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Terms used throughout the CodingBox documentation, grouped by topic. Each entry links to the material where the concept is explained in depth.

Modules and memory

• Transceiver — a pluggable module that converts electrical signals to light and back for fibre-optic links; see What is an optical transceiver?.
• Form factor — the standardised housing, connector and lane count of a module (SFP, QSFP, QSFP-DD, OSFP…); see Form factors.
• MSA — Multi-Source Agreement: an industry agreement that makes modules of one form factor interchangeable; see MSA & standards.
• EEPROM — the module's non-volatile memory holding identity, capabilities, thresholds and configuration; see Memory map quick reference.
• A0h / A2h — the two two-wire addresses of an SFP-class module: identity (A0h) and diagnostics (A2h); see SFF-8472.
• Page / bank — the paged upper memory of QSFP and CMIS modules, selected by byte 127 (and 126 for banks); see SFF-8636, CMIS.
• Serial ID — the identity block: vendor, part number, serial, codes, wavelength, lengths.
• CC_BASE / CC_EXT / CC_DMI — checksums over the identity, extended and diagnostic blocks; must be recalculated after any edit; see EEPROM editor.
• Compliance codes — bytes declaring which PMDs and rates a module supports; values from SFF-8024.
• Vendor lock — a host refusing or flagging modules whose identity it does not recognise; see Vendor lock.
• Coding / recoding — rewriting identity fields so a module presents what a host expects; see EEPROM recoding.
• Write protection / password — mechanisms guarding module memory against writes; see Write-protection types.
• Rate select (RS0/RS1) — pins or bits switching a module between rate groups; see Rate & application selection.
• TX_DISABLE, TX_FAULT, RX_LOS — low-speed control/status signals of SFP-class modules: laser off, transmitter fault, loss of received signal.
• LOL — loss of lock: the CDR cannot recover a clock; see CDR.
• Module state machine — CMIS states (LowPwr, PwrUp, Ready…) a module passes through at start-up; see CMIS issues.
• CDB — Command Data Block: the CMIS message interface for firmware and extended operations.
• VDM — Versatile Diagnostics Monitoring: CMIS pages with pre-FEC BER, SNR and other advanced observables; see Per-lane diagnostics.

Inside the module

• TOSA / ROSA / BOSA — transmitter, receiver and bi-directional optical sub-assemblies; see The optical front end.
• TO-can — a hermetic metal package for a laser or photodiode; contrast Chip-on-board.
• COB — chip-on-board: bare dies bonded directly to the module board; see Chip-on-board.
• VCSEL, FP, DFB, EML — laser types (surface-emitting 850 nm; Fabry–Pérot; distributed feedback; externally modulated); see Laser types.
• DML — directly modulated laser (current switched); MZM — Mach-Zehnder modulator; EAM — electro-absorption modulator.
• ITLA — integrable tunable laser assembly (micro/nano-ITLA in pluggables); see Tunable DWDM transceivers.
• SiPh — silicon photonics: modulators, waveguides and detectors on a silicon chip fed by an external laser.
• PIN / APD — photodiode types (no gain / avalanche gain); TIA / LA — trans-impedance and limiting amplifiers; see Receivers.
• CDR — clock and data recovery: the retimer that extracts a clock and removes jitter; see CDR.
• DSP — digital signal processor performing equalisation and FEC in PAM4 and coherent modules.
• TEC — thermo-electric cooler holding a laser at constant temperature (cooled DWDM/EML modules).
• LPO — linear-drive pluggable optics: modules without a DSP, equalised by the host.
• CPO — co-packaged optics: optical engines on the switch ASIC package.

Signals and modulation

• NRZ — two-level signalling, one bit per symbol; PAM4 — four-level, two bits per symbol; see FEC & link training.
• Baud (GBd) — symbols per second; equals bit rate for NRZ, half of it for PAM4; see Units & conversions.
• FEC — forward error correction (BASE-R, RS(528,514), RS(544,514)); pre-FEC BER — error ratio before correction.
• BER — bit-error ratio, e.g. 10⁻¹².
• Extinction ratio — ratio of "1" to "0" optical levels (dB).
• Chirp — wavelength shift during direct modulation; limits reach via dispersion.
• Coherent — detection using a local-oscillator laser and DSP (QPSK, 16-QAM); see Coherent optics.
• Auto-negotiation (Clause 73), link training — copper/DAC procedures agreeing speed, FEC and equalisation.

Fibre and cabling

• FOL (fibre-optic link) — a communication link on optical fibre; the Russian abbreviation is ВОЛС.
• Single-mode (SMF, OS1/OS2) — 9 µm core, long reach; multi-mode (MMF, OM1–OM5) — 50/62.5 µm core, short reach; see Connectors & fibre.
• LC, SC, MPO/MTP, SN, CS, MDC — optical connector types; UPC / APC — flat vs angled polish (blue / green).
• DAC / AOC — direct-attach copper / active optical cable with fixed module ends; see DAC vs AOC vs transceivers.
• Attenuation — fibre loss in dB/km, wavelength-dependent; dispersion — pulse spreading (chromatic, modal, PMD).
• Link budget — launch power minus sensitivity minus losses and margin; see CWDM mux/demux & link budget.
• OTDR — optical time-domain reflectometer: locates loss and breaks along a fibre.
• Insertion loss / return loss — loss through a component / light reflected back.

Diagnostics

• DDM / DOM — Digital Diagnostic Monitoring: live temperature, voltage, bias, Tx/Rx power; see DDM basics.
• Alarm / warning thresholds — factory limits stored in the module; see Thresholds & alarms.
• Internal / external calibration — whether the module or the host converts raw sensor values; see Calibration.
• OMA — optical modulation amplitude, an alternative to average power for Rx sensitivity.
• Tx bias — laser drive current; the primary ageing indicator.
• Sensitivity / overload — minimum / maximum receiver power for correct operation.
• Link passport — the DDM and OTDR baseline recorded at installation; see Monitoring.

Wavelengths and WDM

• O / E / S / C / L / U bands — the named wavelength bands; see Wavelength bands & channel plans.
• CWDM / DWDM — coarse (20 nm) and dense (0.8/0.4 nm, ITU grid) wavelength-division multiplexing; see CWDM, DWDM.
• LAN-WDM — the 4-wavelength grid around 1300 nm used by 100GBASE-LR4.
• BiDi — bi-directional: two wavelengths on one fibre.
• ITU grid — the DWDM frequency grid anchored at 193.1 THz; see DWDM and the ITU grid.
• Mux / demux, OADM, ROADM — passive combiners/splitters and (re)configurable add/drop; see DWDM components.
• EDFA / Raman / SOA — optical amplifier types.
• OSNR — optical signal-to-noise ratio; the limit of amplified links.

Standards and bodies

• SFF Committee / SNIA SFF TA — publisher of SFF-xxxx specifications; see Specification catalog.
• SFF-8472, SFF-8636, SFF-8024, SFF-8690, INF-8077i — management, code-table and tuning specifications; see Specifications & standards.
• CMIS — Common Management Interface Specification (QSFP-DD MSA → OIF); MIS — SFP-DD Management Interface Specification.
• IEEE 802.3 — Ethernet, including optical PMDs (10GBASE-LR, 400GBASE-DR4…); see PMD reference.
• INCITS T11 / FC-PI — Fibre Channel physical layer; IBTA — InfiniBand Trade Association; ITU-T G-series — PON and WDM recommendations; OIF — Optical Internetworking Forum (400ZR, CMIS).
• PMD — Physical Medium Dependent sublayer: the named optical interface (SR, LR, DR4…).

Networks and technologies

• PON, OLT, ONU/ONT — passive optical network and its provider/subscriber ends; see PON.
• SAN, HBA, ISL — storage area network, host bus adapter, inter-switch link; see Fibre Channel.
• RDMA, RoCE — remote direct memory access, and RDMA over Converged Ethernet; see InfiniBand, AI clusters.
• Breakout — splitting a multi-lane port into independent lower-rate links.
• NOS — network operating system (IOS, Junos, EOS, VRP…); see Vendors & network OS.

CodingBox

• Driver — the local program bridging the browser app and a programmer over USB; see Connecting a board.
• Programmer — the board that physically connects to a transceiver; see Supported models.
• Simulator — the app's default mode without hardware; see Simulator mode.
• Code database — every read saved and chained per module; see Code database.
• Seat — one device slot in a subscription; see Subscriptions & seats.

Expansions of the acronyms used in these definitions, A to Z: Abbreviations; forty short answers to the questions behind them: Optics FAQ.

The fibre-side vocabulary — light in glass, fibre and cable types, passive components, installation, OTDR and testing terms: Fibre-optic glossary.