CH651714A5 - METHOD FOR TRANSMITTING MESSAGES IN A FULLY DIGITAL MESSAGE TRANSMISSION SYSTEM. - Google Patents

Description

The present invention relates to a method for transmitting messages, in which the connection between the subscriber and the telecommunications office takes place via a subscriber loop in digital form, analog signals being converted into digital signals by pulse code modulation.

It is therefore a fully digital message transmission system in which all types of messages, i.e. Voice, data or other telecommunications services, operational information of any kind, can be transmitted in digital form to the subscriber set.

The construction of such systems has only become economically feasible after prices for digital circuits have dropped sharply compared to other devices that have been used in telecommunications systems up to now. Each message, and this also includes monitoring and signaling messages, can now be transmitted as a combination of 1 and O character elements. When receiving, it is only necessary to distinguish between two message states, which greatly reduces the deletion effect of transmitted messages caused by interference,

The present invention describes the transmission of messages in an economical communication system meeting the needs mentioned above.

The characterizing features of the invention can be found in patent claim 1.

An embodiment of the invention will now be explained in more detail with reference to the drawing. Show it:

1 is a message format shown schematically according to the invention,

2 shows a greatly simplified illustration of a subscriber loop arrangement which is suitable for the operation according to the invention,

Fig. 3 is a schematic representation of the participant-side end equipment of the loop, and

Fig. 4 is a schematic representation of the official end equipment of the loop.

So far, the telecommunications industry has limited itself to digitization within the headquarters. In the foreseeable future, however, the subscriber network with the subscriber stations will certainly also be converted into this new technology. The standardization of the separation points is currently being carried out in the relevant international bodies, e.g. CEPT (Association of European Postal and Telecommunications Companies) and CCITT (part of the International Telecommunication Union). In this context, one speaks of a so-called ISDN (Integrated Services Digital Network), in German: Service-integrated digital telecommunications network. It was recognized that full digitization from subscriber to subscriber enables a whole range of new services (image, data, alarm transmission). Such a service-integrated digital telecommunications network (hereinafter referred to as ISDN) requires appropriate terminal equipment for connection to the subscriber loop. Such equipment is known under the name ICE (Integrated Services Circuit Terminating Equipment), in English: terminal equipment for the integrated digital telecommunications network, and provides signaling, monitoring and synchronization messages which are "treated within the band" (ie treated equally) how the user information is transmitted via the subscriber loop; there is therefore no need for an additional digital bandwidth for frame formation and / or signaling. The ICE terminal equipment has facilities for digital voice signals and the connection of data and other digital services, including data in character, packet, frame mode and facsimile. The ICE terminal equipment uses so-called IDLC procedures (Integrated Services Data Link Controll), German: control of the data transmission path in the integrated digital telecommunications network; according to international standards, these procedures are based on frame structures for controlling the data transmission link in the case of transmissions with high bit rate (HDLC - High Level Data Link Control), which effects control of the subscriber loop. In addition, the IDLC procedure enables end-to-end signaling.

The IDLC controller must identify the following types of digital signals:

a) Unformatted, digitally encoded language, e.g. PCM according to the A law (companding law),

b) data and other services in digital form already formatted according to the frame structure for HDLC,

c) data and other services in digital form that are not already formatted as in b,

d) signaling, monitoring, and frame information that has already been formatted in the HWLC frame structure by ICE or by the central equipment.

The HDLC frame structure is internationally standardized and is shown in Fig. La. It contains labels for the start and end of the frame, an address field, a control field, an information field and a frame checking sequence FCS (frame checking sequence). "Transparent" is achieved through a process of bit insertion and deletion to prevent the simulation of the character string.

Figure 1b shows a sequence of HDLC frames, including an idle sequence, which is filled with labels between two such frames.

Signaling and monitoring messages are generated within the terminal equipment ICE or the central equipment and by an HBLC encoder / decoder rah5

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menu formatted. After receiving such messages from the line, they are released from the format by the encoder / decoder. Only the frames with a valid frame control sequence and which correspond to the boundary conditions of the HDLC procedures are considered valid. The generation of a frame control sequence group for a message and the control carried out on a message and its frame control sequence group can be carried out by customary procedures in the field of error detection and correction and is not described further here.

The HDLC procedures used enable signaling between the ICE and the local headquarters as well as between the ICE and a remote ICE as soon as a connection has been established. The subscriber-subscriber signaling device enables changes to be made during a connection.

Unformatted, digitally coded speech of 64kBit / sec is transmitted directly to the line without frame format formation. PCM octets, i.e. 8 bits are connected to the last HDLC identification sequence which was transmitted to the line during the signaling, see FIG. 1c. The risk that such octets could simulate signaling and monitoring messages is reduced to a negligible level by the framework conditions imposed by the frame structure, including the frame control sequence and the HDLC control procedures.

Data and other services in digital form that have already been formatted by the HDLC frame structure (FIG. 1 a) are transmitted to the line without further format formation. Subscriber loop signaling according to the HDLC procedures can be performed by the end equipment, or the ICE end equipment can handle such procedures and connect the end equipment to the line when a connection is made. For terminal equipment operating at speeds below 64 kBit / sec, the ICE absorbs the additional bandwidth by inserting dummy control frames or tag sequences which are carried out by the remote ICE or at a separation point with a «non-ISDN» network to be deleted.

Data and other services in digital form that have not yet been formatted in accordance with the HDLC frame structure are formatted into frames by an HDLC coder / decoder in the ICE terminal equipment (see further), the format resolution in a remote ICE terminal equipment or at a separation point with a non- ISDN network takes place. The HDLC procedure enables the subscriber line signaling to be handled by the terminal equipment, or the ICE terminal equipment can process the HDLC sequence and connect the terminal equipment to the line via the HDLC encoder / decoder when a connection has been established. End equipment with rates up to 48 kbit / sec can be used; Speed differences between the end equipment and the subscriber loop are processed by the frame length and / or by the insertion or deletion of additional character strings and / or control frames.

Fig. 1c shows an example of a typical transmission of a call by the terminal equipment ICE using an IDLC procedure. The signaling, monitoring and frame functions between the ICE terminal equipment and the loop are designated by SSM F. Once a connection is established, formatted data or digitally encoded speech octets that are aligned with the last character string can be transmitted. Controlled by the subscriber, end-to-end signaling can be used, e.g. a change in transmission mode to allow the use of another service, these mode changes being controlled by the HDLC procedure.

Fig. 2 shows in simplified form a subscriber loop arrangement with a terminal equipment ICE 1, which is connected to a local ISDN center via a full-duplex digital connection of 64 kbit / sec. The terminal equipment 1 has a telephone receiver 3 and a data input device 4, whereby an indication of the diversity of the possible services is made. In the center there is a signal extraction circuit 5 which is controlled by a control unit 6; the signaling is called up by the circuit 5 before the application of voice or data, etc. to the switch 7. In some cases this can lead to multiplexing.

3 shows a block diagram of a terminal equipment ICE at the subscriber end of the loop. A telephone receiver 3 is connected to a PCM coder / decoder 8, which in turn can be connected to a line circuit 10 of the control center via switching means 9. There is also a data separation unit 11 for transmitting and receiving data, which unit can be connected to the line circuit in the transmission direction via the switching means 9. In the receiving direction, the isolating point 11 is connected to the line circuit 10 via further switching means 12. The switching means are shown as mechanical switches, but in reality they are electronic switches. A keyboard 13 with the logic assigned to it is connected to a signaling and control unit 14, the function of which includes the control of the switching means 9 and 12 mentioned; a display 15 is also controlled with the logic associated with it, the display showing digits prior to transmission or information received from a remote center or terminal equipment. An incoming call signaling device uses a loudspeaker 16 to attract the subscriber's attention by means of appropriate tones.

The signaling and control unit 14 also controls an HDLC encoder / decoder 17, via which the signaling and monitoring messages go and which is connected to the line circuit 10 when messages are being handled.

The receiver 3, coder / decoder 8, the separation point 11, the keyboard 13, the display 15, the loudspeaker 16 and the line circuit 10 all perform their usual functions.

The control unit 14 decides whether the PCM-C or / decoder 8, the data separation unit 11 or the HDLC coder / decoder 17 should be connected to the line and whether the separation point 11 or the unit 14 should be connected to the coder / decoder 17 according to the further described procedures are to be connected. In the case of outgoing calls, these connections are made as a function of various controls operated by the caller, and in the case of a destination call, this is done on the basis of the signaling or monitoring messages received.

The encoder / decoder 17 forms and resolves the formats mentioned above and provides timing information taken from the confirmed character string to the ICE clock 18 which performs octet alignment and other timing functions. The encoder / decoder 17 continuously monitors the incoming line to determine valid frames while the line is active.

Fig. 4 shows the corresponding equipment at the central end of the subscriber loop; in this case, the equipment is made somewhat simpler since it does not contain any subscriber-controlled elements; a description is therefore unnecessary.

At each time of operation, the loop is monitored at both ends to identify signaling, monitoring, or frame messages, which monitoring includes checking the incoming data for tags.

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2 sheets of drawings

Claims (4)

651 714 1. A method for transmitting messages in a message transmission system, in which connections between subscribers and the telecommunications office take place via a subscriber loop in digital form, analog signals being converted into digital signals by pulse code modulation, characterized in that signals containing voice, data and / or other useful information alternately with operating, control or monitoring signals are transmitted over the loop, that the latter signals are treated the same as the former, and that the code groups of the voice, data and / or other useful information are aligned according to the framework information provided by the Framework structure of the operational, tax or Monitoring signals are derived. 2. The method according to claim 1, characterized in that voice signals via a PCM coder / decoder (8) are fed to a line circuit, this connection being effective only in the presence of voice signals, and that the PCM code combinations are transmitted in the office in time division multiplexing and with other PCM code combinations from other lines to form a multiplex. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that when data signals are transmitted, a data interface unit (11) is connected directly to a line circuit. 4. The method according to claim 1, characterized in that when transferring operating, control, monitoring or. Frame signals, a coder / decoder (17) is connected to a line circuit (10), the coder / decoder mentioned outgoing messages being combined into formats and incoming messages being released from formats.