Title: System uses time pulse that simultaneously transmits with time of day message to synchronize network user stations
Abstract: A network user system and a method of using the same in which one network user station (2c) is connected with another network user station (2a) via a message line (9a) and to which, in a receive mode, the other network user station (2a) can transmit a time message (Un, 5) comprising a time of day. The network user station (2a) also simultaneously transmits along with the time message a plurality of time pulses to the other network user stations (2b, 2d , 2e. . . ) in the system. The network user stations (2a, 2b, 2c, . . . ) record the time difference between the instant when the time pulses Tp are received and the instant when the time message (5) is received, and thereupon adjust the time of day contained in the time message (5) based on the time difference. This ensures that the time of day that is further processed in the receiver (4a, 4b, 4c. . . ) is the correct time at the instant of processing and, further, that the clock (6) of the network user station (2a) and the clock (8) of the other network user station (2c) are substantially synchronized. To measure the time difference in a simple manner, a timer is provided, which is started by the time pulse (Tp) and stopped by the time message (5).
Patent Number: 6,854,019 Issued on 02/08/2005 to Egle
| Inventors:
|
Egle; Fridolin (Durmersheim, DE)
|
| Assignee:
|
Siemens Aktiengesellschaft (Munich, DE)
|
| Appl. No.:
|
853607 |
| Filed:
|
May 14, 2001 |
Foreign Application Priority Data
| Nov 13, 1998[DE] | 298 20 339 U |
| Current U.S. Class: |
709/248; 713/400 |
| Intern'l Class: |
G06F 015//16 |
| Field of Search: |
709/248
713/400,500
318/85
345/708
711/151
455/436
375/354
|
References Cited [Referenced By]
U.S. Patent Documents
| 5276659 | Jan., 1994 | Kotaki | 368/10.
|
| 5580366 | Dec., 1996 | Farkas et al. | 65/158.
|
| 5701446 | Dec., 1997 | Abali et al. | 713/400.
|
| 5784421 | Jul., 1998 | Dolev et al. | 375/354.
|
| 5990638 | Nov., 1999 | Aoyama et al. | 318/85.
|
| 6138019 | Oct., 2000 | Trompower et al. | 455/436.
|
| 6182197 | Jan., 2001 | Dias et al. | 711/151.
|
| 6209106 | Mar., 2001 | Kubala et al. | 713/500.
|
| 6587122 | Jul., 2003 | King | 345/708.
|
| 6725278 | Apr., 2004 | Gonzalez | 709/248.
|
| Foreign Patent Documents |
| 36 38 947 | May., 1988 | DE | .
|
| 43 20 137 | Dec., 1993 | DE | .
|
| 198 08 103 | Sep., 1999 | DE | .
|
| 298 19 806 | Apr., 2000 | DE | .
|
| 96/27822 | Sep., 1996 | WO | .
|
Primary Examiner: Luu; Le Hien
Attorney, Agent or Firm: Sughrue Mion, PLLC
Parent Case Text
This is a Continuation of International Application PCT/DE99/03509 with an
international filing date of Nov. 3, 1999, which was published in German
and the full disclosure of which is incorporated into this application by
reference.
Claims
What is claimed:
1. A synchronized network user station system, comprising:
a first network user station;
a second network user station;
a message line connecting said first network user station and said second
network user station for sending a time message containing a time of day
from said first network user station to said second network user station;
a synchronization line also connecting said first and said second network
user stations for transmitting a time pulse from said first network user
station to said second network user station, wherein said first network
user station simultaneously transmits said time pulse and said time
message to said second network user station; and
a recording and adjusting means that records a time difference between an
instant when said time pulse is received and an instant when said time
message is received by said second network user station and adjusts the
time of day contained in said time message according to said time
difference.
2. The synchronized network user station system as claimed in claim 1,
wherein said second network user station has a timer 5 for recording the
time difference, which is started by said time pulse and stopped by said
time message.
3. The synchronized network user station system as claimed in claim 2,
wherein said first network user station simultaneously transmits to said
second network user station said time message containing a time of day via
said message line and said time pulse via said synchronization line.
4. The synchronized network user station system according to claim 1,
wherein said time message and said plurality of time pulses are
transmitted by a transmitter contained in said first network user station.
5. The synchronized network user station system according to claim 1,
wherein said time message and said plurality of time pulses is received by
said receiver contained in said second network user station.
6. A synchronized network user system for connecting a plurality of network
users comprising:
a plurality of network user stations;
a message line connecting said plurality of network user stations and for
transmitting a time message containing a time of day between said
plurality of network user;
a synchronization line also connecting said plurality of network user
stations and for transmitting a time pulse between said plurality of
network user stations, wherein said time pulse and said time message are
simultaneously transmitted; and
a recording and adjusting unit contained in at least one of said plurality
of network user stations that records a time difference between an instant
when time pulse is received and an instant when said time message is
received by said at least one of said plurality of network user stations
and adjusts the time of day contained in said transmitted time message
according to said time difference.
7. The network user system according to claim 6, wherein said time message
and said time pulse are transmitted by a transmitter contained in at least
one of said plurality of network user stations.
8. The network user system according to claim 6, wherein said time message
and said time pulse is received by said receiver contained in at least one
of said plurality of network user.
9. A method of synchronizing a first network user station with a second
network user station connected in a network comprising:
connecting said first and said second network user station using a message
line, and via said message line transmitting a time message from said
first network user station to said second network user station;
connecting said first network user station and said second network user
station using a synchronization line, and via said synchronization line,
transmitting a time pulse from said first network user station to said
second network user station;
recording a time difference between an instant when said time message is
received by said second network user station and an instant when said time
pulse is received by said second network user station; and
adjusting a time contained in said second network user station according
said time difference.
10. The method according to claim 9, wherein said time message transmitted
by said first network user station contains a time of day read from a
clock in said first network user station.
Description
FIELD OF AND BACKGROUND OF THE INVENTION
The invention relates to a network user system and method of using the
same, which can be used to connect one network user station to another
network user station via a message line and to which, in a receive mode, a
timer message including a time of day can be sent by a network user
station as a means of improving time synchronization accuracy between
network user stations.
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 a timer message via
broadcasting or multicasting. The automation components use this
transmitted timer message to synchronize their clocks. Due to different
dwell times of a timer message in the transmitter of the network user
station and/or in network components, the times contained in the timer
message may be incorrect at the time when they are received.
German Utility Model Application 298 19 806.1 proposes to enable a network
user station to correct the delay times between the instant when the time
is entered into a time message and the instant when it is transmitted, and
to correct the delay times between the instant when the time message is
received and the instant when the time of day is further processed. This
German Utility Model Application 29819806.1 corresponds to International
Application PCT/DE99/03443 (published as WO 00/28400), which was filed in
the United States as a Continuation Application (application number
unknown) on May 7, 2001, and full disclosure of which is incorporated
herein by reference.
OBJECTS AND SUMMARY OF THE INVENTION
Thus, one object of the present invention is to create a network user
system of the type mentioned above with improved time synchronization
accuracy as well as a method of synchronizing network user stations.
This and other objects are achieved by utilizing a network user system that
can be used to connect one network user station to other network user
stations via a synchronization line through which a network user can
transmit time pulses to other network user stations. The network user
station also simultaneously transmits along with the time pulses a time
message to other network user stations in the system. The network user
stations record the time difference between the instant when the time
pulses are received and the instant when the time message is received, and
thereupon adjust the time of day contained in the time message based on
the time difference.
This ensures that the time of day that is further processed in the receiver
is the correct time at the instant of processing and, further, that the
clock of the network user station and the clock of the other network user
station are substantially synchronized.
To measure the time difference in a simple manner, a timer is provided,
which is started by the time pulse and stopped by the time message.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and further advantageous refinements of the invention
according to the features of the dependent claims are explained in more
detail below with the aid of diagrammatic, exemplary embodiments in the
drawing, in which:
FIG. 1 is a schematic diagram of a network and
FIG. 2 is a time diagram of transmission signals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a network 1 is illustrated, e.g., a local area network (LAN). A
plurality of network user stations 2a, 2b, 2c, . . . are connected to the
network 1 via a message line 9a. Each of the network user stations have a
receiver 3a, 3b, 3c, . . . and a transmitter 4a, 4b, 4c. In this
embodiment of the present invention, it is assumed that the transmitter 4a
of network user station 2a transmits a message 5 to the receiver 3c of
network user station 2c. The time message contains the time of day of a
clock 6 of network user station 2a, which is preferably externally
synchronized by a signal 7. A clock 8 of network user station 2c must be
synchronized with the time of day entered in the time message at an input
instant. Also, in this embodiment of the present invention, it is assumed
that the time difference between the instant when the time of day is
entered in the time message 5 and the instant when the time message 5 is
transmitted is negligible, or that suitable means, such as those described
in German Utility Model Application 298 19 806.1, are used to correct this
time difference.
To prevent incorrect synchronization of the clock 8 of the network user
station 2c with the time of another network user station 2a, the
deviations caused by line delays must be substantially compensated. To
this end, a synchronization line 9b is provided for transmitting time
pulses Tp to the receiver 3c of network the user station 2c. At the
instant when the time message 5 is transmitted, a network controller 10
or, as shown in the present example, a time pulse transmission unit 11 of
a recording and adjusting unit 12 of the receiver 3c, simultaneously
transmits a time pulse, e.g., a time pulse in the form of a second pulse.
The controller 10 of the time pulse transmission unit 11 indicates the
instant when the time message 5 is transmitted via a line 13. The time
pulse starts a timer of the recording and adjusting unit 12, which is
stopped when unit 12 receives the time message 5. This allows the
receiving network user station 2c to determine the time difference between
the instant when the time pulse Tp is received and the instant when time
message 5 is received. The recording and adjusting unit 12 thereupon
adjusts the time of day contained in time message 5 in that unit 12 adds
the determined time difference to the stored time of day so that the times
of transmitter 4a and receiver 3c are substantially synchronized.
To illustrate the time adjustment, reference is made to FIG. 2, which
depicts a time diagram of transmission signals.
At an instant t a transmitter T (e.g., 4a in FIG. 1) of a network user
station transmits a time pulse Tp and simultaneously a time message Un to
receivers R1, R2 of other network users. The time pulse Tp starts
corresponding timers in receivers R1, R2, which are stopped at the instant
when time message Un is received. In the example depicted, time message Un
is delayed less during its transmission to receiver R1 (.DELTA.t1) than
during its transmission to receiver R2 (.DELTA.t2). A recording and
adjusting unit 12 in receiver R1 adjusts the time of day contained in the
time message by a time difference .DELTA.t1 and in receiver R2 by a time
difference .DELTA.t2.
*
