Telephonic communications – Supervisory or control line signaling – Signal receiver
Reexamination Certificate
1998-08-04
2001-10-09
Chan, Wing F. (Department: 2643)
Telephonic communications
Supervisory or control line signaling
Signal receiver
C379S282000, C379S008000
Reexamination Certificate
active
06301355
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to diagnostic tools for low cost private branch exchange (PBX) switches, and more particularly, to a method and apparatus for analyzing dual-tone multi-frequency (DTMF) signals.
BACKGROUND OF THE INVENTION
FIG. 1
shows a conventional network environment consisting of a central office switch
110
of the Public Switched Telephone Network (PSTN) and a PBX switch
130
, such as the Merlin Legend™ PBX, interconnected by one or more DS1 digital trunks
120
-
122
. The central office switch
110
may be embodied, for example, as the DMS-100 central office equipment, commercially available from Northern Telecom, Inc. of Ontario, Canada. While PBX switches typically process call dialing signals from the central office switch
110
, the signals are generally DTMF signals.
FIGS. 2
a
through
2
c
illustrate the spectrum of DTMF signals from the central office switch
110
, corresponding to digits “3,” “1” and “5,” respectively. The DTMF signal for digit “1,” for example, as shown in FIG.
2
(
b
), will be the same regardless of the position of the “1” within a ten (10) digit telephone number.
As shown in
FIG. 1
, PBX switches, such as the switch
130
, typically include a touch-tone receiver (TTR)
140
for receiving and processing the DTMF signals. The Legend™ PBX, for example, includes a TTR embodied as a TMS320C17 digital signal processor (DSP), commercially available from Texas Instruments, Inc., of Dallas, Tex.
Typically, the TTR
140
on a PBX switch
130
, such as the Legend™ PBX, is a closed subsystem and does not provide an access interface to obtain information for diagnostic analysis. Generally, PBX switches, such as the switch
130
, do not provide any diagnostic or debugging support for DTMF signals. Thus, the manner in which a PBX switch processes DTMF data is unknown. In addition, such PBX switches do not provide a mechanism for analyzing a call failure problem due to DTMF signals. Currently, it is difficult, if not impossible, to even collect DTMF data on such a PBX switch.
For example, it has been found that inbound calls from a central office switch
110
to a PBX switch
130
are likely to fail on a subset of extension numbers when certain dial plans are implemented. In particular, a high call failure rate has been observed on incoming PBX calls associated with extension numbers having a digit “1” in the dialed telephone number and followed by at least one additional digit, for example, extension “315” or “7150,” even though the incoming DTMF signals comply with the DTMF specification. While preliminary investigations suggested a DTMF detection problem in the TTR of the PBX switch, the PBX switch does not have a diagnostic tool to identify the precise source of the call failure problem. The call failure problem cannot be reproduced with valid test scenarios in a laboratory environment. Furthermore, experimental trials on installed PBX systems are not practical, due to frequent service disruptions.
Since the source of the call failure problem could not be identified, the problem could also not be remedied. Thus, in order to avoid such call failures, PBX customers frequently did not assign extension numbers having a digit “1” followed by at least one additional digit, thereby limiting the effective capacity of the PBX switch.
As apparent from the above-described deficiencies with conventional PBX switches, a need exists for a diagnostic tool that analyzes DTMF signals on such PBX switches. A further need exists for a method and apparatus for simulating the processing of DTMF signals by a TTR. Finally, a need exists for a TTR simulator that facilitates the analysis and debugging of DTMF data.
SUMMARY OF THE INVENTION
Generally, a TTR simulator is disclosed to analyze DTMF signals and facilitate the investigation of call failure problems. According to a further aspect of the invention, the TTR simulator utilizes a general-purpose computing device to simulate the digital signal processing (DSP) instructions employed by a TTR in a PBX switch, such as the Merlin Legend™ PBX. In addition, the TTR simulator records the computational details of the TTR for subsequent data analysis. The TTR simulator allows details of the computation and processing results of the DTMF signals from the central office (CO) to be traced and recorded. In this manner, the TTR simulator allows the underlying cause of a call failure problem due to DTMF signals to be identified.
The TTR simulator captures DTMF data received by a PBX switch and utilizes simulated signal processing instructions to process the received DTMF signals on the simulated TTR. In addition, diagnostic tools to allow step-by-step tracing and recording of the instructions performed by the simulator. In this manner, results of digit interpretation can be compared to expected results.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.
REFERENCES:
patent: 5406621 (1995-04-01), Binal
Patricia Mock, “Add DTMF Generation and Decoding to DSP-&mgr;P Designs,” EDN, 205-20) (Mar. 21, 1985).
Bell Communications Research, Dual-Tone Multifrequency Receiver Generic Requirements for End-to-End Signaling Over Tandem-Switched Voice Links, Technical Reference TR-tsy-000181, Issue 1 (Mar. 1987).
Texas Instruments, TMS320C1x, User's Guide, Assembly Language Instructions, Ch. 4 (Jul. 1991).
Paul M. Embree, C Algorithms for Real-Time DSP, 53-97 (Prentice Hall 1995).
Merlin Legend™ PBX, User's Manual, System Overview, 2-9 thru 2-15 (Jun. 1997).
Avaya Technology Corp.
Bean Thomas J.
Chan Wing F.
Ryan & Mason & Lewis, LLP
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