WO2006100781A1 - セル分解装置、セル組立装置、およびクロック再生方法 - Google Patents
セル分解装置、セル組立装置、およびクロック再生方法 Download PDFInfo
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- WO2006100781A1 WO2006100781A1 PCT/JP2005/005424 JP2005005424W WO2006100781A1 WO 2006100781 A1 WO2006100781 A1 WO 2006100781A1 JP 2005005424 W JP2005005424 W JP 2005005424W WO 2006100781 A1 WO2006100781 A1 WO 2006100781A1
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/062—Synchronisation of signals having the same nominal but fluctuating bit rates, e.g. using buffers
- H04J3/0632—Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5638—Services, e.g. multimedia, GOS, QOS
- H04L2012/5646—Cell characteristics, e.g. loss, delay, jitter, sequence integrity
- H04L2012/5652—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly
- H04L2012/5653—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly using the ATM adaptation layer [AAL]
- H04L2012/5654—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly using the ATM adaptation layer [AAL] using the AAL1
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5638—Services, e.g. multimedia, GOS, QOS
- H04L2012/5664—Support of Video, e.g. MPEG
Definitions
- the present invention relates to a cell disassembly device, a cell assembly device, and a clock recovery method used when a source signal is multiplexed into a fixed-length cell and transmitted through a network, and in particular, a clock whose source signal is asynchronous to the network.
- the present invention relates to a cell disassembling device, a cell assembling device, and a clock recovery method that are applied in the case of having.
- AAL ATM Adaptation Layer
- RTS Residual Time Stamp
- Patent Document 1 Japanese Patent Laid-Open No. 10-242979 (paragraph numbers [0016] one [0020], FIG. 1) Disclosure of the Invention
- the present invention has been made in view of the above points, and even when the synchronization clock of the transmission network is unstable, it is possible to stably reproduce the clock of the source signal multiplexed and transmitted.
- An object of the present invention is to provide an apparatus for disassembling a gas.
- Another object of the present invention is to stably reproduce the source signal clock on the receiving side even when the source signal is multiplexed and transmitted in a cell when the synchronization clock of the transmission network is unstable.
- An object of the present invention is to provide a cell assembling apparatus.
- Another object of the present invention is to provide a clock recovery method capable of stably recovering a multiplexed source signal clock even when the synchronization clock of the transmission network is unstable. It is.
- a cell disassembly apparatus 10 as shown in FIG. 1 is provided.
- This cell disassembly device 10 is a device that separates and reproduces a source signal having an asynchronous clock in the network 30 from fixed-length cells received through the network 30, and transmits the clock of the source signal at regular intervals.
- the transmission timing information obtained by converting the timing with the transmission timing of the synchronous clock of the network 30 is separated from the received cell, and between the adjacent transmission timing information from the timing information separation circuit 11
- a timing information replacement circuit 12 that averages the difference values in predetermined time units and replaces the transmission timing information based on the averaged difference values;
- a clock generation circuit 13 for generating a clock of the source signal based on the converted transmission timing information.
- the source signal is input according to a clock that is not synchronized with the network 30 to be transmitted. Then, the transmission timing information power obtained by converting the transmission timing of the source signal clock at regular intervals with the transmission timing of the synchronous clock of the network 30 is multiplexed to the cell and transmitted to the network 30.
- the timing information separation circuit 11 of the cell disassembly device 10 separates the transmission timing information from the received cell.
- the timing information replacement circuit 12 receives the supplied transmission timing information, averages the difference value between adjacent transmission timing information in a predetermined time unit, and replaces the transmission timing information based on the averaged difference value. . This suppresses fluctuations in transmission timing information.
- the clock generation circuit 13 generates a clock of the source signal multiplexed in the cell based on the transmission timing information replaced by the timing information replacement circuit 12.
- a cell assembling apparatus for multiplexing a source signal having an asynchronous clock in a transmission network and transmitting the source signal to a fixed-length cell.
- a timing information generating circuit that generates transmission timing information obtained by converting transmission timing of the clock of the source signal at regular intervals with transmission timing of the synchronous clock of the network; and the transmission timing adjacent from the timing information generating circuit.
- a difference value between the information is averaged in a predetermined time unit, the timing information replacement circuit that replaces the transmission timing information based on the averaged difference value, and the replaced timing information together with the source signal in the cell.
- a cell assembling apparatus comprising a cell multiplexing circuit for multiplexing is provided.
- the timing information generation circuit generates transmission timing information obtained by converting the transmission timing of the clock of the source signal at regular intervals with the transmission timing of the synchronous clock of the network.
- the timing information replacement circuit averages the difference value between adjacent transmission timing information of the timing information generation circuit power in a predetermined time unit, and replaces the transmission timing information based on the averaged difference value. Thereby, the fluctuation
- the cell multiplexing circuit uses the timing information replaced by the timing information replacement circuit as the source signal. Multiplexed together with the cell in the cell.
- transmission timing information separated from a received cell is replaced based on a value obtained by averaging difference values between adjacent transmission timing information in units of a predetermined time.
- fluctuations in the transmission timing information are suppressed, and a clock of the source signal multiplexed in the cell is generated based on the transmission timing information. Therefore, even when transmission timing information is generated on the cell transmission side based on an unstable network synchronization clock, the received cell power can stably reproduce the clock of the source signal.
- the generated transmission timing information is replaced based on a value obtained by averaging the difference values between adjacent transmission timing information in a predetermined time unit.
- the transmission timing information is multiplexed into the cell.
- the clock of the source signal multiplexed in the cell is recovered based on the transmission timing information in which fluctuations are suppressed. Therefore, even when transmission timing information is generated based on the unstable clock of an unstable network, the clock of the source signal can be stably reproduced from the cell on the receiving side.
- FIG. 1 is a diagram illustrating an outline of a cell disassembling apparatus to which the present invention is applied.
- FIG. 2 is a diagram showing a configuration example of a network system according to the first embodiment.
- FIG. 3 is a diagram showing a data structure of an ATM cell transmitted to an ATM network.
- FIG. 4 is a diagram showing an internal configuration of a CLAD of an ATM apparatus on the transmission side according to the first embodiment.
- FIG. 5 is a diagram showing an internal configuration of a CLAD of the ATM device on the receiving side according to the first embodiment.
- FIG. 6 is a diagram showing a numerical example according to the first RTS replacement processing example.
- FIG. 7 is a diagram showing an example of a conversion table.
- FIG. 8 is a diagram showing a numerical example according to a second RTS replacement processing example.
- FIG. 9 is a diagram showing an internal configuration of a CLAD of an ATM apparatus on the transmission side according to a second embodiment.
- FIG. 10 is a diagram showing a numerical example of RTS generated by CLAD on the transmission side according to the second embodiment.
- FIG. 11 is a diagram showing an internal configuration of a CLAD of an ATM apparatus on the receiving side according to a second embodiment.
- FIG. 12 is a diagram showing an internal configuration of a CLAD of an ATM apparatus on the transmission side according to a third embodiment.
- FIG. 13 is a diagram showing an internal configuration of a CLAD of an ATM apparatus on the receiving side according to a fourth embodiment.
- FIG. 14 is a diagram showing an example of the internal configuration of a fluctuation frequency measurement circuit.
- FIG. 15 is a timing chart showing an example of a transmission signal in the fluctuation frequency measurement circuit.
- FIG. 16 is a diagram showing a numerical example of RTS in CLAD on the receiving side according to the fourth embodiment.
- FIG. 17 is a diagram illustrating a configuration example of a network system according to a fifth embodiment.
- FIG. 18 is a diagram showing an example of the internal configuration of a CLAD of an ATM apparatus on the receiving side according to a fifth embodiment.
- FIG. 19 is a timing chart showing a setting example of input / output data and replacement period in CLAD on the receiving side according to the fifth embodiment.
- FIG. 1 is a diagram for explaining the outline of a cell disassembling apparatus to which the present invention is applied.
- a cell disassembling apparatus 10 shown in FIG. 1 is an apparatus for receiving a cell transmitted from a cell assembling apparatus 20 through a network 30, and separating and outputting a source signal multiplexed in the cell.
- the network 30 is one in which data is transmitted by a fixed-length cell such as an ATM system.
- the source signal to be transmitted is, for example, a CBR signal transmitted at a constant speed, and a clock independent of the network 30 synchronization clock is used. Have.
- the cell device 20 sets the transmission timing of the source signal clock at regular intervals. Transmission timing information converted by the transmission timing of the synchronous clock is generated, and this transmission timing information is multiplexed with the source signal and transmitted to the cell. As a result, the cell decomposition apparatus 10 on the receiving side can regenerate the clock of the source signal based on the transmission timing information, and can regenerate the source signal using this clock.
- the synchronization clock power of the network 30 may become unstable due to frequency fluctuations.
- the cell assembly device 20 receives the source signal, if the synchronization clock of the network 30 is unstable, even if the clock of the original source signal is stable, the synchronization clock of the network 30 is used.
- the transmission timing information generated in the period does not have a constant period.
- the synchronization signal of the source signal reproduced based on unstable transmission timing information also becomes unstable, so that the output quality of the source signal is deteriorated or the source signal cannot be output. Then, the situation will occur.
- the cell disassembly device 10 of FIG. 1 has a function of stabilizing the transition (change) of transmission timing information separated from the cell force, and is based on stable transmission timing information. By regenerating the clock of the source signal, the recovered clock is stabilized and the output quality of the source signal is further improved.
- the cell disassembly device 10 includes a timing information separation circuit 11, a timing information replacement circuit 12, a clock generation circuit 13, and a source signal output circuit 14.
- the timing information separation circuit 11 separates the transmission timing information from the cell received through the network 30 and supplies it to the timing information replacement circuit 12.
- the timing information replacement circuit 12 replaces the transmission timing information from which the cell power is also separated based on a value obtained by averaging the difference values between the adjacent transmission timing information in a predetermined time unit. As a result, the fluctuation of the difference value during the predetermined time is smoothed around the difference average value, and the value of the transmission timing information increases (or decreases) linearly.
- the clock generation circuit 13 is a transmission timing replaced by the timing information replacement circuit 12. Based on the information, a clock of the source signal multiplexed in the cell is generated.
- the clock generation circuit 13 includes, for example, a PLL circuit that receives a clock having a period indicated by the replaced transmission timing information and generates a clock of the source signal. This PLL circuit generates a clock obtained by multiplying the frequency corresponding to the replaced transmission timing information and outputs it as a clock of the source signal.
- the source signal output circuit 14 outputs the source signal from which the received cell force is also separated in synchronization with the clock generated by the clock generation circuit 13, thereby reproducing the source signal.
- the clock generation circuit 13 can generate a stable clock. Therefore, even when the synchronization signal of the network 30 is unstable at the time of transmission, the received source signal separated from the cell force can be stably reproduced.
- such a timing information replacement circuit may be provided on the transmission side instead of the reception side of the cell.
- the transmission timing information generated based on the network 30 synchronization clock is replaced by the timing information replacement circuit in the transmitting cell 20 and the vertical device 20, and the replaced transmission timing information is used as the source. It is multiplexed with the signal in the cell.
- the synchronization clock of the network 30 is unstable, the transition of the multiplexed transmission timing information is stabilized, so that the cell decomposition apparatus 10 on the reception side can clock the source signal. Can be played stably.
- the video signal of the professional digital video standard called “D2” with a clock frequency fs of 143.1818... MHz is used as the source signal, and this video signal is used as the AAL type 1 standard.
- D2 professional digital video standard
- this video signal is used as the AAL type 1 standard.
- SDH Synchronous Digital Hierarchy
- FIG. 2 is a diagram illustrating a configuration example of the network system according to the first embodiment.
- the network system shown in Fig. 2 is a system for transmitting D2 video signals through the ATM network 100 that conforms to SDH.
- the ATM device 200 and the ATM device 300 on the sending side and the receiving side are connected to the ATM network 100, respectively.
- a video output device 410 and a level conversion device 420 are connected to the ATM device 200 on the transmission side
- a level conversion device 510 and a video reception device 520 are connected to the ATM device 300 on the reception side.
- the video output device 410 is a device that outputs a D2 video signal that is a source signal, and is, for example, a transmission device or a relay device of a broadcasting station.
- the D2 video signal output from the video output device 410 is level-converted by the level conversion device 420 so that it can be processed by the ATM device 200 and supplied to the ATM device 200.
- the ATM device 200 on the transmission side includes a CLAD (Cell Assembly and Disassembly) 210 and a relay interface (IZF) 220.
- CLAD 210 has at least a CLA function for ATM data input data.
- the digital video signal from the level converter 420 is ATM cellized according to the AAL type 1 standard.
- the relay I / F 220 has at least the function of the SDH framer 221 that multiplexes the ATM cells generated by the CLAD 210 and sends them to the ATM network 100.
- the ATM device 300 on the receiving side includes a relay IZF 310 and a CLAD 320.
- the relay IZF 310 has at least a function of an SDH termination unit 311 that separates a necessary ATM cell from a received signal from the ATM network 100.
- the CLAD 320 has at least a CLD function for disassembling the ATM cell separated by the relay iZF 310.
- the ATM cell power also separates and outputs the D2 video signal as a source signal.
- the D2 video signal output from the ATM device 300 is level-converted by the level converter 510 so as to correspond to the transmission standard to the video receiver 520 and then received by the video receiver 520.
- the video receiving device 520 is a device that uses the transmitted D2 video signal, and is, for example, a receiving device or a video playback device of a broadcasting station.
- FIG. 3 is a diagram showing a data structure of an ATM cell transmitted to the ATM network 100.
- An AAL type 1 ATM cell follows the 5-byte ATM header, as shown in Figure 3 (A).
- a 1-byte SAR (Segmentaion And Reassembly) -PDU (Protocol Data Unit) header and a 47-byte information field for transferring user data (D2 video signal in this case) are arranged. It has a structure.
- the 1-byte SAR-PDU header consists of a 4-bit SN (Sequence Number) field and a 4-bit SNP (Sequence Number Protection) finale.
- the SN field is divided into two parts: a 1-bit CSI (Convergence Sublayer Identifier) and a 3-bit SC (Sequence Count), and the SNP field is a 3-bit CB (Control Bias field) and a 1-bit EP ( Even Parity bit).
- the SC in the SN field represents a count value that cycles through the ATM cell sequence number in the order of 0-7, thereby checking the cell order.
- the SNP field has a function to verify and correct SN errors.
- the CSI bit is used for timing information of the clock of the source signal by the SRTS method, that is, for transmission and reproduction of the RTS.
- the RTS is composed of 4 bits, and the count value of the lower 4 bits when the source clock is counted and reaches the specified number of bits is used as the RTS. Is done.
- This RTS has a multi-frame configuration using 8 ATM cells.
- the SC value is an odd value of 1, 3, 5, and 7, one bit out of 4 bits of the RTS is used for each CSI. Set and transmitted.
- FIG. 4 is a diagram showing an internal configuration of CLAD 210 of ATM apparatus 200 on the transmission side.
- the CLAD 210 on the transmission side has a general configuration in which the conventional power is also used. As shown in FIG. 4, the CLAD 210 includes a cell assembly circuit 211, a frequency divider 212, a counter 213, and a latch circuit 214. Yes.
- the cell assembly circuit 211 is a circuit that ATM-processes the input D2 video signal.
- the cell assembly circuit 211 incorporates the RTS from the latch circuit 214 into the ATM cell and outputs it.
- the frequency divider 21 2 is the block of the video signal corresponding to the RTS generation interval (the number of counts of the source clock) for the clock of the input video signal that is the source signal (hereinafter referred to as the source clock) 3 Divide by 008.
- the counter 213 is a 4-bit counter that counts a reference frequency fnx (here, fnZ2) from which the synchronization clock (hereinafter referred to as network synchronization clock) power of the ATM network 100 can be obtained.
- the synchronized count value is supplied to the latch circuit 214.
- the latch circuit 214 latches the count value of the counter 213 with the divided clock of the frequency divider 212.
- This latch circuit 214 generates an RTS converted from the transmission time per block length (3008 bits) of the video signal using the clock of the reference frequency fnx, and the cell assembly circuit 211 multiplexes it with the input video signal into the ATM cell. Is done.
- the RTS is multiplexed into the ATM cell in the ATM device 200 on the transmission side, so that the ATM device 300 on the reception side reproduces the source clock based on the RTS and transmits the transmitted video signal. Can be synchronized with the source clock and output at the correct timing.
- the ATM device 300 on the receiving side can derive the frequency of the source clock based on the difference value between adjacent RTSs.
- the RTS difference value on the transmission side is expressed by the following equation (1), and the frequency of the source clock can be obtained by the equation (2) on the reception side.
- the RTS difference value is Y
- the reference frequencies obtained from the network synchronization clocks on the transmission side and the reception side are fnx- cla and fnx-cld, respectively
- the source clock frequency of the input video signal on the transmission side is fs- cla
- the source clock frequency of the output video signal on the receiving side is fs-cld.
- the coefficient X is assumed here to be 204.
- FIG. 5 is a diagram showing an internal configuration of CLAD 320 of ATM device 300 on the receiving side.
- CLAD320 on the receiving side consists of cell disassembly circuit 321, RTS replacement circuit 322, RTS nother 323, counters 324 and 325, comparison circuit 326, gate circuit 327, and PLL (Phase Locked Loop) 328 It comprises.
- the cell decomposition circuit 321 is a circuit that extracts a source signal, that is, a video signal from an ATM cell received through the ATM network 100.
- This circuit has a CDV (Cell Delay Variation) absorption buffer 321a inside, stores the received cell in the CDV absorption buffer 321a, absorbs the delay fluctuation of the cell, and uses the recovered clock output from the PLL328 for video. Output a signal. Also, RTS is separated from the received cell, and 322 RTS replacement circuits are supplied.
- CDV Cell Delay Variation
- the RTS replacement circuit 322 receives the separated RTS, replaces the value of the RTS so that the transition in a predetermined time is stable, and outputs the result. As will be described later, the RTS replacement circuit 322 replaces the difference value of the RTS in a predetermined time unit so that the transition (change) of the difference value of the adjacent RTS is smoothed, and the RTS based on the replaced difference value. RTS transition is stabilized by recalculating.
- the RTS buffer 323 temporarily accumulates the replaced RTS, and outputs the RTS to the comparison circuit 326 in synchronization with the signal output timing of the gate circuit 327.
- the counter 324 is a 4-bit counter that counts the clock of the reference frequency fnx obtained from the network synchronization clock power of the ATM network 100, and supplies the count value to the comparison circuit 326.
- Counter 325 is the number of clocks with a reference frequency fnx, which is the number obtained by converting the transmission period per block length of the source signal (here 3008 bits) to the reference frequency fnx (however, the source signal and the network synchronization clock The tolerance is taken into account in consideration of synchronization mismatch, and the RTS playback period is determined by counting with a period of 8).
- the comparison circuit 326 counts the RTS value output from the RTS buffer 323 and the counter 324. Compare the values and output a pulse when they match.
- the gate circuit 327 inhibits the comparison result obtained by the comparison circuit 326 until the count value of the counter 325 is reached, and reproduces the RTS transmission timing, that is, the signal timing obtained by dividing the source signal clock by 3008.
- the PLL 328 regenerates the source clock based on the output signal of the gate circuit 327, and the source signal (video signal) is regenerated from the CDV absorption buffer 321a of the cell decomposition circuit 321 in synchronization with this regenerated clock.
- RTS replacement circuit 322 replacement processing in the RTS replacement circuit 322 will be described with reference to two examples of using a replacement table of RTS difference values and replacing RTS difference values by calculation.
- FIG. 6 is a diagram illustrating a numerical example according to the first RTS replacement processing example.
- RTS values and their differential values are represented in decimal numbers.
- the RTS differential value is ideally a constant value.
- the RTS replacement circuit 322 integrates such RTS difference values in a predetermined cycle, refers to a conversion table stored in advance, and calculates the RTS in the cycle so that the transition of the RTS difference values is smoothed. Replace.
- the unit period for replacing RTS is called the replacement period.
- the replacement period is the period for which RTS reaches 10 times.
- N is the number of times the RTS arrives in the replacement period
- Rav is the average value of the RTS difference values for N times
- R (n) is the difference value of the RTS that has reached the nth time in the replacement period.
- the RTS difference value in the replacement period is once divided into the quotient x and the remainder y in the equation (3), and the remainder y is divided into minimum units, and the divided value is
- the conversion table force is also extracted for the array that is dispersed within the period. Then, by adding the extracted array to the array of the quotient X, a new stabilized RTS difference value is generated.
- the quotient X corresponds to the integer part of the average value of N RTS difference values
- the remainder y is the first value after the decimal point of the average value (however, This is equivalent to rounding up 2nd place.
- FIG. 7 is a diagram illustrating an example of the conversion table.
- an array of values to be added to the array of quotient X is described for each value of remainder y.
- Each of the array of added values is evenly distributed in an array of N powers (ie, 1-bit value) obtained by dividing the remainder y into minimum units.
- FIG. 8 is a diagram illustrating a numerical example according to the second RTS replacement processing example.
- the Rth difference value (after replacement) in the replacement period is Rav (n), and ro unddown (A / B) is an integer obtained by rounding down the fractional part of the quotient by AZB division. Indicates the part.
- the second and third terms on the right-hand side determine the array of added values that should be added to the quotient X array. In the example of FIG. , 0, 0, 1, 0, 0, 0, 0, 1 ”. Therefore, N RTS difference values are replaced so that the fluctuating points (that is, the points where the difference value is larger by 1) are dispersed according to Equation (4), and the first RTS replacement processing example is based on this RTS difference value.
- the RTS replacement circuit 322 performs replacement in units of N so as to change linearly from the value of the RTS separated from the received ATM cell.
- the RTS after replacement is stored in the RTS buffer 323, and the time interval indicated by the RTS is reproduced based on the reference frequency fnx by the comparison circuit 326 and the gate circuit 327. Since the RTS is stabilized, the output signal interval of the gate circuit 327 is almost constant, and the PLL 328 can stably reproduce the source clock. Therefore, the source signal is output from the CDV absorption buffer 321a of the cell decomposition circuit 321 in synchronization with the output clock of the PL L328, so that the source signal is reproduced at the correct timing and the reproduction quality is improved.
- the frequency of the network synchronization clock periodically changes, and the RTS difference value also periodically changes greatly according to this frequency change.
- the replacement period of the RTS difference value corresponding to the number of arrivals N of the RTS is longer than the above fluctuation period.
- the CLAD 320 of the present embodiment is characterized in that it can cope with such a large fluctuation that appears periodically by providing the RTS replacement circuit 322, and this is related to the fluctuation of the network synchronization clock.
- Received ATM cell power A high-quality source signal can always be reproduced.
- the power of replacing the RTS separated from the cell so as to make a stable transition is applied to the transmitting side of the ATM cell.
- the source clock reproduced on the receiving side is stabilized, the same effect can be obtained.
- FIG. 9 is a diagram showing an internal configuration of the CLAD of the ATM apparatus 200 on the transmission side according to the second embodiment.
- blocks corresponding to those in FIG. 4 are denoted by the same reference numerals and description thereof is omitted.
- the CLAD 210a shown in FIG. 9 is different from the CLAD 210 of FIG.
- An S replacement circuit 215 is provided.
- the RTS replacement circuit 215 replaces the RTS value generated by the latch circuit 214 with the RTS value so that the transition at a predetermined time is stable, and outputs the result.
- the replacement process uses the same method as the conversion table described above in FIGS. In other words, RTS difference values are replaced in predetermined time units so that transitions between adjacent RTS difference values are smoothed, and RTS is recalculated based on the replaced difference values to stabilize RTS transitions. Hesitate.
- the cell assembly circuit 211 incorporates the source signal into the information field and also converts the ATM cell in which the RTS stabilized by the RTS replacement circuit 215 is incorporated into the CSI bit to the ATM network 100 via the relay IZF220. To send.
- FIG. 10 is a diagram illustrating a numerical example of RTS generated by the CLAD 210a.
- FIG. 10 shows an example using the method of calculating the RTS replacement value by the calculation using the equation (4) among the above-described RTS replacement processing examples.
- the CLAD 210a on the transmission side if the network synchronization clock becomes unstable, the count of the counter 213 becomes unstable and the RTS generation interval becomes uneven.
- the difference value of the generated RTS has a fluctuation range of ⁇ 4 at the maximum.
- the quotient X in Eq. (3) is 3, and the remainder y is 2, and the location where the RTS differential value fluctuates is distributed in the 5th and 10th locations according to Eq. As a result, the RTS after replacement changes more linearly.
- FIG. 11 is a diagram showing an internal configuration of the CLAD of the ATM device 300 on the receiving side according to the second embodiment.
- blocks corresponding to those in FIG. 5 are denoted by the same reference numerals and description thereof is omitted.
- a CLAD 320a shown in FIG. 11 is a device used in the prior art, having a configuration in which the CLAD 320 force shown in FIG. 5 and the RTS replacement circuit 322 are removed. That is, the RTS is separated from the received ATM cell by the cell disassembly circuit 321 and stored in the RTS buffer 323. The RTS force output from the RTS buffer 323 also reproduces the RTS generation interval, and the source clock is regenerated by the PLL 328.
- the replacement period at the time of RTS replacement processing in CLAD 210a on the transmission side be longer than the fluctuation period of the RTS difference value.
- the CLAD 320a on the receiving side can always reproduce the high-quality source signal even for the received ATM cell power regardless of the fluctuation of the network synchronization clock.
- the network synchronization clock received by CLAD is switched as a factor that causes the network synchronization clock to become unstable in the transmission side CLAD.
- the PLO operation in the relay IZF 220 that transmits the network synchronization clock to the CLAD 210 becomes unstable.
- the CLAD210 may experience a phase shift in the received clock or a non-received clock period.
- the reproduction quality of the source signal on the receiving side is improved. A decrease can be prevented.
- FIG. 12 is a diagram showing an internal configuration of the CLAD of the ATM device 200 on the transmission side according to the third embodiment.
- blocks corresponding to those in FIG. 9 are denoted by the same reference numerals and description thereof is omitted.
- a CLAD 210b shown in FIG. 12 further includes a CLAD 210a shown in FIG. 9 and a clock switching determination circuit 216.
- the clock switching determination circuit 216 is a circuit that determines whether switching of the output source of the input network synchronization clock has occurred. For example, the clock switching determination circuit 216 determines the occurrence of switching by receiving a notification of switching of the relay device of the network synchronization clock from the relay IZF 220. Alternatively, a function to monitor the received network synchronization clock may be provided to generate the presence or absence of switching.
- the RTS replacement circuit 215 normally outputs the RTS generated by the latch circuit 214 to the cell assembly circuit 211 as it is without replacing it. Then, the clock switching determination circuit 216 When the occurrence of switching is determined, for example, the RTS from the latch circuit 214 is replaced so that the transition is stable at a certain time thereafter, and is output to the cell assembly circuit 211. In addition, when the clock switching determination circuit 216 has a function of determining that the network synchronization clock is normally received again after switching, the RTS replacement circuit 215 starts the RTS replacement processing, and then the clock switching determination circuit 216 When it is determined that the network synchronization clock has been received normally, the RTS replacement process may be stopped in response to the notification, and the RTS may be transferred without replacement.
- the CLAD on the receiving side can stably reproduce the source clock.
- RTS replacement circuit 215 the response characteristic of the source clock recovery operation is deteriorated on the receiving side for the replacement period, but in this embodiment, the network synchronization clock is not valid. Since the RTS is replaced only during the stable period, the bad period of response characteristics can be minimized.
- the network synchronization clock of the ATM network 100 may fluctuate periodically, and the RTS also fluctuates periodically according to this period. Therefore, when replacing the RTS so that the transition is stable, the replacement period is set to be longer than the fluctuation period of the RTS, so that the source clock can be stably recovered on the receiving side regardless of the fluctuation of the network synchronization clock. It ’s a little tricky.
- a CLAD on the receiving side is provided with a function for measuring the fluctuation frequency of the network synchronization clock and setting an appropriate replacement period that satisfies the above conditions according to the frequency.
- FIG. 13 shows the internal configuration of the CLAD of ATM device 300 on the receiving side according to the fourth embodiment.
- FIG. 13 blocks corresponding to those in FIG. 5 are denoted by the same reference numerals and description thereof is omitted.
- the CLAD 320b shown in FIG. 13 further includes the CLAD 320 shown in FIG. 5, a fluctuation frequency measurement circuit 329, and a replacement period calculation circuit 330.
- the fluctuation frequency measuring circuit 329 measures the fluctuation frequency fns of the clock having the reference frequency fnx obtained from the network synchronization clock force based on the reference clock having the frequency fb from the oscillator 329a.
- the oscillator 329a is provided either inside or outside the CLAD 320b.
- the replacement period calculation circuit 330 calculates N, which is the number of RTS replacements corresponding to the replacement period, according to the measured fluctuation frequency fnx, and sets this N in the RTS replacement circuit 322.
- FIG. 14 is a diagram showing an internal configuration example of the fluctuation frequency measurement circuit 329. As shown in FIG.
- the fluctuation frequency measurement circuit 329 includes a plurality of measurement units 90 (in this example, measurement units 90a to 90c) that measure the fluctuation frequency fns, and the minimum value from each unit as the fluctuation frequency fns. And an output circuit 97 for outputting.
- the measurement units 90a to 90c include an M frequency divider 91, an fnx measurement counter 92, a latch circuit 93, a period comparator 94, an fns measurement counter 95, and a latch circuit 96, respectively.
- the M divider 91 outputs a divided clock obtained by dividing the clock of the reference frequency fnx, which also provides the network synchronization clock power, by M.
- This division ratio M is basically the force assumed to be 3008, which is the block length of the source signal corresponding to the RTS generation interval. Since this division ratio M determines the measurement accuracy of the reference frequency fnx, the measurement unit 90a — At 90c, the measurement accuracy is improved by using different division ratios M such as 3008 equal magnification or equally divided values.
- the fnx measurement counter 92 counts the reference clock having the frequency fb from the oscillator 329a, and resets the count value upon reception of the divided clock from the M divider 91.
- the latch circuit 93 latches the count value immediately before the reset of the f nx measurement counter 92. As a result, the value obtained by converting the frequency of the divided clock with the reference clock of frequency fb is obtained.
- the period comparator 94 detects the time interval of the fluctuation period using the following equations (5) and (6) based on the output value of the latch circuit 93.
- the output value of the latch circuit 93 is Cnx
- the number of M divisions by the M divider 91 is m
- the number of comparison stages is p.
- the fns measurement counter 95 counts the reference clock having the frequency fb from the oscillator 329a, and resets the count value at the timing of the noise output from the period comparator 94.
- the latch circuit 96 latches the count value immediately before the reset of the fns measurement counter 95 and outputs it to the output circuit 97.
- the frequency divider 91 performs frequency division using different frequency division ratios M, and the measured value of the variable frequency corresponding to the frequency division ratio M is measured. (Output value of latch circuit 96) is output. The output circuit 97 selects the smallest one of these measured values and outputs it as the fluctuation frequency fns.
- FIG. 15 is a timing chart showing an example of a transmission signal in the fluctuation frequency measurement circuit 329.
- the replacement period calculation circuit 330 is configured to measure the measured fluctuation frequency.
- the number of RTS replacement N corresponding to the RTS replacement period is set according to the wave number fns. N satisfies the following formula (7) !: It can be set by calculating (natural number).
- FIG. 16 is a diagram showing a numerical example of RTS in this CLAD 320b.
- the difference value of RTS separated by ATM cell power is N, that is, the integrated value for 20 is 64 (that is, the average value per 20 is 3.2).
- the RTS substitution circuit 322 for example, the quotient X according to the above equation (3) is 3 and the remainder y is 4, and the changed value array after the substitution is changed (ie, 1 is added to the quotient X The place where the RTS difference value is placed) appears every 5th. Then, by reconstructing the RTS using the replaced difference value array, the transition of the RTS is stabilized in the period including the fluctuation period.
- the average RTS difference value in the replacement period is 2.
- the average value is 3.5 for the next 10 arrival periods.
- the fluctuation frequency fns of the network synchronization clock is appropriately measured.
- the RTS replacement period By changing the RTS replacement period to be optimal according to the measurement time, it is possible to constantly reproduce the source clock related to fluctuations in the network synchronization clock and improve the reproduction quality of the source signal. it can.
- optimizing the replacement period it is possible to minimize degradation of the response characteristics of the source clock recovery operation.
- FIG. 17 is a diagram illustrating a configuration example of a network system according to the fifth embodiment.
- blocks corresponding to those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.
- two ATM devices 201 and 202 for transmitting D1 video signals in ATM cells are connected to ATM network 100, respectively.
- the video signal VI output from the video output device 411 is input to the ATM device 201 via the level conversion device 421.
- the video signal V2 output from the video output device 412 is input to the ATM device 202 via the level conversion device 422.
- the ATM devices 201 and 202 like the ATM device 200 in FIG. 2, have a CLA D having a CLA function and a relay IZF having an SDH framer function, and convert the video signals VI and V2 into ATM cells, respectively. And send it over the ATM network 100.
- the ATM device 300 on the receiving side receives the video signals VI and V2 from the ATM devices 201 and 202 by a repeater on the ATM network 100 (or one of the repeaters of the ATM devices 201 and 202). Switched and supplied.
- the source clock of the multiplexed source signal may be shifted in phase or changed in frequency. There is.
- lowering the cutoff frequency of the PLL loop filter is particularly effective for stably reproducing a source clock such as a video signal.
- a source clock such as a video signal.
- the cut-off frequency is lowered, the followability to the input signal in the PLL will deteriorate. Therefore, when the source clock is switched as described above, it becomes difficult to regenerate the source clock.
- FIG. 18 is a diagram illustrating an internal configuration example of the CLAD of the ATM device 300 on the receiving side according to the fifth embodiment.
- blocks corresponding to those in FIG. 5 are denoted by the same reference numerals and description thereof is omitted.
- the CLAD 320c shown in FIG. 18 has a configuration in which the CLAD 320 shown in FIG. 5 and a buffer monitoring circuit 331 are further provided.
- the noffer monitoring circuit 331 monitors the CD V absorption buffer 321a of the cell disassembly circuit 321, determines that the source clock is switched when this buffer underflows, and sends the determination signal to the RTS replacement circuit. Output to 322. Thereafter, control is performed so that data transmission from this buffer is waited until the accumulated amount of the CDV absorption buffer 321a reaches a predetermined amount. Furthermore, when the accumulated amount of the CDV absorption buffer 321a is restored, the RTS replacement circuit 322 may be notified to that effect.
- the RTS replacement circuit 322 normally replaces the RTS separated by the cell disassembly circuit 321 with a predetermined replacement period by the processing described above. At this time, the replacement period is set to a length equal to or greater than the fluctuation frequency of the network synchronization clock.
- the replacement period is temporarily shortened, and then the replacement period is gradually restored. Further, the replacement cycle may be kept short until the buffer monitoring circuit 331 notifies the recovery of the accumulated amount of the CDV absorption buffer 321a.
- FIG. 19 is a timing chart showing an example of setting input / output data and replacement period in CLAD 320c.
- the transmission source of the source signal is switched from the state in which the video signal VI from the ATM device 201 is received by the ATM cell, and at timing T21, the nofer monitoring circuit 331 detects this switching. At this time, the control of the buffer monitoring circuit 331 stops the output of the CDV absorption buffer 321a, and the number N of RTSs corresponding to the replacement period in the RTS replacement circuit 322 is reduced from 20 to 5.
- the reception of the switched video signal V2 is started, and at the timing T22 when the accumulated amount of the CDV absorption buffer 321a reaches a predetermined threshold value, the CDV is again controlled by the control of the notch monitoring circuit 331. Data transmission from the absorption buffer 321a is started.
- the set value of N in the RTS replacement circuit 322 is gradually increased. For example, N is returned to 20 at timing T22 when transmission of the video signal V2 is started.
- the source clock can always be stably reproduced even when the PLL 328 having a relatively high cutoff frequency of the loop filter is used.
- the replacement period in the RTS replacement circuit 322 is lengthened, and replacement is performed so that the RTS always changes at a constant level. For this reason, even if a loop filter with a high cutoff frequency is used, PLL328 can reproduce a stable source clock with little jitter, and can prevent deterioration in the reproduction quality of the video signal.
- the source clock is switched due to, for example, switching of the ATM device on the transmission side, this switching is detected by the notch monitoring circuit 331, and the replacement period of the RTS is shortened.
- the PLL328 makes it easier to follow the input clock by using a loop filter with a high cutoff frequency that changes the input clock cycle in a shorter cycle than normal. Therefore, a stable source clock can be reproduced in a short time even after switching the source clock. After that, the source clock is reproduced again based on the RTS replaced with a long period again, and the source signal can be reproduced accurately.
- the occurrence of underflow in the CDV absorption buffer 321a is monitored and the switching of the source clock is detected.
- Other detection methods may be employed, such as detection in response to a switching notification signal from the.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Multimedia (AREA)
- Computer Hardware Design (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
- Synchronisation In Digital Transmission Systems (AREA)
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/JP2005/005424 WO2006100781A1 (ja) | 2005-03-24 | 2005-03-24 | セル分解装置、セル組立装置、およびクロック再生方法 |
JP2007509134A JP4526562B2 (ja) | 2005-03-24 | 2005-03-24 | セル分解装置、セル組立装置 |
EP05726984A EP1863216A4 (en) | 2005-03-24 | 2005-03-24 | CELL DECOMPOSITION DEVICE, CELL ASSEMBLY DEVICE AND TACT PLAY PROCESS |
US11/902,130 US20080019399A1 (en) | 2005-03-24 | 2007-09-19 | Cell disassembly unit, cell assembly unit, and clock reproduction method |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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PCT/JP2005/005424 WO2006100781A1 (ja) | 2005-03-24 | 2005-03-24 | セル分解装置、セル組立装置、およびクロック再生方法 |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US11/902,130 Continuation US20080019399A1 (en) | 2005-03-24 | 2007-09-19 | Cell disassembly unit, cell assembly unit, and clock reproduction method |
Publications (1)
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WO2006100781A1 true WO2006100781A1 (ja) | 2006-09-28 |
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PCT/JP2005/005424 WO2006100781A1 (ja) | 2005-03-24 | 2005-03-24 | セル分解装置、セル組立装置、およびクロック再生方法 |
Country Status (4)
Country | Link |
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US (1) | US20080019399A1 (ja) |
EP (1) | EP1863216A4 (ja) |
JP (1) | JP4526562B2 (ja) |
WO (1) | WO2006100781A1 (ja) |
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US8942108B2 (en) | 2012-12-14 | 2015-01-27 | General Electric Company | Method and system for current differential protection |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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JPH09247157A (ja) * | 1996-03-06 | 1997-09-19 | Hitachi Ltd | Srtsクロック再生制御回路 |
JP2001285268A (ja) * | 2000-03-29 | 2001-10-12 | Fujitsu Ltd | Srts法を用いたクロック発生装置 |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB9419611D0 (en) * | 1994-09-29 | 1994-11-16 | Plessey Telecomm | Constant bit rate synchronisation |
US5742649A (en) * | 1995-12-15 | 1998-04-21 | Cisco Technology, Inc. | SRTS clock recovery system for use in a highly stressed network environment |
US5912880A (en) * | 1996-11-07 | 1999-06-15 | Northern Telecom, Limited | System and method for ATM CBR timing recovery |
JP2856189B2 (ja) * | 1997-02-26 | 1999-02-10 | 日本電気株式会社 | Srts法によるクロック再生装置及びクロック再生方法 |
CA2202307A1 (en) * | 1997-04-10 | 1998-10-10 | Newbridge Networks Corporation | Generation of primary rate clocks from correction values derived from the received synchronous residual time stamp |
US5970107A (en) * | 1998-01-06 | 1999-10-19 | Maker Communications, Inc. | Synchronous residual time stamp service clock regenerator phase locked loop phase comparator and loop filter |
JPH11275077A (ja) * | 1998-03-20 | 1999-10-08 | Fujitsu Ltd | Atmネットワークシステム及びそのクロック供給ルート変更方法 |
US7106758B2 (en) * | 2001-08-03 | 2006-09-12 | Adc Telecommunications, Inc. | Circuit and method for service clock recovery |
US6990109B2 (en) * | 2001-10-31 | 2006-01-24 | Adtran, Inc. | Method and apparatus for providing reliable voice and voice-band data transmission over asynchronous transfer mode (ATM) network |
-
2005
- 2005-03-24 WO PCT/JP2005/005424 patent/WO2006100781A1/ja not_active Application Discontinuation
- 2005-03-24 JP JP2007509134A patent/JP4526562B2/ja not_active Expired - Fee Related
- 2005-03-24 EP EP05726984A patent/EP1863216A4/en not_active Withdrawn
-
2007
- 2007-09-19 US US11/902,130 patent/US20080019399A1/en not_active Abandoned
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH09247157A (ja) * | 1996-03-06 | 1997-09-19 | Hitachi Ltd | Srtsクロック再生制御回路 |
JP2001285268A (ja) * | 2000-03-29 | 2001-10-12 | Fujitsu Ltd | Srts法を用いたクロック発生装置 |
Non-Patent Citations (1)
Title |
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See also references of EP1863216A4 * |
Also Published As
Publication number | Publication date |
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JP4526562B2 (ja) | 2010-08-18 |
EP1863216A1 (en) | 2007-12-05 |
JPWO2006100781A1 (ja) | 2008-08-28 |
EP1863216A4 (en) | 2010-12-01 |
US20080019399A1 (en) | 2008-01-24 |
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