Multiplex communications – Wide area network – Packet switching
Patent
1992-10-23
1994-08-09
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
375118, H04J 306
Patent
active
053373154
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a stuffing process and apparatus for reducing waiting time jitter, of the type in which: synchronizer and the first digital signal is written into an elastic memory (ES) in the synchronizer with a first clock pulse (t.sub.A) having a pulse rate which corresponds to the first bit rate of the first digital signal (A); second bit rate with a second clock pulse (t.sub.B) having a pulse rate which corresponds to the second bit rate of the second digital signal (B), whereby the elastic memory (ES) will have a mean loading; and (B) are generated, reading out of the elastic memory is controlled, and stuffing is performed as a function of a control parameter supplied to the frame counter.
If a first asynchronous digital signal is intended to be inserted into a second digital signal, the basic problem of frequency adaption arises. This problem is solved by stuffing. A problem of the conventional stuffing process lies in that the first digital signal recovered by destuffing may contain a low-frequency jitter, waiting time jitter, which can no longer be removed. The size of this jitter is the result of the stuffing process employed.
The conventional process for positive stuffing and the size of waiting time jitter caused by this is known from D. L. Duttweiler, in "Waiting Time Jitter", The BELL system Technical Journal, Vol. 51, No. 1, 1972, pages 165 to 207. Waiting time jitter in the course of positive-null-negative-null stuffing is treated in an article by F. Kuhne, K. Lang, in "Positiv-Null-Negativ-Stopftechnik fur Multiplexubertragung plesiochroner Datensignale" [Positive-Null-Negative Stuffing Technology for Multiplex Transmission of Plesiochronous Data Signals], Frequenz [Frequency], Vol. 32, No. 10, 1978, pages 281 to 287.
It is known from this reference to supply a first digital signal with a first bit rate to a synchronizer and to write it there with a first pulse corresponding to the bit rate of the first digital signal into an elastic memory. A second digital signal is read out of the memory with a second pulse, the second clock rate corresponding to the bit rate of the second digital signal. The frame of the second digital signal is generated and the read activation of the elastic memory is controlled in counters. The mean loading of the elastic memory is determined once per frame of the second digital signal. A difference between the mean loading and the set value for the mean loading is formed for each stuffing frame of the second digital signal. It is known to compare the difference with a maximum deviation. If the difference is greater than the maximum deviation, stuffing is performed.
A process for reducing waiting time jitter in the course of positive-null-negative stuffing was described by D. CHOI in "Waiting Time Jitter Reduction", IEEE Transactions on Communications, Vol. 37, No. 11, 1989, pages 1231 to 1236. The author assumes that a nominal stuffing process from null, such as is the case in the positive-negative stuffing process, results in large waiting time jitter. Therefore, the proposed process initiates a stuffing ratio not equal to null and in this way achieves a reduction of waiting time jitter.
In the publication by W. D. Grover, T. E. Moore, J. A. McEachern in "Waiting Time Jitter Reduction by Synchronizer Stuff Threshold Modulation", GLOBECOM '87, pages 514 to 518, additional stuffing operations are provided for reducing waiting time jitter, which additional stuffing operations take place in such sequence that the effect is a frequency displacement of the jitter. It is only required for executing this process to provide a new control in the synchronizer for the time when stuffing is intended. While up to now stuffing was always performed when constant thresholds were exceeded in either direction, the thresholds are modulated in the present case.
This species-defining reference therefore proceeds from a method corresponding to that in the article by Kuhne and Lang. However, the method does not operate with fixed thresholds,
REFERENCES:
patent: 4811340 (1989-03-01), McEachern et al.
patent: 5067126 (1991-11-01), Moore
patent: 5146477 (1992-09-01), Cantoni et al.
patent: 5172376 (1992-12-01), Chopping et al.
"Waiting Time Jitter Reduction by Synchronizer Stuff Threshold Modulation"; Grover et al; IEEE Proceedings Global Telecommunication Conference; Tokyo Nov. 15-18, 1987, Band 1, IEEE.
"Messung der Langzeit-Phasenschwankungen in Stuffing-Multiplexsystemen fur PCM- Und Datensignale"; Muller, Nachrichtentechnische Zeitschrift, Band 29, Nr. 4, Apr. 1976 (Berlin, DE).
"Positiv-Null-Negativ-Stopftechnik fur Die Multiplexubertragung Plesiochroner Datensignale"; Kuhne et al; Frequenz, 32 10, Seiten 281 bis 287.
"Waiting Time Jitter"; Duttweiler; The Bell System Technical Journal; vol. 51, No. 1, Jan., 1972.
"Waiting Time Jitter Reduction"; Choi; IEEE Transactions on Communications; vol. 37, No. 11, Nov., 1989.
ANT Nachrichtentechnik GmbH
Safourek Benedict V.
Ton Dang
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