Worldcom, Inc.

Mci Communications Corporation

Mci Worldcom, Inc.

Frank A McKiel, Jr

Charles Mao

Niall Robinson

John Arthur Fee

David P Jordan

To prevent fraud perpetrators from using a public pay telephone to illicitly collect account numbers, authorization codes or personal identification numbers from an unsuspecting user of the telephone, the instant invention disables the keypad of the telephone if an incoming call is being received at the time that the handset is lifted from the phone by the user. In one method, the ringing signal and the off-hook condition are detected and a control output is provided which disengages the dialing tone generating circuits of the telephone until the handset is placed back on-hook. According to an alternative method, after the handset is lifted, a dial tone is sensed and evaluated by a dial tone discriminator to determine whether the dial tone is likely to be a valid dial tone from a legitimate service provider. If the dial tone is determined to be invalid, then the keypad of the telephone is disabled until the handset is placed back on-hook.

System and method therefor of preventing fraud on pay phone credit/debit calling card authorization

An optical communication system and method of use thereof which uses dispersion compensators to intentionally create a dispersive condition at the output of subsequent inline optical amplifiers. The present invention reduces four-wave mixing and increases the allowable spacing between optical amplifiers, thus reducing the required number of amplifiers and dispersion compensators for a given length of optical fiber. In one embodiment, dispersion compensators and optical amplifiers are alternately spaced from one another along a length of an optical fiber such that the dispersion compensators render a dispersive condition at the amplifiers allowing each amplifier to be run at a higher power level. In another embodiment, the dispersion compensator is collocated with the amplifier, but is positioned between a pre-amp stage and a high power output stage to overcompensate both the slope and absolute dispersion of the fiber up to that point. The dispersion compensator provides a dispersive condition at the output of the output stage allowing the amplifier to be operated at a higher power level without creating four-wave mixing. In yet another embodiment of the invention, an additional dispersion compensator is provided at the output of a transmitter to overcompensate both the slope and absolute dispersion of the fiber to render a substantially neutral dispersion signal upon arrival at the next optical line element or receiver.

Optical link with reduced four-wave mixing

A method and apparatus performing fault management in an optical communications system including a polarization mode dispersion (PMD) compensator. The method and apparatus utilizes a controller receiving notifications indicative of PMD in the system, as well as at least one indicator from a system device providing an indication of an attribute of the communication system. Such system devices include a receiver providing a Q factor and a bit error rate (BER) of an optical signal, and a signal-to-noise ratio meter providing an SNR of the optical signal. The method intelligently provides fault management by correlating the PMD notifications and system indicators to distinguish between fiber failure, PMD-related degradations, and failure of monitoring equipment itself.

Fault isolation of an optical link by correlating PMD events with other measurements

An optical communications link including a low-level subcarrier to identify the optical carriers that are contributing to an unwanted mixing product. The subcarrier is added to each of the optical carriers, and then the presence or absence of the subcarrier is detected in the mixing product to identify which optical carriers are contributing towards the generation of the mixing product. The subcarrier will appear in the mixing product if its associated optical carrier is participating in the mixing product. The identified optical carriers that contribute to the mixing product can then diminished in amplitude or shifted in wavelength to reduce the impact of the undesirable signals. Several embodiments are described.

Method and system for identifying undesired products of non-linear optical mixing

A system, method and apparatus are described that allow for the updating and transmittal of a low data rate signal providing ancillary network data as a rider on a high data rate optical signal. This subcarrier modulated signal can be processed and updated by using a drop/insert facility without having to alter the high data rate signal component of the data signal. Since the subcarrier signal can be detected by inexpensive equipment without having to detect and demultiplex the high data rate signal, the approach described offers a cost effective solution to the problem of network monitoring. Ancillary network management information can be communicated regardless of the quality or loss of the high data rate signal. In addition, by updating the subcarrier signal rider in a cumulative manner, a complete history of the fiber link the modulated optical signal travels on is provided to network management.

Method and apparatus for updating subcarrier modulation in a

An efficient and inexpensive system and method for reducing crosstalk between adjacent channels in a high density WDM transmission. The technique provided herein cancels out the effects of crosstalk by processing signals in the electrical domain after the optical WDM transmission has been demultiplexed. Specifically, a WDM transmission is received and demultiplexed into its constituent channels via a plurality of optical filters. Each channel is then transduced into an electrical signal using a photodetector or the like. Each electrical signal is then inverted, attenuated and added to one or two adjacent channels to cancel crosstalk therein.

Growing community of inventors

Plano, TX, United States of America

Frank A McKiel, Jr