METHOD FOR TRANSMITTING A TIME-DIVISION DATA COMMUNICATION SIGNAL

Abstract: A method for transmitting a time-division data communication signal, in which method information is transmitted between a transmitting terminal and a receiving terminal in predetermined time-slots (C), at least one of said time-slots being used for transmitting a synchronizing byte (D) for synchronizing a frame (A) in the receiving terminal, said frame comprising the transmitted information and the synchronizing byte (D).

Description: Method for transmitting a time-division data communication signal The invention relates to a method for transmitting a time-division data communication signal, in which method information is transmitted between a transmitting terminal and a receiving terminal in predetermined time-slots, at least one of said time- slots being used for transmitting a synchronizing byte for synchronizing a frame in the receiving terminal, said frame comprising the information transmitted in the time-slots, and the synchronizing byte. When conventional methods have been used for transmitting a time-division data communication signal, the problem has been accurate synchronization and identification of frame time-slots and channel time- slots e.g. in case of errors. It is also difficult to detect how much incorrect information has been transmitted along the data communication line. Another problem with conventional methods has been remote control and monitoring of network terminals. Thus, the network operator must frequently contact the network terminal from the central terminal via some other line, in which case in addition to one data communication line, another remote control line is required for using said data communication line. Thus, remote control and monitoring of the network terminal often requires an extra data communication line, which could be used for normal data communication traffic. European Patent Application 397 138 discloses a control technique for distributed control systems in which technique information is transmitted by means of serial communication technique in certain time-slots. Control information of said system is transmitted by using one or more of the above mentioned time-slots. A control byte comprises bits to determine a certain command, as well as address bits for controlling a certain device. Said control byte further comprises a bit that reports whether said byte is to be taken into account or not. Said byte further comprises two bits, one of which, when being valid, accelerates the command to be carried out, and the other of which is intended for checking the transmitted information, i.e. a so- called check bit. Said byte cannot be used, however, for identifying the frame which is being used, and it is thus not possible in case of an error to determine the frame in which the error has occurred. It must also be taken into account that said byte employs one available channel time-slot, in which case said time-slot cannot be used for normal traffic. It is an object of the present invention to avoid the above mentioned drawbacks, and to enable remote control and monitoring of network terminals without employing a channel time-slot intended for normal traffic. This method of the invention is characterized in that a frame identifier is transmitted in the synchronizing byte, that a bit for error detection is transmitted in the synchronizing byte to the receiving terminal, that a bit describing the state of the frame to be received is transmitted in the synchronizing byte, and that a bit for remote control of the network terminal is transmitted in the synchronizing byte so that the synchronizing byte forms an entity which identifies the frame to be transmitted, and simultaneously transfers information for error detection, information on the state of the received frame, as well as information for remote control of the terminal to the receiving terminal. An essential idea of the invention is that a time-slot is added to each frame for transmitting the synchronizing byte. In this case, transmission speed of the line is increased by the value of the synchronizing byte. Another essential idea is that the synchronizing byte comprises at least four bits to mark the frame to be transmitted, and that the synchronizing byte comprises at least two bits to control the transmitting terminal and the receiving terminal, and monitor the state of the terminals. Another essential idea is to include an error information bit in the synchronizing byte. The synchronizing byte further comprises a bit reporting the state of the frame at the receiving terminal. An essential advantage of the invention is that said synchronizing byte and the bits included in it are used for determining the quality of the data communication line and error-free seconds. In addition, the synchronizing byte can include control channels used for remote control, which channels can be used for determining the settings of the receiving terminal, servicing said terminal, and transmitting statistical data from said terminal to the central terminal, in which case the operator does not need to use a separate data communication channel for servicing and checking the network terminal. Another essential advantage is that information on the state of the frame obtained by the receiving terminal can be transmitted in the synchronizing byte, in which case changes occurring in the line can be monitored extremely rapidly. The invention is described in greater detail in the accompanying drawing, in which Figure 1 shows an overall picture of the frame structure and the multiframe structure of a channel time-slot, and Figure 2 shows the structure of a synchronizing byte of the invention. Figure 1 is a picture showing principles of transmitting an electric time-division data communication signal, where row A represents channel time-slots. In every said time-slot 0-14, an 8-bit byte indicated by arrow B is transmitted. Brace C indicates time-slots, in all of which an 8-bit byte is transmitted. Similarly, a so-called synchronizing byte D has been inserted in time-slot 15. Thus, channel time- slots 0-15 shown in row A form a uniform frame entity, which is synchronized in the desired way by means of synchronizing byte D. Similarly, the frame formed by row A forms a part of the multiframe shown in row E, in which case 16 frames A form a complete multiframe in accordance with row E. The method illustrated in Figure 1 for transmitting data communication signals is fully known as such execpt for the synchronizing byte, and this application deals with the content of the synchronizing byte only. Figure 2 shows synchronizing byte D, which can be used e.g. for indicating the end-point of time-slots 0-14 at time-slot 15, as shown in row A in Figure 1. Similarly, synchronizing byte D can be inserted after the above shown time-slots, in which case synchronizing byte D will not utilize the time-slot intended for data communication, but an extra time-slot is reserved for it. It is also possible to place synchronizing byte D before time-slots 0-15, in which case the devices located at the receiving terminal can conclude that one frame is beginning, or, if the synchronizing byte is located after the time-slots, that the frame is ending. Bits located in bit positions SI, S2, S3 and S4 in the synchronizing byte indicate the beginning of the synchronizing byte, and simultaneously, allow encoding of said frame, in which case the information included in each frame can be easily searched with the aid of information included in the multiframe, which is shown in row E in Figure 1. Similarly, bits located in bit positions S1-S4 can be used for indicating the location of the frame within the multiframe with binary values, i.e. when the bit code is 0000 in positions S1-S4, the location of the frame in the multiframe is 0, and when the bit code is 1111, the location is 15. The synchronizing byte further comprises bit CRC, which forms a part of error information CRC 16. Error information CRC 16 is formed by calculating it on the basis of all data bytes B in the frames included in the multiframes, so that the number of the bits in error information CRC 16 equals to the number of the frames included in the multiframe. Error information CRC 16 is thus transmitted bit by bit in the synchronizing byte from the transmitter to the receiver, in such a way that the most significant bit of error information CRC 16 is transmitted along with the synchronizing byte in which the bit code is 0000 in positions S1-S4, and similarly, the least significant bit of error information CRC 16 is transmitted along with the synchronizing byte with the bit code 1111 in positions S1-S4. Thus, the error information CRC 16 of the data to be transmitted is always transmitted to the receiving terminal along with the following multiframe. Corresponding error information CRC 16 is calculated at the receiving terminal, where, by comparing the error information CRC 16 transmitted along with the multiframe and that calculated at the receiving terminal, it can be concluded whether an error has occurred or not during the transmission. As data communication takes place between two terminals, e.g. a central terminal and a network terminal, communication is bidirectional. Thus, synchronizing byte D further comprises bit RXF, the function of which is to describe the state of the received frame to the transmitting terminal. It is also possible to calculate the error probability of the line by monitoring possible errors occurring in bits located in bit positions S1-S4 of the synchronizing byte. The error probability determined with the aid of bits in positions S1-S4 is equally high at other locations of the time-slots, as well. Bits CHI and CH2 in the synchronizing byte are intended for the network operator, with the aid of which bits the operator may remote control and service subscribers' network terminals. Bits CHI and CH2 can further be used for collecting various statistical information from network terminals. The drawing and the description referring thereto are only intended to illustrate the idea of the invention. The method of the invention may vary in its details within the scope of the claims.

Claims: Claims: 1. A method for transmitting a time-division data communication signal, in which method information is transmitted between a transmitting terminal and a receiving terminal in predetermined time-slots (C), at least one of said time-slots being used for transmitting a synchronizing byte (D) for synchronizing a frame (A) in the receiving terminal, said frame comprising the information transmitted in the time-slots, and the synchronizing byte (D), c h a r a c t e r i z e d in that a frame identifier (S1-S4) is transmitted in the synchronizing byte (D), that a bit (CRC) for error detection is transmitted in the synchronizing byte (D) to the receiving terminal, that a bit (RXF) describing the state of the frame to be received is transmitted in the synchronizing byte (D), and that a bit (CHI, CH2) for remote control of the network terminal is transmitted in the synchronizing byte (D) so that the synchronizing byte (D) forms an entity which identifies the frame (A) to be transmitted, and simultaneously transfers information for error detection, information on the state of the received frame, as well as information for remote control of the terminal to the receiving terminal. 2. A method as claimed in claim 1, c h a r a c t e r i z e d in that a 4-bit (S1-S4) frame identifier is transmitted in the synchronizing byte (D), and that the frames are identified on the basis of the 4-bit (S1-S4) identifier in such a way that the first frame identifier (S1-S4) is denoted by bits 0000, and the last identifier by bits 1111. 3. A method as claimed in claims 1 and 2, c h a r a c t e r i z e d in that the bit (CRC) transmitted for error detection is identified on the basis of the identifier (S1-S4) of the synchronizing byte. 4. A method as claimed in claim 1, c h a r a c t e r i z e d in that the error probability of a data communication signal is calculated in the synchronizing byte (D) with the aid of the errors occurring in the frame identifier (S1-S4). 5. A method as claimed in any of the preceding claims 1 - 4, c h a r a c t e r i z e d in that two bits (CHI, CH2 ) intended for remote control of the network terminal are transmitted in the synchronizing byte.

Inventors: PAAVOLA ARTO, PAAVOLA, ARTO
Applicants: NOKIA TELECOMMUNICATIONS OY, PAAVOLA ARTO, PAAVOLA, ARTO
Application year: 1995
Main classification: H04J3
IPC codes: H04J3