Communications: electrical – Condition responsive indicating system – With particular system function
Reexamination Certificate
1998-09-08
2001-09-25
Pope, Daryl (Department: 2736)
Communications: electrical
Condition responsive indicating system
With particular system function
C340S507000, C340S527000, C340S529000
Reexamination Certificate
active
06294991
ABSTRACT:
FILED OF THE INVENTION
This invention relates to distributed restoration algorithm (DRA) networks, and more particularly to a method and system therefor of ensuring that the triggering of the distributed restoration process in a telecommunications network is not due to false alarms or failures.
BACKGROUND OF THE INVENTION
A telecommunications network may employ a combination of several approaches for restoring traffic flow interrupted by equipment failure or malfunction. For example, a network may rely upon a 1:1 automatic protect switching for some portions, distributed restoration (DRA) for other portions or domains of the network, and finally a centralized control of rerouting for situations not readily handled by the other approaches or schemes.
The automatic protection switching (APS) scheme, although wasteful of bandwidth, nonetheless is useful in some cases where simplicity and speed are required. The DRA scheme, on the other hand, takes slightly longer and may conceivably be considered more complex. But the DRA scheme is also more adaptable than APS and can leverage mesh restorability. For both APS and DRA schemes, restoration is triggered by the detection of transmission alarm conditions that result from occurred failures.
In a network where there are a number of schemes such as APS and DRA, even though the failure may quickly be circumvented by the APS scheme, the DRA provisioned nodes of the network may also begin to respond to the same failure, all of the while oblivious to the activities being carried on by the APS process. Such unnecessary triggering of the DRA process is undesirable, insofar as the DRA provisioned portion of the network, while the DRA process is ongoing, becomes vulnerable as the DRA process seeks to reserve spare links for the distributed restoration. Accordingly, any subsequent real failures could be precluded from complete and timely restoration due to this false triggering of the DRA process. To overcome this shortcoming, the DRA scheme must verify the genuineness of the failure before taking action.
It would appear that a simple solution is the provision of a timer. However, the provision of a timer for such multi-restoration schemes is inadequate because there are numerous links that interconnect the nodes of the network, and any one of those links can generate an alarm condition. It is therefore possible for two or more separate short duration alarm events to overlap enough so that those events would appear to be a single long duration alarm event, thereby activating the DRA process.
There is therefore a need for a robust method for determining when a DRA process may be activated.
Moreover, there is a need to have the DRA process start as quickly as possible, when it is needed, and yet not be triggered by false alarms.
SUMMARY OF THE PRESENT INVENTION
To ensure that a true activation of the DRA process takes place in the DRA provisioned domains of a network, each port of a node, or for example the digital cross-connect or an intelligent device, of the network is provided with a defect validation timer. This timer is user programable and could be preset, for example, with a nominal value of 100 ms. When an alarm condition is received, the timer is started. And if the alarm condition persists until the timer expires, then the alarm is deemed validated. In other words, the alarm is deemed to be a true alarm that merits the activation of the DRA process.
Once validated, an alarm can only be idled if it becomes inactive and remains inactive for a period of time. In practice, the same defect validation timer can be used for idling an alarm. Thus, when an alarm goes inactive, it starts the timer and the inactive state of the alarm is validated when the inactive alarm persists until the defect validation timer expires.
In the meantime, the quantity of the validated alarms is maintained by a defect counter, which is programmed with a predetermined threshold value. If the number of validated alarms, as counted by the counter, exceeds the preset threshold, the DRA process is initiated.
As alarms can come and go in a network, there may actually be continuous incrementing, as well as decrementing, of the count in the defect counter. But so long as the summed validated alarms remains above the preset threshold, the DRA process continues.
The present invention therefore achieves the objective of providing a more reliable, yet timely, initiation of the DRA process in a network so that the DRA process can coexist with other restoration processes such as the APS and central restoration schemes.
The instant invention achieves the further objective of adapting the initiation of the DRA process to the access/egress ports of the nodes of the network.
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Allen John David
Bengston Lee
Shah Jasvantrai
MCI Communications Corporation
Pope Daryl
LandOfFree
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