Part II
Exploiting the Micro-OTDR
ORL/OSNR Measurement Feature
to Improve Network Reliability
The ORL/OSNR Measurement (optical return loss / optical signal to noise ratio) feature of the Micro-OTDR SFPs measures the optical fiber link ORL during the normal Micro-OTDR start-up “handshaking” routine of the SFPs, before the data link is made. The receiver also measures the signal received. Internally the Micro-OTDR SFP calculates the actual OSNR. If the OSNR is deemed to be dangerously low a Warning bit is activated, and when it is too low (i.e., the optical data link bit error rate will be high), an Alarm bit is set and optionally (factory setting based on customer request) the link can be shut down.
Example 1 – New Optical Fiber Link Commissioning
Background
The iSFC® Micro-OTDR SFP Transceivers are designed to provide an initial “Birth Certificate” for both newly installed, and legacy, Optical Fiber Links. The “Birth Certificate” includes the total Optical Fiber Link distance in meters from the local (CO) SFP to the remote (CPE) SFP, as well as the number of reflections detected in the Optical Fiber Link.
Commissioning
Adhering to the standard operating procedures, the Installation Technicians may use the Micro-OTDR feature to instantly generate an accurate Optical Fiber Link distance to serve as a reference against which to compare future measurements.
ORL/OSNL Measurement
In addition to measuring the optical fiber link distance, the iSFC® Micro-OTDR SFP Transceivers can measure the ORL (optical return loss) of the Optical Fiber Link. Depending upon the application, the ORL of the link must meet a certain specified level. This instantaneous measurement of the link ORL, integral to the “Birth Certificate” process, saves time, and money, for the service provider by improving the efficiency of the New Optical Fiber Link Commissioning process.
Example 2 – Fault Detection in Marginal Optical Fiber Links
Link ORL is Marginal
Some older, legacy, Optical Fiber Links, while still in service, might cause network problems in circumstances where the the link ORL does not meet the specified requirements. With the ORL measurement at start-up, the health of the optical fiber link is immediately known, and preventive action may be taken.
Preventive Actions
If the ORL of the optical fiber link is insufficient to support the application, the iSFC® Micro-OTDR SFP Transceiver can be set to not start-up, so to prevent the establishment of a bad (noisy) link, which can cause trouble throughout the network. Alternatively, a Warning, or Alarm, can be set, to allow the network operating center (NOC) personnel to control the status of the noisy link.
