Dual Span Monitoring System for Maintenance Shelf Control

The present invention relates generally to telecommunication transmission facilities and, more particularly, to a maintenance shelf system having a digital network interface and a common control unit with a protection switching mechanism. Many telecommunication transmission facilities include a central office which may transmit data, or "payload," signals over transmission lines to customer equipment on the customer's premises. Typically, digital payload signals are sent over the transmission lines to a digital network interface. These may also be referred to as a Network Interface Unit ("NIU").

The NIU is the demarcation between the telephone operating company's side of the telephone line and a customer's side of the telephone line. Electrically, the NIU is generally transparent to payload signals, but can be used for special maintenance functions, such as loop back. A channel bank receives signals from the NIU and converts the payload signals to analog signals. The channel bank transmits an analog signal for each channel differentially on two wire conductors, known as a Tip-Ring pair.

The Bell telephone system in the United States, for example, has widely utilized digital time-domain multiplexing pulse code modulation systems. This is known as a T-1 transmission system. Each T-1 transmission system carries 24 8-KB/second voice or data channels on two pairs of exchange grade cables. One pair of cables is provided for each direction of transmission. T-1 transmission systems are used in multiples 37 N", providing 37 N"-times-24 channels on 37 N"-times-two cable pairs. The cables exist in sections, called "spans," between and beyond a series of regenerative repeaters.

Payload signals are received by the telephone company and are transmitted, via the first spans of transmission lines, to alternating series of regenerative repeaters and further spans. Regenerative repeaters are spaced approximately every 6,000 feet, and the "spans" are the lengths of the cables between the repeaters. Each repeater receives data from a preceding repeater (or in the case of the first repeater, the central office) via a span on either side of the repeater. Each repeater generally recognizes pulses on the spans, however degraded, and regenerates clean pulses on the next spans.

The repeaters and cable spans continue until the lines extend to the NIU. From the NIU, customer connections continue into the customer premises.

A spare set of transmission cables, or a "spare line," is desirable, to provide for events of natural disaster, accident, maintenance, and upgrade. A spare transmission line is often provided to permit switching the spare transmission line into service in substitution for any one of the 37 N" multiple service lines which might become disabled. This is known as 1:N protection switching.

Since each T-1 span requires a network interface unit and multiple spans are typically routed together, multiple network interfaces are placed in the same physical location. The mounting that provides access to the network interface is called a maintenance shelf. Maintenance shelves are also known to provide a common control unit that serves as a remote control for the switching of a spare line in a 1:N protection system. Remote control of the span switching process reduces the need for technician visits to maintenance shelves located miles from telephone company central offices.

It is known to provide such a protective switching mechanism in which the mechanism monitors the inoperative line for a "restore service" signal and returns the service and spare lines to the original condition in response to such a signal. Unfortunately, while advantageous, such switching mechanisms do not as completely eliminate technician visits to maintenance shelves as would be desired. U.S. Pat. No. 5,224,149 is incorporated by reference, for additional illustration of the state of the art.

As described above, past protection switching mechanisms associated with spare telephone lines (such as T-1 lines) have monitored the "swapped" or interrupted transmission cable pairs, or "line," for a restoration of service signal. The present invention comprises a protection mechanism associated with a spare line, providing a more sophisticated monitoring of the lines, resulting in a higher quality of switching.

In a principal aspect, the present invention is a telecommunications system protective switching mechanism. The mechanism may be utilized in a unit that is interconnected to multiple telecommunication lines. The unit receives a transfer signal and a restoration of service signal. At least one of the lines is a service line, and at least one of the lines is a spare line.

The switching mechanism comprises a bus across the service lines and the spare line, and a common controller. The bus is interconnected to the controller and also includes switches. The switches interconnect and disconnect, on command, one or more of the lines from the bus.

The common controller recognizes and accepts from the bus a transfer signal, where such transfer signal reflects a need to transfer payload from a particular service line to a spare line. The common controller responds to the transfer signal by instructing the bus to interconnect the spare line to the bus and to disconnect the particular service line from the bus. Thereafter, the common controller further recognizes and accepts from the bus a restoration of service signal, regardless of whether the restoration of service signal is transmitted to the bus (i) on the particular service line that has been disconnected from the bus or (II) on the spare line that was connected to the bus as a result of the transfer signal. In response to such a restoration of service signal, the common controller instructs the bus to reconnect the particular service line to the bus. These transfer and restoration of service signals are typically generated externally, whether at the central office or at another remote location, and are in turn transmitted along the appropriate line, through the bus and to the common controller. the invention has the capability of recognizing a restoration of service signal sent to the controller on the interrupted service line, or a restoration of service signal sent to the controller on the spare line. In the event, after an interruption of service, that it is desired to disconnect the spare line from the bus and return the interrupted line to its original connection, a restoration of service signal need not be transmitted on the interrupted line. Among situations not addressed by prior maintenance shelf systems, the situation of a mistaken swap of a service line and the spare line is addressed. As an example, a swap may be mistaken such that a line which is not, and has never been, in service may be swapped for the spare line. With such a swap, it is difficult or impossible to send a restoration of service signal without the invented interface and controller.

This and other advantages of the present invention, in the described aspect, and other aspects, will be fully appreciated from an understanding of the detail of the preferred embodiment, and for that and additional purposes, a detailed description follows.

The preferred embodiment of the invention is described hereafter, with reference to the accompanying drawing. The drawing consists of seven figures. Each figure is briefly described as follows:

FIG. 1 is a schematic diagram of a typical T-1 DS-1 wire telecommunications transmission system, of the general type with which the invention is typically used;

FIG. 2 is a schematic diagram, in greater detail than in FIG. 1, of the interface connection of the system of FIG. 1 to customer equipment;

FIG. 3 is a schematic diagram, in greater detail than FIG. 1 or 2, of the interface connection of FIG. 2, with the switching mechanism of the present invention illustrated in a "ready," or armed, condition;

FIG. 4 is a schematic diagram, similar to FIG. 3, illustrating the preferred embodiment of the present invention as it functions to switch a disabled span and monitor for a return to normal service;

FIG. 5 is a schematic diagram, in still greater detail, of the preferred embodiment of the invention, in its operating environment;

FIG. 6 is again a schematic diagram, in the greatest detail, of the preferred embodiment; and

FIG. 7 is a schematic diagram of the states of operation of the preferred embodiment.

Referring to FIG. 1, a typical T-1, DS-1 wire telecommunication transmission system extends from a central office 10 to customer premises 20. The system comprises multiple regenerative repeaters 12 each labelled "line repeater," a digital network interface 40 adjacent the customer premises, and spans 30 between and among the central office, line repeaters, and digital network interface. According to, for example, the T-1 standard, digital signals are transmitted at a rate of 1.544 M bit per second.

As shown in FIG. 2, large volume applications require several T-1, DS-1 lines to provide all needed communications to a single location. Multiple spans 32, 34, 36 are the terminal spans of multiple T-1, DS-1 systems as in FIG. 1. Multiple digital network interfaces 42, 44, 46 interconnect with the spans 32, 34, 36, respectively. Numerous customer connections are provided.

As in the past, a spare "span" (a complete, spare T-1, DS-1 system) 38 is sometimes provided, as shown in FIG. 3. In such a situation, a bus structure 50 is interconnected with all the spans 32, 34, 36, 38, etc. through a group of relays (not shown in FIG. 3). The relays are operated under control of a common control unit 60, to provide for switching of the spare span into substitution for any disabled span among the spans 32, 34, 36, etc. No special provision is made for signalling of restored service on the disabled span. Instead, the common control unit 60 merely monitors the disabled span for such restore service signals as may be sent on the disabled span, after termination of its disability by repair or the like.

Referring to FIG. 4, the preferred embodiment accomplishes more. The common control unit 70 of the preferred embodiment connects with a bus structure 50, as shown in FIG. 3 (not shown in FIG. 4), and as shown during the exemplary switching of FIG. 4, monitors in a more advantageous manner for restoration of service. Where a span such as span 36 becomes disabled, the common control unit 70 switches the spare span 38 into substitution for the disabled span 36. As in FIG. 4, the spare span 38 interconnects with the digital network interface 46 formerly interconnected with the service span 36, now disabled. In a broader aspect, the common control unit 70 monitors the disabled span, and as shown by the dashed line of connection 72, the common control unit 70 also monitors the spare span 38. A restoration of service signal on either span 36 or 38 is recognized by the common control unit 70.

Referring to FIG. 5, the common controller unit 70 incorporates signal regenerators 74, 76, line drivers 78, 80, a logic control element 82, and termination connections 84, 86. The regenerators 74, 76 are wire connected to provide regenerated signals to the logic control element 82, and the line drivers 78, 80 are wire connected to accept output of the logic control element 82.

The service spans 32, 34, 36, 38 include separate signal-receiving and transmission cable pairs. See FIG. 4. As shown in relation to span 36, by example, the span 36 includes signal-receiving cable pair 88 and transmission cable pair 90. The cable pairs 88, 90 extend to the digital network interlace 46. Two relays 92, 94 are spaced along cable pair 88, and two relays 96, 98 are spaced along cable pair 90. The relays 92, 94, 96, 98 are all normally closed for transmission to and from the digital network interface 46 as indicated by a cross-mark such as 97 across the cables. The first relays 92, 96 are interconnected into the signal cabling 100 of the bus 50, and the second relays 94, 98 are interconnected into the maintenance cabling 102 of the bus 50. All relays 92, 94, 96, 98 are normally open against transmission along the bus 50, as indicated by an "X" such as 99 across the cables.

The spare span 38 has signal-receiving cable pairs 88 and transmission cable pairs 90, as well. The line driver 80 of the common control unit 70 is interconnected to the transmission cabling 90 of the spare span 38, through a spare span transmission relay 104. The signal-receiving cabling 88 of the spare span 38 is directly interconnected to the regenerator 76 of the common control unit 70. The signal-receiving cabling 88 of the spare span 38 is also interconnected to the termination connection 86, through a spare span signal-receiving relay 106, which is normally closed for transmission from the signal-receiving cabling 88 to the termination connection 86.

The relays 104, 106 are also interconnected into the maintenance cabling 102 of the bus 50, and are normally open against transmission along the bus. The signalling cabling of the bus 50 extends from the first relays 96 to the line driver 78 and from the first relays 92 to the termination connection 84 and regenerator 74.

Referring to FIGS. 6 and 7, the common control unit 70 includes a microprocessor or micro-controller 108. The microprocessor 108 is programmed according to the source code following this description, which is incorporated by reference. The program of the microprocessor 108 provides the control unit 70 with three basic states: an idle state or mode, a "ready" and "looped up" state, and a maintenance state or mode. In the idle state, the control unit 70 awaits a "loop up" and arming signal. On receipt of a "loop up" signal, the control unit 70 is armed and begins monitoring for transfer codes. On receipt of a transfer code, indicating that the spare span should be substituted for a service span, the control unit 70 changes to the maintenance state, in which the spare span is substituted, and the control unit 70 monitors for a restore code. A unique transfer code for each service span identifies which service span is to have the spare span "swapped" for it, and the control unit 70 responds uniquely to each transfer code.

On receipt of the restore code, the control unit 70 returns to the idle mode and the spare span returns to an inactive status. The restore code is the same for each line.

As shown in FIG. 6, the microprocessor 108 controls a shift register 110, a pattern detector 112, and a data selector 115. Through the shift register 110, the microprocessor controls a decoder and relay driver 114, and ultimately controls the state of all relays shown in FIG. 5. The microprocessor 108 establishes the patterns for recognition in the pattern detector 112, and the data for selection in the data selector 115. A match of pattern in the pattern detector 112, from data received from the data selector 115, is recognized by the microprocessor 108, and causes change of state of the shift register 110.

The signal to the data selector 115 is from two sources. A first source is the signal-receiving cabling of the spare span, through a transformer 116 and the regenerator 76. The regenerator 76 also supplies the line driver 80, and through a transformer 118 and relay 104, interconnects to the transmission cabling 90 of the spare span 38. A second source is the signal-receiving cabling of the signal bus 100, through a transformer 120 and regenerator 74. The regenerator 74 also provides current to the line driver 78, and through a transformer 122 to the transmission cabling of the signal bus.

Although the foregoing description of the preferred embodiment will enable a person of ordinary skill in the art to make and use the invention, the following detailed assembly language listing is included below. The listing provides detailed information concerning the programming and operation of the overall system. Additional detailed features of the system will become apparent to those skilled in the art from reviewing the program. ##SPC1##

The preferred embodiment of the invention, and the manner and making and using it, is now described in such a full, clear and concise manner as to allow a person of ordinary skill in the art to make and use the same. To particularly point out and distinctly claim the subject matter regarded as invention, the following claims conclude this specification.