Multiplex communications – Diagnostic testing – Fault detection
Reexamination Certificate
1998-02-27
2001-08-28
Kizou, Hassan (Department: 2662)
Multiplex communications
Diagnostic testing
Fault detection
C370S252000, C714S047300, C714S048000, C714S704000
Reexamination Certificate
active
06282173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a processing apparatus for measuring performance monitoring parameters in transmission equipment, and particularly, to a processing apparatus for measuring performance monitoring parameters with improved accuracy in detecting transmission signal errors.
2. Description of the Related Art
Standardization of performance monitoring (PM) has resulted in G.826 and other recommendations formulated by the International Telecommunication Union—Telecommunication Sector (ITU-T), which provide common definitions for signal quality management in transmission paths. In actual error performance measurements, transmission equipment monitors incoming bit streams to detect performance anomalies and defects (e.g., bit errors), collects error data on some prescribed criteria, and reports the statistics of the detected errors, called “PM parameters.”
FIG. 10
is a block diagram which shows a typical configuration of a conventional PM parameter processing unit, which is composed of the following main functional blocks: a failure detection unit
102
, a PM controller
103
, a counter unit
104
, and a control signal generator
105
. Reception signals carried over a transmission line
101
are monitored by the failure detection unit
102
, which comprises a CV detector
102
a
and an LOS detector
102
b
. The CV detector
102
a
detects “Code Violation” (CV) errors in the reception signals, while the LOS detector
102
b
detects “Loss of Signal” (LOS) conditions. CV errors include bit errors, for instance, and LOS means the absence of reception signals lasting for a prescribed period. The detected CV errors are sent to an “Errored Second” (ES) detector
103
a
and a “Severely Errored Second” (SES) detector
103
b
disposed in the PM controller
103
, as well as to a “Code Violation-Line” (CV-L) counter
104
a
in the counter unit
104
. Likewise, the detected LOS condition is sent to the ES detector
103
a
and SES detector
103
b
in the PM controller
103
, an “LOS Second-Line” (LOSS-L) counter
104
b
in the counter unit
104
, and the control signal generator
105
. The CV-L counter
104
a
counts the occurrences of CV errors. The LOSS-L counter
104
b
measures the duration of LOS conditions in seconds. The ES detector
103
a
sends an ES-L indication signal to an ES-L (Errored Second-Line) the counter
104
c
in the counter unit
104
, when one or more CV errors have been observed in a predetermined time period or when an LOS condition has been detected. The ES-L counter
104
c
measures the duration of this ES-L indication signal in seconds. The SES detector
103
b
sends an SES-L indication signal to a “Severely Errored Second-Line” (SES-L) counter
104
d in the counter unit
104
, when 45 or more CV errors have occurred within a predetermined time period or when an LOS condition has been detected. An SES-L counter
104
d
measures the duration of this SES-L indication signal in seconds.
The control signal generator
105
watches the LOS detection signal, and when an LOS condition is detected in a certain time segment, it generates a control signal for that time segment. The control signal generated as such is supplied to the CV detector
102
a
so as to stop its operation. The next section will describe the details of this process, with reference to FIG.
11
.
FIG. 11
is a timing diagram which describes the operation of the conventional PM parameter processing unit of
FIG. 10
, which specifically shows (A) time segments, (B) lower layer failures, (C) upper layer failures, (D) LOS condition, (E) the number of lower layer failures, and (F) failures detected by the CV detector. Note that the time axis is divided into 1-second time segments (A) and some elements in the PM parameter processing unit operate on this segmented time basis.
This timing diagram of
FIG. 11
assumes that some lower layer failures (B) have happened, and thus the LOS detector
102
b
has detected some LOS conditions. The LOS conditions, which mean the absence of the reception signal, derivatively cause bit errors to be sensed by the CV detector
102
a
. As a result, some upper layer failures will be detected as indicated by the upward arrows (e) and (f) in FIG.
11
. Although the upper layer failures (C) seemingly include many error indication pulses, only five pulses (a), (b), (c), and (d) represent the true bit errors independent of the LOS conditions, while the others are false errors derived from the LOS conditions. In such a case, the CV detector
102
a
has to detect only those genuine errors (a), (b), (c), and (d), but not the false ones (e) and (f). In reality, however, the CV detector
102
a
is unable to discriminate the false failures by itself. If the CV detector
102
a
signaled all those failures without discrimination, the counter unit
104
would accumulate the upper layer failures erroneously, and thus the resultant PM parameters would exhibit much larger values than the true values.
The conventional processing unit employs the control signal generator
105
that produces an appropriate control signal to avoid the above-described problem. In the present context shown in
FIG. 11
, the control signal generator
105
recognizes the presence of LOS conditions (D) from the output of the LOS detector
102
b
. It should be noted here that this LOS recognition is conducted on the basis of the predetermined time segments (A). More specifically, the control signal generator
105
drives its control signal output to “1” to disable the CV detector
102
a
, when an LOS is detected in each time segment (e.g., 1 second). In turn, it resets the signal to “0” when no LOS condition is observed. Meanwhile, the number of upper layer failures detected by the CV detector
102
a
in each time segment is indicated in (E) of FIG.
11
. The CV detector
102
a
, however, does not always output the number of upper layer failures (E) as is, but it masks all failures in the time segment when the control signal with a value of “1” has been received from the control signal generator
105
. Only when the control signal is “0,” the CV detector
102
a
reports the number of detected upper layer failures as originally is. As shown in (F) of
FIG. 11
, the CV detector
102
a
indicates no failure in the first three time segments (1) to (3) due to the failure masking operations by the control signal generator
105
.
In this way, the conventional PM parameter processing unit avoids the problem of false failure detection. However, there arises a side effect that the processing unit may fail to detect some true upper layer failures, such as (a), (b), and (c), which must be detected by the CV detector
102
a
. This is because the control signal generator
105
produces the control signal on the basis of discrete time segments, and the control signal masks all upper layer errors regardless of “true” or “false,” within the time segment in which an LOS condition is observed. Accordingly, the counters in the counter unit
104
are unable to correctly accumulate the values of PM parameters.
The errors in the counter values obtained from the counter unit
104
could be compensated for by applying some appropriate firmware processes. However, it is desirable to seek a more accurate, hardware-based way of measuring the PM parameters, not to increase the workload imposed on the firmware.
SUMMARY OF THE INVENTION
Taking the above into consideration, an object of the present invention is to provide a PM parameter processing apparatus for measuring accumulated values of PM parameters, which is capable of detecting upper layer failures in a more accurate, hardware-based way that does not increase the workload imposed on the firmware.
To accomplish the above object, according to the present invention, there is provided a processing apparatus for measuring performance monitoring (PM) parameters concerning a reception signal received by a transmission device. Here, the PM parameters refer to the statistics of events that meet prescribed criteria for defects and anomalies i
Isonuma Yutaka
Kawataka Miyuki
Nakayama Mikio
Fujitsu Limited
Helfgott & Karas P.C.
Kizou Hassan
Stevens Roberta
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