JP2004088394A - Clock information transfer system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of a conventional clock information transfer system wherein it is required to distribute TCM (time compression multiplexing) switching timing information (400Hz clock) through other line than a transmission line in order to assure the line quality due to a crosstalk between metallic subscriber lines in the case of the TCM-ISDN and it is required to separate a TCM-ISDN metallic line for directly containing an exchange station from a TCM-ISDN metallic line contained in other LT (line terminator) for preventing interference when the LT is installed in an area where no wiring is available. <P>SOLUTION: TCM switching timing information is mapped with a downlink frame between an exchange station side 110 and an LT side 120 and a distance measurement frame transmission is detected to measure a propagation delay time between the exchange station side 110 and the LT side 120, and a clock (400Hz) phase control section 129 corrects a phase shift of a TCM switching timing by the propagation delay time. Thus, the phase of the TCM switching timing of the exchange station side 110 is matched with the phase of the TCM switching timing at the LT side 120. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock information transfer system, and more particularly to interference suppression between metal subscriber lines in a system that provides an Integrated Services Digital Network (ISDN) service using a Telecommunications Technology Committee (TTC) standard G961. Related to clock synchronization systems.
[0002]
[Prior art]
In general, the accommodation form of the ISDN line is classified into a direct accommodation of the exchange station and a remote accommodation such as a CT / RT (Central Terminal / Remote Terminal System) or FTTC (Fiber-to-the-Curb). In the case of the CT / RT system in the form of remote accommodation, the DCS (clock distribution device) supplies the RT device with TCM (Time Compression Multiplex: time division direction control transmission system) switching timing information (400 Hz).
[0003]
A conventional technique related to such a technical field is disclosed in, for example, "Digital Subscriber Line Transmission System" in Japanese Patent Application Laid-Open No. H11-341153. In this publication, a synchronization means for transmitting a synchronization signal indicating a phase of a ping-pong transmission signal on an adjacent transmission line to an opposing subscriber communication apparatus is provided in the station side communication apparatus, and the ping-pong transmission of the adjacent transmission path in the opposing apparatus is performed. Disclosed is a digital subscriber line transmission system including noise level detection means for detecting a section distribution of crosstalk noise from a signal in a station side communication device and a subscriber side communication device.
[0004]
FIG. 4 is a system configuration diagram of a conventional clock information transfer system in the case of the FTTC system with a PDS (passive double star) configuration. This system includes three DSUs (Digital Service Units) 11 to 13, LTs (transmission path terminating devices) 14, 15, an SLT 16, an exchange 17, and a DCS 18. The DSU 11 and the exchange 17 are connected by a G961 metal transmission line 21. Also, the GSU1 metal transmission lines 22 and 23 are connected between the DSU 12 and the LT 14 and between the DSU 13 and the LT 15, respectively. On the other hand, between the LT 14 and the SLT 16 and between the LT 15 and the SLT 16 are connected by optical subscriber lines 24 and 25, respectively. The output of the SLT 16 is connected to the exchange 17. The output of DCS 18 is supplied to SLT 16 and exchange 17.
[0005]
As shown in FIG. 4, there is interference between the metal transmission lines 21 to 23. The TCM switching timing information is not supplied from the DCS 18 to the LTs 14 and 15. FIG. 5 is a timing chart of the system shown in FIG. FIG. 5A shows signals on the metal subscriber line in the DSU 11. FIG. 5B shows a signal on the metal subscriber line in the DSU 12. FIG. 5C shows a signal on the metal subscriber line in the DSU 13. Here, the delay between DCS 18 and SLT 16 is delayed 1, the delay in SLT 16 is delayed 2, the delay between SLT 16 and LT 14 is delayed 31, the delay between SLT 16 and LT 15 is delayed 32, and the delay in LT 14 and LT 15 is delayed 4 And In this case, as shown in FIG. 5, the signal on the subscriber line at DSU 12 has a delay time of T1 = delay 1 + delay 2 + delay 31 + delay 4 with respect to the signal on the subscriber line at DSU 11. On the other hand, the signal on the subscriber line at DSU 13 has a delay time of T2 = delay 1 + delay 2 + delay 32 + delay 4 with respect to the signal on the subscriber line at DSU 11. Therefore, since the TCM switching timings do not coincide with each other and are affected by interference, it is necessary to separate the TCM switching timing from the ISDN line accommodated in another system.
[0006]
[Problems to be solved by the invention]
The conventional clock information transfer system as described above has the following problems. First, extra capital and maintenance costs are incurred. The reason is that in the case of TCM-ISDN, switching timing of TCM (Time Division Direction Control Transmission System) must be performed simultaneously in order to secure line quality due to crosstalk between metal subscriber lines. This is because (400 Hz clock) is distributed by a route wiring different from the transmission line.
[0007]
Second, the line design becomes complicated. The reason is that when the above-described LT is installed in an area where the 400 Hz clock cannot be distributed due to the network configuration based on FTTC (Fiber-to-the-Curb) or FTTB (Fiber-to-the-Building), the exchange station is directly connected. This is because it is necessary to separate a metal line between the accommodated TCM-ISDN line and the TCM-ISDN line accommodated by another LT in order to prevent interference.
[0008]
[Object of the invention]
The present invention has been made in view of the above-mentioned problems of the related art, and has a TCM switching timing clock phase for preventing interference between TCM-ISDN metal lines of different systems being the same as a clock phase directly accommodated in an exchange station. Therefore, an object of the present invention is to provide a clock information transfer system realized without using a line other than a transmission line.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the clock information transfer system according to the present invention employs the following characteristic configuration.
[0010]
(1) means for transferring and detecting the phase synchronization timing information, means for detecting the phase difference between the devices installed at different points in the phase synchronization timing information, and means for controlling the phase difference between the devices. Clock information transfer system comprising: means for matching phases.
[0011]
(2) The clock information transfer system according to (1), wherein the transfer of the phase synchronization timing information is shared with a subscriber transmission line.
[0012]
(3) Clock information in a TCM (Time Division Direction Control Transmission) system including an exchange station side and an LT (Transmission Line Terminating Equipment) side connected by an upstream transmission line and a downstream transmission line each having a driver and a receiver at both ends. In the transfer system,
A clock phase information generation unit, a downlink transmission phase control unit, a distance measurement unit, clock phase information from the clock phase information generation unit, and a downlink transmission line frame transmission phase from the downlink transmission phase control unit on the exchange side. A multiplexing unit that multiplexes information and distance information from the distance measurement unit and outputs the multiplexed information to a driver of the downlink transmission line, wherein the distance measurement unit transmits downlink transmission line frame transmission phase information from the downlink transmission phase control unit. And a distance measurement frame from the upstream transmission path to obtain the distance information and transfer the distance information to a clock phase control unit provided on the LT side.
[0013]
(4) The transmission line clock, clock phase information, and distance information from the transmission line clock extraction unit, the clock information extraction unit, and the distance information extraction unit are input to the clock phase control unit on the LT side, respectively. ) Clock information transfer system.
[0014]
(5) A downlink frame synchronization detection unit, a distance measurement frame transmission request extraction unit, and a downlink frame phase from the downlink frame synchronization detection unit and a distance measurement from the distance measurement frame transmission request extraction unit to the receiver of the downlink transmission line. The clock information transfer system according to (3) or (4), further comprising: a distance measurement frame generation unit that inputs frame transmission request information and outputs the frame transmission request information to a driver of the upstream transmission path.
[0015]
(6) The clock information transfer system according to (3) or (4), further comprising: a downlink frame synchronization detection unit connected between the receiver of the downlink transmission line and the driver of the uplink transmission line; and an uplink frame generation unit.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the configuration and operation of a clock information transfer system according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
First, FIG. 1 shows a system configuration diagram of a first embodiment of a clock information transfer system according to the present invention. This clock information transfer system 100A includes a switching center 110A and an LT 120A. The exchange station side 110A includes a receiver 111, a distance measurement unit 112, a downlink transmission phase control unit 113, a 400 Hz phase information generation unit 114, a multiplexing unit 115, and a driver 116. On the other hand, the LT side 120A includes a driver 121, a distance measurement frame generation unit 122, a distance measurement frame transmission request extraction unit 123, a downlink frame synchronization detection unit 124, a receiver 125, a transmission line clock extraction unit 126, a 400 Hz information extraction unit 127, It includes an information extraction unit 128 and a 400 Hz phase control unit 129.
[0018]
At the exchange station 110A, the input 400 Hz clock is input to the 400 Hz phase information generation section 114 and the 400 Hz phase information is output to the multiplexing section 115. The downlink transmission phase control unit 113 determines the transmission phase of the downlink transmission path frame, and is connected to the multiplexing unit 115 and the distance measurement unit 112. The multiplexing unit 115 multiplexes the synchronization frame bit based on the transmission phase information of the downlink transmission line frame, multiplexes the distance measurement frame transmission request information for the LT 120A, the 400 Hz phase information and the distance information, and outputs the downlink transmission line output driver 116 Output to On the other hand, the signal received via the uplink transmission path is demodulated by the receiver 111 and input to the distance measurement unit 112. The distance measuring unit 112 calculates the arrival time of the uplink transmission path reception signal from the uplink receiver 111 from the reception of the downlink transmission phase information, and generates distance information.
[0019]
On the other hand, the LT side 120A demodulates the signal received via the downlink transmission path by the receiver 125. Then, it is connected to a transmission path extraction clock unit 126, a 400 Hz information extraction unit 127, a distance information extraction unit 128, a downlink frame synchronization detection unit 124, and a distance measurement frame transmission request extraction unit 123. The transmission line clock, the 400 Hz phase information, and the distance information extracted by the transmission line extraction clock unit 126, the 400 Hz information extraction unit 127, and the distance information extraction unit 128 are input to the 400 Hz phase control unit 129 and generate an output 400 Hz clock. I do.
[0020]
The downlink frame phase detected by the downlink frame synchronization detector 124 and the distance measurement frame transmission request information detected by the distance measurement frame transmission request extractor 123 are input to the distance measurement frame generator 122. The distance measurement frame generated by the distance measurement frame generation unit 122 is input to the driver 121 and output to the upstream transmission path.
[0021]
Next, the operation of the clock information transfer system 100A shown in FIG. 1 will be described. The exchange station side 110A is input from the input 400 Hz clock to the 400 Hz phase information generation unit 114 and outputs 400 Hz phase information. The transmission phase information of the downlink transmission line frame generated by the downlink transmission phase control unit 113 is input to the multiplexing unit 115 and the distance measurement unit 112. This downlink transmission line frame transmission phase information is the absolute time 1 at the exchange station side 110A. The multiplexing unit 115 inserts a synchronization frame bit based on the transmission phase information of the downlink transmission line frame, and multiplexes distance measurement frame transmission request information to the LT side 120A, 400 Hz phase information, and distance information from the distance measurement unit 112. The signal is modulated by the downlink transmission path output driver 116 and output to the LT side 120A via the downlink transmission path. At this time, the distance information has a default value (for example, zero) before the distance measurement.
[0022]
The LT side 120A demodulates the signal received via the downlink transmission path by the receiver 125. Then, the transmission line clock, 400 Hz phase information, and downlink frame are extracted by a transmission line clock extraction unit 126, a 400 Hz information extraction unit 127, a downlink frame synchronization detection unit 124, a distance measurement frame transmission request extraction unit 123, and a distance information extraction unit 128, respectively. Phase and distance measurement frame transmission request information and distance information are detected. When a distance measurement frame transmission request is received, the LT side 120A sets the detected downlink transmission line frame phase to the absolute time 2, modulates the distance measurement frame by the driver 121, and switches the switching station side 110A via the uplink transmission line. To send to.
[0023]
On the exchange station side 110A, the time until the distance measurement frame demodulated by the receiver 125 is detected by the distance measurement unit 112 is compared with the absolute time 1. Distance information can be calculated from the time of the difference that is the result of this comparison. It should be noted here that the time difference is twice as large as the actual distance since the transmission path is going up and down round trip. The distance information obtained here is transferred to the LT side 120A, where the transmission line clock, 400 Hz phase information, and the distance information are input to the 400 Hz phase control unit 129. Since the difference between the absolute time 1 and the absolute time 2 is known from the distance information, the 400 Hz phase control unit 129 corrects the 400 Hz phase information by the distance information to obtain the 400 Hz clock phase having the same phase as the 400 Hz clock phase of the switching station 110A. A clock can be generated.
[0024]
Next, FIG. 2 is a system configuration diagram of a second embodiment of the clock information transfer system according to the present invention. Among the components of the clock information transfer system 100B, the same reference numerals are used for components corresponding to the components of the clock information transfer system 100A described above for convenience of explanation. The clock information transfer system 100B includes an exchange station side 110B and an LT side 120B. The exchange station side 110B includes a receiver 111, an uplink frame synchronization detection unit 117, a distance measurement unit 112, a downlink transmission phase control unit 113, a 400 Hz phase information generation unit 114, a multiplexing unit 115, and a driver 116. On the other hand, the LT side 120B includes a driver 121, an uplink frame generation unit 130, a downlink frame synchronization detection unit 124, a receiver 125, a transmission line clock extraction unit 126, a 400 Hz information extraction unit 127, a distance information extraction unit 128, and a 400 Hz phase control unit 129. Includes
[0025]
The clock information transfer system 100B shown in FIG. 2 is characterized in that an upstream transmission frame can be used as a distance measurement frame without using a distance measurement frame. Thereby, the distance measurement frame transmission request extraction unit 123 in FIG. 1 can be deleted.
[0026]
Next, FIG. 3 is a system configuration diagram of a third embodiment of the clock information transfer system according to the present invention. The clock information transfer system 200 is a basic configuration diagram in which the technology shown in FIG. 1 or FIG. 2 is applied to an ISDN line of the CT / RT system. The switching system 210 includes a pair of LTs (transmission line terminating devices) 220A and 220B, an SLT 230, a DCS 240, and three DSUs 250A to 250C. The clock phases based on the delay time difference between the transmission paths of the LTs 220A and 220B are made to match by providing a phase control unit and a distance measurement unit.
[0027]
The configuration and operation of the preferred embodiment of the clock information transfer system according to the present invention have been described above in detail. However, such an embodiment is merely an example of the present invention, and does not limit the present invention in any way. It will be readily apparent to those skilled in the art that various modifications and changes can be made in accordance with the particular application without departing from the spirit of the invention. For example, the clock need not always be 400 Hz, and can be applied to clocks of other frequencies.
[0028]
【The invention's effect】
As will be understood from the above description, the clock information transfer system of the present invention has the following remarkable practical effects. First, capital investment and maintenance costs can be reduced. The reason is that the distribution of TCM switching timing information (400 Hz clock) between different LTs does not need to be wired separately from the transmission line.
[0029]
Second, the line design becomes easy. The reason is that the TCM switching timing information (400 Hz clock) between different LTs has the same phase, so that it is not necessary to consider interference on the TCM-ISDN line.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a first embodiment of a clock information transfer system according to the present invention.
FIG. 2 is a system configuration diagram of a second embodiment of a clock information transfer system according to the present invention.
FIG. 3 is a system configuration diagram of a third embodiment of a clock information transfer system according to the present invention using an ISDN line of a CT / RT system.
FIG. 4 is a configuration diagram of a general ISDN line system in an FTTC mode using a PDS scheme.
FIG. 5 is a phase diagram for explaining the operation of the ISDN line system shown in FIG. 4;
[Explanation of symbols]
100A, 100B Clock information transfer system 110A, 110B Switching station side 111, 125 Receiver 112 Distance measuring unit 113 Downstream transmission phase control unit 114 Clock (400 Hz) phase information generation unit 115 Multiplexing unit 116, 121 Driver 120A, 120B LT (transmission path) Terminating device) side 123 distance measurement frame transmission request extraction unit 124 downlink frame synchronization detection unit 126 transmission line clock extraction unit 127 clock (400 Hz) information extraction unit 128 distance information extraction unit 129 clock (400 Hz) phase control unit 130 upstream frame generation unit

Claims (6)

Means for transferring and detecting the phase synchronization timing information; means for detecting the phase difference between the devices installed at different points of the phase synchronization timing information; and controlling the phase difference to match the phases between the devices. Clock information transfer system. The clock information transfer system according to claim 1, wherein the transfer of the phase synchronization timing information is shared with a subscriber transmission line. In a clock information transfer system using a TCM (time division direction control transmission) system, the switching center includes an exchange station side and an LT (transmission path terminating device) side connected by an upstream transmission line and a downstream transmission line each having a driver and a receiver at both ends. ,
A clock phase information generation unit, a downlink transmission phase control unit, a distance measurement unit, clock phase information from the clock phase information generation unit, and a downlink transmission line frame transmission phase from the downlink transmission phase control unit on the exchange side. A multiplexing unit that multiplexes information and distance information from the distance measurement unit and outputs the multiplexed information to a driver of the downlink transmission line, wherein the distance measurement unit transmits downlink transmission line frame transmission phase information from the downlink transmission phase control unit. And a distance measurement frame from the upstream transmission path, and obtains the distance information and transfers the distance information to a clock phase control unit provided on the LT side. The transmission line clock, clock phase information, and distance information from a transmission line clock extraction unit, a clock information extraction unit, and a distance information extraction unit, respectively, are input to the clock phase control unit on the LT side. Item 4. The clock information transfer system according to Item 3. A downlink frame synchronization detection unit, a distance measurement frame transmission request extraction unit, and a downlink frame phase from the downlink frame synchronization detection unit and a distance measurement frame transmission request from the distance measurement frame transmission request extraction unit. The clock information transfer system according to claim 3, further comprising: a distance measurement frame generation unit that inputs information and outputs the information to a driver of the uplink transmission path. The clock information transfer system according to claim 3, further comprising: a downlink frame synchronization detection unit connected between a receiver of the downlink transmission line and a driver of the uplink transmission line; and an uplink frame generation unit.

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