September 1993.
[TR253] Bellcore TR-NWT-000253, Issue 1, "Synchronous Optical
Network (SONET) Transport Systems: Common Generic
Criteria", December 1991.
[G.826] ITU Recommendation G.826, "Error Performance Parameters
and Objectives for International Constant Bit Rate
Digital Paths at or above Primary Rate", September 1995
(COM 13-R57E).
[GR253] Bellcore GR-253-CORE, Issue 2, "Synchronous Optical
Network (SONET) Transport Systems Common Generic
Criteria", December 1995.
[T1.231b] American National Standard for Telecommunications -
Digital Hierarchy - Layer 1 In-Service Digital
Transmission Performance Monitoring, ANSI T1.231-1997,
September 1997.
7.2. Informative References
[RFC1595] Brown, T. and K. Tesink, "Definitions of Managed Objects
for the SONET/SDH Interface Type", RFC 1595, March 1994.
[RFC2495] Fowler, D., "Definitions of Managed Objects for the DS1,
E1, DS2 and E2 Interface Types", RFC 2495, January 1999.
[RFC2496] Fowler, D., "Definitions of Managed Objects for the
DS3/E3 Interface Type", RFC 2496, January 1999.
[RFC2558] Tesink, K., "Definitions of Managed Objects for the
SONET/SDH Interface Type", RFC 2558, March 1999.
[RFC3410] Case, J., Mundy, R., Partain, D. and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
8. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
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proprietary rights by implementors or users of this specification can
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The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Appendix A: The delay-line approach to statistics collection.
According to ANSI T1.231 unavailable time begins at the onset of 10
contiguous severely errored seconds -- that is, unavailable time
starts with the first of the 10 contiguous SESs -- and while an
interface is deemed unavailable all counters for that interface are
frozen except for the UAS count. Since changes in the signal state
lag the data to which they apply by 10 seconds, an implementation
which wishes to avoid making retroactive adjustments to the counts
must pass the the one-second statistics through a 10-second delay
line prior to updating any counters. That can be done by performing
the following steps at the end of each one second interval.
i) Read near/far end line and path CV counts and alarm status flags
from the hardware.
ii) Accumulate the CV counts for the preceding second and compare
them to the ES and SES threshold for the layer in question.
Update the signal state and shift the one-second CV counts and
ES/SES flags into the 10-element delay line. Note that far-end
one-second statistics are to be flagged as "absent" during any
second in which there is an incoming defect at the layer in
question or at any lower layer.
iii) Update the current interval statistics using the signal state
from the previous update cycle and the one-second CV counts and
ES/SES flags shifted out of the 10-element delay line.
This procedure guarantees that the statistical counters will be
correctly updated at all times, although they lag real time by 10
seconds. It is illustrated in the figure below. At the end of each
15 minutes interval the current interval counts are transferred to
the most recent interval entry and each interval is shifted up by
one position, with the oldest being discarded if necessary in order
to make room. The current interval counts then start over from zero.
Note, however, that the signal state calculation does not start anew
at each interval boundary; rather, signal state information is
retained across interval boundaries.
+--------------------------------------------------------------+
| READ COUNTERS & STATUS INFO FROM HARDWARE |
| |
|LOS OOF/ SECT LINE LINE LINE LINE PATH PATH PATH PATH PATH |
| LOF CV AIS CV RDI FEBE AIS LOP CV RDI CV |
+--------------------------------------------------------------+
| | | | | | | | | | | |
| | | | | | | | | | | |
V V V V V V V V V V V V
+--------------------------------------------------------------+
| ACCUM ONE-SEC STATS, CHK ERR THRESHOLDS, & UPDT SIGNAL STATE |
| |
| |
| NEAR END/FAR END NEAR END/FAR END |
|SECT SECT SECT LINE LINE LINE LINE PATH PATH PATH PATH |
|CV ES SES CV ES SES AVA/UNA CV ES SES AVA/UNA |
+--------------------------------------------------------------+
| | | | | | | | | | |
| | | | | | | | | | |
V V V V V V | V V V |
+-------------+ +-------------+ | +-------------+ |
|ONE-SEC DELAY| |ONE-SEC DELAY| | |ONE-SEC DELAY| |
| (1 OF 10) | | (1 OF 10) | | | (1 OF 10) | |
|CV ES SES| |CV ES SES| | |CV ES SES| |
+-------------+ +-------------+ | +-------------+ |
| | | | | | | | | | |
/ / / / / / / / / / /
/ / / / / / / / / / /
| | | | | | | | | | |
V V V V V V | V V V |
+-------------+ +-------------+ | +-------------+ |
|ONE-SEC DELAY| |ONE-SEC DELAY| | |ONE-SEC DELAY| |
| (10 OF 10) | | (10 OF 10) | | | (10 OF 10) | |
|CV ES SES| |CV ES SES| | |CV ES SES| |
+-------------+ +-------------+ | +-------------+ |
| | | | | | | | | | |
| | | | | | | | | | |
V V V V V V V V V V V
+--------------------------------------------------------------+
| UPDATE STATISTICS COUNTERS |
| |
| NEAR END/FAR END NEAR END/FAR END |
| SECTION LINE PATH |
| CV ES EFS SES CV ES EFS SES AS UAS CV ES EFS SES AS UAS |
+--------------------------------------------------------------+
Note that if such a procedure is adopted there is no current interval
data for the first ten seconds after a system comes up.
noSuchInstance must be returned if a management station attempts to
access the current interval counters during this time.
It is an implementation-specific matter whether an agent assumes that
the initial state of the interface is available or unavailable.
Appendix B - RFC 1595 SES interpretation
This appendix contains the values for x for the Section, Line, Path,
and VT Layers as used in [T1M1.3][RFC1595][TR253].
Value for x for SONET/SDH Section SES Definition
Rate x Minimum Bit Error Rate
=======================================================
OC-1 9 1.5 x 10^-7
OC-3 16 1 x 10^-7
OC-9 47 1 x 10^-7
OC-12 63 1 x 10^-7
OC-18 94 1 x 10^-7
OC-24 125 1 x 10^-7
OC-36 187 1 x 10^-7
OC-48 249 1 x 10^-7
Value for x for SONET/SDH Line SES Definition
Rate x Minimum Bit Error Rate
=======================================================
OC-1 12 2 x 10^-7
OC-3 32 2 x 10^-7
OC-9 47 2 x 10^-7
OC-12 124 2 x 10^-7
OC-18 186 2 x 10^-7
OC-24 248 2 x 10^-7
OC-36 370 2 x 10^-7
OC-48 494 2 x 10^-7
Value for x for SONET/SDH STS-Path SES Definition
Rate x Minimum Bit Error Rate
=======================================================
STS-1 9 1.5 x 10^-7
STS-3 16 1 x 10^-7
Value for x for SONET/SDH VT-Path SES Definition
Rate x Minimum Bit Error Rate
=======================================================
VT1.5 4 2 x 10^-6
VT2 6 2 x 10^-6
VT3 8 2 x 10^-6
VT6 14 2 x 10^-6
Author’s Address
Kaj Tesink
Telcordia Technologies
331 Newman Springs Road
P.O. Box 7020
Red Bank, NJ 07701-7020
Phone: (732) 758-5254
EMail: kaj@research.telcordia.com
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