Bell Telephone Laboratories

Henry Mann

John R Colton

Robert Bruce Heick

A local alarm circuit and a remote alarm circuit carry out a plurality of failure monitoring and alarming functions for each of a plurality of digital groups (digroups), of time division multiplexed channels that are time multiplexed together on to a common bus. The local and remote alarm circuits utilize common control techniques and are of a similar circuit configuration. Each alarm circuit comprises an alarm timing store having a shared recirculating memory, and an alarm status store with a shared recirculating memory. The timing store serves to integrate and time failure indications for each of the digroups, and the status store maintains a continuing real time record of the alarm status for each digroup. When the timing store counts out a predetermined failure duration for a given digroup, the alarm status record for the digroup is changed and an alarm signal is generated. Once an alarm is registered for a digroup, the timing store then serves to integrate and time failure-free indications for the digroup. That is, it counts out a predetermined failure-free duration (after appropriate maintenance action has been taken) before it terminates the alarm state record in the status store and the alarm signal.

Common control failure alarm apparatus

The disclosed reframe circuit utilizes common control circuitry to carry out a reframing operation for any, or all, of a plurality of time division multiplexed digital data groups which are out-of-frame. An old data store is used to store a given number (m) of selected data bits, of each digital group, for two frames for framing comparison purposes. A reframe comparator serves to compare, for each digital group, the m bit output of the old data store with m data bits that are two frames later in time. A suitability store is used to record, for each group, which of the compared m data bits have had framing pattern violations and which appears as a suitable candidate for the framing bit. Based on the present set of comparisons and past suitabilities, a shift decoder searches for the framing bit within the current m-bit window until it has either marked all m bits unsuitable or has found the true framing bit within the window. If all m bits are unsuitable, the data bits of an out-of-frame digital group are shifted m bit positions, m new bits are loaded into the old data store, the suitability store is initialized for these new m bits, and the described operation is repeated. When the shift decoder finds a bit that is suitable for a given number of consecutive frames and hence is the true framing bit, the digital group is placed in-frame by shifting the data bits thereof one to m bit positions.

Common control constant shift reframe circuit

A signaling extraction circuit utilizes common control circuitry to carry out the signal extraction function for all of a plurality of time multiplexed, digital data groups (digroups), each of which comprises 24 time division multiplexed, PCM encoded channels. Each digroup uses eight bits for transmitting digital information for each channel, but the eighth bit (D8) is borrowed for signaling purposes in every sixth frame. To identify these signaling digits, signaling frame information is inserted in a digroup bit stream in the framing bit position of every other frame (i.e., the subframes). A signaling subframe pattern store comprising a shared recirculating memory serves to maintain a continuing real time record of the pattern of the signaling framing information for each digroup, as well as a test digroup. When a predetermined pattern has been recorded for a digroup (i.e., a zero subframe bit preceded by a string of exactly three ones, or a one subframe bit preceded by a string of exactly three zeros) a signal bit store is enabled to receive the D8 bits of the signaling frame which follows the recording of said predetermined pattern.

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Holmdel, NJ, United States of America

Henry Mann