Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
  • H04J3/0641—Change of the master or reference, e.g. take-over or failure of the master
• • G—PHYSICS
  • G04—HOROLOGY
  • G04G—ELECTRONIC TIME-PIECES
  • G04G7/00—Synchronisation
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/04—Generating or distributing clock signals or signals derived directly therefrom
  • G06F1/14—Time supervision arrangements, e.g. real time clock
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
  • H04J3/0644—External master-clock
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J3/00—Time-division multiplex systems
  • H04J3/02—Details
  • H04J3/06—Synchronising arrangements
  • H04J3/0635—Clock or time synchronisation in a network
  • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
  • H04J3/0658—Clock or time synchronisation among packet nodes
  • H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
  • H04J3/0667—Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays

Definitions

• Method for time synchronization of at least two measuring computers cooperating with each other via a telecommunication network such as internet, intranet or the like
• the invention relates to a method for time synchronization in at least two together via a telecommunications network, such as Internet, intranet or the like, cooperating measuring computers according to the type specified in the preamble of claim I 1 and an apparatus for performing the method according to claim 24.
• a telecommunications network such as Internet, intranet or the like
• German patent application DE 100 46 240.5 is a measuring system for measuring the Internet Protocol IP) performance parameters, such as one-way delay, runtime fluctuations and packet loss, got in IP networks t.
• the non-prepublished German patent application DE 101 28 927.8 has a method for the subject, which allows the generation of time stamps in the underlying measurement system even with short-term blocked access to a reference clock.
• the measuring system on which these patent applications are based is a distributed measuring system, i. H.
• the individual system components are distributed locally and interconnected via a telecommunications network.
• the measuring system comprises at least two measuring computers, a database in which the measuring results and the configuration of the measuring system are stored, one
• Control computer which controls the measuring computers for the determination of the measuring result, as well as various graphical user interfaces, in particular for the configuration of the measuring system and for the visualization of the obtained measuring results.
• the measuring method is between at least two
• Measuring computers set up a unidirectional test section. On this measuring section, measurement packages with a configurable temporal distribution are sent from a first measuring computer to a second measuring computer. The departure of the measurement packet is detected by the first measurement computer, ie, a first time stamp is generated. This first timestamp is transmitted to the second measurement computer together with the measurement package and other data, such as sequence numbers. The second measuring computer detects the input of the measuring packet and generates a second time stamp. In order to be able to determine the one-way delay, which results from the difference between the two time stamps, with sufficient accuracy, the time stamps generated by the measuring computers must be sufficiently precisely synchronized in time.
• a technical realization is z.
• Example the generation of timestamps by acting as a time source satellite system, such as GPS Global Positioning System).
• the measuring computers continuously receive the universal time UTC Universal Coordinated Time sent by several satellites via a GPS antenna. With the help of a GPS-card integrated into the measuring computer timestamps with an error of
• GPS Antem e and GPS Map is simplified here referred to as GPS Clock.
• the measurement results are retrieved as measurement data by the control computer from the second measurement computer, stored in a database and there provided for visualization.
• the display of the measurement results and the system status can be made either by means of an offline display or online display. Offline display means that the display of the measurement results by means of a WWW
• the configuration of the measuring system also takes place with the aid of the already mentioned graphical user interface. For this the user makes inputs about the type and the course of the measurement.
• the entries made are stored in a database; the control computer reads this data from the database, configures the measuring computers accordingly and starts or stops the measuring connections according to this data.
• the first and the second time stamps are synchronized sufficiently precisely in time. If the first and second timestamps are not synchronized with sufficient accuracy, the measured one-way delay as the difference between the two time stamps can not be determined exactly.
• the invention has the object of providing a method for time synchronization of at least two interconnected via a telecommunications network, such as Internet, Intranet or the like, measuring computer such that while avoiding the disadvantages mentioned even in case of failure of the GPS clock, the implementation of a measurement is possible ,
• the invention is based on the finding that by providing a plurality of independent time sources on the individual measuring computers, the probability is minimized that no time source can be read, and thus the readout of a time stamp is ensured.
• each measuring computer is provided with a plurality of time sources of different accuracy for reading the time stamp from a time source.
• the choice of which time source to generate the Requested time stamp is used is done by the measuring computer and in this case depending on the accuracy of the available time sources.
• This time-source redundancy has the advantage that the generation or read-out of a time stamp from a time source is ensured in a simple manner. The risk of a measurement failure due to a missing time stamp is thereby minimized, since in the event of the failure of a first time source, the reading of the time stamp from a second time source is ensured.
• the measuring computer first selects the time source of highest accuracy for reading out the time stamp from a time source.
• the measuring computer can not read a time source of higher accuracy, it automatically selects a time source of the next best accuracy.
• this graduated method with regard to the selection of the time source it is achieved that the best possible measurement result is achieved under the given circumstances, ie the failure of a more precise time source.
• the highest possible time source is the highest possible time source
• Accuracy signals of a satellite system such as GPS Global Positioning System
• the signals of the satellite system are received by local GPS receivers integrated in the measuring computers.
• a GPS clock By using a GPS clock as the time source of highest accuracy, a tolerance of +/- 0.5 ⁇ s is easily ensured for the reading out of the time stamps.
• the measuring computers preferably each have local clocks that are continuously synchronized to the local GPS receivers-internal synchronization-by means of NTP (Network Time Protocol).
• NTP Network Time Protocol
• the internal synchronization via NTP provides an easy way to generate a second, highly accurate time source.
• the local clock of the first measuring computer by means of NTP (Network Time Protocol) to the local clock at least one predetermined second measuring computer - external Synchronization - synchronized.
• NTP Network Time Protocol
• the time interval from which external synchronization of the local clock of the first measuring computer to the local clock of a second measuring computer takes place is freely adjustable.
• the externally synchronized local clocks of the measuring computers are used as time sources of the third highest accuracy.
• Measuring computers are accordingly called time sources of the fourth highest order.
• the external synchronization of the local clock of the measuring computer is performed only with time sources of the second highest accuracy.
• measurement packets in particular UDP measurement packets (User Datagram Protocol) are transmitted for the transit time measurement between the measurement computers.
• UDP is a connectionless Internet transport protocol that based on the basic protocol for data transmission over the Internet (IP).
• IP Internet
• one measuring computer serves as a transmitter, while the other measuring computer acts as a receiver.
• the sending measuring computer records the timeout - sending time stamp - of the outgoing measuring packet.
• Other data on the transmission time stamp are generated and transmitted together with the measurement packet and optionally further data, for example sequence number or the like, as the first data to the receiving measurement computer.
• the data for the transmission time stamp preferably relate to information about the time source used from which the transmission time stamp was read out, the type of synchronization, the accuracy of the synchronization and an estimate of the accuracy of the generated transmission time stamp.
• the temporal input of the measurement packet-reception time stamp- is detected by the receiving measuring computer as second data and other data is generated at the reception time stamp.
• the data for the reception time stamp preferably again relate to information about the time source used when reading the
• Receive timestamp was used, the type of synchronization, the accuracy of synchronization, as well as an estimate of the accuracy of the generated reception time stamp.
• the first data and the second data become a predetermined one
• the measurement result is determined from the first data still available and the second data.
• Fig. 1 is a schematic representation of a telecommunications network with multiple measuring computers, which have different time sources for carrying out the method according to the invention.
• a telecommunications network 10 is shown schematically, which has a plurality of switching devices 12 to 24, which are interconnected via connecting lines 26.
• the telecommunication network 10 is, for example, the Internet.
• the switching center 12 is assigned a first measuring computer 28. For receiving signals from a multiple satellites 30
• the first measuring computer 28 has a GPS antenna 32 and a GPS card (not explicitly shown here) for processing the received signals.
• the GPS antenna 32 and the GPS card (not explicitly shown) together form the receiver for receiving the GPS signal. Signals necessary local GPS receiver of the first measuring computer 28.
• a local clock 34 is integrated in the first measuring computer 28.
• a second measuring computer 36 which is connected to the switching device 16, also has a GPS antenna 38 and a local clock 40.
• the necessary for the reception of the GPS signals local GPS receiver of the second measuring computer 36 again form the GPS antenna 38 and a not shown here, integrated into the second measuring computer 36 GPS card.
• Corresponding peripheral devices namely a GPS antenna 42 and a local clock 44, are assigned to a third measuring computer 46, which is connected to the switching device 20.
• a GPS map (not further shown) and the GPS antenna 42 form a local GPS receiver of the third measuring computer 46 necessary for receiving the transmitted GPS signals.
• the measuring computers 28, 36 and 46 continuously receive the world time UTC (Universal Coordinated Time) via the already presented local GPS receivers.
• UTC Universal Coordinated Time
• the GPS receivers of the measuring computers 28, 36, 46 are referred to as GPS clocks.
• Switching devices 12, 14 and 16 to the second measuring computer 36 forms a measuring section 48, which is shown in the drawing for clarity two-dot chain.
• a control computer 50 which cooperates with a database 52, is the
• the control computer 50 controls the measuring computers 28, 36.
• a measuring program for measuring the one-way delay is installed in each of the measuring computers 28 and 36.
• the aim of the measuring arrangement is to determine the packet transit time of a measurement packet from the first measurement computer 28 via the measurement path 48 to the second measurement computer 36. It is thus a unidirectional measuring connection in which individual measurement packets are sent from the first measurement computer 28 to the measurement computer 36.
• a measuring packet is sent by the first measuring computer 28 via the measuring path 48, that is via the connecting line 26, the switching center 12, the Vennittlungsstelle 14 and the exchange 16 to the second measuring computer 36.
• the measurement packages are sent using the User Datagram Protocol UDP).
• UDP is a connectionless Internet transport protocol based on IP.
• the measurement packages contain i.a. Timestamp and sequence numbers.
• the reading / setting of the so-called transmission time stamp takes place.
• This value of the transmission time stamp ie the time of the output of the measurement packet, is transmitted to the second measurement computer 36 together with the measurement packet.
• the input of the measurement packet in the second measuring computer 36 is detected.
• a so-called reception time stamp is generated.
• the sought measurement result roughly corresponds to the difference between the two time stamps and is stored by the control computer 50 in the database 52 for later visualization.
• the GPS clocks of the measuring computers 28, 36 and 46 which have already been described serve as time sources of the highest accuracy. With the aid of the GPS clocks, the measuring computers 28, 36 and 46 can generate timestamps with an error of ⁇ 0.5 ⁇ s. As time sources of the second highest accuracy, the measuring computers 28, 36 and 46 have their local clocks 34, 40 and 44 available, which are continuously synchronized by means of NTP (Network Time Protocol) to the GPS clock or the local GPS receiver.
• NTP Network Time Protocol
• the synchronization of the local clocks 34, 40 and 44 by means of NTP to the local GPS receivers of the measuring computers 28, 36 and 46 is also referred to simply as internal synchronization.
• the internal synchronization of the local clock 34 of the first measuring computer 28 is symbolized by an arrow 54.
• the local clocks 34, 40 and 44 of the measuring computers 28, 36, 46 which are synchronized by means of NTP to the internally synchronized clock of another measuring computer 28, 36, 46, serve as the third-order highest-order source. This further synchronization is referred to below as external synchronization and explained further below.
• the reception of the GPS signals for example, due to a defective GPS antenna 38 is not possible.
• internal synchronization of the local clock 40 may no longer be performed after some time.
• the first measuring computer 28 reads out the transmission time stamp from the GPS clock, that is to say the clock with the highest accuracy. This Send time stamp is written in the measurement package. Subsequently, the status "Timestamp GPS-exact" is stored in a status field.
• the first measuring computer 28 that is to say the transmitting measuring computer and the second measuring computer 36, that is to say the receiving measuring computer, there is in each case a separate area in the status field for their status entries.
• the measurement program reads out the local clock 40 of the second measurement computer 36.
• the measuring program determines whether the local clock 40 is synchronized, to which source NTP is synchronized and what the accuracy of the synchronization is. Since NTP retains the status of internal synchronization for a few minutes, the read timestamp is almost as accurate as the timestamp of a GPS watch. In the status field the value "NTP synchronized, exactly” is written, if the read accuracy is less than 1 millisecond. If the read accuracy is less than 2 milliseconds, "NTP synchronized, inaccurate" is written in the status field.
• NTP Global System for Mobile Communications
• Commit the GPS watch for a longer period eg. If you do not read anything longer than about 5 minutes, NTP automatically switches to external synchronization. In this mode, the accuracy of the read timestamps is significantly worse than with internal synchronization. It is therefore only checked if the accuracy of NTP is less than 2 milliseconds. In the status field we then wrote "NTP synchronized, inaccurate".
• the time stamp of the local clock 40 of the second measuring computer 36 is indeed written into the measuring package, but in the status field is entered a special value, so that this measurement package in the later evaluation for the
• Runtime calculation is not taken into account.
• the invention is characterized in that a readout of a time stamp from another time source is made possible even in case of failure of the GPS clock and thus the probability of failure of a measurement due to a lack of time stamp is minimized.
• Telecommunication network Switching device Switching device Switching device Switching device First measuring computer Satellite GPS antenna First measuring computer Local clock of the first measuring computer Second measuring computer GPS antenna of the second measuring recorder Local clock of the second measuring computer GPS antenna Third measuring computer Local clock of the third measuring computer Third measuring computer Measuring distance between first and second measuring computer Control computer Database internal synchronization of the local clock of the first measuring computer Internal synchronization of the local clock of the second measuring computer Internal synchronization of the local clock of the third measuring device Fault Internal synchronization of the local clock of the second measuring computer External synchronization of the local clock of the second measuring recorder

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Synchronisation In Digital Transmission Systems (AREA)
• Electric Clocks (AREA)
• Computer And Data Communications (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Position Fixing By Use Of Radio Waves (AREA)

Applications Claiming Priority (3)

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Citations (1)

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• 2002
  • 2002-03-12 DE DE10210711A patent/DE10210711A1/de not_active Ceased
• 2003
  • 2003-02-21 HU HU0500495A patent/HUP0500495A2/hu unknown
  • 2003-02-21 WO PCT/DE2003/000540 patent/WO2003077086A2/de not_active Ceased
  • 2003-02-21 PL PL03371032A patent/PL371032A1/pl not_active Application Discontinuation
  • 2003-02-21 US US10/507,097 patent/US7542537B2/en not_active Expired - Lifetime
  • 2003-02-21 JP JP2003575236A patent/JP4472994B2/ja not_active Expired - Lifetime
  • 2003-02-21 EP EP03714649A patent/EP1485780A2/de not_active Ceased
  • 2003-02-21 CA CA002475518A patent/CA2475518A1/en not_active Abandoned

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