Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1998-03-27
2001-10-23
Rao, Seema S. (Department: 2661)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S228000, C370S395430, C370S248000, C370S418000, C714S043000, C340S870030
Reexamination Certificate
active
06307834
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for disconnecting or activating a transmission path exhibiting a faulty transmission behavior in a transmission system of the type wherein redundant message cells are respectively transmitted via redundant transmission paths.
2. Description of the Prior Art
Methods of the above type are known from European Application 0 384 936, European Application 0 453 606 (corresponding to U.S. Pat. No. 5,222,063) and European Application 0 453 607 (corresponding to U.S. Pat. No. 5,200,950), which operate as follows.
In ATM (Asynchronous Transfer Mode) transmission, the sequence of message cells that belong to a virtual connection is to be maintained. For the designation of the sequence, the message cells have a sequence number assigned in cyclically progressing fashion in a field for the sequence number. In order to maintain a predetermined loss probability, a parallel forwarding or routing, with through-connections via redundant transmission paths can be required. At the reception location of the redundantly transmitted message cells only a message cell expected as the next one in the sequence is selected. From, the aforementioned European Applications 0 384 936, 0 453 606 and 0 453 607, algorithms are known in which each message cell that is the next message cell following the message cell currently accepted as the last message cell for further processing, which arrives on the same transmission path (active transmission path) as the message cell currently accepted as the last message cell for further processing, is accepted for further processing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method that achieves a rapid disconnection of a transmission path operating in a faulty manner, but having a tolerance for losses of message cells that occur sporadically on the transmission path.
The above object is achieved in a method of the type initially described, wherein, for each transmission path, the sequence number of the last-transmitted message cell is stored, the sequence number of a currently-incoming message cell is compared with the sequence number stored for the relevant transmission path, as a result of the comparison it is determined whether the currently-incoming message cell is accepted for further processing. A counter state (count) is maintained for each transmission path and when a currently-incoming message cell is accepted for further processing, the counter state for the relevant transmission path is increased by a first value. In the event of an incorrect sequence number for the currently-incoming message cell, the counter state of the relevant transmission path is decreased by a second value. A transmission path having a counter state which reaches a lower threshold value is excluded from accepting subsequent message cells for further processing.
In the inventive method, the monitoring for a transmission path that is tolerant in relation to normal losses of individual message cells, but results in a disconnection of the transmission path when there is an increase in the error rate that is characteristic of substantial errors. After a disconnection of the transmission path, a multiplicity of message cells received as error-free is required for re-admission (re-activation) of the disconnected path, which ensures that only a transmission path exhibiting an elevated degree of freedom from error is activated.
In an embodiment of the invention the first value is smaller than the second value. In addition to a tolerance in relation to normal losses of individual message cells, this measure leads to an accelerated disconnection of the transmission path in the event of substantial errors. In relation to the small number of errors required for disconnection, for an admission of the transmission path a large number of message cells received without errors is required, which ensures that only a transmission path with a high degree of freedom from error is activated.
In another embodiment of the invention an admission of a transmission path for the acceptance of message cells ensues only after an upper threshold has been exceeded. This measure results in hysteresis between activation and disconnection, Which prevents overly frequent activation and disconnection, but ensures that the transmission path is activated only when a high degree of freedom from error has been achieved.
In a further embodiment a state character (Q) is allocated to a transmission path, the state character being reset when the lower threshold value is reached, and reset when the upper threshold is exceeded. The exclusion or the admission of the associated transmission path is defined, respectively in accordance with the state character. This measure results in a simple interface to the selection algorithm.
The state character Q can be reset for all transmission paths except one, independent of the associated counter states. This measure results in an operation effected manually by an operator, with only one transmission path.
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patent: 5953337 (1999-09-01), Almay
Rao Seema S.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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