Abstract:
A multiplexing equipment included in an ATM network to transmit control line signals for interfacing data communication terminals. The transmission of the control line signals is realized by reserving a field in a payload in a cell format for the control line signal transmission between the data communication terminals, mapping RS/CD, CS, ER/DR, CI of the control line signals at intervals based on a terminal speed, multiplexing the mapped control line signals at the transmission side, and separating the multiplexed control line signals at reception side.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an ATM network, and particularly to a cell creation method for control line signals and its equipment for transmitting the control line signals via the ATM network. In this specification, the control line signals are defined as signals, which are transmitted in addition to user data, indicating the control line information between data communication equipment (information terminals). 
   2. Description of Related Art 
   In the ATM network of prior art, data transmission between a pair of data communication equipment is operated in a constant fix mode (full duplex communication) because no slot is made available for multiplexing the control line information of the data communication equipment into an ATM Header. 
   Because of the inability to transmit the control line information in the conventional ATM network, it makes difficult to connect on-line terminals, which provide data service by transmitting and receiving the control line signals in a half duplex communication mode, to the ATM network. 
   SUMMARY OF THE INVENTION 
   The present invention is made by considering the above mentioned points. An object of the present invention is to provide a cell creation method for the control line signals in the ATM network which enables to transmit user data and the control line signals used for processing in the data communication equipment, and to provide multiplexing equipment included in the ATM network realizing the cell creation method for the control line signals. 
   Another object of the present invention is to provide means for modifying the signal RS/CD among the control line signals to be transmitted so as to prevent the missing of the head portion or the bottom portion of the user data signal, and to assure the full acquisition of the signal. 
   The objects of the present invention are accomplished by a cell creation method of control line signals for an ATM network comprising a plurality of multiplexing equipment realizing communication among information terminals, comprising the steps of creating cells from user data to be transmitted between a pair of the communicating information terminals and control line signals indicating control line information relating the transmission of the user data at the multiplexing equipment connected to the pair of the communicating information terminals respectively, and transmitting the cells including the user data and the control line information between the pair of the communicating information terminals. 
   In a preferred aspect of the present invention, there is provided a cell creation method of control line signals, wherein a portion of a cell payload to be transmitted is mapped for transmitting the control line signals when creating the cell from the control line signals, and the control line signals are multiplexed into the cell at the transmission side and separated from the cell at reception side. 
   Alternatively, in another preferred aspect of the present invention, the signal RS/CD of the control line signals may be extended for a predetermined period before said signal RS/CD is multiplexed. 
   Furthermore, in another preferred aspect of the present invention, the multiplexing equipment connected to the pair of the communicating information terminals may have two operating modes which can be selected, one being a control line signal transmission mode for transmitting the control line signals by creating the cell from the control line signals, the other being a constant fix mode for executing a full duplex communication. 
   The objects of the present invention are also accomplished by a multiplexing equipment, being one of a plurality of multiplexing equipment included in an ATM network for realizing communication between information terminals, connected to one of the communicating information terminals, comprising, multiplexing means creating cells from control line signals outputted from one of the information terminals at the transmitting side, and separation means separating the control line signals from the cells transmitted via the ATM network and outputting the separated control line signals to one of the information terminals at reception side. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration showing an example of ATM network of the present invention; 
       FIG. 2  is a schematic illustration showing signal lines required for communication between data communication equipment; 
       FIG. 3  is a schematic illustration showing an example of transmission modes of the control signals; 
       FIG. 4  is a schematic illustration showing an example of a cell format used in the present invention; 
       FIG. 5  is a schematic illustration showing an example of a multiplexing format of the control line signal  1  in  FIG. 4 ; 
       FIG. 6  is a schematic illustration showing an example of a multiplexing format of the control line signal  2  in  FIG. 4 ; 
       FIG. 7A  is a schematic illustration showing a block structure of a multiplexing equipment realizing the control line signal multiplexing function in accordance with the present invention; 
       FIG. 7B  is a timing chart of the control line signals to be multiplexed; 
       FIG. 8  is a schematic illustration showing a block structure of multiplexing equipment realizing the control line signal separation function in accordance with the present invention; 
       FIG. 9  is a schematic illustration showing an example of a selector selecting one of the control line signal transmission mode and the constant fix mode in accordance with the present invention; and 
       FIG. 10  is a schematic illustration showing another example of block structure of the multiplexing equipment in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of an ATM network in accordance with the present invention will now be described. 
     FIG. 1  shows an example of configuration of the ATM network in the present embodiment. In the ATM network of the present embodiment, multiplexing equipment A  105  is connected to data communication equipment A  102 , D  103  and E  104  having one of X.21, V.24 and V.35 functions in a building A  101 . Multiplexing equipment B  108  is connected to data communication equipment B  109  having one of X.21, V.24 and V.35 functions in a building B  107 . Multiplexing equipment C  111  is connected to modems  112 ,  113  connected to data communication equipment C  114  having one of X.21, V.24 and V.35 functions, and to data communication equipment F  115  having DCE (Data Circuit Terminating Equipment) function in a building C  110 . 
   As shown by dotted lines in the example of  FIG. 1 , the data communication equipment A  102  connected to the multiplexing equipment A  105  in the building A  101  communicates with the data communication equipment B  109  connected to the multiplexing equipment B  108  in the building B  107  via the ATM network  106 . Furthermore, the data communication equipment D  103  connected to the multiplexing-equipment A  105  in the building A  101  communicates with the data communication equipment C  114  connected to the multiplexing equipment C  111  in the building C  110  via the ATM network  106 . The data communication equipment E  104  connected to the multiplexing equipment A  105  in the building A  101  communicates with the data communication equipment F  115  connected to the multiplexing equipment C  111  in the building C  110  via the ATM network  106 . 
     FIG. 2  shows a group of control lines  202  required for the communication with the data communication equipment  201 . The control lines  202  includes signals such as SD, RD, ST 1 , RT, ST 2 , RS, CS, CD, ER, DR and CI. 
   The signal SD (Send Data) is data transmitted from the data communication equipment. 
   The signal RD (Receive Data) is data transmitted to the data communication equipment. 
   The signal ST 1  (Signal Timing  1 ) is data signal receive element timing from the data communication equipment. 
   The signal ST 2  (Signal Timing  2 ) is data signal send element timing of the data communication equipment. 
   The signal RT (Receive Timing) is data signal receive element timing of the data communication equipment. 
   The signal RS (Request to Send) indicates an existence of data to be output to the DCE. 
   The signal CS (Clear to Send) indicates that the DCE is ready to send data to a communication channel. 
   The signal CD (Carrier Detect) indicates that the DCE is receiving effective signal from a communication channel. 
   The signal ER (Equipment Ready) indicates that a DTE (Data Terminal Equipment) is ready for data input/output from/to the DCE. 
   The signal DR (Dataset Ready) indicates that the DCE is ready to be activate. 
   The signal CI (Call Indicate) indicates that the DCE is called from a communication line. 
   The multiplexing equipment of the present embodiment multiplexes major control line signals such as RS, CS, CD, ER, DR and CI into a cell in addition to use data. 
   Signals to be multiplexed have directions depending on the mode, i.e., DCE or DTE of FIG.  1 . For example, as shown in  FIG. 3 , the data communication equipment A  102 , B  109 . D  103  and E  104  are connected in the DCE mode, and the data communication equipment C  114  and F  115  are connected in the DTE mode. 
     FIG. 3  shows an example of the transmission formats of the control line signals in each building. Note that the ATM network  106  connecting the data communication equipment is omitted in FIG.  3 . 
   The control line signal transmission from the DCE mode to the DCE mode is explained using the data communication equipment A  102  and B  109  as an example. 
   The control line signals RS and ER are transmitted from the multiplexing equipment A  105  to the multiplexing equipment B  108  via the network (not indicated in the figure). The control line signals RS and ER are transmitted to the data communication equipment B  109  as the control line signals CD and DR respectively. 
   The control line signal transmission between the DTE mode and the DCE mode is explained using the data communication equipment E  104  and F  115  as an example. 
   The control line signals RS and ER from the communication equipment E  104  are transmitted to the data communication equipment F  115  as the control line signals RS and ER through the multiplexing equipment A  105 , the network (not indicated in the figure) and the multiplexing equipment C  111 . The control line signals CS, CD, DR and CI from the data communication equipment F  115  are transmitted to the data communication equipment E  104  as the control line signals CS, CD, DR and CI through the multiplexing equipment C  111 , the network (not indicated in the figure) and the multiplexing equipment A  105 . 
   Although the modems  112 ,  113  are disposed between the multiplexing equipment C  111  and the data communication equipment C  114 , the control line signal transmission between the DCE mode and the DTE mode among the data communication equipment D  103  and C  114  may be carried out in the same way as in the example of the data communication equipment E  104  and F  115 . 
     FIG. 4  shows an example of the cell format used in the present embodiment. 
   In this example of the cell format, a payload includes a User Data field, a control line signal transmission field for transmitting the control line signals, SN (Sequence Number) field and SNP (Sequence Number Protect) field, in addition to TTC standard ATM Header. 
   The ATM Header includes data such as GFC (General Flow Control), VPI (Virtual Path Identifier), VCI (Virtual Channel Identifier), PTI (Payload Type Identifier), CLP (Cell Loss Parity display), and HEC (Header Error Control). 
   The payload field includes fields such as the SN (Sequence Number) field, SNP (Sequence Number Protection) field, control line signal transmission field including the control line signal  1  and the control line signal  2 , and the User Data field. In this example, the signal RS/CD are multiplexed as the control line signal  1 , and the control line signals CS, ER/DR, CI are multiplexed as the control line signal  2 . 
   The cell format of the present example enables the communication and the transmission of the control line signals between the data communication equipment A  102  and B  109 , the data communication equipment D  103  and C  114 , the data communication equipment E  104  and F  115  via the multiplexing equipment A  105 , B  108 , C  111  and the ATM network  106  as shown in FIG.  1 . 
     FIGS. 5 ,  6  illustrate examples of a multiplexing format of the control line signals enabling the transmission of the control line signals in the present embodiment. 
     FIG. 5  shows an example of the multiplexing format  501  for the signal RS/CD that becomes the control line signal  1  in the cell format shown in FIG.  4 . In the example, the signal RS is latched at 45-bit interval of the terminal speed, and multiplexed into the cell. 8 bits of the signal RS/CD is multiplexed in each cell. 
     FIG. 6  shows an example of the multiplexing format  601  for the signals CS, ER/DR, CI which become the control line signal  2  with the cell format shown in FIG.  4 . In the example, the signal CS is latched at 90-bit interval of the terminal speed, and multiplexed into the cell. 4 bits of the signal CS is multiplexed in each cell. The signals ER and CI are latched at 180-bit interval, and multiplexed into the cell. 2 bits of the signals ER and CI are multiplexed into each cell. 
   Next, an example of block structure of a multiplexing unit in the multiplexing equipment, and an example of latch timing for each signal in the multiplexing unit will now be explained with reference to FIG.  7 A and FIG.  7 B. 
   As shown in  FIG. 7A , the present example of multiplexing equipment  702  comprises a route selection unit  703 , a latch unit  704 , a S/P cell creation unit  705  and a cell multiplexing unit  706 . In the present example, the multiplexing equipment  702  is assumed to be operated in the DCE/DTE mode. 
   In the present example of the multiplexing equipment  702 , the route selection unit  703  makes the selection of routes in accordance with a current mode (DCE or DTE) for the control line signals RS, CD, CS, ER, DR, CI inputted from data communication equipment  701 , and outputs as the signals RS/CD, CS, ER/DR, CI. The S/P cell creation unit  705  conducts serial/parallel conversion of the data signal at 8-bit unit. 
   The signals RS/CD. CS. ER/DR. CI outputted from the route selection unit  703  are latched at the latch unit  704 . As shown in  FIG. 7B , the signals RS/CD. CS, ER/DR and CI are latched respectively at a RS/CD latch timing (a 45-bit interval of the terminal speed), a CS latch timing (a 90 bit interval of the terminal speed) and a ER/DR/CI latch timing (a 180-bit interval of the terminal speed). 
   The cell multiplexing unit  706  multiplexes the signals RS/CD, CS, ER/DR and CI outputted from the latch unit  704  with predetermined cell creation timings at locations shown in  FIGS. 5 ,  6 . The cell multiplexing unit  706  creates cells with the multiplexed signals and the data signal outputted from the S/P cell creation unit  705 . 
   Information latched at the latch timing numbers shown in  FIG. 7B  are multiplexed at corresponding locations indicated by the latch timing numbers shown in  FIGS. 5 ,  6 . 
   Furthermore, the signal RS/CD is delayed with respect to the data signal in the RS/CD signal multiplexing process of the present embodiment so as to assurance the precise acquisition of the data signal and the control line signal data. Concretely, the signal RS/CD is delayed and multiplexed with an additional period of 45 bits after the latch timing number 1. A hatched area  707  in  FIG. 7B  shows the additional period of the signal RS/CD for the data signal assurance. 
   Accordingly, the signals RS and CD among the control line signals may be guaranteed with respect to the user data, and missing of the head portion or the bottom portion of the user data may be prevented. 
   Next, an example of block structure of a separation unit in the multiplexing equipment will now be explained with reference to FIG.  8 . 
   As shown in  FIG. 8 , the example of multiplexing equipment  802  comprises a cell separation unit  806 , a signal generation unit  804 , a P/S unit  805  and a route selection unit  803 . 
   In the example of the multiplexing equipment, the cell separation unit  806  separates the cells transmitted and inputted through the ATM network into the data signal and the control line signals. 
   The parallel data signal is converted at the P/S unit  805  to serial data signal. The serial data is routed at the route selection unit  803  in accordance with a current mode of DCE or DTE, and outputted to the data communication equipment  801 . 
   The separated control line signals become the signals RS/CD, CS, ER/DR, CI. The signal generation unit  804  generates the signal RS/CD at a 45-bit interval of the terminal speed based on data signal in the cell. Furthermore, the signal generation unit  804  generates the signal CS at a 90-bit interval, and the signal ER/DR/CI at a 180-bit interval. The generated signals are routed at the route selection unit  803  in accordance with a current mode of DCE or DTE, and outputted to the data communication equipment  801 . 
   In the present embodiment, the multiplexing equipment is provided with a function enabling the transmission of the control line signals in the ATM network. Alternatively, the multiplexing equipment of the present invention may comprise additional means for disabling such a transmission function of the control line signals. 
   For example, the multiplexing equipment of the present invention may be provided with a selector  901  shown in FIG.  9 . In this example, a control line transmission signal indicating the control line information and a constant fix signal indicating that an operational mode is in the full duplex communication by sending a ON/OFF signal are inputted to the selector  901 . The selector  901  determines if the input control line information should be outputted by selecting one of those two signals in accordance with a route selection signal indicating a mode to be selected among the control line signal transmission mode and the constant fix mode. 
   Alternatively, as shown in  FIG. 10 , the multiplexing equipment  1000  of the present invention may be provided with a multiplexing unit  1002  performing the multiplexing function shown in  FIG. 7 , a separation unit  1003  performing the separation function shown in  FIG. 8 , selectors  1001   a ,  1001   b  having the similar functions of the selector  901  shown in  FIG. 9 , and a mode setting unit  1004  for controlling selection effort of the selectors  1001   a ,  1001   b.    
   According to the multiplexing equipment  1000  of the present example, when the mode setting unit  1004  sets the control line signal transmission mode to be selected, the selector  1001   a  outputs the control line signals and the user data signal outputted from the data communication equipment  201  to the multiplexing unit  1002  without any changes, and the selector  1001   b  outputs the control line signals and the user data signal outputted from the separation unit  1003  to the data communication equipment  201 . When the mode setting unit  1004  sets the constant fix mode to be selected, no control line signal is transmitted, and only the user data signals are inputted to the multiplexing unit  1002  and outputted from the separation unit  1003 . 
   According to the present invention, it is possible to provide the cell creation method for the control line signals and the multiplexing equipment using such a method by which the control line signals, which are not used in the ATM network of prior art, can be transmitted. 
   Furthermore, according to the present invention, it is possible to provide means for modifying the signal RS/CD among the control line signals to be transmitted so as to prevent the missing of the head portion or the bottom portion of the user data signal, and to assure the full acquisition of the signal.