Finisar FTLF8519P3BNL-CS
Finisar · SFP transceiver, 1000BASE-SX · FTLF8519P3BNL-CS
what it is
A 1000BASE-SX transceiver (Finisar) in the SFP form factor, part number FTLF8519P3BNL-CS. Works over two multimode (MM) fibers (duplex), 850 nm. Reach per manufacturer: OM2 550 m, OM1 270 m. Wavelength from the transceiver memory: 850 nm. Production year stored in memory: 2016. Revisions seen in the examined units: A. The switch reports it as GLC-SX-MMD. Units examined: 3.
what we read from it
The transceiver has optical diagnostics (DOM): the switch reads temperature, supply voltage, transmit power and receive power from it. This makes an aging laser or a dirty connector visible before the link starts losing data.
Reading confirmed in switches: Cisco WS-C3750X-12S-S.
A full read of the transceiver memory gives it a diagnostics score of 9 out of 15 — counted are: presence of measurements, manufacturer thresholds, alarm flags set by the transceiver itself and software loss-of-signal indication.
what the transceiver memory declares
Transceiver memory read directly from a Cisco switch (show idprom, page A0) — 3 units. Each item gives the memory byte and value it comes from; we do not show serial numbers, exact dates or the vendor-reserved area.
- Module type: SFP/SFP+ (byte 0 = 0x03).
- Connector: LC (byte 2 = 0x07).
- Standard (compliance code): 1000BASE-SX (bytes 3, 6 = 0x00, 0x01).
- Nominal rate: 1300 MBd (byte 12 = 0x0D).
- Reach per fiber type: OM2 550 m, OM1 270 m (bytes 14-19 = 0x00 0x00 0x37 0x1B 0x00 0x00).
- Wavelength: 850 nm (bytes 60-61 = 0x03 0x52).
- Hardware signals: loss of signal (RX_LOS), transmitter disable (TX_DISABLE) (byte 65 = 0x12).
- Optical diagnostics (DDM): declared, internal calibration (byte 92 = 0x68).
- Extended options: none (byte 93 = 0x00).
- SFF-8472 diagnostics revision: 10.2 (byte 94 = 0x03).
- Chip vendor identifier (OUI): filled (bytes 37-39).
- Memory checksums: valid (bytes 63 and 95).
- Vendor-reserved area: present (bytes 96-127).
- Vendor alarm thresholds: not shown — the switch did not expose the raw diagnostics memory page, and we do not use the thresholds from its diagnostics table, because they cannot be told apart from the switch's own settings.
- Production year stored in memory: 2016.
A declaration in memory is not the same as a reading: diagnostic measurements were shown by Cisco WS-C3750X-12S-S.
how we checked
The result depends on what the transceiver was read with — the same switch model in a different installation can show different data. That is why each reading is recorded separately:
- Cisco Catalyst 3750-X 12S-S (Cisco WS-C3750X-12S-S), firmware
15.2(4)E10— transceiver memory and diagnostics table read from the console, 2026-10-17: diagnostics read (3 units). Visible data: temperature, supply voltage, transmit power, receive power, manufacturer alarm thresholds, loss of signal indication (RX_LOS), transmitter disable (TX_DISABLE), manufacturing date, wavelength, reach per fiber type, diagnostics standard revision, standard (compliance code), chip vendor identifier, memory checksums, identity (manufacturer, part number, serial number, revision). Cable test: not tested.
The same transceiver in other switches and a comparison with other models: what each device shows.
what we cannot read
- Laser bias current — the switches that read it do not show this value, although a transceiver with diagnostics measures it.
parameters the transceiver returns
The list shows WHAT the device exposes — including parameters we do not use ourselves. There are no values here at all: it is a catalog of capabilities, not a reading from anyone's network. It is not a closed list either — explanation below the table.
18 parameters
| parameter | type |
|---|---|
data_produkcji | date |
dlugosc_fali_nm | number (nm) |
moc_nadawana | number (dBm) |
moc_odbierana | number (dBm) |
napiecie_zasilania | number (V) |
numer_czesci | text — part number (PN) |
numer_seryjny | text |
oui_producenta | text — chip vendor identifier |
producent | text — vendor name from transceiver memory |
progi_alarmow_i_ostrzezen | numbers — vendor thresholds for 5 values |
rewizja | text |
rewizja_sff8472 | text — diagnostics standard revision |
sumy_kontrolne | boolean — transceiver memory validity |
temperatura | number (°C) |
utrata_swiatla_rx_los | boolean |
wylaczenie_nadajnika_tx_disable | boolean |
zasiegi_wlokien | numbers (m / km) for OM1–OM3 and single-mode fiber |
zgodnosc | text — standard (e.g. 1000BASE-LX) |
This is not a closed list. It comes from reading a unit we had access to — it shows what we managed to retrieve, not everything the device can return. A different firmware version, hardware variant or reading path can expose fields that are not here. If you are interested in a specific unit and a specific value — please ask; there is a good chance it can be obtained, even if you do not see it below.
List source: reading of 3 working units (as of 2026-10-19). The list is the sum of what we observed — more units reveal more parameters, so numbers for different models are not directly comparable.