Definitions of Managed Objects for the Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Interface Type
obsoletes
- rfc-2558 — Definitions of Managed Objects for the SONET/SDH Interface Type
Extracted elements (28)
Objects sonetMediumType, sonetMediumLineCoding, sonetMediumLineType, and sonetMediumCircuitIdentifier were changed from read-only to read-write (MAX-ACCESS) relative to RFC 1595 in order to make the SONET-MIB more useful for circuit provisioning; MIN-ACCESS remains read-only.
sonetSESthresholdSet was introduced because the SES error-count thresholds in ANSI T1.231-1993, ITU-T G.826-1995, and ANSI T1.231-1997 are all different from each other and from RFC 1595 thresholds, making a single hard-coded threshold unworkable for multi-vendor interoperability.
The delay-line approach (Appendix A) was introduced to avoid requiring retroactive counter adjustments when available/unavailable time boundaries are detected. An agent passes one-second statistics through a 10-element delay line before updating any counters, removing the need to retroactively modify ES, SES, CV, and UAS counts.
If the definition of a SONET/SDH performance monitoring term in this document conflicts with the definition in ANSI T1.231, implementers SHOULD follow the definition in this document. SDH Performance Monitoring term definitions are similar but not identical to SONET and are found in ITU-T G.783.
SONET/SDH interfaces are identified in the ifTable by three ifType values: sonet(39) for the combined Medium/Section/Line layer, sonetPath(50) for SONET/SDH Paths, and sonetVT(51) for Virtual Tributaries/Containers. The ifStackTable and ifInvStackTable convey the multiplexing relationships between layers.
When available/unavailable time boundaries cross a 900-second (15-minute) statistics window boundary, the CV, ES, SES, SEFS, and UAS counts for the PREVIOUS interval must be adjusted, meaning successive GETs of interval objects may return differing values during the first few seconds of the new window.
A linkDown trap SHALL be sent only after the agent has determined the unavailable state has been entered, but the timestamp on the trap SHALL reflect the time of the first UAS (i.e., 10 seconds earlier). linkUp traps are handled similarly.
A SONET/SDH interface MUST support at least n=4 completed 15-minute intervals; the default is 32 and the maximum is 96. The sonetMediumValidIntervals object reports the count of intervals for which data is available.
ANSI T1.231 compliance requires that unavailable time begins at the onset of 10 contiguous SESs and an implementation MUST NOT increment any counters other than UAS during those 10 seconds — not even temporarily. Implementations may use a 10-second delay-line approach instead of retroactive counter adjustment.
CV counts MUST be frozen during SESs. Far-end one-second statistics SHALL be flagged as 'absent' during any second in which there is an incoming defect at the layer in question or at any lower layer.
For SONET/SDH Medium/Section/Line interfaces, ifOperStatus MUST assume the value down(2) if sonetSectionCurrentStatus or sonetLineCurrentStatus has any value other than sonetSectionNoDefect(1) and sonetLineNoDefect(1) respectively. ifLinkUpDownTrapEnable default is enabled(1).
For SONET/SDH Path interfaces, ifOperStatus MUST assume down(2) if sonetPathCurrentStatus has any value other than sonetPathNoDefect(1). For VT/VC interfaces, ifOperStatus MUST assume down(2) if sonetVTCurrentStatus has any value other than sonetVTNoDefect(1). ifLinkUpDownTrapEnable default is disabled(2) for paths and VTs.
If sonetSESthresholdSet is not implemented, the SES threshold interpretation from RFC 1595 (Appendix B) SHALL apply for backward compatibility. If a manager changes the value of sonetSESthresholdSet, all SES statistics collected prior to the change must be invalidated.
Far-End Line and Far-End Path tables collect statistics derived from the far-end block error (FEBE) code: for Line, from the Z2 byte Line Overhead; for Path, from the G1 byte Path Overhead. Each table covers ESs, SESs, CVs, and UASs in current and interval forms.
Performance statistics are maintained in paired current/interval table groups for each layer (Section, Line, Far-End Line, Path, Far-End Path, VT, Far-End VT). Current tables use PerfCurrentCount for the active 15-minute window; interval tables use PerfIntervalCount indexed 1-96 (interval 1 = most recent) plus a TruthValue ValidData flag per interval.
sonetMediumLoopbackConfig is a BITS field with four named bits: sonetNoLoop(0), sonetFacilityLoop(1) (received signal looped back out the transmitter), sonetTerminalLoop(2) (outgoing signal connected to incoming receiver), and sonetOtherLoop(3).
sonetMediumTable provides per-interface configuration including sonetMediumType (sonet/sdh), sonetMediumLineCoding (B3ZS, CMI, NRZ, RZ), sonetMediumLineType (short/long single-mode, multi-mode, coax, UTP), sonetMediumCircuitIdentifier (DisplayString, 0-255 octets), sonetMediumLoopbackConfig (BITS), and sonetSESthresholdSet. Objects are MAX-ACCESS read-write to support circuit provisioning.
sonetPathCurrentStatus is a bitmask Integer32 (1-62) covering: sonetPathNoDefect(1), sonetPathSTSLOP(2), sonetPathSTSAIS(4), sonetPathSTSRDI(8), sonetPathUnequipped(16), sonetPathSignalLabelMismatch(32). sonetPathCurrentWidth enumerates path widths: sts1(1) through sts768cSTM256(7).
sonetSectionCurrentStatus is a bitmask Integer32 (1-6) representing simultaneous defects: sonetSectionNoDefect(1), sonetSectionLOS(2), sonetSectionLOF(4). sonetLineCurrentStatus uses bits for sonetLineNoDefect(1), sonetLineAIS(2), sonetLineRDI(4).
sonetSESthresholdSet is an enumerated INTEGER selecting the SES threshold set in use: other(1), bellcore1991(2) (TR-NWT-000253/T1M1.3), ansi1993(3) (T1.231-1993/GR-253), itu1995(4) (G.826), or ansi1997(5) (T1.231-1997). If not implemented, RFC 1595 thresholds (Appendix B) apply.
The SONET-MIB is rooted at transmission(39) and organized into three top-level sub-trees: sonetObjects (medium/section/line), sonetObjectsPath (path/far-end-path), and sonetObjectsVT (VT/far-end-VT). Each sub-tree contains current and interval performance tables indexed by ifIndex.
This document places the SONET-MIB module under the transmission(39) OID arc within the IANA-managed SMI network management subtree, consistent with ifType sonet(39) for SONET/SDH interfaces.
Several SONET-MIB objects have read-write access (sonetMediumType, sonetMediumLineCoding, sonetMediumLineType, sonetMediumCircuitIdentifier, sonetMediumLoopbackConfig, sonetSESthresholdSet, sonetPathCurrentWidth). Unauthorized write access could disrupt SONET/SDH interfaces or corrupt performance statistics; SNMPv3 with authentication and privacy is recommended for management of these objects.
Line AIS defect detected as '111' in bits 6-7-8 of K2 byte in 5 consecutive frames; terminated when that pattern absent for 5 consecutive frames. Line AIS failure declared at 2.5 ±0.5 s; cleared when absent 10 ±0.5 s. STS-Path AIS detected as all-ones in H1 and H2 bytes in 3 contiguous frames; terminated on valid STS Pointer with NDF='1001' for 1 frame or '0110' for 3 frames.
LOF defect/failure: OOF declared on 4 contiguous errored frame alignment words; cleared on 2 contiguous error-free words. LOF defect declared when OOF persists ≥3 ms; cleared when signal stays in-frame 1-3 ms. LOF failure declared when LOF defect persists 2.5 ±0.5 s; cleared when LOF defect absent for 10 ±0.5 s.
LOS defect declared when no transitions detected for 2.3-100 µs; cleared after 125 µs interval with no LOS. LOS failure declared when LOS defect persists 2.5 ±0.5 s (or if LOS defect present when LOF failure criteria met); cleared when LOS defect absent for 10 ±0.5 s. LOS failure clears any existing LOF failure.
STS-Path LOP defect declared when no valid pointer detected in 8 consecutive frames, or 8 consecutive frames with NDF='1001' without concatenation indicator; terminated when valid pointer (NDF='0110') or concatenation indicator detected for 3 contiguous frames. LOP failure declared at 2.5 ±0.5 s persistence; cleared when absent 10 ±0.5 s.
Unavailable time begins at the onset of 10 contiguous SESs (those 10 seconds are included in unavailable time). Interface returns to available at the onset of 10 contiguous seconds with no SESs (those 10 seconds are excluded from unavailable time). While unavailable, all counters except UAS are frozen.