Archive for December, 2010
Cisco calls it DOM – Digital Optical Monitoring – and it’s built into some of their SFP, XenPak, and X2 transceivers:
Unfortunately, but not surprisingly, the feature isn’t built into any of the common SFPs that most network engineers use on a day to day basis, such as the GLC-LX or GLC-SX units. Cisco thinks that DOM functionality is worth an extra $300 a pop, putting the cost of a DOM-enabled single mode SFP close to $800.
I have found, however, that some third-party SFPs include the DOM functionality. I’ve been using the single-fiber SFPs from Champion One for many years. They work great, only use a single fiber (instead of a pair) and give you DOM functionality for free.
Here’s how to get started with DOM:
1) Enable support for non-Cisco SFPs:
2) Enable DOM Monitoring :
PSKL_6509(config)#transceiver type all
3) Install some DOM-compatible transceivers.
4) Take some light measurements! In this example, I’m using a 1000SFP31B20L Single Fiber SFP in slot 2/9/22:
PSKL_6509#sh interfaces gigabitEthernet 2/9/22 transceiver ITU Channel not available (Wavelength not available), Transceiver is internally calibrated. If device is externally calibrated, only calibrated values are printed. ++ : high alarm, + : high warning, - : low warning, -- : low alarm. NA or N/A: not applicable, Tx: transmit, Rx: receive. mA: milliamperes, dBm: decibels (milliwatts). Optical Optical Temperature Voltage Current Tx Power Rx Power Port (Celsius) (Volts) (mA) (dBm) (dBm) ---------- ----------- ------- -------- -------- -------- Gi2/9/22 44.1 3.26 22.2 -2.5 -5.1
This feature is incredibly handy when troubleshooting fiber issues. A low value in the Rx Power column indicates that you have a bad fiber, or more commonly, a dirty jumper somewhere. You can even use MRTG or Cacti to log and graph your optical health over time.