Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2001-01-17
2004-03-02
Tran, Pablo N. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S226100, C455S227000, C455S560000, C370S408000, C370S362000, C379S039000
Reexamination Certificate
active
06701131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is concerned with the field of telecommunications and with the detection and analysis of call progress signals generated by a telecommunications system, and, more particularly, with international call progress analysis.
2. Discussion of Related Art
Call progress analysis (CPA) involves the monitoring of a telecommunications channel for identifiable system-generated call progress signals which indicate the status of the call being monitored. Examples of such signals are dial tone, ringback, busy, and the like. These signals not only provide audio information to a user of the telephone line but, if properly monitored, allow steps to be taken toward connection of the call or one of various other appropriate actions.
CPA has been implemented in the past as part of a programmable telecommunications switch. Typically, these conventional digital telecommunications switches employ a time slot interchange (TSI) to effect switching using time division multiplexing (TDM) techniques. In addition to controlling the switching of calls, digital telecommunications switches are also usually required to provide communications or call processing services. Such services include tone generation and tone detection, but may also include more sophisticated services to meet the requirements of a particular application. A switch of this type is used in a system described by U.S. Pat. No. 5,349,579 entitled “TELECOMMUNICATIONS SWITCH WITH PROGRAMMABLE COMMUNICATIONS SERVICES.” That patent is assigned to the assignee of the present invention, and is incorporated herein by reference.
In the past, call progress signals have been distinguished based on a minimum energy level present in one or more frequency bands, which energy had a particular cadence (i.e. how the signal energy alternates between being present and being absent). One example of such a system is demonstrated by European Patent Application EP 0 493 056 A2, submitted by Gupta, et al. (the “Gupta” system).
The Gupta system involves call progress analysis in which different signals are differentiated by the cadence patterns they follow. Different cadence patterns may be stored during setup of the system. The presence of sufficiently similar cadence patterns on the monitored telephone line allows the system to determine when certain call progress signals are present.
The Gupta system relies on combinational logic to verify that the signal energy on the monitored line is in the desired frequency bands. When the detected energy is in any one of the expected frequency bands, and when an expected cadence pattern is detected, the presence of the call progress signal having that cadence is confirmed. The Gupta system does not report all frequencies to all pattern detectors, only to those pattern detectors whose patterns contain these frequencies. The routing of frequencies to pattern detectors is static. This routing cannot be modified on a call-by-call basis. If the signal energy is in one of the expected frequency bands, the system confirms the presence of a call progress signal described by the detected cadence pattern, regardless of whether the signal contains the frequencies associated with that particular call progress signal. As such, a spurious signal having the cadence of one call progress signal, but the frequency content of another, could be confirmed by the Gupta system as being the call progress signal having that detected cadence pattern. In addition, it does not appear that Gupta provides the capability of customization by a user of the types of patterns that user desires in a plan. Gupta requires separate hardware for every defined plan, which could become costly and introduce space constraints on the card.
With the advent of localized telephone systems such as private branch exchanges (PBXs), the types of call progress signals are becoming more diversified. The larger number of different signals allows a system to perform a larger number of various operations. However, it also requires that a CPA system be able to distinguish the additional call progress signals.
One example of the problems confronting modern CPA is that different telecommunications systems use different call progress signals in different capacities. That is, a particular call status may be identified by one signal in a first PBX, and by a completely different signal in a second. A similar problem is prevalent with regard to the public telephone networks of different countries, many of which use vastly different call progress signals for the same functions. In either of these situations, no standard exists with regard to the use of call progress signals. Therefore, a conventional CPA system must either be custom built for the particular country or the particular PBX system for which it is intended, or must be versatile enough to accommodate different sets of call progress signals.
The programmability of the Gupta system allows a system to be set up for a particular designated environment. However, if that environment contains signals, which are too closely, related in cadence (while having a different frequency spectrum), the system will be unable to distinguish them. Also, the frequencies and tones in the Gupta system are not automatically customized by the definitions of the call progress patterns to be detected. A high accuracy CPA system would allow the discrimination of different signals, which were closely related in frequency or cadence, and would reduce the false alarm rate of detection. Such discrimination would be customized on a call-by-call basis. This would greatly increase the number of distinguishable call progress signals and, thus, provide more system versatility.
SUMMARY OF THE INVENTION
The present invention provides a call progress analysis system and method for use with a programmable telecommunications switch. The system is preferably completely generic in that all of the detection parameters may be configured for the specific application of any particular end user. The system includes a host, which communicates with a data processor on the switch. The data processor controls the operations of one or more digital signal processors (DSPs) which are used to monitor channels of the switch for call progress signals.
The data processor runs a main detection program which processes detected signal data and compares it to stored information that represents pre-defined call progress signals. Stored in a memory unit is at least one group of tone descriptors that define different expected tones. Each tone descriptor defines a tone by the presence of particular frequencies at a minimum threshold energy level. For a particular end user who needs to detect a particular set of call progress signals, the tone descriptors may be configured by storing parameters which describe the frequencies and relative energy levels which are associated with the those signals. Also stored in memory is at least one set of pattern descriptors which reference the tone descriptors, and which define different expected cadence patterns. Like the tone descriptors, these pattern descriptors are configured for the particular telecommunications system being serviced by setting the parameters of the pattern descriptors such that they describe those call progress signals which the system user is likely to encounter.
In response to a message to perform CPA, the processor dynamically instructs an assigned DSP to begin monitoring a particular channel. The DSP functions as a signal detector and returns information to the processor. In the preferred embodiment, the DSP has access to the tone descriptors and, upon comparing the detected frequencies to the tone descriptors, assembles a message indicative of individual frequencies that are present in the detected signal. A new message is assembled and sent by the DSP to the processor each time there is a significant change in the detected signal. The DSP also includes in each message an indication of the elapsed time since the last message was sent. Thus, a new time interval sta
Kicklighter Kevin C.
Weller Franz
Excel Switching Corporation
Tran Pablo N.
LandOfFree
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