Managed Objects for Time Division Multiplexing (TDM) over Packet Switched Networks (PSNs)
Extracted elements (25)
Multiple TDM PWs of the same characteristics are expected to share a single pwTDMCfgTable entry, reducing management overhead. The pwTDMCfgIndexNext object provides a manager-safe way to allocate new configuration indices without collision.
TDM PW connections are not represented in the ifTable; instead, a separate pwTDMTable is used, indexed by the same pwIndex as the PW-STD-MIB. This follows the PWE3 layered architecture (RFC 3985) separating TDM service layer, generic PW layer, PSN VC layer, and PSN layer.
The pwTDMIfIndex object SHOULD trigger agent deletion of associated pwTDMTable rows if the TDM interface index is removed. If the agent does not delete the rows, it MUST set pwTDMIfIndex to zero to indicate an undetermined interface.
When pwTDMCfgPktReorder is set to True for out-of-order packet re-sequencing, implementations that do not support this feature MUST reject a SET request with value true and the agent MUST set the value to FALSE in the compliance statement.
Alarm MUST be cleared after the corresponding defect is undetected for the amount of time specified by pwTDMCfgClearAlarmThreshold (default 10000 milliseconds). Alarms are only reported when the defect state persists for pwTDMCfgAlarmThreshold (default 2500 milliseconds).
All writeable objects in pwTDMTable MUST NOT be changed after row activation in the generic pwTable, and their values must persist after reboot.
An agent with TDM capability MUST support at least 4 fifteen-minute intervals (default 32, maximum 96). For daily intervals, the minimum is 1 (default 1, maximum 30). Performance parameters continue to be collected when the interface is down.
If the configured jitter buffer depth (pwTDMCfgJtrBfrDepth) is not supported by the implementation, the agent MUST return an error code 'jtrBfrDepth' in pwTDMConfigError. The actual jitter buffer size SHOULD be at least twice the configured value.
The CE-bound jitter buffer size SHOULD be locally configurable to accommodate PSN-specific packet delay variation. The default value of pwTDMCfgJtrBfrDepth is 3000 microseconds.
The CE-bound TDM IWF SHOULD use the sequence number in the control word to detect lost (LOPS) and mis-ordered packets. If RTP header is used, the RTP sequence numbers MAY be used for the same purposes.
The pwTDMCfgMissingPktsToSes threshold (default 30%) determines the percent of missing packets within a 1-second window needed to count a Severely Error Second (SES). Excessive packet loss rate is separately detected by comparing the average loss rate over pwTDMCfgAvePktLossTimeWindow against pwTDMCfgExcessivePktLossThreshold.
When pwTDMCfgPayloadSize is in use and the LEN field in the control word is set to 0, the payload MUST assume the configured size; if the actual packet size is inconsistent with this length, the packet MUST be considered malformed.
The PW-TDM-MIB module (pwTDMMIB, OID mib-2 186) consists of five tables: pwTDMTable (generic TDM PW info), pwTDMCfgTable (generic configuration parameters), pwTDMPerfCurrentTable (current 15-minute statistics), pwTDMPerfIntervalTable (historical 15-minute intervals), and pwTDMPerf1DayIntervalTable (daily interval statistics).
The pwTDMCfgPktReplacePolicy determines the filler pattern played on the TDM line when packets are missing: allOnes (default, plays AIS), implementationSpecific, or filler (uses user-defined pwTDMCfgPktFiller byte pattern, default 0xFF).
The pwTDMCfgSetUp2SynchTimeOut (default 5000 ms) defines how long the host waits before declaring PW down if insufficient consecutive packets are received after administrative status change to up. PW 'down' notifications MUST NOT be sent before this timer expires after an administrative change.
The pwTDMCfgTimestampMode object controls RTP timestamp generation: absolute mode (PSN-bound IWF uses clock recovered from TDM attachment circuit, mandatory for all implementations supporting RTP) or differential mode (both IWFs share a common timing source, OPTIONAL).
The pwTDMConfigError BITS object indicates configuration incompatibilities: tdmTypeIncompatible (bit 1), peerRtpIncompatible (bit 2, local sends RTP but remote cannot accept), and peerPayloadSizeIncompatible (bit 3). Bit 0 is notApplicable when no signaling is available.
The pwTDMRate object represents the bit-rate of the TDM service in multiples of 64 Kbit/s: Satop E1=32, Satop T1=24 (basic) or 25 (octet-aligned), Satop E3=535, Satop T3=699, and for structure-aware emulation it MUST be set to N (number of DS0 channels).
The pwTDMTable is indexed by pwIndex (shared with PW-STD-MIB) and is automatically populated by the agent for every pwTable entry with pwType values 17–24 (e1Satop, t1Satop, e3Satop, t3Satop, basicCesPsn, basicTdmIp, tdmCasCesPsn, tdmCasTdmIp). All writable objects MUST NOT be changed after row activation, and values must persist after reboot.
Three performance monitoring tables track identical counters at different granularities: pwTDMPerfCurrentTable (current 15-minute interval), pwTDMPerfIntervalTable (up to 96 historical 15-minute intervals covering 24 hours), and pwTDMPerf1DayIntervalTable (up to 30 daily intervals). Counters include MissingPkts, PktsReOrder, JtrBfrUnderruns, MisOrderDropped, MalformedPkt, ESs, SESs, UASs, and FC.
Unavailable Seconds (UASs) are counted as follows: any ten consecutive Severely Error Seconds (SES) trigger UAS state, and those 10 SES are added to the UAS counter when first entering UAS state; each additional UAS increments the counter by one.
IANA assigned OID { mib-2 186 } to the pwTDMMIB MODULE-IDENTITY, recorded in the SMI Numbers registry under the descriptor 'pwTDMMIB'.
The pwTDMTable, pwTDMPerfCurrentTable, pwTDMPerfIntervalTable, and pwTDMPerf1DayIntervalTable collectively expose TDM pseudowire connectivity topology and performance characteristics. Read access (GET/NOTIFY) to these objects should be controlled, and values should be encrypted when transmitted over SNMP if the topology information is sensitive.
Unauthorized access to pwTDMTable and pwTDMCfgTable objects (which contain TDM PW parameters on PE devices) could result in disruption of network traffic. SNMPv3 VACM and USM MUST be used with any SNMPv3 agent implementing this MIB module, and deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED.
Loss of Packet State (LOPS) is entered when pwTDMCfgConsecMissPktsOutSynch (default 10) consecutive packets are missing, and exited when pwTDMCfgConsecPktsInSynch (default 2) consecutive packets with sequential sequence numbers are received. A TDM Failure Count event begins at LOPS declaration and ends at LOPS clearance.