Definitions of Managed Objects for the DS1 and E1 Interface Types
obsoleted by
- rfc-2495 — Definitions of Managed Objects for the DS1, E1, DS2 and E2 Interface Types
obsoletes
- rfc-1232 — Definitions of managed objects for the DS1 Interface type
Extracted elements (25)
A design decision was made to closely align the MIB with the set of objects that can generally be read from DS1 devices currently deployed. The intent is to facilitate common management of all devices with DS1 interfaces (multiplexors, CSUs, DSUs) rather than exhaustively modeling all conceivable DS1 management functions.
All Counters from RFC 1232 were changed to Gauges. Counters that only increase are inappropriate for performance parameters accumulated within a fixed 15-minute measurement interval and then reset; Gauge is the correct SMI type for bounded, resettable values.
RFC 1406 entirely replaces RFC 1232 because RFC 1232 contains a fundamental error: many objects are encoded as Counters that must be encoded as INTEGERs or Gauges. The magnitude of the required change is sufficient that virtually every object changed, so the MIB documented in RFC 1232 should not be implemented.
DS1 interfaces appear as ifType ds1(18) and e1(19) in MIB-II. The ds1 OID subtree (transmission 18) subsumes cept(19); there is no separate CEPT MIB. Both T1 and E1 disciplines are covered by this single MIB because 'the various T1 and E1 line disciplines are similar enough that separate MIBs are unwarranted.'
Terminology in this document is based on ANSI T1M1.3/92-005R1. Where definitions in this document conflict with the ANSI draft, the implementer should follow the definitions described in this document rather than the ANSI draft.
When the 10-second SES/UAS boundary-crossing condition spans a 900-second (15-minute) statistics window boundary, successive GETs of dsx1IntervalSESs and dsx1IntervalUASs will return differing values if the first GET occurs during the first few seconds of the new window. This is an unavoidable side-effect of the selected managed objects.
Implementation of the DS1 Far End Group is optional. It may only be implemented by DS1 systems that use the facilities data link to exchange far-end statistics; both T1.403 and PUB 54016 define ways to exchange this information over the FDL.
Implementation of the DS1 Fractional Group is mandatory for systems dividing a DS1 into channels containing different data streams of local interest. Systems indifferent to data content, such as CSUs, need not implement it.
Implementation of the DS1 Near End Group (DS1 Configuration Table, DS1 Current Table, DS1 Interval Table, and DS1 Total Table) is mandatory for all systems that attach to a DS1 Interface.
dsx1Fdl is a read-write bitmap describing facilities data link usage: other(1), dsx1Ansi-T1-403(2) for ANSI-recommended FDL exchange, dsx1Att-54016(4) for AT&T ESF FDL exchanges, dsx1Fdl-none(8) indicating the device does not use the FDL. The bitmap allows simultaneous capabilities to be indicated.
dsx1LineCoding is a read-write INTEGER specifying zero code suppression: dsx1JBZS(1) forces pulse in bit 8 of each channel limiting data to 1.344 Mbps, dsx1B8ZS(2) replaces 8 zero bits with bipolar violations pattern, dsx1HDB3(3) for E1, dsx1ZBTSI(4) Zero Byte Time Slot Interchange for ANSI Clear Channels, dsx1AMI(5) no suppression (higher layer must ensure pulse density), other(6).
dsx1LineStatus is a read-only INTEGER (1..8191) bitmap representing the sum of active alarm and loopback flags: dsx1NoAlarm(1), dsx1RcvFarEndLOF(2), dsx1XmtFarEndLOF(4), dsx1RcvAIS(8), dsx1XmtAIS(16), dsx1LossOfFrame(32), dsx1LossOfSignal(64), dsx1LoopbackState(128), dsx1T16AIS(256), dsx1RcvFarEndLOMF(512), dsx1XmtFarEndLOMF(1024), dsx1RcvTestCode(2048), dsx1OtherFailure(4096). Multiple conditions can be active simultaneously.
dsx1LineType is a read-write INTEGER specifying the DS1/E1 variant: other(1), dsx1ESF(2) Extended SuperFrame, dsx1D4(3) AT&T D4, dsx1E1(4) G.704 Table 4a, dsx1E1-CRC(5) G.704 Table 4b, dsx1E1-MF(6) G.704 Table 4a with TS16 multiframing, dsx1E1-CRC-MF(7) G.704 Table 4b with TS16 multiframing. The type governs error statistics interpretation.
dsx1LoopbackConfig is a read-write INTEGER with four states: dsx1NoLoop(1) used when loopback is not active or not supported, dsx1PayloadLoop(2) loops received signal after framing function, dsx1LineLoop(3) loops received signal with minimum device penetration, dsx1OtherLoop(4) for vendor-specific loopbacks. Agents must return badValue for unsupported loopback states.
dsx1TransmitClockSource is a read-write INTEGER specifying transmit clock: loopTiming(1) uses recovered receive clock, localTiming(2) uses a local clock source, throughTiming(3) uses recovered receive clock from another interface. This object was added in RFC 1406 and did not exist in RFC 1232.
Error events defined in section 3.3.1: BPV (same-polarity pulse in AMI, or same-polarity pulse outside zero substitution for B8ZS/HDB3), EXZ (more than 15 contiguous zeros for AMI; more than 7 for B8ZS), LCV (either BPV or EXZ), PCV (framing bit error for D4/E1-noCRC or CRC error for ESF/E1-CRC), CS (controlled slip — replication or deletion of DS1 frame payload bits).
Near-end performance counters tracked per interval (all Gauge type): Errored Seconds (ES), Severely Errored Seconds (SES), Severely Errored Framing Seconds (SEFS), Unavailable Seconds (UAS), Controlled Slip Seconds (CSS), Path Coding Violations (PCV), Line Errored Seconds (LES), Bursty Errored Seconds (BES), Degraded Minutes (DM), and Line Code Violations (LCV).
Performance parameters are accumulated in 15-minute intervals; up to 96 intervals (24 hours) are retained by an agent, plus a rolling 24-hour total. Fewer than 96 intervals are available if the agent has been restarted within the last 24 hours. There is no requirement to align intervals with wall-clock quarter-hours.
Severely Errored Seconds (SES) thresholds differ by line type: ESF = 320+ PCV events or 1+ OOF defects or detected AIS; E1-CRC = 832+ PCV events or 1+ OOF defects; E1-noCRC = 2048+ LCVs; D4 = 1+ framing errors or OOF defect or 1544+ LCVs. Controlled slips are excluded. ES and SES are not incremented during Unavailable Seconds.
The dsx1FracTable maps DS1 channels to logical interfaces. dsx1FracIfIndex specifies the ifIndex of the interface using each channel (0 if unmanaged). For North American DS1, channels 1-24 are valid; for G.704 (E1), channels 1-31 correspond directly to time-slots 1-31. Channel assignments are indexed by DS1 interface and channel number.
Two interface indices are introduced to support mixed SNMP agent deployments. dsx1IfIndex always equals MIB-II ifIndex. dsx1LineIndex identifies DS1 interfaces including internal ones: if no corresponding ifEntry exists, the value exceeds ifNumber with even numbers for equipment-side interfaces and odd numbers for network-side interfaces.
The MIB includes several read-write objects in the DS1 Configuration Table (including dsx1LineType, dsx1LineCoding, dsx1LoopbackConfig, dsx1SendCode, dsx1TransmitClockSource) that control operational behavior of DS1 interfaces. Unauthorized modification of these objects could disrupt DS1 service; SNMP community-string-based access control (SNMPv1) is the protection mechanism.
Loss Of Frame failure: for T1, declared when OOF or LOS defect persists for T seconds (2 <= T <= 10), cleared when no OOF or LOS defects for period T (0 <= T <= 20). For E1, declared immediately when OOF defect is detected. AIS failure is declared after LOF failure is declared (unframed all-ones nature causes LOF first); cleared when LOF clears.
Out Of Frame (OOF) defect: declared when 2+ framing errors occur within 3 ms (ESF) or 0.75 ms (D4), or 2+ errors in 5 consecutive framing bits. For E1, declared on 3 consecutive frame alignment signals with error. Cleared for T1 when fewer than 2 frame bit errors in 3 ms (ESF) or 0.75 ms (D4); for E1 when a 3-frame in-frame sequence is complete.
Unavailable Seconds (UAS): a DS1 interface becomes unavailable at the onset of 10 contiguous SES or a failure condition onset (with preceding contiguous SES also counting). It returns to available at the onset of 10 contiguous non-SES seconds (if failure-cleared within 10 seconds) or the later of 10 non-SES seconds and the failure clearing onset. Only UAS is incremented while unavailable.