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Tier 1 and Tier 2 testing: what LSPM and OTDR each prove

Loss against a budget, or every event on the link: the difference, when a specification asks for both, and why results get rejected.

The short answer

Tier 1 (a light source and power meter, LSPM) measures the total loss of a link against its loss budget, plus length and polarity. Tier 2 adds an OTDR trace that locates and measures every connector and splice along the link. Tier 1 says whether the link passes; Tier 2 says why, and where.

Tier 1: loss against a budget

A light source at one end and a power meter at the other measure how much light the link loses.

That figure is compared with a loss budget built from the standard or the specification: so much per kilometre of fibre, per mated connector pair and per splice. Tier 1 also records length and confirms polarity. It is fast, repeatable and the basis of acceptance on most projects.

The reference matters. Most specifications call for a one-jumper reference, set before testing and checked during the day, and for multimode, launch conditions that meet encircled flux requirements. A wrong reference gives results that look like passes and are not.

Tier 2: every event on the link

An OTDR sends pulses down the fibre and reads what comes back. The trace shows each connector and splice as an event, with its position and its loss, and reflectance for connectors.

It finds the one bad splice in a run that passes Tier 1 overall, and it gives the client a fingerprint of the link to compare against later.

When a specification asks for both

  • Backbones and inter-building links, where a fault is expensive to locate later.
  • Spliced links, so each splice is proven, not just the total.
  • Handover to operators who keep traces as a baseline for maintenance.

Why results get rejected

  1. The wrong limit was selected in the tester, so the pass is against the wrong standard.
  2. No valid reference, or a reference set with the wrong cords.
  3. Results named differently from the labels and the as-built, so nobody can match them.
  4. Retyped or summarised results instead of the tester's own files.
  5. Missing links: the pack does not cover every link on the schedule.

We set the limit from the specification, name every result by its cable ID and check the pack against the schedule before it leaves us.

Work out the budget for a link, check splices on bidirectional averages and read OTDR events in the free Loss Budget & OTDR tool.

Questions

Is Tier 1 enough?
For many links, yes: it is the acceptance test most standards require. Specifications add Tier 2 on backbones, on spliced links, and wherever the client wants proof of each event.
Why do OTDR results need launch and tail cords?
The OTDR cannot see the first and last connectors without a length of fibre before and after them. Launch and receive cords let those connectors be measured.
What file should be handed over?
The tester's own result file, plus a PDF report. Retyped results in a spreadsheet are not evidence and are often rejected.

GO2DataWorks technical note, updated 18 October 2026. General guidance: your project specification and the standards it names always take precedence.

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