NMS520-MIB

MIB Reference — IPNetwork Monitor · Updated October 06, 2026

All MIBs › NMS520-MIB

Category: Hardware Inventory

Description: Provides product-specific management objects for the NMS Communications NMS520 network device.

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What Is NMS520-MIB?

NMS520-MIB is not, as its name and 'NMS Communications' vendor label might suggest, a MIB from the telecom vendor NMS Communications -- the module's own copyright header and OID registration ('Copyright 1994 General DataComm Inc.', nested under the dsu subtree imported from DDS-MIB) show it is a General DataComm (GDC) enterprise MIB for the NMS520, a Digital Data Service (DDS) line DSU/CSU unit. The nms520UnitCfgTable augments GDC's SC5520 unit configuration table with NMS520-specific settings such as NMS510 compatibility mode, DTE port type (RS-232/V.35/auto), RTS/CTS delay timing, daisy-chain data rate, firmware level, and front-panel test-switch inhibit/enable controls. A large nms520AlarmData branch defines over 30 alarm conditions (jitter, bipolar violations, frame loss, signal-to-noise ratio, low receive signal, DSR/DTR/DCD/RXD/TXD loss, shorted leads, and more), configured for threshold and hysteresis via nms520AlarmCfgTable, while nms520LineStatsTable reports rolling 1-15 minute DDS line statistics (Tx/Rx level, signal-to-noise ratio, jitter percentage, bipolar-violation and frame-loss counts) and nms520DiagCfgTable/nms520DiagExcTable drive on-demand loopback, self-test, and network-delay diagnostics. It depends on the GDCCMN-MIB and DDS-MIB enterprise trees for its parent OID and SCinstance indexing, and it is deployed on General DataComm NMS520 DSU/CSU units in DDS point-to-point or multipoint circuits, and administrators can download the NMS520-MIB file to monitor and diagnose these legacy DDS lines.

IPNetwork Monitor allows you to monitor SNMP objects defined in NMS520-MIB. Use the built-in SNMP Monitoring Browser to explore available variables, view their current values and descriptions, and select the objects you want to monitor. You can then create SNMP monitors, configure thresholds, and receive alerts when monitored values change.

Supported Devices

  • General DataComm (GDC) NMS520 DDS DSU/CSU units

Monitoring Examples

An operator polls nms520LineStatsSignalToNoiseRatio and nms520LineStatsBpvCount over the last 1-15 minute interval (nms520LineStatsInterval) to gauge DDS line quality, and checks nms520AlarmCfgThreshold against nms520JitterAlm; a signal-to-noise ratio dropping below its configured threshold alongside rising bipolar-violation counts would indicate a degrading copper DDS circuit needing carrier attention.

What Can Be Monitored

  • DDS line jitter, bipolar violation, and frame-loss counts
  • signal-to-noise ratio and receive signal level
  • DSR/DTR/DCD/RXD/TXD loss alarms
  • unit configuration (DTE port type, compatibility mode, firmware level)
  • on-demand loopback/self-test diagnostic status
Imported Objects

From DDS-MIB

dsuOBJECT-IDENTITY

From GDCCMN-MIB

gdcOBJECT-IDENTITY

From GDCMACRO-MIB

SCinstance

From RFC-1212

OBJECT-TYPE

From RFC1213-MIB

DisplayString
OIDs

RFC description

Manages General DataComm NMS520 digital service unit configuration, alarms, diagnostics, and HDLC operations.

Start monitoring General DataComm (GDC) NMS520 DDS DSU/CSU unit with a free 30-day trial of IPNetwork Monitor. Import MIBs, browse SNMP OIDs, create custom SNMP monitors, configure alerts, and monitor any SNMP-enabled network device from a single console.

Download NMS520-MIB