SE512034C2 - Method and apparatus for synchronizing nodes - Google Patents

Abstract

The present invention relates to a method and apparatus for synchronising at least one node (N1-N4) in a net (n), which node (N1-N4) is used as an example for packet oriented transmission. A server (C), generating a stable frequency (fs), and the node (N1-N4) measures the number of cycles of the stable frequency (fs) respective the number of cycles of a local frequency (f1-f4), generated by the node (N1-N4). These measurements are started respective stopped at the instant of time when a phase of a signal, generated by a power network (PN) connected to the server (C) and the node (N1-N4), equals zero. The results of the measurements are compared and the node (N1-N4) is adjusted accordingly. Measurements can continuously be performed by the server (C) and the node (N1-N4).

Description

10 15 25 25 512 034 0.05 ppm (parts per million).

Each base station is connected to a power network, which network supplies the base station with power.

The local frequency generated by a local oscillator located in the base station is normally used as a local reference to generate the carrier frequencies belonging to the different radio channels of the base station.

In the case where the transmission between the network and a base station consists of information sent in packets, also called packet-oriented information, no PCM link is used and therefore the frequency of the PCM link cannot be used by the base station to synchronize the local frequency in the base station.

An example of packet-oriented information is information transmitted over an intranet / internet. In this case, an IP network (internet protocol network) is used instead of the PCM link to transport the packet-oriented information between the corresponding devices.

A known method for synchronizing the local frequency in a base station when transmitting packet-oriented information is to use highly stable furnace oscillators in each base station, which oscillators synchronize the local oscillators in the corresponding base station.

A problem with this method is that the furnace oscillators are large and expensive and they must be calibrated at regular intervals, which is an expensive task. 602, 340 disclose a system for distributing, at 41254, values of coded time or other information signals through the existing electrical network in a building by reading values of a clock in one location and formatting the read information into a suitable one. serial form. The formatted information is transmitted over the electrical network by a type of modulation via the grounded leg of the electrical network. SUMMARY OF THE INVENTION The problem addressed by the present invention is to synchronize at least one frequency in at least one node in a network, also called a network.

An object of the invention is thus to synchronize at least one frequency in at least one node in the network.

The problem is essentially solved by using the phase of a signal, generated by a power grid, connected to the node, as a reference to define a stable time interval during which time interval at least one measurement is performed of the frequency in the node to be synchronized.

Furthermore, at least one server is used which generates a stable frequency, which server is connected to the power grid and the server performs a measurement of the stable frequency during the same time interval as the measurement is performed of the frequency in the node to be synchronized.

More specifically, the problem is solved in the following way.

During the well-defined time interval, the server and the node perform at least one measurement of the number of cycles of the stable frequency generated by the server and the number of cycles of a local frequency generated by a local oscillator in the node, respectively.

When a measurement is to start, the server sends a message to the node containing information about the length of the measurement, ie. 10 15 20 25 30 5 512 034 the time interval during which the measurement is to be performed. A measurement in both the server and in the node is started and stopped, respectively, when the phase of the signal generated by the power grid PN is the same as a predefined threshold value.

The resulting calculated number of cycles of the stable frequency in the server and the local frequency in the node are compared and the oscillator in the node is adjusted accordingly.

In an alternative embodiment of the invention, measurements are performed continuously in the server and in the node.

An advantage offered by the invention is that it proposes a simple and general method for synchronizing a frequency in a node.

Another advantage is that the method according to the invention works even if there is a phase difference between the server and the node to be synchronized.

The invention will now be described in more detail with reference to exemplary embodiments and also with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows a system containing different networks according to the invention, Figs. 2a and 2b are flow charts illustrating a method according to the invention, and Fig. 3 is a block diagram schematically illustrating a node and a clock server according to the invention. 10 DETAILED DESCRIPTION OF THE EMBODIMENTS Fig. 1 shows a schematic view of a number of nodes N1-N4 in a network n, also called a network. The network n is, for example, an Internet network or a cellular network such as GSM, NMT, AMPS, UMTS. Fig. 1 shows as an example four nodes N1-N4, but of course more or fewer nodes can be located in the network n.

Each node N1-N4 is connected to a packet network IP, which in turn is connected to a mobile telephone exchange MSC. The packet network IP is, for example, an internet protocol network.

The mobile telephone exchange MSC connects the network n to other networks n2, n3 and the public telephone network PSTN, as shown in Fig. 1.

Each node N1-N4 is also connected to a power network PN, which power network PN supplies the nodes N1-N4 with power.

A local oscillator LO1-LO4 is located in each node N1-N4, which local oscillator LO1-LO4 generates a local frequency of, for example, 10 MHz. the local frequency is in turn used as a reference to generate a number of carrier frequencies in the corresponding emergency N1-N4. A carrier frequency corresponds, for example, to a radio channel in the node N1-N4.

The packet transmission units PC are, for example, connected to the nodes N1-N4 via the packet network IP, as shown in Fig. 1.

The packet transmission units PC are used to send packet-oriented information to a corresponding node N1-N4 in the network n. 10 15 20 25 30 v 512 054 The packet transmission units PC in Fig. 1 illustrate, as an example, a method of transmitting packet-oriented information to a corresponding node N1 -N4. Packet-oriented information can also be transmitted between the nodes N1-N4 and further between the mobile telephone exchange MSC and a corresponding node N1-N4, but this is not described in this example. The invention is applicable to all types of packet-oriented transmissions to and from the nodes N1-N4 in the network n.

Furthermore, packet-oriented transmission is described in the examples below to illustrate the invention, but the method according to the invention is also applicable to other types of transmissions to and from a corresponding node N1-N4 which are to be synchronized. For example, the invention could be applied for ATM transmission (asynchronous transmission mode) or for SDH / PDH transmission (synchronous digital hierarchy / plesiochronous digital hierarchy) in cases where the clock stability is poor.

A clock server C, with a stable reference frequency fs, is connected to the power network PN and the packet network IP. The clock server C is, for example, a personal computer equipped with a GPS receiver (global positioning system).

A method according to the invention is described below in connection with Figs. 1, 2a, 2b and the above examples.

The power network PN generates a signal with a frequency of, for example, 50 or 60 Hz and the moment when the phase of this signal is equal to zero, is used in this example as a reference to start and stop both a measurement of the reference frequency fs in the clock server C and of a local 10 15 20 25 30 512 054 i; frequency f1-f4 in a node N1-N4 in the network n. The said phase is used as a reference to define a stable time interval which starts and ends when the phase of said signal is equal to zero, during which time interval the measurement is performed by the reference frequency in the clock server C and of a local frequency f1-f4 in a node N1-N4.

This is done to synchronize the local frequency f1-f4 in the corresponding node N1-N4.

The phase of the mentioned signal does not necessarily have to be equal to zero to define the start and stop of the stable time interval. A threshold value close to zero or a threshold value comprising a hysteresis function could, according to the invention, also be used as a reference to trigger a start and a stop for the measurement. For simplicity, the threshold value is equal to zero in the examples described below.

Fig. 2a illustrates a flow chart of a method according to the invention.

In the following example, it is assumed that the node N1-N4, the power network PN, the packet network IP, the clock server C, the packet transmission units PC and the mobile telephone exchange MSC are located as described above.

One or more of the packet transmission units PC is assumed to communicate with a first node N1, a local frequency f1 in the first node N1 being synchronized, as will be described in this example. The first node N1 is located in the network n as shown in Fig. 1 and connected to the packet network IP and the power network PN.

Of course, the method according to the invention can be applied to more than one node at a time, i.e. more than one node N1-N4 can be synchronized simultaneously by having the clock server C send start messages and end reports as described below to more than one node at a time. For the sake of clarity, the first node N1 is synchronized, as an example, below.

In step 101, the clock server C sends a start message to the first node N1 via the packet network IP. The start message contains information about the time interval, e.g. during how many cycles of the signal generated by the power network PN, as a measurement of the local frequency f1 in the first node N1 and of the reference frequency fs in the clock server C is to be performed.

For illustrative purposes, the mentioned measurement time interval may be 180,000 cycles of the signal generated by the power grid PN.

When the clock server C in step 103 senses that the phase of the signal generated by the power network PN is equal to zero, a first measurement of the reference frequency fs is performed in the clock server C in step 105.

The clock server C performs a second measurement of the reference frequency f S in step 109 at the end of said time interval when the measurement of the reference frequency fs is to end in accordance with step 107.

The second measurement is performed when the phase of the signal generated by the power network PN is equal to zero and at the end of said time interval.

In step III, the clock server C calculates the difference between the second and the first measurement of the reference frequency fs, whereby the number of cycles of the reference frequency fs which has passed during said time interval is obtained. This result is included in a final report, which final report is sent to the first node N1 via the packet network IP in step 113.

An example of performing the measurement of the number of cycles of the reference frequency fs, generated by a reference oscillator located in the clock server C, which has passed during said time interval is described below. In this example, it is assumed that a counter (not shown in the figure) is connected to the reference oscillator. The calculator counts the number of cycles of the reference frequency fs.

When, as described above, the first measurement of the reference frequency fs in the clock server C is performed in step 105, it is in fact the value of the counter, connected to the reference oscillator, which is checked. This value, referred to below as the first value, is registered in, for example, a register.

Similarly, the value of the counter is checked when the second measurement of the reference frequency fs in the clock server C is performed in step 109, as described above. This value, hereinafter referred to as the second value, is also registered in the register.

The first and second values of the counter are checked when the phase of the signal generated by the power grid PN is equal to zero, at the start and at the end of as described above, i.e. 10 15 20 25 30 11 512 054 said time interval.

In step 111, the clock server C calculates the difference between the second and first values of the counter, whereby the number of cycles of the reference frequency fs which have passed during said time interval is obtained.

In step 115, the first node N1 receives the start message, marked in Fig. 2a with A1, which is sent from the clock server C in step 101. The first node N1 senses in step 117 when the phase of the signal generated by the power network PN is equal to zero. In step 119, the first node N1 then performs a first measurement of the local frequency f1, generated by the local oscillator LO1 in the first node N1 when said phase of the signal has been sensed to be equal to zero.

The first measurement of the local frequency f1 is performed, for example, by checking the value of the counter (not shown in the figure), connected to the local oscillator LO 1 in the first node N1. This value, hereinafter referred to as the first value, is registered in a register. The calculator counts the number of cycles of the local frequency fl.

The first node N1 performs a second measurement of the local frequency f1 in step 123 at the end of said time interval when the measurement of the local frequency f1 is to end, according to step 121. The second measurement is performed when the phase of the signal generated by the power network PN is equal to zero and at the end of said time interval. The second measurement of the local frequency f1 is, for example, performed by checking the value of said counter, connected to the local oscillator LO1. This value, hereinafter referred to as the second value, is registered in the said register.

In the next step 125, the first node N1 calculates the difference between the second and the first measurement of the local frequency f1. More specifically, it is the difference between the second and first value of the counter which is calculated, whereby the number of cycles of the local frequency f1 which have passed during said time interval is obtained. In step 127, the first node N1 receives the final report from the clock server C.

The first node N1 compares in step 129 the result in the final report from the clock server C with the result of the number of cycles of the local frequency f1 which has passed during said time interval.

If the result from the clock server C is different from the result in the first node N1 according to step 131, then the first node N1 in step 133 adjusts the local oscillator LO1 in the first node N1. An adjustment of the local oscillator LOI is performed by changing the voltage level that controls the local oscillator LO1 so that the local frequency f1 is equal to the reference frequency fs in the server C.

In another example according to the invention, several measurements of the local frequency f1 in the first node N1 are performed in order to continuously synchronize the local frequency f1 in the lg, 512 054 the first node N1. This is described below in connection with Fig. Zb.

In this example, it is assumed that a new measurement of the local frequency f1 in the first node N1 and of the reference frequency fs the clock server C is started every minute. In this example, each measurement is performed in the clock server C and in the first node N1 over a time interval of 180,000 cycles of the signal in the power network PN. Of course, this is only an example and other lengths of the time interval are, according to the invention, possible.

Initially, a first counter t is set to one in step 200. The first counter t increases by one every minute.

The process begins in step 201 whereby the clock server C sends a start message mt to the first node N1 via the packet network IP. The first counter t is equal to one the first time a start message is sent from the clock server C, the start message mt being equal to ml.

The start message includes information about the length of the time interval, e.g. during how many cycles of the signal generated by the power network PN, as a measurement of the local frequency f1 in the first node N1 and of the reference frequency fs in the clock server C is to be performed. In this example, the time interval is 180,000 cycles of the signal generated by the power grid PN, as mentioned above.

The start message further includes information about the status of the first counter t so that the node N1 and the clock server C can keep track of the number of corresponding measurements.

It is also possible to use predefined lengths for said time intervals, which lengths are known by the server C and by the first emergency N1, whereby only a start message mt must be used according to the invention to start a sequence of measurements in the clock server C and in the first nöden Nl. Start messages for starting each measurement are, however, described in these examples to better illustrate the method according to the invention.

When the clock server C in step 203 senses that the phase of the signal generated by the power network PN is equal to zero, the clock server C performs a first measurement of the reference frequency fs in the clock server C in step 205 of the measurement number t.

The first measurement of the reference frequency fs is, for example, performed by checking the value of a counter (not shown in the figure), connected to the reference oscillator in the clock server C. This value, hereinafter referred to as the first value, is registered in a register. The calculator counts the number of cycles of the reference frequency fs.

In step 207, the first counter t is checked and if it has increased by one, i.e. one minute has elapsed, the clock server C continues to send a new start message mt to the first node N1 via the packet network IP in step 201 as described above. For illustrative purposes, the new start message mt is equal to m2 the second time a start message is sent from the clock server C. 10 15 20 25 30 lg 512 034 The clock server C continues to send a new start message mt to the first node N1 via the packet network IP according to the steps here above each time t increases by one according to step 207.

In step 211, the clock server C performs a second measurement of the reference frequency fs for a measurement when said time interval for the corresponding measurement has ended and this measurement of the reference frequency fs is to end according to step 209. Said time interval is, as described above, 180,000 cycles of the signal generated by the power grid PN. The second measurement is performed when the phase of the signal, generated by the power grid PN, is equal to zero and when 180,000 cycles of this signal have passed.

The second measurement of the reference frequency fs is performed, for example, by checking the value of the mentioned counter, connected to the reference oscillator. This value, hereinafter referred to as the second value, is registered in the said register.

If said time interval has not ended according to step 209, the procedure returns to step 207 and the first counter t is checked. If the value of the first counter t has increased, the procedure returns to step 201 where a new start message mt will be sent from the clock server C.

However, if the measurement time interval has ended, the clock server C in step 213 calculates the difference between the second and the first measurement value of the reference frequency fs during a corresponding measurement. More specifically, it is the difference between the second and the first value of the counter, connected to the reference oscillator, which is calculated for the corresponding measurement, the number of cycles of the reference frequency fs which has passed during said time interval being obtained for this measurement . This result is included in a final report, corresponding to the measurement, which final report is sent to the first node N1 via the packet network IP in step 215.

In step 217, the first node N1 receives the start message, marked with A2 in Fig. 2b, for the measurement number t. The first node N1 senses in step 219 when the phase of the signal generated by the power network PN is equal to zero. In step 221, the first node N1 then performs a first measurement of the local frequency f1, generated by the local oscillator LO1 in the first node N1 of the measurement number t when said phase of the signal is sensed to be equal to zero.

The first measurement of the local frequency f1 is performed, for example, by checking the value of a counter (not shown in the figure), connected to the local oscillator LO 1 in the first node N1. This value, hereinafter referred to as the first value, is registered in a register. The calculator counts the number of cycles of the local frequency fl.

The first node N1 performs a second measurement of the local frequency f1 for a measurement in step 225 when said time interval, corresponding to the measurement, has ended and the corresponding measurement of the local frequency f1 is to end, according to step 223. The second measurement is performed when the phase of the signal generated by the power grid PN is equal to zero and when 180,000 cycles of this signal have passed.

The second measurement of the local frequency f1 is, for example, 10 15 20 25 30 1; 512 054 performed by checking the value of said counter, connected to the local oscillator LO1. This value, hereinafter referred to as the second value, is registered in said register.

In the next step 227, the first node N1 calculates the difference between the second and the first measurement of the local frequency f1 for a corresponding measurement. More specifically, it is the difference between the second and the first value of the counter, connected to the local oscillator LO1, for the corresponding measurement that is calculated, whereby the number of cycles for the local frequency f1 which has passed during said time interval is obtained, corresponding to the measurement.

In step 229, the first node N1 receives the final report from the clock server C for the corresponding measurement.

In step 231, the first node N1 compares the result in the final report from the clock server C with the result of the number of cycles of the local frequency f1 which has passed during said time interval for the corresponding measurement.

If the result from the clock server C differs from the result in the first node N1 for the corresponding measurement according to step 233, then in step 235 the first node N1 will adjust the local oscillator LO1 in the first node N1, as described above.

The process proceeds to step 207 and the process is repeated as described above during the remainder of the measurements performed in the clock server C and in the first node N1. 10 15 20 25 30 512 054 18 A certain error in the phase difference in the power grid PN can cause an error as regards the results of a measurement in the clock server C and in the first node N1. The error in the phase difference is due to the distance between the clock server C and the first node N1 and the PN topology of the power network. For example, an error in the phase difference of about 5 degrees is obtained, i.e. 1.5%, in the power grid PN between Enköping and Ringhals in Sweden.

To minimize these measurement errors, the measurements are performed in the clock server C and in the first node N1 over a long time interval according to the above example, for example during 180,000 cycles of the signal in the power network PN. This corresponds to about 60 minutes (1 cycle = l / 50 seconds - + 180,000 cycles = 3600 seconds).

An example of the precision of the method according to the invention is described below.

In this example, it is assumed that the error of the phase difference in the power grid PN is 2 degrees, 2/360 = 0.56%. gives rise to a time difference of 0.00556xl / 50 = 0.000ll ie. This phase error gives seconds = 0, ll ms between the clock server C and the first node Nl.

This time difference must be counted twice because it will occur both at start and stop of a measurement performed in the clock server C and in the first node N1.

In this example, it is further assumed that the time interval for a measurement is set to sixty minutes, i.e. 3600 seconds.

The precision obtained is then 0.1x2 ms / 3600 = 0.00000006ll%. The local oscillator LO1 in the first node N1 does not need to be adjusted after each result comparison from a measurement as described in the above example. An average value can be calculated on results from several measurements after these measurements have been performed in the clock server C and in the first node N1.

The average value is calculated as an example in the first node N1 of the results from a number of measurements in the clock server C, which results are received by the first node N1 in the corresponding final reports and on the results of corresponding measurements in the first node N1. These averages are compared in the first node N1, the local oscillator LO1 in the first node N1 being adjusted accordingly.

The results of a number of measurements can be processed in any type in filters, for example low-pass filters or Kalman filters in the first node N1 to also improve the method according to the invention.

In another embodiment of the invention, the clock server C performs the processing of the results obtained in the clock server C and in the node N1-N4 to be synchronized, the clock server C controlling the corresponding node N1-N4. This is described below in connection with the previous embodiments.

In this example, it is assumed that the local frequency fl in the first node N1 is to be synchronized. Of course, several nodes N1-N4 can be synchronized simultaneously, but for the sake of clarity, as an example, the first node N1 below is synchronized. In the following example it is also assumed that the node N1-N4 in the power network PN, the packet network IP, the clock server C, the packet transmission units PC and the mobile telephone exchange MSC are located as described above.

In the same manner as described above, the clock server C and the first node N1 perform a measurement of the reference frequency fs and of the local frequency f1, respectively, during the stable time interval when a start message is sent to the first node N1 via the packet network IP. The time interval is defined to start and end when the phase of the signal generated by the power grid PN is equal to zero, as described above.

The result obtained from the number of cycles of the local frequency f1 which has passed during said time interval is included in a report which report is sent from the first node N1 to the clock server C via the packet network IP.

The clock server C compares the result in the report from the first node N1 with the result of the number of cycles of the reference frequency fs which have passed during said time interval.

If the result from the first node N1 deviates from the result in the clock server C, the clock server C sends an adjustment message to the first node N1.

The adjustment message includes, for example, information on how much the local oscillator LO1 in the first node N1 is to be adjusted to cause the local frequency f1 to be the same as the reference frequency fs in the clock server C.

In the same manner as described in connection with Fig. 2b, several measurements can be made of the local frequency f1 in the first node N1 and of the reference frequency fs in the clock server C to continuously synchronize the local frequency f1 in the first node N1.

The clock server C may further comprise a filtering function in which results from a number of measurements, performed in the clock server C and in the first node N1, may be processed to improve the method according to the invention, the local oscillator LO1 in the first node N1 being adjusted accordingly .

The node N comprises, for example, a receiver 303, a transmitter 305, a local oscillator LO 309, a memory unit 311, a filter unit 313, a calculation unit 315, a measuring unit 307, a comparator unit 317, an adjusting unit 319, a power connector 321, a sensing unit 322 and a control unit Fig. 323, which are the components shown in 3. The receiver 303 and the transmitter 305 are connected to an antenna 301. All units are connected to each other via a data bus 300 as shown in the figure.

The measuring unit 307 in the node N is used to measure the local frequency f1, which local frequency f1 is used as a reference to generate several carrier frequencies in the node N.

The memory unit 311 stores the measurements from the measuring unit 307, results from the calculation unit 315 and in some cases results from the calculation unit 415 in the server C, which is described here below.

The calculation unit 315 in the node N calculates, for example, a difference between two measurements stored in the memory unit 311, which measurements are obtained at the start and at the end of a measurement, and an average value of the results from several measurements stored in the memory unit 311.

The power connector 321 connects the node N to the power network PN.

The sensing unit 322 in the node N senses when the phase of the signal generated by the power network PN is equal to zero.

The sensing unit 322 also performs the calculation of the cycles of the local frequency f1. In some cases, a comparator unit 317 and a filter unit 311 are located in the node N, as shown in the figure.

The comparator unit 317 is used, for example, to determine whether the result of measurements transmitted from the clock server C, as described in the above example, deviates from the result of corresponding measurements stored in the memory unit 311 in the node N.

The adjusting unit 319 adjusts the local oscillator LO 309 when necessary by changing the voltage controlling the local oscillator LO 309 so that the local frequency f1 is the same as the reference frequency fs in the server C.

The units 303, 305, 307, 311, 313, 315, 317, 317, 319, 321, 322 and 323 are connected to the data bus 300 through LO 309, which the units communicate with each other. The control unit 323 in the node N controls the various units via the data bus 300 and influences them to perform desired operations in accordance with the invention.

The clock server C comprises, for example, a sensing unit 405, a measuring unit 407, a reference oscillator 409, a memory unit 411, a calculation unit 415, a timer unit 416, a power connector 417 and a control unit 419 which are the components shown in Fig. 3. All units are connected to each other by a data bus 400 as shown in the figure.

The sensing unit 405 senses when the phase of the signal generated by the power grid PN is equal to zero.

The sensing unit 405 also performs calculation of the cycles of the reference frequency fs which stable reference frequency fs is generated by the reference oscillator 409.

The measuring unit 407 in the clock server C is used to measure the reference frequency fs.

The memory unit 411 is used, for example, to store measurements from the measuring unit 407, results from the calculation unit 415, and in some cases results from the calculation unit 315 in the node N as described above.

The calculation unit 415 calculates the difference between two measurement values stored in the memory unit 411, which measurement values are obtained at the start and at the end of a measurement and an average value of results from different measurements stored in the memory unit 411.

The timer unit 416 in the clock server C is used to operate the first counter t as described above. 10 15 20 25 30 512 034 24 The power connector 417 connects the clock server C to the power network PN.

In some cases, a comparator unit and a filter unit are located in the clock server C, but this is not shown in the figure.

In this case, the comparator unit in the clock server C is used, for example, to determine whether the result of measurements sent from the node N, as described above, differs from the result of the corresponding measurements stored in the memory unit 411 in the clock server C.

The units 405, 407, 409, 411, 415, 416, 417 and 419 are connected to the data bus 400 through which the units communicate with each other. The control unit 419 in the clock server C controls the various units via the data bus 400 and influences them to perform desired operations in accordance with the invention.

The signal generated by the power grid PN comprises a voltage part and a current part. The moment when the phase of this signal is equal to zero is used above as a reference to start and stop a measurement in the clock server C and in the nodes N1-N4. More specifically, it is the moment when the phase of the voltage part of this signal is equal to zero which is used above as a reference to start and stop a measurement in the clock server C and in the nodes N1-N4, i.e. as a reference to define the stable time interval during which a measurement is performed in the clock server C and in the nodes N1-N4.

The invention can be applied to all types of nodes where an exact frequency is required. An example is a base station. The invention as described above can be embodied in still other specific forms within the scope of its meaning or essential characteristics. Thus, the present embodiments are to be considered in all respects as illustrative and not restrictive, and the scope of the invention is set forth in the appended claims rather than in the foregoing descriptions, and all changes within the scope of the claims and in the equivalence of claims are therefore to be considered as included.

Claims (9)

A method for synchronizing at least one node (N1-N4) in a network (n), which node (N1-N4) is connected to a power network (PN) and a transmission network (IP). ), the method comprising the steps of: performing a measurement of a stable frequency (f generated S), said server being connected to (IP), by a server (C), the power grid (PN) and the transmission grid for a predetermined time interval, which time interval starts and ends when a phase of a signal, generated by the power grid (PN), corresponds to a threshold value; performing a measurement of a local frequency (f1-f4) in the node (N1-N4) during said time interval; comparing a result of the measurement obtained in the server (C) with a result of the measurement obtained in the node (N1-N4); and setting the node (N1-N4) if said result in the server (C) is different from said result in the node (N1-N4). The method of claim 1, wherein the method further comprises the step of sending a start message from the server (C) to the node (N1-N4). The method of claim 2, wherein the method further comprises the step of sending a final report from the server (C) to the node (N1-N4) when said time interval has ended, said final report comprising the result of the measurement obtained in the server (C). The method of claim 2, wherein the method further comprises the step of sending a final report from the node (N1-N4) to the server (C) when said time interval has ended, which final report comprises the result of the measurement which obtained in the node (N1-N4). A method according to claim 3, wherein the method comprises the step of allowing the node (N1-N4) to perform the comparison between said results obtained in the server (C) and in the node (N1-N4). The method of claim 4, wherein the method comprises the step of having the server (C) perform the comparison between said results obtained in the server (C) and in the node (N1-N4). A method according to claim 2, 3, 4, 5 or 6, wherein the method further comprises the step of allowing the start message to contain information about the length of said time interval for the measurement in the server (C) and for the corresponding measurement in the node (N1-N4). The method of claim 7, wherein the method further comprises the step of allowing the time interval to be a number of cycles of the signal generated by the power grid (PN). A method according to any one of claims 1-8, wherein the step of performing the measurement in the server (C) and in the node (N1-N4), respectively, comprises the following steps: sensing when the phase of the signal, generated by the power network (PN), is the same as said threshold value; to perform a first measurement of the stable frequency (fs) in the server (C) and of the local frequency (f1-f4) in the node (N1-N4) when the phase of the signal, generated by the power grid 10 15 25 25 512 034 28 (PN), is sensed to be the same as said threshold value; sensing when the phase of the signal generated by the power grid (PN) is the same as said threshold value at the end of said time interval; and performing a second measurement of the stable frequency (fs) in the server (C) and of the local frequency (f1-f4) in the node (N1-N4) at the end of said time interval when the phase of the signal, generated by the power network (PN) ), is sensed to be the same as said threshold value. A method according to claim 9, wherein the method comprises the step of allowing the result of the measurement in the server (C) to be the number of cycles of the stable frequency (f) which has passed during said time interval, and allowing the result of the measurement in the node (N1). N4) be the number of cycles of the local frequency (f1-f4) that have passed during said time interval. ll. A method according to any one of claims 1-10, wherein the method comprises the step of allowing the local frequency (f1-f4) to be generated by an oscillator (LO1-LO4) located in the node. The method of claim 11, wherein the step of setting the node (N1-N4) comprises setting the oscillator (LOI-LO4) in the node (N1-N4) by changing a voltage controlling the oscillator (LO1-LO4) so that it the local frequency (fl-f4) becomes the same as the stable frequency (f) in the server (C). A method according to any one of claims 1 to 12, wherein the method comprises the step of making said threshold value equal to zero. A method for synchronizing at least one node (N1-N4) in a network (n), which node (N1-N4) is connected to a power network, which method (PN) and a transmission network (IP), comprises the following steps: performing a measurement of a stable frequency (f generated S), said server being connected to (IP), (C), (PN) aV the SGIVEI power network and the transmission network during a predetermined time interval, which time interval starts and ends when a phase of a signal, generated by the power grid (PN), is the same as a threshold value; performing a measurement of a local frequency (f1-f4) in the node (N1-N4) during said time interval; comparing a result of a measurement obtained in the server (C) with a result of a corresponding measurement obtained in the node (N1-N4); and setting the node (N1-N4) if said result in the server (C) is different from said result in the node (N1-N4) for the corresponding measurement. The method of claim 14, wherein the method further comprises the step of sending a start message (mt) from the server (C) to the node (N1-N4). The method of claim 15, wherein the start message (mt) is transmitted from the server (C) to the node (N1-N4) at predetermined intervals, the start message (mt) corresponding to a measurement. The method of claim 15 or 16, the method further comprising the step of sending a final report from the server (C) to the node (N1-N4) when said time interval for a measurement has ended, the final report comprising the result of the corresponding measurement obtained in the server (C) and an identity for the corresponding measurement. The method of claim 15 or 16, wherein the method further comprises the step of sending a final report from the node (N1-N4) to the server (C) when said time interval for a measurement has ended, the final report comprising the result of the corresponding measurement obtained in the node (N1-N4) and an identity of the corresponding measurement. The method of claim 17, wherein the method comprises the step of allowing the node (N1-N4) to perform the comparison between said results obtained in the server (C) and in the node (N1-N4). The method of claim 18, wherein the method comprises the step of having the server (C) perform the comparison between said results obtained in the server (C) and in the node (N1-N4). A method according to claim 15, 16, 17, 18, 19 or 20, wherein the method further comprises the step of allowing the start message (mt), corresponding to a measurement, to contain information about the length of said time interval for the measurement in the server (C) and for the corresponding measurement in the node (N1-N4). The method of claim 21, wherein the method further comprises the step of allowing the time interval to be a number of cycles of the signal generated by the power grid (PN). A method according to any one of claims 14-22, wherein the step of performing the measurement in the server (C) and in the node (N1-N4), respectively, comprises the following steps: sensing when the phase of the signal, generated by the power grid (PN), is the same as said threshold value; to perform a first measurement of the stable frequency (fâ) in the server (C) and of the local frequency (f1-f4) in the node (N1-N4) when the phase of the signal, generated by the power network (PN), is sensed to be same as said threshold value; sensing when the phase of the signal, generated by the power grid (PN), is the same as said threshold value at the end of said time interval; and performing a second measurement of the stable frequency (fs) in the server (C) and of the local frequency (f1-f4) in the node (N1-N4) at the end of said time interval when the phase of the signal, generated by the power network (PN) ), is known to be the same as said threshold value. The method of claim 23, wherein the method comprises the step of allowing the result of a measurement in the server (C) to be the number of cycles of the stable frequency (fs) that have passed during said time interval for the corresponding measurement, and allowing the result of a measurement in the node (N1-N4) is the number of cycles of the local frequency (f1-f4) that have passed during said time interval for the corresponding measurement. The method of claim 24, wherein the method further comprises the steps of: processing a result, from a predetermined number of measurements performed in the server (C), in a filter; processing a corresponding result, from the predetermined number of corresponding measurements made in the node (N1-N4), in the filter; allowing the step of comparing said results obtained in the server (C) and in the node (N1-N4) for a corresponding measurement to comprise the step of comparing said results from the filter for the corresponding predetermined number of measurements; and allowing the step of setting the node (N1-N4) if said result in the server (C) is different from said result in the node (N 1. -N4) for the corresponding measurement include the step of setting the node (N1-N4) if said result from the filter deviates from each other for the corresponding predetermined number of measurements. The method comprising the step of including the node (N1-N4) with the filter. The method of claim 25, The method of claim 25, wherein the method comprises the step of allowing the server (C) to include the filter. The method of claim 26 or 27, wherein the method comprises the step of allowing the filter to be an average filter, a low pass filter or a Kalman filter. A method according to any one of claims 14-28, wherein the method comprises the step of allowing the local frequency (f1-f4) to be generated by an oscillator (LO1-LO4) located in the node - A method according to claim 29, wherein the step of setting the node (N1-N4) comprises adjusting the oscillator (LO1-LO4) in the node (N1-N4) by changing a voltage that controls the oscillator (LO1-LO4) so that the local frequency (fl-f4) 10 15 20 25 30 33 512 034 becomes the same as the stable frequency (fi server (C). S) 31. A method according to any one of claims 14-30, wherein the method comprises the step of making said threshold value equal to zero. 3 Device in a network with a power network (PN) (n), which device is connected and a transmission network (IP), wherein at least one measurement is performed by a local frequency (f1-f4) in the device during a predetermined time interval, which time interval starts and ends when a phase of a signal, generated by the power network (PN), is the same as a threshold value, the device comprising receiving means (303) for receiving signals from the network (n); (305) (n); transmitter means for transmitting signals to the network measuring means (307) for measuring the local frequency (f1-f4); oscillator means (LO 309) for generating the local frequency (fl-f4); (315) for calculating a difference between two measurements stored in a memory means (311), which measurements calculation means are obtained at the start and at the end of a measurement; memory means (311) for storing measurements performed by the measuring means (307) and the results from the calculation means (315): setting means (319) for setting the oscillator means (LO 309); sensing means (322) for sensing when the phase of the signal, (PN), is the same as the threshold value and generated by the power grid for calculating the cycles of the local frequency (f1-f4); and control means (323) for controlling said means. 3 The device of claim 32, wherein the device further comprises filter means (313) for processing the results of a number of measurements; and comparator means (317) for determining whether the results of the corresponding measurements are different. 3 The apparatus of claim 32 or 33, wherein the calculating means (315) calculates an average of results from several measurements. 3 Device according to claim 32, 33 or 34, wherein said time interval is a number of cycles of the signal, generated by the power grid (PN). 3 The device of claim 32, 33, 34 or 35, wherein said setting means (319) changes a voltage controlling the oscillator (LO1-LO4). 3 The device of claim 36, wherein said threshold value is equal to zero. which server device is (IP), (H), (PN) 3 A server device in a network connected to a power network and a transmission network, wherein at least one measurement is performed by a reference frequency (f) in the server device during a predetermined time interval, which time interval starts and ends when a phase of a signal generated by the power network (PN) , is the same as a threshold value, the server device comprising (407) measuring means for measuring the reference frequency (fS); oscillator means (409) for generating the reference frequency (fs); calculating means for calculating a difference between two (415) 512 054 measurements stored in a memory means (411), which measurements are obtained at the start and at the end of a measurement; (411) memory means for storing measurements performed by the measuring means (407) and results from the calculating means (4115); sensing means (405) for sensing when the phase of the signal, (PN), generated by the power grid is the same as the threshold value and for calculating the cycles of the reference frequency (fs); and control means (419) for controlling said means. 3 The server device of claim 38, wherein the server device further comprises filter means for processing results from a plurality of measurements; and comparison means for determining whether the results of the corresponding measurements are different. The server device of claim 38 or 39, wherein the computing means (415) calculates an average value of results from several measurements. The server device of claim 38, 39 or 40, wherein said time interval is a number of cycles of the signal generated by the power grid (PN). The server device of claim 41, wherein said threshold value is equal to zero.