Telephonic communications – Supervisory or control line signaling – Signal reception at substation
Reexamination Certificate
1998-10-06
2001-03-27
Zele, Krista (Department: 2645)
Telephonic communications
Supervisory or control line signaling
Signal reception at substation
C379S067100, C379S082000, C379S088120, C379S100050
Reexamination Certificate
active
06208731
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to Visual Message Waiting Indication (VMWIs) circuitry and more particularly to a VMWI device that intelligently detects both CLASS signals and stutter dial tones which are used by telephone companies to alert users regarding the status of their voice mail box.
Regional Bell Operating Companies (RBOCs) and Local Exchange Carriers (LECs) provide central office (CO) based voice mail services to business and residential customers. A shortcoming of these services has emerged over the past few years as the service has reached over 12,000,000 voice mail subscribers. The most frequent subscriber complaint concerning these voice mail services is the lack of visual notification. Currently, voice mail services provide notification to the user with a stutter dial tone. The user must physically pick up the phone and listen for the stutter dial tone. A preferred method would be visual notification that voice messages are in the user's mailbox. A second form of notification is based on a CLASS (Custom Local Area Signaling Services) signal that is transmitted to a subscriber's location and requires a CLASS VMWI detection device.
Stutter dial tone detection on the public phone service was approved by the Federal Communications Commission (FCC) with some limitations on Sep. 28, 1995. One important limitation is a ban on periodic sampling of the phone line. This limitation means that stutter-based VMWI may not detect messages forwarded from another voice mailbox. Other FCC limitations also prevent a stutter detection device from detecting messages cleared by a user from a remote telephone.
The limitations of FCC-approved stutter detection has motivated many telephone companies to offer a second signaling service. VMWI is one of the services defined by the Custom Local Area Signaling Services (CLASS
TM
) specification. CLASS VMWI is based on Frequency Shift Keying (FSK) signals transmitted from the CO whenever new messages are present in the user's voice mailbox and when messages are saved or deleted. CLASS VMWI has few of the limitations imposed on stutter dial tone VMWI. However, CLASS VMWI has several unique problems which can affect reliability.
If a user is on the telephone for a long period of time in a CLASS signaling environment and the CO switch attempts to send a CLASS VMWI signal, the CO switch will recognize that the telephone is off-hook and automatically reschedule the CLASS VMWI signal transmission for a later time. The interval before the CLASS VMWI signal is retransmitted may be as long as 30 minutes. If the user is constantly on the phone, the CLASS VMWI signal could be rescheduled almost indefinitely. As a result, detection of a CLASS VMWI signal could be significantly delayed.
Tests have proven that the CLASS VMWI signal is often blocked when a telephone line is connected to the CO through a Subscriber Loop Carrier (SLC). Stutter dial tone signaling is unaffected by SLCs.
VMWI circuits require a large amount of power to continuously detect either stutter dial tone VMWI or CLASS VMWI. Additional power is required to activate the visual indicator that reflects a waiting voice mail message. Standard A.C./D.C. power adapters must be connected to a wall socket that may be inconveniently located away from the telephone socket. A.C. power is also more susceptible to temporary outages and power transients than alternative D.C. battery supplies.
Accordingly, a need remains for an energy efficient VMWI circuit that identifies voice mail status more quickly and reliably in a wider variety of telephone systems.
SUMMARY OF THE INVENTION
A VMWI multisense detection circuit solves both the problem of long CLASS VMWI signal retransmission delays and unreliable CLASS VMWI signal transmission by simultaneously enabling both stutter dial tone detection and CLASS VMWI signal detection.
To resolve the delayed CLASS VMWI signal problem, the multisense circuit schedules a sample each time the phone is placed on-hook or after the phone goes unanswered after a ring. If a valid CLASS VMWI signal is detected, the circuit operates only in a CLASS detection mode and cancels the dial tone sample. In the exclusive CLASS detection mode, the phone does not have to be placed temporarily off-hook to detect stutter dial tone. If no CLASS VMWI signal is detected before the scheduled dial tone tests, the VMWI circuit performs the stutter dial tone detection, thus eliminating potentially lengthy delays waiting for the CO to retransmit CLASS signals. The VMWI circuit then operates in a dual CLASS/stutter dial tone detection mode. The multisense mode has the substantial advantage of reevaluating stutter dial tone detection after different voice mail trigger conditions. The reevaluation process looks for the CLASS signal for the predetermined time interval. If the CLASS signal is present, stutter dial tone detection is cancelled for that trigger event. If the CLASS signal is still not detected, stutter dial tone detection remains enabled.
This continuous stutter/CLASS multisense detection scheme allows the VMWI circuit to operate reliably with unreliable CLASS VMWI signal transmissions in an SLC based environment. If no CLASS signal is detected after a triggering event such as an off-hook condition or a no-answer after a ring, the multisense detection unit always switches to a dual sensing mode. For phone lines connected through a SLC, the multisense detection circuit ensures that the VMWI circuit is not “fooled” into operating as a CLASS-only unit by an inconsistent CLASS VMWI signal.
In a stable and prompt CLASS VMWI transmission environment, the CLASS VMWI signal arrives before the stutter dial tone sampling is scheduled to occur. Thus, the multisense circuit does not tax the CO by requesting unnecessary dial tone service.
In another aspect of the invention, the VMWI detection circuitry is designed to operate on a small amount of D.C. power for extended periods of time. The detection circuitry periodically polls for a preamble field of the FSK/CLASS signal to determine whether a valid FSK/CLASS signal is about to be transmitted. If the preamble is detected indicating a CLASS signal, the detection circuitry remains on and the CLASS signal is received and processed. If no preamble is detected, the detection circuitry is shut off until the next polling period. This polling technique allows the VMWI detection unit to operate only on batteries for long periods of time.
The VMWI circuit continuously measures the on-hook and off-hook line voltages and readjusts a reference voltage according to the measured values. The VMWI circuit then uses the reference voltage to detect triggering events such as an off-hook condition. Readjusting the reference voltages allows the VMWI circuit to operate in different telephone systems that have different on-hook and off-hook line voltages.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.
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DePond Paul F.
Larson Gaylan
Neal Greg
Yewell David
Hoosain Allan
Marger Johnson & McCollom PC
Zele Krista
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