Discovering a DWDM network with Tomography#

Annalisa Morea (Nokia), Jani Myyry (CSC/Funet), Kurosh Bozorgebrahimi (Sikt), Magnus Bergroth (SUNET)

• Why: Turns the coherent transponder from a transmission component into a sensing device that infers the physical network topology with no prior knowledge — directly relevant to anyone operating optical plant whose documentation drifts from reality. (from abstract only; the programme page was not retrievable)
• What: Nokia Bell Labs' "Tomography" method estimates fiber types, span lengths, and amplifier types from data the DSP already computes. In a February 2026 field trial on a multi-vendor Scandinavian network (CSC, Sikt, SUNET), a signal ran Tromsø→Espoo over two routes with characteristics unknown to the Nokia team, in C-band alongside live traffic, three wavelengths measured per route, using PSE-Vs (SFM6) transponders. Results: fiber length estimated with less than 4% error, good amplifier-type match, operators corrected erroneous database entries, and a path commissioning error was detected.
• How: The DSP analyzes received symbols to determine accumulated chromatic dispersion and nonlinearities; an algorithm exploits the non-commutative property between CD and nonlinear effects to convert this into power-versistance distance maps, and from those into span/topology estimates — no additional hardware, coexisting with revenue traffic.
• Where applicable: Requires coherent DSP transponders (Nokia PSE-Vs in the trial); the fiber plant itself was multi-vendor and heterogeneous. It's a partner (Nokia) session, but the field trial is independently hosted by three NRENs with named, verifiable outcomes — not a pitch.