Abstract:
A network user station ( 2 ), which in a transmitting mode transmits telegrams ( 5 ) to another network user station ( 2 ) and in a receiving mode receives telegrams ( 5 ) from another network user station. Said telegrams contain messages of identical message length in a message string. One of said messages is a time message ( 5   d ) provided with a time of day. The network user station is provided with means ( 11; 13 ) for substantially preventing inaccuracies with respect to a transmittal and/or processing instant of the time of day.

Description:
[0001]    This is a Continuation of International Application PCT/DE99/03443, with an international filing date of Oct. 28, 1999, which was published under PCT Article 21(2) in German, and the complete disclosure of which is incorporated into this application by reference.  
         FIELD OF AND BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a network user station, which can be connected with another network user station and which, in a transmitting mode, transmits telegrams to the other network user station and in a receiving mode receives telegrams from the other network user station. These telegrams contain messages of identical message length in a message string. One of these messages is a time message provided with a time of day.  
           [0003]    Such a network user station is known from the Siemens catalog ST 70, chapter 12, 1997 edition. This network user station is suitable for use in a distributed automation system including a plurality of automation components, which must be synchronized for controlling a technical process in accordance with an automation task. To this end, a time transmitter connected to the network cyclically transmits via broadcasting or multicasting a time message which forms part of a message string comprising a plurality of messages. The automation components use this transmitted time message to synchronize their clocks. Due to different dwell times of a time message in the transmitter and/or receiver of the network user station, it can occur that the times stored in the time message are erroneous with respect to the transmittal and/or receive time in the transmitting and/or receiving mode.  
         OBJECTS OF THE INVENTION  
         [0004]    One object of the invention is thus to create a network user station of the initially mentioned type which substantially prevents inaccuracies with respect to a transmittal and/or processing instant of the time of day.  
         SUMMARY OF THE INVENTION  
         [0005]    This and other objects are solved providing an algorithm and/or a component, which in transmitting mode records a first delay time between the instant when the time message is input in the message string and the instant when transmission of the time message begins, and which adjusts the time of the time message corresponding to this recorded first delay time.  
           [0006]    The messages in the message string are processed in the sequence in which they are deposited in said message string. An underlying idea of the invention is to detect the time delay that is caused by a delayed processing of the time message within the message string and accordingly to correct the time stored in the time message. If the network user station operates in a transmitting mode, the algorithm/component of the network user station detects a first delay time between the instant when the time message is entered in the message string and the instant when transmission of the time message starts and adjusts the time stored in the time message based on this detected first delay time. If the network user station operates in a receiving mode, the algorithm/component detects a second delay time between the instant when the time message is received and the instant when the time message is processed and adjusts the time stored in the time message based on this detected second delay time.  
           [0007]    This ensures that the time stored in the time message is the correct time of day at the transmitting instant of the time message. It further ensures that the time to be processed in the receiver is the correct time of day at the processing instant.  
           [0008]    In preferred embodiments of the invention, the algorithm/component in the transmitting mode provides the time message to be transmitted with an identification code. In a receiving mode the algorithm/component analyzes the code, which indicates to a network user station operating in receiving mode whether the time stored in the time message has been adjusted. This makes it possible for the receiving network user station to introduce corresponding measures, e.g., in such a way that a non-adjusted time of a time message is not further processed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention as well as embodiments and advantages thereof are described below in greater detail, by way of example, with reference to the drawings in which:  
         [0010]    [0010]FIG. 1 is a schematic diagram of a preferred embodiment of the network of the present invention showing time adjustment by the transmitting unit;  
         [0011]    [0011]FIG. 2 is a schematic diagram of another embodiment of the network user station of the present invention showing time adjustment by the receiving unit; and  
         [0012]    [0012]FIG. 3 is a schematic diagram of an integrated network of the present invention showing a network junction connecting multiple networks. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    In FIG. 1, reference numeral  1  identifies a network, e.g., a local area network (LAN). A plurality of network user stations  2   a ,  2   b ,  2   c , . . . is connected to the network  1 , each of which has a receiver  3   a ,  3   b ,  3   c , . . . and a transmitter  4   a ,  4   b ,  4   c , . . . . The present example assumes that the transmitter  4   a  of the network user station  2   a  is to transmit to receiver  3   c  of network user station  2   c  messages  5   a ,  5   b ,  5   c ,  5   d ,  5   e  in a message string  6 , via a network connection  23 . Message  5   d  is a time message. The time message  5   d  contains the time of day of a timer  7  of the network user station  2   a , which can be externally synchronized by a signal  8 . A timer  9  of network user station  2   c  must be synchronized with the time of day entered in time message  5   d  at an input instant. Due to the fact that a network controller  10  of the transmitter  4   a  transmits messages  5   a ,  5   b ,  5   c ,  5   d ,  5   e  to receiver  3   c  in the time sequence in which they were deposited in the message string  6 , the time entered in the time message  5   d  deviates from the actual time of day at the instant when transmission begins. In the present example, five processing cycles pass between the moment when the time of day is entered in time message  5   d  and the moment when this time message  5   d  is transmitted to the receiver  3   c  by the network controller  10 . As a result, the time stored in time message  5   d  must be corrected by this delay time of five processing cycles. It is assumed that for each processing cycle the network controller  10  transmits a message  5   a ,  5   b , . . . to the receiver  3   c . The delay time is recorded and the time of day is adjusted according to the delay time by a recording and adjusting unit  11  of the transmitter  4   a . The time of day is supplied to the unit  11  at the moment when the time is entered in the time message  5   d . First, the unit  11  records the delay time in the form of the number of processing cycles up to the instant when the time message  5   d  is transmitted and finally adjusts the time of day in the time message  5   d  according to the delay time.  
         [0014]    [0014]FIG. 2, which depicts another schematic diagram of a network, will now be described. The parts that are identical in FIGS. 1 and 2 are provided with identical reference numbers. Transmitter  4   a  of user station  2   a  transmits messages  5   a , . . . of message string  6  to a network controller  12  and a recording and adjusting unit  13  of the receiver  3   c  of the user station  2   c  via a network connection  23 . This recording and adjusting unit  13  decodes messages  5   a ,  5   b , . . . , detects the time message and records the number of processing cycles required between the instant when time message  5   d  is received and the instant when time message  5   d  is forwarded to the timer  9 . According to this number of processing cycles, the unit  13  adjusts the time of day and enters this corrected time in time message  5   d , so that a correct time of day is supplied to timer  9  for its synchronization.  
         [0015]    [0015]FIG. 3 shows an integrated network  16  formed of two networks  14 ,  15 . A network user station  18 , e.g., a network user station in the form of a gateway, a router, a relay, or a bridge, forms the network junction and provides the connection between the two networks  14 ,  15 . This network user station  18  has recording and adjusting units  19 ,  20 . If a user station  21  of the network  14  transmits a time message to user station  22  of network  15 , recording and adjusting unit  19  adjusts the time to be received from user station  21  and the recording and adjusting unit  20  adjusts the time in the time message to be transmitted to user station  22 . If the user station  22  of network  15  transmits a time message to the user station  21  of network  14 , the recording and adjusting unit  19  adjusts the time of day to be received from user  22  and recording and adjusting unit  20  adjusts the time in the time message to be transmitted to user station  21 .  
         [0016]    The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.