Managed Objects for ATM over Packet Switched Networks (PSNs)
Extracted elements (26)
An ATM PW connection is not treated as an interface and therefore is not represented in the ifTable. This follows the PWE3 Architecture layering model, which isolates PW services from the underlying PSN while connecting them to existing ATM MIB structures.
Point-to-point ATM PW connections are supported; point-to-multipoint and multipoint-to-point connections are explicitly deferred for future study. This scoping decision keeps the initial MIB tractable while acknowledging the topology limitation.
The MIB adopts a three-layer architecture: a service layer (this module, ATM-specific), a generic PW layer (PW-STD-MIB), and a PSN layer (e.g., PW-MPLS-MIB). This layering sufficiently isolates PW services from the PSN so that any service can be carried over any supported PSN type without structural changes.
The TrafficParamDescr table is intentionally not defined in this MIB module; instead, a RowPointer object references an entry in any existing ATM Traffic Descriptor table. This allows operators to reuse or override the TD already assigned to the ATM endpoint in the native ATM service MIB (RFC 2515), avoiding redundant definitions.
A device capable of implementing N:1, 1:1, and transparent cell mode may use the Nto1 tables for all modes. In that case, creating an entry for 1:1 or transparent mode only in pwAtmInboundNto1Table will automatically create the corresponding entry in pwAtmOutboundNto1Table.
In atmTransparent(3) mode, VPI and VCI index fields in the Nto1 tables must be set to 0xFFFF (the ATM identifier maximum) during set operations, since transparent mode carries cells without interpreting VPI/VCI values.
The pwAtmCfgFarEndMaxCellConcatenation object reports the maximum cell concatenation count as advertised by the far end via LDP. If LDP is not in use, the object either returns 0 or can be set manually for calculating protocol overhead, enabling interoperability in both signaled and manually configured deployments.
All read-create objects in the pwAtmOutboundNto1Table and pwAtmInboundNto1Table MUST NOT be changed after row activation and SHOULD remain unchanged after reboot.
All writeable objects in the pwAtmOutboundTable and pwAtmInboundTable MUST NOT be changed after row activation in the generic pwTable, and their values must persist after reboot.
Deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED. It is RECOMMENDED to deploy SNMPv3 with cryptographic security enabled for authentication and privacy of ATM PW MIB data.
In transparent cell transport mode, the value of pwAtmClpQosMapping MUST be false(2). In other cases, the object can be changed at any time. This prevents CLP bits from being mapped to PSN QoS fields when cell transparency is required.
SNMPv3 VACM and USM MUST be used with any SNMPv3 agent that implements this MIB module, to protect sensitive ATM PW configuration and performance objects on Provider Edge devices.
The PW-ATM-MIB module is organized into four categories of tables: (1) a generic ATM PW configuration table (pwAtmCfgTable), (2) outbound tables for 1:1 and N:1/transparent modes, (3) inbound tables for 1:1 and N:1/transparent modes, and (4) three performance tables covering current 15-minute, historical 15-minute, and one-day intervals.
The pwAtmCfgMaxCellConcatenation object (Unsigned32, range 1..29) specifies the maximum number of ATM cells that can be concatenated into one PW packet toward the PSN. In non-LDP environments this MAY be changed at any time (though traffic may be interrupted); with LDP signaling it may only be changed when the PW is not active.
The pwAtmCfgTable provides generic per-PW ATM configuration applicable to all ATM PW types. Key objects are pwAtmCfgMaxCellConcatenation (Unsigned32, range 1..29, maximum cells concatenated per PSN packet), pwAtmCfgFarEndMaxCellConcatenation (far-end advertised limit), pwAtmCfgTimeoutMode (notApplicable/disabled/enabled), and pwAtmClpQosMapping (TruthValue for CLP-to-QoS field mapping).
The pwAtmCfgTimeoutMode object (notApplicable/disabled/enabled) determines whether a packet may be transmitted to the PSN based on timeout expiration while collecting cells for concatenation. The actual timeout handling is implementation-specific and may be changed at any time with consideration for traffic interruption.
The pwAtmClpQosMapping object (TruthValue) controls whether ATM Cell Loss Priority (CLP) bits are mapped to PSN QoS fields such as the MPLS EXP bits in the label stack, allowing drop precedence to be preserved across the PSN. Reference: section 12 of RFC 4717 (ATM encapsulation over MPLS).
The pwAtmInboundTable configures ATM PW in the inbound (CE-bound) direction for 1:1 service modes. It mirrors the outbound table structure, indexed by pwIndex, and covers the same set of pwType values. For atmTransparent mode, pwAtmInboundVpi is set to zero; for atmTransparent, atmCell1to1Vpc, or atmCellNto1Vpc, pwAtmInboundVci is also set to zero.
The pwAtmOutboundNto1Table and pwAtmInboundNto1Table handle N:1, 1:1, and transparent cell mode ATM PWs. Up to N entries can be created per pwIndex for atmCellNto1Vcc(9) or atmCellNto1Vpc(10). The table includes MappedVpi and MappedVci objects representing egress-generated VPI/VCI values, valid for Nto1 and 1to1 types; other types return 0xFFFF.
The pwAtmOutboundTable configures ATM PW in the outbound (PSN-bound) direction for 1:1 service modes. It is indexed by pwIndex and applies to pwType values atmAal5SduVcc(2), atmCell1to1Vcc(12), atmCell1to1Vpc(13), atmAal5PduVcc(14), and atmTransparent(3). Fields include pwAtmOutboundAtmIf (InterfaceIndex), pwAtmOutboundVpi (AtmVpIdentifier), pwAtmOutboundVci (AtmVcIdentifier), and pwAtmOutboundTrafficParamDescr (RowPointer).
The pwAtmPerf1DayIntervalTable provides daily performance statistics indexed by pwAtmPerf1DayIntervalNumber (1..365), covering up to one month of one-day intervals. Counters use Counter32 (versus PerfIntervalCount in the 15-minute table) and include the same eight metrics: missing packets, reordered packets, misordered packets, timeout packets, cells transmitted, cells dropped, cells received, and unknown cells.
The pwAtmPerfCurrentTable tracks current 15-minute interval statistics per ATM PW, including pwAtmPerfCurrentMissingPkts, pwAtmPerfCurrentPktsReOrder, pwAtmPerfCurrentPktsMisOrder, pwAtmPerfCurrentPktsTimeout, pwAtmPerfCurrentCellsXmit, pwAtmPerfCurrentCellsDropped, pwAtmPerfCurrentCellsReceived, and pwAtmPerfCurrentUnknownCells (N:1 mode only). After 15 minutes, counts are copied to the interval table and reset.
The pwAtmPerfIntervalTable stores historical 15-minute performance intervals indexed by pwIndex and pwAtmPerfIntervalNumber (1..96, covering up to 24 hours). Interval 1 is the most recently completed 15-minute interval. Includes pwAtmPerfIntervalValidData and pwAtmPerfIntervalDuration to account for clock adjustments.
The PW-ATM-MIB module is assigned the OID { mib-2 183 } (pwAtmMIB). This value is recorded in the IANA SMI Numbers registry under descriptor 'pwATMMIB'.
The pwAtmCfgTable, pwAtmPerfCurrentTable, pwAtmPerfIntervalTable, and pwAtmPerf1DayIntervalTable collectively reveal the ATM pseudowire connectivity topology and performance characteristics. Even GET and NOTIFY access to these readable objects should be controlled, and values should potentially be encrypted when transmitted over the network.
The pwAtmOutboundTable, pwAtmInboundTable, pwAtmCfgTable, pwAtmOutboundNto1Table, and pwAtmInboundNto1Table contain ATM PW configuration parameters on Provider Edge devices. Unauthorized SET access to these read-write/read-create objects could disrupt traffic on the network; they should be protected with SNMPv3 or equivalent.