WO1992022152A1 - Pcm monitor - Google Patents
Pcm monitor Download PDFInfo
- Publication number
- WO1992022152A1 WO1992022152A1 PCT/AU1992/000265 AU9200265W WO9222152A1 WO 1992022152 A1 WO1992022152 A1 WO 1992022152A1 AU 9200265 W AU9200265 W AU 9200265W WO 9222152 A1 WO9222152 A1 WO 9222152A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- pcm
- sample
- data
- circuit
- data sample
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B14/00—Transmission systems not characterised by the medium used for transmission
- H04B14/02—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation
- H04B14/04—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation using pulse code modulation
Definitions
- the present invention relates to a method and apparatus for acquiring and analysing PCM data in a communications system.
- PCM pulse code modulation
- PCM channels sequentially to provide estimates of voice and data traffic.
- Other devices require introduction of test signals, thereby utilising valuable system capacity, and do not examine real life telephony signals.
- One aspect of the present invention relates to a method of analysing PCM communications, comprising:
- the present invention comprises apparatus for analysing PCM communications, comprising in combination:
- interfacing means for connecting to at least one PCM stream and allowing selection of any circuit within said PCM stream;
- sampling means for extracting a PCM sample of predetermined duration from said circuit;
- processing means for producing a non-compressed data sample corresponding to said PCM sample;
- memory means for storing said data sample;
- FIG. 1 is a block schematic diagram of the overall arrangement of the invention.
- Figures 2 to 7 illustrate visual displays of samples of circuit waveforms in various circumstances. Detailed Description
- the quality monitor according to the present invention is preferably hosted by a PC, such as an IBM compatible PC (AT type). It should be appreciated that the exact processor used to implement the invention is by no means a limitation on the scope of the present invention.
- the embodiment of the present invention which will be described in detail can monitor 8 PCM streams (both transmit and receive paths) with up to 248 PCM circuits. It can detect, measure, and report on echo and other transmission impairments such as excessive signal levels, PCM coding errors, and codec level saturation. It can also help in the investigation of more obscure defects such as incomplete echo cancellation due to distortion of the echo signal.
- the inventive device will also provide reports on traffic classifications such as Voice, Data and Other (idle AIS etc).
- the present invention allows for non-intrusive measurement of live telephone traffic so as to provide objective measurements of call quality.
- the inventive device operates such that the measurements are indicative of call quality as experienced by users of the communications network.
- sample data is acquired from PCM streams 30 via a 4- wire interface 19 to acquisition module 17. This requires the steps of :
- the interface with the PCM stream is preferably via high impedance probes, so as to minimise the intrusiveness of the operation.
- Step (iv) is preferably performed by means of a look-up table.
- each compressed format 8-bit value has a non-compressed 12-bit equivalent.
- the conversion may be performed by referring to the memory location referenced by the compressed format and extracting the corresponding non-compressed
- the sample data may then be dealt within a variety of ways as required.
- An important advantage of the present invention is that the data once extracted for each sample period may be stored and reviewed or processed at leisure. The exact reasons for sampling or monitoring need not be apparent when the sample is monitored -any desired analysis may be performed as and when required. Moreover, analyses' may be performed which are difficult or impossible in real time, for example echo estimation, noise measurements, peak and average signal levels, PCM coding saturation and PCM coding errors. This analysis is carried out by the DSPU 15. It may be directly stored for later review, using memory 18 or external memory devices 22, or displayed on the VDU screen 21 after processing by display module 13.
- One of the first operations which is generally performed during either sampling or monitoring is to determine the type of signal being dealt with i.e. whether we have speech or data or no activity. This is done by quantifying the way the activity level is changing in the captured sample. Data type activity tends to be very constant in its activity pattern while speech activity tends to be variable.
- STATIC/IDLE or AIS which is the case depends on the value itself. Also the range of values in a sample is examined. The analysis of the values in a given range yields such information as the presence of level saturation and/or the presence of coding errors. if a display of the captured sample is required then the video controller of the PC is switched into 'bit-mode' and the captured sample is 'bit-mapped' onto the screen, as is well understood by those skilled in the art.
- Passive echo analysis may be carried out to determine echo delay and magnitude. Delays of at least 1050 ms may be identified and quantified using the illustrated embodiment of the invention. This is performed by cross-correlation to locate signals and images, and the time delay and reflection coefficient can then be readily determined. This technique can therefore passively monitor both near and far end echo. Further, when this data and the known circuit and the time data are compared with TCDP data relating to call destination and routing, the source of echo can be located and rectified. This is a very powerful tool for locating and eliminating problems in local and remote networks.
- the algorithm that detects and quantifies echo is a two stage process. The first process consists of a cross-correlation (done in the frequency domain) to detect and 'roughly' quantify an echo. The second process consists either of cross-correlation in time or an adaptive-filter type process (least-mean-squares), both evaluated over the delay reported by the first process. The purpose of the second process is to precisely quantify the echo.
- the monitor is adapted to be left on a poll, monitor, and store basis connected to a set of PCM streams, the data may be accumulated for later attention to abnormalities.
- the monitor can monitor noise on a long term basis and highlight unsuspected or unlocated problems. Trials of the system have located problems associated with peak clipping, coding errors, and harmonic distortion whose existence was previously not suspected.
- the present invention is capable of discovering and locating errors which would either go undetected with existing apparatus or whose discovery would be extremely time consuming and labor intensive. It will be appreciated that in the monitor mode of operation, samples are generally held for so long as necessary to extract the required data and then deleted.
- a further advantage of the present invention is that it provides for display of the PCM streams, not merely statistics. This has proved experimentally to be of great assistance in locating and recognising problems and is not provided in existing systems.
- Figure 2 illustrates a typical normal speech transmission with no echo evident.
- the RX signal is a delayed and attenuated replica of the transmitted signal.
- the RX signal is amplified to make the trace more legible.
- the horizontal axis represents about 5 seconds
- the echo is delayed by about 1 second.
- Figure 4 illustrates a trace exhibiting near-end echo - the near end of the transmitting link is transmitting echo back to the far end of the transmission link. The delay is, as a consequence, much shorter.
- PCM can handle signal levels which, when quantised, correspond to the 12-bit number +/- 4032.
- analogue signals above this level are input into a PCM coder it 'clips off the levels above the saturation threshold.
- the PCM signal is converted back to analogue form in the receiving end, it will look as if its peaks have been clipped off.
- Figure 5 illustrates a signal exhibiting level saturation on the receive path.
- the invention may be used to detect codec saturation and excessive levels, and report the maximum and average levels for both the transmit and receive lines. Level measurements are vital in the quality-monitoring process because saturation may cause perceptible harmonic and intermodulation distortion to conversations. Moreover, excessive levels may cause problems to data equipment and are likely to jeopardise the correct functioning of echo cancellers, resulting in excessive echo. Coding errors occur when an analogue signal is within amplitude range of the
- PCM scheme but is not coded correctly from analogue form at the transmitting end. When this occurs customers are likely to hear 'hollow', distorted speech, and data traffic may be corrupted.
- Figure 6 illustrates the display associated with such errors. Because the inventive monitor detects and displays coding errors, corrective action can be initiated early.
- Figure 7 illustrates the display associated with data traffic on both transmit and receive paths.
- the monitor is arranged such that an initial sampling for about 1 second occurs, after which the sample is processed to determine whether the circuit is carrying voice or non voice traffic. If the sample is non voice, no further sample is required. If , however, the sample is a voice signal a further about 4 second sample is required to allow for echo detection.
- control software 12 via an operator interface 11 and suitable input means such as a keyboard 20.
- the monitor according to the present invention may be remotely accessed and data downloaded via any suitable link, for instance serial or telephone lines. This in turn allows for a set of monitors to be controlled from a single central location. It is also noted that the inventive device may also be used to monitor 4-wire analogue connections.
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Monitoring And Testing Of Exchanges (AREA)
- Monitoring And Testing Of Transmission In General (AREA)
- Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9223673A GB2261801B (en) | 1991-06-07 | 1992-11-12 | PCM monitor |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AUPK657891 | 1991-06-07 | ||
AUPK6578 | 1991-06-07 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1992022152A1 true WO1992022152A1 (en) | 1992-12-10 |
Family
ID=3775458
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/AU1992/000265 WO1992022152A1 (en) | 1991-06-07 | 1992-06-05 | Pcm monitor |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0542976A4 (en) |
GB (1) | GB2261801B (en) |
WO (1) | WO1992022152A1 (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2295299B (en) * | 1994-11-16 | 1999-04-28 | Network Services Inc Enterpris | Enterprise network management method and apparatus |
GB2337903B (en) | 1998-05-28 | 2000-06-07 | 3Com Corp | Methods and apparatus for collecting storing processing and using network traffic data |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1572582A (en) * | 1977-03-03 | 1980-07-30 | Northern Telecom Ltd | Circuit and method for digitally measuring signal level of pcm encoded signals |
US4821267A (en) * | 1986-04-11 | 1989-04-11 | Siemens Aktiengesellschaft | Monitoring apparatus for monitoring the operating condition of transmission facilities of communications transmission technology |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CH545560A (en) * | 1971-05-06 | 1974-01-31 | ||
JPS6167330A (en) * | 1984-09-11 | 1986-04-07 | Nec Corp | Echo eliminating method |
JPS6351734A (en) * | 1986-08-21 | 1988-03-04 | Nec Corp | Testing instrument for pcm signal band compressing and reproducing device |
JP2671758B2 (en) * | 1993-06-25 | 1997-10-29 | 住友金属工業株式会社 | Welding bead shaping method and apparatus for hot dip galvanized H-section steel |
-
1992
- 1992-06-05 EP EP19920912387 patent/EP0542976A4/en not_active Ceased
- 1992-06-05 WO PCT/AU1992/000265 patent/WO1992022152A1/en not_active Application Discontinuation
- 1992-11-12 GB GB9223673A patent/GB2261801B/en not_active Expired - Fee Related
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1572582A (en) * | 1977-03-03 | 1980-07-30 | Northern Telecom Ltd | Circuit and method for digitally measuring signal level of pcm encoded signals |
US4821267A (en) * | 1986-04-11 | 1989-04-11 | Siemens Aktiengesellschaft | Monitoring apparatus for monitoring the operating condition of transmission facilities of communications transmission technology |
Non-Patent Citations (2)
Title |
---|
PATENTS ABSTRACTS OF JAPAN, E104, page 110, JP,A, 57-9151 (Mitsubishi Denki K.K.) 18 January 1982 (18.01.82). * |
See also references of EP0542976A4 * |
Also Published As
Publication number | Publication date |
---|---|
GB2261801B (en) | 1994-01-05 |
GB2261801A (en) | 1993-05-26 |
EP0542976A1 (en) | 1993-05-26 |
GB9223673D0 (en) | 1993-03-17 |
EP0542976A4 (en) | 1993-08-11 |
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