Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation over Packet (CEP) MIB Using SMIv2
Extracted elements (27)
A CEP connection is modeled as a pseudowire and is therefore not represented in the ifTable, following the spirit of RFC 2863. This keeps the service layer cleanly separate from physical interface management.
High-capacity (HC) Counter64 objects are used in performance tables because 32-bit counters would overflow in minutes for high-speed paths; a SONET STS-48c path can roll over non-HC counters in a few minutes.
The MIB is structured in three layers (service/PW/PSN) following the PWE3 architecture (RFC 3985), isolating CEP service objects from both PW-generic management (PW-STD-MIB) and the underlying PSN-specific modules.
The pwCepCfgTable is designed so that a single configuration entry may be referenced by many pwCepTable entries. This N:1 sharing reduces NMS burden and avoids redundant configuration for PWs with identical parameters.
The PW-CEP-STD-MIB is explicitly designed to be independent of PSN type; the same module manages CEP PWs regardless of whether the underlying packet network is MPLS, IP, or other PSN variants.
All read-create objects in pwCepCfgEntry MUST NOT be changed while pwCepCfgRowStatus is active(1). The agent MUST NOT allow pwCepCfgRowStatus to be changed from active(1) while the entry is referenced by at least one active PW.
An agent with CEP capability MUST support at least 4 performance intervals in pwCepValidIntervals. The RECOMMENDED default is 32 intervals, and n MUST NOT exceed 96.
In the pwCepPerf1DayIntervalTable, if any error counter overflows during a one-day interval, the counter MUST NOT wrap around and MUST return the maximum value instead.
Manual entries in the pwCepTable SHOULD be preserved after a reboot; the agent MUST ensure their integrity. If a row's entries are found inconsistent after reboot, the PW's pwOperStatus MUST be declared as notPresent(5).
Setting the 'ais' bit in pwCepCfgEnableDBA MUST cause CEP payload suppression when AIS is detected on the SONET path; setting 'unequipped' MUST cause payload suppression when an unequipped condition is detected.
The actual jitter buffer depth MUST be at least twice the configured pwCepCfgJtrBfrDepth value for proper operation. If the agent does not support the configured value, it MUST reject the SNMP Set operation.
The cepAis indication MUST NOT in itself cause a CEP PW down notification; AIS on the incoming SONET stream is signaled to the peer but does not declare the PW down.
The ooRngDropped indication in pwCepIndications MUST be supported regardless of whether the implementation supports packet reordering. Writing a non-zero value to pwCepIndications MUST fail.
When the agent updates performance statistics in real time, it MUST retroactively reduce ES and SES counts by the SesToUas value and increase UAS count by that value when UAS state is entered (mirroring RFC 3592 behavior).
The pwCepCfgTable (pwCepObjects 3) holds shareable CEP PW configuration parameters (payload length, jitter buffer depth, DBA settings, LOPS thresholds, etc.). A single entry may be referenced by many pwCepTable entries, reducing NMS burden.
The pwCepFracTable (pwCepObjects 4) extends configuration for fractional-SPE PWs, covering STS-1/VC-3 and VC-4 fractional modes including EBM (Equipped Bit Mask), VTG/TUG-2 maps, and asynchronous (DS3/E3) payload types.
The pwCepIndications BITS object (pwCepEntry 7) accumulates defect indications including missingPkt, ooRngDropped, jtrBfrUnder, pktMalformed, lops, cepRdi, cepAis, badHdrStack, cepNeFailure, and cepFeFailure. It holds accumulated state until cleared by an SNMP write.
The pwCepSonetConfigErrorOrStatus BITS object (pwCepEntry 3) reports local and peer configuration mismatches, including timeslotInUse, timeslotMisuse, and per-feature Incompatible/Asymmetric peer bits for DBA, EBM, RTP, and async parameters.
The pwCepTable (pwCepObjects 1) is the central CEP PW table, indexed by pwIndex, associating each SONET/SDH path or VT with a pseudowire. An entry is created automatically by the agent for every pwTable entry whose pwType equals 'cep'.
The pwCepType object specifies the CEP sub-type: 'spe'(1) for SONET STS-Nc signals, 'vt'(2) for SONET VT-x signals, or 'fracSpe'(3) for fractional STS-1/VC-3/VC-4. Support for 'vt' and 'fracSpe' modes is optional.
Three performance tables are defined: pwCepPerfCurrentTable (current 15-minute interval, pwCepObjects 5), pwCepPerfIntervalTable (up to 96 historical 15-minute intervals, pwCepObjects 6), and pwCepPerf1DayIntervalTable (current and previous days, pwCepObjects 7). All track DBA packets, pointer adjustments, missing/malformed packets, jitter buffer events, ES, SES, UAS, and FC counters.
The PW-CEP-STD-MIB module is assigned the OID { mib-2 200 }, registering it under the standard MIB-2 subtree managed by IANA.
The MIB contains read-write and read-create objects (e.g., pwCepCfgJtrBfrDepth, pwCepCfgEnableDBA, pwCepCfgRowStatus) whose unauthorized modification can disrupt active pseudowires and corrupt performance data. Implementations should apply SNMPv3 access control to restrict write access to authorized managers.
The LOPS (Loss of Packet Synchronization) state machine has two states: in-sync and LOPS. The trigger to enter LOPS is pwCepCfgConsecMissingOutSync consecutive missing packets (default 10); the trigger to exit LOPS is pwCepCfgConsecPktsInsync consecutive in-sequence packets (default 2).
PwCepSdhVc4Ebm is a 32-bit Unsigned32 textual convention where the Equipped Bit Mask occupies the 30 least significant bits, used per TUG-3 in fractional VC-4 circuits.
PwCepSonetEbm is a 32-bit Unsigned32 textual convention where the Equipped Bit Mask occupies the 28 least significant bits, used for fractional STS-1/VC-3 circuits.
PwCepSonetVtgMap is a 32-bit Unsigned32 textual convention encoding the VT/VC types carried in seven VTG/TUG-2s as a 28-bit EBM in the least significant bits, specifying maximal occupancies per VTG.