Definitions of Managed Objects for the DS3/E3 Interface Type
obsoletes
- rfc-2496 — Definitions of Managed Object for the DS3/E3 Interface Type
Extracted elements (29)
An agent may choose to delay updates to performance statistics by 10 seconds (using a 10-element delay line) to avoid retroactive adjustments when the unavailable seconds determination crosses interval boundaries. Appendix B sketches this delay approach as an alternative to real-time updates with retroactive corrections.
Performance statistics objects (PerfCurrentCount, PerfIntervalCount, PerfTotalCount) are defined as Gauge32 rather than Counter32 because these objects can decrease. Specifically, UAS and related counts may be retroactively adjusted when the 10-second UAS determination window crosses a 15-minute interval boundary.
The dsx3IfIndex object was deprecated in favor of using ifStackTable to represent the proxy relationship between pairs of DS3 interfaces (e.g., router-side and CSU network-side). The ifStackTable approach is consistent with its standard use for sub-layer associations, where entire DS3 frames are exchanged between interface pairs.
The dsx3LoopbackConfig (desired state) and dsx3LoopbackStatus (actual state) are split into two separate objects to distinguish manager-requested loopback from the actual state which may also include far-end-requested loopbacks. This allows duals (both near-end inward and far-end line loopback) to be represented simultaneously.
The MIB design decision was to closely align objects with those readable from currently deployed DS3/E3 devices, rather than attempting to model all possible management functions (multiplexors, CSUs, DSUs). This pragmatic approach facilitates common management across heterogeneous devices.
E3 AIS detection differs from DS3: E3 AIS is a continuous stream of ones and consequent actions must be completed within 1 ms, whereas DS3 AIS uses stuck-stuffing with specific bit patterns and has a declaration time T where 0.2 ms <= T <= 100 ms.
In proxy agent scenarios, some historical performance intervals may be unavailable due to periods when the proxy was not communicating with the DS3/E3 device. dsx3ValidIntervals reports the maximum interval number for which data is available, and dsx3InvalidIntervals counts intervals with missing data.
The DS3 Fractional Table (dsx3FracTable) has been deprecated since RFC 2496. Implementors must use ifStackTable combined with channelization objects (dsx3Channelization, dsx1ChanMappingTable, dsx0ChanMappingTable) to represent DS3-to-DS1-to-DS0 and DS3-to-DS2-to-DS1 channelization hierarchies.
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 is handled similarly.
If the DS3 terminology definitions in this document conflict with ANSI T1.231, implementors MUST follow the definitions described in this document rather than T1.231.
Only the ifGeneralInformationGroup needs to be supported for the DS3 layer in the ifTable. The ifType value for DS3 is ds3(30), ifSpeed is 44736000 for DS3 and 34368000 for E3, and ifPhysAddress carries the Circuit Identifier value.
Performance parameters are accumulated in 15-minute intervals; up to 96 intervals (24 hours) are kept by an agent. Fewer intervals will be available if the agent has been restarted within the last 24 hours. There is also a rolling 24-hour total for each parameter.
The dsx3LineIndex object SHOULD be made equal to ifIndex to allow proper use of ifStackTable. The legacy numbering scheme using values greater than ifNumber is preserved for informational purposes in Appendix A.
The dsx3NoAlarm bit in dsx3LineStatus MUST be set if and only if no other flag is set. This ensures unambiguous representation of the alarm-free state.
The dsx3Channelization object controls whether a DS3/E3 is unchannelized (disabled), channelized into DS1s (enabledDs1, creating 28 ifEntries), or channelized into DS2s (enabledDs2, creating 7 ifEntries). Setting this object causes creation or deletion of subordinate ifTable entries.
The dsx3ConfigTable is the primary DS3/E3 configuration table, indexed by dsx3LineIndex (equal to ifIndex). It contains 18 objects covering line type, coding, loopback config/status, circuit identifier, channelization, line length, line status, and transmit clock source.
The dsx3CurrentTable collects near-end performance statistics for the current 15-minute interval, including PESs, PSESs, SEFSs, UASs, LCVs, PCVs, LESs, CCVs, CESs, and CSESs, all using the PerfCurrentCount (Gauge32) textual convention.
The dsx3FarEndConfigTable carries far-end equipment identification data reported via C-bits in C-bit Parity DS3 framing. Objects include dsx3FarEndEquipCode (10 chars), dsx3FarEndLocationIDCode (11 chars), dsx3FarEndFrameIDCode (10 chars), dsx3FarEndUnitCode (6 chars), and dsx3FarEndFacilityIDCode (38 chars).
The dsx3FarEndCurrentTable and dsx3FarEndIntervalTable collect far-end C-bit statistics (CESs, CSESs, CCVs, UASs) derived from the far end block error code within C-bits. These tables are only meaningful for C-bit Parity and SYNTRAN DS3 applications.
The dsx3IntervalTable stores near-end performance data for up to 96 completed 15-minute intervals (24 hours), indexed by dsx3IntervalIndex and dsx3IntervalNumber (1=most recent). Includes a dsx3IntervalValidData TruthValue flag to indicate whether interval data is valid.
The dsx3LineStatus object is a bitmap (INTEGER 1..4095) representing simultaneous failure and loopback states. Defined bit positions include: dsx3NoAlarm(1), dsx3RcvRAIFailure(2), dsx3RcvAIS(8), dsx3LOF(32), dsx3LOS(64), dsx3LoopbackState(128), dsx3UnavailSigState(1024), and dsx3NetEquipOOS(2048).
The dsx3LineType object enumerates DS3/E3 framing variants: dsx3M23 (ANSI T1.107-1988), dsx3SYNTRAN (ANSI T1.107-1988), dsx3CbitParity (ANSI T1.107a-1990), dsx3ClearChannel (ANSI T1.102-1987), e3Framed (CCITT G.751), e3Plcp (ETSI T/NA(91)18), and the newly added dsx3M13 (ANSI T1.107a-1990).
The dsx3LoopbackStatus object is a read-only bitmap (INTEGER 1..127) reflecting the current actual loopback state, including near-end and far-end loopbacks and their sources. Distinct from dsx3LoopbackConfig, which represents desired state.
The dsx3TotalTable provides cumulative 24-hour totals for near-end performance parameters. Invalid 15-minute intervals contribute 0 to the total rather than being excluded from the count.
The DS3-MIB module is registered as ds3 MODULE-IDENTITY at OID { transmission 30 }, corresponding to ifType value ds3(30). This assignment is shared with the ifTable ifType value for DS3 interfaces.
Several read-write objects in this MIB can disrupt DS3/E3 service if written by unauthorized parties: dsx3LoopbackConfig (can activate loopbacks), dsx3SendCode (can inject test patterns or loopback activation codes), and dsx3LineLength (can alter line build-out circuitry settings). SNMP access control should restrict write access to these objects.
The dsx3LineStatusChangeTrapEnable object defaults to disabled(2). Enabling traps exposes operational state to SNMP notification receivers; operators should ensure trap destinations are authorized. The MIB relies on SNMPv2 security infrastructure for authentication and access control.
The DS3 Unavailable Seconds state machine transitions from available to unavailable at the onset of 10 contiguous P-bit Severely Errored Seconds (PSESs) or upon a failure condition. It returns to available at the onset of 10 contiguous seconds with no PSESs (with additional conditions if a failure is also present). All counters except UAS are frozen during unavailable time.
The loopback state machine for dsx3LoopbackConfig supports states: NoLoop, PayloadLoop, LineLoop, OtherLoop, InwardLoop, and DualLoop (LineLoop + InwardLoop simultaneously). A manager can undo far-end-established loopbacks, but the far end cannot undo manager-established loopbacks. A far-end NoLoopback request leaves a manager-established InwardLoop in place.