Triple-Play Service Deployment

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Another approach uses a loss test set, consisting of a source and a
power meter within the same unit, at each end. In some cases one
or two ORL meters are also used. This approach improves
repeatability by performing bi-directional loss measurements over
two fibers.
JDSU SmartClass OLS-55
Bi-directional Loss Test Sets
A final option is to use two bi-directional loss test sets containing
built in ORL measurement capabilities at each end of the link. This
approach automates bidirectional loss and ORL measurements for
faster handling and test time and for improved repeatability. Some
bidirectional loss test sets can also provide link distance information.
JDSU OFI2000 Multifunction Lost Test Set
Chapter 3: Deploying and Troubleshooting Fiber Networks