DDM / DOM monitoring

What DDM/DOM is

Digital Diagnostics Monitoring (DDM, also called Digital Optical Monitoring or DOM) is a standardized interface, defined by SFF-8472 for SFP and SFF-8636 / CMIS for QSFP — that exposes real-time module health data. Every NetAPI module supports DDM with the full set of A2h-page monitor values.

DDM gives you five core measurements per lane:

All five have alarm and warning thresholds programmed into the EEPROM. Hitting an alarm threshold typically triggers a syslog/SNMP trap on the switch.

Healthy operating ranges by module type

These are the typical "happy zone" Tx and Rx power ranges. Outside this range, the module is either over-driving the link (potential receiver saturation) or under-driving it (low margin, prone to errors).

Reading DDM from the CLI

Cisco IOS-XE

Switch# show interface tengigabitEthernet 1/0/49 transceiver detail

Optical Lane Tx Power:
  Lane 1: -2.8 dBm

Optical Lane Rx Power:
  Lane 1: -4.9 dBm

Module Temperature: 41.2 C

Tx Bias Current:
  Lane 1: 35.4 mA

Supply Voltage: 3.297 V

Cisco NX-OS

N9K# show interface ethernet 1/1 transceiver detail

Ethernet1/1
    transceiver is present
    type is QSFP-100G-LR4
    name is CISCO-NETAPI
    part number is QSFP-100G-LR4-S
    revision is V03

    DOM is supported
    Temperature   : 47.31 C
    Voltage       : 3.30 V
    Current       : 53.99 mA Lane 1, 54.20 mA Lane 2, ...
    Tx Power      : -2.41 dBm Lane 1, -2.55 dBm Lane 2, ...
    Rx Power      : -4.18 dBm Lane 1, -3.97 dBm Lane 2, ...

Juniper Junos

> show interfaces diagnostics optics et-0/0/0
Physical interface: et-0/0/0
  Laser bias current               :   38.234 mA
  Laser output power               :   -2.06 dBm
  Module temperature               :   42 degrees C
  Module voltage                   :   3.2980 V

  Receiver signal average optical power:    -4.84 dBm

Arista EOS

arista# show interfaces ethernet 1 transceiver dom

Et1
    Temperature: 39.74 °C
    Voltage: 3.286 V
    Tx Bias Current: 7.43 mA
    Tx Power: -2.85 dBm
    Rx Power: -5.12 dBm

NVIDIA / Mellanox / Cumulus

switch# show interface swp1 transceiver
swp1: present
  ...
  temperature: 42.5 C
  voltage: 3.298 V
  rx_power: -5.43 dBm
  tx_power: -2.34 dBm
  tx_bias_current: 35.6 mA

SNMP polling

For continuous monitoring, poll DDM via SNMP and feed it into your NMS (LibreNMS, PRTG, Datadog, Observium, etc.).

Vendor-specific MIBs with per-module DDM

Alert thresholds

The thresholds programmed into the EEPROM follow the MSA-defined alarm and warning levels.

Drift over time, what to watch for

Capture a baseline at install. Re-measure quarterly. Trends to watch:

Laser aging

• Tx power slowly drops (−0.5 to −1 dB per year is normal)
• Laser bias current slowly rises (+10% per year is normal)
• When Tx power approaches the Tx-min threshold or bias exceeds 1.3× baseline, plan replacement

Fiber contamination or degradation

• Rx power drops without a corresponding Tx drop at the far end
• Symptoms develop over days/weeks (vs. laser aging which is months/years)
• Inspect and clean the connectors; if that doesn't fix it, the fiber itself may be the issue

Environmental

• Temperature rises seasonally or in line with chassis temperature trends
• Suggests airflow or cooling issues, not a module problem