIG. In the first frame 50, a protocol identifier composed of a Q.931 user / network call control message indicating layer 3 call control is set. In the second frame 52, a call number is set. The third frame 54 is composed of two octets (8 bits), and the first octet 542 and the second octet 544 are set with a message type indicating that this control message is an extension communication. In an octet 542 at the beginning of this message type, an escape code used to extend the protocol protocol by the user is set. As this escape code, “00H” represented by a hexadecimal number, that is, all “0” is used. In the octet 544 next to the message type, a second message extended by the user is set. In this embodiment, as shown in FIG. 6, the second message has an operation code indicating extension communication in the fifth to eighth bits.
600 is set, and communication channels B1 and B2 are set in the first to fourth bits.
Is set. A loop pattern 610 indicating the use condition of is set.

The operation code 600 indicates the type of the extension communication control message, indicates an extension communication request by a code of “0H” represented by a hexadecimal number, indicates “1H”, indicates that extension communication is possible, and indicates “2H”. Indicates an extension communication release request, and “3H” indicates extension communication release acceptance.

In the loop pattern 610, the use conditions of the communication channels B1 and B2 are indicated by symbols “0H” to “5H”. This use condition includes half-duplex communication using only the same communication channel by returning only communication channel B1 or B2, such as “0H” to “3H”, and communication channel using “4H” and “5H”. B1
And with full duplex using B2 respectively.

Referring again to FIG. 5, a fifth octet 56 is set with a calling subaddress information element in which calling terminal information such as a calling terminal address is written, and a sixth octet 58 is used for receiving a called terminal such as a called terminal address. Destination subaddress information in which terminal information is written is set. In this embodiment, when half-duplex communication such as “0H” or “2H” is specified in the loop pattern 610 of the second message 544, whether the address of a plurality of terminals is specified in the destination subaddress information element 58 Alternatively, by specifying a global address in the destination sub-address information element 58, it is possible to perform extension communication in a broadcast format.

Next, the operation and processing of each unit of the extension communication system in this embodiment will be described with reference to FIGS. 7 and 8.

FIG. 7 shows the control of the layer 3 processing of the control channel D in the network termination device 10. In this figure,
First, upon receiving the control message from the calling terminal (100), the network terminating device 10 determines whether the first octet 542 of the message type of the control message is an escape code (102). As a result of the interpretation, the network termination device 1
A value of 0 is ignored if the first octet 542 is other than an escape code, and the control message is transmitted to the network side as it is, so that normal office line communication is performed. If the first octet 542 is an escape code,
The network terminating device 10 receives the second octet 54 of the message type 54
Enter reading 4 (106). As a result of the interpretation, if the operation code 600 is the extension communication request “0H”, the control message is sent to the network side as it is. The operation code 600 of the second message 544 is "1.
If "H", a set signal is sent to the J terminal of the JK flip-flop 19 to turn on its Q terminal (108). Thus, the extension communication possible message 42 is sent to the network side as an insignificant signal. Further, the network terminating device 10 sends a set signal to the J terminal of the JK flip-flop 16 to turn on its Q terminal (110), whereby the loopback circuit 14 is turned on.
Is activated and the upstream communication channel B
The signals of 1 and B2 are looped back to the downstream communication channels B1 and B2 to perform extension communication. When the operation code 600 is the extension communication release request “2H”, the network termination device 10 waits for the transmission of the extension communication release acceptance message while maintaining the state of the extension communication. When the operation code 600 is "3H", the reset signal is sent to the K terminals of the JK flip-flops 16 and 19 to turn off the respective Q terminals (112). As a result, the loopback function of the loopback circuit 12 is released and the OR circuit
The function of turning the control channel into an insignificant signal in step 16 is released, and the state returns to the normal state from the state of extension communication.

FIG. 8 shows a control message reception process in terminals TE1 to TEn. In this figure, first, when the called terminal receives a layer 3 control message by the E bit of the downlink control channel D returned from the network terminating device 10 (120), it receives the first of the message types of the control message. Of the octet 542 is an escape code (122). If this octet 542 is not an escape code, ignore the message. If so, the next octet 544 is read (124). As a result of the interpretation, if the operation code 600 of the octet 544 is the extension communication request “0H”, it is determined whether or not the destination subaddress information element 58 is the address of the own terminal (126). If the destination sub-address information element 58 is not the own terminal, it is ignored. If so, the ringing tone of the own terminal is sounded (127), and waiting for operator intervention by off-hook or the like (128). Then, if there is operator intervention due to off-hook or the like, the ringer is turned off (13
0), and sends an extension communication possible message 42 (132). As a result, the called terminal enters a transmission / reception process on the communication channel indicated by the loop pattern 610 of the second octet 544 in the message type in the extension communication request message, and enters a communication state (134). .

On the other hand, the calling terminal receives the extension communication possible message 42 transmitted from the called terminal by the E bit of the control channel D by the return of the network terminating device 10 (120). The calling terminal determines that the first octet 542 of the message type of the control message 44 is an escape code (122). When it is determined that the operation code 544 of the second octet 544 of the extension communication possible message is "1H" (124), it is determined whether or not the calling sub-ares information element 58 is its own terminal. (136).
As a result, if the calling subaddress information element 58 matches its own terminal, the calling terminal matches the use condition of the communication channel indicated by the loop pattern 610 of the octet 544,
The transmission / reception process on the communication channel is started (136). Thus, extension communication is performed between the calling terminal and the called terminal. This communication is performed without returning the signal of the communication channel to the network terminating device 10 and transmitting the signal to the network 30 without transmitting the signal to the network 30 side. Becomes

When the communication is completed, an extension communication release request message 46 is transmitted from the calling terminal or the called terminal. In this case, upon receiving the extension communication release request message 46 by the E bit of the control channel D in the same manner as described above,
0), it is determined that the first octet 542 of the message type 54 is an escape code in the same manner as described above (12).
2), operation code 600 of second octet 544
Is an extension communication cancellation request “2H” (12
4) and the terminal requests the destination sub-address information 58
(140), and if the address matches the terminal's own address, an extension communication release acceptance message
48 is transmitted (142), whereby the terminal releases the extension communication mode and returns to the normal waiting state (144).
In addition, when one terminal receives the extension communication release request message 46 transmitted from the other terminal (120), the first octet 544 of the message type determines whether or not there is an escape code (124). Then, the terminal judges whether or not the calling sub-address information element 56 is its own terminal (146), and when it matches the address of its own terminal, releases the extension communication mode and returns to the normal waiting state. (148). Thereby, the extension communication ends.

As described above, in this embodiment, the firmware of the terminals TE1 to TEn is additionally changed to control the extension communication at the layer 3 level without improving the hardware and software in the network 30. It has each of the above functions for extension communication control, and the network terminating device 10 has a communication channel loopback function in addition to the control channel return function. When performing communication, extension communication can be performed via a home line without performing the communication via the network 30.

The embodiments described here are for explaining the present invention, and the present invention is not necessarily limited thereto. In particular, for example, each message of the above-mentioned extension communication control message and its code and pattern Is
The present invention is an example for carrying out the present invention, and the present invention is not limited thereto. Variations and modifications that can be made by those skilled in the art without departing from the spirit of the present invention are included in the present invention.

(Effects of the Invention) As described above, according to the extension communication method between home terminals and the network termination device according to the present invention, the following effects can be obtained.

1. A communication terminal loopback function is provided in the network terminating device, and a plurality of control messages for layer 3 extension communication on a control channel are provided between the network and the terminal by adding and changing the firmware of the terminal. It is possible to realize extension communication without going through a network without performing a change work on the network side. Therefore, the processing capacity of the network can be reduced, and the efficiency of line use can be increased.

2. When extension communication is performed, all signals of the communication channel and the control channel are looped back by the network terminating device, and the processing is performed only by the home system regardless of the control of the network.
Even when a failure such as an accident or a failure occurs in the subscriber transmission line or the network, the extension communication can be continued.

3. This method is effective in both half-duplex and full-duplex communication of one and two communication channels,
Multiple terminals or global
By specifying an address, extension communication in a broadcast format can be realized. Therefore, it is advantageous when the same message is sent to all terminals, and efficient communication can be performed.

4. By using the loopback function of the network terminator, it is possible to perform a loopback test between the terminal and the network terminator and between the network and the network terminator, facilitating the line break test between the terminal and the network. Can do it. In particular, the in-home turnaround test in the network termination device can be started from the terminal side, and therefore, labor costs can be reduced without having to arrange a maintenance person or the like at the office side. At this time, the loopback test on the network terminating device side can be performed at the same time, so that the test time can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an embodiment of an extension communication system between home terminals according to the present invention, FIG. 2 is a block diagram showing a relay system to which the extension communication system of the present invention is applied, and FIG. FIG. 4 is a circuit diagram showing an internal configuration of the network termination device in the example, FIG. 4 is a diagram showing a sequence of a layer 3 message in the embodiment, and FIG. 5 is a format example of a layer 3 extension communication control message in the embodiment. FIG. 6 is a structural diagram showing a format example of the second message in FIG. 5, FIG. 7 is a flowchart showing layer 3 processing of a control channel in the embodiment, and FIG. 8 is each terminal in the embodiment. 5 is a flowchart showing the receiving process of FIG. Description of Signs of Main Parts TE1 to TEn Terminal 10 Network Terminator 12 Extension Communication Control Unit 14 Loopback Circuit 16, 19 JK Flip-Flop 18 OR Circuit 20 Passive Bus 30 … Network 35… Subscriber transmission line 40… Extension communication request message 42… Extension communication enable message 44… Extension communication release request message 46 …… Extension communication release acceptance message 54 …… Message type 56 …… Sub address Information element 58: Destination sub-address information element 542: Escape code 544: Second message 600: Operation code 610: Loop pattern

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masaaki Takahashi 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A 64-81596 (JP, A) JP-A JP-A-1-309495 (JP, A) JP-A-2-79698 (JP, A) JP-A-2-86391 (JP, A) JP-A-2-174495 (JP, A) Minoru Akiyama et al. Reader, ”Ohmsha, p. 110 (58) Field surveyed (Int.Cl. ⁶ , DB name) H04M 11/00-11/10 H04Q 5/00-5/24

Claims (8)

(57) [Claims] 1. A network terminator having a function of terminating a subscriber transmission line accommodated in a network includes a plurality of terminals each having two communication channels for uplink and downlink and one for each of uplink and downlink.
In an extension communication system between home terminals accommodated by sharing one control channel, the network terminating device transmits control messages transmitted from these terminals to the network side when performing extension communication between the terminals. To return to these terminals without sending the control message to another terminal to control the extension communication between the terminals, and when performing the extension communication, the signal of the communication channel is transmitted to the network side. The terminal returns to the terminal without transmitting the call to the terminal, and performs extension communication in the same house. The method further includes transmitting a layer 3 control message in a control channel between the network terminating device and the terminal from the calling terminal. Extension communication request message to be transmitted, an extension communication enable message transmitted from the called terminal that has received the extension communication request message, An extension communication control message including an extension communication cancellation request message sent from the calling terminal or the called terminal, and an extension cancellation reception message returned from the called terminal or the calling terminal that has received the extension communication cancellation message. When extension communication is performed between each terminal, these extension communication control messages are used by each terminal, so that the network terminating device that wraps these extension communication control messages communicates with the office line and the extension communication. An extension communication method between in-home terminals, wherein extension communication is controlled between terminals in the same home by distinguishing between them. 2. The extension communication system between home terminals according to claim 1, wherein said network terminating device receives an extension communication enable message from a called terminal after receiving an extension communication request message from a calling terminal. An extension communication method between home terminals, wherein a control message transmitted from the terminal is transmitted as an insignificant signal to the network side from time to time until the extension communication is released. 3. The extension communication system between home terminals according to claim 1, wherein said network terminating device receives an extension communication enable message from a called terminal after receiving an extension communication request message from a calling terminal. Activate the loopback function that loops back the signal of the communication channel, and after receiving an extension communication release request message from one of the calling terminal and the called terminal, loops when an extension communication release acceptance message is received from the other. An extension communication method between home terminals, wherein the back function is canceled. 4. The extension communication system between home terminals according to claim 1, wherein the extension communication control message is composed of a plurality of frames, and a first octet defining a message type in the plurality of frames includes a local line. An escape code is set for distinguishing between communication by extension and extension communication. In the second octet, the message type of the extension communication control message, the return state of the communication channel at the network termination device, and the communication channel An extension communication method between in-home terminals, which includes transmission / reception use conditions. 5. An extension communication system between home terminals according to claim 4, wherein the transmission / reception use conditions of a communication channel at said calling / receiving terminal include half-duplex communication for performing extension communication using the same channel; An extension communication method between home terminals, comprising: full-duplex communication for performing extension communication using different channels. 6. An extension communication system between home terminals according to claim 5, wherein half-duplex communication is set in a transmission / reception use condition of a communication channel in said calling / receiving terminal, and an address of a plurality of terminals is set as a destination sub-address. , Or by setting a global address designating all terminals as a destination sub-address, thereby performing extension communication in a broadcast format. 7. An extension communication system between home terminals according to any one of claims 1 to 4, wherein the extension communication in a broadcast format is performed. 8. An extension communication system between home terminals according to claim 7, wherein a broadcast address is set by setting an address of a plurality of terminals as a destination sub-address or a global address designating all terminals as a destination sub-address. An extension communication method between in-home terminals, which performs extension communication of a type.