ISDN Management Information Base using SMIv2
Extracted elements (27)
For hyperchannel calls, two multiplexing schemes are permitted (DS0Bundle MIB or multiple ifStackTable entries with the same HigherLayer value); the choice is left to the implementor because the ISDN MIB itself treats a hyperchannel as a single call in isdnSignalingStatsTable regardless of B channel count.
isdnDirectoryTable entries have no associated ifEntry and therefore cannot be used for router port attachment; separate isdnSignalingTable entries must be created per router port for incoming call identification, even though this increases configuration complexity for customers.
isdnSignalingCallingAddress cannot store the SPID because the SPID (9–20 digits, North America only) and the calling address may differ and both must be present simultaneously; a separate isdnEndpointSpid object in isdnEndpointTable is therefore required.
Speech (speech(2)) and 3.1 kHz Audio (audio31(6)) bearer capabilities are sometimes used to carry 56 kbit/s data to exploit favorable speech tariffs. Implementations typically ignore the bearer capability on the receive side and answer such calls as data, using separate directory numbers for voice vs. data.
The ISDN-specific information is split between this MIB and the Dial Control MIB so that peer and call history management can be reused for non-ISDN demand-access interfaces such as modems and X.25 virtual connections, avoiding duplication.
Implementation of the DS1/E1 MIB is not required but is recommended for entities supporting Primary Rate interfaces; implementation of the DS0 MIB is optional; DS0Bundle MIB may be required only if hyperchannels are used with DS0Bundle-based multiplexing.
SPID handling applies only to BRI interfaces in North America and is required for DMS-100, NI-1, and NI-2 switch protocols, and optional for 5ESS; up to 8 SPIDs per BRI are possible. The EID (USID + TID, 2 bytes) returned by the switch during registration is used by some switch firmware versions to route incoming SETUP messages to the correct endpoint.
For D channel backup, exactly one LAPD interface must be designated primary via isdnLapdPrimaryChannel; inactive backup LAPD interfaces must have ifOperStatus of dormant(5). The controlling signaling entry is layered over all attached LAPD interfaces via ifStackTable.
For ISDN leased-line BRI interfaces (no signaling channel available), isdnBasicRateSignalMode of isdnBasicRateTable must be set to inactive(2); for Primary Rate leased lines, dsx1SignalMode in the DS1/E1 MIB must be set to none(1).
If the agent also supports the DS0 MIB, the values of isdnBearerChannelNumber and dsx0Ds0Number must be identical for the same B channel.
Implementation of the Dial Control MIB is required for any entity implementing this ISDN MIB, as peer information and call history management are defined there.
The compliance statement mandates isdnMibSignalingGroup, isdnMibBearerGroup, and isdnMibNotificationsGroup unconditionally; isdnMibBasicRateGroup is mandatory for entities supporting BRI interfaces; endpoint and directory groups are optional.
ISDN interface layering uses the ifStack table of the Interfaces MIB to correlate B channels (ifType ds0(81)), LAPD (ifType lapd(77)), D channel Network Layer/Terminal Endpoints (ifType isdn(63) or x25ple(40)), and physical interfaces (ifType isdns(75), isdnu(76), or ds1(18)) into a coherent hierarchy.
isdnBasicRateTable provides per-BRI-interface configuration: isdnBasicRateIfType (isdns(75) for S/T four-wire or isdnu(76) for U two-wire), isdnBasicRateLineTopology (pointToPoint or pointToMultipoint), isdnBasicRateIfMode (te or nt), and isdnBasicRateSignalMode (active or inactive).
isdnBearerInfoType enumerates the ISDN Information Transfer Capability for a call: unknown(1), speech(2), unrestrictedDigital(3), unrestrictedDigital56(4), restrictedDigital(5), audio31(6), audio7(7), video(8), packetSwitched(9); referenced from Q.931 section 4.5.5 octet 3.
isdnBearerTable records per-B-channel operational data including channel type (dialup/leased), peer ISDN address and subaddress (E.164 preferred, '+' prefix), call origin, information transfer capability (isdnBearerInfoType), multirate flag, call setup and connect timestamps (TimeStamp), and charged units (Gauge32).
isdnDirectoryTable (optional) maps additional directory numbers to signaling channels via isdnDirectoryNumber (E.164 preferred) and isdnDirectorySigIndex; used when the Called Number on incoming calls differs from isdnSignalingCallingAddress or when multiple numbers (hunt groups, local/LD/international variants) must be accepted.
isdnEndpointTable (optional) configures Terminal Endpoints with isdnEndpointIfType (isdn(63) or x25ple(40)), isdnEndpointTeiType (dynamic or static), isdnEndpointTeiValue (0–255; 0–63 valid for static), and isdnEndpointSpid (9–20 numeric characters, required for NI-1/NI-2 BRI in North America).
isdnLapdTable provides per-LAPD-interface data: isdnLapdPrimaryChannel (TruthValue indicating primary D channel for backup), isdnLapdOperStatus (inactive/l1Active/l2Active), isdnLapdPeerSabme (peer-initiated connection count), and isdnLapdRecvdFrmr (framing error count).
isdnMibCallInformation NOTIFICATION carries ifIndex, isdnBearerOperStatus, isdnBearerPeerAddress, isdnBearerPeerSubAddress, isdnBearerCallSetupTime, isdnBearerInfoType, and isdnBearerCallOrigin; sent on rejected incoming calls, ultimately-failed outgoing calls, and successful connections (with isdnBearerCallConnectTime added).
IsdnSignalingProtocol is a textual convention enumerating 25 ISDN switch protocols including dss1(2), etsi(3), ess4(5), ess5(6), dms100(7), ni1(9), ni2(10), ins64(17), itr6(19), qsig(23), and others; new values are assigned by IANA.
isdnSignalingStatsTable (augments isdnSignalingEntry) counts per-signaling-channel call statistics: isdnSigStatsInCalls, isdnSigStatsInConnected, isdnSigStatsOutCalls, isdnSigStatsOutConnected, and isdnSigStatsChargedUnits (local charges only, Counter32 each).
isdnSignalingTable provides per-Terminal-Endpoint configuration: signaling protocol, calling address (isdnSignalingCallingAddress, E.164 format preferred with '+' prefix), subaddress, B channel count, and a RowStatus for dynamic row creation/deletion. isdnSignalingGetIndex (TestAndIncr) is used to safely allocate new row indices.
The ISDN MIB is organized into five groups: isdnMibBasicRateGroup (BRI physical interfaces), isdnMibBearerGroup (B channels), isdnMibSignalingGroup (D channels including LAPD and signaling tables), optional isdnMibEndpointGroup (Terminal Endpoints, TEI, SPID), and optional isdnMibDirectoryGroup (directory numbers per signaling channel).
Several objects in the ISDN MIB (isdnBasicRateIfType, isdnBasicRateLineTopology, isdnBasicRateIfMode, isdnBasicRateSignalMode, isdnBearerChannelType, isdnSignalingProtocol, isdnSignalingCallingAddress, isdnSignalingInfoTrapEnable, and isdnLapdPrimaryChannel) have read-write or read-create access; unauthorized modification could disrupt ISDN connectivity or enable unauthorized call setup. SNMPv2 security mechanisms should be used to restrict write access.
isdnBearerOperStatus defines four B channel call-control states: idle(1) — no call activity; connecting(2) — outgoing call attempt in progress; connected(3) — incoming call under validation; active(4) — call is active. Transitions are driven by signaling channel events.
isdnLapdOperStatus defines three LAPD layer states: inactive(1) — all layers down; l1Active(2) — Layer 1 up but Layer 2 datalink not established; l2Active(3) — both Layer 1 and Layer 2 established. Used to track D channel Data Link Layer readiness.