Alarm and test system for a digital added main line

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This application is related to application Ser. No. 07/385,610, filed Jul. 25, 1989, which is completely incorporated herein by reference for all purposes.

MICROFICHE APPENDIX

This application includes a microfiche of Appendices 1, 2, 3, and 4, having 10 sheets totalling 819 frames.

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BACKGROUND OF THE INVENTION

The present invention relates to the field of telephone communication. More particularly, in one embodiment the present invention provides a method and apparatus for simultaneously transmitting information from multiple phone connections over a single twisted pair line.

Techniques for transmission of multiple voice or data signals over a single phone line are well known in the telecommunications industry and are commonly referred to as concentration techniques. In the past, frequency division multiplexing was the most commonly used technique for simultaneous transmission of multiple voice or data signals over a single line. Frequency multiplexing techniques are still commonly used in, for example, wideband transmission media.

Digital time division multiplexing techniques have been used since the 1960's and have become the most common concentration technique in, for example, interoffice circuits. An entire family of T-carrier (Trunk carrier) systems such as T1, T1C, T1D, T2, and T4, have been developed for concentration of multiple voice and data signals over a common line. Digital concentration techniques are described in, for example, Bellamy, Digital Telephony, Wiley and Sons, 1982, which is incorporated herein by reference for all purposes.

Digital communication has become relatively standard in, for example, intraoffice trunks. One example of a method for transmitting multiple voice or data signals over a single two- or four-wire transmission line is disclosed in Kaiser et al., "Digital Two Wire Local Connection Providing Office Subscribers With Speech, Data, and New Teleinformation Services," ISSLS, Mar. 20-24 (1978). In Kaiser et al., telephone data, viewdata, telecopier information and the like are transmitted in a digital fashion over a two- or four-wire line to a local exchange. Digital data are transmitted in data bursts which are later expanded and recovered using, e.g., time division multiplexing techniques.

Despite advances in the multiplexing techniques a variety of problems remain. For example, some multiplexing techniques continue to require complex and, therefore, uneconomical equipment. This equipment is particularly unsuitable for individual or small office users. Further, when applied to residential users, small office users, and the like, some systems require that the user provide a power source such as a transformer connection to a 120 v. power source, a battery power source or the like. Some systems require that the user replace existing two-wire connections with less conventional connections and/or are limited in the distance of twisted pair line over which information may be transmitted. In spite of certain advances in the ability to transmit multiple voice and data signals over single twisted pairs, most local switching units continue to provide a single analog signal over a single twisted pair to a typical home or office.

Prior techniques for providing service to home or office users have also provided limited capability for detection of failures in the system. Testing equipment has previously included, for example, the so-called MLT or 4TEL mechanical line testers and the SLIC 96. While meeting with some success, prior failure detection systems have met with certain limitations, particularly when applied to digital systems over twisted pairs between telephone company equipment and a subscriber. For example, some prior systems have been able to detect that a failure has occurred, but have been unable to identify the location of the failure. Other systems have been incompatible with existing telephone company facilities, or with digital twisted pair systems. Other equipment has required the installation of a test line between the central office terminal and a remote terminal at a customer facility. Still other systems have been exceedingly complex and/or costly.

Limitations with the mechanical enclosures for telephone equipment at customer facilities have also been encountered. Some enclosures have provided insufficient weather protection. Some enclosures have provided only limited access to frequently used components, have been excessively complex, utilize expensive components or fabrication techniques, or combinations of the above.

Problems have also arisen in connection with test ports for customer telecommunications equipment such as remote terminals at customer facilities. It is often desirable to provide an RJ11 connector of the type well known to those of skill in the art, or other such connector, at an external location at subscriber facilities such as a junction box leading to a house or a remote terminal of the type described above. Previously, such access is provided by installing a female RJ11 socket at such locations which is normally connected to a male RJ11 plug. The tip and ring wires (among others in some cases) lead from the female RJ11 socket, and connect to tip and ring connections in the male RJ11 plug, thereafter leading into the subscriber facility. When it is desired to connect test equipment to the RJ11 female socket, the plug is removed, and another male RJ11 is inserted into the female socket, thereby providing tip and ring connections for the test equipment.

Problems have arisen with such arrangements, however. For example, it is sometimes difficult to establish and maintain an adequate environmental seal in a removable male RJ11 plug, particularly when wires lead from the male RJ11 plug. Accordingly, moisture and other environmental contaminants are allowed to enter such plugs, sometimes resulting in corrosion and/or failure of the connection of the tip and ring connections in the socket/plug combination.

It is desirable to provide an improved and more economical method and associated apparatus for multiplexing multiple phone line connections over a single twisted pair connection especially for use in providing multiple phone lines over a single twisted pair into a home or office from a local telephone exchange. It would further be desirable to provide a system which provides useful alarm and failure detection systems which are also compatible with conventional telephone company service facilities. It is also desirable to provide an improved protection system for such equipment, as well as test access to customer equipment.

SUMMARY OF THE INVENTION

An improved method and apparatus for transmission of multiple signals over a single twisted pair is disclosed which provides in its various embodiments for the previously recited desirable features among others. In a preferred embodiment the invention provides for transmission of multiple voice and/or data signals over a single twisted pair from a local telephone exchange to a subscriber.

An improved test and alarm system for the digital transmission system is also disclosed. The alarm system provides for both automatic and self test. The system provides identification of the location of any failures in the system and is compatible with current telephone company repair and service facilities such as MLT/2 manufactured by AT&T, the Pair Gain Test Control (PGTC) system manufactured by AT&T, and 4TEL by Teradyne.

In one embodiment the test and alarm system comprises a test system for a digital main line system, the digital main line system including a line card (LC) at central office facilities and a remote terminal (RT) at a subscriber location. The digital added main line (DAML) system is adapted to transmit multiple signals in digital form from the line card to the remote terminal location over a twisted pair wire. The line card converts conventional analog signals to 2B1Q signals for transmission and the remote terminal converts the 2B1Q signals back to analog for use with conventional subscriber equipment. In a preferred embodiment, the system includes a remote terminal emulator at the central office facilities, the remote terminal emulator emulating output of the remote terminal with a predefined data pattern; and means for comparing a response of the line card to the emulated output so as to detect failures in the line card. The test system may further include a voltage source current monitor attached to the twisted pair, the voltage source current monitor adapted to detect failures in the twisted pair and generate ring and test request voltage for checking parts of the line card; a line card emulator, the line card emulator emulating output of the line card for transmission over the twisted pair; and means for detecting terminations, so as to detect failures in the remote terminal.

The test system may also include a voice frequency emulator, the voice frequency emulator connected to the line card or line card emulator for conversion to a digital signal for transmission over the twisted pair to the remote terminal, and means for evaluating a returned amount of noise or reflected signal so as to evaluate the function of the line card, the twisted pair and/or the remote terminal.

The test system includes testing of the digital-to-analog conversion equipment at the remote terminal, i.