I remember that there was a specific term to define the problem that
occurs when you have two protection schemes at the same time: the
traffic hits generated by one protection scheme can fool the other
protection scheme which will generate again some traffic hits and so on.
This is normally solved by having an "hold-off timer" on one of the two protection schemes, so that if the other protection scheme fails, after
a certain time (i. e. when the hold-off timer expires) traffic can be restored.
Does anyone remembers this term?
Hello Aldbert,
You wrote:
I remember that there was a specific term to define the problem that occurs >> when you have two protection schemes at the same time: the traffic hits
generated by one protection scheme can fool the other protection scheme which
will generate again some traffic hits and so on. This is normally solved by >> having an "hold-off timer" on one of the two protection schemes, so that if >> the other protection scheme fails, after a certain time (i. e. when the
hold-off timer expires) traffic can be restored.
Does anyone remembers this term?
Do you mean "hysteresis" ?
This term refers to the mechanism that is used when a fault is
repaired in case revertive protection switching is used.
When a fault has been detected on the working link, immediately
the traffic is switched to the protecting link.
When the fault is repaired traffic in NOT switched back immediately
to the working link but with a delay, this to make sure that
the failed is really repaired.
This to prevent toggling between working and protecting link
on degraded links with bit-errors.
Best regards, Huub.
Huub van Helvoort wrote:
Hello Aldbert,Thank you very much for your reply, Huub.
You wrote:
I remember that there was a specific term to define the problem that
occurs when you have two protection schemes at the same time: the
traffic hits generated by one protection scheme can fool the other
protection scheme which will generate again some traffic hits and so
on. This is normally solved by having an "hold-off timer" on one of
the two protection schemes, so that if the other protection scheme
fails, after a certain time (i. e. when the hold-off timer expires)
traffic can be restored.
Does anyone remembers this term?
Do you mean "hysteresis" ?
This term refers to the mechanism that is used when a fault is
repaired in case revertive protection switching is used.
When a fault has been detected on the working link, immediately
the traffic is switched to the protecting link.
When the fault is repaired traffic in NOT switched back immediately
to the working link but with a delay, this to make sure that
the failed is really repaired.
This to prevent toggling between working and protecting link
on degraded links with bit-errors.
Best regards, Huub.
I expressed myself in a very bad way :-): I was not referring to the "hysteresis" you mention.
An example could be routers connected to each other via an SDH network
(yes, something belonging to the past ;-)). Let's assume that the
traffic is protected by SNCP in the SDH layer and that the routers use
some kind of Layer 3 protection, e.g. FRR (Fast ReRoute).
Normally it is suggested to have an hold-off timer on the FRR in order
to let SNCP to recover traffic first. If after the hold-off timer
expiration traffic has not recovered than FRR can try to recover traffic. Without the hold off timer, both protections will work in parallel and
the hits introduced by SNCP might fool FRR to think that the failure is
not recovered and trigger more protection events, making traffic
recovery longer than needed.
I think that there was a word describing this situation of concurrency between the two protections, but may be I am simply becoming too old... ;-) Best regards.
Aldbert
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