COMMUNICATION TERMINAL APPARATUS

Abstract: Disclosed is a communication terminal apparatus for use in a communication system in which at least one line having a plurality of channels is used by a plurality of commnicaiton apparatuses (4, 5, 6, 7, 8, 9, 10), wherein when all the information channels are engaged, the not-in-use condition thereof is automatically monitored, and a call is originated when the not-in-use condition is detected, thereby eliminating the wastefulness of operation and improving the efficiency of the line. In particular, when the communicaiton terminal apparatus in connected to a subscriber's line (3) of an ISDN system, communication is effected by using B channels, and if all the B channels are found to be busy upon origination of a call, the not-in-use condition of one of the B channels is monitored from the contents of a D channel, a call being originated again when a B channel becomes idle.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a communication terminal apparatus, and more particularly to a communication terminal apparatus for use in a communicaiton system in which at least one line having a plurality of channels is used by a plurality of communication apparatuses. Description of the Prior Art: Conventionally, an ISDN (integrated services digital network) system is known as a communication system of this type. For instance, in a basic interface of a user network of this ISDN line, one line is provided with three communication channels comprising two information channels (B channels) and one control channel (D channel), and a maximum of eight terminals are connected to this line. When a communication line is not in use, it is possible to effect communication in response to a request for communication from each terminal. When a small number of lines are utilized by a plurality of terminals as in the case of the ISDN system, even if one terminal attempts communication, it is impossible to communicate when all the information channels are busy. At that time, there is a drawback in that it is impossible for the user to know whether or not communication is possible unless a request for communication is actually made on each such occasion. DATA COMMUNICATIONS Vol 16 No. 11 October 1987, pages 237 to 255 "Standards Makers Cementing ISDN Sub-Network Layers" discloses a protocol for exchange of messages between one of a plurality of terminal equipment connected to common passive bus and a network termination. Because a plurality of items of terminal equipment use a common passive bus, there is a need to arbitrate channel access. D channel arbitration is done using a physical layer protocol. Transmissions from pieces of terminal equipment and from the network termination are in frames, in which specific bit positions are allocated to the D channel, to the two B channels (B1 and B2) and to other purposes such as framing and DC balancing. Predetermined bit positions in a network termination frame are designated as echo bit positions, and whenever the network termination receives a D channel bit the network termination will echo that bit in its current frame's next echo bit position. When a piece of terminal equipment does not have any D channel information to send, it will transmit bits of value "1" on the D channel, which will, of course, be echoed by the network termination in the echo bit positions of the network termination frame. When a piece of terminal equipment has D channel information to transmit, it monitors the bits arriving on the line from the network termination, and counts the number of successive echo bit positions containing bits at the binary value "1". When a predetermined number of successive echo bits have the value "1", this indicates that the D channel is not in use, and accordingly at that point the piece of terminal equipment will transmit its D channel information. Arbitration of B channel information is handled by layers 2 and 3. When a piece of terminal equipment wishes to set up a call, it places a set up or call originating message on the D channel. The network termination detects this and determines whether the desired call connection can be made. It may not be possible to make the desired call connection if, for example, no suitable channel is available. A message from the network termination to the piece of terminal equipment, over the D channel, conveys this information to the piece of terminal equipment. SUMMARY OF THE INVENTION According to the present invention there is provided a communication terminal apparatus as set out in claims 1 and 13. The remaining claims set out preferred and optional features. An embodiment of the present invention provides a communication terminal apparatus in which a request for communication is automatically made when an information channel is not in use, so as to eliminate the wastefulness of operation. In an embodiment of the present invention monitoring means monitors the not-in-use condition of an information channel, when all the information channels are engaged, and the call originating means originates a call when the not-in-use condition is detected. An embodiment of the present invention provides a communication terminal apparatus which is capable of making a request for communication automatically when an information channel is not in use, thereby eliminating the wastefulness of operation and improving the efficiency of the line. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating a configuration of a digital facsimile apparatus in accordance with an embodiment of the present invention; Fig. 2 is a flowchart illustrating the operation of the digital facsimile apparatus in accordance with the embodiment of the present invention; Fig. 3 is a diagram illustrating a configuration of system in which communication terminal apparatuses in accordance with the embodiment are connected to an ISDN system; Fig. 4 is a diagram illustrating an example of the contents of a call origination acceptance message; Fig. 5 is a diagram illustrating an example of a sequence of a common channel-type protocol; and Fig. 6 is a flowchart illustrating an example in which the not-in-use condition of a B channel is monitored from a D channel. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the accompanying drawings, a detailed description will be given of an embodiment of the present invention. In this embodiment, a description will be given, by way of an example, of a digital facsimile apparatus which is connected to a basic interface of an ISDN system. In addition, it is assumed that a common channel-type protocol is used as a protocol. Fig. 3 is a diagram illustrating a configuration of a system in which communication terminal apparatuses in accordance with this embodiment are connected to an ISDN system. As shown in the drawing, this system comprises the following: a network termination 1; an ISDN bus line 2 which connects the network termination 1 to a plurality of terminal apparatuses; a subscriber's line 3 which connects an ISDN exchanger (not shown ) to the network termination 1; general digital telephone sets 4, 7, 8, 10, 11; a telex apparatus 6; and digital facsimile apparatuses 5, 9 in accordance with this embodiment. Fig. 1 is a block diagram illustrating a configuration of a digital facsimile apparatus in accordance with this embodiment. In fig. 1, a digital facsimile apparatus controlling section 21 comprises the following components: and EPROM 23 for storing a processing program; a central processor 22 (CPU 22) for effecting processing in accordance with the processing program stored in the EPROM 23; a RAM 24 for storing data; a keyboard 28; an I/O controller 25 for controlling the keyboard 28; a reader 29 for reading an image; a printer 30 for outputting an image; an I/O controller 26 for controlling the reader 29 and the printer 30; and a communication chip 27 for an interface with the ISDN bus line 2. A description will now be given of the operation of the above-described embodiment. Fig. 2 is a flowchart illustrating the operation of a digital facsimile apparatus in accordance with this embodiment. In this embodiment, it is assumed that the ISDN line is provided with a basic interface, one D channel and two B channels. When a call is originated in a digital facsimile apparatus, in step S1 the operator first inputs the number of the other office from the keyboard 28. In Step S2, the start key is depressed to complete a call originating operation. In Step S3, the digital facsimile apparatus concerned sends a call origination request command, and in Step S4 a call origination acceptance command is received in response to the call origination request command. Subsequently, in Step S5 a parameter included in the call origination acceptance message is analyzed to determine whether or not either of the B channels is in use. Fig. 4 illustrates an example of the contents of the call origination acceptance messsage. In Fig. 4, the protocol identifier shows that this message is a common channel-type protocol in an ISDN line. The call number is one peculiar to a terminal apparatus, and the type of message shows that this message is a call origination acceptance message. Information on whether or not a B channel is in use is included in the channel identifier. When there is a B channel which is not in use, in Step S6 a call originating operation in continuously effected, and a communicating condition is thereby established. If it is determined in Step S5 that all the B channels are in use, the sequence of signals of the D channel is monitored in Step S7 to determine whether or not a B1 channel is in use. In Step S8, a determination is made in a similar manner as to whether or not a B2 channel is in use. Fig. 5 shows a signal sequence based on a general common channel-type protocol. In this embodiment, when disconnection (DISC) and release (REL) sequentially occur in the same B channel on the basis of a message from the D channel, it is determined that either of the B channels is not in use. Fig. 6 is a flowchart which illustrates another form of flow for monitoring the not-in-use condition of either of the B channels from the D channel in Steps S7 and S8 shown in fig. 2. In Step S61, a DISC message from the D channel is monitored and, if there is a DISC message, a determination is made in Step S62 as to whether the DISC message is for the B1 or B2 channel. Subsequently, a REL message is monitored from the D channel in Step S63, and if there is a REL message, a determination is made in Step S64 as to whether or not the B channel concerning that REL message is the same B channel as that concerning the DISC message determined in Step S62. If it is the same, it is determined that that B channel is not in use. If it is not the same, the operation returns to Step S63 and waits for an ensuing REL message. It should be noted that the flowchart shown in Fig. 6 is one example of determination, and, for example, only the REL message may be monitored. At the time when it is confirmed in Steps S7 and S8 that either of the B channels is not in use, the operation returns to Step S3, and a call origination request message is sent again in Steps S3 to S5, a call origination acceptance message is received to confirm the not-in-use condition of the B channels. Since either of the B channels is not in use this time, the operation proceeds to Step S6, and a call originating operation is carried out continuously, thereby establishing a communicating condition. As described above, in accordance with this embodiment, when all the B channels on the calling party's side are busy, since there is a function which allows a communication terminal apparatus to monitor the state of use of the B channels, and a call is automatically originated again when either of the B channels is not in use, the burden placed on the operator can be alleviated, thereby making it possible to improve the efficiency of the line. In the above-described embodiment, if it is determined that either of the B channels is not in use, the monitoring of the B channels is effected in Steps S7 and S8 by monitoring the sequence of the D channel. However, an arrangement may be alternatively provided such that the operation returns directly to step S3 without performing Steps S7 and S8, a call origination request message is repeatedly transmitted, a call origination acceptance message is received on each such occasion, a parameter is then analyzed, and only when either of the B channels is not in use, the operation proceeds to the continuation of the call originating operation in Step S6. In addition, although a description has been given of a case where the not-in-use condition of either of the B channels is monitored, the not-in-use condition of the D channels can be similarly monitored in the case of terminal of, for example, a packet exchange mode in which the D channel is used for transmission of information. Furthermore, although in this embodiment a description has been given by taking a digital facsimile apparatus as an example, the terminal apparatus is not restricted to the same. While but one embodiment of the present invention has been described, it will be apparent to those skilled in the art that various modifications and variations may be made therein.

Claims: A communication terminal apparatus for a communication system in which at least one line (2) having a plurality of channels is used by a plurality of communication apparatuses, the communication terminal apparatus comprising a call originating means (21) for originating a call characterised in that the call originating means (21) has a mode of operation in which, if a response to originating a call indicates that no channel is available for it, the call originating means (21) monitors channel availability and automatically originates the call again when a channel is available. Apparatus according to claim 1 comprising input means (28) for an operator to input an identification of the desired destination of a call. Apparatus according to claim 1 or claim 2 in which the plurality of channels comprise a D channel and a plurality of B channels. Apparatus according to claim 3 in which the call originating means (21) originates a call by using the D channel. Apparatus according to claim 3 or claim 4 in which the line is a line of an ISDN system. Apparatus according to any one of the preceding claims in which the call originating means monitors channel availability by repeatedly originating the call and monitoring the responses thereto. Apparatus according to any one of claims 1 to 5 in which the call originating means (21) monitors channel availability by monitoring messages in a pre-existing communication using a said channel. Apparatus according to any one of claims 3 to 5 in which the call originating means (21) monitors channel availability by monitoring the release of a B channel. Apparatus according to any one of claims 3, 4, 5 and 7 in which the call originating means (21) monitors channel availability by monitoring the D channel. Apparatus according to claim 9 in which the call originating means monitors the D channel for B channel release messages. Apparatus according to claim 10 in which the call originating means (21) monitors the D channel for B channel disconnection messages. Apparatus according to claim 11 in which the call originating means (21) originates the call again when it detects a disconnection message and a release message for the same B channel. A communication terminal apparatus for a communication system having a plurality of channels, the apparatus having input means (28) for receiving a communication request and call originating means (21), characterised in that when the input means (28) receives a communication request the call originating means (21) monitors a D channel of the system to determine the availability of a B channel of the system, and originates a call when it determines that a B channel is available.

Inventors: NAKATSUMA, TAKUJI
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H04Q11
IPC codes: H04M11, H04Q11, H04Q5