Definitions of Managed Objects for the DS1, J1, E1, DS2, and E2 Interface Types
obsoletes
- rfc-3895 — Definitions of Managed Objects for the DS1, E1, DS2, and E2 Interface Types
Extracted elements (26)
A single MIB covering DS1, J1, E1, DS2, and E2 was chosen because the line disciplines are similar enough to make separate MIBs unwarranted. Differences such as LOF definition rigor between ESF and D4, or Yellow Alarm generation between T1 and J1, exist in both specifications and are handled by object semantics rather than separate MIBs.
As an alternative to retroactive counter adjustment, an agent may delay all statistics updates by 10 seconds (sketched in Appendix B). This avoids the case where successive GETs of dsx1IntervalSESs and dsx1IntervalUASs return differing values when the first GET occurs during the first few seconds of a new 900-second window.
Degraded Minutes (DM) objects (dsx1CurrentDMs, dsx1IntervalDMs, dsx1TotalDMs) were deprecated in RFC 4805 following their removal from ITU performance standards. They remain in the MIB with STATUS deprecated for backward compatibility with RFC 3895 implementations.
dsx1LineImpedance was added in RFC 4805 (not present in RFC 3895) to express nominal line impedance: balanced 100 ohms for T1/J1, unbalanced 75 ohms or balanced 120 ohms for E1. This object provides information needed for physical layer configuration that was not expressible in earlier versions of the MIB.
Performance statistics use PerfCurrentCount, PerfIntervalCount, and PerfTotalCount (all Gauge32 textual conventions) rather than Counter32 because these values can decrease—specifically when Unavailable Seconds occur across a 15-minute interval boundary, requiring retroactive subtraction of 10 from ES, BES, SES, and SEFS counts and addition of 10 to UAS.
DS1, J1, E1, DS2, and E2 interfaces all use ifType ds1(18); ifTypes e1(19) and g703at2mb(67) have been obsoleted. No separate J1 ifType exists. DS2 and E2 are distinguished from DS1/E1 by ifSpeed or dsx1LineType, not by a distinct ifType value.
The object dsx1IfIndex has been deprecated; the ifStackTable should now be used to represent the proxy relationship between paired DS1 interfaces (e.g., router-side and CSU network-side). ifStackTable entries show HigherLayer/LowerLayer ifIndex pairs for all interface associations, consistent with its general use for sub-layer relationships.
When a DS3 is channelized into DS1s, the dsx3Channelization object in the DS3 MIB (RFC 3896) must be set to enabledDs1; the DS1 MIB dsx1ChanMappingTable then provides per-channel mapping. When E3/E1 channelization is used, the number of DS0s per E1 varies with framing (31 for plain E1, 30 with multiframing).
A linkDown trap shall be sent only after the agent has determined for certain that the unavailable state has been entered, but the timestamp on the trap will be that of the first UAS (i.e., 10 seconds earlier). A linkUp trap shall be handled similarly.
Agents supporting read/write access to dsx1LoopbackConfig should return inconsistentValue in response to a requested loopback state that the interface does not support. A device incapable of performing a loopback shall always return dsx1NoLoop.
An ANSI T1.231-compliant implementation must not increment any counters other than UAS—even temporarily—as a result of anything that happens during the 10-second period leading to unavailable state. It must pass one-second statistics through a 10-second delay line prior to updating any counters.
dsx1LineIndex should be made equal to ifIndex to allow proper use of the ifStackTable and ds0/ds0bundle MIBs. A device directly associated with one DS1 interface should have dsx1LineIndex equal to ifIndex; otherwise unique identifiers greater than ifNumber are used.
dsx1NoAlarm must be set if and only if no other flag is set in the dsx1LineStatus bitmap. This invariant ensures that a zero-alarm condition is unambiguously represented and distinguishable from any alarm combination.
dsx1ChanMappingTable maps a parent interface ifIndex plus dsx1Ds1ChannelNumber to dsx1ChanMappedIfIndex for each channelized sub-interface. For DS3 channelized to DS1, 28 entries are created; for DS3 to DS2, 7 entries; for DS2 to DS1, 4 entries per DS2. This table enables navigation of the multiplexing hierarchy.
dsx1Channelization is a read-write object with values disabled(1), enabledDs0(2), and enabledDs1(3). Setting enabledDs0 causes the agent to create 24 DS0 ifTable entries per DS1; enabledDs1 creates DS1 entries within a DS2 (4 DS1s per DS2). Resetting to disabled destroys the created ifTable entries.
dsx1Fdl is a read-write INTEGER bitmap (1..15) describing Facility Data Link usage as a sum of capabilities: other(1), dsx1AnsiT1403(2) for ANSI-recommended FDL exchange, dsx1Att54016(4) for ESF FDL exchanges, and dsx1FdlNone(8) when the device does not use the FDL.
dsx1LineCoding is a read-write enumeration specifying zero code suppression: dsx1JBZS (forces pulse in bit 8, limits to 1.344 Mbps), dsx1B8ZS (bipolar violation pattern replaces 8 zeros), dsx1HDB3 (E1 links), dsx1ZBTSI (ANSI clear channels), dsx1AMI (no suppression, higher layer must ensure pulse density), dsx1B6ZS (replaces 6 zeros, used for DS2).
dsx1LineStatus is a read-only INTEGER bitmap (1..131071) simultaneously representing loopback state and 17 alarm/failure conditions: NoAlarm (1), RcvFarEndLOF/Yellow Alarm (2), XmtFarEndLOF (4), RcvAIS (8), XmtAIS (16), LossOfFrame/Red Alarm (32), LossOfSignal (64), LoopbackState (128), T16AIS (256), DS2-specific flags (32768, 65536), and others. dsx1NoAlarm must be set if and only if no other flag is set.
dsx1LineType is a read-write enumeration with 16 values covering DS1-ESF (T1.107), D4, E1 with/without CRC, E1 with/without multiframing, unframed variants, DS2-M12, E2, E1-Q50 with/without CRC, J1-ESF (JT-G704/JT-G706/JT-I431), and J1-Unframed. It determines line speed and interpretation of usage and error statistics.
dsx1LoopbackStatus is a read-only INTEGER bitmap (1..127) indicating currently active loopbacks and their source: NoLoopback (1), NearEndPayloadLoopback (2), NearEndLineLoopback (4), NearEndOtherLoopback (8), NearEndInwardLoopback (16), FarEndPayloadLoopback (32), FarEndLineLoopback (64). It distinguishes manager-established loopbacks from far-end-requested ones.
The DS1 statistics architecture uses three tables: dsx1CurrentTable (current 15-minute interval), dsx1IntervalTable (up to 96 completed 15-minute intervals, index 1=most recent), and dsx1TotalTable (24-hour cumulative totals). Per-table counters cover ESs, SESs, SEFSs, UASs, CSSs, PCVs, LESs, BESs, and LCVs; DM objects are deprecated.
The dsx1ConfigTable is the DS1 configuration table indexed by dsx1LineIndex (= ifIndex), containing 23 objects including LineType, LineCoding, SendCode, CircuitIdentifier, LoopbackConfig, LineStatus, SignalMode, TransmitClockSource, Fdl, LineLength, LineStatusLastChange, LineStatusChangeTrapEnable, LoopbackStatus, Ds1ChannelNumber, Channelization, LineMode, LineBuildOut, and LineImpedance.
The ifTable entries for DS1 use ifType ds1(18) with ifSpeed values: DS1/J1=1,544,000; E1=2,048,000; DS2=6,312,000; E2=8,448,000 bps. ifPhysAddress carries the Circuit Identifier (zero-length if unassigned); ifLinkUpDownTrapEnable should be enabled(1); only ifGeneralInformationGroup needs to be supported.
Section 5 addresses SNMP security for this MIB. Read-write objects such as dsx1LoopbackConfig, dsx1LineType, dsx1LineCoding, dsx1Channelization, and dsx1SendCode can disrupt DS1 interface operation if accessed by unauthorized parties; implementers should restrict write access using SNMPv3 or equivalent security mechanisms.
Loopback control: a manager can set LineLoopback, PayloadLoopback (ESF only), InwardLoopback, DualLoopback (Line+Inward), or NoLoopback via dsx1LoopbackConfig. The far end may request LineLoopback, PayloadLoopback, or NoLoopback via FDL (ESF) or inband (D4). The far end cannot undo manager-set loopbacks; a manager can undo far-end loopbacks. LineLoopback and InwardLoopback may coexist simultaneously.
Unavailable Seconds state machine: a DS1 interface enters unavailable state at the onset of 10 contiguous SESs (or at onset of a failure condition). It returns to available state at onset of 10 contiguous seconds with no SESs when no failure is present. During unavailable state only the UAS counter increments; ES, BES, SES, SEFS, PCV, and DM counters are frozen per ANSI T1.231.