Subject: [ifmib] RFC 2495 - Managed Objects ... DS1 Question on Unavailable Seconds

From: Andrew Worsley <[email-masked]>
Date: Mon, 24 Sep 2001 14:49:49 +1000

Hi, I hope this is the most appropriate mailing list for this type of
  question. A question has come up about the exact interpretation of UAS
  (Unavailable Seconds) as defined in RFC 2495 - "Definitions of Managed
  Objects for the DS1, E1, DS2 and E2 Interface Types". 

  Basically if a failure state persists for less than 10 seconds but you have
  only a smaller period of SES (Severly Errored Seconds) the definition
  implies that the interface becomes available when the SES cease *even*
  though the fault might be still present at this time. This appears to be
  inconsistant with the requirement that UAS start as soon as a fault
  appears.

  I can quote more details if people would like, including an example. I will
  restrict myself to just reproducing the paragraph that holds the apparent
  contradiction.

     Thanks for any help people can provide

     	Andrew Worsley

    "Unavailable Seconds (UAS)
        Unavailable Seconds (UAS) are calculated by counting the number
        of seconds that the interface is unavailable.  The DS1 interface
        is said to be unavailable from the onset of 10 contiguous SESs,
        or the onset of the condition leading to a failure (see Failure
        States).  If the condition leading to the failure was
        immediately preceded by one or more contiguous SESs, then the
        DS1 interface unavailability starts from the onset of these
        SESs.  Once unavailable, and if no failure is present, the DS1
        interface becomes available at the onset of 10 contiguous
        seconds with no SESs.  Once unavailable, and if a failure is
        present, the DS1 interface becomes available at the onset of 10
        contiguous seconds with no SESs, if the failure clearing time is
        less than or equal to 10 seconds.  If the failure clearing time
        is more than 10 seconds, the DS1 interface becomes available at
        the onset of 10 contiguous seconds with no SESs, or the onset
        period leading to the successful clearing condition, whichever
        occurs later.  With respect to the DS1 error counts, all
        counters are incremented while the DS1 interface is deemed
        available.  While the interface is deemed unavailable, the only
        count that is incremented is UASs. "

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