JP2642043B2 - SRTS control apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ATM (Asynch).
(Round Transfer Mode: Asynchronous Transfer Mode) In a method of transferring a signal that is asynchronous with a network clock into cells in communication and transmitting it to a receiving side,
SRTS control device for reproducing the frequency information of the transferred transfer signal
Placement and method .

[0002]

2. Description of the Related Art International Telegraph and Telephone Consultative Committee (CCITT)
Recommendation I. In 363, as a means for transferring the frequency information of the original signal when a signal asynchronous with the network clock is converted into a cell by the ATM and transferred, the SRTS (Synchr) is used.
onous Residual Time Stam
p). This is because 363, the network clock and the original signal
RTS (Resi
Dual Time Stamp)
The principle is as follows. Now f
s is the frequency of the original signal and fn is the frequency of the network clock.
The wave number and fnx are divided into x frequency division clocks of the network clock fn.
RTS interval, where N is the number of fs periods, and T is seconds
RTS interval in M, R is the RTS interval (nominal value, maximum
Value, minimum value), the number of periods of fnx, Mq
The largest integer below. At this time, on the transmitting side, the original signal
At a fixed time interval T corresponding to N cycles
The number Mq of periods of the x-divided clock of the work clock is obtained.
It is. Mq has the necessary information: fnx, Mq and N
So, if Mq is sent to the receiver,
The frequency can be reproduced on the receiving side. Mq is actually
Is composed of a nominal value part and a remainder part. Nominal value
The partial Mnom is the public of the number of fnx periods in T seconds.
Nominal value, fixed for service. The remainder is quantum
The frequency difference information is transmitted along with the effect of
is there. Since the nominal part is constant, the nominal part of Mq
It may be known at the calling party. And
Only the remainder of Mq is sent to the receiver. Specifically
Is the x-divided clock fnx of the network clock fn
Drives the p-bit counter, and latches the output of this counter every N counts of the clock fs of the transferred signal. The latched result is RTS (Residual Ti).
meStamp) is information. This RTS information is transferred to the CSI (Convergence Sublayer) in the cell.
Indication) bit, and the receiving side uses the phase locked loop P based on the received RTS information.
The clock fs is reproduced by LL.

[0003]

In the above-mentioned SRTS, it is necessary to consider a case where a cell is lost and RTS information is lost. I. According to R.363, R
TS information is transferred using 4 cells out of 8 cells.
If at least one of the four cells transferring the TS information is lost, the RTS information is lost. Therefore, even if cell loss continues once every eight cells, RTS information may be continuously lost. At this time, the receiving side PL
The signal L may run at a frequency completely unrelated to the clock fs of the signal to be transferred, and the output on the receiving side may deviate from the allowable frequency range of the clock fs. Further, even if the correct RTS information can be received thereafter, the PLL keeps the clock f.
It may take time to converge to s.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and is intended to solve the above problem. It is intended to provide means for self-propelling near the clock fs.

For this purpose, the present invention uses the RT
The S information is predicted in advance, and when the RTS information to be received is lost, the predicted RTS information is used.

[0006]

As examples of RTS information to be transferred, 44.736 MHz which is a digital tertiary group in North America as a clock fs of a signal to be transferred, and a synchronous digital hierarchy SDH 15 as a network clock fn.
5.52 MHz, dividing frequency x by 2 and dividing clock f by 2
When nx is 77.76 MHz, the RTS information is as shown in FIG. 1 when a 4-bit binary number is represented by a decimal number. Taking the difference in this RTS sequence gives 12 or 1
It is understood that the information is simple repetition information, such as 3 and almost 12 and 13 appear alternately. The reason why the period of the differential sequence is 2 is described, for example, in the paper “Jitter in SRTS” (1992 Spring Meeting of IEICE
This is because the parameter called the remainder is around 1/2, as discussed in (Coming soon in March 993). The remainder is defined as the fraction of Nfnx / fs. Generally, when the remainder is approximated by a convention fraction, the denominator of the convention fraction is the cycle of the difference series. More specifically, the period of the difference sequence can be determined from a parameter called a remainder, and the remainder R is obtained as follows. First, M is defined by the following equation. M = Nfnx / fs where fs is the nominal bit rate of the transmitted signal, f
nx is the x-divided clock frequency of the network clock fn. N is fs in the RTS information transfer cycle.
Since the RTS information is transferred once in eight cells with the number of bits of, the number of bits is equal to the number of bits of the signal included in the eight cells. Here, the remainder R is defined as a decimal part of M. When the remainder is approximated by a fixed fraction, the denominator of the fraction becomes the cycle of the difference series. In the above example, if fs = 44.736 MHz, R = 0.4979, which can be approximated by 、, so that 2 of the denominator is the cycle of the difference sequence. Intuitively, the remainder R indicates how much the RTS increases further. Again, the 4-bit binary numbers (1 to 1)
For an example in which 6) is represented by a decimal number, the RTS sequence in FIG.
Consider with reference to a difference series. The RTS information is actually 1
Increases by 12 + R each time. Therefore, if the first RTS value is “0”, the transferred RTS value is “0”. The next RTS value is “12 + R”, but since the RTS value to be transferred is a 4-bit integer, “12” is transferred,
The difference from the previous is 12. The next RTS value is “24 + 2”
R ", but since R is slightly smaller than 1/2,"
8 ”(24 = 8 mod 16) is transferred, and the difference from the previous is 12. Further, the next RTS value is“ 36 + 3 ”.
R ", but since 3R = 1.4937," 5 "(3
7 = 5 mod 16) is transferred, and the difference from the previous is 13. Similarly, it can be seen that the period of the difference sequence becomes 2 because R is close to 1/2. In the same way,
When the remainder is approximated by a fixed fraction, if R is set close to 1/3, it can be seen that the cycle of the difference sequence is 3. this
The known bit rate fs of the transmitted signal, known as
X-divided clock frequency fn of network clock fn
x and the number of bits N of fs in the RTS information transfer cycle
It is possible to know in advance the cycle of the difference series from the obtained residue R.
Therefore, for example, the receiving side of the transmission system in which the cycle of the differential sequence is 2 uses this fact to determine whether the previous RTS and the current RTS
The difference in S is taken, and if the difference is 12, the difference prediction value of the next RTS is set to 13, and if the difference is 13, the difference prediction value of the next RTS is set to 12. Then, the value obtained by adding the difference prediction value to the previous RTS is used as the prediction RTS value.
If S is lost, this predicted RTS value is
Use as

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the SRTS control apparatus and method of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of the embodiment of the present invention when the period of the difference sequence is 2.

In FIG. 1, reference numeral 1 denotes a reception RT which is an input.
This is an input selection unit that selects either S or the predicted RTS based on the presence or absence of the RTS loss signal, and outputs the selected RTS this time. The received RTS is the received RTS information,
Predicted RTS means that RTS information is lost and not received,
RTS information predicted according to the present invention.
The S loss indicates a detection signal when the RTS information is lost. Reference numeral 2 denotes first storage means for storing the current RTS output from the input selection means 1, and reference numeral 3 denotes subtraction means for calculating a difference between the current RTS and the previous RTS stored in the first storage means. Reference numeral 4 denotes a second storage unit that stores the difference obtained by the subtraction unit 3, and reference numeral 5 denotes a determination unit that determines the next difference value from the difference value stored by the second storage unit. 6 is the predicted difference value obtained by the judgment means 5 and this time R from the first storage means.
The predicted RTS is obtained by adding the TS to the TS, and is output to the input selecting means 1.

Next, the operation of the SRTS control method according to the embodiment will be described. When the RTS information transferred by the SRTS method in the ATM is input to the input selecting means 1, it is output as the RTS this time. On the receiving side, this time R
Clock f of signal transferred by PLL based on TS
Used to reproduce s. At the same time, the current RTS is input to and stored in the first storage means 2, and is output to the subtraction means 3 as the previous RTS. In the subtraction means 3, the RT
A difference value is obtained by taking the difference between S and the current RTS from the input selection means 1, and the obtained difference value is stored by the second storage means. When the difference value output from the second storage unit 4 is 12, the determining unit 5 outputs 13 to the adding unit 6 as a predicted difference value. The adding means 6 calculates the predicted difference value as the first
The predicted RTS is obtained by adding to the previous RTS from the storage means 2. The obtained predicted RTS is transmitted to the input
When the RTS loss is input without S being lost and input, this is used as the current RTS instead of the lost RTS information.

The clock fs of the signal to be transferred again is 4
4.736MHz, frequency-divided clock fns is 77.76M
Hz, the RTS predicted by this embodiment is
Since the information corresponds to the case where fs is around 44.736 MHz, if the RTS information is lost, the PL on the receiving side is lost.
L is controlled to oscillate around fs. Therefore, even when the RTS information is lost due to the cell loss, the PLL on the receiving side does not oscillate outside the allowable frequency range of fs.
Moreover, when the RTS information is correctly received, the pull-in time is shortened.

FIG. 2 shows a case where the period of the differential sequence of the RTS is 2, but the present invention can be applied even when the period of the differential sequence is other than 2. FIG. 3 is a block diagram showing the configuration of the embodiment of the present invention when the difference sequences are 12, 12, and 13 and period 3. In FIG. 3, the obtained difference values are stored twice by the two second storage units 4-1 and 4-2. The judgment means 5 sets 13 as the predicted difference value when both of the stored difference values are 12, and sets 12 as the predicted difference value otherwise.
Is the prediction difference value.

In general, even if the cycle of the difference sequence is 4 or more, the present invention can be applied by increasing the number of stored difference values.

As is apparent from the embodiment shown in FIG. 2 or FIG. 3, the present invention operates correctly even when the reception RTS is continuously lost. That is, when the received RTS is continuously lost, the next predicted RTS value is generated based on the predicted RTS value used in the past.
TS is a correct predicted value.

[0015]

As described above, according to the present invention,
Even when RTS information is lost due to cell loss or the like when an asynchronous signal is transferred by ATM, the lost RTS can be predicted, and the PLL on the receiving side can be free-running in the vicinity of fs. When the RTS is received correctly, there is an effect that the PLL synchronization is quickly achieved.

[Brief description of the drawings]

FIG. 1 shows an example of an RTS information sequence.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention when the period of the difference sequence is 2;

FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention when the period of the difference sequence is 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input selection means 2 1st storage means 3 Subtraction means 4,4-1, 4-2 2nd storage means 5 Judgment means 6 Addition means

Continuation of the front page (72) Inventor Hiromi Ueda 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References IEICE Technical Report CS 92-106 ITU-T Recommendation I . 363

Claims (2)

(57) [Claims] 1. An asynchronous transfer mode communication network network
When transferring signals that are not synchronized with the
Kokusai Telegraph and Telephone as a means of transmitting frequency information on transmitted signals
Advisory Committee (CCITT) Recommendation I. 363
RTS (Residual Time Stamp) information
(Synchronous) that transfers the information to the receiving side
s Residual Time Stamp) method
The receiving apparatus used, wherein each time the RTS information is received from the transmitting side, it is received last time.
Between the value of the RTS information received and the value of the RTS information received this time
A difference value calculating means for calculating a differential value, and the network of the transmission system for sequentially storing the difference values.
Clock clock frequency and the nominal value of the transfer signal frequency
The same difference value of the difference value obtained in advance from the relationship
Number of storage units that can confirm the period of the difference series appearing in the column
From the series of difference values stored in the storage means,
Predicts the difference value to be input to and outputs the predicted difference value.
Difference value predicting means for adding the predicted difference value to the value of the previously received RTS information.
Adding means for outputting predicted RTS information, and inputting RTS information and the predicted RTS information from the transmitting side
When the transmission side detects loss of RTS information, the prediction R
Outputs TS information as received RTS information from sender
SRTS provided with input selection means for changing
Control device . 2. An asynchronous transfer mode communication network
When transferring signals that are not synchronized with the
Kokusai Telegraph and Telephone as a means of transmitting frequency information on transmitted signals
Advisory Committee (CCITT) Recommendation I. 363
RTS (Residual Time Stamp) information
(Synchronous) that transfers the information to the receiving side
s Residual Time Stamp) method
Each time the receiving side receives the RTS information from the transmitting side , the receiving side compares the value of the previously received RTS information with the currently received RTS information.
, And calculates the difference value as the network clock of the transmission system.
From the relationship between the frequency of the transfer signal and the nominal value of the frequency of the transfer signal.
The same difference value of the difference values appears in time series
The period of the difference sequence is sequentially stored in the number of storage units that can be confirmed.
From the series of difference values all stored in the storage means,
Predicts the difference value to be input to and outputs the predicted difference value
Then, the prediction difference value is added to the value of the previously received RTS information.
Output the predicted RTS information, and detect that the RTS information from the transmitting side has been lost.
The predicted RTS information is regarded as received RTS information from the transmitting side.
A SRTS control method for use in clock recovery .